Class Notes (1,100,000)
CA (650,000)
UTSC (30,000)
BIOB11H3 (300)
Dan Riggs (200)
Lecture 16

BIOB11H3 Lecture Notes - Lecture 16: Sister Chromatids, Coiled Coil, Condensin

Biological Sciences
Course Code
Dan Riggs

This preview shows half of the first page. to view the full 3 pages of the document.
BIOB11-L16: Cell Cycle II (Chromosome condensation & Movement)
Events of Mitosis: Overview of Critical Steps
- Chromosomes condense; Sister chromatids become visible
- Cytoskeleton disassembles; Spindle apparatus forms; Nuclear membrane breakdown
- Chromosomes ‘captured’ by MTs at centromeres/kinetochores; begin movement to equator
- Chromosomes aligned on metaphase plate (equator)
- Sister chromatids separate; Begin poleward movement, Poles also move apart
- Chromosomes cluster at opposite poles, Decondense. Nuclear membrane reforms
Chromosome Terminology
- After Replication 2 identical sister chromatids
- Each sister chromatid assembles a functional kinetochore at the centromere region
Cyclin-CDK complexes promote cell cycle progression
- START: G1/S cyclin + CDK Triggers G1/S transition
- MPF: Mitotic cyclin + CDK Triggers G2/M transition
What are the targets of these protein kinases?
During S phase:
1. DNA replication must be initiated (Replication licensing events)
2. Centrioles must be replicated
Targets for MPF For M phase to occur:
1. Nuclear membrane breaks down (lamins)
2. Chromosomes condense (condensin / cohesin)
3. Cytoskeleton undergoes dramatic reorganization (MT associated proteins)
MPF target 1) Promotes lamina disassembly
- MPF phosphorylates Lamins A and C
- Induces disassembly of lamina Release of chromatin
- Chromatin now free to condense (Able to form mitotic chromosome)
MPF target 2) Cohesin & Condensin
Cohesin: 2 large SMC coiled coil proteins (Smc1,3) + several regulatory subunits (Scc1,3)
- Wrap along axis after Replication occurs & first part of Prophase
- Metaphase: Cohesin remains only at centromere regions
- Maintains sister chromatid cohesion until metaphase checkpoint has passed
Condensin: 2 SMCs (Smc2,4) + regulatory proteins
- Organizes chromatin into supercoiled loops Forming mitotic chromosome
- Act as a hinge, when hinge closes, bring chromatin into a more condense shape
Cohesin & Condensin function in chromosome architecture
Cohesin: Added as replication occurs
Held sister chromatids together during most of S, G2, M phase
Condensin: Exerts its function at Prophase to condense chromatin
Cohesin lost from chromosome arms but remains at centromere
Cohesin lost after passing Metaphase checkpoint Able to be separated in Anaphase
You're Reading a Preview

Unlock to view full version