The fibrous protein keratin has a secondary structure with a helical arrangement.

(i) State the type of interaction responsible for holding the protein in this arrangement.

(ii) Identify the functional groups responsible for these interactions.

Identify the type of bond between two cysteine residues in the tertiary structure of a protein.

Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.

An aqueous buffer solution contains both the zwitterion and the anionic forms of alanine. Draw the zwitterion of alanine.

Explain why an increase in temperature reduces the rate of an enzyme-catalyzed reaction.

A mixture of amino acids is separated by gel electrophoresis at pH 6.0. The amino acids are then stained with ninhydrin.

(i) On the diagram below draw the relative positions of the following amino acids at the end of the process: Val, Asp, Lys and Thr.

(ii) Suggest why glycine and isoleucine separate slightly at pH 6.5.

Deduce the structural formula of the dipeptide Cys-Lys.

A mixture of phenylalanine and aspartic acid is separated by gel electrophoresis with a buffer of pH = 5.5.

Deduce their relative positions after electrophoresis, annotating them on the diagram. Use section 33 of the data booklet.

Draw a circle around the functional group formed between the amino acids and state its name.

Name: 

Some proteins form an α-helix. State the name of another secondary protein structure.

A mixture of phenylalanine and aspartic acid is separated by gel electrophoresis with a buffer of pH = 5.5.

Deduce their relative positions after electrophoresis, annotating them on the diagram. Use section 33 of the data booklet.

Deduce the structural formula of the predominant form of cysteine at pH 1.0.

The breakdown of a dipeptide in the presence of peptidase was investigated between 18 °C and 43 °C. The results are shown below.

Comment on the rate of reaction at temperature X in terms of the enzyme’s active site.

Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.

Deduce the strongest intermolecular forces that would occur between the following amino acid residues in a protein chain.

Identify the name of the amino acid that does not move under the influence of the applied voltage.

Deduce, giving a reason, which amino acid will develop closest to the negative electrode.

A mixture of the three amino acids, cysteine, glutamine and lysine, was placed in the centre of a square plate covered in polyacrylamide gel. The gel was saturated with a buffer solution of pH 6.0. Electrodes were connected to opposite sides of the gel and a potential difference was applied.

Sketch lines on the diagram to show the relative positions of the three amino acids after electrophoresis.

The isoelectric point of amino acids is the intermediate pH at which an amino acid is electrically neutral.

Suggest why Asp and Phe have different isoelectric points.

Draw the structures of the main form of glycine in buffer solutions of pH 1.0 and 6.0.

The pK_a of glycine is 2.34.

Draw a circle around the functional group formed between the amino acids and state its name.

Name:

Some proteins form an α-helix. State the name of another secondary protein structure.

Explain why a change in pH affects the tertiary structure of an enzyme in solution.

Proteins are polymers of amino acids.

Glycine is one of the amino acids in the primary structure of hemoglobin.

State the type of bonding responsible for the α-helix in the secondary structure.

Proteins are polymers of amino acids.

A paper chromatogram of two amino acids, A1 and A2, is obtained using a non-polar solvent.

© International Baccalaureate Organization 2020.

Determine the ${\mathrm{R}}_{\mathrm{f}}$ value of A1.

Explain why an increase in temperature reduces the rate of an enzyme-catalyzed reaction.

Proteins are polymers of amino acids.

The mixture is composed of glycine, $\mathrm{Gly}$, and isoleucine, $\mathrm{Ile}$. Their structures can be found in section 33 of the data booklet.

Deduce, referring to relative affinities and ${\mathrm{R}}_{\mathrm{f}}$, the identity of A1.

Outline why amino acids have high melting points.

Draw the structural formula of a dipeptide containing the residues of valine, Val, and asparagine, Asn, using section 33 of the data booklet.

Compare and contrast the bonding responsible for the two secondary structures.

One similarity:

One difference:

Proteins are polymers of amino acids.

The mixture is composed of glycine, $\mathrm{Gly}$, and isoleucine, $\mathrm{Ile}$. Their structures can be found in section 33 of the data booklet.

Deduce, referring to relative affinities and ${\mathrm{R}}_{\mathrm{f}}$, the identity of A1.

Proteins are polymers of amino acids.

Glycine is one of the amino acids in the primary structure of hemoglobin.

State the type of bonding responsible for the α-helix in the secondary structure.

Proteins are polymers of amino acids.

Describe how the tertiary structure differs from the quaternary structure in hemoglobin.

Compare and contrast the bonding responsible for the two secondary structures.

One similarity:

One difference:

Proteins are polymers of amino acids. A paper chromatogram of two amino acids, A1 and A2, is obtained using a non-polar solvent.

© International Baccalaureate Organization 2020.

Determine the ${\mathrm{R}}_{\mathrm{f}}$ value of A1.

Draw the dipeptide represented by the formula Ala-Gly using section 33 of the data booklet.