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Biological Molecules - Multiple Choice Questions

1 A carbohydrate test procedure was carried out on the urine of an infant who was nourished with a synthetic milk formula. A sugar was found to be in the urine. This compound was tested positive for Benedicts test but was tested negative when tested with Clinistix test (a test used by diabetics). Acid hydrolysis of the urine sample did not increase the amount of reducing sugar measured.

Which of the following compound is most likely to be present in this infants urine?

A Glucose

B Fructose

C Maltose

D Sucrose

2 Each polypeptide chain of haemoglobin contains a number of regions in the form of an alpha helix. Which feature of the haemoglobin molecule is responsible for this?

A Disulphide bonds between the four polypeptide chains at the quaternary structure.

B Hydrogen bonds between R groups of the amino acids in the secondary structure.

C Hydrogen bonds within the polypeptides chain in the secondary structure.

D Hydrophobic interactions within the polypeptide chain in the tertiary structure.

3 At which levels of protein structure do hydrophobic interactions occur?

A Primary, secondary and tertiary

B Secondary, tertiary and quaternary

C Tertiary and quaternary

D Quaternary only

4 How many different polypeptides, each consisting of r amino acids, can be made if the number of different amino acids available is n?

A nr

B rn

C nr

D n

5 Which of the following is an example of polymerisation?

A Bonds created between amino acids in the formation of a peptide chain.

B Formation of a covalent bond between two monomers that provide an -OH group each.

C Fatty acids joined to a glycerol molecule.

D A process involving addition of water molecules.

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6 A student uses centrifugation to separate the various subcellular structures of human epithelial cells by size and density. Which of the following molecule(s) would you expect to find in the pellet containing the cell membrane?

I

II

III

IV

A II only

B III only

C II and IV only

D I, III and IV only

7 Which of the following statement(s) describe(s) unsaturated fats?

I They have a higher melting point than saturated fats.

II Each molecule is an ester formed by a fatty acid with an alcohol other than glycerol.

III Each molecule has straight-chain fatty acids of the stearic series.

IV Each molecule has some carbon atoms which do not have covalent bonds linked with H atoms.

A I and IV only

B II and III only

C IV only

D II, III and IV only

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8 The figure shows two biological molecules.

Molecule X Molecule Y

Which of the following statement(s) about the molecules X and Y is/are true?

I Only molecule Y is a phospholipid because it does not contain a glycerol backbone.

II Both molecules X and Y are amphipathic as they both have polar and non-polar components.

III When molecules X and Y are treated with phospholipases, the same products are produced.

A I only

B II only

C I and III only

D II and III only

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9 The R group of the amino acid serine is CH2 OH. The R group of the amino acid alanine is CH3. Where would you expect to find these amino acids in a fibrous protein?

A Serine would be in the interior, alanine would be on the exterior of the fibrous protein.

B Alanine would be in the interior, serine would be on the exterior of the fibrous protein.

C Both serine and alanine would be in the interior of the fibrous protein.

D Both serine and alanine would be on the exterior of the fibrous protein.

10 Diagrams 1, 2 and 3 show the structural formulae of three polysaccharides.

What are the names of these polysaccharides?

1 2 3

A amylose cellulose glycogen

B amylose glycogen cellulose

C cellulose glycogen amylose

D glycogen amylose cellulose

11 The diagram below shows the structure of an inhibitor of lysozyme.

Which substance is most likely to be a normal substrate for lysozyme?

A lipid

B polynucleotide

C polypeptide

D polysaccharide

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12 Which statement about triglycerides is correct?

A They are made up of three fatty acids combined with glycogen.

B They are more saturated with hydrogen compared with phospholipids.

C They form a bilayer in the membranes of cells.

D They have a lower ratio of oxygen to carbon compared with carbohydrates.

13 The key below can be used to separate the following carbohydrates:

amylopectin, cellulose, maltose, ribulose, sucrose

I (a) readily soluble in water Go to II

(b) insoluble in water Go to IV

II (a) is a reducing sugar Go to III

(b) is a non-reducing sugar V

III

(a) phosphorylated form is the carbon dioxide acceptor in photosynthesis

W

(b) product of starch digestion by amylase X

IV

(a) linked by (14) glycosidic bonds and (16)

glycosidic bonds Y

(b) linked by (14) glycosidic bonds Z

What are V, W, X, Y and Z?

V W X Y Z

A sucrose maltose sucrose amylopectin ribulose

B maltose ribulose sucrose cellulose amylopectin

C cellulose ribulose maltose sucrose amylopectin

D sucrose ribulose maltose amylopectin cellulose

14 The diagram shows two molecules of a biological substance.

Which type of bond is formed when these molecules react to form a larger molecule?

A Phosphodiester C Peptide

B Glycosidic D Hydrogen

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15 A solution of a protein was completely hydrolyzed using a protease. The resulting amino acids were separated using paper chromatography. The resulting chromatogram is shown in the figure below. (Rf = distance moved by spot distance moved by solvent)

I The identity of the amino acid marked X on the chromatogram is alanine.

II The identity of the amino acid marked X on the chromatogram is valine.

III Although the protein contains 5 different amino acids, all 5 did not appear on the chromatogram as some spots were too close together to distinguish between them.

Which of the above statement(s) is/are correct?

amino acid Rf value

lysine 0.14

glycine 0.26

alanine 0.38

valine 0.58

leucine 0.73

A I only

B II only

C II and III only

D I and III only

16 The diagram below shows two molecules.

What is formed when a large number of these molecules are condensed?

A Amylose

B Cellulose

C Phospholipid

D Protein

solvent front

x x

origin

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17 Which feature is true of cellulose and accounts for its strength?

A It is a fibrous molecule which is insoluble in water.

B It is made up of long, branched and coiled chains of glucose units with 1,4 links.

C It contains both -1,4 and -1,6 links between glucose units.

D It has OH groups that form hydrogen bonds with adjacent cellulose molecules.

18 Which of the following is/ are true of triglycerides and phospholipids?

i. Both contain fatty acid tails

ii. Only phospholipids are amphipathic

iii. Phospholipids are formed from fatty acids and phosphoric acid while triglycerides are formed from fatty acids and glycerol.

iv. Both fatty acids and glycerol are soluble in organic solvents

v. Phospholipids have a higher carbon content than triglycerides for storage purposes

A i, ii, and iii

B i, ii and iv

C ii, iii and iv

D ii, iii and v

19 Fig. 1 below shows the structure of 4 monomers.

Figure 1

Which of the following combination of polymer, monomer and bond formed between monomers is correct?

starch cellulose polypeptide polynucleotide

A X, -1,4 glycosidic bond

U, -1,4 glycosidic bond

Z, ester linkage Y, disulphide linkage

B U, -1,4 glycosidic bond

X, -1,4 glycosidic bond

Y, peptide bond Z, phosphoester linkage

C Z, peptide bond X, hydrogen bond Z, ionic bond U, hydrogen bond

D X, ionic bonds Y, peptide bond U, hydrogen bond Z, -1,6 glycosidic bond

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20 The figure below shows part of the molecular structure of a polysaccharide.

Key: - - - hydrogen bonds

Which of the following statements are true?

1. The structure contains -glucose.

2. The polysaccharide, which is an important food source for animals, can be digested by humans.

3. The polysaccharide may associate in groups to form microfibrils, which are arranged in larger bundles to form macrofibrils.

A 1 and 2 only

B 2 and 3 only

C 1 and 3 only

D All of the above

21 Raffinose is a trisaccharide which can be degraded by enzymes. The results of two different enzymatic incubations are shown as follows:

Enzyme used Products

Sucrase Melibiose and fructose

Galactosidase Galactose and sucrose

Which of the following statements are consistent with the results shown above?

I Raffinose is composed of three different monosaccharides.

II Melibiose is a dissaccharide.

III Acid hydrolysis of raffinose would yield glucose.

IV The products of raffinose digestion by sucrase and galatosidase respectively will yield a brick red precipitate when heated with Benedict reagent.

A I and III only

B II and IV only

C I, II and III only

D All of the above

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Structured questions

1 Pepsin is a protease that is active in the stomach. The human pepsin molecule is displayed in Fig. 1. The molecule has a deep cleft and contains a pair of aspartic acids at position 32 and 215 on either side of the cleft, which break peptide bonds in proteins.

Figure 1

(a) State how peptide bonds in the protein are broken. [1]

Hydrolysis

(b) Explain what determines the precise positions of Asp 32 and Asp 215 in the pepsin structure. [3]

[Total: 4]

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2 Fig. 2.1 shows the molecular structures of -glucose and glycine.

-glucose Glycine

Fig 2.1

Table 2.1 shows the buffering capacities of -glucose and glycine in weak acidic and basic solutions.

Biological molecule

-gluco

se Glycin

e

In weak acid - +

In weak base - +

Table 2.1

(a) Explain how glycine can function as a buffer while -glucose cannot. [3]

(b) Glucose has the ability to form large macromolecules.

(i) In the space below, draw and label how -glucose molecules are joined to form the chains found in glycogen. [2]

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(ii) Name the reaction that forms the bonds in (b)(i). [1]

Hydrolysis

(c) An experiment was done to compare glycogen and triglycerides. Both biological molecules were burned in excess oxygen to raise the temperature of 100 cm3 of water initially at 25 C. Fig. 2.2 shows the results of the experiment.

Fig. 2.2

(i) Suggest how burning the biological molecules leads to a rise in water temperature. [1]

Hydrolysis

(ii) With reference to Fig. 2.2, explain the differences in energy content between glycogen and triglycerides. [3]

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(d) The structure of agarose, another commonly occurring polysaccharide, is shown in Fig. 2.3 below. Agarose is a polymer of two isomers of galactose (D-galactose and L-galactopyranose) forming the repeating unit in brackets.

Fig. 2.3

(i) State two structural differences between cellulose and agarose. [2]

(ii) Agarose serves an important role in maintaining the cell walls of algae. Suggest what this role is and explain how the structure of agarose allows it to perform its function. [3]

Role:

Explanation:

[Total: 15]

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3 Collagen is the main structural protein in the human body. It strengthens the tendons and supports the skin and internal organs. Bones and teeth are made by adding mineral crystals to collagen.

(a) Explain why collagen is described as a fibrous protein. [2]

(b) Describe the main features of collagen that contribute to its tensile strength. [3]

[Total: 5]

4 Stachyose is a storage oligosaccharide found in beans, peas and other legumes. Stachyose can only be metabolized by anaerobic microorganisms in the large intestine. It is responsible for the production of carbon dioxide, hydrogen sulfide and other gases that collectively make up what is known as flatulence. The structure of stachyose is shown in Fig. 4.1.

Figure 4.1

(a) Define the term glycosidic bond. [1]

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(b) Several commercial products are available to assist in the digestion of oligosaccharides like stachyose. Suggest how such products prevent the production of flatulence. [1]

(c) When small amounts of paper containing cellulose are ingested by children, there is usually no gas production. Suggest one reason and a possible consequence of such an event. [2]

An enzyme known as -galactosidase cleaves -1,6-glycosidic bonds to sequentially release terminal galactose residues. The breakdown of stachyose by -galactosidase is a two-step process. In the first step of this process, stachyose is hydrolysed to galactose and raffinose.

(d) With reference to Fig. 4.1, draw the products of the first step in this hydrolysis. [2]

Fig. 4.2 illustrates the activity of -galactosidase on the substrate stachyose over a period of time.

Fig. 4.2

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(e) With reference to Fig. 4.2, explain why the level of raffinose remains relatively constant. [2]

(f) Suggest why the rate at which stachyose is broken down decreases as the concentration of galactose increases. [2]

[Total: 10]

5 Lactose is a sugar which is found in milk. It can spoil milk products such as ice cream by producing an unpleasant sandy texture. Lactase is an enzyme which is used in making ice cream. It breaks down lactose to glucose and galactose.

Mature human lactase consists of a single 160 kDa polypeptide chain that localizes to the brush border membrane of intestinal epithelial cells. Two amino acids present in the active site, Glu-1271 and Glu-1747, are vital for the catalytic action of lactase.

When ice cream is made, lactase is added to milk and left for about a day at 5 C. The reaction is very slow.

(a) Explain how the two amino acids at positions 1271 and 1747 in the amino acid sequence are brought close to form the active site. [3]

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(b) Use your knowledge of enzymes to explain why the rate of this reaction is very slow at 5C. [2]

(c) Adult cats are unable to digest lactose. Lactase is used to reduce the amount of lactose in milk for cats. The milk is heated to sterilise it. It is then cooled and the lactase added before packaging. Explain why lactase is added after cooling the milk rather than before heating it. [2]

(d) Table 5.1 shows the diet of the large white butterfly and the enzymes it produces at different stages of its life cycle.

Table 5.1

Stage in life cycle

Diet Enzymes secreted by

salivary glands mid-gut

Larva Leaves Amylase

Amylase

Maltase

Proteases

Lipases

Adult Nectar None Sucrases

(i) The larva and adult of the large white butterfly occupy different ecological niches. With reference to the table, explain how the diets and enzymes secreted are related to the demands of these stages of the life cycle of the large white butterfly. [2]

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(ii) Leaves contain little glucose, yet large amounts of glucose can be found in the mid-gut of the larva of the large white butterfly. Explain why. [2]

[Total: 11]

6 Collagen, a quaternary protein, is used as a solid substratum for cells to adhere to in order to proliferate.

(a) Explain the term quaternary protein. [1]

(b) Describe how the structure of collagen allows it to function as a structural support for cells. [3]

(c) Lysozyme is an enzyme found in many places within the human body. It consists of a single polypeptide folded into a complex shape. Explain how a globular protein, such as lysozyme, differs from a fibrous protein, such as collagen. [2]

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Essay

1. Distinguish between the structures of collagen and cellulose. [7]

2. Explain how the molecular structure of triglycerides is related to their functions. [6]

3. Suggest why plant cells mainly store carbohydrates and animal cells mainly store lipids. [4]

4. Suggest reasons why it is more advantageous for animals to store lipids instead of carbohydrates. [4]