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Introduction to Bi 102
• Pass out Syllabus & Homework.
• Go over syllabus and schedule.
• Go over Homework 1.
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