Practise CAIE AS Biology 6.2 by converting DNA and RNA sequences into polypeptides, tracing RNA processing, and judging how mutations alter protein products.
One gene provides the code for the production of which type of molecule?
amino acid
DNA
nucleotide
polypeptide
The mRNA codons ACU, ACC, ACA and ACG all code for the same amino acid, threonine.
Which anticodons could specify an amino acid other than threonine?
1 UCA
2 ACC
3 UGU
4 UGC
1,3 and 4
1 and 2
2 and 3
3 and 4 only
Which statements correctly describe the process of translation?
1 The nucleotide sequence on an mRNA molecule is used to produce a specific amino acid chain.
2 A section of DNA is copied into an mRNA molecule by RNA polymerase.
3 A polypeptide is produced because anticodons on tRNA molecules attach to mRNA codons through peptide bonds.
1 and 2
1 and 3
1 only
2 and 3
A molecule of mRNA was used in translation. Part of its sequence is shown.
There were no introns present in the section of DNA that was transcribed to make this mRNA.
What is the sequence of the non-transcribed DNA strand for this section?
CTA GAC ATT GCC
CUA GAC AUU GCC
GAT CTG TAA CGG
GAU CUG UAA CGG
Smooth muscle is a tissue composed of smooth muscle cells. The cells contain cytoplasm packed with proteins that are involved in contraction and relaxation.
Caldesmon is a large protein with a number of binding sites to attach to other proteins.
Caldesmon exists in two different forms, H-caldesmon and L-caldesmon.
H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells.
L-caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein.
- Caldesmon is coded for by a gene known as CALD1.
- CALD1 has 17 exons.
- The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon.
Researchers now know that the two different forms of caldesmon are the result of events occurring directly after transcription of DNA. Changes occur to the primary transcript that is formed by DNA transcription.
Suggest how the smooth muscle cells and non-muscle cells can produce different forms of caldesmon from the same primary transcript.
Smooth muscle is a tissue composed of smooth muscle cells. The cells contain cytoplasm packed with proteins that are involved in contraction and relaxation.
Caldesmon is a large protein with a number of binding sites to attach to other proteins.
Caldesmon exists in two different forms, H-caldesmon and L-caldesmon.
H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells.
L-caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein.
- Caldesmon is coded for by a gene known as CALD1.
- CALD1 has 17 exons.
- The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon.
Researchers have discovered that a gene mutation is not the cause of the two different forms of caldesmon.
Explain what is meant by a gene mutation.
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
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.
Cathelicidin LL-37 is a cell signalling compound that stimulates many different cells in humans. One role of cathelicidin LL-37 is stimulating the production of endothelial cells in the formation of capillaries during wound healing.
Mutations of DNA base sequences in a gene can affect the primary structure of proteins.
Use the information in Table 5.1 and Table 5.2 to suggest the effect on the primary structure of cathelicidin LL-37 of:
the substitution of the base T with the base A in the middle of the triplet at position 5
the deletion of base T in the triplet at position 2
the insertion of base G between bases G and T in the triplet at position 3 .
Use Table 5.2 to explain why some mutations have no effect on the primary structure of a protein.