exam 3 (translation) Flashcards
what material does translation use to make protein
DNA-encoded info
translation in what step of the central dogma
last step
where are proteins synthesized
ribosomes
describe the structure of a bacteria ribosome
- large subunit has a short and long strand of rRNA and proteins L1, L2, L3
- small subunit has strand of rRNA and proteins S1, S2, S3
how many proteins are in the large subunit of a bacteria ribosome? how many are in the small subunit?
large- 36
small- 21
how many proteins are in the large subunit of a eukaryotic ribosome? how many are in the small subunit?
large- 50
small- 33
what results in loss of ribosome function in yeast
cells grow slowly, can’t complete well with wild-type strains
what results in loss of ribosome function in Drosphila
a class of mutations (called minute)
what is Diamond-Blackfan anemia (DBA) and what is it a result of?
lack of red blood cells and congenital abnormalities. caused by mutations in 10-15 diff ribosomal protein genes (RPS19)
what is Treacher-Collins syndrome and what is it a result of?
craniofacial defects, hearing loss.
results from mutations of TCOF1, which participates in rRNA processing and genes that encode subunits of RNAPi
what programs ribosomes for protein synthesis
mRNA
mRNA is read in which direction
5’ –> 3’
what are codons
triplets of bases in mRNA that specify which amino acids are a part of the protein strand
what is the open reading frame (ORF)
portion of mRNA encoding a protein, that is a way the nucleotide sequence can be divided
reading frames start with which codon
ATG (AUG) methionine
what is the wobble in codon-anticodon pairing
the 5’ end of the tRNA anticodon can recognize multiple bases at the 3’ end of the codon
what provides the greatest flexibility for codon-anticodon pairing
inosine
what are the 3 codons that terminate translation
UAA
UAG
UGA
which of the stop codons can be repurposed to incorperate nonstandard amino acids into proteins
UGA
UAG
what is the 21st amino acids in proteins and is found in all domains of life
SEC- selenocysteine
selenocysteine is encoded by what codon
UGA codon
what is the function of the selenocysteine incorporation sequence (SECIS)
recoding of UGA as a U codon
what is the 22nd amino acid found in proteins of bacteria and archea
pyrrolysine
what is pyrrolysine encoded by
UAG
what is the adapter hypothesis
proposed by francis crick
states that there is some molecule that tells protein synthesis machinery which amino acids are specified by the mRNA
was later discovered that tRNAs are the adapters
what is the function of the acceptor stem on tRNA
responsible for the interaction with an amino acid
what is the function of the anticodon on the tRNA
responsible for the interaction with the mRNA codon
the anticodon of the tRNA pairs with what during translation
codon on mRNA
what are aminoacyl-tRNA synthetases
attach amino acids to their cognate tRNA (called=charging)
must be able to discriminate between amino acids with similar side chains
explain the proofreading process of aminoacyl-tRNA synthetases
double-sieve model to only allow isoleucine
have course sieve on the activation site to reject larger amino acids
have fine sieve on editing site to reject smaller amino acids
what can cause tRNA recognition by aminoacyl synthetases to be altered
mutation of the identity element alters the specificity of the tRNA for the synthetase
what are the 4 mechanisms of translation
initiation
elongation
chain termination
recycling
what other codons could start
GUG
UUG
lacl has what starting codon
GUG
lacA has what starting codon
UUG
what is generally the first amino acid incorporated into a new protein
methionine
but can also occur in the middle
what are the 2 methionine tRNAs in bacteria
initiator
elongator
what hydrolyzes GTP to GDP during prokaryotic translation initiation
IF2
what is the shine-dalgarno sequence
- observations made by john shine and Lynn Dalgarno
- many bacterial ORFs have purine-rich consensus sequence, 5-7 nt upstream of initiating AUG codon
- the 16S rRAN has a complementary pyrimidine-rich sequence near its 3’ end
how are eukaryotic translation initiation different that prokaryotic
- mRNAs are much more highly processed
- no shine-dalgarno sequence
- ribosomes bind to the mRNA and scnas for a proper AUG
what is the Kozak sequence
sequence that has AUG embedded, to start
describe the 3 sites of the ribosome
A site: entry point for a charged tRNA
P site: where the peptidyl tRNA is located (tRNA is attached to the growing polypeptide chain)
E site: exit point for an uncharged tRNA
when does translation termination occur
when a termination codon enters the A site
translation termination requires 3 release factors
- RF1 and 2 interact with the termination codon
- RF3 stimulates cleavage of the completed peptide from the last tRNA
how does Diphtheria toxin target ribosomes
adds an ADP-ribose molecule to eEF2
how does ADP-ribosylation and exotoxin A impair eEF2 function
inhibits protein synthesis
What are and the functions of saponin, shiga toxin, adn ricin
they are ribosomal posions, of which each remove a single adenine base from the 28S rRNA
where are many ribosomal toxins found
they are found in: staple crops–rice, maize, and barley because they aren’t toxic to humans
how are ribosomes used in cancer therapy
they are a part of “immunotoxin”, where they are an antibody against cancer cell-specific proteins, where they inhibit protein synthesis
what are chaperones
factors that mold disordered protein chains into proper shapes
what is the bacterial chaperone’s role in it exit of a ribosome
the trigger factor associates with the nascent polypeptide chain
what is the signal hypothesis
- states that free and ER-asscoaited ribosomes are the same
- it was originally hypothesized that all protein synthesis begins on free ribosomes and proteins were specifically functionized to be directed to ribosomes on the ER
what is the function of proteasome
protein complex that gets rid of unnecessary/damaged proteins
what is the structure of a proteasome
barrel-like structure that is capped by regulatory subunits
explain the function of ubiquitin and ubiquitination with proteasomes
- proteins that are to be degraded are tagged with ubiquitin
- ubiquitination targets the protein to the proteasome
- proteasomes hydrolyze peptide bonds, chopping proteins into small fragments
