Quiz Translation and Protein Analysis

Comprehensive practice flashcards based on the translation and molecular protein analysis quiz lecture.

What is the main purpose of translation in cells?

To convert mRNA into a protein.

Where does translation occur in eukaryotic cells?

In the rough endoplasmic reticulum and cytoplasm.

Which molecule carries amino acids to the ribosome?

tRNA

What is the start codon in most organisms?

AUG

What enzyme attaches an amino acid to its corresponding tRNA?

Aminoacyl-tRNA synthetase

What occurs at the A site of the ribosome?

The new incoming tRNA enters.

During elongation, peptide bonds are formed by which catalytic enzyme?

Peptidyl transferase

When can translation begin in prokaryotes?

While transcription is still occurring.

What are the two binding sites of aminoacyl-tRNA synthetase?

One for an amino acid and one for tRNA.

If a tRNA carries the anticodon $3'\text{-UAC-}5'$, what codon does it pair with?

$$5'\text{-AUG-}3'$$

What is "wobbling" in codon-anticodon pairing?

The third base of a codon can pair flexibly with multiple anticodons.

What do aminoacyl-tRNA synthetases use ATP for?

To form a high-energy bond between the amino acid and tRNA.

What is the intermediate formed during the tRNA charging reaction?

Aminoacyl-AMP

What happens if aminoacyl-tRNA synthetase loses its proofreading function?

Misincorporation of amino acids increases.

Which statement is true about isoacceptor tRNAs?

They carry the same amino acid but have different anticodons.

Where is the Shine–Dalgarno sequence found?

In prokaryotic mRNA upstream of the start codon.

What is the first step in prokaryotic translation initiation?

The small subunit binds to the mRNA.

Which initiation factor in eukaryotes binds the $5'$ cap of mRNA?

eIF4E

Which event triggers the joining of the large ribosomal subunit?

Release of initiation factors and GTP hydrolysis.

During elongation, which site of the ribosome receives the incoming aminoacyl-tRNA?

The A site

Which elongation factor delivers aminoacyl-tRNA to the ribosome in prokaryotes?

EF-Tu

In eukaryotes, how does the ribosome recognize the mRNA?

Via the Kozak sequence and $5'$ cap structure.

What is the main function of the Signal Recognition Particle (SRP)?

To recognize and target proteins to the endoplasmic reticulum.

What happens when SRP binds to the signal sequence on a growing polypeptide?

Translation temporarily pauses.

Where does the SRP direct the ribosome–nascent chain complex?

Endoplasmic reticulum

What is the main purpose of mRNA decay?

To regulate gene expression and remove defective transcripts.

What does nonsense-mediated decay (NMD) target?

mRNAs with premature stop codons.

Which cellular compartment is most involved in the glycosylation of proteins?

ER + Golgi apparatus

What is the addition of phosphate groups to serine, threonine, or tyrosine residues known as?

Phosphorylation

What is the cellular function of poly-ubiquitination?

Marks proteins for degradation in the proteasome.

What is "codon optimization"?

Modifying DNA codons to match the preferred usage of the host organism.

Why is codon optimization used in recombinant protein expression?

To improve translation efficiency and protein yield.

What is the main reason codon bias exists among organisms?

Variation in tRNA abundance.

Which problem can occur if codon usage is not optimized for the host organism?

Slow translation or ribosome stalling.

What is the main function of an internal ribosome entry site (IRES)?

It allows ribosomes to initiate translation internally on mRNA, independent of the $5'$ cap.

Why are IRES sequences useful in molecular biology?

To allow expression of multiple proteins from a single mRNA.

How does a 2A peptide function?

It induces ribosome skipping, resulting in the production of two separate proteins from one mRNA.

What is a key advantage of 2A peptides over IRES for polycistronic expression?

2A peptides produce relatively stoichiometric amounts of proteins.

What is a potential consideration when designing a polycistronic vector using 2A peptides?

The 2A peptide sequence may leave a few extra amino acids at the C-terminus of the upstream protein.

What is cell-free protein synthesis (CFPS)?

Protein synthesis in vitro using cellular extracts, without living cells.

What components are typically included in a cell-free protein synthesis (CFPS) system?

DNA or mRNA template, ribosomes, tRNAs, amino acids, energy source, and cofactors.

Which modern biotechnology procedure is an application of CFPS?

On-demand synthesis of vaccines.

What is the main purpose of immunofluorescence in protein studies?

To visualize the location and expression of specific proteins.

How can immunofluorescence detect post-translational modifications (PTMs) on proteins?

By using antibodies specific to modified residues.

What are three key applications of immunofluorescence (IF) for proteins?

Protein localization, protein-protein interaction studies (via co-localization), and detecting post-translational modifications.

What is the primary purpose of Western blotting?

To detect and quantify specific proteins.

How are proteins separated in Western blotting?

By size using SDS-PAGE.

What is the purpose of SDS in SDS-PAGE?

To give proteins a uniform negative charge and denature them.

In Western blotting, which antibody binds directly to the target protein?

Primary Antibody

What is a loading control in Western blotting?

A standard protein used to normalize sample amounts.

What is the main purpose of immunoprecipitation (IP)?

To isolate a specific protein from a mixture.

What is the primary difference between IP and Co-IP?

IP isolates a single protein; Co-IP identifies interacting proteins.

What is a common method to analyze proteins after IP or Co-IP?

WB (Western blotting)

What does ChIP primarily study?

Protein-DNA interactions

Why is formaldehyde used in ChIP?

To crosslink proteins to DNA.

What is the advantage of ChIP-seq over ChIP-PCR?

It identifies binding sites across the entire genome.