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Biochemistry (Cole) > Lecture 34 DNA Repair and How mutations occur > Flashcards

Lecture 34 DNA Repair and How mutations occur Flashcards

1
Q

what are the types of genetic diseases?

A
  • chromosome disorders
  • single gene disorders
  • multifactoral or complex
  • sex linked and mitochondrial
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2
Q

Chromosome disorders

A
  • most common disease
  • rearrangements/ translocations
  • deletions
  • insertions
  • duplications
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3
Q

Single gene disorders

A
  • best characterized (several thousand)
  • Dominant
  • Recessive
  • Codominant
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4
Q

Multifactorial or complex

A
  • Multiple genes

- gene-environment

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5
Q

Sex linked and mitochondrial

A
  • small genome that encodes for proteins
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6
Q

What are the general categories of mutations

A
  • somatic

- germline

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7
Q

Are somatic mutations inheritable?

A
  • no
  • they arise other than gametes
  • ex: cigarette smoking an lung cancer, p53 mutations
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8
Q

Are germline mutations inherited?

A
  • yes

- 12,000 + entries in OMIM currently

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9
Q

What are the causes of mutations?

A
  • spontaneous and induced
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10
Q

What mutations arise naturally during DNA replication (mitosis) or during meiosis?

A
  • spontaneous
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11
Q

What type of mutations arise from radiation or chemicals?

A
  • induced
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12
Q

What are the types of mutations?

A
  • silent
  • missense
  • Nonsense
  • Transition
  • Transverse
  • Deletion
  • Insertion
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13
Q

Silent

A
  • no change

- nucleotide change but resulting amino acid is the same

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14
Q

Missense

A
  • single amino acid change
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15
Q

Nonsense

A
  • stop codon produced and Truncated protein

- could have stop codon eliminated and get long protein

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16
Q

Transition

A
  • Pur/Pur

- Pyr/Pyr

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17
Q

Transversion

A
  • Purine/ Pyrimidine
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18
Q

Deletion or insertion

A
  • extra or missing amino avids
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19
Q

Frameshift

A
  • altered protein

- phasing that mRNA is read is shifted

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20
Q

Other types of mutations through regulatory elements

A
  • all these regulatory elements can be mutated
  • promoter/enhancer - nuclear receptors
  • splice site
  • expanded repeat
  • transposons
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21
Q

What mutation is associated with huntingtons disease?

A
  • expanded repeat
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22
Q

Transposons

A
  • mobile regulatory elements that jump around
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23
Q

What mutation results in a different amino acid that is encoded?

A
  • missense (1 base 1 amino acid)
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24
Q

What goes into the nomenclature of mutations?

A
  • amino acid designations
  • genomic (gDNA) vas mRNA(cDNA) vs proteins
  • coordinates
  • substitutions that took place
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25
Q

What are alleles?

A
  • sequence variants of a gene
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26
Q

How many alleles of each autosomal gene from your mother and father do you recieve?

A
  • one
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27
Q

What chromosomes do females inherit

A

XX

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28
Q

What chromosomes do males inherit

A

XY

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29
Q

What are single nucleotide polymorphisms?

A
  • single base differences at a specific position in the genome
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30
Q

Can SNPs occurring within a gene give rise to an allele

A
  • Yes
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31
Q

How many SNPs are in the genome?

A
  • hundreds of thousands of SNPs in the genome

- walking mutation

32
Q

Why are SNPs helpful to us?

A
  • they give us land marks at nucleotide (crack) level
33
Q

Are most of the spontaneous changes that happen in DNA eternal?

A
  • no they are temporary because our body corrects them through DNA repair
34
Q

What are some factors that can cause random changes?

A
  • heat
  • metabolic accidents
  • radiation of various sorts
  • exposure to substances in the environment
    (only a few of these actually accumulate as mutations in DNA sequence)
35
Q

fewer than 1 in ____ accidental base changes in DNA results in a permanent mutation

A
  • 1000
36
Q

How do we know that DNA repair is important?

A
  • it is evident from the large investment that cells make in DNA enzymes or DNA repair proteins.
37
Q

What happens when you have inactivation of DNA repair gene?

A
  • increased rate of mutation and can lead to cell death or disease
38
Q

Which is more stable, DNA or RNA?

A

DNA

39
Q

how often is there sponaneous deamination of cytosine to uracil in DNA?

A
  • rate of about 100 bases per cell per day
40
Q

How much DNA of each human cell is lost daily?

A
  • 5000 purine bases per cell due to their deoxyribose hydrolyzation of N-glycosyl
41
Q

Depurination

A
  • hydrolyzation of N-glycosly linkages
42
Q

What are DNA bases also occasionally damaged by?

A
  • an encounter with reactive metabolites produced in the cell ( including reactive forms of oxygen, H2o2, -OH, and -O2)
  • exposure to chemicals in the environment
  • UV radiation from sun can produce a covalent linkage between two adjacent pyrimidine bases in DNA to form thymine dimers
43
Q

Hydrolytic attack

A
  • deamination and , most frequent chemical reactions
44
Q

What happens when you deaminate adenine?

A
  • you get hypoxanthine
45
Q

What happens when you deaminate guanine?

A
  • you get xanthine
46
Q

What happens when you deaminate cytosine?

A
  • you get uracil
47
Q

Can you deaminate thymine?

A
  • No it doesnt have an amine group
48
Q

Would a 5 methyl cytosine changing to thymine be considered natural or unnatural?

A
  • natural
49
Q

The spontaneous deamination products of A and G are recognized as unnatural when they occur in DNA and thus are readily recognized and repaired

A
  • deamination of DNA nucleotides
50
Q

Base excision repair

A

unnatural bases are recognized and removed by a specific DNA glycoslylase

51
Q

Deamination and depurination

A
  • hydrolytic reactions are the two most frequent spontaneous chemical reactions know to create serious DNA damage in cells
52
Q

Deamination

A
  • cytosine to uracil in DNA is estimated to occur at a rate of 100 bases per genome per day
53
Q

Depurination

A
  • lose 5000 purine bases A or G per day in each cell due to thermal disruption of their N-glycosyl linkages to deoxyribose
  • this adenine or guanine is gone
54
Q

Pyrimidine (C or T) dimer formation

A
  • covalent linkage of two adjacent pyrimidines by UV light from the sun
55
Q

What do pyrimidine dimers do?

A
  • alter the structure of DNA and consequently inhibit polymerases and arrest replication
56
Q

can dimers be repaired?

A
  • they might be repaired by photo reactivation or nucleotide excision repair, but unrepaired dimers are mutagenic
57
Q

Deamination Leads to

A
  • DNA substitution (point mutation)
58
Q

In the case of depurination leads to?

A
  • DNA deletion
59
Q

Do deamination and depurination change both strands?

A
  • no one strand remains unchanged
60
Q

How do nucleotide excision repair work?

A
  • remove large chunk of DNA next to pyrimidine dimer and then DNA polymerase and DNA ligase add new chunk
  • end up exactly like parental strand
61
Q

Quick and dirty solution

A
  • non homologous end joining

- DNA scars

62
Q

Homologous recombination

A

-delays progression of G1 to S phase and from S to M phase (through G2) in the cell cycle

63
Q

same allele

A

homozygous

64
Q

different allele

A

heterozygous

65
Q

Principle of segregation

A
  • sexually reproducing organisms possess genes that occur in pairs and that only one member of this pair is transmitted to the offspring
  • one copy from dad and one from mom
66
Q

Principle of independent assortment

A
  • genes at differ loci are transmitted independently

- genetic info is scrambled

67
Q

What is homologous recombination?

A
  • genetic exchange between a pair of homologous DNA sequences
  • DNA breaks often occur from radiation damage or reactive chemicals
  • DNA breaks also arise from DNA replication forks that become stalled or broken
68
Q

Homologous recombination is a mechanism to

A
  • accurately repair double strand DNA breaks
  • exchange bits of genetic information
  • assures accurate chromosome segregation during meiosis
69
Q

Repair of broken replication fork can lead to

A
  • exchange of DNA information
70
Q

What drives homologous recombination?

A
  • DNA base pairing
71
Q

What happens when you separate DNA into single stranded molecules in test tube?

A
  • DNA will spontaneous reform into double stranded DNA

- proteins bind to DNA and hold it into open configuration for synthesis

72
Q

Inadvertent joining of two segments of DNA from different chromosomes results in?

A
  • inadvertent translocations
73
Q

What proteins are involved in DNA repair?

A
  • the enzymes. catalyzing repair are present at high concentrations in the nucleus
  • number of accessory proteins are involved in control of repair
  • loss of essential proteins needed for repair are generally lethal events
  • Loss or alterations (mutations) of accessary proteins often leads to cancer
74
Q

When do holliday junctions form?

A
  • during homologous recombination
75
Q

What are holiday junctions?

A
  • two DNA strands switch partners between two double helices
76
Q

Can somatic tissues give rise to cancer?

A
  • yes despite them not being inherited
77
Q

What measures how frequently chromosomes cross over?

A
  • centemorgan

Biochemistry (Cole) (25 decks)

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