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BIOL181 > Material for Test #3 > Flashcards

Material for Test #3 Flashcards

1
Q

What are the three major steps in chromosome dynamics and the cell division cycle?

A
  1. cell growth and chromosome replication
  2. chromosome segregation
  3. cell division
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2
Q

What are three essential DNA sequence elements for efficient replication and segregation of chromosomes in eukaryotes?

A
  1. DNA replication origins
  2. Centromeres (required for segregation of chromosomes during mitosis).
  3. Telomeres (today’s focus)

A. Protection from nucleases AND B. Prevention of chromosome fusion AND C. DNA replication of chromosome ends.

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3
Q

What is telomerase?

A

a specialized DNA polymerase that replicates telomeres

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4
Q

Why can’t DNA polymerase replicate linear chromosomes?

A

DNA polymerase synthesized 5 prime to 3 prime so cant fill in the gap from the lagging strand

Due to the requirement for an RNA primer, the ends of linear chromosomes can’t be replicated by conventional DNA polymerase.

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5
Q

What does telomerase do to the ends of linear chromosomes?

A

replicates the ends

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6
Q

what are characteristics of telomerase?

A

RNA-dependent DNA polymerase •

Synthesizes DNA in a 5’ to 3’ direction •

Uses its own RNA as a template •

Uses the 3’ overhang as a primer •

Synthesizes a short (6 nucleotide) sequence over and over

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7
Q

What happens when telomerase is done replicating the ends?

A

After action of telomerase, conventional DNA polymerase can synthesize the complementary strand •

However, the 3’ overhang is never filled in

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8
Q

What happens to cells that lack telomerase activity?

A

Cells that lack telomerase activity exhibit shortening of chromosome ends each generation; eventually this causes cells to cease dividing (they are said to be “senescent”)

Yeast cells with inactive telomerase eventually stop growing (“senesce”) and die.

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9
Q

why do human cells lack telomerase?

A

anti-cancer mechanism

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10
Q

Hayflick Limit

A

Cells taken directly from mammals (e.g., fibroblasts/skin cells) and grown in vitro have a limited capacity to divide; most survive 40-50 generations, then cease dividing (this is known as the “Hayflick Limit” after the scientist who made this observation in 1961).

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11
Q

do mammalian cells have telomerase?

How many generations can they correctly grow?

A

• Most mammalian cells lack telomerase activity; mammalian cells grown in vitro divide for 40-60 generations and then senesce.

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12
Q

what is the effect of an addition of telomerase?

A

Addition of telomerase allows mammalian cells to grow indefinitely in culture (it “immortalizes” them).

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13
Q
A
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14
Q

How are chromosomes duplicated and transmitted to two new cells during cell division?

A
  1. Mechanics of mitosis
  2. Regulation of cell cycle progression (Cdk-cyclin action)
  3. Quality control: checkpoints
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15
Q

How are chromosomes equally distributed to daughter cells during mitosis?

A

Cohesin proteins hold replicated chromosomes together

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16
Q

what are the phases of the cell cycle?

A

interphase (G1, S Phase, G2), M phase (mitosis, cytoplasmic division)

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17
Q

cohesin vs condensin

A
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18
Q

what happens to chromosomes in mitosis?

A

• chromosomes are pulled to each pole by microtubules

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19
Q

how is anaphase triggered?

A

anaphase is triggered by the destruction of cohesin rings

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20
Q

What are the two steps in mitosis to focus on?

A

metaphase ((duplicated chromosomes line up)

anaphase (separation of duplicated chromosomes)

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21
Q

How are chromosomes pulled apart in mitosis?

A
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22
Q

kinetochore

A

kinetochore = protein structure, forms on the centromere

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23
Q

microtubules

A

microtubules = protein fibers, attach to the kinetochore

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24
Q

centromere

A

DNA sequence

?????? more explanation

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25
Q

chromosome structure in eukaryotes

A
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26
Q
A
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27
Q

What happens in cohesin failure?

A

The sister chromatid are not held together by cohesion rings in metaphase

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28
Q

How can you preform an assay for chromatid cohesion? What do the spots indicate?

A

A specific region of a single chromosome is labeled with a fluorescent protein; a failure of chromosome cohesion will lead to two distinct spots. In the G phase there is one spot of labeled fluorescence and the chromatid undergoes DNA replication.

Under normal cohesion the sister chromatid are held by cohesion rings but there remains one spot as the chromosomes are too close to resolve two separate spots.

In cohesion failure the cohesion rings don’t hold the chromatid together and there are two spots (chromosomes prematurely separated)

29
Q

How are orderly transitions in the cell cycle regulated?

A

S-phase and mitosis must occur sequentially

DNA replication must not begin before newly replicated chromosomes are distributed to daughter cells.

30
Q

How do you prevent mitosis from starting before DNA replication is complete?

A

We know that a protein exists that destroys cohesin in mitosis to allow sister chromatids to separate; how does the cell prevent this protein from working at other times?

Cells must regulate the presence or activity of key regulatory proteins

31
Q

what proteins regulate cell cycle progression?

A

cyclin dependent kinases (CDKs)

32
Q

What is phosphorylation carried out by?

What is phosphate removal carried out by?

A

phosphorylation by kinases

phosphate removal by phosphatases

33
Q

How are proteins regulated by phosphorylation?

A

addition of a phosphate group on serine, threonine, or tyrosine amino acid residues

34
Q

How is CDK activity regulated?

A

Cdk enzymes are only active in the presence of cyclin molecules. Cdk enzymes are present at constant levels throughout the cell cycle

35
Q

How do specific proteins get phosphorylated?

A

The specific cyclin determines the kinase substrate (determines which specific proteins get phosphorylated)

36
Q

How is the anaphase promoting complex activated? What does it trigger?

A

activated by Cdk/M-cyclin

triggers mitosis

37
Q

What is APC?

How does APC activation lead to cohesion degradation?

What does APC do to M-phase cyclin?

A

APC

APC activation indirectly leads to degradation of cohesin, allowing chromosome separation

APC also degrades the M-phase cyclin, allowing cells to progress to G1

38
Q

How do the chromosomes separate in APC?

A
39
Q

What controls the G1 to S phase transition?

A
  • a resting (non-dividing) cell receives an exogenous signal to proliferate
  • a signal transduction pathway results in activation of the G1 Cdk-cyclin complex
  • Cdk-cyclin phosphorylates Rb, inactivating it, allowing transcription of S-phase specific genes Rb is inactive in many human cancers
40
Q

3 steps in cell division for how chromosomes are duplicated and transmitted to two new cells during cell division?

A
  1. Mechanics of mitosis
  2. Regulation of cell cycle progression (Cdk-cyclin activity) 3. Quality control: checkpoints
41
Q

How are chromosomes duplicated and transmitted to two new cells during cell division?

A
42
Q

what is condensin?

A

a ring-shaped protein complex that binds DNA • creates DNA loops by stably associating (“anchoring”) at one site, and forcing DNA through its ring

43
Q

How does condensin condense DNA/chromatin?

A

creates DNA loops

44
Q

How does APC mediates destruciton of the M-phase cyclin?

A

active Cdk complex is ubiquitylated by active APC and then cyclin is destructed in the proteosome leaving inactive CK

45
Q

How do specific events for a certain cycle get triggered?

A

Distinct Cdks associate with different cyclins to trigger the different events of the cell cycle

46
Q

what does p53 activate the transcription of

A
  1. p21 gene (to inhibit cell cycle progression)
  2. DNA repair genes (to repair damage)
47
Q

What happens after DNA damadge in G1 and G2?

A
  1. DNA damage sensed; a signal transduction pathway activates p53
  2. p53 binds the promoters of several genes, including p21, a Cdk inhibitor
  3. p21 blocks the action of Cdk proteins, halting the cell cycle
  4. p21 blocks the action of Cdk proteins, halting the cell cycle. DNA repair proteins can try to fix the damage
  5. If damage is fixed p53 is no longer activated, p21 turned off, and cell cycle progression continues.
48
Q

What if the cell can’t fix all the DNA damage?

A

If the DNA damage is extensive then p53 levels will continue to rise; high levels of p53 activate transcription of the Bax gene. The Bax protein will cause apoptosis (programmed cell death).

49
Q

what are the consequences of mutation?

A

better for a cell to commit suicide than to accumulate mutations and risk developing into a cancer cell

50
Q

What does meiosis do to diploid cells?

what is haploid?

What is diploid?

A

produces haploid cells from diploid cells

haploid cells fuse to reconstitute diploid state

haploid is one set of chromosomes (one copy of each gene

diploid is two sets of chromosomes (chromosomes in pairs; two copies of each gen

51
Q

homologous chromosomes

A

Pairs of chromosomes, one maternally derived, one paternally derived

52
Q

karyotype

what is a normal human karyotype

A

karyotype is an individual’s collection of chromosomes. The term also refers to a laboratory technique that produces an image of an individual’s chromosomes.

contains 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes, generally arranged in order from largest to smallest. The short arm of a chromosome is referred to as the p arm, while the long arm is designated the q arm

53
Q

mitosis definition

A

duplicated chromosomes (sister chromatids) line up in metaphase; each new cell gets one of the two duplicated chromosomes

54
Q

meiosis 1 definition

meiosis 2 definition

A

M1: duplicated chromosomes (sister chromatids) pair with their homologous duplicated chromosomes; each cell gets one pair of duplicated chromosomes (sister chromatids do not separate in meiosis I)

M2: duplicated chromosomes (sister chromatids) line up in metaphase; each new cell gets one of the two duplicated chromosomes

55
Q

what are homologues?

A

organism has 4 chromosomes (2 pairs of chromosomes), marked “P” (paternal source) and “M” (maternal source)

56
Q

what does Meiosis 2 produce?

A

Four haploid cells, each with one set of unduplicated chromosomes

57
Q

what does Meiosis 1 produce?

A

two cells are produced, each carrying one set of homologues (either the paternal or maternal homologue of each chromosome)

58
Q

How does Meiosis 1 go to Meiosis 2?

A

In the absence of any new DNA replication these cells go through mitosis again, now separating the duplicated chromosomes (separating the sister chromatids) and producing four cells, each with one set of chromosomes (i.e., four haploid cells) [product of meiosis 2]

59
Q

How are homologous chromosomes held together in meiosis I?

A

Sister chromatids are held together via cohesin rings; homologous pairs of chromosomes are linked by DNA recombination: crossing over in meiosis

60
Q

what does crossing over result in?

A

Crossing over results in a physical swapping of chromosome segments, a recombination event; recombination between non-identical paternal and maternal chromosomes results in new combinations of gene alleles.

61
Q

difference between Meiosis 1 and Meiosis 2?

A
62
Q

what are the effects of independent reassortment and crossing over?

A

Independent reassortment and crossing over in meiosis increases genetic diversity

63
Q

what are Harlequin Chromosomes?

A

Harlequin chromosomes are characterized by differential staining of the two sister chromatids of a chromosome

Sister chromatids that stain differently, so that one appears dark and the other light (harlequin-like).

An experimental method used to demonstrate ‘sister chromatid exchange’ in chromosomes; one of the ‘sisters’ is chemically altered and made to fluoresce more brightly than its sister

recombination between chromosomes indicated by staining patterns

64
Q

what is a sister chromatid?

A

one half of a duplicated chromosome joined to the other identical copy by a centromere

65
Q

where does crossing over occur?

A

meiotic prophase 1

66
Q

where does independent assortment occur?

A

independent assortment of materal and paternal homologs during meiosis 1

67
Q

what are R, r

A

gene alleles - alternate form of a single gene

68
Q

punnet square with rr and RR produces what genotypes and phenotypes for F1 and F2?

A

F1 will produce genotypes of 4 Rr and phenotypes of all round

F2 wil produce genotypes of 1 RR, 2 Rr, 1 rr and phenotypes of 3 round and 1 wrinkled

69
Q

what does independent segregation on twp chromosomes yield

A

BIOL181 (4 decks)

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