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MD2S3: Molecular Biology > Organization of the Genome > Flashcards

Organization of the Genome Flashcards

(65 cards)

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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
Which parts of the histones are affected by histone modification?
N-terminals
26
Histone modification is an example of ____
epigenetics
27
How does histone acetylation affect the DNA?
Acetyl group binds to lysine residue of histones Removes the +ve charge reducing affinity of DNA for histone making DNA transcriptionally active
28
Histone acetylation is catalysed by ...
Histone Acetyltransferase (HAT)
29
Histone deactylation is calaysed by ...
Histone Deacetylases (HDACs)
30
The histones in ____ are deactylated whereas in ____ it is acetylated
__Heterochromatin__ __Euchromatin__
31
What does Histone Methylation cause?
Inactivation of gene expression
32
Exon meaning
Coding sequences of genes
33
Introns/Intervening Sequence meaning
Non-coding sequence separating coding sequences of genes
34
Where is non-coding DNA found in prokaryotes?
Intergenic DNA (between genes)
35
Where is non-coding DNA found in eukaryotes?
Between and within genes
36
Mbp meaning
Million Base Pairs/Megabase Pairs
37
Stem and loop structure
RNA complementary intermolecular base pairing within the same molecule ## Footnote NNN represents the unpaired bases
38
A Unique Sequence is ...
a sequence which occurs twice in diploid genomes (or once in haploid genome) ## Footnote Comprises >20% of total DNA of higher organisms
39
What are the possible distributions of repeat sequences?
Tandem Repeats Interspersed Sequences
40
Categories of repeated DNA sequences
Moderately Repetitive Sequences Highly Repetitive Sequences
41
What are Moderately Repetitive Sequences?
Present in hundreds or thousands of copies Formed mostly from Long Interspersed Elements (LINEs) E.g. ribosomal RNA genes
42
What are Highly Repetitive Sequences?
Present in hundreds of thousands to millions of copies Formed mostly from Short Interspersed Elements (SINEs) E.g. 300 bp Alu element
43
Types of Short Tandem Repeats (STRs)
Microsatellite Repeats Variable Number of Tandem Repeats (VNTRs)
44
What are Microsatellite Repeats?
Non-coding DNA formed from repeats of 2-8 bp
45
How many times can microsatellite repeats appear?
100 times
46
Microsatellite repeats exist in long clusters of ...
Short Tandem Repeats (STRs)
47
Diseases related to microsatellites
Microsatellite expansion in protein-coding genes causes **Huntington's Disease** and **Fragile-X Syndrome**
48
How can genetic links be determined between family members?
PCR detects number of microsatellite repeats
49
What are VNTRs?
Segments of short tandem repeats Fewer copies than satellites
50
What is the most common location of VNTRs?
Eukaryotic telomeres
51
Why is the number of repeats of VNTR variable between individuals?
Due to unequal crossing over ## Footnote Variations between VNTRs are called alleles
52
What can VNTRs be used for?
DNA fingerprinting
53
Characteristics of Human Mitochondrial DNA
Circular Double-Stranded
54
What does mitochondrial DNA encode?
Mt rRNA Mt tRNA molecules Proteins of respiratory chain
55
What are the methods of altering/rearranging genetic material?
Chromosomal Recombination Chromosomal Integration of viruses Transposition Immunoglobin genes rearrange
56
How does Chromosomal Recombination occur?
Crossing-Over
57
How may Chromosomal Integration occur?
Bacteriophages recombine with bacterial DNA
58
How does transposition occur in eukaryotic cells?
Small DNA elements are capable of transposing themselves in and out of the host genome
59
Describe how immunoglobin genes rearrange
VL and CL genes are closer together in plasma cells than other cells
60
What are telomeres?
Short repeating sequences at the end of each chromosome
61
Nucleotide sequence of telomeres
TTAGGG
62
How do telomeres change with age?
Length of telomeres decreases over time
63
What can happen when telomeres shorten too much?
Cells become senescent, die or sustain genetic damage causing cancer
64
In which cells do telomeres no longer shorten?
Germ Cells Stem Cells Cancer Cells
65
Why do telomeres no longer shorten in germ, stem and cancer cells?
Enzyme called telomerase prevents telomeres from getting shorter

MD2S3: Molecular Biology (10 decks)

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