Chapter Chapter Four (Cell Structure and Function)Four ...€¦ · Chapter Chapter Four (Cell Structure and ... Four (Cell Structure and Function) SECTION ONE: ... Cells are the basic

UNIT TWO: CELL BIOLOGY (Text from Modern Biology, Holt, Rinehart, and Winston)

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Chapter Chapter Chapter Chapter Four (Cell Structure and Function)Four (Cell Structure and Function)Four (Cell Structure and Function)Four (Cell Structure and Function) SECTION ONE: THE HISTORY OF CELL BIOLOGYSECTION ONE: THE HISTORY OF CELL BIOLOGYSECTION ONE: THE HISTORY OF CELL BIOLOGYSECTION ONE: THE HISTORY OF CELL BIOLOGY

THE DISCOVERY OF CELLS

A cell cell cell cell is the smallest unit that can carry on all of the process of life. By using microscopes, naturalists in the 17th century were able to study objects two small to be seen with the naked eye. Hooke Using an early light microscope, English scientist Robert Hooke looked at a thin slice of cork from the bark of a cork oak tree in 1665. He described “a great many little boxes” that reminded him of the cells where monks live. Leeuwenhoek A Dutch trader named Anton van Leeuwenhoek made microscopes that had 10 times the magnification of Hooke’s instruments. In 1673, he was able to observe living cells of algae and protists.

THE CELL THEORY It was not until about 150 years later than biologists began to organize information about cells more completely. The observations of botanist Matthias Schleiden, zoologist Theodor Schwann, and physician Rudolf Virchow were combined to form the cell cell cell cell theory, a basic theory about how cells are related to life. Developments in Cell Biology After the initial formation of the cell theory, scientists began to further investigate how cells function. In 1827, Karl Von Baer discovered the mammalian egg and in 1855, Rudolf Virchow added to the cell theory. The Cellular Basis in Life In addition to the seven characteristics mentioned in the last chapter, all living things share a common history. All cells share characteristics.

The Cell TheoryThe Cell TheoryThe Cell TheoryThe Cell Theory All living organisms are composed of one or more cells. Cells are the basic units of structure and function in an organism. Cells come from only the reproduction of existing cells.


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SECTION TWO: INTRODUCSECTION TWO: INTRODUCSECTION TWO: INTRODUCSECTION TWO: INTRODUCTION TO CELLSTION TO CELLSTION TO CELLSTION TO CELLS

CELL DIVERSITY

Cell Shape The diversity in cell shapes reflects the different functions of cells. To perform its function effectively, a cell’s shape has evolved to be either simple or complex. Cell Size The size of a cell is limited by its surface area –to-volume ratio. When a cell grows, its volume increases much faster than its surface area. If cells became too large, their surface area wouldn’t be able to allow materials to enter or leave the cell quickly enough to meet the cell’s needs.

BASIC PARTS OF A CELL

Plasma Membrane The plasma membraneplasma membraneplasma membraneplasma membrane (cell membrane) is the cell’s outer boundary that acts as a barrier between the inside and outside of a cell. All materials exit or enter through the plasma membrane. Cytoplasm The region of the cell that is in the plasma membrane that includes the fluid, cytoskeleton, and all of the organelles excluding the nucleus is the cytoplasmcytoplasmcytoplasmcytoplasm. The cytosolcytosolcytosolcytosol is the part of the cytoplasm that includes molecules and small particles.

SECTION 1 REVIEWSECTION 1 REVIEWSECTION 1 REVIEWSECTION 1 REVIEW

1.1.1.1. Describe the major contributions of Hooke and Leeuwenhoek to cell biology. 2.2.2.2. Identify the advance that enabled Leeuwenhoek to view the first living cells. 3.3.3.3. Describe the research that led to the development of the cell theory. 4.4.4.4. State the three fundamental parts of the cell theory. 5.5.5.5. List three major events in the history of cell biology. 6.6.6.6. Name eight characteristics that all living things share.

CRITICAL THINKING

7.7.7.7. If you could go back in time, how would you explain the cell theory to someone who had never heard of cells? 8.8.8.8. A biologists photographs a cell in a microscope magnified at 40 times. The cell in the

photo is 2 mm in diameter. What is the true diameter to the cell in micrometers (µm)? 9.9.9.9. If organisms exist on other planets, would they consist of cells? Defend your answer.


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Control Center Cells carry information in the form of DNA for regulating their functions and reproducing themselves. Some cells have a membrane-bound organelle that contains a cell’s DNA, called the nucleusnucleusnucleusnucleus. It maintains its shape with the help of a protein skeleton called the nuclear matrix. Below is the nucleus of a typical animal cell.

TWO BASIC TYPES OF CELLS Prokaryotes ProkaryotesProkaryotesProkaryotesProkaryotes are organisms that lack a membrane bound nucleus and membrane-bound organelles. Their genetic information is concentrated in a part of the cell called a nucleoid. Eukaryotes Organisms made up of one or more cells that have a nucleus and membrane-bound organelles are called eukaryoteseukaryoteseukaryoteseukaryotes. Eukaryotic cells also have subcellular structures called organellesorganellesorganellesorganelles, which are intracellular bodies that perform specific functions for the cell.

CELLULAR ORGANIZATION

Colonies A colonial organism is a collection of genetically identical cells that live together in a connected group.


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True Multicellularity A group of similar cells and their products that carry out a specific function is a tissuetissuetissuetissue. Groups of tissues that perform a particular job in an organism are called organsorgansorgansorgans. An organ systemorgan systemorgan systemorgan system is a group of organs that accomplish related tasks. SECTION THREE: CELL ORGANELSECTION THREE: CELL ORGANELSECTION THREE: CELL ORGANELSECTION THREE: CELL ORGANELLES AND FEATURESLES AND FEATURESLES AND FEATURESLES AND FEATURES

PLASMA MEMBRANE

Membrane Lipids The plasma membrane is made of phospholipids with their nonpolar tails pointing inward and their polar head pointing outward. The result is a double layer called a phospholipid bilayerphospholipid bilayerphospholipid bilayerphospholipid bilayer. The cell membranes of eukaryotes also contain lipids, called sterols, between the tails of the phospholipids. They prevent the membrane from freezing at low temperatures and keep it firm.

SECTION 2SECTION 2SECTION 2SECTION 2 REVIEW REVIEW REVIEW REVIEW

1.1.1.1. Describe the relationship between a cell’s shape and its function. 2.2.2.2. Explain the factor that limits cell size. 3.3.3.3. Identify and describe three basic parts of a cell. 4.4.4.4. Summarize the differences between prokaryotic cells and eukaryotic cells. 5.5.5.5. List four levels of organization that combine to form an organism.

CRITICAL THINKING

6. 6. 6. 6. If a cube-shaped cell grew from 1 cm per side to 3 cm per side, how much would its volume change? 7777.... Why do you think there are three basic structures common to all cell types? Support your answer. 8888.... How are the functions of prokaryotic cells controlled without a nucleus?


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Membrane Proteins Plasma membranes often contain specific proteins embedded within the lipid bilayer, called integral proteins. Proteins that extend across the plasma membrane and are exposed to both the interior and exterior have the ability to detect environmental signals and transmit them to the inside of the cell. Peripheral proteins lie on only one side of the membrane and are not embedded in it. Integral proteins exposed to the cell’s external environment often have carbohydrates attached to them. They play important roles in transporting molecules into the cell. Fluid Mosaic Model The fluid mosaic model states that the phospholipid bilayer behaves like a fluid more than a solid. Because the lipids and proteins in the membrane can move laterally, the pattern (“mosaic”) of the lipids/proteins in the cell membrane constantly changes.

NUCLEUS

The nucleus is filled with nucleoplasm, which a jelly-like substance holds the contents of the nucleus and works much like a cell’s cytoplasm. The nucleus is home to a cell’s genetic information, and protects it. When a cell is not dividing, the DNA in the nucleus is in the form of a threadlike material called chromatin. When a cell is about to divide, the chromatin condenses to form chromosomeschromosomeschromosomeschromosomes, structures in the nucleus made of DNA and protein. In the nucleus, DNA is transcribed into RNA, which moves to the cytoplasm to carry out its function.


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Nuclear Envelope Surrounding the nucleus is a double membrane, the nuclear envelopenuclear envelopenuclear envelopenuclear envelope. It is made of two phospholipid bilayers. The surface of the nuclear envelope is covered with nuclear pores, which are protein-lined holes. They provide passageways fro materials to enter and leave the nucleus. Nucleolus Most nuclei contain at least one denser area, called the nucleolusnucleolusnucleolusnucleolus. It is the site where DNA is concentrated when in the process of making ribosomal RNA. RibosomesRibosomesRibosomesRibosomes are organelles made of protein and RNA that direct protein synthesis in the cytoplasm.

MITOCHONDRIA

MitochondriaMitochondriaMitochondriaMitochondria are tiny organelles that transfer energy from organic molecules to ATP, which powers most of the cell’s chemical reactions. The more active a cell is the more mitochondria it has. Like a nucleus, a mitochondrion has an inner and outer phospholipid membrane. The outer membrane separates the mitochondrion from the cytosol and the inner membrane contains proteins that carry out energy-harvesting chemical reactions. The inner membrane is also known as cristae.


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Mitochondrial DNA Mitochondria have their own DNA and can only reproduce by division.

RIBOSOMES

Ribosomes are small, somewhat spherical organelles that build protein. They do not have a membrane, and are composed of RNA molecules and protein. Their assembly begins in the nucleolus and is completed in the cytoplasm. One large and one small subunit come together to make a functioning ribosome.

ENDOPLASMIC RETICULUM

The endoplasmic reticulumendoplasmic reticulumendoplasmic reticulumendoplasmic reticulum (ER), is a system of membranous tubes and sacs (cisternae). Acting as a highway for molecules, the amount of ER inside a cell fluctuates depending on the cell’s activity. There are both smooth and rough ER. Rough Endoplasmic Reticulum The rough ER is a system of interconnected, flattened sacs covered with ribosomes, which produces proteins and phospholipids. Certain types of proteins are produced by the rough ER’s ribosomes which later move out of the cell or into one of the cell’s membranes. Rough ER is common in cells that produce large amount of proteins for export into the body. Smooth Endoplasmic Reticulum Smooth ER lacks ribosomes, which makes it appear smooth. Most cells have little smooth ER, which builds lipids such as cholesterol. In skeletal and heart muscle cells, smooth ER releases calcium. In liver and kidney cells, it detoxifies drugs and poisons.


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GOLGI APPARATUS

The Golgi apparatusGolgi apparatusGolgi apparatusGolgi apparatus is another system of flattened, membranous sacs. The sacs nearest the nucleus receive vesicles (small sacs surrounded by single membrane) from the ER containing newly made proteins or lipids. These sacs travel from the different parts of the Golgi apparatus, transporting substances. The Golgi apparatus’ membranes modify the contents of the different vesicles and direct them to various parts of the cells.

VESICLES

Surrounded by a single membrane, vesicles are small, spherically shaped sacs that are classified by their contents. They migrate to and merge with the plasma membrane, releasing their contents to the outside of the cell. Lysosomes LysosomesLysosomesLysosomesLysosomes are vesicles that bud from the Golgi apparatus and contain digestive enzymes. As previously discussed, these enzymes can break down large molecules. Within a cell, lysosomes digests worn-out organelles. This process is called autophagy. They also break down cells when it is time for the cell to die. By destroying cells when they no longer work properly, lysosomes help maintain an organism’s health. The digestion of damaged or extra cells by their own lysosomes is called autolysis. Peroxisomes Not produced by the Golgi apparatus, peroxisomes contain different enzymes than lysosomes. They are abundant in liver and kidney cells, where they neutralize oxygen ions that can damage cells and detoxify drugs. They can also break down fatty acids so mitochondria can use them as an energy source.


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Other Vesicles Glyoxysomes are specialized peroxisomes which can be found in the seeds of some plants. They break down stored fats to provide energy for the plant embryo. Some cells surround material with a plasma membrane, which becomes a vesicle inside the cell called an endosome. These act as food for lysosomes. Contractile vacuoles are vesicles that can contract and get rid of extra water in a cell. Protein Synthesis One of a cell’s major jobs is to produce protein. Below you can see the path proteins take from synthesis to export.

CYTOSKELETON

The cytoskeletoncytoskeletoncytoskeletoncytoskeleton is a network of thin filaments and tubes that crisscrosses the cytosol. They give shape to the cell from the inside, much like the way tent poles support a tent’s shape. It also acts as a system of internal tracks, on which items move around in the cell. The cytoskeleton’s functions are based on several structures, including microtubules, microfilaments, and intermediate filaments. Microtubules MicrotubulesMicrotubulesMicrotubulesMicrotubules are hollow tubes made of a protein called tubulin. Each tubulin molecule is made up of two slightly different subunits. Microtubules radiate outward from the centrosome, a central point near the nucleus. Their job is to hold organelles in place, maintain a cell’s shape, and guide the movement of organelles and molecules.


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Microfilaments Long threads of actin (beadlike protein) linked end to end and wrapped around each other are microfilamentsmicrofilamentsmicrofilamentsmicrofilaments. Finer than microtubules, they contribute to cell movement. Intermediate Filaments Intermediate filaments are rods that anchor the nucleus and some other organelles to their designated spot in the cell. They maintain the internal shape of the nucleus. Large quantities of intermediate filament proteins are produced by hair-follicle cells. Cilia and Flagella CilCilCilCiliaiaiaia and flagellaflagellaflagellaflagella are hair-like structures that extend from the surface of the cell, and help the cell move. Cilia are short and present in large numbers on certain cells, and flagella are longer, appearing in less numerous quantities. Cilia and flagella have a membrane on their outer surface and also have nine pairs of microtubules around two central tubules in their internal structure. Cilia and cells in the inner ear vibrate and help detect sound. On protists, cilia can cover their surface and move them through water. Cells also use flagella to propel themselves. Centrioles CentriolesCentriolesCentriolesCentrioles consist of two shot cylinders of microtubules at right angles to each other, situated in the cytoplasm near the nuclear envelope. These occur in animal cells, and organize the microtubules of the cytoskeleton during cell division. Plant cells do not have centrioles, and instead have basal bodies. Basal bodies organize the development of cilia and flagella.


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SECTION FOUR: UNIQUE FEATURES OF PLANT CELSECTION FOUR: UNIQUE FEATURES OF PLANT CELSECTION FOUR: UNIQUE FEATURES OF PLANT CELSECTION FOUR: UNIQUE FEATURES OF PLANT CELLSLSLSLS

PLANT CELLS

Most of the parts of the cell previously discussed are common to all eukaryotic cells. However, plant cells have additional kinds of structures important to plant function: cell walls, large central vacuoles, and plastids.

SECTION 3 REVIEWSECTION 3 REVIEWSECTION 3 REVIEWSECTION 3 REVIEW

1.1.1.1. Explain how the fluid mosaic model describes the plasma membrane. 2.2.2.2. List three cellular functions that occur in the nucleus. 3.3.3.3. Describe the organelles that are found in a eukaryotic cell. 4.4.4.4. Identify two characteristics that make mitochondria different from other organelles. 5.5.5.5. Contrast three types of cytoskeletal fibers.

CRITICAL THINKING

6. 6. 6. 6. If a cell has a high energy requirement, would you expect the cell to have many mitochondria or a few mitochondria? Why? 7.7.7.7. How do scientists think that mitochondria originated? Why? 8.8.8.8. It is not completely accurate to say that organelles are floating freely in the cytosol. Why not?


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CELL WALL

The cell wallcell wallcell wallcell wall is a rigid layer that lies outside the cell’s plasma membrane. The carbohydrate cellulose is embedded in proteins and other carbohydrates, forming a box around each cell. Pores in the cell wall allow water, ions, and certain molecules to enter and exit the cell. Primary and Secondary Cell Walls Cellulose is made directly on the surface of the plasma membrane by enzymes traveling along the membrane. These enzymes are directed by microtubules inside the plasma membrane. Based on the orientation of the microtubules, the growth of the primary cell wall occurs in one direction. In some plants, when the cell stops growing, it secrets the secondary cell wall between the plasma membrane and the primary cell wall. The secondary cell wall can no longer expand.

CENTRAL VACUOLE

A large, fluid-filled organelle that stores water, enzymes, metabolic wastes, and other materials in a plant cell is the central vacuolecentral vacuolecentral vacuolecentral vacuole. It forms as smaller vacuoles fuse together. The central vacuole makes up 90 percent of the plan cell’s volume. When there is plenty of water, the central vacuole expands and a plant stands upright, as opposed to where there is little water and the central vacuole shrinks. Once it shrinks, the plant wilts. Other Vacuoles Some vacuoles store toxic materials as defense against plant-eating animals. Others can store plant pigments.

PLASTIDS

PlastidsPlastidsPlastidsPlastids are organelles that are surrounded by a double membrane and contain their own DNA. Chloroplasts ChloroplastsChloroplastsChloroplastsChloroplasts use light energy to make carbohydrates from carbon dioxide and water. Each one contains a system of flattened, membranous sacs called thylakoidsthylakoidsthylakoidsthylakoids, containing the green pigment chlorophyllchlorophyllchlorophyllchlorophyll.


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Plant cell chloroplasts can arise only by division of preexisting chloroplasts, which may mean that they are descendants of ancient prokaryotic cells that were incorporated into plant cells through endosymbiosis. Chromoplasts Chromoplasts are plastids that contain colorful pigments that may or may not have a part in photosynthesis. Other Plastids Several other types of plastids share the general features of chloroplasts but differ in content. Amyloplasts store starch. Chloroplasts, chromoplasts, and amyloplasts arise form a common precursor, called a proplastid.

COMPARING CELLS

All cells share common features such as a cell membrane, cytoplasm, ribosomes, and genetic material. Even so, there is a high level of diversity among cells. Prokaryotes Versus Eukaryotes Prokaryotes lack a nucleus and membrane-bound organelles. Prokaryotes have a nucleoid, where their genetic material is concentrated. However, prokaryotes lack an internal membrane system. Plant Cells Versus Animal Cells Plant cells have three distinguishing features from animal cells. They produce cell walls, contain a large central vacuole, and contain a variety of plastids.


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CHAPTER HIGHLIGHTSCHAPTER HIGHLIGHTSCHAPTER HIGHLIGHTSCHAPTER HIGHLIGHTS

SECTION 1: The History of Cell BiologySECTION 1: The History of Cell BiologySECTION 1: The History of Cell BiologySECTION 1: The History of Cell Biology

All living things are made up of one or more cells. Robert Hooke discovered cells. Anton van Leeuwenhoek was the first to observe living cells.

The cell theory states that all living organisms are made of one or more cells, cells are the basic units of structure and function, and cells come only from pre-existing cells.

All living things are made of organized parts, obtain energy from their surroundings, perform chemical reactions, change with time, respond to their environment, and reproduce

SECTION 2: Introduction to CellsSECTION 2: Introduction to CellsSECTION 2: Introduction to CellsSECTION 2: Introduction to Cells

A cell’s shape reflects its function. Cell size is limited by a cell’s surface area-to-volume ratio. The three basic parts of a cell are the plasma membrane, the cytoplasm, and the

nucleus. Prokaryotes are organisms that lack a nucleus or membrane-bound organelles. In multicellular organisms, cells organize into tissues, organs, organ systems, and finally

organs. SECTION 3: Cell Organelles and FeaturesSECTION 3: Cell Organelles and FeaturesSECTION 3: Cell Organelles and FeaturesSECTION 3: Cell Organelles and Features

Cell membranes are made of two phospholipid layers and proteins. The nucleus directs the cell’s activities and stores DNA. Mitochondria harvest energy from organic compounds and transfer it to ATP.

SECTION SECTION SECTION SECTION 4444 REVIEW REVIEW REVIEW REVIEW

1.1.1.1. Identify three unique features of plant cells. 2.2.2.2. List the differences between the plasma membrane, the primary cell wall, and the secondary cell wall. 3.3.3.3. Identify three functions of plastids. 4.4.4.4. Name three things that may be stored in vacuoles. 5.5.5.5. Describe the features that distinguish prokaryotes from eukaryotes and plant cells from animal cells.

CRITICAL THINKING

6. 6. 6. 6. One student says vacuoles keep plants from wilting. Another says cell walls do this. Who is right? Explain. 7.7.7.7. If you discovered a new cell, what characteristics would you use to determine which kind of cell it is? Explain. 8.8.8.8. Tobacco plant cells contain a toxic chemical. Why don’t tobacco plant cells poison themselves? Explain.


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Ribosomes are either free or attached to the rough ER and play a role in protein synthesis.

The rough ER prepares proteins for export or insertion into the cell membrane. The smooth ER builds lipids and participates in detoxification of toxins.

The Golgi processes and packages proteins. Vesicles are classified by their contents. The cytoskeleton is made of protein fibers that help cells move and maintain their shape.

Unique Features of Plant CellsUnique Features of Plant CellsUnique Features of Plant CellsUnique Features of Plant Cells

Plant cells have cell walls, central vacuoles, and plastids. In plant cells, a rigid cell wall covers the cell membrane and provides support and

protection. Large central vacuoles store water, enzymes, and waste products and provide support

for plant tissue. Plastids store starch and pigments. The chloroplast converts light energy into

chemical energy by photosynthesis. Prokaryotes, animal cells, and plant cells can be distinguished from each other by their

unique features.

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Chapter Chapter Four (Cell Structure and Function)Four ...€¦ · Chapter Chapter Four (Cell Structure and ... Four (Cell Structure and Function) SECTION ONE: ... Cells are the basic