2018 Euk-Gene-Exp Organisation Control STQ QP

2018 Gene Expression, Organisation and Control STQ 2018 / H2 / ACJC PRELIM / P2 Q31tRNA molecules have an important role in gene expression. They can be found in the cytoplasm, mitochondria and chloroplasts of eukaryotic cells. Fig. 3.1 shows the structure of a tRNA molecule that is able to carry the amino acid threonine in the cytoplasm of a eukaryotic cell. It is 77 ribonucleotides long. Fig. 3.1(a)(i)With reference to Fig. 3.1, describe how the structure of a tRNA molecule differs from the structure of a mRNA molecule.[2](ii)Explain how these differences allow tRNA and mRNA molecules to perform their roles.[2] 3’5’

Fig. 3.2 shows a tRNA molecule that is able to carry the amino acid threonine in mitochondria. It is 62 ribonucleotides long. Fig. 3.2(b)The structures of the tRNA molecules in the mitochondria and the cytoplasm of a eukaryotic cell are different although they are both able to carry the amino acid threonine. Suggest a reason for this difference.[2]There are 61 unique tRNA molecules in the cytoplasm of a eukaryotic cell. (c)(i)Explain why there are 61 unique tRNA molecules in the eukaryotic cell.[2](ii)Scientists found that there are more than 120 gene loci coding for tRNA molecules in the nuclear DNA, many of which are duplicate copies of the same tRNA gene. 3’5’

Suggest an advantage of having more than 120 gene loci coding for the 61 tRNA molecules in the eukaryotic cell.[1](d)Explain how the structure of RNA polymerase allows for the synthesis of tRNA molecules.[3] [Total: 12]

2018 / H2 / AJC PRELIM / P2 Q22RNA molecules play important roles within cells. One of the major types of RNA found in all cells is the ribosomal RNA (rRNA).Fig. 2.1 shows rRNA molecules forming the large ribosomal subunit in eukaryotes. Fig. 2.1(a)Explain why the rRNA molecules must adopt the shapes shown in Fig. 2.1.……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….[3] (b)Another important RNA molecule found in eukaryotic cells is the telomerase RNA.

Telomerase RNA is found within the telomerase enzyme, an enzyme essential for elongating telomeres. (i)Outline how RNA molecules such as telomerase RNA and rRNA are synthesised.……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… [3]Fig. 2.2 shows the mode of action of telomerase. Fig. 2.2(ii)Describe three visible differences between telomere elongation shown in Fig. 2.2 and translation. ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[3][Total:9]

2018 / H2 / AJC PRELIM / P2 Q33Eukaryotes regulate the expression of their genes at various levels of protein synthesis. (a)Describe the effect of histone acetylation on gene expression. ……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….[3](b)Eukaryotic gene expression can also be regulated at translation initiation after the mRNA is synthesised.Fig. 3.1 shows translation occurring on a eukaryotic mRNA. Fig. 3.1(i)Explain the significance of the pattern of translation, labelled A in Fig. 3.1.………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2](ii)During translation initiation, translation initiation factors like elF4E and elF4G form part

of a complex which aid in recruiting ribosomal subunits to mRNA. With reference to Fig. 3.1, describe the role of the poly-A tail and 5’ cap in the assembly of ribosomes. …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2](iii)State one other function of the poly-A tail. ……………………………………………………………………………………………………………………………………………………………………………………[1](c)In mammals, sex is determined by the X and Y chromosomes, females being XX and males XY. In females, the expression of all the genes on one of the two X chromosomes in each cell is inactivated throughout the life of the female. This ensures that the effective dosages of products of X-linked genes are equal in males and females since a double dose of X-linked genes may potentially be toxic. Suggest if the inactivation of gene expression on the X chromosome occurs via chromatin modification or at translation initiation. Explain your answer. ……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….[3][Total: 11]2018 / H2 / DHS PRELIM / P2 Q4Question 4For Examiner’s useThe APP gene provides instructions for making a protein called amyloid precursor protein. This protein is found in many tissues and organs, including the brain and spinal cord. The most common mutation on the APP gene involves one codon being changed from GCC to GUC. Fig. 4.1 shows the genetic code.

Fig. 4.1(a)Explain the significance of codon in translation. [3]

(b)With reference to Fig. 4.1, describe the mutation that has occurred. [2]For Examiner’s use(c)Amyloid precursor protein is cut by enzymes to create smaller fragments, some of which are released outside the cell. Two of these fragments are called soluble amyloid precursor protein (sAPP) and amyloid beta (β) peptide. This mutation in the APP gene can lead to the production of a “stickier” form of the β peptide. When these protein fragments are released from the cell, they can accumulate in the brain and form clumps called amyloid plaques. These plaques are characteristic of Alzheimer disease. Fig. 4.2Fig. 4.2 shows the structures of alanine and valine. Both amino acids contains non-polar R group. Suggest how a change from alanine to valine can result in a mutated amyloid precursor protein which then give rise to amyloid plaques. [2]Total:[7]

2018 / H2 / JJC PRELIM / P2 Q45Fig. 4.1 shows the elongation phase of translation. Fig. 4.1(a)On Fig. 4.1, draw an arrow to show the direction of translocation of the ribosome. [1](b)Name the structures A and B in Fig. 4.1. [2] A _________________________________________________________________B _________________________________________________________________(c)Explain how the molecular structure of A is related to its functions. [2]____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(d)Describe the phase of translation that occurs before elongation. [3]__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(e)State two differences between translation in prokaryotes and translation in eukaryotes. [2]