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Molecular Biology Test 1 > Chapter 9 - Chromosomes > Flashcards

Chapter 9 - Chromosomes Flashcards

(62 cards)

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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
Polytene Chromosomes
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
Polytene “puffs”
• 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
Facultative Heterochromatin
• Euchromatin regions that become highly condensed heterochromatin and reversed.
28
Constitutive Heterochromatin
Permanently condensed. - last region to replicate - few genes exist in this region - mostly highly repetitive sequence - Ex. centromere & telomere
29
Centromere
- 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
Centromere
- 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
Parts of centromere critical for propagation of genetic | information during Mitosis:
1. α-satellite/CENP-A provide site for segregation of replicated chromosome 2. Kinetochore 3. Spindle apparatus
32
Kinetochore
A network of protein that bind at the centromere - Inner component: define site of attachment - Outer component: anchoring to the spindle microtubules
33
Spindle apparatus
- 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
Prometaphase
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
Metaphase
sister chromatids are held together by cohesion proteins and are aligned in the center of the cell (metaphase plate).
36
Prometaphase
Condensed chromosome attach to mitotic spindle
37
Metaphase
Sister chromatids are held together by cohesion proteins and are aligned in the center of the cell (metaphase plate).
38
Anaphase
The cohesion degrade and release the bound chromosomes.
39
Telophase
Kinetocore-bound centromeres are propelled to the spindle poles.
40
Acentric fragment
Absence of a centromere; unable to attach to spindle = lost chromosome; lost genetic information
41
Dicentric/polycentric chromosome
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
Holocentric chromosome
Diffuse, elongated centromere | Kinetochore form along the length of the chromosome = normal cell division
43
Neocentromere
- 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
Telomere
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
Features that protect telomere from the DNA damage machinery
1. G-quartets/ G-quadruplex 2. T-Loop Formation 3. Binding of the Shelterin Complex
46
G-quartets/G-quadruplex
- Transient DNA structure | - Role in telomere function unknown
47
T-loop
- 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
Binding of the Shelterin
- 6 telomeric protein: TRF2, TRF1, Rap1, TPP1, TIN2, POT1 - Also function to regulate telomere length
49
Telomerase
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
hTERC
Human telomerase RNA RNA component of telomerase Template for RNA sequence to generate G-rich strand
51
Telomerase Action:
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
What dictates number of repeats in telomere?
Additional proteins dictate the number of repeats added by dictating binding efficiency of telomerase and access of telomerase to the telomere
53
What dictates number of repeats in telomere?
Additional proteins dictate the number of repeats added by dictating binding efficiency of telomerase and access of telomerase to the telomere
54
Telomerase activity ON in
actively dividing cells.
55
Telomerase activity OFF in
Terminally differentiated cells (non-dividing) cells
56
Telomerase mutation
Affects dividing cells since telomerase is required to maintain telomere length in dividing cell. Causes telomere to shorten after cell division
57
Telomerase mutation
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
Senescence
Maintains telomere length by reactivating telomerase and homologous recombination.
59
Senescence
Maintains telomere length by reactivating telomerase and homologous recombination. Indicative of an Aging Cell.
60
Homologous Recombination at Telomere
Also called Alternative Lengthening of Telomeres (ALT) Changes binding proteins and/or epigenetics allows for initiation of ALT and thereby inter-telomere recombination
61
Telomere lengthening is common in
Cancer cells
62
Telomere lengthening is common in
Cancer cells

Molecular Biology Test 1 (4 decks)

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