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BIOLOGY, M5 2024 HSC 30

The diagram shows a simplified version of the process of polypeptide synthesis.
 

  1. Compare Process \(A\) with DNA replication.   (3 marks)
  1. Explain the importance of mRNA and tRNA in polypeptide synthesis.   (5 marks)

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a.   Process \(A\) vs DNA replication:

→ Both DNA replication and transcription (Process \(A\)) begin with unwinding the DNA double helix.

→ DNA replication’s goal is to create two identical DNA molecules, with each containing one original and one new strand.

→ In contrast, transcription copies just one DNA strand to produce a single mRNA strand.
 

b.   mRNA and tRNA’s role in polypeptide synthesis:

→ mRNA is created in the nucleus by copying a DNA template during transcription.

→ This mRNA molecule serves as a messenger, carrying genetic instructions (in the form of codons) from the nucleus out to ribosomes in the cytoplasm.

→ At the ribosome, translation kicks in – this is where the genetic code gets converted into protein.

→ tRNA molecules are key players here – each has an anticodon that matches up with specific codons on the mRNA strand.

→ The process flows like an assembly line: mRNA codons are read in sequence, tRNA molecules bring in matching amino acids, and these amino acids are linked together to form a polypeptide chain.

Show Worked Solution

a.   Process \(A\) vs DNA replication:

→ Both DNA replication and transcription (Process \(A\)) begin with unwinding the DNA double helix.

→ DNA replication’s goal is to create two identical DNA molecules, with each containing one original and one new strand.

→ In contrast, transcription copies just one DNA strand to produce a single mRNA strand.
 

b.   mRNA and tRNA’s role in polypeptide synthesis:

→ mRNA is created in the nucleus by copying a DNA template during transcription.

→ This mRNA molecule serves as a messenger, carrying genetic instructions (in the form of codons) from the nucleus out to ribosomes in the cytoplasm.

→ At the ribosome, translation kicks in – this is where the genetic code gets converted into protein.

→ tRNA molecules are key players here – each has an anticodon that matches up with specific codons on the mRNA strand.

→ The process flows like an assembly line: mRNA codons are read in sequence, tRNA molecules bring in matching amino acids, and these amino acids are linked together to form a polypeptide chain.

♦ Mean mark (b) 60%.

BIOLOGY, M6 2023 HSC 35

5-Bromouracil (bU) is a synthetic chemical mutagen. It bonds with adenine in place of thymine in DNA. During replication, it then binds with guanine.

This will then make a guanine-cytosine pair on one strand of DNA instead of an adenine-thymine pair.
 

  1. Identify the type of mutation that is caused by bU.  (1 mark)

  2. Describe the possible effects on a protein if this mutation occurred within a gene.  (4 marks)

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a.   Point mutation or substitution mutation

b.   Protein effects if mutation within gene:

→ If this mutation occurred within coding DNA, then the RNA produced would be G–C instead of A–T (depending on the strand).

→ As a result, when it is read by a ribosome a different codon will be read, which may or may not code for the same amino-acid.

→ If the mutation codes for a different amino-acid, a different polypeptide chain will form. 

→ This mutation process could cause the protein to fold differently which can alter it’s function or render it completely dysfunctional.

→ Alternatively, the new codon could also be interpreted as a stop codon, pre-emptively stopping production of the rest of the polypeptide chain. 

Show Worked Solution

a.   Point mutation or substitution mutation
 

b.   Protein effects if mutation within gene:

→ If this mutation occurred within coding DNA, then the RNA produced would be G-C instead of A-T (depending on the strand).

→ As a result, when it is read by a ribosome a different codon will be read, which may or may not code for the same amino-acid.

→ If the mutation codes for a different amino-acid, a different polypeptide chain will form. 

→ This mutation process could cause the protein to fold differently which can alter it’s function or render it completely dysfunctional.

→ Alternatively, the new codon could also be interpreted as a stop codon, pre-emptively stopping production of the rest of the polypeptide chain. 

♦ Mean mark (b) 46%.

BIOLOGY, M5 SM-Bank 24

Explain how transcription factors control cell differentiation, using an example.  (3 marks)

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→ Transcription factors are proteins that turn specific genes on or off by binding to nearby sections of DNA.

→ This allows different genes to be expressed in different cell types.

→ For example, the SRY gene on the Y chromosome promotes the development of testes by producing a protein that regulates the expression of genes (production of proteins) required by Sertoli cells.

Show Worked Solution

→ Transcription factors are proteins that turn specific genes on or off by binding to nearby sections of DNA.

→ This allows different genes to be expressed in different cell types.

→ For example, the SRY gene on the Y chromosome promotes the development of testes by producing a protein that regulates the expression of genes (production of proteins) required by Sertoli cells.

BIOLOGY, M5 2018 HSC 26b

Antidiuretic hormone (ADH) is a protein produced by cells in the hypothalamus. The AVP gene codes for the production of ADH.

  1. Outline the steps to show how a mutation in the AVP gene could result in changes in the ADH protein.    (3 marks)

  2. Identify ONE possible effect of the AVP mutation on kidney function.   (1 mark)

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i.   Steps: AVP mutation → Change in ADH protein

  1. AVP gene base sequence is changed.
  2. During transcription an error would occur in the mRNA strand produced.
  3. The wrong amino acids would be transported to the ribosome by tRNA at translation.
  4. The polypeptide chain produced is incorrect, dysfunctional or different.
  5. Altered ADH protein results.
     

ii.  Malfunction of ADH will result in less re-absorption of water.

Show Worked Solution

i.   Steps: AVP mutation → Change in ADH protein

  1. AVP gene base sequence is changed.
  2. During transcription an error would occur in the mRNA strand produced.
  3. The wrong amino acids would be transported to the ribosome by tRNA at translation.
  4. The polypeptide chain produced is incorrect, dysfunctional or different.
  5. Altered ADH protein results.
     

ii.  Malfunction of ADH will result in less re-absorption of water.


♦ Mean mark (i) 41%.
Mean mark (ii) 51%

BIOLOGY, M5 2022 HSC 31b

Lung cancer can be linked to genetic causes. One of the genes frequently studied in lung cancer tissue is the Epidermal Growth Factor Receptor (EGFR) gene. It codes for EGFR protein, which is composed of one polypeptide chain.

  1. Construct a flow chart to outline the synthesis of the EGFR protein from the EGFR gene.   (4 marks)

The structure of the EGFR protein includes a receptor and an enzyme component. The function of the protein is to help the cell to regulate cell division.

EGFR mutations are present in about 32% of cases of Non-Small Cell Lung Cancer (the most common type of lung cancer).

  1. Explain how a mutation in the EGFR gene could result in changes in protein structure and function to increase the risk of lung cancer.   (4 marks)

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i. 

ii.   → A mutation is a permanent change to any section of DNA.

→ It can include the change in a single nucleotide base, the deletion or insertion of a base, which will alter all codons proceeding it, or the translation, deletion or addition or entire segments of a chromosome.

→ If this occurred in the EGFR gene, this will be copied onto the mRNA, which will be transcribed into the EGFR protein.

→ The change of the removal or addition of certain amino acids within the polypeptide chain or even the change in a single amino acid will change the function of the protein or make it unusable at all. In rare cases, this could be beneficial, or a change in an amino acid will be insignificant and not change the proteins shape.

→ In most cases however, the mutation on the EFGR gene will render it useless, leading to uncontrolled cell division (cancer).

Show Worked Solution

i. 

 


♦♦♦ Mean mark (i) 28%.

ii.   → A mutation is a permanent change to any section of DNA.

→ It can include the change in a single nucleotide base, the deletion or insertion of a base, which will alter all codons proceeding it, or the translation, deletion or addition or entire segments of a chromosome.

→ If this occurred in the EGFR gene, this will be copied onto the mRNA, which will be transcribed into the EGFR protein.

→ The change of the removal or addition of certain amino acids within the polypeptide chain or even the change in a single amino acid will change the function of the protein or make it unusable at all. In rare cases, this could be beneficial, or a change in an amino acid will be insignificant and not change the proteins shape.

→ In most cases however, the mutation on the EFGR gene will render it useless, leading to uncontrolled cell division (cancer).


♦♦ Mean mark (ii) 32%.

BIOLOGY, M5 2021 HSC 9 MC

Streptomycin is an antibiotic that kills bacteria by interfering with the function of their ribosomes.

The primary effect of the antibiotic is that it prevents the bacteria from producing 

  1. tRNA.
  2. mRNA.
  3. amino acids.
  4. polypeptides.
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`D`

Show Worked Solution

→ Ribosomes form polypeptide chains as part of protein synthesis.

→ By interfering with the function of ribosomes, Streptomycin prevents bacteria from producing polypeptides.

`=>D`

♦♦ Mean mark 34%.