Week 11 (Gene structure and expression) Flashcards
central dogma
DNA - replication
RNA - transcription
Proteins - translation
rRNA
site of polypeptide assembly
tRNA
transports and positions amino acids
mRNA
directs which amino acids are assembled into polypeptides
snRNA
is involved in splicing
transcription
-synthesize any type of RNA from a DNA template
-DNA strand provides template for complementary RNA strand
translation
-occurs at ribosomes
-mRNA is used to determine the amino acid sequence of a polypeptide
genetic code
-unambiguous
-nearly universal
-redundant
ORF and what terminus
start (AUG) N terminus to stop codon C terminus
each amino acid in a protein is specified by ____
a codon
triplet code
64 codon combinations
start of transcription
when RNA polymerase binds to a promoter (binding site on template strand of DNA)
how many of the 2 DNA template strands is transcribed
only 1
RNA polymerase
-adds ribonucleotides to the growing 3’ end of an RNA chain
-does NOT need a primer
which way does the template strand run
3’ to 5’
which way does complementary strand run
5’ to 3’
what signals the end of transcription
the terminator
how many RNA polymerase does eukaryotes have
3
how pre mRNA is modified
5’ cap - protects mRNA
3’ poly A tail - prevents hydrolysis
Introns
spliced out (non coding )
Exons
spliced together to be translated into amino acids
spliceosome and what is made up of
made from snRNPs and does splicing
(RNA and proteins)
ribozymes
RNA molecules that catalyze chemical reactions
RNA splicing
removing introns and keeping exons
how many nucleotides are moved at at time in translation
3
what begins translation
when portion of mRNA binds to a ribosome
SSU
small ribosomal subunit
-acts first settles on 5’ end
LSU
large ribosomal subunit
-settles down on top
translation : initiation
-tRNA has a anticodon on its bottom
which base pairs with codons in mRNA
-Met binds to AUG on mRNA
activating enzymes
aminoacyl tRNA Synthetase
-attaches the appropriate amino acid to its corresponding tRNA
translation: elongation
-new amino acids enter with tRNA to the A site
-LSU transfers the polypeptide from the P site to the new amino acid
-moves 3 nucleotides over
-old tRNA leaves out of E site (exit)
translation : termination
stop codons are recognized by release factors that release the newly made polypeptide from the ribosome
prokaryotic mRNA vs euk
pro- polycistronic
euk- monocistronic
what is special about prokaryotic mRNA
they are often translated before transcription is complete
what is a large scale mutation
long segments of DNA are affected
what are point mutations
chemical change in just one base pair of a gene
types of point mutations
silent - replacement of a pair of complimentary nucleotides with another as long as it doesn’t change structure of function
missense - same as silent but changes structure or function of protein
nonsense- changes an amino acid codon to a stop codon
framesshift mutations
-single insertions or deletions that affect open ready frame ORF
-groups of 3 do not cause a frame shift
where do mutations affect
affect DNA replication and transcription
what is an operon
cluster of genes under the control of a single promoter
operator
dna sequence in which the represor protein may bind
represor protein
protein that only binds to the operator inhibits transcription
activator protein
protein that that binds near the promotor and enhances transcription
inducer
molecule that inactivates a represor protein
corepressor
actives the represor protein
jacob and monod proposed what
operon model for bacterial gene expression
inducible gene
normally turned OFF but can be turned ON
-> lac operon
repressible gene
normally turned ON but can be turned OFF
->trp operon
positive control
uses an activator protein
negative control
uses a represor protein
allolactose
inactivities the represor, removing it from the operator
lac operon
-transcribed only when lactose is present
when lactose is absent lac operon is ____
OFF
when lactose is present lac operon is ____
ON
when glucose is low cAMP levels are ______ and binds to ____
high binds to CAP protein
when glucose is high cAMP levels are ______ and what doesn’t bind
low and CAP doesn’t bind
when trp is present the trp operon is _____ the operator is _____
OFF and bound
when the is little or no trp the operon is ______ and ______ and the operator is _____ bound
ON and transcribed and not bound
