Protein Synthesis and Gene Expression

Comprehensive practice questions covering protein synthesis, including transcription, RNA processing, translation, and proteomics based on lecture notes.

According to the VCAA Key Knowledge, what are the characteristics of the genetic code?

It is a universal triplet code that is degenerate.

What are the two main steps involved in gene expression or protein synthesis?

1. Transcription and 2. Translation.

Where does the process of transcription occur within the cell?

In the nucleus.

What is the primary function of transcription?

Copying the DNA code to make a single stranded mRNA molecule.

Where does translation occur?

In the ribosome.

Why must the process of transcription take place in the nucleus?

Because DNA cannot leave the nucleus and ribosomes cannot enter the nucleus.

What is the definition of a gene in the context of protein synthesis?

A segment of DNA that codes for a specific protein.

What role does tRNA play in the ribosome during translation?

It translates mRNA and leaves an amino acid behind to make a polypeptide.

What is a gene sequence?

The correct order of the nucleotide sequence.

Which specific enzyme is required to synthesize mRNA during transcription?

RNA Polymerase.

What occurs during the initiation step of transcription?

Initiation factors (proteins) bind to the DNA strand to ‘switch on’ the gene.

What happens during the binding step of transcription?

RNA polymerase binds to the promoter region of the template strand.

What is produced during the elongation phase of transcription?

Preliminary-RNA (pre-RNA).

Which strand is also referred to as the coding strand or non-template strand?

The Sense strand.

Which strand is referred to as the template strand or non-coding strand?

The Antisense strand.

The Sense strand has the same code as which molecule?

mRNA.

The Antisense strand has the same code as which molecule?

tRNA.

In which direction does transcription move on the template (Antisense) strand?

Upstream, which is $3' ightarrow 5'$.

In which direction is mRNA synthesized?

Downstream, which is $5' ightarrow 3'$.

What are the four components of RNA processing in eukaryotic cells?

1. Capping, 2. Poly-A tail, 3. Introns removed, and 4. Exons spliced.

What is added during the capping phase of RNA processing?

A methylated cap is added at the $5'$ end.

What is a Poly-A tail?

A string of adenine nucleotides added at the $3'$ end of pre-RNA.

What is the difference between introns and exons?

Introns are the non-protein coding part ('intrusions'), while exons are the protein coding part.

What is the result of alternative pre-RNA processing (exon juggling)?

One gene can produce more than one protein by creating different mRNA sequences.

How does mRNA exit the nucleus to reach a ribosome?

Via a nuclear pore.

Where can ribosomes be located for translation to occur?

Either on the rough ER or free-floating in the cytosol.

What are the two main parts of a tRNA molecule?

An amino acid and an anticodon.

What is an anticodon?

Three complementary bases to the triplet base (codon) of the mRNA.

What is the designated START codon and what amino acid does it code for?

$AUG$, which codes for methionine (MET).

What is the function of a STOP codon?

It stops the translation process for a specific protein, acting like a 'full stop'.

Name the three specific STOP codons mentioned in the notes.

$UGA$, $UAA$, and $UAG$.

Why is the genetic code considered 'degenerate'?

Different triplet base pairs (codons) can code for the same amino acid.

What is the biological advantage of a degenerate genetic code?

It provides a 'margin of error' to minimize the effects of mistakes like point mutations during transcription.

Why is the DNA code referred to as 'universal'?

Every known living organism uses the same system of transcribing DNA to RNA and translating RNA into proteins.

What is a triplet code?

A code where each codon consists of three non-overlapping nucleotides.

Give an example of degeneracy using the amino acid lysine.

Both $AAA$ and $AAG$ code for lysine.

What is the definition of a proteome?

The totality of proteins expressed within a cell, tissue, or organism at a certain time.

What is proteomics?

The study of the proteome.

Why is the proteome of an individual unique?

Because protein expression patterns are determined by an individual’s unique genes.

Why is the proteome significantly larger than the genome?

Due to alternate RNA splicing (one gene producing multiple proteins) and post-translational modification.