Expanded Syllabus

AP BiologySyllabus

Course Overview

My AP Biology course is developed based upon the standards put forth by the College Board for all AP courses. Using the AP Biology Course Description as a guide, all topics are covered prior to the AP Biology exam in May. The topics include biochemistry, cell structure and function, metabolism, genetics, molecular basis of inheritance, DNA technology, evolution, microbiology, classification, plants, animals, animal physiology, and ecology.

The eight major themes, as expressed in the AP Biology Curriculum requirements, are the building blocks for my AP Biology course. [C6]

Key to Evidence of Curricular Requirement

[C1] - The course emphasizes the biological concepts as specified in the three overarching topics listed in the Topic Outline in the Course Description, the first being Molecules and Cells.

[C2] - The course emphasizes the biological concepts as specified in the three overarching topics listed in the Topic Outline in the Course Description, the second being Heredity and Evolution.

[C3] - The course emphasizes the biological concepts as specified in the three overarching topics listed in the Topic Outline in the Course Description, the third being Organisms and Populations.

[C4] - The course provides students with an opportunity to develop a conceptual framework for modern biology emphasizing evidence of an understanding of science as a process rather than an accumulation of facts.

[C5] - The course provides students with an opportunity to develop a conceptual framework for modern biology emphasizing recognition of evolution as the foundation of modern biological models and thought.

[C6] - The integration of the general topics of biology through the eight major themes as specified in the Course Description - Science as Process; Evolution, Energy Transfer; Continuity and Change; Relationship of structure to function; Regulation; Interdependence in nature; and Science, technology, and society.

[C7] - Applications of biological knowledge and critical thinking to environmental and social concerns.

[C8] - The course includes a laboratory component that fulfills all of the objectives ofthe recommended AP Biology labs as listed in the Course Description. Students must spend a minimum of 25% of instructional time engaged in hands-on laboratory work.

AP Biology is a laboratory course in which students will complete required and critical procedures, collect data, analyze data, and formulate detailed conclusions. [C4]

The objectives of AP Biology are that each student shall

Be able to use knowledge gained in lecture to help solve biological problems. Learn how to write informative biological essays. Be able to analyze collected data to understand key biological principles. [C4]

Apply knowledge, research skills, and critical thinking to answer a question posed in a national essay competition regarding environmental and social concerns. [C7]

Be able to integrate the major themes of evolution into virtually every unit of study via labs, homework assignments, critical thinking, and writing. [C5]

Gain successful AP credit upon completion of the course.

Typically, AP Biology is broken down into subunits that take approximately two weeks to complete. A subunit may be broken down into the following lesson plan schedule:

Day 1 Day 2 Day 3 Day 4 Day 5

Lecture Lecture Lecture/Quiz Lecture Lecture/Review

Day 6 Day 7 Day 8 Day 9 Day 10

AP Lab [C8] AP Lab [C8] Lecture/Review Internet Lab Activity [C8]

Unit Exam

Textbook and Lab Manual Information

Text: Campbell, N., Reece, J., and Mitchell, L., 2004. Biology, Seventh Edition, Addison Wesley Publishing, 1312 pp.

Lab Manual: AP Biology Laboratory Manual for Students Exercises 1-12, 2001 Edition. Additional lab activities are teacher-generated.

Course Planner

AP Biology Lecture and Exam Schedule

Unit Lecture and Lab Titles Readings Month

1.

2.

3.

I. Molecules and Cells

Chemistry of Life [C1]

Water Organic molecules in organisms Free energy changes Enzymes

Unit one exam

Cells [C1]

Prokaryotic and Eukaryotic cells Membranes Subcellular organization Cell cycle and its regulation

Unit two exam

Cellular Energetics [C1] Coupled reactions Fermentation and cellular respiration Photosynthesis

Unit three exam

Chapters 3-5, 8Concepts 3.1-3.3Concepts 4.1-4.3, 5.1-5.5Concepts 8.1, 8.2Concepts 8.4, 8.5

Chapters 6, 7, 11, 12Concepts 6.1-6.7, 26.3, 26.4, 27.1Concepts 6.2, 6.4, 7.1-7.5, 11.1-11.4Concepts 6.2-6.7Concepts 12.1- 12.3

Chapters 8-10Concepts 8.3, 9.1-9.4, 10.2Concepts 9.2-9.6Concepts 10.1-10.4

Sept

Sept

Oct

4.

5.

II. Heredity and Evolution

Heredity [C2] Meiosis and gametogenesis Eukaryotic chromosomes Inheritance patterns

Unit four exam

Molecular Genetics [C2]

RNA and DNA structure and function Gene regulation Mutation Viral structure and replication Nucleic acid technology and application

Unit five exam

Chapters 13-15Concepts 13.1-13.4, 29.2-29.4, 30.1-30.3,46.4Concepts 15.1-15.5Concepts 14.1-14.4, 15.3-15.5

Chapters 16-20Concepts 16.1, 16.2, 17.1-17.6, 18.3Concepts 18.4, 19.1-19.3Concepts 15.4, 17.7, 18.3, 19.3, 19.5Concepts 18.1, 18.2Concepts 20.1-20.5

Oct/Nov

Dec

Evolutionary Biology [C2] [C5] Chapters 22-26

6. Early evolution of life Evidence for evolution Mechanisms of evolution

Unit six exam

Concepts 26.1-26.5Concepts 22.2, 22.3, 25.1-25.5Concepts 22.1-22.3, 23.1-23.4, 23.1-24.3, 25.4, 25.5

Jan

7.

8.

III. Organisms and Populations

Diversity of organisms [C3]

Evolutionary patterns Survey of the diversity of life

Phylogenetic classification

Evolutionary relationships

Unit seven exam

Structure and Function of Plants and Animals [C3]

Reproduction, growth, and development (plants)

Reproduction, growth, and development (animals)

Structural, physiological, and behavioral adaptations (plants)

Structural, physiological, and behavioral adaptations (animals)

Response to environment (plants) Response to environment (animals)

Unit eight exam

Ecology [C3]

Population Dynamics Communities and ecosystems Global issues

Unit eight exam

Chapters 25-34Concepts 29.1, 29.2, 31.1, 32.1-32.3Concepts 26.6, 27.1-27.4, 28.1-28.8, 29.2-2.4, 30.2-30.4, 31.2-31.5, 32.4, 33.1-33.8, 34.1-34.8Concepts 25.2, 26.6, 27.1, 27.3, 28.1-28.8, 29.1-29.4, 30.1-30.4, 31.1-31.4, 32.1, 32.4, 33.1-33.8, 34.1-34.8Concepts 25.1-25.5

Chapters 21, 29, 30, 35-39, 40-49, 51Concepts 21.1-21.4, 29.2-29.4, 30.1-30.3, 35.2-35.5, 38.1-38.3Concepts 21.1-21.4, 46.1-46.5, 47.1-47.3

Concepts 29.1-29.4, 30.1-30.4, 35.1, 36.1-36.5, 37.1-37.4, 38.1-38.3, 39.1-39.5Concepts 40.1-40.5, 41.1-41.5, 42.1-42.7, 43.1-43.3, 44.1-44.6, 45.1-45.5, 46.1-46.5, 48.1-48.6, 49.1-49.7, 51.2-51.6Concepts 39.1-39.5Concepts 40.4, 40.5, 43.1, 43.2, 44.1, 44.2, 45.1-45.5, 48.1, 49.1-49.4, 51.1, 51.2

Chapters 50, 52-55Concepts 52.1-52.6Concepts 50.2-50.4, 53.1-53.5, 54.1-54.5Concepts 50.1, 50.2, 54.5, 55.1-55.4

Feb

Feb-April

April

9.Review for the AP Exam and final exam Final exam – Date to be announced

May

Teaching StrategiesI have created lecture notes for every topic covered above. I have also created a virtual classroom via the publisher of our textbook. Students login to the website to view video clips, pictures, perform lab based activities, pre tests, post tests, and various reinforcing activities. The website is patterned after our textbook so students can easily match up with what is happening in lecture and where they should be on the website. Students

submit electronic assignments and assessments through the website, including many web based lab assignments. My lecture is based upon “storytelling” and student participation. Homework questions are based upon questions that arise during lecture and demand an understanding of concepts rather than memorization of facts. [C4]

In addition to the textbook and associated website, students watch one important video at the beginning of the year. Lorenzo’s Oil is shown as a preview to the importance and complexity of biochemistry, genetics, and ethics. [C6]

Students are assigned a genetic disorder as molecular genetics is approaching the end. They must prepare a lecture and present their disorder to their peers. The use of power points, video, overheads, and handouts are encouraged. The lecture is graded using a rubric and is worth 100 points. [C4]

Students are encouraged but not required to take the AP Biology Exam. While some kids to opt out of the exam, the majority of students do take it. I use a wide variety of testing strategies to prepare them for the exam in May.

I believe in testing the students at a level that is above the AP exam. The multiple choice questions given during unit exams usually require a fair amount of critical thinking in order to discover the right answer. I use multiple choice questions, taken from AP Released Exams, in my midterm and final exam. I have discovered that students that have reached high and achieve success on my unit exams have no problem handling the AP Biology exam.

I include at least one free response question with every unit exam. Many of these questions are written by me, while some are taken from the AP Released Exams. Practicing the art of free response writing all year enables the student to be ready for the four free response questions on the exam in May.

Other Test Prep Aids: Students are encouraged to purchase an AP Biology review book to prepare for the midterm, final and AP Biology exam. I have also created a website for my classes with tons of links for students to navigate through and learn more.

Lab Component [C8]

Students work in groups of 2-4 to complete most AP Biology labs. Most labs are completed within a double period of work, with some extending to a third period the next day. I make sure the students have an understanding of the lab objectives and procedure before they are free to work on the lab with little or no assistance from me.

AP Biology Lab #6 is completed at the Dolan DNA Learning Center in Cold Spring Harbor, New York. Here students can work with state of the art equipment to complete restriction analysis, mitochondrial sequencing, or DNA fingerprinting labs (Molecular Biology).

All labs completed in AP Biology are turned in and graded individually. All data, graphs, and analysis questions are submitted along with a well thought out and complete conclusion. Below is a schedule of the mandated AP Biology labs. In addition to the required AP Biology Labs, many other teacher generated labs are assigned during the year. [C8]

Lab Schedule of Required AP Biology LabsLab # Lab Title Month

Lab #1

Diffusion and Osmosis [C8]

OVERVIEW

In this laboratory you will investigate the process of diffusion and osmosis in a model of a membrane system. You also will investigate the effect of solute concentration on water potential as it relates to living plant tissues.

OBJECTIVES

Section A: Before doing this laboratory you should understand:

the mechanisms of diffusion and osmosis and their importance to cells the effects of solute size and concentration gradients on diffusion across

selectively permeable membranes the effects of a selectively permeable membrane on diffusion and osmosis

between two solutions separated by the membrane the concept of water potential the relationship between solute concentration and pressure and the water

potential of a solution the concept of molarity and its relationship to osmotic concentration

Section B: After doing this laboratory you should be able to:

measure the water potential of a solution in a controlled experiment determine the osmotic concentration of living tissue or an unknown

solution from experimental data describe the effects of water gain or loss in animal and plant cells relate osmotic potential to solute concentration and water potential

Sept

Lab #2

Enzyme Catalysis [C8]

OVERVIEW

In this laboratory you will measure the amount of product generated and then calculate the rate of conversion of hydrogen peroxide (H2O2) to water and oxygen

Sept.

gas by the enzyme catalase.

OBJECTIVES


the general functions and activities of enzymes the relationship between the structure and function of enzymes the concepts of initial reaction rates of enzymes how the concept of free energy relates to enzyme activity how pH relates to enzyme activity that changes in temperature, pH, enzyme concentration, and substrate

concentration can affect the initial reaction rates of enzyme-catalyzed reactions


measure the effects of changes of temperature, pH, enzyme concentration, and substrate concentration on reaction rates of an enzyme-catalyzed reaction in a controlled experiment

explain how environmental factors affect the rate of enzyme-catalyzed reactions

Lab #3

Mitosis and Meiosis [C8]

OVERVIEW

Exercise 3A is a study of mitosis. You will use prepared slides of onion root tips to study plant mitosis and to calculate the relative duration of the phases of mitosis in the meristem of root tissue. Prepared slides of the whitefish blastula will be used to study mitosis in animal cells and to compare animal mitosis and plant mitosis

Exercise 3B is a study of meiosis. You will simulate the stages of meiosis by using chromosome models. You will study the crossing over and recombination that occurs during meiosis. You will observe the arrangements of ascospores in the asci from a cross between wild type and mutants for tan spore coat color in the fungus Sordaria fimicola. These arrangements will be used to estimate the percentage of crossing over that occurs between the centromere and the gene that controls that tan spore color.

OBJECTIVES


the key mechanical and genetic differences between meiosis and mitosis the events of mitosis in animal and plant cells

Oct.

the events of meiosis (gametogenesis) in animal and plant cells


recognize the stages of mitosis in a plant or animal cell calculate the relative duration of the cell cycle stages describe how independent assortment and crossing over can generate

genetic variation among the products of meiosis use chromosome models to demonstrate the activity of chromosomes

during Meiosis I and Meiosis II relate chromosome activity to Mendelian segregation and independent

assortment calculate the map distance of a particular gene from a chromosome's center

for between two genes using an organism of your choice in a controlled experiment

demonstrate the role of meiosis in the formation of gametes using an organism of your choice, in a controlled experiment

compare and contrast the results of meiosis and mitosis in plant cells compare and contrast the results of meiosis and mitosis in animal cells

Lab #4

Plant Pigments and Photosynthesis [C8]

OVERVIEW

In this laboratory you will separate plant pigments using chromatography. You also will measure the rate of photosynthesis in isolated chloroplasts. The measurement technique involves the reduction of the dye, DPIP. The transfer of electrons during the light-dependent reactions of photosynthesis reduces DPIP and changes its color from blue to colorless.

OBJECTIVES


how chromatography separates two or more compounds that are initially present in a mixture

the process of photosynthesis the function of plant pigments the relationship between light wavelength or light intensity and

photosynthetic rate


separate pigments and calculate their Rf values describe a technique to determine photosynthetic rates compare photosynthetic rates at different temperatures, different light

intensities, and different wavelengths of light in a controlled experiment explain why the rate of photosynthesis vary under different environmental

conditions

Oct

Lab #5

Cell Respiration [C8]

OVERVIEW

Seeds are living but dormant. When conditions necessary to begin growth are achieved, germination occurs, cellular reactions are accelerated, and the rate of respiration greatly increases. In this laboratory you will measure oxygen consumption during respiration as the change in gas volume in respirometers containing either germinating or nongerminating peas. In addition, you will measure the respiration of these peas at two different temperatures.

OBJECTIVES


how a respirometer works in terms of the gas laws the general process of metabolism in living organisms


test the effects of temperature on the rate of cell respiration in ungerminated versus germinated seeds in a controlled experiment

calculate the rate of cell respiration from experimental data relate gas production to respiration rate

Oct./Nov.

Lab #6

Molecular Biology [C8]

OVERVIEW

In this laboratory, you will investigate some basic principles of genetic engineering. Plasmids containing specific fragments of foreign DNA will be used to transform Escherichia coli cells, conferring antibiotic (ampicillin) resistance. Restriction enzyme digests of phage lambda DNA also will be used to demonstrate techniques for separating and identifying DNA fragments using gel electrophoresis.

OBJECTIVES


how gel electrophoresis separates DNA molecules present in a mixture the principles of bacterial transformation the conditions under which cells can be transformed the process of competent cell preparation how a plasmid can be engineered to include a piece of foreign DNA how plasmid vectors are used to transfer genes how antibiotic resistance is transferred between cells

Dec

how restriction endonucleases function the importance of restriction enzymes to genetic engineering experiments


use plasmids as vectors to transform bacteria with a gene for antibiotic resistance in a controlled experiment

demonstrate how restrictions enzymes are used in genetic engineering use electrophoresis to separate DNA fragments describe the biological process of transformation in bacteria calculate transformation efficiency be able to use multiple experimental controls design a procedure to select positively for antibiotic resistant transformed

cells determine unknown DNA fragment sizes when given DNA fragments of

known size

Lab #7

Genetics of Organisms [C8]

OVERVIEW

In this laboratory, you will use fruit flies to do genetic crosses. You will learn how to collect and manipulate fruit flies, collect data from F1 and F2 generations, and analyze the results from a monohybrid, dihybrid, or sex-linked cross.

OBJECTIVES


chi-square analysis of data the life cycle of diploid organisms useful in genetics studies


investigate the independent assortment of two genes and determine whether the two genes are autosomal or sex-linked using a multi-generation experiment

analyze the data from your genetic crosses chi-square analysis techniques

Dec.

Lab #8

Population Genetics and Evolution [C8]

OVERVIEW

Jan.

In this activity, you will learn about the Hardy-Weinberg law of genetic equilibrium and study the relationship between evolution and changes in allele frequency by using your class as a sample population.

OBJECTIVES


how natural selection can alter allelic frequencies in a population the Hardy-Weinberg equation and its use in determining the frequency of

alleles in a population the effects on the allelic frequencies of selection against the homozygous

recessive or other genotypes


calculate the frequencies of alleles and genotypes in the gene pool of a population using the Hardy-Weinberg formula

discuss natural selection and other causes of microevolution as deviations from the conditions required to maintain Hardy-Weinberg equilibrium

Lab #9

Transpiration [C8]

OVERVIEW

In this laboratory, you will apply what you learned about water potential from Laboratory 1 (Diffusion and Osmosis) to the movement of water within the plant. You will measure transpiration under different laboratory conditions. You also will study the organization of the plant stem and leaf as it relates to these processes by observing sections of tissue.

OBJECTIVES


how water moves from roots to leaves in terms of physical/chemical properties of water and the forces provided by differences in water potential

the role of transpiration in the transport of water within a plant the structures used by plants to transport water and regulate water

movement


test the effects of environmental variables on rates of transpiration using a controlled experiment

make thin section of stem, identify xylem and phloem cells, and relate the function of these vascular tissues to the structures of their cells

Feb.

Lab #10

Physiology of the Circulatory System[C8]

OVERVIEW

In Exercise 10A, you will learn how to measure blood pressure. In Exercise 10B, you will measure pulse rate under different physiological conditions: standing, reclining, after the baroreceptor reflex, and during and immediately after exercise. The blood pressure and pulse rate will be analyzed and related to a relative fitness index. In Exercise 10C, you will measure the effect of temperature on the heart rate of the water flea, Daphnia magna.

OBJECTIVES


the relationship between temperature and rates of physiological processes basic anatomy of various circulatory systems


measure heart rate and blood pressure in a human volunteer describe the effect of changing body position on heart rate and blood

pressure explain how exercise changes heart rate determine a human's fitness index analyze pooled cardiovascular data discuss and explain the relationship between heart rate and temperature

March

Lab # 11

Animal Behavior [C8]

OVERVIEW

In this laboratory, you will observe the behavior of an insect and design an experiment to investigate its responses to environmental variables. You also will observe and investigate mating behavior.

OBJECTIVES


the concept of distribution of organisms in a resource gradient the difference between a kinesis and a taxis


April

measure the effects of environmental variables on habitat selection in a controlled experiment

describe the different types of insect mating behaviors

Lab #12

Dissolved Oxygen and Aquatic Primary Productivity [C8]

OVERVIEW

In Exercise 12A, you will measure and analyze the dissolved oxygen concentration in water samples at varying temperatures. In Exercise 12B, you will measure and analyze the primary productivity of natural waters or laboratory cultures as a function of light intensity.

OBJECTIVES


the biological importance of carbon and oxygen cycling in ecosystems how primary productivity relates to the metabolism of organisms in an

ecosystem the physical and biological factors that affect the solubility of gasses in

aquatic ecosystems the relationship between dissolved oxygen and the process of

photosynthesis and respiration as they affect primary productivity


measure primary productivity based on changes in dissolved oxygen in a controlled experiment

investigate the effects of changing light intensity and/or inorganic nutrient concentrations on primary productivity in a controlled experiment

April

Student EvaluationThe grade a student earns each ten week marking period is based upon their performance on the unit exams, labs, homework, textbook website submissions, quizzes, and participation. I assign a point value to every assignment and the final grade is determined based upon the percentage of total points earned during the marking period.

Assignment PointsUnit Exams 100

Midterm/Final Exam 200

AP Biology Labs 100Quizzes 10-25

Homework 10-50

Sample Evaluation

Assignment Points Points Earned

Quiz #1 10 8Homework #1 10 7

Lab #1 100 95Quiz #2 20 15

Unit Exam #1 100 82Quiz #3 10 10Lab #2 100 95

Homework #2 50 45Unit Exam #2 100 99

Web Site Submissions/Effort 40 30540 486/540 = 90%

Research Paper [C4]

Students enter the March of Dimes Essay Competition every January. The March of Dimes essay committee develops an important question based on current trends in science. Past topics included the cause of autism, AIDS vaccine potential, and pandemics. All student essays will be submitted to the March of Dimes for evaluation and a second copy will be graded by me. Students from the tri-state area submit essays and are invited to attend the Nelson Rosenthal Convocation held at NYU each spring. If our school has a first or second winner, the March of Dimes will pay for transportation to the convocation. Students will be able to hear leaders in the field discuss the latest research and answer student questions. Students have at least one month to work on their essay (5 pages) and the paper is worth 100 points.

Sample Lecture OutlineI have included the following outline in order to illustrate the depth of coverage and how the eight major themes (as specified in the AP Biology course description) are integrated.This detailed outline is taken from the media resources that came with our purchase of the AP Biology textbook (Campbell, N., Reece, J., and Mitchell, L., 2004. Biology,

Seventh Edition, Addison Wesley Publishing, 1312 pp.). I have edited the outline slightly to match what will be taught in my classroom.

Overview: The Key Roles of Cell Division [C1]

The ability of organisms to reproduce their kind is the one characteristic that best distinguishes living things from nonliving matter.

The continuity of life is based on the reproduction of cells, or cell division.

Cell division functions in reproduction, growth, and repair.

The division of a unicellular organism reproduces an entire organism, increasing the population.

Cell division on a larger scale can produce progeny for some multicellular organisms.

Cell division enables a multicellular organism to develop from a single fertilized egg or zygote.

In a multicellular organism, cell division functions to repair and renew cells that die from normal wear and tear or accidents.

Cell division is part of the cell cycle, the life of a cell from its origin in the division of a parent cell until its own division into two.

Abnormal cell division can develop into cancer.

Concept 12.1 Cell division results in genetically identical daughter cells [C2]

Cell division requires the distribution of identical genetic material—DNA—to two daughter cells.

What is remarkable is the fidelity with which DNA is passed along, without dilution, from one generation to the next.

A dividing cell duplicates its DNA, allocates the two copies to opposite ends of the cell, and then splits into two daughter cells.

A cell’s genetic information, packaged as DNA, is called its genome.

In prokaryotes, the genome is often a single long DNA molecule.

In eukaryotes, the genome consists of several DNA molecules.

DNA molecules are packaged into chromosomes.

Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus

Human somatic cells (body cells) have 46 chromosomes, made up of two sets of 23 (one from each parent).

Human gametes (sperm or eggs) have one set of 23 chromosomes, half the number in a somatic cell.

Eukaryotic chromosomes are made of chromatin, a complex of DNA and associated protein.

Each single chromosome contains one long, linear DNA molecule carrying hundreds or thousands of genes, the units that specify an organism’s inherited traits.

The associated proteins maintain the structure of the chromosome and help control gene activity.

When a cell is not dividing, each chromosome is in the form of a long, thin chromatin fiber.

Before cell division, chromatin condenses, coiling and folding to make a smaller package.

Each duplicated chromosome consists of two sister chromatids, which contain identical copies of the chromosome’s DNA.

The chromatids are initially attached by adhesive proteins along their lengths.

As the chromosomes condense, the region where the chromatids connect shrinks to a narrow area, the centromere.

Later in cell division, the sister chromatids are pulled apart and repackaged into two new nuclei at opposite ends of the parent cell.

Once the sister chromatids separate, they are considered individual chromosomes.

Mitosis, the formation of the two daughter nuclei, is usually followed by division of the cytoplasm, cytokinesis.

These processes start with one cell and produce two cells that are genetically identical to the original parent cell.

Each of us inherited 23 chromosomes from each parent: one set in an egg and one set in sperm.

The fertilized egg, or zygote, underwent cycles of mitosis and cytokinesis to produce a fully developed multicellular human made up of 200 trillion somatic cells.

These processes continue every day to replace dead and damaged cells.

Essentially, these processes produce clones—cells with identical genetic information.

In contrast, gametes (eggs or sperm) are produced only in gonads (ovaries or testes) by a variation of cell division called meiosis.

Meiosis yields four nonidentical daughter cells, each with half the chromosomes of the parent.

In humans, meiosis reduces the number of chromosomes from 46 to 23.

Fertilization fuses two gametes together and doubles the number of chromosomes to 46 again.

Concept 12.2 The mitotic phase alternates with interphase in the cell cycle [C2]

The mitotic (M) phase of the cell cycle alternates with the much longer interphase.

The M phase includes mitosis and cytokinesis.

Interphase accounts for 90% of the cell cycle.

During interphase, the cell grows by producing proteins and cytoplasmic organelles, copies its chromosomes, and prepares for cell division.

Interphase has three subphases: the G1 phase (“first gap”), the S phase (“synthesis”), and the G2 phase (“second gap”).

During all three subphases, the cell grows by producing proteins and cytoplasmic organelles such as mitochondria and endoplasmic reticulum.

However, chromosomes are duplicated only during the S phase.

The daughter cells may then repeat the cycle.

A typical human cell might divide once every 24 hours.

Of this time, the M phase would last less than an hour, while the S phase might take 10–12 hours, or half the cycle.

The rest of the time would be divided between the G1 and G2 phases.

The G1 phase varies most in length from cell to cell.

Mitosis is a continuum of changes.

For convenience, mitosis is usually broken into five subphases: prophase, prometaphase, metaphase, anaphase, and telophase.

In late interphase, the chromosomes have been duplicated but are not condensed.

A nuclear membrane bounds the nucleus, which contains one or more nucleoli.

The centrosome has replicated to form two centrosomes.

In animal cells, each centrosome features two centrioles.

In prophase, the chromosomes are tightly coiled, with sister chromatids joined together.

The nucleoli disappear.

The mitotic spindle begins to form.

It is composed of centrosomes and the microtubules that extend from them.

The radial arrays of shorter microtubules that extend from the centrosomes are called asters.

The centrosomes move away from each other, apparently propelled by lengthening microtubules.

During prometaphase, the nuclear envelope fragments, and microtubules from the spindle interact with the condensed chromosomes.

Each of the two chromatids of a chromosome has a kinetochore, a specialized protein structure located at the centromere.

Kinetochore microtubules from each pole attach to one of two kinetochores.

Nonkinetochore microtubules interact with those from opposite ends of the spindle.

The spindle fibers push the sister chromatids until they are all arranged at the metaphase plate, an imaginary plane equidistant from the poles, defining metaphase.

At anaphase, the centromeres divide, separating the sister chromatids.

Each is now pulled toward the pole to which it is attached by spindle fibers.

By the end, the two poles have equivalent collections of chromosomes.

At telophase, daughter nuclei begin to form at the two poles.

Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system.

The chromosomes become less tightly coiled.

Cytokinesis, division of the cytoplasm, is usually well underway by late telophase.

In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.

In plant cells, vesicles derived from the Golgi apparatus produce a cell plate at the middle of the cell.

The mitotic spindle distributes chromosomes to daughter cells: a closer look.

The mitotic spindle, fibers composed of microtubules and associated proteins, is a major driving force in mitosis.

As the spindle assembles during prophase, the elements come from partial disassembly of the cytoskeleton.

The spindle fibers elongate by incorporating more subunits of the protein tubulin.

Assembly of the spindle microtubules starts in the centrosome.

The centrosome (microtubule-organizing center) is a nonmembranous organelle that organizes the cell’s microtubules.

In animal cells, the centrosome has a pair of centrioles at the center, but the centrioles are not essential for cell division.

During interphase, the single centrosome replicates to form two centrosomes.

As mitosis starts, the two centrosomes are located near the nucleus.

As the spindle microtubules grow from them, the centrioles are pushed apart.

By the end of prometaphase, they are at opposite ends of the cell.

An aster, a radial array of short microtubules, extends from each centrosome.

The spindle includes the centrosomes, the spindle microtubules, and the asters.

Each sister chromatid has a kinetochore of proteins and chromosomal DNA at the centromere.

The kinetochores of the joined sister chromatids face in opposite directions.

During prometaphase, some spindle microtubules (called kinetochore microtubules) attach to the kinetochores.

When a chromosome’s kinetochore is “captured” by microtubules, the chromosome moves toward the pole from which those microtubules come.

When microtubules attach to the other pole, this movement stops and a tug-of-war ensues.

Eventually, the chromosome settles midway between the two poles of the cell, on the metaphase plate.

Nonkinetochore microtubules from opposite poles overlap and interact with each other.

By metaphase, the microtubules of the asters have grown and are in contact with the plasma membrane.

The spindle is now complete.

Anaphase commences when the proteins holding the sister chromatids together are inactivated.

Once the chromosomes are separate, full-fledged chromosomes, they move toward opposite poles of the cell.

How do the kinetochore microtubules function into the poleward movement of chromosomes?

One hypothesis is that the chromosomes are “reeled in” by the shortening of microtubules at the spindle poles.

Experimental evidence supports the hypothesis that motor proteins on the kinetochore “walk” the attached chromosome along the microtubule toward the nearest pole.

Meanwhile, the excess microtubule sections depolymerize at their kinetochore ends.

What is the function of the nonkinetochore microtubules?

Nonkinetochore microtubules are responsible for lengthening the cell along the axis defined by the poles.

These microtubules interdigitate and overlap across the metaphase plate.

During anaphase, the area of overlap is reduced as motor proteins attached to the microtubules walk them away from one another, using energy from ATP.

As microtubules push apart, the microtubules lengthen by the addition of new tubulin monomers to their overlapping ends, allowing continued overlap.

Cytokinesis divides the cytoplasm: a closer look.

Cytokinesis, division of the cytoplasm, typically follows mitosis.

In animal cells, cytokinesis occurs by a process called cleavage.

The first sign of cleavage is the appearance of a cleavage furrow in the cell surface near the old metaphase plate.

On the cytoplasmic side of the cleavage furrow is a contractile ring of actin microfilaments associated with molecules of the motor protein myosin.

Contraction of the ring pinches the cell in two.

Cytokinesis in plants, which have cell walls, involves a completely different mechanism.

During telophase, vesicles from the Golgi coalesce at the metaphase plate, forming a cell plate.

The plate enlarges until its membranes fuse with the plasma membrane at the perimeter.

The contents of the vesicles form new cell wall material between the daughter cells.

Mitosis in eukaryotes may have evolved from binary fission in bacteria.

Prokaryotes reproduce by binary fission, not mitosis.

Most bacterial genes are located on a single bacterial chromosome that consists of a circular DNA molecule and associated proteins.

While bacteria are smaller and simpler than eukaryotic cells, they still have large amounts of DNA that must be copied and distributed equally to two daughter cells.

The circular bacterial chromosome is highly folded and coiled in the cell.

In binary fission, chromosome replication begins at one point in the circular chromosome, the origin of replication site, producing two origins.

As the chromosome continues to replicate, one origin moves toward each end of the cell.

While the chromosome is replicating, the cell elongates.

When replication is complete, its plasma membrane grows inward to divide the parent cell into two daughter cells, each with a complete genome.

Researchers have developed methods to allow them to observe the movement of bacterial chromosomes.

The movement is similar to the poleward movements of the centromere regions of eukaryotic chromosomes.

However, bacterial chromosomes lack visible mitotic spindles or even microtubules.

The mechanism behind the movement of the bacterial chromosome is becoming clearer but is still not fully understood.

Several proteins have been identified and play important roles.

How did mitosis evolve?

There is evidence that mitosis had its origins in bacterial binary fission.

Some of the proteins involved in binary fission are related to eukaryotic proteins.

Two of these are related to eukaryotic tubulin and actin proteins.

As eukaryotes evolved, the ancestral process of binary fission gave rise to mitosis.

Possible intermediate evolutionary steps are seen in the division of two types of unicellular algae.

In dinoflagellates, replicated chromosomes are attached to the nuclear envelope.

In diatoms, the spindle develops within the nucleus.

In most eukaryotic cells, the nuclear envelope breaks down and a spindle separates the chromosomes.

Concept 12.3 The cell cycle is regulated by a molecular control system [C2]

The timing and rates of cell division in different parts of an animal or plant are crucial for normal growth, development, and maintenance.

The frequency of cell division varies with cell type.

Some human cells divide frequently throughout life (skin cells).

Others have the ability to divide, but keep it in reserve (liver cells).

Mature nerve and muscle cells do not appear to divide at all after maturity.

Investigation of the molecular mechanisms regulating these differences provide important insights into the operation of normal cells, and may also explain cancer cells escape controls.

Cytoplasmic signals drive the cell cycle.

The cell cycle appears to be driven by specific chemical signals present in the cytoplasm.

Some of the initial evidence for this hypothesis came from experiments in which cultured mammalian cells at different phases of the cell cycle were fused to form a single cell with two nuclei.

Fusion of an S phase cell and a G1 phase cell induces the G1 nucleus to start S phase.

This suggests that chemicals present in the S phase nucleus stimulated the fused cell.

Fusion of a cell in mitosis (M phase) with one in interphase (even G1 phase) induces the second cell to enter mitosis.

The sequential events of the cell cycle are directed by a distinct cell cycle control system.

Cyclically operating molecules trigger and coordinate key events in the cell cycle.

The control cycle has a built-in clock, but it is also regulated by external adjustments and internal controls.

A checkpoint in the cell cycle is a critical control point where stop and go-ahead signals regulate the cycle.

The signals are transmitted within the cell by signal transduction pathways.

Animal cells generally have built-in stop signals that halt the cell cycle at checkpoints until overridden by go-ahead signals.

Many signals registered at checkpoints come from cellular surveillance mechanisms.

These indicate whether key cellular processes have been completed correctly.

Checkpoints also register signals from outside the cell.

Three major checkpoints are found in the G1, G2, and M phases.

For many cells, the G1 checkpoint, the “restriction point” in mammalian cells, is the most important.

If the cell receives a go-ahead signal at the G1 checkpoint, it usually completes the cell cycle and divides.

If it does not receive a go-ahead signal, the cell exits the cycle and switches to a nondividing state, the G0 phase.

Most cells in the human body are in this phase.

Liver cells can be “called back” to the cell cycle by external cues, such as growth factors released during injury.

Highly specialized nerve and muscle cells never divide.

Rhythmic fluctuations in the abundance and activity of cell cycle control molecules pace the events of the cell cycle.

These regulatory molecules include protein kinases that activate or deactivate other proteins by phosphorylating them.

These kinases are present in constant amounts but require attachment of a second protein, a cyclin, to become activated.

Levels of cyclin proteins fluctuate cyclically.

Because of the requirement for binding of a cyclin, the kinases are called cyclin-dependent kinases, or Cdks.

Cyclin levels rise sharply throughout interphase, and then fall abruptly during mitosis.

Peaks in the activity of one cyclin-Cdk complex, MPF, correspond to peaks in cyclin concentration.

MPF (“maturation-promoting factor” or “M-phase-promoting-factor”) triggers the cell’s passage past the G2 checkpoint to the M phase.

MPF promotes mitosis by phosphorylating a variety of other protein kinases.

MPF stimulates fragmentation of the nuclear envelope by phosphorylation of various proteins of the nuclear lamina.

It also triggers the breakdown of cyclin, dropping cyclin and MPF levels during mitosis and inactivating MPF.

The noncyclin part of MPF, the Cdk, persists in the cell in inactive form until it associates with new cyclin molecules synthesized during the S and G2 phases of the next round of the cycle.

At least three Cdk proteins and several cyclins regulate the key G1 checkpoint.

Similar mechanisms are also involved in driving the cell cycle past the M phase checkpoint.

Internal and external cues help regulate the cell cycle.

While research scientists know that active Cdks function by phosphorylating proteins, the identity of all these proteins is still under investigation.

Scientists do not yet know what Cdks actually do in most cases.

Some steps in the signaling pathways that regulate the cell cycle are clear.

Some signals originate inside the cell, others outside.

The M phase checkpoint ensures that all the chromosomes are properly attached to the spindle at the metaphase plate before anaphase.

This ensures that daughter cells do not end up with missing or extra chromosomes.

A signal to delay anaphase originates at kinetochores that have not yet attached to spindle microtubules.

This keeps the anaphase-promoting complex (APC) in an inactive state.

When all kinetochores are attached, the APC activates, triggering breakdown of cyclin and inactivation of proteins holding sister chromatids together.

A variety of external chemical and physical factors can influence cell division.

For example, cells fail to divide if an essential nutrient is left out of the culture medium.

Particularly important for mammalian cells are growth factors, proteins released by one group of cells that stimulate other cells to divide.

For example, platelet-derived growth factors (PDGF), produced by platelet blood cells, bind to tyrosine-kinase receptors of fibroblasts, a type of connective tissue cell.

This triggers a signal-transduction pathway that allows cells to pass the G1 checkpoint and divide.

Each cell type probably responds specifically to a certain growth factor or combination of factors.

The role of PDGF is easily seen in cell culture.

Fibroblasts in culture will only divide in the presence of a medium that also contains PDGF.

In a living organism, platelets release PDGF in the vicinity of an injury.

The resulting proliferation of fibroblasts helps heal the wound.

At least 50 different growth factors can trigger specific cells to divide.

The effect of an external physical factor on cell division can be seen in density-dependent inhibition of cell division.

Cultured cells normally divide until they form a single layer on the inner surface of the culture container.

If a gap is created, the cells will grow to fill the gap.

At high densities, the amount of growth factors and nutrients is insufficient to allow continued cell growth.

Most animal cells also exhibit anchorage dependence for cell division.

To divide, they must be anchored to a substratum, typically the extracellular matrix of a tissue.

Control appears to be mediated by pathways involving plasma membrane proteins and elements of the cytoskeleton linked to them.

Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence.

Cancer cells have escaped from cell cycle controls.

Cancer cells divide excessively and invade other tissues because they are free of the body’s control mechanisms.

Cancer cells do not stop dividing when growth factors are depleted.

This is either because a cancer cell manufactures its own growth factors, has an abnormality in the signaling pathway, or has an abnormal cell cycle control system.

If and when cancer cells stop dividing, they do so at random points, not at the normal checkpoints in the cell cycle.

Cancer cells may divide indefinitely if they have a continual supply of nutrients.

In contrast, nearly all mammalian cells divide 20 to 50 times under culture conditions before they stop, age, and die.

Cancer cells may be “immortal.”

HeLa cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in culture.

The abnormal behavior of cancer cells begins when a single cell in a tissue undergoes a transformation that converts it from a normal cell to a cancer cell.

Normally, the immune system recognizes and destroys transformed cells.

However, cells that evade destruction proliferate to form a tumor, a mass of abnormal cells.

If the abnormal cells remain at the originating site, the lump is called a benign tumor.

Most do not cause serious problems and can be fully removed by surgery.

In a malignant tumor, the cells become invasive enough to impair the functions of one or more organs.

In addition to chromosomal and metabolic abnormalities, cancer cells often lose attachment to nearby cells, are carried by the blood and lymph system to other tissues, and start more tumors in an event called metastasis.

Cancer cells are abnormal in many ways.

They may have an unusual number of chromosomes, their metabolism may be disabled, and they may cease to function in any constructive way.

Cancer cells may secrete signal molecules that cause blood vessels to grow toward the tumor.

Treatments for metastasizing cancers include high-energy radiation and chemotherapy with toxic drugs.

These treatments target actively dividing cells.

Chemotherapeutic drugs interfere with specific steps in the cell cycle.

For example, Taxol prevents mitotic depolymerization, preventing cells from proceeding past metaphase.

The side effects of chemotherapy are due to the drug’s effects on normal cells.

Researchers are beginning to understand how a normal cell is transformed into a cancer cell.

The causes are diverse, but cellular transformation always involves the alteration of genes that influence the cell cycle control system.

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