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Introduction to Bi 102

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The Need for Cell Division

• During development– One fertilized egg cell begins to divide– Develops into a mature multicellular organism

• In adults– To repair damage– To replace worn out tissue

Stages of the Cell Cycle

• Before a cell can divide:– Key cellular components must be duplicated

• Proteins, membranes, and organelles– Chromosomes must be duplicated

• Complete set of genetic information– Ensures that the new cells can survive

The Cell Cycle (eukaryotes):

MitosisInterphase

cytokinesis

Interphase has 3 phases:

G1 Phase or Gap 1:

• Longest phase

• Cell growth,

• Proteins/lipids synthesized,

• Prepares for replicating DNA

G1

Start after cell division

Interphase: S Phase

G1

SDNA Synthesis (Chromosomes/

chromatin Replicated)

Interphase: G2 Phase

G1

S

G2

• Prepares for cell division, proteins made

• Mitochondria replicate

• Centrioles replicate

• Microtubule synthesis

Mitosis: • Nuclear division

• Microtubules separate chromosomes

G1

S

G2

Mitosis

Cytokinesis: • Cell division, divides into 2 daughter cells

• Cell may renter cell cycle

• Or leave cell cycle (G0)

G1

S

G2

Mitosis

Cytokinesis

G0

G0 Phase

• Most cells are not actively dividing

• These cells are in G0 phase

– Can leave cell cycle for days to years– Some cells will divide again; e.g. liver cells

– Some cells stay in G0; e.g. nerve cells

Interphase – G1, S, & G2 Phases

Mitosis: Prophase

Mitosis: Metaphase

1. Microtubules grow, connect to centromeres,

2. and align the chromosomes

Mitosis: Anaphase

1. Sister chromatids separate, move to opposite poles.

2. Microtubules shorten & pull them in.

Mitosis: Telophase

4

1. Chromosomes at poles

2. Nucleus reforms

3. Chromosomes unwind into chromatin

4. Spindle degraded

Cytokinesis

1. Cytokinesis follows mitosis.

2. In animal cells, actin filaments (protein) pinch the cell in two.

3. Seen as a cleavage furrow on the cell membrane.

4. Plant cells divide by growing a new cell wall (cell plate) between the 2 nuclei.

DNA Synthesis

DNA Synthesis & Replication:

• DNA “unzips”

• Two opposite strands separate

• Matching bases are added to each side

• Result: Two copies of the original DNA

molecule