transcription & translation - exam 1 Flashcards
gene
a segment of DNA that contains instructions for making an RNA
features of a gene
start site - transcription unit - terminator
promoter
RNA transcript = compl. to template strand of DNA
promoter
where RNA polymerase binds
enzyme that transcribes RNA from DNA
RNA polymerase
catalyzes formation of RNA using DNA template
initiation
RNA pol binds promoter
RNA pol finds promoter & unwinds DNA
adds nts complementary to template
builds RNA in 5’-3’ direction
elongation
RNA pol moves “downstream” elongating RNA transcript
termination
RNA pol recognizes terminator & falls off
where does transcription occur
nucleus
replication product
2 double stranded dna molecules
direction of synthesis in replication
5’-3’
enzymes in replication
dna pol, helicase, primase, ligase
where does replication occur
nuclues
when does replication occur
before cell division
of template strands in replication
2
transcription product
single stranded rna molecule
direction of synthesis in transcription
5’-3’
enzymes in transcription
rna pol
when does transcription occur
always
of template strands in transcription
1
mRNA
messenger
info carrier
used by ribosomes to make proteins
tRNA
transfer
connection between mRNA & protein
single stranded & folded into “t” shape
doesn’t contain info found in protein coding gene
rRNA
ribosomal
snRNA
small nuclear
how do eukaryottes modify mRNA after transcription
addition of cap & a tail
intron removal
5’ cap
stability of RNA molecule so single strand doesn’t get cut off
position of mRNA on ribosome
poly-A tail
stability of RNA molecule so nuclease doesn’t chop it away
- longer tail = longer life
- doesn’t matter if repeated As get chopped
exit form nucleus
- polyA binding proteins w/ a nuclear export signal
intron
intervening sequence must be removed
exon
expressed sequence stays in
RNA splicing
introns removed & exons spliced together
pre mRNA w/ introns: “B!0)0g% is my f@^0r!t3”
mature mRNA w/out introns: “Biology is my favorite.”
how can eukaryotes produce many more proteins than they have genes
alternative RNA splicing
one gene can encode more than 1 polypeptide
where are ribosomal subunits made
nucleolus - made separately
leave the nucleolus thorough nuclear pores into cytosol
where does translation occur
in cytosol
4 binding sites on a ribosomal unit
E - exit
P - tRNA w/ polypeptide
A - tRNA w/ amino acid
on small subunit - mRNA binding
translation initiation
mRNA binds to small subunit
- 5’ cap helps w/ positioning
- start codon in P site
1sr tRNA comes in & binds to start codon
large subunit binds
translation elongation
anticodon of next charged tRNA binds to codon in A site
tRNA-met bond brokem
- met forms peptide bond w/ next amino acid
ribosome moves down mRNA
- A site is vacant
=tanslocation
uncharged tRNA in E site exits
translation termination
stop codon enters A site
release factor binds in A site
complex falls apart
missense mutation
different amino acid put into protein
consequence: it depends, hydrophobic & philic, where in protein mutation is (active site)
nonsense mutation
stop codon replaces amino acid encoding codon
consequence: shortened protein – BAD
silent mutation
no change in amino acid & no protein folding issues
consequence: often none
frameshift mutaion
nucleotide pair insertion/deletion
everything after insertion/deletion is wrong, all shifted down one
consequence: wrong protein is made – BAD
mutation in germ cell
mutation can be passed to offspring
mutation in somatic cell
mutation not present in offspring
