6. Nucleic acids and protein synthesis
A section of Biology, 9700
Listing 10 of 441 questions
is a diagram showing the structure of part of a DNA molecule. F E adenine adenine key one hydrogen bond Identify structure E and structure F in . E F On draw a circle around one nucleotide. State the name of the covalent bond that links two nucleotides together. shows the RNA base sequence of a short length of primary transcript. Complete by writing the DNA base sequence of the template strand used to form the primary transcript. DNA base sequence used to form the primary transcript primary transcript G G U G C U A A U C U A In eukaryotic cells, the primary transcript is modified to form mRNA. Explain how the primary transcript is modified to form mRNA. The mRNA strand is translated at the ribosome to form a polypeptide. Describe how the process of translation results in the formation of a polypeptide.
9700_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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Cysteine is an amino acid containing sulfur. shows the structure of the molecule formed by joining two cysteine molecules together. C C CH2 N C O O O H C CH2 SH H H H SH N H H Draw a circle around an R-group in the molecule shown in . Goblet cells in the human gas exchange system produce proteins called mucins. The ends of mucin molecules contain many cysteine residues. Mucin strands are formed by joining the ends of mucin molecules together through covalent bonds between R-groups. State the name of these covalent bonds. Mucin strands are transported out of the goblet cells and then absorb water to form mucus. Suggest and explain how mucin strands are transported out of the goblet cells. Cystic fibrosis is a genetic disease caused by a mutation in the human CFTR gene. This results in mucus that is thicker than normal. Suggest how thicker mucus interferes with the maintenance of healthy gas exchange surfaces in the lungs. Row 1 and row 2 of Table 2.1 show the DNA base sequences of part of the normal CFTR allele and the same part of a mutated CFTR allele. The base sequences shown are for the DNA strands used in the synthesis of RNA. When Table 2.1 is completed, row 3 will show the base sequence of the RNA synthesised from the same part of the mutated CFTR allele. Table 2.1 DNA base sequence of part of the normal CFTR allele T A G T A G A A A C C A DNA base sequence of part of the mutated CFTR allele T A G T A A C C A C A A RNA base sequence synthesised from the mutated CFTR allele The difference between the DNA base sequence in row 1 and the DNA base sequence in row 2 of Table 2.1 is caused by a single gene mutation. State the name of this type of gene mutation. Row 1 and row 2 in Table 2.1 show the DNA strands used in the synthesis of RNA. State the term used to describe the DNA strand that is used in the synthesis of RNA. Complete Table 2.1 to show the missing bases in row 3. The normal CFTR allele is approximately 189 000 base pairs in length. The CFTR polypeptide consists of only 1480 amino acids. Explain the reasons for this difference between the number of base pairs and the number of amino acids.
9700_m23_qp_22
THEORY
2023
Paper 2, Variant 2
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Complete the table to show three ways in which the structure of DNA differs from RNA. DNA RNA Table 2.1 shows two messenger RNA (mRNA) codons. Fill in the complementary transfer RNA (tRNA) anticodons in the spaces provided. Table 2.1 mRNA codons GCG ACA complementary tRNA anticodons Calculate the minimum number of DNA nucleotides necessary to code for a polypeptide with 238 amino acids. Show your working. answer nucleotides Describe the role played by tRNA in polypeptide synthesis.
9700_s11_qp_23
THEORY
2011
Paper 2, Variant 3
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The two strands of a DNA molecule are held together by hydrogen bonds between complementary base pairs. Explain why the hydrogen bonding between the two strands of DNA is important for it to carry out its functions. Switching genes on and off allows proteins to be synthesised only when required. Processes P and Q occur when a gene is switched on, as shown in . DNA mRNA polypeptide P Q Name processes P and Q. P Q DNA is a very stable molecule. This means that it is not broken down either chemically or by enzymes during the normal life of the cell. In contrast, mRNA is described as being highly labile. This means that most mRNA molecules are broken down in the cytoplasm within a few hours of their release from the nucleus. Suggest the significance of: DNA being very stable mRNA being highly labile.
9700_s12_qp_23
THEORY
2012
Paper 2, Variant 3
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441