Chapter 13 Flashcards
how much of the human genome comprises repeated sequences?
~50%
what are
mini satellites?
micro satellites?
> what are microsatellites also called?
mini satellites: tandem repeats with 10-50 nucleotides
micro satellites: tandem repeats with shorter nucleotides
> micro satellites are also called: short tandem repeat polymorphisms (STRPs)
what are two types of variation between human genomes?
variation between human genomes
> mutations: change in nucleotide sequence, small scale
> recombination: restructuring of part of the genome, large scale
what are two types of mutations?
mutations
- base substitutions (point mutation)
> replacement of a singe base (mistake DNA polymerase)
- deletions & insertions
> one or more nucleotides are inserted/deleted
what are the two possible consequences of base substitution?
base substitution can result in
- synonymous mutations
> do not change the sequence of the gene product
- non synonymous mutations
> result in altered sequence in the polypeptide or functional RNA
> nonsense/missense mutations
insertions and deletions can cause ….?
insertions and deletions can cause frameshifts
how often does an uncorrected error occur?
how many mutations in new cell?
why is that not a problem?
estimation: uncorrected error occur 1 in every 50 million nucleotides added to the chain
>> new cells contain 120 new mutations
>> but over 97% of our DNA does not encode “anything”
how many % of the genome made up of repeated sequences?
> where are those located?
about 50% are repeated sequences
> those are scattered throughout genome, not clustered together
what are 3 external agents that can damage DNA?
external threats to DNA
- ionizing radiation: breaks up sugar-phosphate backbone
- ultraviolet radiation: causes cross-linking between adjacent pyrimidines
- environmental chemicals
what are 4 internal agents that can damage DNA?
internal threats to DNA
- depurination
- deamination
- attack by reactive oxygen species
- nonenzyme methylation
>> plus errors that arise during normal DNA metabolism
internal vs external threats to DNA
> which one major/minor?
external threats generally minor threat
internal threats generally major threat
what are 3 DNA repair mechanisms when DNA is damaged single stranded?
single stranded damage to DNA
- base excision repair (BER)
> DNA glycosylase cuts out mutation, polymerase replaces
- nucleotide excision repair (NER)
> remove & resynthesize large patch around damaged DNA
- direct reversal of DNA damage
> infrequent!
what are 2 repair mechanisms when DNA is damaged on both strands?
double stranded DNA damage
- homologous recombination
> single strand from homologous chrom invades damaged DNA and acts as a template for accurate repair
- nonhomologous end joining
> rejoin broken ends regardless of their sequence
> desparate, likely to cause mutation
why do some mutations not change anything in the protein output of a sequence?
> how are those mutations called?
amino acids are coded for by multiple codons
> changing one of the nucleic acids does not necessarlily change the amino acid it codes for
> those mutations are called silent/synonimous mutations
what is “nonsense mediated decay”?
nonsense mediated decay
> a cell mechanism to protect from premature termination through nonsense mutations
> cell detects mRNA containing premature termination codons and degrades them (whole mRNA is degraded)
