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Year 1- Principles of Disease (FOM) > Chromosomes > Flashcards

Chromosomes Flashcards

1
Q

Describe the structure of a chromosome.

A

Two sister linear chromatids which are held together by the centromere.

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2
Q

What are the ends of the chromosomes known as?

A

Telomeres

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3
Q

What are the functions of telomeres?

A

They protect the chromosome ends from degradation in the cell and also potentially from inappropriate repair.

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4
Q

What are heterochromatins?

A

Large amounts of DNA in the eukaryotic genome that is not active.

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5
Q

How is euchromatin characterised?

A

By the ability to be expressed

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6
Q

Why does the entire genome need to get replicated?

A

So that a complete copy of the DNA can be passed to each of the daughter cells.

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7
Q

What is the DNA synthesis reaction carried out by?

A

DNA polymerase

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8
Q

What direction does DNA polymerase synthesis DNA?

A

In a five prime to three prime direction due to the anti parallel nature.

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9
Q

So the replication can stay in the same direction, how do the second strand (lagging strand) get replicated?

A

In short fragments known as Okazaki Fragments

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10
Q

What enzyme stitches the shorter fragments together in DNA replication?

A

Ligase

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11
Q

What is the end replication problem?

A

RNA primers get removed in the lagging strand so the fragments can join together.
However, at the end, the removal of a primer leaves a gap meaning this could lead to degradation and loss of DNA.

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12
Q

What is the solution to the end replication problem?

A

Expression of the enzyme telomerase which adds repeats and resynthesizes and fills in the end of DNA during DNA replication.

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13
Q

G1=?
S=?
G2?
M+?

A

G1=growth phase
S=replication of DNA
G2=cells grow and prepare to divide
M= mitosis

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14
Q

Name the order of the five stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

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15
Q

Describe prophase.

A

Chromosomes condense
Nuclear membrane disappears
Spindle fibres form from the centriole

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16
Q

Describe metaphase

A

Chromosomes aligned at the equator of the cell
Attached by fibre to each centriole
Maximum condensation of chromosome

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17
Q

Describe anaphase

A

Sister chromatids separate at centromere
Separate longitudinally
Move to opposite ends of cell

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18
Q

Describe telophase.

A

New nuclear membranes form
Each cell contains 46 chromosomes (diploid)

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19
Q

Describe cytokinesis.

A

Cytoplasm separates
Two new daughter cells

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20
Q

What is the centromere?

A

Constricted region joining sister chromatids

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21
Q

What are centromeres characterised by?

A

Repetitive DNA sequences
->like satellite DNA

22
Q

What are centromeres the site of?

A

The kinetochore which is a protein complex that binds to microtubules.

23
Q

What is the kinetochore required for?

A

Required for chromosome separation during cell division.

24
Q

What stages of the cell cycle make up interphase?

A

G1, S, G2

25
Q

Describe the structure and genes of Heterochromatin.

A

-Condensed structure
-Silenced genes

26
Q

Describe the structure and genes of Euchromatin

A

-Open structure
-Active genes

27
Q

What percentage of our DNA is protein coding?

A

2%

28
Q

What is chromatin?

A

DNA protein assembly into which our DNA is assembled and packaged to make it possible to fit it within the nucleus

29
Q

What is the central component of chromatin.

A

Histone proteins

30
Q

Why are histones well suited to packaging DNA?

A

They are positively charged and the phosphate backbone is negatively charged.

31
Q

What are the four main histone particles called?

A

Histone 3
Histone 4
Histone 2A
Histone 2B

32
Q

What does Histone 1 do?

A

Binds to the base of the nucleosome and helps to hold DNA in place.

33
Q

What charge do histones have?

A

Positive

34
Q

Describe how DNA gets wrapped up into chromosomes.

A

-Short region of DNA double helix wrapped around nucleosomes
-These then get assembled into a chromatid fibre
-Chromatid fibres become attached to a scaffold complex so that the fibre is assembled in a series of loops on a chromatin scaffold
-DNA condensed

35
Q

Give some of the purposes of the packaging of DNA

A

-Negatively charged DNA neutralised by positive charged histone proteins
-DNA takes up less space
-Inactive DNA can be folded into inaccessible locations until required
-Inactive chromatin characterised by specific histone convalent modification (e.g. methylation)

36
Q

What side of the chromosome is known as the P side?

A

The shorter side
P= petite arm

37
Q

Which side of the chromosome is known as the Q arm?

A

The longer side
Contains more DNA

38
Q

Give an example of a chromosome in which the P arm is so small that it doesn’t have any function.

A

Chromosome 21

39
Q

Describe simply the process of chromosome analysis

A

-Blood sample taken
-Want to separate off the white blood cells through incubation.
-Cells put on slide and stained
-Photographed
-Chromosomes assembled into a karyotype

40
Q

What does a karyotype show?

A

All the chromosomes lined up in their pairs

41
Q

In each chromosome pair, how many strands of DNA are there?

A

4

42
Q

Define metacentric.

A

The centromere constriction is close to the centre of the the chromosome

43
Q

Define sub-metacentric.

A

Centromere is displaced from the centre of the chromosome.

44
Q

Define acrocentric.

A

Q arm is so small that it doesn’t consist of any functional DNA.

45
Q

Name the stain which can be used to highlight the differences in chromosomes.

A

Giemsa

46
Q

Name four type of FISH (Fluorescent in situ hybridisation) probes

A

Unique sequence probes
Centromeric probes
Whole chromosome probes
Telomeric probes

47
Q

Why are centromeric probes useful?

A

Useful for determining chromosome number

48
Q

Why are telomeric probes useful?

A

Useful for detecting subtelomeric rearrangements
Often present in children with unexplained mental retardation

49
Q

Where would you find satellite DNA?

A

Centromeres
Telomeres

50
Q

What type of DNA is used for finger printing?

A

Minisatellite DNA

Year 1- Principles of Disease (FOM) (40 decks)

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