Lecture 8 Translation Flashcards
______ is a set of rules that convert the nucleotide sequence of a gene into the amino acid sequence of a protein using mRNA as an intermediate
Genetic code
each group of 3 consecutive nucleotides in RNA is called a ____
codon
a total of ____ triplet codons code for the 20 known amino acids, thus the code is _____
61, degenerate
The _____ hypothesis postulates that the genetic code is read by molecules that recognize a codon and carry the corresponding amino acid
adaptor hypothesis
______ serves as an adaptor that binds to a specific codon and brings with it an amino acid for incorporation into the polypeptide chain
Transfer RNA or tRNA
_____ secondary structure of tRNA. tRNA folds up into a defined 3-D structure and contains 4 short double-helical segments
Cloverleaf
___ regions of unpaired nucleotides are crucial to the functions of tRNA. What are they
- Anticodon loop (as set of 3 consecutive nucleotides that pair with a a complementary codon in an mRNA molecule) The other is 3’ CCA terminal region (which binds the amino acid that matches the corresponding codon)
is there more than one tRNA for most amino acids
yes
some tRNAs require accurate base-pairing only at the first two positions of the codon and can tolerate a mismatch (or ____) at the third position
Wobble
The amino acid is activated for protein synthesis by an ________ in two steps
aminoacyl-tRNA synthetase enzyme
Recognition and attachment of the correct amino acid to the corresponding tRNA is catalyzed by
aminoacyl-tRNA synthetases
aminoacyl-tRNA syntheses covalently couple an amino acid to the
3’-terminal ribose residue of its corresponding tRNA to form an aminoacyl-tRNA
do most cells have a different aminoacy-tRNA synthetase enzyme for each amino acid
yes
Aminoacyl-tRNA syntheses contain highly discriminating amino acid
activation sites
The correct amino acid has the ______ affinity for the active-site pocket of its aminoacyl-tRNA synthetase and is therefore favored over the other 19. Amino acids larger than the correct on ______
highest affinity, do not bind to active site
do aminoacyl-tRNA synthetases contain an editing site for proofreading
yes
The editing (hydrolytic) site of aminoacyl-tRNA synthetase cleaves ________ species that are _______
cleaves activated species that are smaller than the correct one
Hydrolytic editing raises the overall accuracy of tRNA charging to approximately one mistake in ______ couplings
40,000
what is the molecular weight of the eukaryotic 80S ribosome
4,200,000
what is the molecular weight of the prokaryotic 70S ribosome
2,500,000
What is the size of the prokaryotic ribosome
70S
What is the size of the eukaryotic ribosome
80S
Ribosome is a complex catalytic machine, consisting of two subunits, each contains different ________ and several _____
ribosomal proteins and several ribosomal RNAs (rRNAs)
____ and not proteins determine the overall shape of the ribosome, its ability to position tRNA on the mRNA, and its catalytic activity in forming peptide bonds
rRNAs
____ provides the framework on which the tRNAs are accurately matched to the codons of the mRNA
small subunit of ribosome
____ catalyzes the formation of the peptide bonds that link the amino acids together into a polympetide chain
the large subunit of the ribosome
Protein synthesis is performed on the ______, which ensures accuracy and maintains _____
ribosome, correct reading frame
When not synthesizing proteins the 2 ribosome subunits are
separate
mRNA is pulled through the ribosome in a _____ direction
5’-3’ direction
The 2 ribosomal subunits join together at the __ end of an mRNA and initiate protein synthesis
5’
As the codons enter the core of the ribosome the mRNA sequence is ______ using ___
translated into amino acid sequence using tRNAs
The ribosome releases protein when encountered by a ____
stop codon
The ribosome contains ___ binding sites for RNA. What are they
- 4
- tRNA A (for aminoacyl), P (for peptidyl), and E (for exit) sites and 1 for mRNA
The A-,P-, and E-sties on the ribosome are formed by the rRNA of the ____ subunit
large
The mRNA is bound within the ___ subunit of the ribosome
small
The tRNA molecules are held in the A and P sites only if
their anticodon forms base pairs with complementary codons in mRNA threaded through the ribosome
Amino acids are added to ____ terminus of polypeptide
C-Terminus
The fundamental reaction of protein synthesis is formation of _____ bond between amino acids
peptide
The peptide bond formation between amino acids occurs between the _____ at the end of the polypeptide and an ____ of the incoming amino acid
Carboxyl group, amino group
A protein is synthesized stepwise from its _____ to ____ terminal end
N-terminal to C-terminal
Once protein synthesis has been initiated, each new amino acid is added to the elongation chain in a cycle of reactions containing ____ steps; what are they
- 4
- tRNA binding
- peptide bond formation
- large subunit translocation
- small subunit translocation
all known mRNA molecules contain signals that define the
beginning of each encoded polypeptide chain
Translation begins with the ____ codon ____, which codes for ____
initiation codon AUG, which codes for methionine
The 70S subunits are
50S and 30S
The 80S subunits are
60S and 40S
in eukaryotes, the initiator tRNA-methionine complex is first loaded into the ____ subunit along with additional proteins called
small ribosomal, eukaryotic initiation factors, or eIFs
After the initiator tRNA has bound to the small ribosomal subunit, the small ribosomal subunit
binds to the 5’ end of mRNA (recognized by its 5’ cap and the bound initiation factors (eIF4E and elF4G)
What ins the recognition consensus site ahead of AUG in eukaryotes
5’-ACCAUGG-3’
after initiation, the factors ____, the large subunit ___
drop off, the large subunit joins the small subunit and the protein synthesis starts
What are the bound initiation factors that the small ribosomal subunit uses to recognize the 5’ cap
eIF4E and eIF4G
____ factors makes translation more efficient and accurate
Elongation factors
Elongation factors care called _____ and ____ in bacteria and ____ and ____ in eukaryotes
EF-Tu and EF-G in bacteria and EF1 and EF2 in eukaryotes
EF-Tu binds ____ and the _____ and then functions to
GTP and the aminoacyl tRNA ad then escorts it to the ribosome (checks whether amino acid-tRNA match is correct) and monitors interaction between anticodon o incoming aminoacyl tRNA and the codon of mRNA
Interaction of EF-Tu, tRNA and ribosome introduces critical _____ steps into protein synthesis
proof-reading
GTP hydrolysis brings about conformation changes in ribosome that
increase efficiency greatly
What are the stop codons
UAA, UAG, UGA
The stop codons are recognized by ______, proteins that promote the release of the completed protein from the tRNA
Release Factors (RFs)
Release factors bind to ____ site of ribosome containing the stop codon and catalyze the addition of a water molecule instead of an amino acid. This reaction frees the ___ group of the polypeptide from ___
A site, Carboxyl group of the polypeptide from tRNA
many effective antibiotics are compounds made by fungi that inhibit ________
bacterial protein synthesis
Antibiotics are able to exploit
structural and functional differences between bacterial and eukaryotic ribosomes
Many antibiotics bind to ______ and interfere with protein synthesis by blocking ribosomal function
Ribosomes
Specific effect of tetracycline
blocks binding of aminoacyl-tRNA to the A site of ribosome
Specific effect of streptomycin
prevents the transition from translation to chain elongation and also causes miscoding
Specific effect of Erythromycin
Binds in the exit channel of the ribosome and thereby inhibits elongation of the peptide chain
Specific effect of Puromycin
Causes the premature release of nascent polypeptide chains by its addition to the growing chain end
Specific effect of Cycloheximide
Blocks the translocation reaction on ribosomes
What antibiotics bind to small ribosomal subunit (30S) of bacterial ribosome
- Tetracycline, Spectinomycin, Hygromycin B, Streptomycin
What antibiotics bind to the large ribosomal subunit of the bacterial ribosome
- Chloramphenicol, streptogramin B, and erythromycin
