OCR A Level Biology

Topic Questions

A LevelBiologyOCRTopic Questions6. Genetics, Evolution & Ecosystems6.1 Cellular Control

6.1 Cellular Control

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1
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Which of the following statements applies/apply to insertion mutations?

1 Insertion mutations occur when a different nucleotide replaces a nucleotide in the DNA sequence.
2 Insertion mutations are more likely to be harmful because they cause a frameshift in the DNA sequence.
3 Insertion mutations are more likely to change the amino acid sequence of a protein than substitution mutations.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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2
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What is the function of the promoter region in the lac operon?

  • Provides a binding site for RNA polymerase to begin transcription.

  • Encodes the proteins which digest lactose.

  • Represses gene expression.

  • Transcribes the genes of the lac operon.

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3
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Gene expression can be regulated at the post-transcriptional level. For example, introns (non-coding regions) of mRNA can be removed, and then exons (coding regions) are joined together. This produces mRNA ready for translation.

What is the name of this process?

  • Transcription

  • Protein activation

  • mRNA activation

  • Splicing

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4
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Figure 1 below depicts a representation of the hox genes which control the development of the body plan of the fruit fly. ocr-a-6-1e-drosophila

The Antp gene (indicated with cross-hatching), turns on genes which induce the development of the second set of the fruit fly’s legs. It is normally expressed in the thorax.

In some cases, a genetic mutation can cause the expression of Antp to extend into the head region. Suggest which of A - D  would happen to the fruit fly in this case?

  • The second pair of legs would not develop

  • There would be the development of a pair of legs in the head region

  •  The thorax would be absent

  • The head would be absent

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5
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Mitosis and apoptosis are important processes which play a role in the body plan development of organisms. Genes that control the cell cycle and cell death can respond to various stimuli.

Which of the following are examples of internal stimuli which affect the cell cycle and cell death?

1 DNA damage
2 Production of cyclin D
3 Increase in heart rate

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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1
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Which of the following statements about mutations in genes is/are correct?

1 Substitutions never have significant effects on the resulting polypeptide because the DNA code is degenerate
2 Insertions and deletion of bases usually cause significant changes in the resulting polypeptide
3 Mutations always cause changes to the amino acid sequence of the resulting polypeptide

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

  • Only 2

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2
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Order the probable effects of the following point mutations on polypeptide structure from least severe to most severe:

1 Insertion in the final nucleotide of the penultimate triplet of the gene
2 Substitution turning ATG (Tyrosine) into ATC (STOP) in the middle of the gene
3 Substitution of the first nucleotide in a triplet in the middle of the gene leading to a missense mutation
4 Insertion of a nucleotide in a non-coding region

  • 1, 2, 3, 4

  • 4, 1, 3, 2

  • 4, 3, 2, 1

  • 1, 4, 3, 2

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3
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Which of the following best describes how oestrogen affects the transcription of genes in a cell?

  • It binds to receptors on the cell membrane which causes transcription factors to be activated inside the cell

  • It binds to a promoter region on the DNA and causes transcription to occur

  • It binds to an oestrogen receptor complex in which releases a transcription factor

  • It binds to an oestrogen receptor in the nucleus and binds to the promoter region of a target gene.

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4
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Which of the following statements do not apply to the importance of RNA analysis for understanding gene expression in cells?

1 All cells have a complete genome but only some genes are expressed
2 Post-translational activation of a polypeptide by cAMP is sometimes necessary
3 mRNA can be modified post-transcription to increase the variety of possible proteins
4 DNA contains large non-coding regions around genes

  • 2 only

  • 1 and 3 only

  • 3 and 4 only

  • 2 and 4 only

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5
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Which of the following statements correctly describe(s) the importance of post-transcriptional modification?

1 Introns are non-coding sections so must be removed
2 Modifying mRNA helps ensure that gene mutations are corrected
3 Splicing allows multiple proteins to be produced from the same gene
4 Only mature mRNA can be translated

  • 1 only

  • 1 and 3 only

  • 2 and 4 only

  • 1, 3 and 4

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6
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What is the action of lac operon when lactose is present?

  • Lactose binds to the lac repressor, moving it away from the operator, and allowing RNA polymerase to begin transcription of the operon.

  • The lac repressor binds to the operator, allowing RNA polymerase to begin transcription of the operon.

  • Lactose binds to the lac repressor, moving it away from the operator, and preventing RNA polymerase from transcribing the operon.

  • The lac repressor binds to the operator, preventing RNA polymerase from transcribing the operon.

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1
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Hox genes contribute to the overall body plan of an animal.

Which of the following rows correctly describes Hox genes?

  Base sequence Product Mutations
A. varies between taxonomic groups transcription factor entirely random
B. varies between taxonomic groups transcription factor never occur
C. similar in all animals polypeptide have little or no effect
D. similar in all animals polypeptide are often lethal

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2
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Below are three processes that occur within living organisms.

  1. Apoptosis
  2. Mitosis
  3. Meiosis

Which of these processes is important in determining the body plan of an organism?

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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3
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What is an operon?

  • The binding site for a repressor protein.

  • Any group of genes responsible for the metabolism of lactose in prokaryotes or eukaryotes.

  • A cluster of genes under the control of a promoter.

  • A regulatory gene.

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4
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A DNA nucleotide base sequence and its associated sequence of four amino acids can be seen below:

AGG   ACA   CCT   GGA

Serine   Tyrosine   Glycine   Proline

The table shows mRNA codons and their associated amino acids.

h-1

A single mutation occurred in the original nucleotide base sequence shown above. This resulted in only one amino acid from the sequence of four amino acids being produced.

Which of the following could be the correct nucleotide base sequence which was found in the DNA after the mutation occurred?

  • AGT   ACA   CCT   GGA

  • AGG   ACT   CCT   GGA

  • AGG   ACC   CCT   GGA

  • AGG   ACA   UGA   GGA

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5
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Which of the following best describes the importance of regulating gene expression?

  • To ensure that essential genes are expressed all the time in all cells.

  • To ensure that genes are only expressed at certain times and in certain cells.

  • To ensure that certain genes are expressed in the relevant cells at all times.

  • To ensure that the same group of essential genes is expressed in all cells of the organism at certain times.

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6
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Which of the following occur in Escherichia coli bacteria if no lactose is present?

  • The lac repressor protein is deactivated.

  • Lactose binds to the lac repressor protein, preventing it from binding to DNA.

  • The gene that codes for the lac repressor protein is silenced.

  • The lac repressor protein binds near the promoter.

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7
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Gibberellin is a plant hormone which stimulates seed germination by the following mechanism:

  1. PIF is required to stimulate the synthesis of amylase
  2. DELLA is a protein attached to PIF
  3. When gibberellin is present it binds to a receptor and an enzyme
  4. This complex breaks-down the DELLA protein
  5. PIF is released
  6. PIF binds to the promotor region on the amylase gene
  7. Transcription of amylase begins.
  8. Amylase enzyme is responsible for the initiation of seed germination.

Which kind of regulatory components are DELLA and PIF in the mechanism described.

  DELLA PIF
A. Repressor protein Promotor of amylase
B. Repressor protein Transcription factor
C. Promotor of amylase Activator protein
D. Transcription factor Promotor of amylase

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8
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Which of the following statements correctly describe(s) a promoter?

  1. The first part of a gene to be transcribed.
  2. Acts as a binding site for RNA polymerase.
  3. A non-coding sequence located near the gene.
  4. Only found in eukaryotes.

  • Only 1 and 2

  • Only 1 and 3

  • Only 2 and 3

  • 1, 2, 3 and 4

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9
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Apoptosis and mitosis are important processes in controlling the development of body form. If the balance between these processes is lost, cancerous cell growth can occur.

Two genes responsible for maintaining the balance are tumour suppressor genes, which can initiate apoptosis in body cells, and proto-oncogenes, which are responsible for stimulating mitosis.

Which of the following scenarios may lead to the development of a cancerous cell growth?

  • Proto-oncogenes are activated and tumour suppressor genes are transcribed.

  • Proto-oncogenes are inactivated and tumour suppressor genes are transcribed.

  • Tumour suppressor genes stimulate apoptosis and proto-oncogenes are activated.

  • Proto-oncogenes are activated and tumour suppressor genes are inactivated.

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10
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Which of the following methods of gene regulation is an example of post-transcriptional modification?

  • Introns are removed during splicing.

  • DNA may be tightly wound around histone proteins, preventing RNA polymerase from binding.

  • Oestrogen binds to a receptor protein inside cells, enabling the protein to bind to a promoter region.

  • When present, lactose binds to a repressor protein.

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