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MD2S3: Molecular Biology > Organization of the Genome > Flashcards

Organization of the Genome Flashcards

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1
Q

What is a chromosome formed from?

A

2 chromatids joined at the centromere

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2
Q

Structural unit of Eukaryotic DNA

A

Nucleosomes

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3
Q

What is chromatin?

A

Repeating Nucleosome Units

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4
Q

The structure of chromatin is stabilized through …

A

the interactions between DNA and DNA-binding proteins

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5
Q

What are the classes of DNA-binding proteins?

A

Histones
Non-histones

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6
Q

What is chromatin composed of?

A

Nuclear DNA
Histone Proteins
Small amount of Non-Histone Proteins
Small amount of RNA (snRNA)

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7
Q

What are the forms of chromatin?

A

Heterochromatin
Euchromatin

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8
Q

What is heterochromatin?

A

Transcriptionally inactive chromatin
Darkly-stained regions

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9
Q

What is euchromatin?

A

Transcriptionally active chromatin
Lightly-stained regions

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10
Q

What are the types of heterochromatin?

A

Constitutive Heterochromatin
Facultative Heterochromatin

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11
Q

What is constitutive heterochromatin?

A

Always condensed and inactive
E.g. Chromosomal Centromere and Telomeres

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12
Q

What is facultative heterochromatin?

A

Sometimes condensed and sometimes uncondensed for transcription
E.g. one X chromosome in mamillian females

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13
Q

Histones are ____ proteins

A

basic

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14
Q

What makes histones basic?

A

Rich in lysine and arginine

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15
Q

How do histones interact with DNA?

A

Form ionic bonds with -vely charged acidic DNA phosphate group

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16
Q

What are the types of histones?

A

H1
H2A
H2B
H3
H4

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17
Q

What are the functions of histones?

A

Help DNA condensation
Protect DNA from exonuclease digestion

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18
Q

What is the structure of a nucleosome?

A

dsDNA wound twice around an octameric core

dsDNA is 150bp long

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19
Q

What forms the octameric core

A

Two molecules of each: H2A, H2B, H3 and H4

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20
Q

How are neighbouring nucleosomes linked?

A

By linker DNA (20-200bp long)
H1 histones bind linker DNA

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21
Q

What is the purpose of the H1 histone?

A

Facilitates packing of nucleosome
Protects DNA from exonuclease digestion

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22
Q

Nucleofilaments

A

Tightly stacked nucleosomes arranged as a coil

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23
Q

What is the purpose of histone modification?

A

Affect how tightly histones bind to DNA affecting gene expression

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24
Q

What are the methods of histone modification?

A

Acetylation
Methylation
Phosphorylation

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25
Q

Which parts of the histones are affected by histone modification?

A

N-terminals

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26
Q

Histone modification is an example of ____

A

epigenetics

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27
Q

How does histone acetylation affect the DNA?

A

Acetyl group binds to lysine residue of histones
Removes the +ve charge reducing affinity of DNA for histone making DNA transcriptionally active

28
Q

Histone acetylation is catalysed by …

A

Histone Acetyltransferase (HAT)

29
Q

Histone deactylation is calaysed by …

A

Histone Deacetylases (HDACs)

30
Q

The histones in ____ are deactylated whereas in ____ it is acetylated

A

__Heterochromatin__
__Euchromatin__

31
Q

What does Histone Methylation cause?

A

Inactivation of gene expression

32
Q

Exon meaning

A

Coding sequences of genes

33
Q

Introns/Intervening Sequence meaning

A

Non-coding sequence separating coding sequences of genes

34
Q

Where is non-coding DNA found in prokaryotes?

A

Intergenic DNA (between genes)

35
Q

Where is non-coding DNA found in eukaryotes?

A

Between and within genes

36
Q

Mbp meaning

A

Million Base Pairs/Megabase Pairs

37
Q

Stem and loop structure

A

RNA complementary intermolecular base pairing within the same molecule

NNN represents the unpaired bases

38
Q

A Unique Sequence is …

A

a sequence which occurs twice in diploid genomes (or once in haploid genome)

Comprises >20% of total DNA of higher organisms

39
Q

What are the possible distributions of repeat sequences?

A

Tandem Repeats
Interspersed Sequences

40
Q

Categories of repeated DNA sequences

A

Moderately Repetitive Sequences
Highly Repetitive Sequences

41
Q

What are Moderately Repetitive Sequences?

A

Present in hundreds or thousands of copies
Formed mostly from Long Interspersed Elements (LINEs)
E.g. ribosomal RNA genes

42
Q

What are Highly Repetitive Sequences?

A

Present in hundreds of thousands to millions of copies
Formed mostly from Short Interspersed Elements (SINEs)
E.g. 300 bp Alu element

43
Q

Types of Short Tandem Repeats (STRs)

A

Microsatellite Repeats
Variable Number of Tandem Repeats (VNTRs)

44
Q

What are Microsatellite Repeats?

A

Non-coding DNA formed from repeats of 2-8 bp

45
Q

How many times can microsatellite repeats appear?

A

100 times

46
Q

Microsatellite repeats exist in long clusters of …

A

Short Tandem Repeats (STRs)

47
Q

Diseases related to microsatellites

A

Microsatellite expansion in protein-coding genes causes Huntington’s Disease and Fragile-X Syndrome

48
Q

How can genetic links be determined between family members?

A

PCR detects number of microsatellite repeats

49
Q

What are VNTRs?

A

Segments of short tandem repeats
Fewer copies than satellites

50
Q

What is the most common location of VNTRs?

A

Eukaryotic telomeres

51
Q

Why is the number of repeats of VNTR variable between individuals?

A

Due to unequal crossing over

Variations between VNTRs are called alleles

52
Q

What can VNTRs be used for?

A

DNA fingerprinting

53
Q

Characteristics of Human Mitochondrial DNA

A

Circular
Double-Stranded

54
Q

What does mitochondrial DNA encode?

A

Mt rRNA
Mt tRNA molecules
Proteins of respiratory chain

55
Q

What are the methods of altering/rearranging genetic material?

A

Chromosomal Recombination
Chromosomal Integration of viruses
Transposition
Immunoglobin genes rearrange

56
Q

How does Chromosomal Recombination occur?

A

Crossing-Over

57
Q

How may Chromosomal Integration occur?

A

Bacteriophages recombine with bacterial DNA

58
Q

How does transposition occur in eukaryotic cells?

A

Small DNA elements are capable of transposing themselves in and out of the host genome

59
Q

Describe how immunoglobin genes rearrange

A

VL and CL genes are closer together in plasma cells than other cells

60
Q

What are telomeres?

A

Short repeating sequences at the end of each chromosome

61
Q

Nucleotide sequence of telomeres

A

TTAGGG

62
Q

How do telomeres change with age?

A

Length of telomeres decreases over time

63
Q

What can happen when telomeres shorten too much?

A

Cells become senescent, die or sustain genetic damage causing cancer

64
Q

In which cells do telomeres no longer shorten?

A

Germ Cells
Stem Cells
Cancer Cells

65
Q

Why do telomeres no longer shorten in germ, stem and cancer cells?

A

Enzyme called telomerase prevents telomeres from getting shorter

MD2S3: Molecular Biology (10 decks)

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