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Introduction to Genetics & Biochemistry > DNA Replication, Cell Differentiation & The Cell Cycle > Flashcards

DNA Replication, Cell Differentiation & The Cell Cycle Flashcards

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Biology 101 flashcards
1
Q

Before the division of a cell:
Chromosomes ………….. and ……………. .
Cells …………… and expand in …………. .
Separation of organelles is mostly ……………. , except for the ……………… , which is duplicated and migrates to oppposite …………… .
……………….. allow for regulation and cell growth.

A

Chromosomes REPLICATE and SEGREGATE.
Cells GROW and expand in VOLUME.
Separation of organelles is mostly RANDOM, except for the CENTROSOME / SPINDLE BODY, which is duplicated and migrates to opposite POLES.
GAP PHASES allow for regulation and cell growth.

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2
Q

The cell cycle is a sequence of events which leads to…?

A

…reproduction of the cell.

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3
Q

If cells divided but did not grow, what would happen?

A

The cells would increase in number but keep getting smaller and smaller.

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4
Q

The critical ratio triggers chromosome replication - but what is the critical ratio?

A

The critical ratio is when the cell senses that the ratio of DNA to cell mass increases when DNA is duplicated, then it decreases as the cell grows until the cell has doubled in size - this is the critical ratio and the point at which the cell divides.

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5
Q

Describe the structure of DNA.

A

DNA is a double helix of two strands of polynucleotides running antiparallel. Each polynucleotide is comprised of a series of nucleotides.

Phosphate groups are joined by phosphodiester linkages. Each phosphate group is attached to a pentose sugar and together they form the sugar-phosphate backbone.

Nitrogenous bases are attached to the 1’ carbon of the pentose sugar.

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6
Q

Name the four nitrogenous bases of DNA and match them as they pair up.

A

Adenine=Thymine.
Guanine=Cytosine.

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7
Q

DNA is unidirectional - what does this mean?

A

DNA has directionality. It is always read from the 5’ end to the 3’ end.

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8
Q

Is the hydroxyl group attached to the 3’ end or the 5’ end of the pentose sugar?

A

The hydroxyl group is attached to the 3’ end of the pentose sugar.

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9
Q

Is the phosphate group attached to the 3’ end or the 5’ end of the pentose sugar?

A

The 5’ end.

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10
Q

Which direction is DNA read? 5’ to 3’ or 3’ to 5’?

A

DNA is alwayds from the 5’ end to the 3’ end.

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11
Q

Does DNA run parallel or antiparallel?

A

Antiparallel.

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12
Q

Each strand of DNA forms covalent bonds between corresponding base pairs. True or false?

A

False. DNA forms non-covalent bonds between the base pairs. They are joined by hydrogen bonds.

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13
Q

In a DNA double helix, it is slightly easier to break the bonds between adenine and thymine and than it is between cytosine and guanine. Why is this?

A

There are three hydrogen bonds between cytosine and guanine but only two hydrogen bonds between adenine and thymine, so adenine and thymine are slightly easier to pull apart.

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14
Q

What type of bonds hold the corresponding base pairs of DNA together?

A

Hydrogen bonds.

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15
Q

How many nitrogenous base pairs are there for every turn of the DNA double helix (every 3.4nm)?

A

There are 10 base pairs for every turn of the DNA helix, meaning that the nitrogenous bases are 0.34nm apart.

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16
Q

How far are the strands of the DNA double helix apart?
a. 2nm.
b. 5nm.
c. 8nm.

A

a. 2nm.

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17
Q

What does the ‘minor groove’ and the ‘major groove’ of the DNA structure refer to? What implication does this have for interactions with DNA binding proteins?

A

In the major groove the sugar-phosphate backbones arre further apart and in the minor groove the sugar-phosphate backbones are closer together.

DNA binding proteins interact more readily with the nitrogenous bases on the mojor groove more readily.

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18
Q

Which two of the DNA base pairs are pyramidines and which are purines?

A

Cytosine and thymine are pyramidines.

Adenine and guanine are purines.

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19
Q

What is the difference between pyramidines (e.g. cytosine and thymine) and purines (e.g. adenine and guanine)?

A

Pyramidines have one ring of atoms, whereas purines have two rings of atoms.

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20
Q

Where in the cell does DNA take place in eukaryotes?

A

In the nucleus.

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21
Q

During which phase of the cell cycle does eukaryotic DNA replication occur?

A

In the distinct S phase.

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22
Q

The …………… protein binds to the origin to start DNA replication. This then forms the …………. …………. .

A

The INITIATOR protein binds to the origin to start DNA replication. This then forms then REPLICATION BUBBLE.

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23
Q

What part does DNA helicase play in DNA replication?

A

DNA helicase causes the two strands of DNA to untwist, forming a y-shaped replication fork by breaking the hydrogen bonds between the bases, resulting in two single-stranded template strands.

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24
Q

During DNA replication, what are the proteins that bind to each single-stranded DNA molecule to prevent them rejoining called?

A

Single-stranded binding proteins.

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25
Q

What is the function of the topoisomerase enzyme in DNA replication?

A

Topoisomerase enzyme moves ahead of the replication fork, helping to relieve the tension created by unwinding the DNA strands.

It does this by cutting the phosphate backbone of one or both DNA strands , allowing the strands to unwind, and then resealing the backbone.

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26
Q

What is the function of RNA primase?

A

RNA primase synthesises a short (5-10 bases) RNA primer.

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27
Q

Which end of the templaste strand does the RNA primer attach to?

A

The 3’ end.

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28
Q

What are the two functions of DNA polymerase?

A
  1. DNA polymerase is the causes the addition of nucleotides to the RNA primer, in complementary base strands with the template strand.
  2. Polymerase also catalyses the formation of a phosphodiester bond between the 3’ carbon of the last nucleotide and the 5’ carbon of the incoming nucleotide.
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29
Q

In which direction does DNA polymerase move along the old DNA template strand? And in which direction is the new strand of DNA built?

A

The DNA polymerase moves along the old DNA template strand in the 3’ to 5’ direction, meaning that the new strand of DNA is built in the 5’ to 3’ direction.

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30
Q

What happens at the proofreading site of DNA polymerase?

A

Any ‘wrong’ nucleotides that have been inserted by DNA polymerase are cut out at the proofreading site (from the 3’ end to the 5’ end).

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31
Q

What happens at the exonuclease site of DNA polymerase?

A

Faulty DNA is degraded, including DNA primer (from the 5’ end to the 3’ end).

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32
Q

The new strand of DNA being made in the opposite direction to the movement of the replication fork is called the ………….. strand.

A

Lagging.

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33
Q

The new strand of DNA being made in the same direction as the replication fork is called the ……………. strand.

A

Leading.

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34
Q

To maintain 5’ to 3’ polarity, DNA is …………….. in …………….. directions on the two template strands.

A

Synthesised.
Opposite.

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35
Q

On the leading template strand, is DNA synthesised:
a) continuously, requiring only one RNA primer, or
b) in pieces called okazaki fragments, which require multiple RNA primers.

A

a) DNA is synthesised continuously on the leading template strand, requiring only one RNA primer.

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36
Q

The DNA on the lagging strand is synthesised in pieces - what are these pieces of DNA called?

A

Okazaki fragments.

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37
Q

True or false? The okazaki fragments of DNA synthesised on the lagging template strand require multiple RNA primers.

A

True.

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38
Q

Which two enzymes join the okazaki fragments which are synthesised on the lagging template strand?

A

DNA polymerase and DNA ligase.

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39
Q

What form does prokaryotic DNA take?

A

A single circle.

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40
Q

In prokaryotic DNA replication, the replication forks move ……………… from the single origin of replication (OriC) to the terminus (TerC).

A

Bidirectionally.

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41
Q

Which period of the prokaryotic cell cycle is this?
Analogous to the S phase in eukaryotes.
Takes around 40 minutes and is independent of growth rate.

A

This is the C phase of the prokaryotic cell cycle, when DNA synthesis occurs.

42
Q

True or false? The prokaryotic cell can stop and reverse the cell cycle at any point.

A

False. Once DNA replication has started, the cell must go through the full cell cycle.

43
Q

In which period of the prokaryotic cell cycle does cytokinesis occur? It is analogous to G2 in eukaryotes and takes around twenty minutes.

A

D period.

44
Q

Which period of the prokaryotic cell cycle can be almost instantaneous in favourable conditions?

A

B period - analogous to the resting phase in eukaryotes.

45
Q

The generation time in E.Coli is how long it takes the culture to ………………… .

A

Double.

46
Q

The cell cycle of prokaryotic replication can overlap - one cycle can start before another is finished, and so on. True or false?

A

True.

47
Q

True or false - prokaryotic cells can only divide with a fully replicated genome.

A

False. Prokaryotic cells can divide with a partially replicated genome - as long as replication has started, the cell can divide and replications can continue.

48
Q

In general, what happens in the M period of the cell cycle?

A

Chromosomes condense and separate and the cell divides.

49
Q

Which cells does meiosis occur in?

A

Reproductive cells.

50
Q

In mitosis, there is …………. cell division, creating genetically ……………… daughter cells.

A

One.
Identical.

51
Q

How many stages of mitosis are there? Name them.

A

Four - prophase, metaphase, anaphase and telophase.

52
Q

How many daughter cells are produced in mitosis?

A

Two.

53
Q

In which stage of mitosis do sister chromatids separate?

A

Anaphase.

54
Q

In meiosis, there are ………….. successive cell divisions, creating genetically …………… daughter cells.

A

Four.
Different.

55
Q

Meiosis and mitosis - which produces haploid daughter cells, and which produces diploid daughter cells?

A

Mitosis = diploid.
Meiosis = haploid.

56
Q

How many daughter cells are produced in meiosis?

A

Four.

57
Q

How many stages are there in meiosis?

A

Eight - twice round the four stages.

58
Q

Why is prophase I longer in meiosis?

A

To allow for crossing over of genetic material.

59
Q

In metaphase I of meiosis, the chromosomes line up along the metaphase plate …………… . This is called …………… …………….. .

A

Randomly.
Independent assortment.

60
Q

True or false? The DNA content is conserved from parent cells to daughter cells in meiosis.

A

False - the DNA content is halved in meiosis.

61
Q

At which points of meiosis does the following occur:
a) the separation of homologous chromosomes.
b) the separation of sister chromatids.

A

a) anaphase I.
b) anaphase II.

62
Q

What are the three sources of genetic variation in meiosis?

A
  1. crossing over - the recombination of DNA in prophase I. This produces four chromatids that are all genetically different from one another and from the parent cells.
  2. Random assortment of chromosomes at metaphase I.
  3. Random fusion of gametes from parents.
63
Q

True or false - there is no such thing as too much crossing over!

A

False. Too much crossing over can lead to mutations.

64
Q

The offspring produced in meiosis have combinations of genes not found in either of their parents.

A

True, this is as a result of recombination.

65
Q

What happens at prophase in mitosis?

A

The chromatin condenses into chromosomes of two sister chromatids.

66
Q

What happens in metaphase in mitosis?

A

The chromatin aligns on the metaphase plate and spindle fibres attach to the individual chromosomes.

67
Q

What happens in anaphase in mitosis?

A

Sister chromatids separate and move to opposite poles of the cell.

68
Q

What happens in telophase of mitosis?

A

The chromosomes decondense back to chromatin and two nuclei are formed, still within a single cell.

69
Q

What happens in cytokinesis of mitosis?

A

One cell divides into two at the cleavage furrow as the cytoplasm of the cell is divided by formation of a contractile ring.

70
Q

True or false? The two daughter cells produced in mitosis are genetically different.

A

False. The daughter cells produced in mitosis are genetically identical.

71
Q

In mitosis and meiosis, what is going on in interphase?

A

Nothing. It is a resting phase.

72
Q

Name the phases of mitosis (and meiosis I), in the order that they occur.

A
  1. interphase.
  2. prophase.
  3. metaphase.
  4. anaphase.
  5. telophase and cytokinesis.
73
Q

At which stage of meiosis does crossing over occur?

A

Meiosis I.

74
Q

What are chiasma?

A

The points where arms of chromosomes overlap and are held together during crossing over.

75
Q

What did Walter Flemming define about the cell cycle and how?

A

He defined interphase and mitosis, using a light microscope.

76
Q

Howard and Pelc defined which three stages of the cell cycle?

A

G1 (gap) phase, S (synthesis) phase and G2 (gap) phase.

77
Q

How did Howard and Pelc define the G1, S and G2 stages of the cell cycle?

A

With radioactive labelled phosphorous, the could see when cells which had had the nucles removed took the radioactive phosphorous into their DNA, which represented the stage when DNA is being replicated.

78
Q

Name the stage of the cell cycle:

Cells are growing, the chromosomes are prepared for replication and cellular components are duplicated.

A

G1.

79
Q

Which is the only stage of the cell cycle which can vary in length, and why?

A

G1, because cell generation time varies.

80
Q

In which stage of the cell cycle is DNA made?

A

S.

81
Q

At which stage of the cell cycle do cells that stop dividing (e.g. due to starvation) go no further?

A

G1.

82
Q

Name the stage of the cell cycle:

The cell prepares for the cell cycle. Many genes are expressed.

A

G2.

83
Q

Describe the function of the ‘relative timing mechanism’ of the cell cycle.

A

This mechanism tells the cell when it is time to move onto the next stage of the cell cycle by accumulating proteins (cyclins) in a pile until they reach a trigger point, when they move onto the next phase.

84
Q

True or false? Cells do not have the ability to stop or pause the cell cycle, it is a continuous process.

A

False. If a cell is under stress, it can arrest or pause the cell cycle until the situation is resolved.

85
Q

What are the two possible scenarios for the cell cycle if genees are mutated?

A

If the cell senses the damage, the cell arrests the cell cycle but because the DNA damage cannot be fixed the cell dies.

If the cell does not sense the DNA damage, it continues replicating but cannot function properly, resulting in a colony of dead cells.

86
Q

What are cyclins?

A

Small proteins active during the cell cycle.

87
Q

What are CDKs?

A

Cyclin-dependent kinases, they interact with cyclins during the cell cycle.

88
Q

At which checkpoints of the cell cycle are CDKs activated?

A

G1/S and G2/M.

89
Q

What is destroyed at the metaphase-to-anaphase transition checkpoint?

A

Cyclins and sister-chromatid cohesion.

90
Q

What are the master regulators of the cell cycle?

A

Cyclin dependent kinases.

91
Q

What are associators in the cell cycle and what do they associate with?

A

Cyclins. They associate with cyclin dependent kinases.

92
Q

What do cyclin dependent kinases do to downstream cyclins?

A

They phosphorylate them.

93
Q

True or false? The level of cyclin proteins oscillates with specific cell cycle stages.

A

True. The level of cyclins accumulates and degrades throughout the cell cycle to activate the different cell stages.

94
Q

What is APC, and what is the effect of CDKs on it?

A

Anaphase promoting complex. Different cyclins / CDKs regulate APC to varying degrees.

95
Q

Which cell cycle checkpoint is this?

The rate of cell cycle progression can be governed, dependent on external factors.

Progression through this checkpoint represents an irreversible commitment to going through the whole cell cycle.

Cell size and DNA damage can be controlled from this checkpoint.

A

Restriction point or G1/S checkpoint.

96
Q

What is controlled at the S checkpoint of the cell cycle?

A

DNA damage and DNA replication.

97
Q

What is controlled at the G2/M checkpoint of the cell cycle?

A

Cell size and DNA damage.

98
Q

What is the S-M dependency?

A

Entry into M-phase is dependent upon successful completion of S-phase (DNA replication).

99
Q

What happens at the M-checkpoint of the cell cycle?

A

DNA damage control and separation of sister chromatids.

100
Q

How can CDC 25 be used to treat cancer?

A

They are highly conserved phosphatases that specifically target CDKs, acting as dose-dependent inducers of cell cycle transitions. This can arrest the cell and prevent its progression through the cell cycle, so it does, leading to tumour regression.

101
Q

What does SSB stand for?

A

Single stranded binding (of DNA).

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