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Lecture 19
Homework Review
Today: Apoptosis and Cancer
Monday April 23rd- Cell-Cell Interactions/Tissues
Thursday April 26th -Early Development and Stem Cells
Monday April 30th- Review
Final Exam May 9th 12-1:30pm in this classroom
For Exam III- You are not responsible for any material in assigned
chapters relating to Plants!
Homework Lecture 15 and 16
1)
In cells, the concentration of actin monomer is higher than
required for purified actin monomers to polymerize in vitro.
Thymosin is a protein that can bind actin monomers and
sequesters them. If you add a drug that inhibits the ability of
thymosin to bind actin monomers, what would be the effect on
actin polymerization? INCREASE POLYMERIZATION
Actin Filament
Assembly
2. Which of the following changes occurs when a skeletal muscle fiber
contracts?
A) The A bands Shorten
B) The I Bands Shrink
C) The Z lines slide farther apart
D) The Thin Filaments Contract
E) The Thick Filaments Contract
Dark Band- A band
Light Band- I band
3.Consider an Individual Microtubule:
What must happen at the end of the microtubule in order for it to stop shrinking
and start growing?
-Binding of GTP Tubulin Heterodimers to form a GTP Cap
How would a change in the tubulin concentration affect this switch?
Increase in Tubulin Heterodimers- Promote Rescue
Decrease in Tubulin Heterodimers- Continue Shrinking
What would happen if only GDP, but no GTP, were present in the solution?
MT Depolymerization would occur
What would happen if the solution contained a nonhydrolyzable form of GTP?
MT Continued Polymerization until no available Heterodimers left
MAPs to Influence
MT Filament Stability
4. Nucleation of Actin Monomers or Microtubule Heterodimers is
the Slow Step in the formation of Actin and Microtubule
Filaments in vitro. How do cells bypass the slow step in vivo in
the formation of A) MT filaments – MTOCs and B) Actin
Filaments? ARP COMPLEX
5) What is the role of Nexin in the Axoneme
of Cilia and Flagella. What would happen if
it wasn’t present? Couldn’t bend-filaments would slide
With NEXIN
6)The Hydrolysis of GTP to GDP carried out
by Tubulin Molecules:
A) Provides Energy Needed for Tubulin to
Polymerize
B) Occurs Because the Pool of Free GDP
Has Run Out
C) Tips the Balance in Favor of Assembly
D) Allows the Behavior of Microtubules
called Dynamic Instability
D
Homework 17 and 18. Due Monday- we will
go over these answers.
True or False and Why?
1) Cells do not pass from G1 to M phase of
the cell cycle unless there are sufficient
nutrients to complete the whole cell cycle.
No cell goes from G1 directly to M
Homework 17 and 18. Due Monday- we will go over these answers.
True or False and Why?
2) Rb is a transcription factor that must be phosphorylated in order for
expression of G1/S and S phase Cyclins.
FALSE- not
functioning as a transcription factor in this case- but as inhibitor of
transcription factor
True or False and Why?
3) Once a Cyclin binds to a CDK, the kinase
is active and can immediately begin
phosphorylating targets.
FALSE
4) Separation of sister chromatids requires kinetochore MT
assembly and cytoplasmic dynein activity. FALSE
Anaphase A Movement
Plus End of Kinetochore
Microtubules Dissassembles
Minus End Directed Motor
(Dynein) Proteins Pull
Toward Spindle Pole
Pac Man Mechanism
(-)
MT Depolymerize
Dynein Walks
Toward Minus End
5) When a cell that is in the process of replicating DNA is
fused with a cell in G1:
A) The replication of DNA occurring in the original S
nucleus is terminated
B) DNA synthesis begins immediately in the original G1
nucleus
C) The two Nuclei Fuse and Further Division is Arrested
D) The Chromosomes of the Original G1 Nucleus
condense in preparation for mitosis
E) The original G1 cell will divide immediately
B
6.) Sister chromatids:
A) Are created when DNA is replicated
B) Are attached at the centromere prior to Division
C) Are separated during anaphase
D) Have matching copies of the chromosome’s DNA
E) all of the above
E
7.) In some cases, Mitosis occurs without cytokinesis occurring.
This will result in:
A) Cells with more than one nucleus
B) Cells that are unusually small
C) Cells lacking nuclei
A
D) Destruction of chromosomes
E) Cell cycles lacking an S phase