BIOB11H3 Lecture Notes - Lecture 18: Spindle Pole Body, Ubiquitin Ligase, Cyclin
Lec 18- Cell Cycle III: Biochemical Regulation of Mitosis
Lecture Notes
• Review
• Molecular motors move chromosomes/spindle- dyneins (minus end directed) & kinesins
(plus end directed)
• Microtubules associated w/ the mitotic spindle are astral, kinetochore & polar MTs
• Fig 14-33 →
• Prometaphase
• 1. Initial movement of spindle poles away from each other [kinesin on polar MTs]
• 2. Movement of chromosomes towards a pole [dynein]
• 3. Movement of chromosomes away from a pole [kinesins]. This is also termed the polar
wind: force generated when kinesins located along non-kinetochore regions of the
chromosomes interact w/ polar MTs to move chromosomes
• Metaphase
• 4. Spindle poles remain separated due to activity of kinesin-like motor (like step 1).
• 5. Chromosomes remain at the equatorial plate by balanced activity of both plus & minus
end motors at the kinetochore (mechanical tension equivalent in both directions).
• Anaphase
• At anaphase there is…
o Sister chromatids lose affinity for one another
o Anaphase A = poleward movement of sister chromatids (step 6)
o Anaphase B = separation of opposite spindle poles (step 7 & 8)
• 6. Chromosomes move poleward due to activity of a dynein-like motor & kinesin like
depolymerase depolymerizing the plus & minus end of the microtubule
• 7. Separation of spindle poles also occurs via a kinesin-like motor operating on polar
microtubules (like step 1)
• 8. Dynein-like motor associated w/ cell cortex (just inside plasma membrane) operating
on astral microtubules
o Motor pulls spindle pole body closer to plasma membrane & poles move apart
• Controlled Proteolysis Influencing Cell Cycle Progression
• E.g. G1 cyclins begins to be destroyed in S phase & mitotic cyclins destroyed at M
• Q: How are molecules recognized for destruction?
• A: Some evidence that phosphate groups added by CDKs are responsible for recognition
• Q: How is destruction mediated?
o Target molecule recognized by one of two multisubunit complexes (SCF or APC
= ubiquitin ligases)
o Ubiquitin: small protein which is covalently linked to the target protein w/
ubiquitin ligase
o Ubiquitinated protein destroyed in proteasome
• Proteasome: multisubunit complex involved in protein destruction
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Lec 18- cell cycle iii: biochemical regulation of mitosis. Lecture notes: review, molecular motors move chromosomes/spindle- dyneins (minus end directed) & kinesins (plus end directed, microtubules associated w/ the mitotic spindle are astral, kinetochore & polar mts, fig 14-33 , prometaphase, 1. Initial movement of spindle poles away from each other [kinesin on polar mts: 2. Movement of chromosomes towards a pole [dynein: 3. Movement of chromosomes away from a pole [kinesins]. This is also termed the polar wind: force generated when kinesins located along non-kinetochore regions of the chromosomes interact w/ polar mts to move chromosomes: metaphase, 4. Spindle poles remain separated due to activity of kinesin-like motor (like step 1): 5. Chromosomes move poleward due to activity of a dynein-like motor & kinesin like depolymerase depolymerizing the plus & minus end of the microtubule: 7. Separation of spindle poles also occurs via a kinesin-like motor operating on polar microtubules (like step 1: 8.
