D1.2 Protein Synthesis

What is transcription?

The process of copying a DNA gene sequence into mRNA.

Where does RNA polymerase bind to begin transcription?

It binds to the promoter region of the DNA.

What is the role of the template strand in transcription?

It is the DNA strand that RNA polymerase uses to create a complementary RNA sequence.

Which RNA bases pair with the DNA bases A, T, C, and G?

A pairs with U, T pairs with A, C pairs with G, and G pairs with C.

When does the process of transcription end?

It ends when RNA polymerase reaches a termination sequence, and the RNA is released.

How does the RNA sequence compare to the DNA coding strand?

It is identical to the coding strand, except U replaces T.

Why is the DNA double helix chemically stable during transcription?

The double helix reforms quickly after RNA polymerase passes, and hydrogen bonding maintains base pairing.

What is the role of repair enzymes in DNA templates?

They correct damage to preserve the genetic sequence.

Why are the sugar-phosphate backbone and DNA bases resistant to breakdown?

They are chemically stable and supported by strong bonding.

What must happen to hydrogen bonds for RNA synthesis to occur?

They must be broken to allow the DNA strands to separate.

How do C-G bonds affect DNA stability compared to A-T bonds?

More C-G bonds result in higher DNA stability because they share three hydrogen bonds.

What is a common mistake when writing RNA sequences?

Writing "A-T" instead of "A-U".

What determines if a gene is expressed (switched on/off)?

The cell type and the environment.

What is a transcriptome?

The set of all RNAs present in a cell at a given time.

What is translation?

The process of decoding mRNA into a polypeptide chain.

Where does translation occur?

On ribosomes in the cytoplasm.

What is the start codon that initiates translation?

AUG (which codes for methionine).

What are the three stop codons?

UAA, UAG, and UGA.

What molecules bring amino acids to the ribosome?

tRNA (transfer RNA).

What are the three stages of translation?

Initiation, elongation, and termination.

What is the role of the small subunit of the ribosome?

It binds to the mRNA strand.

What is the role of the large subunit of the ribosome?

It forms peptide bonds between amino acids.

What are the three sites within a ribosome?

A (arrival), P (polypeptide), and E (exit).

What ensures the correct amino acid is added to the growing chain?

Complementary base pairing between the mRNA codon and the tRNA anticodon.

In which direction does the ribosome move along the mRNA?

In a unidirectional 5' to 3' direction.

Why is the genetic code described as "universal"?

Because it is the same in nearly all organisms.

What does it mean that the genetic code is "degenerate"?

Multiple different codons can code for the same amino acid.

What does "non-overlapping" mean in the genetic code?

Codons are read sequentially, one after another.

How do you find an amino acid using a genetic code table?

Find the 1st base (left), 2nd base (top), and 3rd base (right).

What is a silent point substitution?

A mutation where a base change does not result in a change to the amino acid.

What is a missense mutation?

A mutation that results in a different amino acid being added to the polypeptide.

What is a nonsense mutation?

A mutation that creates a premature stop codon.

How do insertions or deletions cause frameshift mutations?

By adding or removing bases in numbers not divisible by 3, altering all downstream codons.

What determines the severity of a mutation's effect?

Its position (active site vs. flexible loop) and the chemistry change (e.g., hydrophobic to hydrophilic).

What specific mutation causes Sickle-cell anemia?

A Glu to Val substitution in the beta-globin chain, changing hemoglobin interactions and RBC shape

Globular protein

round, functional, irregular amino acid sequence, sensitive to pH and temperature, e.g. enzymes, soluable in water generally

Fibrous protein

long, narrow, structural, repetitive amino acid sequence, less sensitive to pH and temperature, e.g. keratin, collagen, insoluable in water generally

Polysome/ polyribosome

A polysome (or polyribosome) is a group of two or more ribosomes translating the same mRNA molecule simultaneously.

How come condensation releases water? (between 2 amino acids)

when a peptide bond forms between 2 amino acids, the H of the amine group is lost and the OH of the carboxyl group is lost so together it makes water