Cell Division and Gene Expression The Need for Cell Reproduction - The Nature of Chromosomes - The...

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Cell Division and Gene ExpressionCell Division and Gene Expression

• The Need for Cell Reproduction

- The Nature of Chromosomes

- The Cell Cycle

- Mitosis and Cytokinesis

- Cancer Cells: Abnormal Cell Cycle

• The Expression of Genes as Proteins: DNA gene --> RNA --> Protein

- Transcription by RNA Polymerase

- The Three Types of RNA

- Translation by Ribosome

What Cell Reproduction Accomplishes

• Reproduction

– The birth of new organisms.

– Occurs much more often at the cellular level

• Cell division plays a role in

– The replacement of lost or damaged cells.

– Cell reproduction and growth.

Passing On Genes from Cell to Cell

• Before a parent cell divides, it duplicates its chromosomes.

• The two resulting “daughter” cells are genetically identical, each getting a duplicate set of chromosomes

Cell Division and Gene Expression Cell Division and Gene Expression

- Copying Chromosomes

- The Cell Cycle

Types of Reproduction

• Asexual reproduction

– Single cells reproduce by mitosis

– Two daughter cells produced from one parent cell

• Daughter cells are genetically identical to each other

• Daughter cells are genetically identical to the parent cell

• Sexual reproduction

– Single or multi-celled organisms reproduce by meiosis

– Four daughter cells called gametes (eggs and sperm) produced from one parent cell

• Gametes are genetically different from each other and parent cell

• Gametes must unite with other gametes of opposite type to produce viable organism

– Use for growth and repair as well as producing new individuals

– Finding a mate is unnecessary

– Relatively “cheap” energetically

– Used solely for making more individual single or multicellular organisms

– A mate or a second organ for producing other gametes is required

– Relatively “expensive” energetically; lower efficiency in producing offspring

Both Daughter Cells in Mitosis Must Get Chromosomes

chromosomes

12 + 12

chromosomes

Duplication (Replication)

DNA Replication (Duplication) Occurs in S Phase of the Cell Cycle

Figure 3.32

AdenineThymineCytosineGuanine Old (template) strand

Two new strands (leading and lagging)synthesized in opposite directions

DNA polymerase

Laggingstrand

Leading strand

Free nucleotides

Old strand acts as atemplate for synthesisof new strandChromosome

Helicase unwindsthe double helix andexposes the bases

Old DNA

Replicationfork

DNA Replication is Performed by DNA Polymerase

- The Cell Cycle

The Cell Cycle

Growth

SGrowth and DNA

synthesis G2

Growth and finalpreparations for

divisionM

G2 checkpoint

G1 checkpoint(restriction point)

>95% of the cells in your body are not progressing through the cell cycle and will never divide

Chromosomes Must Be Condensed or Packaged Before Cell Division

DNA Packing

- The Cell Cycle

Mitosis Overview

Prophase Metaphase Anaphase Telophase/

Cytokinesis

Mitosis (All Phases)

Animal Mitosis

Sea Urchin (time lapse)

Figure 8.8.1

G2 of Interphase:

• Chromosomes indistinct

• Centrosomes replicate

Mitosis Overview

To M Phase:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase and Cytokinesis

Late Interphase

Figure 8.8.2

1. Chromosomes condense, become visible2. Nuclear membrane dissolves3. Centrioles move to opposite poles, grow fibers

1. Chromosomes line up in a column 90o to spindle

Prophase Prometaphase Metaphase

1. Sister chromatids separate and move towards opposite poles

2. Two nuclear membranes reform

3. Cell divides in half (cytokinesis)

1. Chromosomes unwind (decondense)

Anaphase Telophase

• Cytokinesis

– Typically occurs during telophase.

– Involves contracting microfilaments

Cytokinesis

Cell Splitting in Telophase: Cytokinesis

Mitosis Overview

Prophase Metaphase Anaphase Telophase/

Cytokinesis

Mitosis (All Phases)

Animal Mitosis

Sea Urchin (time lapse)

- The Cell Cycle

Cancer Cells: Growing Out of Control

• Normal plant and animal cells have a cell cycle control system.

• Cancer is a disease of the cell cycle.

• Cancer cells do not respond normally to the cell cycle control system.

• Cancer cells can form tumors,

– Abnormally growing masses of body cells.

• If a tumor is malignant and metastasizes it can spread to other parts of the body.

Figure 8.10

Breast Cancer

- The Cell Cycle

Central Dogma of Biology: How Shape and Form Are Dictated By DNA Genes

A segment of DNA (gene)

carries specific coded

instructions for the making

of a single proteins.

Genotype:The genes carried in a cell for a particular trait

Phenotype: The physical expression of genes for a particular trait

Figure 3.34

Nuclearpores

Pre-mRNARNA Processing

Transcription

Translation

Nuclearenvelope

Ribosome

Polypeptide

Cell Division and Gene Expression The Need for Cell Reproduction - The Nature of Chromosomes - The...

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