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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)
  2. 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, M5 SM-Bank 22

Describe the roles of messenger RNA and transfer RNA in protein synthesis.  (2 marks)

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  • Messenger RNA (or mRNA) provides copies of the gene from the DNA template strand.
  • Transfer RNA (or tRNA) decodes mRNA sequences by matching amino acids to codons of the mRNA.
Show Worked Solution
  • Messenger RNA (or mRNA) provides copies of the gene from the DNA template strand.
  • Transfer RNA (or tRNA) decodes mRNA sequences by matching amino acids to codons of the mRNA.

BIOLOGY, M5 EQ-Bank 14 MC

Haemophilia A is a blood clotting disorder that arises from a defect in the gene F8 which is carried on the X chromosome. The disorder affects the production of a glycoprotein that is one of many components needed to form the platelets which form blood clots when a bleed occurs. It is typically treated with infusions of FVIII product, an inactive single chain polypeptide of 2332 amino acids, which is manufactured using DNA technology on human endothelial cells.

Why is the inactive FVIII polypeptide chain used in the treatment of Haemophilia A?

  1. It will prevent bleeds from occurring.
  2. It can take the place of platelets in clotting blood.
  3. It can be used to manufacture the glycoprotein that is affected by the defective F8 gene.
  4. It is used as a gene therapy to help the patient manufacture FVIII in their own endothelial cells.
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`C`

Show Worked Solution
  • An inactive single chain polypeptide that has been manufactured by DNA technology from endothelial cells (the single cell layer of blood vessels) would imply that it is the mRNA strand which codes for the glycoprotein.
  • Haemophilia A is a mutation of the F8 which codes for the glycoprotein (or part of it), and therefore injections of this mRNA strand will ‘bypass’ the mutation and allow the body to manufacture the protein itself.

`=>C`

BIOLOGY, M5 2014 HSC 32a

  1. Name the process for the synthesis of a polypeptide chain from a messenger-RNA base sequence.   (1 mark)

  2. Outline the steps in the formation of a functional enzyme from polypeptide chains.   (3 marks)

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i.    Translation

ii.   Formation of a functional enzyme from polypeptide chains

  • A polypeptide will fold in a certain three-dimensional shape dependent on the amino acids, such as a sheet or a coil.
  • Multiple polypeptide chains will then link together to form a more specific shape. This shape will then go on to do a specific task as a protein.

Note: The following point is old syllabus knowledge.

  • One type of protein is an enzyme, which acts as a biological catalyst on certain substrates, primarily in metabolic reactions. The certain shape an enzyme makes due to the polypeptide chains within it is what dictates which substrate it will act on. 
Show Worked Solution

i.    Translation

ii.   Formation of a functional enzyme from polypeptide chains

  • A polypeptide will fold in a certain three-dimensional shape dependent on the amino acids, such as a sheet or a coil.
  • Multiple polypeptide chains will then link together to form a more specific shape. This shape will then go on to do a specific task as a protein.

Note: The following point is old syllabus knowledge.

  • One type of protein is an enzyme, which acts as a biological catalyst on certain substrates, primarily in metabolic reactions. The certain shape an enzyme makes due to the polypeptide chains within it is what dictates which substrate it will act on. 

♦♦ Mean mark (ii) 31%.

BIOLOGY, M5 2019 HSC 33a

Alzheimer's disease causes destruction of brain tissue, dementia and eventually death.

The diagram shows the effect of Alzheimer's disease on the brain.

Amyloid beta protein is produced in the human brain throughout life. In people with Alzheimer's disease, it accumulates in excessive amounts.

Outline the main steps that brain cells use to make proteins such as amyloid beta.   (3 marks)

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 Steps that brain cells use to make proteins such as amyloid beta

  1. A complementary mRNA strand is transcribed from a section of DNA by RNA polymerase in the nucleus.
  2. mRNA moves to the cytoplasm where it binds to ribosomes.
  3. Each 3 nucleic bases (a codon) has a corresponding anticodon of tRNA with an amino acid attached.
  4. The amino acids are ‘stitched’ together in a chain by the ribosomes, forming a polypeptide chain.
  5. The single polypeptide chain or multiple polypeptide chains are folded to form a protein.
Show Worked Solution

     Steps that brain cells use to make proteins such as amyloid beta

  1. A complementary mRNA strand is transcribed from a section of DNA by RNA polymerase in the nucleus.
  2. mRNA moves to the cytoplasm where it binds to ribosomes.
  3. Each 3 nucleic bases (a codon) has a corresponding anticodon of tRNA with an amino acid attached.
  4. The amino acids are ‘stitched’ together in a chain by the ribosomes, forming a polypeptide chain.
  5. The single polypeptide chain or multiple polypeptide chains are folded to form a protein.

♦ Mean mark 41%.

BIOLOGY, M5 2020 HSC 32b

The rabies virus is a single-stranded RNA virus. It contains and codes for only five proteins. The diagrams show the structure and reproduction of the virus.
 

 

  1. Use the information provided in Diagram 1 to explain why the rabies virus cannot be classified as a cellular pathogen.   (3 marks)

  2. After infection the virus reproduces in muscle cells near the bite site and in the central nervous system. This requires the single-stranded rabies RNA to be transcribed, translated and replicated in the cytoplasm of host cells. These processes are shown in Diagram 2.
  3. Use the information provided in Diagrams 1 and 2 to explain the role of viral RNA polymerase in the reproduction of the virus.   (5 marks)

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i.   Rabies virus cannot be a singular pathogen:

  • This pathogen contains only a single strand of RNA which only codes for five proteins.
  • Cellular pathogens such as bacteria contain a much larger genome in the form of DNA that allows the pathogen to perform complex processes without relying on a host. 

ii.   The Role of Viral RNA 

  • The viral RNA polymerase (which is made from L and P proteins) is responsible for the production of the viral proteins and RNA, components of the rabies viruses.
  • RNA polymerase is responsible for transcription of viral RNA into mRNA, which is then used by the host’s ribosomes to produce respective viral proteins.
  • RNA polymerase is also responsible for the replication of the viral RNA. In this process, a complementary RNA strand is produced from the original RNA strand. This strand is then used as a template for RNA polymerase to rapidly produce more RNA, complementary to the template. The new RNA will therefore be identical to the original.
  • In this way, RNA polymerase is essential in producing viral proteins and new RNA strands which form new rabies virus particles.
Show Worked Solution

i.   Rabies virus cannot be a singular pathogen:

  • This pathogen contains only a single strand of RNA which only codes for five proteins.
  • Cellular pathogens such as bacteria contain a much larger genome in the form of DNA that allows the pathogen to perform complex processes without relying on a host.

♦♦ Mean mark (i) 33%.

ii.   The Role of Viral RNA 

  • The viral RNA polymerase (which is made from L and P proteins) is responsible for the production of the viral proteins and RNA which are components of the rabies viruses.
  • RNA polymerase is responsible for transcription of viral RNA into mRNA, which is then used by the host’s ribosomes to produce viral proteins.
  • RNA polymerase is also responsible for the replication of the viral RNA. In this process, a complementary RNA strand is produced from the original RNA strand. This strand is then used as a template for RNA polymerase to rapidly produce more RNA, complementary to the template. The new RNA will therefore be identical to the original.
  • In this way, RNA polymerase is essential in producing viral proteins and new RNA strands which form new rabies virus particles.

♦♦♦ Mean mark (ii) 29%.

BIOLOGY, M5 2019 HSC 14 MC

The following DNA base sequence is used to code for a sequence of four amino acids.

`text{CGC  ATC  ATG  CTA}`

Which of the following correctly represents the anticodons on the transfer RNA during synthesis of this string of amino acids?

  1. `text{GCG  UAG  UAC  GAU}`
  2. `text{CGC  AUC  AUG  CUA}`
  3. `text{CGC  ATC  ATG  CTA}`
  4. `text{GCG  TAG  TAC  GAT}`
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`B` or `A`

Show Worked Solution

By Elimination:

  • RNA has Uracil (U) in replace of Thymine (T) (eliminate C and D).
  • The DNA segment above must be copied into mRNA with complementary bases (with U replacing T), then anticodons on tRNA have complementary bases again. Therefore the tRNA associated with he DNA segment above will be the same with U instead of T.

`=>B`

*Note: `A` also considered an acceptable answer due to confusion as to whether the segment above was DNA or RNA.

BIOLOGY, M5 2021 HSC 28a

Describe the role of mRNA in human cells.   (3 marks)

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  • mRNA carries a complementary copy of a gene, with uracil replacing thymine as a base, into the cytoplasm.
  • At ribosome sites this provides a template; each codon (three nucleotides) results in the addition of a specific amino acid, which forms a polypeptide chain.
Show Worked Solution
  • mRNA carries a complementary copy of a gene, with uracil replacing thymine as a base, into the cytoplasm.
  • At ribosome sites this provides a template; each codon (three nucleotides) results in the addition of a specific amino acid, which forms a polypeptide chain.

Mean mark 58%.