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BMS 100 Test 2 > DNA synthesis & cell cycle > Flashcards

DNA synthesis & cell cycle Flashcards

1
Q

The cell cycle consists of how many phases and what are they called?

A

2; Mitotic (M), and Interphase (cell growth and copying of chromosomes in preparation for cell division

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2
Q

Which phase consists of 90% of the cell cycle?

A

Interphase

G1 phase: first gap
S phase: synthesis
G2 phase: Second gap
G0 phase: Resting phase, postmitotic quiescent

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3
Q

G1 phase:

A

-1st gap phase
-Preparatory growth phase prior to cell entering DNA synthesis phase
-Cell is metabolically active; requires nutrients and growth factors, RNA/protein/lipid & carbohydrate synthesis occurs
-Many organelles are duplicated; No DNA replication yet

Duration: (6-24hrs); short in embryonic and cancer cells; Rapid or non-existent in rapidly dividing cells

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4
Q

S phase:

A

-DNA & chromosomal protein synthesis occurs
-Duration: approx 7-8 hours
-Cell is now committed to cell division; growth factors are no longer needed at this phase, DNA replication occurs here, creating two identical daughter genomes

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5
Q

G2 phase:

A

-2nd growth phase
-Interval between DNA synthesis (S phase) & mitosis (M phase)
-Enzyme, protein and ATP synthesis occurs (cell growth continues)

-Duration: lasts approx 3 hours

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6
Q

M phase:

A

-Mitotic phase
-Cell undergoes mitosis & then cytokinesis

Duration: 1-2 hours

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7
Q

What are the steps in the mitosis phase in order?

A

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

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8
Q

G0 phase:

A

-State of withdrawal from cell cycle
-Cell is neither dividing nor preparing to divide
-Instead, the cell is “doing its job”; performing it’s function within the tissue (common for differentiated cells)
-Examples of cells in G0; Hepatocytes, neurons

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9
Q

Checkpoints are based on series of _______________________ to initiate a specific cell-cycle events. What is this called?

A

biochemical switches
-Cell cycle control system

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10
Q

What are the three features of the biochemical switches?

A

1) Generally binary (on/off) to launch an event in a complete & irreversible fashion

2) Robust & Reliable; Contains back up mechanisms to ensure efficacy under variable conditions & if some components fail

3) Adaptable & modified to suit specific cell types (Responds to specific intracellular or extracellular signals); Cyclin dependant kinases (Cdks)

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11
Q

Points in the eukaryotic cell division cycle where progress through the cycle can be halted until conditions are suitable for the cell to proceed to the next stage:

A

Checkpoints “Transitions”

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12
Q

Checkpoints can be regulated by:

A

-Factors within the cell, mostly controlled by the “health” or “state of preparation” of the cell.

-Factors from outside the cell (messages from other cells within the same tissue or distant cells.

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13
Q

What are the three major regulatory transitions?

A

1) Start transition (aka G1/S)
2) G2/M transition
3) Metaphase to anaphase transition (aka M-to-A)

For most cells; G1/S seems to be the rate-limiting & committing step of the cell cycle

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14
Q

Cell signals are not necessary for a cell to pass through check points. (True/False)

A

False: all checkpoints rely on cell signals to keep the cell cycle moving. If these signals are not present, they will stop.

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15
Q

If there is a problem with completion of DNA replication, the cell will be held at what check point?

A

G2/M checkpoint

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16
Q

What is the key to cell cycle control sytem?

A

Cyclin-dependent kinases (Cdks); Controlled by a group of proteins called-Cyclins

-Correct and functional cyclin- cdk complexes are needed to progress through a checkpoint

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17
Q

Cdks are responsible for cyclical changes in _______________ of intracellular proteins that initiate/regulate the major events of the cell cycle.

A

phosphorylation

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18
Q

What causes the cyclic assembly and activation of cyclin-cdk complexes at specific stages of the cell?

A

Cyclical changes in cyclin protein levels

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19
Q

What are the 4 classes of cyclins that form specific complexes with cdks?

A

1) G1 cyclins: Cyclin D

2) G1/S cyclins: Cyclin E

3) S cyclins: Cyclin A

4) M cyclins: Cyclin B

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20
Q

What does G1 cyclins: Cyclin D do?

A

-Forms complex w/ cdk4 or cdk6
-Involved in G1 phase of cell cycle, needed for initiation of transcription of G1/S cyclins to help promote passage through the start transition

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21
Q

What do G1/S cyclins: Cyclin E do?

A

-Forms complex w/ Cdk2
-Bind Cdk’s at the end of G1 & help trigger progression through start transition
-Levels decrease in S phase

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22
Q

What do S cyclins: Cyclin A do?

A

-Forms complex with Cdk1 & Cdk2
-Bind Cdks after progression through start transition & helps stimulate chromosome duplication during S phase
-Levels remain elevated until mitosis; contributes to control of some early mitotic events

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23
Q

What do M cyclins: Cyclin B do?

A

-Forms complex with Cdk1
-Bind Cdk’s to stimulate entry into mitosis at the G2/M transition
-Levels decrease in mid-mitosis

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24
Q

How do cyclin Cdk complexes work?

A

Cyclins function by activating the Cdk (cyclin activating kinase; CAK needed for full activation)

-Cyclin protein also directs it to its specific target

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25
Q

Progression through which check point is different from the rest?

A

Metaphase to Anaphase

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26
Q

Metaphase to anaphase checkpoint is regulated via what? What complex is needed?

A

Proteolysis; anaphase promoting complex (APC/C; aka cyclosome)

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27
Q

What family is the APC/C; aka cyclosome part of?

A

ubiquitin ligase

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28
Q

APC/C; aka cyclosome is used to stimulate what? and what are the target proteins?

A

-Stimulates proteolytic destruction of specific regulatory proteins. (APC/C polyubiquitinated specific target proteins for destruction in proteasomes)

Target proteins: Securin, M-cyclins, S-cyclins

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29
Q

What are the early response genes?

A

usually, transcription factors-will induce the transcription of delayed response genes.

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30
Q

What are delayed response genes?

A

usually Cdks, cyclins, or other proteins needed for cell division

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31
Q

Growth factors bind to specific receptors to stimulate cellular growth & proliferation (turns on early response and delayed response genes)

Which phase of the cell cycle does this process belong to?

A

G1

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32
Q

In the G1 phase, what happens in response to the binding of the growth factor?

A

Cyclin D & E are transcribed & translated
-Cyclin D forms complexes with Cdk4 & 6(G1 Cdk complex)
-Cyclin E forms complexes with Cdk 2 (G1/S cdk complex)

Active G1-Cdk & G1/S-cdk allow for progression through the checkpoint

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33
Q

Active G1-cdk (and G1/S-cdk) complex will target a protein called______________.

A

RB

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34
Q

What does RB function as and which checkpoint is it associated with?

A

transcription co-repressor; G1/S checkpoint

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35
Q

What will inactivate RB?

A

Hyperphosphorylation

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36
Q

What does an inactive RB release to allow transcription to proceed?

A

E2F

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37
Q

What checkpoint phase is this diagram showing?

A

G1 phase->G1/S checkpoint

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38
Q

What 2 complex’s get targeted for destruction in the S phase?

A

cyclin D (G1-cdk complex) , and E (G1/S-cdk complex)

-promotes progression through the S phase

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39
Q

Active S-cdk complex allows progression through the S phase.

1) What was the S-cdk complex?

2) What is occurring during the S phase of the cell cycle?

A

1) Cyclin A: Forms complex with Cdk1 & Cdk2

2) DNA replication happens here

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40
Q

Phase G2:
s-cdk complex levels are _______
M-cyclin levels _____________

A

-still high
-begin to rise

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41
Q

M cyclin forms M-cdk, which cyclins and cdks are part of this complex?

A

Cyclin B; Cdk1

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42
Q

M-cdk complex is needed for what?

A

To pass through the G2/M checkpoint

-Bind Cdk’s to stimulate entry into mitosis at the G2/M transition

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43
Q

What happens to the S cyclins at the end of G2?

A

They are destroyed. Targeted for proteolysis by APC/C.

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44
Q

Once the M-Cdk complex is assembled, what happens to it?

A

It is immediately inhibited via phosphorylation.

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45
Q

Inhibitory phosphorylation in the M-phase occurs by a kinase called what?

A

Wee1

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46
Q

When the cell cycle is ready for mitosis to begin, the _____________ complex is ____________________

A

M-Cdk; de-phosphorylated

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47
Q

De-phosphorylation occurs by a phosphatase called what?

A

Cdc25

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48
Q

Cell progresses through the G2/M checkpoint and __________ begins.

A

Mitosis

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49
Q

What is needed for activation of various proteins needed for mitosis?

A

M-Cdk complex

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50
Q

An inhibitory protein that protects protein linkages that hold sister-chromatid pairs together in early mitosis.

A

Securin

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51
Q

Destruction of Securin activates a protease that separates ____________ allowing progression to ______________

A

The sister chromatids; anaphase

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52
Q

APC/C complex targets what? During what?

A

Securin; Metaphase to anaphase checkpoint in mitosis

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53
Q

What process is used to progress through M-to-A checkpoint?

A

Regulated proteolysis

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54
Q

After anaphase, the cell cycle continues through what?

A

Telophase -> cytokinesis

55
Q

At the end of mitosis, the ___________ re also targeted for destruction by _________.

A

M-cyclins; APC/C

56
Q

What happens after M-cyclins are destroyed?

A

-Inactivates most Cdks in cell

-Then many proteins phosphorylated by Cdks from S phase to early mitosis are dephosphorylated by various phosphatases in the anaphase cell.

57
Q

_______________________ is required for the completion of M phase, including the __________ & then _________.

A

Dephosphorylation; telophase; cytokinesis

58
Q

Progression through G1 is delayed if:

A

-DNA is damaged by radiation, chemicals, or errors
-Absence of nutrients or growth factors
-Abnormal cell size

59
Q

Entry of M is prevented when:

A

-DNA replication is not complete
-Presence of DNA damage
-Abnormal cell size

60
Q

Progression of M-to-A is prevented if:

A

-Chromosomes are not properly attached to mitotic spindle

61
Q

Binding of ____________ inactivates cyclin-Cdk complex.

A

Cdk inhibitory protein (CKI)

-Primarily used in cells to govern the activities of G1/S and S-Cdks early in cell cycle

62
Q

What are the three important CKI’s?

A

p16, p21, p27

63
Q

p16 inhibits:

A

Cyclin D-cdk4 & Cyclin D-cdk5 (G1-cdk complex)

64
Q

p21 inhibits:

A

Cyclin E-cdk2 (G1/S-cdk complex)
Cyclin A-cdk2 & Cyclin A-cdk1 (S-cdk complex)
Cyclin B-cdk1 (M-cdk complex)

65
Q

p27 inhibits:

A

Cyclin A-cdk2 & Cyclin A-cdk1 (S-cdk complex)
Cyclin E-cdk2 (G1/S-cdk complex)
Cyclin B-cdk1 (M-cdk complex)

66
Q

What are the two tumor suppressor genes?

A

p53 & RB

67
Q

p53:

A

-Recognizes and binds damaged DNA
-Unstressed cells have lower levels of p53 since it will be bound by a protein called Mdm2 & be degraded

68
Q

RB:

A

-Generally found in active form (hypo or hyper phosphorylation)
-Can also recognize damaged cells

69
Q

In the presence of DNA damage, p53 will be __________________, releasing ____________

A

Phosphorylated;Mdm2

(will not be degraded)

70
Q

Active p53 binds DNA & promotes the transcription of ______

A

p21

71
Q

p21 binds with _________, _________ it.

A

G1/S-cdk complex; inhibiting

72
Q

An inactive G1/S-cdk complex will pause the cell cycle at the ____________ transition.

A

G1-S

73
Q

RB: In the presence of a growth suppressor signal or DNA damage:

A

-p16 is transcribed; Inhibits the G1/cdk complex(needed to inactivate RB)

-RB remains activated & bound to E2F (no transcription of G1/S-cyclins or S cyclins-Cell is paused at the start of the transition)

74
Q

Contact inhibition: The cell cycle progression can also be inhibited due to contact with:

A

-Other cells (density-dependent inhibition)
-A basement membrane or other matrix component (anchorage-dependent/most animal cells must be attached to a substratum in order to divide

75
Q

How is contact inhibition reglated?

A

With cadherins & beta-catenin pathway

76
Q

__________ promotes the cell cycle and prevent apoptosis.

A

Survival signals (PI3K-Akt-mTOR C Pathway)

77
Q

Akt can promote the cell cycle progression by:

A

Activates/increases:
-Cyclin A->activation of CDK-1
-Cyclin D->activation of CDK-4/6

Decreases/inactivates:
p21 & p27

78
Q

DNA replication occurs in what phase of the cell cycle?

A

S-phase

79
Q

_____________ acts as a template for it’s own duplication.

A

DNA double helix

80
Q

Each daughter cell will inherit a DNA double helix containing _______________________________

A

1 original strand & 1 new strand
(semi-conservative replication)

81
Q

What are the steps of DNA synthesis?

A

1) Strand separation
2) Primer creation
3) DNA replication
4) Primer removal

82
Q

What two proteins are needed to open up the DNA strand during the 1st step of DNA synthesis?

A

1) DNA helicase
2) Single strand binding proteins

83
Q

DNA helicase:

A

-Unwinds double helix

84
Q

What type of bond is DNA helicase breaking?

A

Hydrogen bonds

85
Q

Single strand binding proteins:

A

Bind tightly and cooperatively to stabilize the single strand conforming

86
Q

Opening of the double helix creates a ________________

A

Replication fork

87
Q

At the replication fork a multienzyme complex, ____________________ will be used to synthesize both new daughter strands of DNA.

A

DNA Polymerase; can only add nucleotides to existing strand of DNA (works in 5’-3’ direction)

88
Q

In what step of DNA synthesis does the replication fork appear?

A

1st step: Strand seperation

89
Q

Step 2 of DNA synthesis:

The primer is made of _____ by an enzyme called ___________

A

RNA; DNA primase

90
Q

Leading strand:

A

Synthesized continuously

91
Q

Lagging strand:

A

Synthesized discontinuously
-The direction of nucleotide polymerization is opposite to the overall direction of DNA chain growth

92
Q

On the leading strand, how many primers are needed?

A

1

93
Q

On the lagging strand, how many primers are needed?

A

1 primer is needed for each Okazaki fragment

94
Q

How many nucleotides are there per each Okazaki fragment?

A

10 nucleotides long & made at intervals of 100-200 nucleotides on the lagging strand

95
Q

Step 3 of DNA synthesis:

Once primers are built, _________________ can add nucleotides in the 5’-3’ direction.

A

DNA polymerase

96
Q

Step 4 of DNA synthesis:

_________ are removed by a DNA __________ and replaced with ___________

A

RNA primers; repair system (RNAse H); DNA

97
Q

Step 4 of DNA synthesis:

____________ joins 3’ end of the new DNA fragment with the 5’ end of the previous fragment.

A

DNA ligase

98
Q

As the replication fork moves along the double-strand DNA, anything in front of the replication fork will become overwound forming ____________________

A

Supercoils

99
Q

________________ relieves the super-helical tension by breaking the phosphodiester bond.

A

DNA topoisomerase

(this allows the two sections to rotate freely and relieve tension)

-The phosphodiester bond will reform as DNA topoisomerase leaves.

100
Q

Label the diagram with the enzymes or proteins needed for each step:

A

Answers:

101
Q

What must also be synthesized so that the newly replicated DNA can be packaged into nucleosomes?

A

Histones

102
Q

Histone synthesis occurs where in the cell cycle?

A

S phase

103
Q

Assist formation of assembly of histone octomer & nucleosomes:

A

Histone Chaperones (aka; Chromatin assembly factors)

104
Q

How many mistakes occur for every 10^10 nucleotides during DNA replication?

A

1 mistake

105
Q

DNA polymerase proofreading consists of what steps?

A

1) DNA polymerase activity
2) Exonucleolytic proofreading
3) Strand-directed mismatch repair system

106
Q

DNA polymerase activity takes place when?

A

Prior to a new nucleotide being covalently added to the growing daughter chain.

107
Q

Exonucleolytic proofreading occurs when?

A

Immediately after an incorrect nucleotide has been covalently added to the growing daughter chain.

108
Q

Incorrectly added nucleotides will not provide an effective _________ end for ___________ to add on the next nucleotide.

A

3’-OH; DNA polymerase

109
Q

A ________________ on DNA polymerase will initiate DNA polymerase to move in 3’-> 5’ direction, clipping off any unpaired residues.

A

Separate catalytic site
(3’-5’ proofreading exonuclease)

110
Q

Since DNA replication occurs discontinuously on the lagging strand we end up with a shorter DNA fragment on the _______________ once the RNA primer has been removed.

A

daughter strand

111
Q

Specialized nucleotide sequences at the end of their chromosomes:

A

Telomeres
(tandem repeats of GGGTTA)
-1 Telomere is 1000 GGGTTA repeats-

112
Q

What recognizes the telomere DNA sequence?

A

Telomerase

113
Q

Telomerase:

A

-Replenishes the sequence each time the cell divides

-The activity of telomerase varies based on the cell type

114
Q

What type of cells have full telomerase activity?

A

Stem cells

115
Q

Most cells have what type of telomerase activity?

A

Minimal

116
Q

Telomerase gradually shorten untila descendant cell inherits chromosomes that lack telomere function. This initiates a response causing them to withdraw permanently from the cell cycle and cease dividing. This is called what?

A

Replicative Cell Senescence

117
Q

Telomerase will recognize what?

A

The tip of an existing telomere DNA repeat on the parent strand & elongate it in a 5’-3’ direction.

(uses intrinsic RNA template as a template)

118
Q

Following telomerase recognizing the tip of an existing telomere, what happens next?

A

The replication of the daughter strand can be completed by the conventional DNA polymerase.

(The extended telomere will be used as a template for synthesis of the daughter strand)

119
Q

hat is the end product of mitosis?

A

2 identical daughter cells

120
Q

What happens during prophase?

A

-Chromosomes condense (2 closely-associated sister chromatid)

-Mitotic spindles assemble between the two centromeres (centromeres have been replicated and are being moved apart)

121
Q

What is a centrosome?

A

Protein organelle; consists of a pair of centrioles

122
Q

What are centrioles surrounded by?

A

A cloud of amorphous material (pericentriolar matrix)

123
Q

The minus ends of microtubules are associated with:

A

The centrosome

124
Q

The plus end of microtubules do what:

A

Radiates out

125
Q

Centrosomes undergo _____________ during the cell cycle in preparation for ___________

A

replication; Mitosis

126
Q

What happens during prometaphase?

A

-Nuclear envelope breaks down
-Chromosomes attach to spindle microtubules via a protein called Kinetochore

127
Q

Chromosomes attach to spindle microtubules via a protein called what?

A

Kinetochore

128
Q

What happens during metaphase?

A

-Chromosomes align at the equator of the cell
(kinetochore microtubules attach sister chromatids to opposite poles of the spindle)

129
Q

What happens during anaphase?

A

-Chromatids synchronously separate forming two daughter chromosomes
-Kinetochore microtubules get shorter while the spindle pole moves apart

(both contribute to the separation of chromosomes)

130
Q

What happens during telophase and cytokinesis?

A

-Daughter chromosomes arrive at poles of the spindle

-Chromosomes decondense and a new nuclear envelope reassembles around each set

-Cytokinesis: cytoplasm divides in two forming daughter cells

131
Q

What is the number of chromosomes in G1 phase of the cell cycle?

A

2n

132
Q

What is the number if chromosomes in Prophase of mitosis?

A

2n

133
Q

What is the number of chromosomes after cytokinesis?

A

4n

BMS 100 Test 2 (16 decks)

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