Extended Response Answers

Module 1 -
Short answer questions

Please answer these questions BEFORE looking at the perfected answers

  1. What is the process that copies a DNA gene in to a complimentary RNA copy? Describe the steps occurring in this process. (2 marks)

    “Transcription. It begins when RNA polymerase binds to the promoter region, and moves along the template strand (3′ to 5′), adding free RNA nucleotides and joining them together. This forms a pre-mRNA sequence, and the process stops once the RNA polymerase reaches the terminator sequence.”

    Marks:

        • 1 mark = identifying the name of the process (transcription)
        • 1 mark = briefly outlining the steps involved.  (use the terms: RNA polymerase, promoter, terminator, and state that it forms a new mRNA strand)

           

2. Describe the steps occurring at the ribosome that results in the formation of a polypeptide. (3 marks)

“The mRNA binds to the ribosome at the 5′ end. The ribosome moves along the mRNA strand 5′ to 3′ until it reaches a start codon. The appropriate tRNA will carry the specific amino acid to the site. The tRNA anticodon will bind to the complimentary mRNA codon, causing peptide bonds to form between adjacent amino acids. This process continues, synthesising a polypeptide chain, until a stop codon is reached. This causes the polypeptide to detach.”

Marks:

        • 1 mark = start codon initiates translation
        • 1 mark = explain complementarity of tRNA anticodon and mRNA codon
        • 1 mark = talk about peptide bonds forming between amino acids

 

3. How does tRNA play a role in the production of the protein hormone insulin? (2 marks)

“Each tRNA molecule has an anticodon that is complimentary to a certain codon. Each tRNA will carry a specific amino acid to the ribosome, and the tRNA anticodon will bind to the mRNA codon, causing peptide bonds to form between adjacent amino acids. This forms a polypeptide chain, which will later fold to form the protein insulin.”

Marks:

            • 1 mark = carries specific amino acid (coded by the mRNA sequence)
            • 1 mark = the tRNA anticodon binding to the mRNA codon causes adjacent amino acids to join

4. Explain the difference between the primary and secondary structure of a protein? (2 marks)

“The primary structure of a protein consists of the specific sequence of amino acids within the poly peptide chain. The secondary structures describe the locally folded structures such as alpha helices and beta pleated sheets.

Marks:

            • 1 mark = use the word “specific” when describing the primary structure
            • 1 mark = secondary structure includes alpha helices and beta pleated sheets

               

5. Describe what is meant by tertiary and quaternary protein structure. (2 marks)

“The tertiary structure is the overall 3-dimensional folded structure of the protein. Some proteins have a quaternary structure, which is more than one folded polypeptide joined together to form a functioning protein.

            • 1 mark = tertiary structure is the 3-dimensional folded structure
            • 1 mark = quaternary structure is more than one polypeptide

               

6. After transcription occurs, the molecule produced is not able to leave the nucleus at first. Explain the process it must undergo before it can leave the nucleus and travel to the ribosome. (2 marks)

“The pre-mRNA produced during transcription must undergo post-transcriptional modifications. This includes removing the non-coding regions of the gene via intron splicing, adding a 5′ methyl cap and a 3′ poly A tail.”

Marks:

            • 1 mark = state that it must undergo RNA processing or post-transcriptional modifications
            • 1 mark = explain what these processes are (mention that introns are non-coding regions)

               

7. In some cases, the same proteins can be coded for by different DNA sequences. Explain how this is possible. (2 marks) 

“The pre-mRNA produced during transcription must undergo post-transcriptional modifications. This includes removing the non-coding regions of the gene via intron splicing, adding a 5′ methyl cap and a 3′ poly A tail.”

Marks:

            • 1 mark = state that it must undergo RNA processing or post-transcriptional modifications
            • 1 mark = explain what these processes are (mention that introns are non-coding regions)

               

8. B cells produce vast amounts of proteins called antibodies and release them into the blood. B cells have unusually large areas of certain organelles within the cell. Name two of these organelles, and explain why they are present in such large areas? (2 marks)

“As the primary function of B cells is to produce and secrete proteins, they would have large areas of organelles involved in the protein secretory pathway, such as the rough endoplasmic reticulum and the Golgi apparatus.”

Marks: 

1 mark = the B cell is secreting a large quantity of protein
1 mark = requires organelles involved in the protein secretory pathway (ribosomes, rough endoplasmic reticulum or Golgi apparatus)

 

9. Explain the difference between structural and regulatory genes (2 marks)

“Regulatory genes code for proteins that control the expression of structural genes. Structural genes code for all other proteins excluding regulatory proteins.”

Marks: 

          • 1 mark = Regulatory genes code for proteins that control the expression of other genes
          • 1 mark = structural genes include all other genes.

10. The trp operon is controlled by a repressor protein. Explain what would happen in terms of gene expression, if tryptophan was present within the cell. Why is this beneficial to the cell? (2 marks)

“Due to the presence of tryptophan, it will bind to the repressor, causing it to bind to the operator region of the trp operon. Therefore RNA polymerase will not be able to transcribe the genes, and so they will not be expressed into functioning proteins. As tryptophan is already present, it does not need to be produced. This conserves energy.

Marks: 

              • 1 mark = tryptophan binds to repressor protein, causing it to bind to operator region
              • 1 mark = This means RNA polymerase cannot transcribe the gene. (The gene will not be expressed), conserving energy

 

11. The trp operon is controlled by a repressor protein. Explain whether the trp operon would be expressed if tryptophan was absent.  (2marks)

“If tryptophan is absent, the repressor protein will detach from the operator of the trp operon,  allowing RNA polymerase to transcribe the genes. After transcription, translation will occur to form functioning proteins, leading to the production of tryptophan.”

Marks:

              • 1 mark = No tryptophan, so repressor protein detaches from operator region
              • 1 mark = RNA polymerase can transcribe the genes. (expression of tryptophan occurs)

 

 

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