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Med Year 1 - IMS > Nucleic Acids - The Human Genome > Flashcards

Nucleic Acids - The Human Genome Flashcards

1
Q

What is the genome?

A

All the genetic information of an organism

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2
Q

How many nucleotides in humans? How many protein coding genes does this make up?

A

3.2 billion nucleotides making up 20,000 protein coding genes

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3
Q

What is a genome divided into?

A
  • 2 sex chromosomes = XX and XY
  • 44 autosomes = non -sex chromosomes
  • (37 genes on circular mitochondrial chromosomes)
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4
Q

Why do mitochondria have their own separate set of genes?

A

Evolved from bacteria (endosymbiosis) which had roughly the same size, shape and had circular DNA

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5
Q

Why do mitochondria have their own separate set of genes?

A

Evolved from bacteria (endosymbiosis) which had roughly the same size, shape and had circular DNA

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6
Q

What is a karyotype and how is ordered?

A

The number and visual appearance of chromosomes.
Autosomes numbered in order of size (1 is biggest).

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7
Q

What percentage of DNA is coding DNA?

A

1%

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8
Q

What does non-coding DNA include?

A
  • Genes for other RNAs
  • Promoter regions
  • Introns
  • Tandem repeats
  • Telomeres
  • Pseudogenes
  • Viral DNA
  • “Junk DNA”
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9
Q

What are tandem repeats?

A
  • Repeated short DNA sequences which occur due to polymerase slippage.
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10
Q

What can tandem repeats be used in? Why?

A
  • Used in forensic DNA testing and paternity testing
  • Number of repeats are variable and differ between individuals
  • Easier way of testing than using the whole genome.
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11
Q

What are telomeres?

A

Long stretches of DNA at the end of chromosomes

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12
Q

How are telomeres the basis of aging?

A

Telomeres shorten after each replication, at senescence, telomeres are so short that the specific cell cannot divide anymore and any damage incurred cannot be repaired.

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13
Q

What is special about cancer cell telomeres?

A

Cancer cells are good at keeping their telomeres long

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14
Q

What are pseudogenes

A

A DNA sequence that resembles a gene but has been mutated into an inactive form over the course of evolution

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15
Q

What is viral DNA?

A

We have more viral DNA than we do our own coding DNA. Most from retroviruses that replicate by inserting their genome into our DNA

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16
Q

What is “junk DNA”

A

Has no obvious purpose yet

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17
Q

What are haploid cells?

A

n=23 one copy of each chromosome
e.g. sperm and eggs

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18
Q

What are polyploid cells? Examples?

A

cells that copy their DNA several times (2n, 4n, 8n) without division
- Megakaryocytes (parent cell of platelets)
- cardiomyocytes (unknown why as it impairs heart regeneration after damage.

19
Q

What are diploid cells?

A

2n= 46 two copies of each chromosome (half maternal and half paternal)
most of the cells in the body

20
Q

How does inactivation of the X chromosomes in women take place?

A
  • Takes place in the early embryo where inactivation is by random selection in each cell
  • Each cell generates a clone with the same X active
21
Q

What is a Barr body?

A

Inactivated X chromosome which shrinks and is pushed to the edge of the nucleus

22
Q

When and why do red blood cells lose their nucleus?

A
  • Lose their nucleus during maturation
  • Makes room for haemoglobin
  • Maintains a concave shape to maximise oxygen diffusion
  • provides red blood cells with the flexibility to squeeze through capillaries
23
Q

What is an example of a species with a more compact genome?

A

Pufferfish have 10% more coding DNA, 90% non coding DNA

24
Q

What is an example of species which have a different ability to repair cardiac myocytes?

A
  • Zebra fish have 2n chromosomes per cardiomyocyte throughout life and can repair heart damage as adults
  • Newborn mice have 2n chromosomes per cardiomyocyte and can repair heart damage while newborn
25
Q

What is an example of a species that have different shaped chromosomes?

A

Bacteria have ring chromosomes (we have linear chromosomes)

26
Q

What is an example of a species with a different number of chromosomes? (An example of synteny)

A

Chimps have 2n=48 chromosomes (our chromosome 2 is a fusion of chimp chromosomes 12 and 13)

27
Q

what is synteny?

A
  • When long DNA sequences are present in the same order in two different species
  • Occur as a result of chromosome breakage and re-joining (translocation) throughout evolution
28
Q

What percentage identical are the genomes of any two individuals? How many base pairs difference is this?

A
  • 99.6% identical
  • leaves about 24 million base pairs of difference
29
Q

What is the genotype?

A

unique DNA sequence responsible for a trait

30
Q

What is the phenotype?

A

observable expression of the trait e.g. tall, curly hair

31
Q

What is a single nucleotide polymorphism (SNP)?

A

a variation at a single position in a DNA sequence among individuals; if more than 1% of the population does not carry the same nucleotide at a specific position in the DNA sequence = SNP

32
Q

What is a single nucleotide polymorphism (SNP)?

A

a variation at a single position in a DNA sequence among individuals; if more than 1% of the population does not carry the same nucleotide at a specific position in the DNA sequence = SNP

33
Q

How can a gene be described if it has an SNP in the coding region?

A

The gene is described as having more than one allele, some may alter our relative disease risks

*SNPs can also occur in non-coding DNA

34
Q

What two factors can result in multifactorial diseases? Example?

A
  • SNPs in multiple genes (polygenic)
  • The environment

e.g. Hypertension

35
Q

What is aneuploidy? How does it occur? Example?

A

wrong number of chromosomes often due to non-dysjunction (failure of chromosomes to properly separate) during meiosis

e.g. Downs Syndrome (Trisomy 21)

36
Q

What is an example of a disease that can be caused by translocations in somatic cells?

A

Chronic myeloid leukaemia (due to formation of Philadelphia chromosome t(9;22))

37
Q

What is an example of a disease that can be caused by translocations in germ cells?

A

Rarer forms of Downs Syndrome (less severe - where a big chunk of chromosome 21 can get stuck onto another chromosome so you almost have 3 chromosome 21s)

38
Q

What is an example of a disease caused by single gene mutations? How does infection occur?

A

Cystic fibrosis
- mutation in CFTR gene which is a chloride ion transporter so build up of thick mucus which cannot be cleared = infections

39
Q

What are single gene mutations?

A
  • Result from a single mutation in a single gene
  • little influence from other genes or environment on phenotype
40
Q

Where do tandem repeats normally occur?

A

In non-coding regions of DNA, but can occur in coding regions which alters protein structure

41
Q

What is an example of a disease due to tandem repeats? How can it become more severe with inheritance?

A
  • Huntington’s Disease = increased CAG repeats in the Huntington protein
  • With inheritance, the genes for the disease get longer so disease becomes more severe in subsequent generations
42
Q

How do diseases from mitochondrial DNA occur?

A
  • Mutations inherited in mitochondrial DNA
  • rare and severe
  • 37 mitochondrial genes, if there is a mutation in these, it is normally incompatible with life
43
Q

Why can mitochondrial DNA only be inherited from the mother?

A

only the egg contains mitochondria, the sperm mitochondria is in the tail, the head which releases genetic material fuses with the egg and leaves the tail behind

Med Year 1 - IMS (9 decks)

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