Chapter 9 Flashcards
_______ different amino acids serve as building blocks for polypeptides
20
All amino acids have a central _______ an _______ and a ________
carbon
amino group
carboxyl group
An enzyme of the ribosome catalyzes the formation of a _______ between the carboxyl group of one amino acid and the amino group of the next.
peptide bond
The _______ of each amino acid is distinct
R-group
Ribosomes translate mRNA in the _________ direction reading each triplet codon and assembling the amino acid in the order specified
5’->3’
Ribosomes are composed of 2 subunits, what are they?
The small ribosomal subunit and the large ribosomal subunit
Ribosomal subunit size is measured in _______ a property based on size, shape, and hydration state.
svedberg units (S)
Boundaries of translation are defined by:
- Start codon (5’) @ the __-terminus of the protein
- stop codon (3’) @ the __ -terminus of the protein
N
C
In primary peptide structure, what kind of bonds are formed?
peptide bonds
in secondary peptide structure, what kind of bonds are formed?
H-bonds
The prokaryote small subunit is 30s and contains ____ proteins and __ 16s rRNA molecule
21
1
The prokaryote large subunit is 50s and contains __ proteins, __ small 5s rRNA, and __ large 23s rRNA
31
1
1
What is the size of the small bacterial ribosomal subunit? What about the large? What is the size of the full ribosome?
30 S
50 S
70 S
The A-site (_______ site) binds the incoming _______ carrying the next amino acid to be added to the growing polypeptide chain
aminoacyl
tRNA
The P-site (_______ site) holds the tRNA to which the growing _______ chain is attached
peptidyl
polypeptide
The E-site provides a pathway for _______ of the tRNA after amino acid has been added to the growing chain
exit
The eukaryotic small subunit contains __ proteins and __ 18s rRNA
3
1
The eukaryotic large subunit contains __ proteins and __ rRNA molecules
45-50
3
What is the size of the small eukaryotic ribosomal subunit? What about the large? What is the size of the full ribosome?
40 S
60 S
80 S
What are tRNA’s carrying an amino acid called?
charged tRNA’s
What are tRNA’s without amino acids attached called?
uncharged tRNA’s
What are the steps to bacterial translation initiation? (4)
1) IF3 binds to small subunit
2) small subunit-IF3 complex binds to mRNA near 5’ end and shine-delgarno sequence lines up with sequence on 16s rRNA to align the start codon with the P site
3) tRNA containing N-formylmethionine, IF2, and GTP binds at P site and IF1 binds at A site
4) Hydrolysis of GTP and disassociation of IF1, IF2, and IF3 allow large subunit to bind to small subunit
What is the purpose of IF3
to prevent the large subunit from binding to the small subunit
The Shine-Dalgarno sequence is a _______ rich sequence of about 6 nucleotides upstream of the start codon
Purine (A/G)
A complimentary (to the Shine-Delgarno sequence) _______ rich sequence is found near the 3’ end of the 16s rRNA
pyrimidine (U/C)
What is the start codon?
AUG
The _______ forms when the 16s rRNA base pairs with the shine-delgarno sequence on the mRNA
pre-initiation complex
What are the steps to eukaryotic translation initiation? (4)
1) eIF1, eIF1A, and eIF3 bind to small ribosomal subunit forming the pre-initiation complex
2) initiator tRNA and eIF5 join the pre-initiation complex
3) The pre-initiation complex + initiator tRNA and eIF5 then bind eIF4 to the 5’ end of the mRNA forming the initiation complex and searches for the start codon
4) The large ribosomal subunit binds to the initiation complex using GTP and disassociation of eIF’s
the start codon is found in the _______ sequence (eukaryotes)
kozak
_______ is required for the initiation complex to find the start codon in eukaryotes
ATP hydrolysis
What is the difference between Archaeal translation initiation and eukaryotic translation initiation?
1) some archaeal mRNA’s contain the shine-dalgarno sequence
2) use aIF’s (archaeal initiation factors)
What is connected to charged tRNA’s as they enter the A site in polypeptide elongation in bacteria?
1) EF-TU
2) GTP
_______ catalyzes peptide bond formation between the amino acids at the P and A sites
peptidyl transferase
Using _______ hydrolysis, _______ translocates the ribosome, moving it 3 nucleotides toward the 3’ end of the mRNA. This moves the tRNA at the __ site to the P site.
GTP
EF-G
A
What is the archaeal homolog to EF-TU? what about eukaryotic homolog?
aEF-1
eEF-1
What is the archaeal homolog to EF-G? what about eukaryotic homolog?
aEF-2
eEF-2
All organisms use _______ to bind to a stop codon in the A-site
release factor (RF)
In bacteria: RF1 recognizes codons _______ and _______
UAG and UAA
In bacteria: RF2 recognizes codons _______ and _______
UGA and UAA
What is the purpose of RF3
to recycle RF1
What is the release codon in eukaryotes and archaea
eRF1
What are the 3 stop codons?
UAG
UGA
UAA
Prokaryotes can have _______, which are all actively translating the same RNA
polyribosomes
Compare and contrast translation in bacteria and eukaryotes
1) bacteria allow for coupling of translation and transcription, eukaryotes don’t (need nucleus then cytoplasm)
2) eukaryotes produce monocistronic mRNA while bacteria produce polycistronic mRNA
Each polycistronic mRNA contains several _______ and _______, and the _______ separates the segments
Start and stop codons
intercistronic spacer sequence
_______ describes the correspondence between the nucleotide sequence of mRNAs and the amino acid sequences of the resulting polypeptides
genetic code
_______ are adaptor molecules that interpret and then act on information carried in mRNA
Transfer RNA’s
_______ groups of three consecutive nucleotides in an mRNA each correspond to one amino acid
Codons
The genetic code contains 64 different codons but there are only 20 amino acids. This is an example of _______
redundancy
_______ codons code for the same amino acid
Synonymous
_______ tRNA’s are tRNA molecules with different anticodons that carry the same amino acid
Iso-accepting
_______ creates flexible pairing at the 3’ nucleotide of the codon
third base wobble
because the genetic code is universal, _______ can be used to produce important proteins from plants and animals
bacteria
_______ are enzymes that catalyze the addition of the correct amino acid to tRNA’s. What provides this energy for the attachment?
aminoacyl-tRNA synthetases
ATP
At what end does the tRNA does the amino acid bind?
3’ end
True or False: Each aminoacyl tRNA synthetase is specific for one amino acid and a small number of tRNAs.
True
_______ refers to the specific codon sequence as determined by the start codon
reading frame
Mutations that alter the reading frame are called _______ and garble the sense of the translated message
frameshift mutations
In 1957, _______ determined that an overlapping code was not possible because it was too restrictive
Sidney Brenner
in 1960, _______ and colleagues showed that single nucleotide changes led to a single amino acid change
Fraenkel-Conrat
N___ and L___ used mini-RNA’s just three nucleotides long (one for each of the possible codons) to resolve the ambiguities of previous experiments
Nirenberg and Leder
Describe Nirenberg and Leder’s experiment
Mini mRNA’s with a bunch of codons (one C14 labeled) passed through a filter
What are the 2 different types of protein folding and post-translational processing?
1) post-translational polypeptide processing
2) protein sorting using signal (leader) sequences
A form of _______ is the removal of one or more amino acids from a polypeptide
post-translational protein processing
One of the most common modifications of amino acids is phosphorylation, carried out by _______
kinases
polypeptides may be cleaved into _______ segments that have _______ functions or that _______ to form a functional protein
multiple
separate
aggregate
_______ of about 15 to 20 amino acids at the N-terminal end directs proteins to their cellular destinations
Signal (leader) sequences
polypeptides destined for secretion are produced at the _______
rough ER
What term is used to identify a functional protein that is formed when two identical polypeptides join together?
homodimer
Thanks to flexible base pairing, the wobble nucleotides in anticodons can be one or more of the standard RNA nucleotides or which modified nucleotide?
Inosine (I)
