Cell Reproduction

Chapter 9

Cell Growth

Main Idea: Cells grow until they reach their size limit, then stop growing or divide

Objectives: Explain why cells are relatively small Summarize the primary stages of cell cycle Describe the stages of interphase

Review: What’s the cell theory say? All organism are made of cells Cells are the smallest unit of living organisms Cells only come from other cells

Cell Size

Imagine yourself on a tennis court playing 1 on 1. Wouldn’t it be hard if the court were the size of a

football field? Cells have a size limit to ensure all the needs of

the cell are met

Surface Area to Volume

Limits to cell size: ratio of its surface area to its volume Surface area is the area covered by the plasma membrane Volume is the space inside the cell Figure 9.1 and Pg. 244 Connection to Math By remaining small, cells have a much higher ratio of

surface area to volume and can sustain themselves easier Demo! So: Do large cells perform their tasks more efficiently than

small cell? Mini Lab pg. 245

More About Size…

Small cells can transport substance easier than large cells

Diffusion would not be efficient, since it is passive transport, if the cell were large It would be like trying to float a toy boat across a

small puddle or across a large pond Cell size also limits the ability of a cell to

communicate Signals for processes might not occur fast enough

to signal another reaction Signals for protein synthesis need to reach the ribosomes

in time to continue the cycle

What happens when a cell reaches its size limit?

It will either: Stop growing Divide

Most cells divide because it prevents the cell from becoming too large and it helps the cell reproduce

Cell Cycle: the growing and dividing of cells There are 3 main stages

Interphase, Mitosis, Cytokinesis Time of division varies with the cell

Most cells take 12-24 hours to divide in animals

Cell Cycle

During Interphase, the cell grows, develops, duplicates its DNA and prepares for division

Three stages of Interphase: G1, S and G2

Cell Cycle

Interphase: Cells spend most of their life G1 stage- Time immediately after the cell

divides; cells grow to mature size G stands for “Gap” time between cell reproductions Some cells don’t divide after this

Example: nervous system cells only divide once

S Phase- DNA is copied G2 stage- Cell prepares for division

Find your 7 o’clock partner Designate partner A and partner B Partner A asks: What are the stages of the cell

cycle? Partner B: What occurs in G1? PA: What happens in G2? PB: What’s the S phase?

Review

Main Idea: Cells grow until they reach their size limit, then stop growing or divide

Objectives: Explain why cells are relatively small Summarize the primary stages of cell cycle Describe the stages of interphase

Section 9.2

Main Idea: Eukaryotic cells reproduce by mitosis, the process of nuclear division and cytokinesis, the process of cytoplasm division.

Objective: Describe the events of each stage of mitosis

Objective: Explain the process of cytokinesis

Think of events in your life that are cyclical Example: The passing of comets in the year Deer in the rut Turkeys in spring breeding season Day routine

Mitosis

Goal: replicated genetic material separates and the cell prepares to split into two cells Why?

It allows genetic information to be passed onto daughter cells

Uses? Replace damaged cells Increases the cell number of an organism- in other

words, the organism grows

SQR3 for “The Stages of Mitosis”, pg. 248

Chromosomes

Contain coiled DNA and proteins Chromatin is the relaxed form of DNA in the

cell’s nucleus, looks like a single strand Sister chromatids are structures that contain

identical copies of DNA Centromere holds the sister chromatids

together Socks!!

Mitosis

Prophase: Longest phase Chromatin tightens into chromosomes

The chromosomes become shaped like an X Centromeres are present

Nucleus disappears Microtubules called spindle fibers form in the

cytoplasm Centrioles (also microtubules) migrate to the end of

the cell (only in animal cells) Spindle apparatus: name given to the group of

spindle fibers, centrioles, etc. that help move the chromosomes around in the cell

Mitosis

Prophase Cont’d: Nuclear envelop

disappears Spindle fibers attach

to the sister chromatids to move the chromosomes around

Mitosis

Metaphase Chromosomes are easy

to identify Spindle fibers move

chromosomes to center

of cell

Anaphase

Chromatids are separated and move toward opposite poles caused by shortening spindle fibers

Whiles the chromatids separate, they are considered to be individual chromosomes

Centromere first

Telophase

Spindle fibers disappear after chromosomes are separated

Chromosomes loosen up Nuclear envelope and

nucleus reappears

Mitosis

Cytokinesis: Cell pinches inward

and cytoplasm seperates cell into two new cells

Cleavage furrow appears and cell divides (animals)

Cell Plate (plants)

Animations

Mitosis Video Fly Mitosis Cells Alive Mitosis Interactive Classroom

Video

Onion Root Tips

http://www.biologycorner.com/flash/onion_mitosis.swf

Review

Main Idea: Eukaryotic cells reproduce by mitosis, the process of nuclear division and cytokinesis, the process of cytoplasm division.

Objective: Describe the events of each stage of mitosis

Objective: Explain the process of cytokinesis Card Sort on Mitosis Stages What are the two differences between plant and

animal cells in mitosis?

Cell Cycle Regulation

The timing and rate of cell division are important Cyclins (proteins) bind to an enzyme, cyclin-

dependent kinases, to start the different stages of cell cycle

Cancer

Although cell cycle has a system of checks for quality, sometimes things go wrong

Cancer is the uncontrolled growth and division of cells (caused by the failure of the regulation of the cell cycle)

Cancer cells spend less time in interphase Pg. 254 picture

Stomach Cells

Normal Chicken Interphase 120 min Prophase 60 min Metaphase 10 min Anaphase 3 min Telophase 12 min

Cancerous Chicken Interphase 16 min Prophase 15 min Metaphase 2 min Anaphase 1 min Telophase 3 min

What effect do you think the difference in times have on the organism?

Causes of Cancer

Does not just occur in weak organisms Mutations or changes in the DNA, usually

that control the cell cycle, cause cancer Often, the mutations are repaired

Environmental factors Smoking, asbestos, chemicals, etc Radiation, x-rays

Not all cancers can be prevented Genetics

Apoptosis

Programmed cell death Why would cells WANT to die?

Cells in hands and feet Tree leaves falling in autumn Cells that are damaged

Stem Cells

Discovered in 1998 Unspecialized cells

Embryonic Results after a sperm fertilizes an egg controversial

Adult Found in tissues in body Can be used to maintain/repair the same kind of

tissue they came from Newborns have adult stem cells Less controversial

Paralysis Cured?

Pg. 258 Mapping Stem Cells MJF Video Video- Terra Incognita

Meiosis- Sect. 10.1

Main Idea: Meiosis produces haploid gametes

Objectives: Explain the reduction in chromosome number that occurs during meiosis

Recognize and summarize the stages of meiosis

Analyze the importance of meiosis in providing genetic variation

Which Cells?

The only cells that go through meiosis are the reproductive cells The results of meiosis are sperm or egg cells

In females: meiosis takes place in the ovaries, before birth

In males: meiosis takes place in the testes, usually starting at puberty

Chromosomes

Instructions for traits are located on chromosomes Found in the nucleus

DNA on chromosomes is arranged as genes (which control the production of proteins)

Chromosomes consist of hundreds of genes

Homologous Chromosomes

Human body cells have 46 chromosomes

At conception, each parent contributes 23 chromosomes

The chromosomes that match from each parent make homologous chromosomes

They have the same length, same genes and same centromere position

Haploid and Diploid

Gametes: sex cells that have half the number of chromosomes

Gamete number change with the species n represents the haploid chromosome

number Fertilization is the process when one haploid

gamete combines with another n + n = 2n 2n represents the diploid number

Numbers

Different species have different number of chromosomes

Meiosis

Remember: Gametes are formed during meiosis It reduces the number of

chromosomes in the cell When the gametes

combine (sperm and egg) a zygote is formed (a diploid group of cells that grow into an embryo)

Meiosis consists of two stages

Meiosis I

Meiosis I: MOST of the phases are the

same as mitosis: Interphase, prophase, metaphase,

anaphase and telophase

Exception: Prophase I-Instead of pairing on top

of each other, they pair side by side with the homologue – Synapsis is the name given to the pair

Meiosis I

Crossing-over occurs in Prophase I: genes are shared from each pair

Norwegian wrestling…

Results in genetic recombination

Meiosis I

Metaphase I: the pairs of homologous chromosomes line up at the equator of the cell

Can we borrow you shoes?

Meiosis I

Anaphase I- Instead of pulling apart the single chromosome, the homologous pairs are separated

Chromosome number is reduced from 2n to n when the pairs get separated

Meiosis I

Telophase I: new cells are haploid, but still has it’s sister chromatid

The chromatids might not be identical anymore

After cytokinesis, the cells go into interphase before the second set of divisions But, the DNA is not

duplicated

Meiosis II

Cytokinesis results in four haploid cells, each with n number of chromosomes.

Four cells are produced instead of two

Visualizing Meiosis Meiosis Video Comparison Video United Streaming Video Two interactive games

online to quiz yourself with

Questions for you

1. How many chromosomes will there be in the gametes of an organism with 18 chromosomes?

What would happen if the sister chromatids of one pair did not separate during anaphase II? Down Syndrome

Numbers

Karyotype: Picture of the pairs

Of chromosomes in

a cell

Why is Meiosis Important?

It results in genetic variation In Prophase I the

homologous chromosomes line up randomly

Depending on the order they line up in determines who they “cross over” with

Asexual Reproduction

Asexual- one parent Does not involve meiosis or the union of

gametes Bacteria- prokaryotes Offspring are identical to parents Rely on binary fission or mitosis

Cell Division- Prokaryotes

Use binary fission Three steps:

Chromosome copies itself Cell grows double it’s size New cell wall forms between the two chromosomes

and the cell splits

Bet you wish Eukaryotes were that easy…

Sexual Reproduction

Offspring are genetically different from parents because genes are combined in meiosis

Twins, contain unique combinations of parents’ genes

Advantage, through evolution, offspring can adapt rapidly to new conditions If disease strikes a crop of grain, the plants that

survive have the genes to overcome the disease

Cell Division- Eukaryotes

Mitosis- results in new cells with genetic info identical to the old

Meiosis- reduces chromosome number by half, then join other cells to restore the diploid number

Review Sect. 10.1

Main Idea: Meiosis produces haploid gametes

Objectives: Explain the reduction in chromosome number that occurs during meiosis

Recognize and summarize the stages of meiosis

Analyze the importance of meiosis in providing genetic variation