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6 (a) DNA is transcribed and translated during protein synthesis - Edexcel - GCSE Biology - Question 6 - 2018 - Paper 1
Question 6
6 (a) DNA is transcribed and translated during protein synthesis. Describe how DNA is transcribed. (b) (i) Which of the statements about gene mutations are true? 1.... show full transcript
Worked Solution & Example Answer:6 (a) DNA is transcribed and translated during protein synthesis - Edexcel - GCSE Biology - Question 6 - 2018 - Paper 1
Step 1
Describe how DNA is transcribed.
Answer
DNA transcription is the process by which the genetic information encoded in DNA is transcribed into messenger RNA (mRNA). This process involves several key steps:
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Unwinding of DNA: The DNA double helix unwinds, specifically at the region where the gene is located. This unwinding is facilitated by enzymes, often referred to as helicases, that break the hydrogen bonds between nucleotide base pairs.
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Template Strand: One strand of the DNA molecule serves as a template for the synthesis of mRNA. The complementary base pair rules dictate that:
- Adenine (A) pairs with Uracil (U) in RNA (instead of Thymine, T, in DNA).
- Cytosine (C) pairs with Guanine (G).
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Building the mRNA Strand: RNA polymerase, an enzyme, binds to the promoter region of the gene and starts adding RNA nucleotides that are complementary to the DNA template. This process continues until a termination signal is reached, signaling the end of the gene.
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Maturation of mRNA: After transcription, the newly synthesized mRNA undergoes processing which includes the capping of the 5’ end, polyadenylation at the 3’ end, and splicing out of introns if present. The processed mRNA then exits the nucleus.
Overall, transcription is a fundamental step in gene expression, producing mRNA that carries the genetic information from DNA to be translated into proteins.
Step 2
(b) (i) Which of the statements about gene mutations are true?
Answer
The correct answer is D: neither statement 1 nor 2. Gene mutations do not only affect one strand of a DNA molecule, as mutations can occur on both strands or affect overall chromosome integrity. Additionally, while some mutations can be harmful, others may be neutral or even beneficial depending on the environmental context.
Step 3
(ii) Explain how a gene mutation can change the function of a protein.
Answer
A gene mutation can alter the function of a protein in several ways:
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Amino Acid Changes: If a mutation results in a change in the nucleotide sequence of DNA, it can lead to a different amino acid being incorporated into the protein during translation. For instance, a substitution mutation may cause glutamic acid to be replaced by valine in a protein, potentially altering its structure and function.
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Premature Stop Codons: Some mutations may introduce premature stop codons, truncating the protein and preventing it from performing its intended function. A shorter protein might not interact correctly with other cellular components.
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Altered Protein Folding: Changes in the amino acid sequence can disrupt normal protein folding, leading to a misconfigured protein that is less effective or dysfunctional.
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Regulation of Activity: Mutations may also impact regulatory sequences associated with genes, which can lead to overexpression or underexpression of proteins, thus affecting cellular function.
In summary, mutations can have a significant impact on protein structure and function, which in turn can affect overall cellular processes and organismal health.