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Molecular Biology > Copying DNA in Eukaryotes > Flashcards

Copying DNA in Eukaryotes Flashcards

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1
Q

Does a cell divide on it’s own?

A

No

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2
Q

What role does growth factor have in the external signaling of cell division.

A

Growth factor binds to a protein on the cell surface called a receptor.

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3
Q

What does the receptor that growth factor binds to on the cell surface do?

A

Transmits a signal from outside of the cell to the inside (cytoplasm) where it phosphorylates a protein (normally cyanase - an enzyme which phosphorylates another protein). Starts a cycle.

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4
Q

What are the two main types of genes that control cell growth and division?

A

Proto-oncogenes and Tumor suppressor genes.

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5
Q

What is the role of Proto-oncogenes specifically? What happens is this mutates?

A

Aid in cell growth. It can become an oncogene, which activates cell growth when it is not supposed to.

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6
Q

What do tumor suppressor genes do specifically?

A

Slow down cell division, repair DNA damage or tell cells when its time to die (apoptosis).

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7
Q

How can cancer develop?

A

Mutation in a tumor suppressor gene and another mutation in the same cell that allows these cells to grow.

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8
Q

What is meant by the genetic basis of cancer?

A

Mutations (changes in your DNA), may be inherited or acquired.

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9
Q

What is cancer?

A

A disease caused by the uncontrolled division of abnormal cells in a part of the body.

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10
Q

How does cancer spread?

A

Abnormal, mutated cells can change or invade the surrounding tissues, or spread to other parts of the body.

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11
Q

What are the stages of cancer development?

A
  1. Have a cell with a mutation
  2. Hyperplasia - an increase of the amount of tissue infected with the cell mutation
  3. Dysplasia - abnormal development of cells, they start to not look right
  4. In situ cancer - abnormal cells have not spread beyond initial area
  5. Invasive cancer - spreading to other parts of the body
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12
Q

The template for replication in eukaryotes is ______ than in prokaryotes.

A

Much larger

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13
Q

Cell division in eukaryotes is known as the ______ and takes ______ hours to complete.

A

Cell cycle. 18-24 hours.

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14
Q

What does the cell cycle consist of (steps?).

A

Look at physical card 11.

G1
S
G2
M

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15
Q

What happens in G1 phase of the cell cycle?

A

Growth and preparation of chromosomes for replication.

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16
Q

What happens in S phase of the cell cycle?

A

Synthesis of DNA - amount of DNA in the nucleus in this phase doubles

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17
Q

What happens in G2 phase of the cell cycle?

A

Preparation for mitosis - getting ready to distribute DNA into two daughter cells

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18
Q

What happens in M phase of the cell cycle?

A

Mitosis - chromosome segregation. Cells will complete the cycle again.

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19
Q

What is G0 in cell cycle?

A

The cell has opted out of the cell cycle - it is a non-dividing cells and is terminally differentiated.

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20
Q

What is interphase in the cell cycle?

A

The time between the end of one mitosis and the start of the next.

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21
Q

The percentage of cells in ____ phase increases with age.

A

G0

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22
Q

How does the time cells spend in G0 differ for cell type eg fibroblasts, adult liver cells and adult brain cells?

A

Fibroblasts almost never in G0.
Adult liver cell enters cell cycle 1 x per year.
Adult brain cells are almost always in G0.

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23
Q

What is a quiescent cell?

A

Cell that can be induced to re-enter the cell cycle by a mitotic signal.

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24
Q

What is a senescent cell?

A

Can not re-enter the cell cycle.

25
Q

What happens if a cell reaches a checkpoint in a phase of the cell cycle and there is something wrong?

A

The cell cycle can be aborted.

26
Q

What happens if a cell remains in the aborted state for too long?

A

It will be directed to undergo cell apoptosis.

27
Q

Where is the restriction point in the cell cycle and what does this mean?

A

Late in G1, the cell is committed to cell division.

28
Q

What are the three important checkpoints in cell cycle?

A
  1. DNA damage is checked for at G1 before the cell enters S
  2. A check for the completion of S phase (replication) is the presence of the Okazaki fragments i.e. if there are gaps no sealed it is not complete.
  3. Spindles are checked before the cell actually divides (M phase)
29
Q

What are cyclins?

A

At the critical stages, G1, S and M, cytoplasmic proteins known as cyclins increase in concentration and subside once the cell has passed through that stage.

30
Q

What are cyclin-dependent kinases (CDKs)?

A

A group of enzymes which phosphorylate protein targets involved in the control of the cell cycle. Only activated when they bind to the appropriate cyclin.

31
Q

What are the cyclins and what CDK do they bind to?

A

Cyclin D - CDK4 and 6
Cyclin E - CDK2
Cyclin A - CDK2 and 1
Cyclin B - CDK 1

32
Q

How does each CDK/cyclin bond drive the cell cycle?

A

E and A binding drives the cell from G1 to S.

B drives the cell from G2 to M.

33
Q

How is the cell cycle impacted by Myc?

A

Myc is a proto-oncogene - transcription factor. It switches on the gene for cyclin D which allows CDK 4 and 6 to be activated.

34
Q

CDK 4 and 6 do what?

A

Phosphorylate retinoblastoma which is a tumor suppressor gene which deactivates it.

35
Q

What is P53?

A

Makes sure tumor suppressor gene is in all cells.

36
Q

Proto-oncogenes can be described as the ______. Mutation in it can lead to ______.

A

Accelerator. Increased levels of a protein which promotes growth.

37
Q

Tumor Suppressor Proteins can be described as _______. Mutations can lead to _________.

A

Gatekeepers. Presence prevents growth. Mutations can lead to constraint of growth.

38
Q

What needs to happen to a tumor suppressor gene before it loses it’s gatekeeper effect? Example.

A

Inactivate both copies.

P53

39
Q

Difference in replication between Eukaryotic and Prokaryotic cells?

A

Eukaryotic:
Linear chromosomes with ends or telomeres.
More genetic material.
More packaging; nucleosomes and scaffolds.
Different enzymes; slower in eukaryotes - more careful when copying the sequence.

40
Q

Initiation of eukaryotic replication occurs in two stages. What are they?

A

Selecting origins and activating the origins.

41
Q

Are all origin sites used in each round of replication?

A

No.

42
Q

How many origin sites are initiated at a time?

A

20-80

43
Q

Replication takes place in what phase of cell division?

A

S

44
Q

What phase does origin site selection take part in?

A

G1

45
Q

What is a pre-replicative complex?

A

In G1 assemble and sit and wait until the cell phases from G1 to S. Then become activated during phosphorylation by CDKs - enables them to recruit DNA polymerases.

46
Q

What are the Eukaryotic polymerases?

A

DNA polymerase alpha - like polymerase 1 coupled with primase so enzyme complex can lay down its RNA primer.
DNA polymerase delta - like DNA polymerase 3 - does majority of synthesis in a replicating cell.

47
Q

Describe in greater depth the role of DNA polymerases in eukaryotes

A

Physical card 12.

48
Q

How does the cell repackage it’s DNA after DNA synthesis?

A

Histones can be unpacked and recycled - but need more as there is 2x DNA after synthesis in S phase.

49
Q

What are the unique features of histones?

A

Many copies of the histone gene in the genome.
Have no introns - don’t need to splice these sequences out before beginning.
Histone mRNA’s don’t have a poly-A tail.

50
Q

What is the end problem?

A

Physical card 13. After each round of replication we lose more dsDNA - cell runs out of divisions.

51
Q

What are telomeres?

A

eukaryotic chromosomes are composed of repeating structures called telomeres.

52
Q

What is telomerase?

A

Telomerase recognizes the overhang (the end problem). It is an enzyme.

53
Q

What are the components of telomerase?

A

It has both protein and RNA components. (Ribonucleoprotein).
Protein: reverse transcriptase carrying its own template with it.
RNA: includes about 1 and a half copies of the complement of the telomere sequence.

54
Q

What is the role of each component in Telomerase?

A

RNA is a template for reverse transcriptase and catalyzes reaction where telomere at the ends of chromosomes are rebuilt.

55
Q

Explain in depth how telomerase aids the end problem.

A

Physical card 14.

56
Q

A zygote starts with full length telomeres?

A

Yes.

57
Q

Somatic cells (any except germ-line cells sperm and eggs) - have very little telomerase activity. What is the implication of this?

A

Every time a cell undergoes mitosis the telomere shortens. Eventually gets so short that the cell is in danger of eroding the coding genes. Hayflick limit.

58
Q

What makes a cell immortal? Give an example?

A

They have telomerase activity which means it doesn’t shorten and hence wont run out of divisions. Cancer cells.

59
Q

What is thought to be the cause of aging in organisms…why?

A

Telomere shortening. Cells progress to terminal differentiations they cant divide.

Molecular Biology (14 decks)

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