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Cell Bio > Lecture 6 > Flashcards

Lecture 6 Flashcards

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Biology 101 flashcards
1
Q

The cell-cycle control system depends on _________

A

cyclically activated cyclin-
dependent kinases (Cdks)

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2
Q

true/false: Cyclins have no enzymatic activity

A

true

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3
Q

A ______ is a protein that adds a phosphate to other
proteins; the activity of the target protein is modified

A

kinase

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4
Q

cyclins and cell cycle kinases bind to become ___________ active

A

enzymatically

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5
Q

true/false: Cyclin levels rise and fall in a cyclical fashion throughout cell cycle

A

true

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6
Q

_____ triggers entry into
the M phase from G2 by
forming the _____ complex

A

M cyclin
M-Cdk

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7
Q

_______ and _______ help
launch the S phase by
forming ______ and _______
complexes

A

S cyclin and G1/S cyclin
S-Cdk and G1/S-Cdk

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8
Q

_____ form ______,
helping to drive the cell
through G1 toward the S
phase

A

G1 cyclins
G1-Cdks

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9
Q

_________ in cyclin concentration - transcription of cyclin genes and
synthesis of cyclin proteins

A

increase

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10
Q

_______ in cyclin concentration - targeted destruction of the
protein

A

Rapid fall

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11
Q

how does a protein get marked for desctruction?

A

by getting tagged with ubiquitin by APC/C

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12
Q

_____ concentrations increase gradually.
The activity of _________ are
turned on abruptly

A

Cyclin
the cyclin–Cdk complexes

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13
Q

What triggers the abrupt activation of cyclin Cdk
complexes?

A

Protein kinases and phosphatases act together
to regulate the activity of specific cyclin–Cdk

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14
Q

true/false: Cyclin-Cdks catalyze the phosphorylation
and activation of hundreds of different
target proteins in the cell

A

true!

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15
Q

true/false: cyclin-cdks shut down the protein phosphatase
that opposes its activity

A

true!

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16
Q

G1-to-S transition: Cdk inhibitors keep
cells from entering S phase

G2-to-M transition: Activation of M-Cdk is
inhibited by inhibiting the phosphatase

Delay the exit from mitosis: Inhibiting
APC/C and preventing the degradation of
M cyclin

are all ways to _________

A

pause the cell cycle

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17
Q

to pause the cell cycle-
what happens at the G1-to-S transition: _________

A

Cdk inhibitors keep
cells from entering S phase

18
Q

to pause the cell cycle-
what happens at the G2-to-M transition: _________

A

Activation of M-Cdk is
inhibited by inhibiting the phosphatase

19
Q

to pause the cell cycle-
what happens to delay the exit from mitosis: _________

A

Inhibiting
APC/C and preventing the degradation of
M cyclin

20
Q

DNA damage in G1 causes an increased concentration and
activity of _______

A

protein p53

21
Q

protein p53 activates the gene encoding a protein called _____ (a Cdk inhibitor)

A

p21

22
Q

true/false: The p21 protein binds to G1/S-Cdk and S-Cdk, preventing them from driving the cell into the S phase

A

true

23
Q

what happens when the p53 protein is defective?

A

It can lead to a higher rate of mutations in cells and the
formation of cancerous cells

50% of human cancers cells have mutations in p53 gene

Defects in cell cycle genes can cause cancer

24
Q

what drives the entry into mitosis?

A

M-Cdk

25
Q

how long does mammalian M phase typically take?

A

one hour

26
Q

true/false: the centrosome is duplicated before M phase

A

true!

27
Q

What is a centrosome?

A

Principal microtubule-
organizing center in animal
cells

28
Q

The metaphase mitotic spindle has _____ sets of microtubules

A

three

29
Q

Microtubules contain _______ subunits

A

tubulin

30
Q

______ microtubules: Radiate from centrosome

A

Astral

31
Q

what do astral microtubules do?

A

Help position mitotic apparatus, determine
cleavage plane

32
Q

_______ microtubules: Attach to chromosomes at kinetochore

A

Kinetochore

33
Q

what do kinetochore microtubules do?

A

Pull chromosomes to different poles

34
Q

________ microtubules: Interdigitate with opposing pair

A

Non-kinetochore (interpolar)

35
Q

what do kinetochore microtubules do?

A

Support framework
Help push centrosomes apart via motor proteins

36
Q

true/false: microtubules don’t have polarity

A

false

37
Q

what pole of the microtubule points toward the centrosome? (away from kinetochore -> point of attachment to centrosome)

A

minus end (-)

38
Q

what pole of the microtubule points away from the centrosome?

A

plus end (+)

39
Q

how do the (+) and (-) ends of microtubules differ in their rates of assembly?

A

high at plus end
low at minus end

40
Q

what are the two key events in spindle assembly?

A

Formation of Poles:
Spindle microtubules must “attach” or
anchor to poles

Capture of Chromosomes:
Spindle microtubules must attach to
chromosomes

Cell Bio (11 decks)

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