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22 (a) (i) Fig - OCR Gateway - GCSE Biology - Question 22 - 2021 - Paper 1
Question 22
22 (a) (i) Fig. 22.1 shows the cell cycle. The letters represent different stages. Which processes happen during stage S and stage M? Write your answers in the tab... show full transcript
Worked Solution & Example Answer:22 (a) (i) Fig - OCR Gateway - GCSE Biology - Question 22 - 2021 - Paper 1
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Step 4
Describe how cells make proteins for growth.
Answer
Cells synthesize proteins through a process called transcription and translation. During transcription, the DNA sequence of a gene is copied into messenger RNA (mRNA) in the nucleus. The mRNA then travels to the ribosomes, where translation occurs. At the ribosomes, transfer RNA (tRNA) molecules transport the appropriate amino acids, which are then linked in a sequence dictated by the mRNA, forming a protein.
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Explain why the drug Actinomycin D inhibits some but not all protein synthesis.
Answer
Actinomycin D binds to the unzipped DNA strands during transcription and prevents the RNA polymerase from synthesizing mRNA. As a result, new proteins cannot be synthesized. However, it does not affect the pre-existing RNA in the cell, meaning that proteins that are already translated from previously made mRNA can still function. Therefore, it inhibits new protein synthesis but not all protein synthesis.
Step 6
Explain how the structure of DNA determines the type of protein made.
Answer
The structure of DNA consists of sequences of nucleotides, which are organized into genes. Each gene encodes the information for a specific protein. The sequence of nucleotides determines the sequence of amino acids in a protein, as groups of three nucleotides (codons) correspond to specific amino acids. Therefore, the particular arrangement of nucleotides in DNA dictates the type of protein that will be synthesized.