Protein Synthesis (HL 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. 

Describe the process of transcription in eukaryotic cells.

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.

Messenger RNA (mRNA) and transfer RNA (tRNA) are important molecules required for the transcription and translation of proteins. 

Contrast the structures of mRNA and tRNA.

Describe the role of tRNA in the process of translation.

Tobacco plants have been genetically modified to produce human haemoglobin. The first three triplets of the non-coding (template) strand of the human haemoglobin gene are:

ATG GTG CAT 

Deduce the anticodons of the corresponding tRNA molecule.

The base sequence below is found in a section of the mRNA strand used to synthesise an enzyme found in tobacco plants.

G   U   U   A   A   A   G   U   U   U   C   A   A   C   G   A   A   A   A   A   C

Using the diagram, deduce how many different types of tRNA molecules would attach to the section of mRNA shown in the diagram?

Describe the function of ribosomes in protein synthesis.

Within a cell ribosomes can be found free or bound to structures.

Contrast free ribosomes with bound ribosomes.

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.

Describe how the process of translation leads to the production of a polypeptide.

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]

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.   

Transcription factors are proteins that influence the process of transcription. One mechanism by which transcription factors affect transcription is illustrated and described below.

• • 1. The transcription factor binds to region X at the start of a gene, also known as a promoter region.
    2. This causes enzyme Y to bind to the DNA.
    3. Transcription is initiated and enzyme Y moves along the DNA in the direction shown.

Identify enzyme Y.

[1]

State the precise role of enzyme Y.

[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).

The transcription factor shown in part a) is an example of a type of transcription factor known as an activator. This means that it initiates transcription or increases the rate at which transcription takes place.

Use the illustration in part a) to suggest how a transcription factor might have the opposite effect and function as a repressor.

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.

Ricin is a protein produced by castor beans. In animal cells, ricin acts as an enzyme which removes the adenine base from one of the nucleotides in the RNA of ribosomes. As a result, the ribosome changes shape. Ricin causes the death of cells and is very poisonous to certain animals.

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

The image below shows the structure of ricin.

Image courtesy of Aza Toth. Licensed under Creative Commons Attribution 3.0 Unported license. Reused and distributed under conditions found at: https://creativecommons.org/licenses/by/3.0/deed.en

Discuss the level(s) of protein structure visible in the diagram.

The Flavr Savr tomato plant was genetically engineered to ripen and soften more slowly than a normal tomato. The inserted gene prevents the enzyme Beta polygalacturonase from breaking down pectin which softens the tomatoes.

The diagram below shows the matching parts of the base sequences for the mRNA produced from the transcription of the softening gene in a normal tomato and that of the inserted gene.

Suggest how the inserted gene reduces the production of the softening enzyme.

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.