40 Questions
What is the function of aminoacyl-tRNA synthetases?
To catalyze the reaction of esterifying amino acids to tRNA molecules
A specific aminoacyl-tRNA molecule can only recognize one codon on mRNA.
False
What is the name of the complex that binds to formylmethionine-tRNAfmet during initiation?
[IF-2–GTP] complex
The ______________ phase of translation requires mRNA to be translated, 30S and 50S ribosome subunits, aminoacyl-tRNA molecules, and accessory proteins.
initiation
Match the following components with their roles in translation:
30S ribosome subunit = 3. Prevents premature association of 30S and 50S subunits Aminoacyl-tRNA molecules = 2. Provides amino acids for protein synthesis Initiation factors (IF-1, IF-2, IF-3) = 1. Binds to mRNA
What is the result of an amino acid being esterified to the incorrect tRNA molecule?
The error is corrected by aminoacyl-tRNA synthetases
The Shine-Dalgarno sequence is involved in translation initiation.
True
What is the overall reaction for amino acid activation?
amino acid + tRNA + ATP → aminoacyl-tRNA + AMP + PPi
What is the function of the amino acid arm in tRNA?
To serve as the point for amino acid attachment and subsequent transport to the ribosome
The genetic code is ambiguous, meaning that one codon can specify multiple amino acids.
False
What is the term used to describe the phenomenon where multiple codons specify the same amino acid?
Degeneracy
The secondary structure of tRNA resembles a _______________________
clover-leaf
Match the following tRNA regions with their functions:
Amino acid arm = Serves as the point for amino acid attachment and subsequent transport to the ribosome Anticodon loop = Forms a complementary base pair interaction with the codon in mRNA DHU and T\C arms = May play a role in binding of the tRNA to the ribosome
How many different codons specify the amino acid leucine?
6
The genetic code is composed of 64 codons that specify the 20 standard amino acids.
False
What is the function of termination codons in protein synthesis?
To signal the termination of translation
What percentage of total cellular RNA does mRNA account for in E. coli?
3%
The genetic code is overlapping.
False
What is the function of tRNA during protein synthesis?
binds and carries amino acids to the ribosome
RRNA, together with several _______________, constitute the ribosome.
proteins
Match the type of RNA with its function:
mRNA = specifies the amino acid sequence during protein synthesis tRNA = binds and carries amino acids to the ribosome rRNA = constitute the ribosome together with several proteins small RNA = involved in processing of the above RNA molecules
What is the function of the codon AUG in the genetic code?
Specifies methionine and initiates translation
In prokaryotes, all AUG codons encode a modified methionine residue called formyl-methionine.
False
Why is mRNA generally more unstable than tRNA and rRNA?
because mRNA is rapidly degraded after translation
What is the sugar unit present in RNA?
D-Ribose
The nitrogenous base Thymine is found in RNA instead of Uracil in DNA.
False
What is the type of bond that connects the nucleotides in RNA?
3'-5' phosphodiester bonds
The number of nucleotides in RNA can range from as few as _______ to many thousands.
seventy five
Match the following nitrogenous bases with their correct pairing partners:
Adenine = 1. Adenine Uracil = 2. Uracil Cytosine = 3. Cytosine Guanine = 4. Guanine
What is the primary difference between the sugar unit in RNA and DNA?
RNA has a 2'-hydroxyl group, while DNA does not
The molecular structure of RNA is identical to DNA.
False
What is the name of the type of bond that connects the ribonucleotide residues in a RNA strand?
3'-5' phosphodiester linkages
What is the role of IF-2 in the initiation of prokaryotic translation?
Recognizing and transporting the initiator tRNA to the 30S subunit
The 30S subunit binds to mRNA in a non-specific manner.
False
What is the purpose of translational regulation?
To control gene expression and cellular protein levels
The Shine-Dalgarno sequence is located near the ______________ end of mRNA.
5’
During which phases of protein synthesis can translational regulation occur?
During initiation, elongation, or termination
In prokaryotes, the synthesis of ribosomal proteins is uncoupled from the rate of ribosome assembly.
False
The ______________ site is where the AUG initiation codon is positioned in the 30S subunit.
P (peptidyl)
Match the following components with their roles in prokaryotic translation initiation:
IF-2 = Recognizing and transporting the initiator tRNA IF-3 = Assisting with the specificity of mRNA binding Shine-Dalgarno sequence = Forming a complementary base pair interaction with 16S RNA GTP = Hydrolyzed to release IF-2-GDP and Pi
Study Notes
Structure of RNA
- RNA is a long, unbranched macromolecule consisting of nucleotides joined by 3'-5' phosphodiester bonds.
- The number of nucleotides in RNA ranges from as few as 75 to many thousands.
- RNA differs from DNA in two ways:
- The sugar unit in RNA is D-Ribose, which contains a 2'-hydroxyl group not present in deoxyribose.
- Uracil is found in RNA instead of thymine, which is present in DNA.
Types of RNA
- There are several types of RNA, including:
- tRNA (transfer RNA): interprets the genetic code and is the crucial link between the genetic code in mRNA and the sequence of amino acids in a protein.
- rRNA (ribosomal RNA): constitutes the ribosome, together with several proteins, and is involved in protein synthesis.
- mRNA (messenger RNA): specifies the amino acid sequence during protein synthesis.
- Small RNA molecules: have catalytic activity and are involved in processing the above RNA molecules.
tRNA Structure and Function
- tRNA molecules are approximately 73-93 nucleotides long.
- The secondary structure of tRNA resembles a clover-leaf, with stem and loop formations due to self-complementary intrachain base pairing.
- tRNA contains unusual bases, such as dihydrouridine and pseudouridine.
- The amino acid arm (at the 3' end) serves as the point for amino acid attachment and subsequent transport to the ribosome.
- The anticodon loop contains the anticodon, which forms a complementary base pair interaction with the codon in mRNA.
Translation in Prokaryotes
- The translation process contains three distinct phases: initiation, elongation, and termination.
- Initiation requires:
- mRNA to be translated
- 30S and 50S ribosome subunits
- Aminoacyl-tRNA molecules
- Accessory proteins (initiation, elongation, and release/termination factors)
- Initiation factors 1 and 3 bind to the 30S ribosome subunit, with IF-3 preventing premature association with the 50S subunit.
Aminoacyl-tRNA Synthetases
- A specific amino acid is esterified to the 3' end of a correct tRNA molecule, forming an aminoacyl-tRNA molecule.
- Aminoacyl-tRNA is a high-energy molecule, with the attached amino acid "activated" for incorporation into a polypeptide.
- Aminoacyl-tRNA synthetases have an error-checking function and rapidly correct errors.
Genetic Code
- The genetic code refers to the triplet base sequences in mRNA (or DNA) that specify the amino acids to be incorporated into a protein.
- The genetic code contains all the information for initiating translation, specifying amino acid sequence, terminating translation, and releasing the nascent protein.
- The genetic code is non-overlapping and made up of 64 codons.
Regulation of Translation
- Translational regulation is essential in controlling gene expression and provides a means of controlling cellular protein levels.
- Regulation of translation can be achieved during the initiation, elongation, or termination phases of protein synthesis.
This quiz covers the structure and function of transfer RNA (tRNA), including its role in protein synthesis and the recognition of codons encoding amino acids. Learn about the importance of modified bases and the action of aminoacyl-tRNA synthetases.
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