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BB10005 > Chromosomes > Flashcards

Chromosomes Flashcards

1
Q

What are chromosomes made up of?

A

Histones and the nucleosome.

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2
Q

How are chromosomes altered to regulate gene expression?

A

Histone modification, DNA methylation, DNA loops and LADs and TADs.

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3
Q

What are the specialised regions of chromosomes?

A

Telomeres and centrosomes.

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4
Q

When were chromosomes first observed?

A

Plant cells in the 1840s.

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5
Q

What is each chromosome made up of?

A

One linear strand of DNA.

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6
Q

What does karyotype mean?

A

The number, size and shape of chromosomes.

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7
Q

What is the case with chromosomes in down syndrome?

A

They have 3 copies of chromosome 21.

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8
Q

What is the case with chromosomes in Klinefelter’s syndrome?

A

XXY instead of just XX or XY.

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9
Q

What is a nucleosome?

A

147 base pairs of DNA wound many times around a protein core of histones.

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10
Q

What are histone cores made up of?

A

H2A, H2B, H3 and H4 tetramers. Two tetramers form an octamer.

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11
Q

What are chromatin remodelling factors?

A

Protein complexes that slide along the DNA strand and exchange histone octamers or subunits and remove core histones. They alter the structure of the nucleosomes, making them dynamic.

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12
Q

What is the significance of histone tails sticking out?

A

They can be modified by chemical groups.

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13
Q

What groups can be added to histone tails?

A

1,3-methyl groups, acetyl groups. These are mostly added onto lysines.

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14
Q

What is acetylation involved in?

A

Chromatin decondensation and gene expression.

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15
Q

What is methylation involved in?

A

Chromatin condensation and gene repression.

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16
Q

How can chromatin modifications spread along chromosomes?

A

Methylated histones recruit more histone methylases.

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17
Q

What is the position effect?

A

The idea that a normally active gene is silenced because of proximity to heterochromatin after DNA breakage and rejoining.

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18
Q

What are some other histone modifications?

A

Serine phosphorylation, ubiquitination and SUMOlyation.

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19
Q

What regulatory proteins bind to marked histones to read the histone code?

A

Chromatin remodelling complexes, transcription activators, transcription repressors and DNA damage repair complexes.

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20
Q

What is epigenetics?

A

The study of changes in organisms due to modification of gene expression rather than alteration of the code itself.

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21
Q

What may cause epigenetic imprints over the course of life?

A

Exposure to pollutants, stress, drugs.

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22
Q

What does methylation in DNA cause?

A

Repressed gene transcription.

23
Q

Why is methylation important for normal development?

A

Embryonic stem cells are mostly de-methylated, so methylation is important for cell differentiation.

24
Q

What is maintenance methylation?

A

Maintaining methylation patterns on newly-synthesised DNA strands after replication.

25
Q

How are nucleosomes packaged?

A

They are assembled into loops on the protein scaffold - 30nm fiber of nucleosomes. The loops on the scaffold form coiled coils of heterochromatin.

26
Q

What are LADs?

A

Lamina-associated domains - they are part of the chromatin that heavily interact with the lamina (network like structure at the inner membrane of the nucleus)

27
Q

What are TADs?

A

Topologically associated domains - a self interacting genomic region - the sequences within a TAD interact with each other more frequently than sequences outside the TAD.

28
Q

How are TADs formed?

A

By cohesin (a ring shape protein complex that physically bundle chromatin)

29
Q

What are TAD boundaries formed by?

A

CTCF (CCCTC binding factor) which is a transcription factor expressed in all cell types.

30
Q

What are the two types of heterochormatin?

A

Facultative heterochromatin and constitutive heterochromatin.

31
Q

What is facultative heterochromatin?

A

It has the potential for gene expression and the modification of histones or DNA. It can switch between hetero and euchromatin states.

32
Q

What are the features of constitutive heterochromatin?

A

It remains condensed throughout the cell cycle and is made up of highly repetitive sequences. It may play a role in chromatin structure and it contains telomeres and centromeres.

33
Q

What are telomeres?

A

Long repetitive sequences on the ends of chromosomes. There are 4kb in adults. They protect the ends of the DNA strands.

34
Q

Why do telomeres get shorter?

A

DNA replication enzymes cannot replicate the very ends of DNA strands and there is some lost with every cell division.

35
Q

In which case will telomeres not get shorter?

A

If cells express telomerase.

36
Q

What cells express telomerase?

A

Germ cells, embryonic stem cells and cancer cells.

37
Q

What are centromeres?

A

Large arrays of repetitive DNA. They form the junctions of replicated chromosomes (sister chromatids) and are where microtubules attach during mitosis.

38
Q

What can instability of centromeres result in?

A

Embryonic death and cancer malignancy.

39
Q

What is the significance of multiple origins on each chromosome?

A

Each origin fires once per cell cycle to ensure that the DNA is only copied once.

40
Q

At which points are euchromatin and heterochromatin replicated?

A

Euchromatin is replicated early whereas heterochromatin is replicated later.

41
Q

What is ALL?

A

Acute lymphoblastic leukaemia - a type of cancer affecting white blood cells.

42
Q

What is AML?

A

Acute Myeloid Leukaemia - cancer of the myeloid cells.

43
Q

What is the BCR-ABL fusion protein?

A

A constitutively active kinase. It’s an oncogene that undergoes over-proliferation and has a stem-like state. It is resistance to cell death.

44
Q

What is telomere-to-telomere fusion?

A

It happens on chromosome 2 to reduce the chromosome number from 24 pairs to 23 pairs.

45
Q

What does the duplication of SRGAP2 result in?

A

Changes in neurons - expansion of the neocortez (grey matter) that affects sensory perception, memory and language.

46
Q

What is the organisation of DNA within chromosomes?

A

Organised into nucleosomes - beads on a string.

47
Q

What is the difference between heterochromatin and euchromatin?

A

Heterochromatin is part of the chromosomes and is tightly packed and genetically inactive, whereas euchromatin is loosely packed and genetically active.

48
Q

What are the purpose of telomeres?

A

They protect the ends of chromosomes from sticking together and protect genetic information during cell division - short pieces of chromosome are lost every division.

49
Q

What does telomerase do?

A

It maintains the length of telomeres by adding guanine-rich repetitive sequences.

50
Q

What happens when the length of telomeres becomes too small?

A

The chromosome reaches a critical length and can no longer replicate - the cell becomes old and dies by apoptosis.

51
Q

What is a kinetochore?

A

A complex of proteins associated with the centromere of a chromosome during cell division, to which microtubules of the spindle attach.

52
Q

What causes leukaemia?

A

There is a translocation event - part of chromosome 9 and 22 swap.

53
Q

What is Philadelphia chromosome?

A

The 9/22 swap observed in leukaemia.

BB10005 (22 decks)

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