Topic one extra questions Flashcards
what were the experiments that gave evidence for the genetic code
griffith - two strains of deadly streptococcus in mice
avery - showed dna was a transforming agent
hershey and chase - protein and dna bacteriophage - showed dna contained genetic info
chargaff - studied the bases - and the ratios of them
watson and crick built first model of the complimentary base pairing
how is DNA packaged into a chromosome
supercoiled into chromosomes around histones making chromatin - active genes more loosely coiled
what did meselson stahl do
showed that dna was semi conservative using two separately labelled isotopes with different weight
describe the basic mechanism of replication
helicases unwind and single stranded binding proteins hold it apart
dna primase makes a primer
DNA polymerase 3 makes more caries out elongation of the next strand
lagging strand lots of short primers then dna polymerase fills in gaps on lagging strand and dna ligase joins them together
what does EMS do to DNA
alkylates it producing a GC-AT mutation
what are some repair mechanisms in DNA
base excision repair - cuts out individual bases
nucleotide excision repair - less specific and cuts out sections of DNA
how many base pairs do we have
around 3 billion
what does VNTR stand for and what does it mean
variable number tandem repeats
each person has a different number of repeated sequences in our genome which makes us unique
what is the difference between DNA polymerase and rna polymerase
rna does not require a primer for transcription
how does RNA polymerase work
reads dna in anti sense 3-5’ so that the result is a strand in the 5’ to 3’
what is the role of CpG islands and why is it significant in transcription
they are a promoter element with C followed by g - there can be lots of them rather than a tata box and usually further upstream from target gene - they cab be methylated to turn of transcription and switch off gene expression
where does polyadenylation not occur
in histone proteins
what is the loop called that is produced in splicing of the introns
lariat
what are which cells have the larger ribosomes
eukaryotes are larger the prokaryotes
what modifications can occur to secretary proteins after translation
disulphide bridges - two cysteine residues
glycolysation - trees of sugar added - characteristic of membrane proteins
