Protein Synthesis (SL IB Biology)

The following base sequences represent sections of two different alleles of the gene which determines an individual's ability to roll their tongue. 

Allele A (tongue roller): GCCGTAAC
Allele B (non-tongue roller): GCGCTTAC

Outline why two different alleles result in different expressions of a gene.

Sickle cell anemia is a genetic disorder with symptoms such as dizziness, a rapid heart rate and fatigue. It is caused by an allele that leads to altered haemoglobin proteins. These altered proteins undergo aggregation (sticking together), an event which changes the shape of red blood cells.  This can be seen in the image below.

Suggest how sickled red blood cells may result in the symptoms noted above.

Suggest why the shape of white blood cells is not affected by sickle cell anaemia.        

Mutations such as the one seen in sickle cell patients are usually caused by an error during DNA replication. 

Identify the enzyme that is responsible for catalysing the process of DNA replication.

Myoglobin is a eukaryotic protein consisting of a single polypeptide chain of 153 amino acids. 

Calculate the minimum number of DNA bases needed to code for Myoglobin.

Haemoglobin is another eukaryotic protein; it contains both α and ꞵ polypeptide chains.
Some of the first seven amino acids of an α chain of haemoglobin, along with the corresponding bases in the sequence are shown below.  An mRNA codon and amino acid table is also provided.

Use the information provided to identify the missing amino acids from the sequence of seven shown above.

A third eukaryotic protein, cytochrome c, is involved in the process of aerobic respiration. The diagram below shows part of the mRNA sequence and its corresponding amino acid sequence for cytochrome c in Mus musculus (house mouse) and Loxodonta africana (African elephant).

Identify the tRNA anticodon that corresponds to the amino acid serine (Ser).

The triplet codes for the amino acid Ile in part (c) demonstrate a property of the genetic code known as degeneracy, or redundancy. 

Use the information in part (c) to:

Disease X is a genetic condition. It is caused by various mutations, one of which is shown in the diagram below.

Identify the process marked Y in the diagram.

The table below shows mRNA codons and their corresponding amino acids.

Use the table above and your knowledge of protein synthesis to identify the contents of boxes (i)-(iii) in the diagram in part (a).

Outline the role of transfer RNA in the process of protein synthesis.

Explain why the protein produced as a result of the disease X mutation shown in part (a) does not function as it should.

The table below shows the exposed bases of two tRNA molecules involved in the synthesis of a protein.

Identify the base sequences found on the corresponding sections of the DNA antisense strands.

Outline how a gene codes for a polypeptide.

A polypeptide is formed when a series of amino acids join to form a chain. 

Identify the following:

Draw an annotated diagram to illustrate the structure of a DNA double helix. You do not have to show the helical shape in your diagram. 

The human genome is approximately 3 billion, or 3 000 000 000, base pairs long. A DNA sequencing machine allows for 5.5 x 10⁸ base pairs to be sequenced per hour. 

Using this information calculate the number of days it would take to sequence 1500 genomes of hospital patients using this machine. Give your answer to the nearest day.

The table below shows part of the DNA base sequence coding for β-haemoglobin and two mutations of this sequence detected in a sickle cell sufferer.

Complete the table with the DNA sequences that will undergo transcription to produce β-haemoglobin, mutated protein 1, and mutated protein 2.

The table below shows some examples of amino acids, their structures, and the mRNA codons that code for them.

Suggest why mutation 2 from part (b) is of no concern to the scientists studying this patient's DNA

A karyogram, such as the one shown in the image below, can be used to detect some Mutations

State why this karyogram could not be used to detect sickle cell anaemia.

Describe the role of tRNA in the process of translation.

Ribosomes are made of ribosomal RNA (rRNA). Messenger RNA (mRNA), transfer RNA (tRNA) and DNA are all involved in the synthesis of proteins.

Complete the table to show the differences between DNA, mRNA and tRNA.

Enzymes play an important role during transcription and translation.

Discuss the importance of enzyme-substrate specificity in the activation of tRNA molecules.

The tRNA-activating enzyme relies on phosphorylation.

Outline the role of phosphorylation during translation.

Enzymes, such as the tRNA-activating enzyme, are proteins.

State, with named examples, two functions of proteins.

Contrast protein synthesis in eukaryotes with protein synthesis in prokaryotes. 

Radiation and mutagenic chemicals can cause mutations in DNA that result in new alleles. 

Explain how mutations in DNA can affect the final protein product.

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

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

The image shows the genetic code (mRNA codons).

Use the image 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 coding strand sequence for leucine.

[1]

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

[1]

As enzyme Y in part a) moves along the DNA, the base sequence on the template strand is as follows:

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

Identify the tRNA anticodons that would bind with the mRNA produced from this section of DNA.

The transcription factor shown in part a) is a protein.

Suggest, with a reason, how a mutation in the gene that codes for the transcription factor protein might affect the expression of the gene shown in part a).

One mark is available for clarity of communication throughout this question.

Compare and contrast the processes of DNA replication and transcription.

Explain the relationship between the genetic code and proteins.

Discuss the importance of hydrogen bonds in the process of translation.

Draw labelled diagrams contrasting the structure of an mRNA and tRNA molecule.

Part of the gene coding for a specific polypeptide contains the following base sequence:

                     CATAGTTGGCCA

The following table contains some of the codons on messenger RNA and the amino acids that they code for:

Using the information provided, identify the amino acid sequence for this part of the polypeptide.

The cells that synthesise this polypeptide was exposed to a mutagen that caused a substitution mutation that changed the DNA base sequence in the following way:

                  CATACTTGGCCA

Using the table from part a), explain the effect this mutation will have on the polypeptide produced.

This polypeptide forms part of the active site of an enzyme that catalyses a metabolic reaction.

Suggest the effect that the mutation mentioned in part b) would have on the enzyme.

Based on the information provided in part a), explain how it could be possible for a mutation to have no effect on the polypeptide.