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Student No.

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Final Mark

UNIVERSITY OF LIMPOPO FACULTY OF SCIENCE AND AGRICULTURE SCHOOL OF MOLECULAR AND LIFE SCIENCES DEPARMENT OF BIOCHEMISTRY, MICROBIOLOGY & BIOTECHNOLOGY DEGREE AND DIPLOMA EXAMINATION

MAY/JUNE: 2019

MODULE:

PAPER:

SBIA021

P

(ESSENTIAL BIOMOLECULES, STRUCTURES, FUNCTIONS AND SIGNAL TRANSDUCTION) TIME

:

3 HOURS

INTERNAL EXAMINER

:

PROF TM MATSEBATLELA

SECOND EXAMINER

:

MR RT MAKOLA

INTERNAL MODERATOR:

MARKS:

100

DR Z MBITA

THIS PAPER CONSISTS OF …15…PAGES INCLUDING COVER PAGE

INSTRUCTIONS: EXAMINERS 1. Answer all the questions. 2. Use the MULTIPLE CHOICE ANSWER SHEET to answer questions from Section A. 3. Answer SECTION B in the spaces provided.

SECTION A SECTION B TOTAL FINAL (%)

DATE OF EXAMINATION: _________________

INITIALS

VENUE:_____________DESCK NO.______

Date

1

2

WARNING 1. A candidate who without authorization takes into the examination room any book, document or object which could assist him in the examination, and does not hand over such material to the invigilator before the official commencement of the examination will be guilty of infringing the University's examination regulations and will be liable to punishment as determined by Council. 2. Rough work may be done only on the question paper or in the book containing the candidate's answers, and must be labeled as such. 3. No notes may be made on any part of the body such as the hands or on any garment. 4. This book is the property of the University and under no circumstances may the candidate· retain it, take it out of the examination room, or remove any of its pages. 5. No cellphone nor any other communication device (lap top, tablet etc) is allowed to be inside an examination hall during the examination period.

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SECTION A Choose the correct answer QUESTION 1 1.1.

In glucose, the orientation of the —H and —OH groups around the carbon atom 5 adjacent to the terminal primary alcohol carbon determines (A) D- or L- series. (B) dextrorotatory or levorotatory. (C) Α- and β-anomers. (D) epimers.

1.2.

The sugar found in milk is known as (A) galactose. (B) glucose. (C) fructose. (D) lactose.

1.3.

A test for reducing sugar “Benedict’s test” is not given positive by (A) sucrose. (B) lactose. (C) maltose. (D) glucose.

1.4.

Most individials who are lactose intolerant and can consume milk products (A) are of northern European background. (B) combine milk products with a high fiber diet. (C) process them with heat prior to consumption. (D) take milk products along with lactase tablets.

1.5.

Polysaccharides ___________ (A) contain many monosaccharide units which may or may not be of the same kind. (B) function mainly a storage or structural compounds. (C) are present in large amounts in connective tissue. (D) all of these.

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SBIA021 MAY/JUNE EXAMINATION 1.6.

2019

Triacylglycerols __________ (A) contain at least a glycerol molecule and two hydroxyl groups. (B) are components of membranes. (C) contain a glycerol molecule and three fatty acyl groups. (D) have the alcohol groups forming ether linkages with fatty acids.

1.7.

Which of the following is a metabolic precursor of prostaglandins and leukotrienes? (A) Vitamin A. (B) Arachidonic acid. (C) Sphingomyelin. (D) Cholesterol.

1.8.

Facilitated diffusion through a biological membrane is: (A) driven by a difference of solute concentration. (B) driven by ATP. (C) endergonic. (D) generally irreversible.

1.9.

Which is a general property of cell membranes? (A) Membranes contain more lipid than protein. (B) Membrane proteins have a polar head and a non-polar tail. (C) Membrane lipids are amphipathic. (D) Membranes contain covalent bonds between fatty acids.

1.10.

Which will be a characteristic of a steroid that is part of a cell membrane? (A) It will contain a hydroxyl group. (B) It will contain four aromatic rings. (C) It will contain choline. (D) It will contain an amide bond.

1.11. In non-competitive inhibition which of the following kinetic effect is true? (A) Both Km and Vmax decrease. (B) Both Km and Vmax increase. (C) Only Km decreases without affecting Vmax. (D) Only Km stays the same while Vmax decreases. 4|Page

SBIA021 MAY/JUNE EXAMINATION 1.12. Enzymes increase the rates of reactions by (A) Increasing the free energy of activation. (B) Decreasing the amount energy required to start a reaction. (C) Changing the equilibrium constant of the reaction. (D) Increasing the free energy change of the reaction. 1.13. Which of the following molecules is most likely to dissolve in water? (A) CH2(CH2)10OH. (B) CH2(CH2)6OH. (C) CH2(CH2)4OH. (D) CH3OH. 1.14. The true statement about solutions of amino acids at physiological pH is (A) All amino acids contain both positive and negative charges. (B) All amino acids contain positively charged side chains. (C) Some amino acids contain only positive charge. (D) All amino acids contain negatively charged side chains.

1.15. The charge of alanine at pH 1 of alanine is (A) 0. (B) -1. (C) +1. (D) +2.

1.16. The pI of aspartic acid is (A) 3.0. (B) 3.9. (C) 5.9. (D) 6.0.

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SBIA021 MAY/JUNE EXAMINATION

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1.17. The sulphur containing amino acid is (A) Methionine. (B) Cysteine. (C) Serine. (D) Both (A) and (B). 1.18. Which of the following amino acids contain an aromatic group? (A) Lysine. (B) Tyrosine. (C) Alanine. (D) Arginine. 1.19. Which of the following is an essential amino acid? (A) Aspartate (B) Tyrosine (C) Methionine (D) Serine 1.20.

Which of the following is an amino acid important in oxygen-binding by haemoglobin? (A) Histidine. (B) Iron. (C) Heme group. (D) All of the above.

1.21.

Which of the following amino acids is important in the structure of elastin? (A) Lysine. (B) Proline. (C) Cysteine. (D) Glycine.

1.22. Which of the following is more hydrophobic? (A) Serine. (B) Valine. (C) Asparagine. (D) Threonine. 6|Page

SBIA021 MAY/JUNE EXAMINATION 1.23.

The tertiary structure of proteins is stabilised by______ (A) Hydrogen bonds. (B) Ionic bonds. (C) Disulphide bonds. (D) All of the above.

1.24. In proteins the α-helix and β-pleated sheets are examples of (A) Primary structure. (B) Secondary structure. (C) Tertiary structure. (D) Quaternary structure.

1.25. Which of the following is an example of basic amino acids? (A) Lysine. (B) Glutamate. (C) Glycine. (D) Alanine. 1.26. Electrostatic bonds can be formed between the side chains of (A) Alanine and leucine. (B) Leucine and valine. (C) Aspartate and glutamate. (D) Arginine and aspartate. 1.27. The α-Helix is stabilised by (A) Hydrogen bonds. (B) Hydrophobic bonds. (C) Electrostatic bonds. (D) Disulphide bonds.

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1.28. All the following are branched chain amino acids except (A) Isoleucine. (B) Lysine. (C) Leucine. (D) Valine.

1.29. An –OH group is present in the side chain of (A) Threonine. (B) Serine. (C) Tyrosine. (D) All of the above. 1.30. The amino acids in which the R groups have a net positive charge at pH 7.0 are (A) Lysine, Arginine. (B) Lysine, Asparagine. (C) Histidine, Asparagine. (D) Glutamine, Arginine. [30]

SECTION B Question 1 1.1. Outline 5 differences between DNA and RNA.

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(5)

SBIA021 MAY/JUNE EXAMINATION

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1.2. Draw the titration curve of Glutamine and show their ionisation state in all stages.

(10)

(The Table of pKa values is provided on page 15).

1.3. Study the structure below and determine if it is likely to dissolve in water or not? Show the number water molecules likely to interact with it. Will this molecule dissolve in water? _______________.

(6)

Support your answer:____________________________________________________________ _____________________________________________________________________________ 9|Page

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Question 2 2.1. The following data points were obtained from an enzyme-catalysed reaction. [S] mM 0.01 0.05 0.15 0.25 0.50

V mM/s (No inhibitor) 0.26 0.92 1.36 1.50 1.65

V mM/s (With Inhibitor) 0.10 0.40 0.86 1.20 1.42

a) Draw a Michaelis-Menten plot for the enzyme reaction.

(6)

b) Draw the Lineweaver-Burk plot for the enzyme reaction.

(8)

c) Determine the Km and Vmax using the Michaelis-Menten plot.

(4)

d) Determine the Km and Vmax using the Lineweaver-Burk plot.

(4)

e) What is the Km and Vmax of the enzyme?

Km = ___________________________

Vmax = _________________________

(2)

f) Is this inhibition competitive or non-competitive? _____________________________ Support your answer:___________________________________________________ ____________________________________________________________________ (2)

2.2. Determine the nett charge of the pentapeptide “SHAKE” at pH 1.

(5) [31]

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Question 3 3.1. Define the following terms: Enantiomers: ___________________________________________________________________ _______________________________________________________________________________

Epimers: _________________________________________________________________ _________________________________________________________________________ (2) 3.2. Study structures A, B and C below and answer questions that follow.

a) Identify the following polysaccharides molecules. A____________________ B___________________ C___________________ (3) b) What is the storage form of carbohydrates in the (A) Plants and (B) Animals? A____________________ B___________________ 13 | P a g e

(2)

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c) From literature we know animals do not have cellulose, the enzyme that break cellulose glyosidic bonds. How does grazing animals such as horses break those bonds to simple sugar? (3) ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ d) What are the structural differences and similarities between peptidoglycans that constitute a bacterial cell wall and chitins that form part of the exoskeleton of insects and cell wall of fungi and yeast cells? Hint: structural components. ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ (4)

3.3. What important factor (s) influence (s) the melting point of the following fatty acids? Laurate (12:0)

44.2˚C

Stearate (18:0)

69.1˚C

Linoleate (18:2)

-9˚C

Oleate (18:1)

13.2˚C

_________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ (4) [18]

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