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Biology 2 > Lecture 13- The cell cycle > Flashcards

Lecture 13- The cell cycle Flashcards

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1
Q

What do unicellular organisms primarily use cell division for?

A

Reproduction

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2
Q

What 4 events must occur for a cell to divide?

A
  • Reproductive signal
  • Replication of DNA (and other cell components)
  • Segregation
  • Cytokinesis
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3
Q

What is segregation?

A

When the cell distributes replicated DNA to each of the two new cells

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4
Q

How do prokaryotes divide?

A

Binary fission

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5
Q

What do reproductive rate in prokaryotes respond to?

A

conditions in the environment

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6
Q

What bacterium is commonly used in genetic studies?

A

Escherichia coli

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7
Q

How long does it typically take for E.coli to divide at 37 degrees Celsius?

A

40 minutes

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8
Q

How can the rate of division of E.coli be sped up?

A

Abundant carbohydrates and mineral nutrients

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9
Q

What bacterium stops dividing when food supplies are low and continues dividing when conditions improve?

A

Bacillus subtilis

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10
Q

What is the structure of the E.coli DNA?

A

A continuous molecule called a circular chromosome

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11
Q

How does DNA fit into a cell?

A

It is compacted

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12
Q

How is DNA compacted in prokaryotes?

A

It folds in on its self- + proteins bind to negative DNA to contribute to this folding

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13
Q

Where are circular chromosomes found?

A

Prokaryotes,
some viruses,
chloroplasts and mitochondria of eukaryotic cells

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14
Q

What are the two regions of the prokaryotic chromosome that play a functional role in reproduction?

A

ori

ter

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15
Q

What is the ori?

A

The site where replication of the circle starts

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16
Q

What is the ter?

A

The site where replication ends

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17
Q

What is the DNA threaded through as chromosome replication takes place?

A

A replication complex of proteins including DNA polymerase

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18
Q

What happens when the DNA is being replicated in prokaryotic cells?

A

The ori regions move towards opposite ends of the cell

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19
Q

What does DNA adjacent to the ori do?

A

Binds proteins essential for this segregation

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20
Q

What type of process is segregation in prokaryotes?

A

Active process- binding proteins hydrolyze ATP

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21
Q

What else is involved in DNA segregation?

A

The prokaryotic cytoskeleton

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22
Q

How does the prokaryotic cytoskeleton help in DNA segregation?

A

Either actively moving DNA along or passively acting as a ‘railroad’ track along which DNA moves

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23
Q

What is cytokinesis?

A

Cell separation

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24
Q

When does cytokinesis begin in prokaryotes?

A

After chromosome replication is finished

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25
Q

What is the first event in prokaryotic cytokinesis?

A

Pinching in of the plasma membrane to form a ring structure similar to a purse.

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26
Q

What happens in prokaryotes after the plasma mebrane has been pinched in?

A

The membrane pinches in, new cell wall materials are synthesised which separates the cell.

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27
Q

What is the major component of the ring that is made when the pinching in of plasma membranes form a ring in prokaryotes?

A

Fibers composed of proteins similar to eukaryotic tubulin are major components of this ring.

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28
Q

By what two processes do eukaryotic cells divide?

A

Mitosis, meiosis

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29
Q

What is development?

A

The formation of a multicellular organism from a fertilized egg

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30
Q

What does development involve?

A

Cell reproduction

Cell specialization

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31
Q

How does the rate of division in eukaryotic and prokaryotic cells differ?

A

Eukaryotic cells do not constantly divide whenever environmental conditions are adequete

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32
Q

How do eukaryotes and prokaryotes differ in regards to the number of chromosomes?

A

Eukaryotes usually have many

Prokayotes usually have a single main chromosome

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33
Q

How many chromosomes do humans have?

A

46

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34
Q

What does having more chromosomes in eukaryotes do?

A

Makes segregation more intricate

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35
Q

What are newly replicated chromosomes in eukaryotes known as?

A

Sister chromatids

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36
Q

What mechanism is used to segregate chromosomes in eukaryotes?

A

Mitosis

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37
Q

What does the presence of a nucleus in eukaryotes do?

A

Makes cytokinesis distinct from segregation (because the nucleus divides first)

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38
Q

Why does cytokinesis proceed differently in plant cells/

A

Plant cells have a cell wall

Animal cells do not

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39
Q

What happens to some cells such as red blood cells as they mature?

A

They lose the ability to divide

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40
Q

What type of cells divide rarely?

A

Cortical cells in plant stems

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41
Q

What cells are specialized for rapid division?

A

Cells in a developing embryo

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42
Q

What is the cell cycle?

A

The events that occur to produce two eukaryotic cells from one

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43
Q

What is the phase between divisions called?

A

Interphase

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44
Q

What are the three sub phases of interphase?

A

G1, S, G2

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45
Q

What happens during S (synthesis) phase?

A

The cells DNA replicates

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46
Q

What is G1?

A

Gap 1

Period between the end of mitosis and the onset of S phase

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47
Q

What is G2?

A

Gap 2

Separates the end of S phase and the beginning of mitosis

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48
Q

What is mitosis and cytokinesis reffered to as in the cell cycle?

A

M phase

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49
Q

What happens during G1 phase?

A

Preparing for S phase

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50
Q

What is the structure of DNA during G1?

A

Single, unreplicated structure

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51
Q

How long is G1?

A

Variable in different cell types

52
Q

What happens when a cell in G1 enters a resting phase?

A

It enters G0

53
Q

What is needed to enter leave G0 phase?

A

Special internal and external cells prompt a cell to leave G0 and reenter G1

54
Q

What is the transition between G1 to S called?

A

The commitment to cell division

55
Q

How many chromosomes are there at the end of S phase?

A

Double

Two sister chromatids jointed together, awaiting segregation

56
Q

What happens during G2 phase?

A

Cell makes preparations for mitosis:

-synthesizing microtubule components to move chromatids to opposite ends of dividing cell

57
Q

How was the hypothesis that a cell in S phase contains an activator of DNA replication tested experimentally?

A

Fuse cells- 1 in S phase and one in G1.

Both enter S phase

58
Q

What is the conclusion to the experiment that tested that a cell in S phase contains an activator of DNA replication?

A

The S phase cell produces a substance that diffuses to the G1 nucleus and activates DNA replication

59
Q

How are cells induced to fuse to certain substances?

A

In sugar alcohol polytheylene glycol, plasma membranes are disaggregated

60
Q

What is the fused cells in the experiment called?

A

Binucleate cell

61
Q

What does the transition from G1 to S phase depend on?

A

An activator protein called cyclin-dependent kinase (Cdk)

62
Q

How does phosphorylation effect an enzyme?

A

Phosphorylation changes the shape and function of a protein by changing its charges

63
Q

What experiment was taking place when Cdk was discovered?

A

James Maller
University of Colorado
Studying immature sea urchin eggs
Finding out how they are stimulated to divide

64
Q

What protein was found by James Maller at the University of Colorado?

A

Maturation promoting factor

Prodded immature eggs into division

65
Q

What experiment was also taking place when maturation promoting factor was discovered?

A

Leland Hartwell
University of Washington
Studying cell cycle in yeast

66
Q

What did Leland Hartwell find when studying cell cycle in yeast?

A

A strain of yeast stalled in G1-S boundary that lacked Cdk

67
Q

What was discovered about Leland Hartwell’s strain?

A

yeast Cdk very similar to sea urchins maturating promoting factor

68
Q

How are Cdk’s activated?

A

Binding to cyclin (a protein)

69
Q

What is the binding of Cdk to cyclin an example of?

A

Allosteric regulation

70
Q

How does cyclin activate Cdk?

A

Changes its shape, exposes active site

71
Q

What does the cyclin-Cdk complex act as?

A

A protein kinase

72
Q

What happens after cyclin-Cdk complex triggers transition from G1 to S phase?

A

Cyclin breaks down, Cdk is inactivated

73
Q

What is the restriction point?

A

A key decision point beyond which the rest of the cell cycle is normally inevitable

74
Q

What activator acts in the middle of G1 to move the cell past the restriction point?

A

Cyclin-D-Cdk4

75
Q

What other activator acts in the middle of G1?

A

Cyclin-E-Cdk2

76
Q

What does cyclin-E-Cdk2 do?

A

Works in concert with Cyclin-D-Cdk4 to move the cell past the restriction point

77
Q

What act at the G2-M boundary?

A

Cyclin-B-Cdk1- initiates the transition into meiosis

78
Q

What does Cyclin-A-Cdk2 do?

A

Acts during S phase to stimulate DNA replication

79
Q

What does retinoblastoma do?

A

Normally inhibits the cell cycle

80
Q

What happens when retinoblastoma is phosphorylated by a protein kinase?

A

It becomes inactive
Doesn’t block restriction point
Cell progresses past G1 into S

81
Q

What do cyclin-Cdk complexes act as?

A

Checkpoints- points which a cell cycle’s progress is monitored to determine whether the next step can be taken

82
Q

Give an example of a cyclin-Cdk complex acting as a checkpoint

A

When DNA is damaged by radiation during G1, p21 binds to G1’s Cdk’s to prevent their activation by cyclins

83
Q

What is p21?

A

A tumour suppressor

84
Q

What does the 21 stand for in p21?

A

Its molecular weight

21,000 daltons

85
Q

What happens to p21 after cell repairs have been made?

A

It breaks down

86
Q

What checkpoint is there at the end of S phase?

A

A checkpoint for complete DNA replication- if not complete, the cell cycle stops.

87
Q

What is disrupted in cancer cells?

A

Cyclin-Cdk controls

88
Q

What do some fast-growing cancers have?

A

Too much cyclin D overstimulates Cdk4 and thus cell division

89
Q

What does p53 do?

A

Prevents normal cells dividing by stimulating synthesis of p21

90
Q

What do more than half of human cancers have?

A

Faulty p53- absence of cell cycle controls

91
Q

What is RB, p52 and p21 examples of?

A

Tumor suppressors

92
Q

How do cells that no longer divide enter the cell cycle?

A

Stimulated by external chemical signals called growth factors

93
Q

Give an example of a growth factor

A

Platelet derived growth factor

produced by platelets after a cut

94
Q

What does platelet derived growth factor do?

A

Diffuses to adjacent cells in the skin and stimulates them to divide and heal wounds

95
Q

What type of growth factor does white blood cells produce?

A

Interleukins

96
Q

What do interleukins do?

A

Promote cell division in other cells essential for the bodies immune system

97
Q

What growth factor does the kidney produce?

A

Erythropoietin

98
Q

What does erythropoietin do?

A

Stimulates the division of bone marrow cells and production of red blood cells

99
Q

Additionally, what else can act as a growth factor?

A

Hormones which promote division in many cells types

100
Q

How do growth factors initiate the cell cycle?

A

Bind to target cells via specialized receptors on target cells surface
Binding triggers events within the target cell to initiate the cell cycle

101
Q

How are growth factors and cancer related?

A

Cancer cells divide inappropriately because they make their own growth factors of no longer require growth factors to start cycling

102
Q

What can mutations in retinoblastoma gene do?

A

render it inactive

103
Q

What happens when mutations render retinoblastoma inactive?

A

The cell cycle progresses through the cell cycle

104
Q

What happens in retinoblastoma tumors in retinal cells?

A

Retinal cells divide uncontrollably

This leads to blindness

105
Q

What is a risk factor for retinoblastoma tumors in the retina?

A

Hereditary/ inherited

106
Q

What are the two types of cell death?

A

Necrosis

Apoptosis

107
Q

When does necrosis occur?

A

When cells are damaged by toxins or starved of essential nutrients or oxygen

108
Q

What happens when cells are damaged by toxins or starved of essential nutrients/oxygen?

A

The cells swell up and burst, releasing contents into the extracellular environment

109
Q

What does the swelling and bursting of cell during necrosis lead to?

A

Inflammation

110
Q

What is apoptosis?

A

The genetically programmed series of events that result in cell death

111
Q

What are the two reasons for a cell initiating cell death?

A
  • The cell is no longer needed by the organism

- The longer cells live, the more prone to genetic damage, leads to cancer.

112
Q

Give an example of apoptosis due a cell no longer being needed.

A

Human fetus- web-like hands with connective tissue between fingers. This undergoes apoptosis as development proceeds.

113
Q

What cells under go apoptosis more commonly because of they are prone to genetic damage?

A

Blood and epithelia lining organs such as the intestine

114
Q

What is blood and epithelia lining organs more prone to genetic damage?

A

They are exposed to high levels of toxic substances

115
Q

How often is blood/ epithelia lining organs replaced?

A

Days or weeks

116
Q

What events occur in apoptosis?

A

Cell become isolated from neighbors
Cell cuts up chromatin into nucleosome sized pieces
Forms membranous lobes/ ‘blebs’ that break into cell fragments

117
Q

What happens after a cell has undergone apoptosis?

A

Surrounding living cells ingest the remains of the dead cell

118
Q

How is the cell death cycle controlled?

A

Signals inside or outside of the cell

119
Q

What type of signals initiate apoptosis?

A
  • Lack of mitotic signal / growth factor

- Recognition of damaged DNA

120
Q

How do external signals, or lack of them, initiate apoptosis?

A

Receptor protein in the plasma membrane changes shape and activates a class of enzymes called caspases

121
Q

How are caspases activated by internal signals?

A

Internal signals cause mitochondria release molecules which activate caspases

122
Q

What do caspases do?

A

Hydrolyze proteins of the nuclear envelope, nucleosomes and plasma membranes

123
Q

What is it important to understand how cells die?

A

Drugs used to treat diseases of cell proliferation (such as cancer) work through apoptosis signals

124
Q

What cancer treatment drug blocks the synthesis of thymine?

A

5-flurouracil

125
Q

What cancer treatment drug blocks the function of microtubules?

A

Paclitaxel

126
Q

How does radiation treat cancer?

A

Extensive DNA damage promotes apoptosis

Biology 2 (14 decks)

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