Chapter 7: Genes and Protein Synthesis

Question 1

Central Dogma of Molecular Genetics

Answer 1

It states that:

• DNA is transcribed into complementary messenger RNA (mRNA).
• The mRNA is then translated by ribosomes into a specific sequence of amino acids.
• These amino acids are linked together to form a protein, which carries out various functions in the cell.

Dogma definition “a principle or set of principles laid down by an authority as incontrovertibly true”

Question 2

Error during transcription:

Poly-A Tail Error

example

Answer 2

• What it does: The poly-A tail protects the mRNA and helps it leave the nucleus.
• Error effect: Without the poly-A tail, the mRNA could break down too quickly or might not get properly used, leading to no protein being made or an incomplete protein.

Question 3

Error during transcription:

Spliceosome Error

example

Answer 3

• What it does: The spliceosome removes non-coding parts (introns) from the mRNA.
• Error effect: If the spliceosome doesn’t remove these parts properly, extra non-coding sections could stay in the mRNA. This can confuse the cell and mess up the protein it makes.

Question 4

Error during Transcription:

RNA Polymerase Error

example

Answer 4

• What it does: RNA polymerase makes the mRNA by copying the DNA.
• Error effect: If RNA polymerase adds, skips, or deletes wrong bases, it can cause:
  
  • Frameshift mutations: This changes the reading of the mRNA, causing the wrong protein to be made.
  • Missense mutations: A wrong base could change one amino acid in the protein, possibly making it less effective.
  • Nonsense mutations: A mistake might create a stop signal too early, cutting the protein short and making it useless.

Question 5

Silent Mutations

Answer 5

• What it does: A silent mutation doesn’t change the protein, even though the DNA has changed.
• Error effect: Even though the DNA is altered, the protein stays the same, so there’s no problem.

Question 6

Error during transcription:

Substitution

Answer 6

• Effect on Transcription:
  
  • If nucleotides are added or deleted in a way that shifts the reading frame of the mRNA, the entire sequence of amino acids after the mutation could be altered, often producing a nonfunctional protein.

Includes:
- Missense: amino acid is swapped for another
- Nonsense: amino acid is swapper for a stop codon
- Silent mutation: amino acid is altered but codes for same amino acid

Question 7

Effect on transcription:

Missense

Answer 7

• Missense Mutation:
  - Effect: If a wrong nucleotide is incorporated, it could change a codon in the mRNA, leading to the incorporation of the wrong amino acid in the protein during translation.

Question 8

Effect on transcription

Insertion or deletion

Answer 8

• Effect on Transcription:
  
  • Insertion: Adds an extra base to the DNA sequence.
  • Deletion: Removes a base or group of bases.
  • Both of these changes shift the reading frame, which alters the entire sequence of amino acids in the protein. This is called a frameshift mutation and it often leads to a nonfunctional protein.

Question 9

Effect on transcription:

Frameshift

Answer 9

• Effect:
  
  • If nucleotides are added or deleted in a way that shifts the reading frame of the mRNA, the entire sequence of amino acids after the mutation could be altered, often producing a nonfunctional protein.

Result of insertion or deletion

Question 10

Codons

what do they represent? Explain the wobble hypothesis

Answer 10

• Codons: Codons are sequences of 3 bases (nucleotides) in mRNA that represent specific amino acids.
• Function: Each codon codes for a specific amino acid, helping to build proteins in the ribosome.
• Wobble Hypothesis:
  
  • The third base of a codon can often vary without changing the amino acid it codes for.
  • This allows flexibility in the genetic code, so some codons with different third bases can still code for the same amino acid.

Question 11

Start and stop codons

what is their significance?

Answer 11

• A start codon signals when translation should begin
• a stop codon signals when translation should stop.

Question 12

Lac operon

Answer 12

• the lac operon is an inducer.
• When lactase is present it acts as a signal molecule so when it binds to the repressor it deactivates it and allows for the transcription of the enzyme necessary to digest lactase.

Question 13

Trp operon

Answer 13

the trp operon is a repressor, the cell always produces trp but when its present in the environment it does not need to, tryptophan will act as a signal molecule and activate the repressor stopping the transcription of tryptophan.

Question 14

Effect on transcription

Nonsense

Answer 14

An error could lead to the formation of a premature stop codon in the mRNA, resulting in an incomplete protein that is usually nonfunctional

Question 15

What happens during translation?

Answer 15

Translation (RNA to Protein):
1. Initiation:
- The mRNA binds to the ribosome, and the ribosome identifies the start codon (AUG).
- The first tRNA carrying the corresponding amino acid binds to the start codon.

2. Elongation:
   
   • The ribosome moves along the mRNA, reading each codon.
   • tRNA molecules bring the correct amino acids, which are linked together by peptide bonds, forming a growing polypeptide chain.
3. Termination:
   
   • When the ribosome reaches a stop codon (UAA, UAG, or UGA), the translation process stops.
   • The polypeptide chain is released and folds into its functional protein form.

Question 16

What happens during transcription?

Answer 16

Transcription (DNA to RNA):
1. Initiation:
- The enzyme RNA polymerase binds to the promoter region of the DNA and separates the DNA strands.

2. Elongation:
   
   • RNA polymerase reads the template strand of DNA and synthesizes a complementary mRNA strand in the 5’ to 3’ direction.
3. Termination:
   
   • Once the RNA polymerase reaches a termination signal, it detaches from the DNA, and the newly formed mRNA strand is released.