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Genetics, Cancer and Development Emily > 001 Structure of the human genome > Flashcards

001 Structure of the human genome Flashcards

1
Q

describe the 6 layers of genome organisation from DNA strands

A
  1. DNA double helix
  2. DNA double helix strands wrapped around histone proteins to form nucleosome
  3. nucleosomes packed together in a fiber to form chromatin
  4. lots of chomatin strands together form chromosome
  5. chromosome is condensed
  6. 2 sister chromatids join at the centromere to form a chromosome
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2
Q

what is a nucleosome?

A

DNA wrapped around histone proteins

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3
Q

what is a chromatin?

A

lots of nucleosomes (DNA wrapped around histone proteins) packed together to form chromatin

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4
Q

what is a chromatosome?

A
  • nucleosome and 1 histone protein
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5
Q

what is a chromosome

A

packaged DNA wrapped around histone proteins carrying genetic information
- 2 sister chromatids form a chromosome

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6
Q

what is a chromatid?

A
  • one of the 2 identical halves of a chromosome that has been replicated for cell division
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7
Q

what is the human genome split into?

A
  • nuclear genome
  • mitochondrial genome
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8
Q

what is the nuclear genome split into?

A
  • genes and gene-related sequences (30%)
  • extragenic DNA (70%)
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9
Q

what is genes and gene-related sequences split into?

A
  • coding DNA
  • non-coding DNA
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10
Q

what is non-coding DNA split into?

A
  • pseudo-genes (resembles a gene but does not code for anything)
  • introns, leaders, trailers, promoter regions (parts of a gene that influence expression of gene)
  • gene fragments
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11
Q

what is extragenic DNA and what is it split into?

A
  • DNA between genes
  • split into repetitive DNA and unique/low copy number
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12
Q

what is repetitive DNA split into?

A
  • tandemly repeated DNA
  • interspersed genome-wide repeats
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13
Q

what are the 3 types of tandemly repeated DNA?

A
  • satellite
  • minisatellite
  • microsatellite
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14
Q

what are the 4 types of interspersed genome-wide repeats?

A
  • LTR elements (long terminal repeats)
  • LINEs (long interspersed retrotransposable elements)
  • SINEs ( short interspersed retrotransposable elements) - DNA transposons
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15
Q

what are DNA transposons?

A

= move from one genomic location to another by a cut-and-paste, can be used to introduce a piece of foreign DNA into a genome

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16
Q

what are the 6 components to a typical gene?

A
  • exons (coding part)
  • introns (non-coding part)
  • 5’UTR (untranslated region) directly upstream of initiation codon
  • 3’UTR (untranslated region) directly after termination codon
  • promoter region/ TATA box/ transcription factors upstream to gene where RNA polymerase binds and begin/regulatates transcription
  • upstream enhancers/silencers
17
Q

how is DNA altered to produce mature mRNA?

A
  • add 5-methyl guanosine cap and 3’ poly-A tail
  • remove introns (splicing)
18
Q

what are exons?

A
  • coding part of DNA and mature mRNA
  • codes for proteins
19
Q

what are introns?

A
  • non-coding part of coding region of DNA
  • removed via splicing to form mature mRNA
20
Q

generally in DNA, are there more introns or exons?

A
  • more introns than exons
21
Q

whats the relationship between proportion of introns and size of gene?

A
  • the larger the gene, this bigger the proportion of introns
  • the larger the gene the smaller the proportion of exons
22
Q

what are genes within genes?

A

you can get small genes within introns of larger genes

23
Q

describe the relationship between gene densities and size of region

A
  • the larger the number of bases, the lower the gene density
24
Q

what are some different features of gene families?

A
  • members may exhibit high sequence homology (similarity of bases conserved through evolution)
  • sometimes contain a highly conserved domain
  • sometimes contain a very short conserved motif sequence
  • superfamilies (e.g. immunoglobulin superfamily)
  • sometimes clustered (globin genes)
  • often associated with truncated (lost function) and non processed pseudo genes (e.g. salivary amylase)
25
describe the length and location of satellite DNA
- 100kb to 5Mb - repeat = 5bp-5kb - locations = heterochromatin (regions of genome that are gene poor and very variable), particularly at centromeres
26
describe the length and location of minisatellite DNA
- 0.1-20kb - repeats = 6-64bp - scattered but concentrated near telomeres
27
describe the length and location of microsatellite DNA
- <100 bp - repeats = 1-5bp - dispersed throughout genome
28
describe a use of satellite DNA
- used in forensics/DNA fingerprinting as the number of repeats are very variable as there is a very high chance the number of repeats will change from parent to offspring - making them almost completely unique in each individual
29
describe ultracentrifugation of satellite DNA
- DNA has a density of 1.8g/ml - Filling DNA with a CsCl solution (high density) and then centrifuging the solution causes DNA to float and form bands at different densities - satellite bands form above the main DNA band as they are shorter so less dense
30
give some examples of dispersed repetitive DNA
- SINE, LINE ( short and long interspersed retrotransposable elements) - LTR elements (Long terminal repeats) - DNA transposons - Alu = a family of SINE repeats ( very common in genome)
31
why do mitochondria have their own DNA?
- use for oxidative phosphorylation to produce ATP (need to live) - endosymbiotic theory = mitochondria used to be free living prokaryotes, and thus needed their own DNA
32
describe the structure/differences of mitochondrial DNA
- it is naked ( not associated with histone proteins) - circular (continuous ring, similar to prokaryotes) - very gene-rich with little 'junk DNA' - has 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes
33
what is the mutation rate of mitochondrial DNA vs nuclear DNA?
much higher mutation rate of mitochondrial DNA than nuclear DNA as mitochondrial DNA produces a lot more free radicals
34
how does the size of mitochondrial DNA compare to nuclear DNA?
- mitochondrial DNA is much smaller - 1/180,000 the size of nuclear genome
35
how does mitochondrial DNA coding compare to nuclear DNA coding?
- the same codons do not often code for the same thing, e.g. AGA codes for arginine in nuclear DNA and stop in mitochondria - not really a universal genetic code as such
36
what is the pattern of mitochondrial inheritance?
mitochondria are in both males and females - however the sperm does not contribute its mitochondria to the fertilised egg, only the egg mitochondria does - therefore we only inherit mother's mitochondrial DNA

Genetics, Cancer and Development Emily (8 decks)

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