Lecture 8 Translation Flashcards by Tyler Turner

______ 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

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each group of 3 consecutive nucleotides in RNA is called a ____

codon

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a total of ____ triplet codons code for the 20 known amino acids, thus the code is _____

61, degenerate

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The _____ hypothesis postulates that the genetic code is read by molecules that recognize a codon and carry the corresponding amino acid

adaptor hypothesis

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______ 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

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_____ secondary structure of tRNA. tRNA folds up into a defined 3-D structure and contains 4 short double-helical segments

Cloverleaf

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___ 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)

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is there more than one tRNA for most amino acids

yes

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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

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The amino acid is activated for protein synthesis by an ________ in two steps

aminoacyl-tRNA synthetase enzyme

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Recognition and attachment of the correct amino acid to the corresponding tRNA is catalyzed by

aminoacyl-tRNA synthetases

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aminoacyl-tRNA syntheses covalently couple an amino acid to the

3’-terminal ribose residue of its corresponding tRNA to form an aminoacyl-tRNA

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do most cells have a different aminoacy-tRNA synthetase enzyme for each amino acid

yes

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Aminoacyl-tRNA syntheses contain highly discriminating amino acid

activation sites

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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

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do aminoacyl-tRNA synthetases contain an editing site for proofreading

yes

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The editing (hydrolytic) site of aminoacyl-tRNA synthetase cleaves ________ species that are _______

cleaves activated species that are smaller than the correct one

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Hydrolytic editing raises the overall accuracy of tRNA charging to approximately one mistake in ______ couplings

40,000

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what is the molecular weight of the eukaryotic 80S ribosome

4,200,000

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what is the molecular weight of the prokaryotic 70S ribosome

2,500,000

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What is the size of the prokaryotic ribosome

70S

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What is the size of the eukaryotic ribosome

80S

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Ribosome is a complex catalytic machine, consisting of two subunits, each contains different ________ and several _____

ribosomal proteins and several ribosomal RNAs (rRNAs)

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____ 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

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____ 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

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