CfE Higher Sht1_4A
HBiol Sheet 1_4A
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1. a) The diagram shows part of an mRNA molecule being formed on a strand of DNA.
(i) In which part of the cell is mRNA formed?
(ii) In your jotter write down the correct sequence of bases of the mRNA molecule in the diagram.
(iii) How many amino acids are coded for by this section of mRNA?
(b) Some diseases are caused when cells in the body produce a harmful protein.
Recent research has led to the development of antisense drugs to treat such diseases. These drugs carry a short strand of RNA nucleotides designed to attach to a small part of the mRNA molecule that codes for the harmful protein.
Suggest how these drugs may prevent the production of a harmful protein.
2. The table shows the base sequences of some mRNA codons and the amino acids for which they code.
(a) (i) State the mRNA codon for methionine.
(ii) Use information from the table to identify the common feature of all mRNA codons which code for the amino acid arginine.
(b) Name amino acid A and amino acid B corresponding to the bases on the strand of DNA shown in the diagram below.
3. The diagram shows part of a primary transcript of an mRNA molecule.
a) Name the two substances that make up part X.
b) Give the sequence of bases on the DNA strand from which this primary mRNA has been transcribed.
c) Give one way in which the structure of an mRNA molecule is different from the structure of a tRNA molecule.
d) Explain the difference between pre-mRNA and mRNA.
The table shows the percentage of different bases in two pre-mRNA molecules.
The molecules were transcribed from the DNA in different parts of a chromosome.
e) Complete the table by providing the percentage of uracil (U) for each of the two parts of the chromsome.
f) Explain why the percentages of bases from the middle part of the chromosome and the end part are different.
4. Recently a new class of RNA, called microRNA, has been discovered. These small RNA molecules have an important role in controlling the translation of mRNA. This type of control is called RNA interference.
A microRNA is formed from a precursor RNA molecule that folds into a double-stranded hairpin” structure. The hairpin is then processed and one strand of this short molecule attaches to RISC proteins; the resulting complex binds to target mRNA molecules and prevents translation. (Figure 1)
Recent research has investigated the importance of microRNA in controlling the fate of stem cells. Stem cells can either divide rapidly to make more stem cells, a process called self-renewal, or differentiate into specialised cell types. To determine the role of
microRNAs in these processes, stem cells were modified to “knock out” microRNA production.
Figure 2A compares the growth rate in knockout and normal cells.
(a) What proces is responsible for the production of the microRNA precursor?
(b) What role does rRNA play in the cell?
(b) During the formation of microRNAs, single-stranded RNA molecules form hairpin structures as shown in the diagram below.
(i) Which covalent bonds join nucleotides in RNA molecules?
(ii) What is the role of hydrogen bonding in maintaining the hairpin shape?
(c) Refer to Figure 2A. Calculate the percentage reduction in growth at 90 hours caused by the microRNA knockout.
(d) What conclusion can be draw from the results in Figure 2A?
(e) Chemicals which inhibit microRNA attachment have been developed.
i) Based on the results in Figure 2A, what disease might these chemicals have the potential to treat?
ii) Why might these chemicals have undesirable side effects?
