2.1 The diagram below represents a process that occurs during protein synthesis - NSC Life Sciences - Question 2 - 2023 - Paper 2
Question 2
2.1 The diagram below represents a process that occurs during protein synthesis.
(a) The DNA base triplet complementary to the middle codon on molecule Z
(b) Y
2.... show full transcript
Worked Solution & Example Answer:2.1 The diagram below represents a process that occurs during protein synthesis - NSC Life Sciences - Question 2 - 2023 - Paper 2
Step 1
Identify the DNA base triplet complementary to the middle codon on molecule Z
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Answer
The DNA base triplet complementary to the middle codon on molecule Z (AUG) is TAC.
Step 2
Identify molecule Y
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Answer
Molecule Y is tRNA (transfer RNA).
Step 3
Name and describe the process shown in the diagram during the formation of a protein
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Answer
The process shown in the diagram is Translation. During translation, the mRNA codon is matched by the tRNA anticodon, bringing the specific amino acid to the ribosome. The amino acids then form peptide bonds to create the polypeptide chain, which will fold into a functional protein.
Step 4
Describe the effect of this mutation on the protein shown
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Answer
The mutation changing the DNA base triplet from CTG to CTA results in both codons coding for the same amino acid, leucine. Therefore, there will be no effect on the protein because the amino acid sequence remains unchanged.
Step 5
Tabulate TWO differences between DNA and RNA nucleotides
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Answer
Feature
DNA
RNA
Sugar
Deoxyribose
Ribose
Nitrogenous base
Thymine (T)
Uracil (U)
Step 6
Type of mutation that leads to Trisomy 21
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Answer
The type of mutation that leads to Trisomy 21 is Chromosomal mutation.
Step 7
Abnormal process during gamete production that leads to three copies of chromosome 21
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Answer
The abnormal process is Non-disjunction.
Step 8
Type of cell division that occurs after fertilisation
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Answer
The type of cell division is Mitosis.
Step 9
Describe how the process in QUESTION 2.4.1(b) leads to Trisomy 21
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Answer
During non-disjunction, the chromosome pair or chromatids fail to separate during anaphase I or II, resulting in a gamete that has an extra chromosome. When this gamete fuses with a normal gamete, the zygote will end up with 47 chromosomes instead of the usual 46, leading to Trisomy 21.
Step 10
Describe TWO differences between Trisomy 21 and Mosaic Down syndrome
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In Trisomy 21, there are extra copies of chromosome 21 in every somatic cell, whereas in Mosaic Down syndrome, the extra chromosome is present only in some cells.
Trisomy 21 occurs due to non-disjunction in meiosis, while Mosaic Down syndrome results from abnormal cell division during early embryonic development.
Step 11
Describe what is meant by an autosomal disorder
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An autosomal disorder is a genetic condition controlled by genes located on the autosomes (non-sex chromosomes) and can be inherited from either parent.
Step 12
How many sons do individuals 1 and 2 have?
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Individuals 1 and 2 have one son.
Step 13
Explain why it can be concluded that Tay-Sachs disease is controlled by a recessive allele
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Tay-Sachs disease is controlled by a recessive allele because individuals 3 and 4, who are both phenotypically normal and do not express the disease, can still produce a child (individual 7) with Tay-Sachs. This indicates that both parents must be carriers of the recessive allele.
Step 14
List ALL the genotypes that have a 25% chance of being produced
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The genotypes that have a 25% chance of being produced are: TT, Tt, and tt.
Step 15
Use a genetic cross to show the percentage chance of the couple having a daughter who is homozygous for normal blood clotting
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The genetic cross can be represented as follows:
P1:
Phenotype: Woman without haemophilia x Man with haemophilia
Genotype: X^H X^h x X^h Y
Meiosis:
Gametes:
X^H, X^h x X^h, Y
F1:
Phenotype: 1 daughter without haemophilia, 1 daughter with haemophilia, 1 son without haemophilia, 1 son with haemophilia
Probability of daughter being homozygous for normal blood clotting: 0%.
