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