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Molecular Biology Test 1 > Chapter 9 - Chromosomes > Flashcards

Chapter 9 - Chromosomes Flashcards

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1
Q

Nucleoid

A

Structure in bacterial cells that contains the genome.

  • Not Confined by a membrane
  • DNA bound by proteins
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2
Q

In eukaryotes, the genetic information is confined to the

A

Nucleus

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3
Q

Chromatin

A

Mass of DNA and DNA-bound proteins that occupies a large portion of the nucleus

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4
Q

Chromosome

A

Maximally condensed chromatin visible at the metaphase stage of cell division.

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5
Q

Chromosome visible in the most condensed form during

________ stage of mitosis.

A

Metaphase

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6
Q

What allows DNA to transition from the loosely organized interphase chromatin state to the highly condensed metaphase state and vice versa?

A

DNA Scaffold/Matrix

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7
Q

How does DNA maintain metaphase structure even when depleted of 92% of histone protein?

A

Arrangement of condensed metaphase structure is due

primarily to the arrangement of the DNA fibers in space.

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8
Q

At _______, the protein framework moves to occupy a

larger portion of the nucleus and constitutes the nuclear matrix.

A

Interphase

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9
Q

Metaphase (mitotic) scaffold

A

Protein framework that maintains the highly condensed

form of the DNA (independent of the histone proteins).

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10
Q

DNA sequence that allows for attachment to the protein scaffold:

A
  • No consensus sequence
  • A-T rich
  • Close to the Regulatory Region
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11
Q

Matrix attachment region (MAR)

A

In Interphase

DNA sequence that allows for attachment to the matrix

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12
Q

Scaffold attachment region (SAR) in Metaphase

A

In Metaphase

DNA sequence that allows for attachment to the scaffold

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13
Q

DNA Staining

A

Utilized to generate a “gene roadmap” independent of

size and shape.

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14
Q

G-banding (Giemsa)

A

A-T rich

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15
Q

R-banding (reverse)

A

G-C rich

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16
Q

C-banding

A

Centromere, telomeres, constitutive heterochromatin

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17
Q

G-C rich regions are commonly

A

Gene start sites

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18
Q

Each band represents

A

Each band represents ~ 10^7 bp and multiple gene
• p-arm: short arm of the chromosome
• q-arm: long arm of the chromosome

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19
Q

P-arm

A

short arm of the chromosome

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20
Q

Each band represents

A

Each band represents ~ 10^7 bp and multiple gene

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21
Q

P-arm

A

Short arm of the chromosome

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22
Q

Q-arm

A

Long arm of the chromosome

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23
Q

Euchromatin

A
  • loosely packed chromatin regions
  • diffuse staining for DNA in this state
  • dispersed throughout the nucleus
  • the state of the majority of a cell’s chromatin
  • active areas of gene transcription
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24
Q

Heterochromatin

A
  • highly condensed chromatin regions
  • concentrated staining for DNA in this state
  • confined to select region of the nucleus (chromocenter)
  • less frequently transcribed
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25
Q

Polytene Chromosomes

A

Form bands that expand at sites of Gene Expression
• DNA repeatedly replicates but the daughter chromosomes do not separate
• Found commonly in the salivary gland of Drosophila

26
Q

Polytene “puffs”

A

• Site of DNA transcription on polytene chromosomes
• Indicate chromatin remodeling in areas of active transcription
• The expansion of the bands or a “puff ” is due to the relaxation of the condensed chromatin to allow for
binding of protein required for DNA transcription (ex. RNA polymerase)
• Puff can be induced.

27
Q

Facultative Heterochromatin

A

• Euchromatin regions that become highly condensed heterochromatin and reversed.

28
Q

Constitutive Heterochromatin

A

Permanently condensed.

  • last region to replicate
  • few genes exist in this region
  • mostly highly repetitive sequence
  • Ex. centromere & telomere
29
Q

Centromere

A
  • In mammals, called α-satellite DNA
  • A-T rich
  • ~ 170 bp constitute one α-satellite sequence = ~ 3000 kb
    total
  • Nucleosome = incorporation of specific histone (CENP-A)
  • Chromatin-remodeling proteins = cohesions, condensin,
    topoisomerase II
30
Q

Centromere

A
  • In mammals, called α-satellite DNA
  • A-T rich
  • ~ 170 bp constitute one α-satellite sequence = ~ 3000 kb total
  • Nucleosome = incorporation of specific histone (CENP-A)
  • Chromatin-remodeling proteins = cohesions, condensin,
    topoisomerase II
31
Q

Parts of centromere critical for propagation of genetic

information during Mitosis:

A
  1. α-satellite/CENP-A provide site for segregation of replicated chromosome
  2. Kinetochore
  3. Spindle apparatus
32
Q

Kinetochore

A

A network of protein that bind at the centromere

  • Inner component: define site of attachment
  • Outer component: anchoring to the spindle microtubules
33
Q

Spindle apparatus

A
  • Includes microtubule fibers that bind the kinetochore and guide the chromosomes to the cell ends during cell division
  • Originate from the microtubule organizing center (centrosomes)
34
Q

Prometaphase

A

Condensed chromosome attach to mitotic spindle.
2. Metaphase: sister chromatids are held together by cohesion
proteins and are aligned in the center of the cell (metaphase
plate).
3. Anaphase: the cohesion degrade and release the bound
chromosomes.
4. Telophase: kinetocore-bound centromeres are propelled to
the spindle poles.

35
Q

Metaphase

A

sister chromatids are held together by cohesion
proteins and are aligned in the center of the cell (metaphase
plate).

36
Q

Prometaphase

A

Condensed chromosome attach to mitotic spindle

37
Q

Metaphase

A

Sister chromatids are held together by cohesion proteins and are aligned in the center of the cell (metaphase plate).

38
Q

Anaphase

A

The cohesion degrade and release the bound chromosomes.

39
Q

Telophase

A

Kinetocore-bound centromeres are propelled to the spindle poles.

40
Q

Acentric fragment

A

Absence of a centromere; unable to attach to spindle = lost chromosome; lost genetic information

41
Q

Dicentric/polycentric chromosome

A

A single chromosome with 2 or more centromeres (commonly due to to fusion of two chromosomes)
Only one centromere is functional (centromere that most efficiently assembles the kinetochore) for normal cell
division

42
Q

Holocentric chromosome

A

Diffuse, elongated centromere

Kinetochore form along the length of the chromosome = normal cell division

43
Q

Neocentromere

A
  • Formation of a new centromere at a non-centromeric site on the chromosome after the loss of the conventional centromere
  • Rare and usually associated with onset of congenital
    and cancer abnormalities
44
Q

Telomere

A

The natural end of a chromosome
- Ensure the stability of chromosome ends from fusion with other chromosomes
- Short tandem repeating DNA sequence
Highly conserved DNA repeats:
- 5’ C-rich strand
- 3’ G-rich strand
G-rich extends beyond the C-rich strand due to specific resection of the C-rich strand

45
Q

Features that protect telomere from the DNA damage machinery

A
  1. G-quartets/ G-quadruplex
  2. T-Loop Formation
  3. Binding of the Shelterin Complex
46
Q

G-quartets/G-quadruplex

A
  • Transient DNA structure

- Role in telomere function unknown

47
Q

T-loop

A
  • 3’ ss G-rich strand forms a telomere loop (T-loop)
  • Displaces analogous sequence in the telomere duplex to form a loop that resembles “D” (D-loop)
  • Catalyzed via the TRF2 protein
48
Q

Binding of the Shelterin

A
  • 6 telomeric protein:
    TRF2, TRF1, Rap1,
    TPP1, TIN2, POT1
  • Also function to regulate telomere length
49
Q

Telomerase

A

An ribonucleoprotein complex that uses the G-rich strand as a template to extend the telomere
• Includes a reverse transcriptase (human telomerase reverse transcriptase (TERT))
- the catalytic subunit that transcribes RNA template

50
Q

hTERC

A

Human telomerase RNA
RNA component of telomerase
Template for RNA sequence to generate G-rich strand

51
Q

Telomerase Action:

A

The G-rich strand serves as the DNA primer
hTERC provides the RNA template
DNA bases are added via the action of the hTERT
Telomerase translocates and begins again

52
Q

What dictates number of repeats in telomere?

A

Additional proteins dictate the number of repeats added by dictating binding efficiency of telomerase and access of telomerase to the telomere

53
Q

What dictates number of repeats in telomere?

A

Additional proteins dictate the number of repeats added by dictating binding efficiency of telomerase and access of telomerase to the telomere

54
Q

Telomerase activity ON in

A

actively dividing cells.

55
Q

Telomerase activity OFF in

A

Terminally differentiated cells (non-dividing) cells

56
Q

Telomerase mutation

A

Affects dividing cells since telomerase is required to maintain telomere length in dividing cell.
Causes telomere to shorten after cell division

57
Q

Telomerase mutation

A

Affects dividing cells since telomerase is required to maintain telomere length in dividing cell.
Causes telomere to shorten after cell division. Leads to chromosome breaks and genetic instability.

58
Q

Senescence

A

Maintains telomere length by reactivating telomerase and homologous recombination.

59
Q

Senescence

A

Maintains telomere length by reactivating telomerase and homologous recombination.
Indicative of an Aging Cell.

60
Q

Homologous Recombination at Telomere

A

Also called Alternative Lengthening of Telomeres (ALT)
Changes binding proteins and/or epigenetics allows for
initiation of ALT and thereby inter-telomere recombination

61
Q

Telomere lengthening is common in

A

Cancer cells

62
Q

Telomere lengthening is common in

A

Cancer cells

Molecular Biology Test 1 (4 decks)

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