Chapter 8Chapter 8Cell ReproductionCell Reproduction

R. LeBlanc, MS

MPHS

Modified: 10/’11

Chromosome StructureChromosome Structure• Chromosomes are rod-shaped structures made of DNA and protein.

Chromatin uncoils to make RNA and replicate itself.Chromatin uncoils to make RNA and replicate itself.

Most of cell’s life, chromosomes Most of cell’s life, chromosomes exist as chromatin (short strands of exist as chromatin (short strands of DNA wrapped around protein).DNA wrapped around protein).

Before cell division chromatin Before cell division chromatin threads coil (shorten and thicken) threads coil (shorten and thicken) forming tightly packed forming tightly packed chromosomes.chromosomes.

Parts of a ChromosomeParts of a Chromosome

Chromosome Numbers of Various Chromosome Numbers of Various OrganismsOrganisms

Each species has a

characteristic number of

chromosomes in each cell.

Sex Chromosomes and Sex Chromosomes and AutosomesAutosomes

–Sex chromosomes are chromosomes that determine the sex of an organism.

– All of the other chromosomes in an organism are autosomes.

Chromosome NumbersChromosome Numbers

Diploid and Haploid CellsDiploid and Haploid Cells– Cells having two sets of chromosomes areCells having two sets of chromosomes are

diploid diploid (2n).(2n). – Haploid Haploid cells cells (1n)(1n) have only one set of have only one set of

chromosomes.chromosomes.

KaryotypeKaryotype

Cell ReproductionCell Reproduction

Cells divide so organisms can Cells divide so organisms can grow and grow and replace damaged or worn out cells. replace damaged or worn out cells.

Binary fissionBinary fission is the process of cell is the process of cell division in prokaryotes.division in prokaryotes.

Cell Division in EukaryotesCell Division in Eukaryotes

Cell CycleCell Cycle– The The cell cyclecell cycle is the repeating set of events in is the repeating set of events in

the life of a cell. the life of a cell. – The cell cycle consists of cell division and The cell cycle consists of cell division and

interphase.interphase.– Cell division in eukaryotes includes nuclear Cell division in eukaryotes includes nuclear

division, called mitosis, and the division of division, called mitosis, and the division of cytoplasm, called cytoplasm, called cytokinesis.cytokinesis.

Cell Cycle IntroductionCell Cycle Introduction

What are the three parts of the cell cycle?

1. Interphase2. Mitosis3. Cytokinesis

Cell Cycle

Sequence of Sequence of growthgrowth and and divisiondivision of a cell: of a cell: 11. . GrowthGrowth: : (Interphase)(Interphase) Most of a cell’s life Most of a cell’s life 22. . DivisionDivision: : (Mitosis)(Mitosis) Nucleus and cytoplasm Nucleus and cytoplasm dividedivide to form to form

2 2 “daughter cells”“daughter cells” identical to “parent cell”. identical to “parent cell”. 3. 3. CytokinesisCytokinesis: The division of the cytoplasm equally into : The division of the cytoplasm equally into

both new cells. Animal cells will develop a both new cells. Animal cells will develop a cleavage cleavage furrow furrow which pinches in an eventually develops into 2 which pinches in an eventually develops into 2 cells.cells.

Comparing Cell Division in Plants and Animals

•During cytokinesis in animal cells, a cleavage furrow pinches in and eventually separates the dividing cell into two cells. •In plant cells, a cell plate separates the dividing cell into two cells.

Control of the Cell Cycle•When Control is Lost: Cancer

–Cancer may result if cells do not respond to control mechanisms.

In the final stage of cancer, cells enter the circulatory system and spread throughout the body forming other tumors that disrupt normal functions. Cancer - 2nd leading cause of death in U.S. (Heart disease = #1)

Cancerous cells take up space and deprive normal cells of nutrients.

Lung, Colon, Breast and Prostate cancers kill the most people in the U.S.

Both genetic and environmental factors are involved.

Environmental factors - Smoke, Air and Water pollution, Exposure to U.V. Radiation from sun, and some viruses.

Ex. Cancer patterns follow the country in which a person lives not their country of origin.

Interphase “Resting Phase” - Nucleus is visible but chromosomes

are not (thin chromatin).

1. G1: Protein production (normal cell growth).2. S: DNA synthesis (replicates its chromosomes).3. G2: Organelles are duplicated; the cell is preparing for

cell division (mitosis).

Mitosis4 phases Prophase, Metaphase, Anaphase & Telophase

Prophase (Packed) Chromatin coils into chromosomes (visible

near center of cell). Copies of chromosomes called sister

chromatids held together by a centromere. 2 centrioles migrate to poles. Nucleus disappears. Nucleolus and nuclear envelope disintegrate. Spindle fibers form between centrioles.

Metaphase (Middle) Chromosomes attached to

spindle fibers at centromeres. Chromosomes line up at

equator.

Anaphase (Away, Apart) Sister chromatids separate at

centromeres. Spindle fibers “pull” chromatids to

opposite poles.

Telophase (Two) Chromatids are at opposite ends of cell. Chromosomes uncoil into chromatin Spindles break down. Nucleolus and Nuclear membrane reappear. Will result in formation of 2 “daughter cells”.

Stages of MeiosisStages of Meiosis

Stages of Meiosis, con’tStages of Meiosis, con’t

Comparing Mitosis to MeiosisComparing Mitosis to Meiosis

Section 3 MeiosisChapter 8

Sexual ReproductionSexual Reproduction Sexual reproductionSexual reproduction is the formation of is the formation of

offspring through meiosis and the union of offspring through meiosis and the union of a sperm and an egg. a sperm and an egg.

Offspring produced by sexual reproduction Offspring produced by sexual reproduction are genetically different from the parents are genetically different from the parents (because of a process called crossing-over (because of a process called crossing-over of genetic information).of genetic information).