3.4.2 DNA and Protein Synthesis

Question 1

Q: What is the genome?

Answer 1

A: The genome is the complete set of genes in a cell.

Question 2

Q: What is the proteome?

Answer 2

A: The proteome is the full range of proteins that a cell is able to produce.

Question 3

Q: Describe the structure of messenger RNA (mRNA).

Answer 3

A: mRNA is a single-stranded molecule that carries genetic information from DNA to the ribosomes. It has a ribose sugar, a phosphate group, and four nitrogenous bases (adenine, uracil, cytosine, guanine).

Question 4

Q: Describe the structure of transfer RNA (tRNA).

Answer 4

A: tRNA is a single-stranded molecule that folds into a cloverleaf shape. It has an anticodon at one end that pairs with mRNA codons and an amino acid binding site at the other end.

Question 5

Q: What is transcription in prokaryotes?

Answer 5

A: Transcription in prokaryotes involves the direct production of mRNA from DNA. RNA polymerase binds to the DNA and synthesizes mRNA by joining nucleotides together.

Question 6

Q: How does transcription differ in eukaryotes compared to prokaryotes?

Answer 6

A: In eukaryotes, transcription produces pre-mRNA, which undergoes splicing to remove introns, resulting in mature mRNA.

Question 7

Q: What is the role of RNA polymerase in transcription?

Answer 7

A: RNA polymerase catalyzes the formation of mRNA by joining RNA nucleotides together, using the DNA strand as a template.

Question 8

Q: What happens during the splicing of pre-mRNA in eukaryotes?

Answer 8

A: Splicing removes non-coding regions called introns from pre-mRNA, leaving only exons, which are coding regions. This process produces mature mRNA ready for translation.

Question 9

Q: What is translation?

Answer 9

A: Translation is the process by which ribosomes synthesize polypeptides using the sequence of codons on mRNA.

Question 10

Q: What role do ribosomes play in translation?

Answer 10

A: Ribosomes facilitate the assembly of amino acids into polypeptides by matching tRNA anticodons with mRNA codons.

Question 11

Q: What role does tRNA play in translation?

Answer 11

A: tRNA carries specific amino acids to the ribosome, matching its anticodon to the mRNA codon, ensuring the correct amino acid sequence in the polypeptide.

Question 12

Q: What is the role of ATP in translation?

Answer 12

A: ATP provides energy for the attachment of amino acids to tRNA and for the formation of peptide bonds between amino acids during protein synthesis.

Question 13

Q: How do codons relate to amino acids in translation?

Answer 13

A: Each codon on mRNA corresponds to a specific amino acid. The sequence of codons determines the sequence of amino acids in a polypeptide.

Question 14

Q: How is the base sequence of nucleic acids related to the amino acid sequence of polypeptides?

Answer 14

A: The sequence of bases in DNA determines the sequence of codons in mRNA, which in turn determines the sequence of amino acids in the resulting polypeptide.

Question 15

Q: How can experimental data be used to investigate the role of nucleic acids?

Answer 15

A: Experimental data can show how changes in nucleic acid sequences (mutations) affect the structure and function of proteins, illustrating the link between genes and traits.

Question 16

Explain the process by which a gene in eukaryotic cells is transcribed into mRNA, including the role of RNA polymerase. (6 marks)

Answer 16

Marking Points:

Initiation: RNA polymerase binds to the promoter region of the DNA, signaling the start of transcription.
Unwinding: The DNA strands separate, exposing the template strand for RNA synthesis.
Complementary Base Pairing: RNA polymerase aligns RNA nucleotides with their complementary DNA bases (A-U, T-A, C-G, G-C).
Elongation: RNA polymerase joins the RNA nucleotides together, forming a pre-mRNA strand.
Termination: RNA polymerase reaches a terminator sequence, and the newly formed pre-mRNA detaches.
Splicing: In eukaryotes, introns are removed from pre-mRNA, and exons are joined together to form mature mRNA.

Question 17

Describe how the sequence of nucleotides in a gene determines the sequence of amino acids in a polypeptide. (5 marks)

Answer 17

Marking Points:

Codon Definition: A triplet of nucleotide bases (codon) in mRNA codes for a specific amino acid.
Transcription: DNA sequence is transcribed into mRNA.
mRNA Role: mRNA leaves the nucleus and attaches to ribosomes in the cytoplasm.
tRNA Function: Each tRNA molecule with an anticodon brings the corresponding amino acid to the ribosome.
Peptide Bond Formation: Amino acids are joined by peptide bonds in the order specified by the mRNA codons.

Question 18

Using the genetic code provided, identify the sequence of amino acids coded for by a given mRNA sequence. (4 marks)

Answer 18

Marking Points:

Identify Codons: Break the mRNA sequence into codons (groups of three nucleotides).
Match Codons to Amino Acids: Use the genetic code table to find the corresponding amino acid for each codon.
Sequence Formation: Write down the sequence of amino acids.
Check for Start/Stop Codons: Include any start codon (e.g., AUG for methionine) and stop codon recognition if present.

Question 19

Explain how the structure of tRNA is related to its function in translation. (4 marks)

Answer 19

Marking Points:

Anticodon Loop: The tRNA has an anticodon loop that pairs with complementary codon on mRNA.
Amino Acid Binding Site: The opposite end of the tRNA carries a specific amino acid corresponding to the anticodon.
Cloverleaf Structure: The cloverleaf shape allows tRNA to fit into the ribosome during translation.
tRNA Activation: Enzymes attach the correct amino acid to the tRNA based on its anticodon.

Question 20

Describe the impact of a point mutation in a gene on the structure of a protein. (4 marks)

Answer 20

Marking Points:

Change in Codon: A point mutation alters one nucleotide in the DNA sequence.
Altered mRNA: The change in DNA is transcribed into a different mRNA codon.
Different Amino Acid: The altered codon may code for a different amino acid, changing the polypeptide chain.
Protein Function: The change in the amino acid sequence can affect the protein’s folding and function, possibly leading to a non-functional protein.

Question 21

Discuss how a mutation might lead to a non-functional enzyme. (5 marks)

Answer 21

Marking Points:

Altered Active Site: A mutation can cause a change in the amino acid sequence that forms the enzyme’s active site.
Substrate Binding: If the active site shape is altered, the substrate may no longer fit, preventing enzyme-substrate complex formation.
Loss of Catalytic Activity: The enzyme may lose its ability to catalyze the reaction due to structural changes.
Protein Misfolding: Mutations can lead to improper folding of the enzyme, making it unstable or non-functional.
Impact on Metabolism: The loss of enzyme function can disrupt metabolic pathways, potentially leading to disease.