6.2 Protein Synthesis

The sequence below shows the DNA bases coding for seven amino acids in the enzyme papain. Note that the sequence shown is from the non-template strand.

C  A  A  T  T  T  C  A  A  A  G  T  T  G  C  T  T  T  T  T  G

Fig. 1 shows the genetic code and the amino acids coded for.

Fig. 1

Use the information in Fig. 1 to identify the sequence of amino acids in this part of the enzyme.

Table 1 below shows some mRNA codons and the amino acids for which they code.

Table 1

Identify the DNA non-template strand sequence for leucine.

[1]

Identify the amino acid carried by the tRNA with the anticodon CAU.

[1]

Ricin is a protein produced by castor beans. In animal cells, ricin acts as an enzyme. This enzyme removes the adenine molecule from one of the nucleotides in the RNA that makes up the structure of ribosomes. As a result, the ribosome changes shape. Ricin causes the death of cells and is highly toxic to many animals.

Suggest how the effect of ricin on ribosomes could cause the death of cells.

Cycloheximide is a fungicide produced by the bacterium Streptomyces griseus, which binds to specific sites on the eukaryotic ribosomes. This is shown in Fig. 2 below.

Fig. 2

Explain how cycloheximide stops protein synthesis.

Explain the role of hydrogen bonds in the process of transcription.

mRNA is a single-stranded molecule involved with the process of protein synthesis.

Explain the importance of mRNA being a single-stranded molecule.

The genome refers to the complete set of genes in a cell while the proteome is the full range of proteins that a cell can produce.

Suggest why the proteome of different cells in an organism may vary despite having the same genome.

Hereditary transthyretin (hATTR) amyloidosis is an inherited condition that causes a blood protein called transthyretin to form clumps in the cardiovascular system, digestive system and around nerve fibres. Drugs designed to bind to the mRNA molecules are used as a form of treatment for this condition.

Suggest why these drugs could be used as a treatment for hereditary transthyretin (hATTR) amyloidosis.

Describe the role of the ribosome in translation.

Fig. 1 shows the base sequence of a gene that codes for a short polypeptide, the RNA codons and the primary structure of this polypeptide.

Fig.1

Describe the role of DNA as indicated in Fig.1.

Fig. 2 illustrates some changes that are made to the RNA that is produced during transcription.

Fig. 2

Contrast the main differences between R and S in Fig.2.

Fig.1 is a diagram of a section of mRNA showing the sequence of five of the codons.

The triplets of bases in a DNA molecule that codes for some of the amino acids are listed in Table 1.

Fig.1

Table 1

Identify the amino acid sequence on this section of the mRNA molecule, using the information in Fig.1 and Table 1.

The five codons in Fig.1 are near the start of the sequence coding for a polypeptide.

Explain the consequence of a mutation which deletes one of the bases from codon 3.

If the guanine (G) in codon 4 changed to adenine (A), describe and explain the effect this would have on the amino acid sequence of this section of mRNA shown in Fig.1.

Explain why substitution mutations are less likely to have a dramatic effect on polypeptides than frameshift mutations.

The DNA in the nucleus is known as nuclear DNA.

In the cells of the grasshopper, Chorthippus brunneus, 20% of the nucleotides in nuclear DNA contain thymine.

Calculate the percentage of nucleotides in the nuclear DNA of C. brunneus that contain guanine and explain your answer in terms of the structure of DNA.

State another location, other than the nucleus, where DNA occurs in cells of C. brunneus.

Fig. 1 is a diagram of a molecule of tRNA.

The region labelled R shows detail of part of the tRNA molecule.

Fig. 1

Complete Fig.1 by writing the sequence of bases in the region labelled R.

State the name of region Q and explain the role of region Q in translation.

State the function of region P.