Exam 4 Lecture 1: Cell Cycle I Flashcards
Which kind of cells are the most abundant in your body?
RBCs / erythrocytes are the most abundant type of cell in your body in total cell count
Explain what happens in S phase and how long it takes
Explain what happens in M phase and how long it takes
S phase: DNA synthesis (10-12 hours)
M phase: Mitosis (nuclear division) and cytokenesis (cytoplasmic division) takes roughly 1-2 hours
What steps make up interphase?
Interphase: G1, S, G2
and then mitosis completes the cell cycle
What are the four phases of the cell cycle?
what is the specialized resting state that some cells get stuck in?
Four phases: G1, S, G2, M
Go is a specialized resting state that some cells get stuck in, it is essentially when they never leave G1
Mitosis: splitting of the ______
Cytokinesis: splitting of the ______
Mitosis is splitting of the nuclei
cytokinesis is splitting of the cytoplasm
What is the longest phase in the cell cycle?
Longest phase in the cell cycle is S phase
What are some model systems used to study the cell cycle?
Xenophus (frogs)
Cell and Cell Free systems
Yeast
Explain HeLa cells
They are “immortilized”, never have a Go phase
continually proliferate
The time required for the cell cycle phases is remarkably consistent between cells and even between different organisms. This results in _______ of division in developing organisms
The time required for the cell cycle phases is remarkably consistent between cells and even between different organisms. This results in apparent synchronization of divisions in developing organisms.
The cell cycle is controlled by the products of ____ genes. Mutational studies have demonstrated which genes orchestrate each part of the cell cycle
Cell cycle is controlled by the products of cell division cycle genes (CDC genes)
Cells that are synthesizing DNA in S phase can be identified by the incorporation of a ________
Cells that are not in S phase appear red
Cells that are making DNA in S phase can be identified by the incorporation of a fluorescently labeled thymidine analog (BrdU green)
The DNA content doubles during _____, so researches can staing the DNA and measure the brightness of each cell using a cytometer
DNA doubles during S phase
you can stain DNA and measure brightness with cytometer
What are the three major checkpoints in the cell cycle
Checkpoints in the cell cycle:
Start checkpoint at end of G1 to enter S phase
G2/M checkpoint
Metaphase to Anaphase transition
Explain what cyclin dependent kinases do
Cyclin dependent kinases (Cdk’s) are enzymes that phosphorylate cell cycle machinery at the appropriate time. The activity of Cdk’s is controlled by a regulatory partner cyclin. Without cyclin, Cdk’s are inactive.
There are G1/S Cdk , S-Cdk, and M-Cdk’s
level remains same at all time, its their activity that changes
Cdk activity is also regulated by the ___________ at multiple sites. One site activates the kinase, while another deactivates it.
Cdk activity is also decreased by _____
Cdk activity is also regulated by phosphorylation of the kinase itself at multiple sites. One site activates the kinase, the other deactivates it.
Cdk activity is also decreased by Cdk inhibitor proteins (CKIs)
Explain how unfavorable conditions inhibit Cdks
Explain the activation of M-Cdk
Feedback mechanisms control the activity of Cdk. Cdk phosphorylates a phosphatase, which removes the inhibitory phosphate on Cdk
M-Cdk activates its own activator (CAK) and inactivates its own inactivator (Wee1). Allows abrupt and complete activation and inactivation of the cell cycle.
Explain the checkpoints by explaining what the cell is looking for at each spot
Start Checkpoint (end of g1): is the enviornment favorable to start DNA synthesis?
G2/M checkpoint: is all the DNA replicated? and is the enviornment favorable to enter mitosis?
Metaphase to Anaphase transition: are all of the chromosomes attached to the spindle?
Explain the Initiation of DNA Replication:
Its accomplished by the formation of a large multiprotein complex called the ________, which binds to specific regions of DNA and initiates the recruitment of a prereplicative complex. This complex is composed of _____
Initiation of DNA Replicaiton:
Accomplished by formation of large multiprotein complex called the “origin recognition complex (ORC)” which binds to specific regions of DNA and initiates the recruitment of a prereplicative complex. This complex is composed of DNA polymerase and other replication proteins such as helicase, which unwinds DNA and allows replication to begin.
What is so important about the G2/M checkpoint?
It allows for the cell to check and make sure the DNA is replicated and that the DNA is NOT damaged/is of quality to proceed to mitosis.
Most important checkpoint?
Start checkpoint: G1/S checkpoint
What happens during the beginning of M phase?
Beginning of M phase:
M-Cdk is “stockpiled”
Induces assembly of mitotic spindle
Triggers chromosome condensation
Initiates breakdown of the nuclear envelope
Explain prophase
Prophase:
- the replicated chromosomes (each containing two sister chromatids) condense.
- Outside the nucleus, the mitotic spindle assembles
Sister chromatids are held together by ____
It’s important that they stay together so that they can be found by the spindle apparatus and segregated to opposite poles
Sister chromatids are held together by cohesins
Explain condensin
Condensin is a five subunit complex that is structurally similar to cohesin. It supports the condensation of the DNA. This is important because otherwise the DNA would get tangled up and break during segregation in anaphase.
Explain what happens in prometaphase
Prometaphase: starts abruptly with the breakdown of the nuclear envelope. Chromosomes can now attach to spindle microtubules via their kinetochores and undergo active movement.
Explain what happens during metaphase
Metaphase: chromosomes are aligned at the equator of the spindle, midway between the spindle poles.
The kinetochore microtubules attach sister chromatids to opposite poles of the spindle.
Explain what happens during anaphase
Anaphase: the sister chromatids seperate to form daughter chromosomes, and each is pulled apart toward spindle pole
Kinetochores get shorter, spindle poles move apart
Explain what happens during telophase
During telophase:
two sets of daughter chromosomes arrive at poles of the spindles and decondense.
two distinct nuclei
During cytokinesis:
the cytoplasm is divided in two by a contractile ring composed of _____ and ____ (and also ____), which pinches the cell in two to create two daughter cells, each with one nucleus
Cytokinesis:
contractile ring is composed of actin and myosin filaments
(and septins)
Cdc15 mutation leads to a cell that____
Cdc15 mutation: cell gets stuck in anaphase
