Modification of Proteins - Understanding Proteins and Enzymes - Past Exam, Exams of Biology

Download Modification of Proteins - Understanding Proteins and Enzymes - Past Exam and more Exams Biology in PDF only on Docsity! Page 1 of 7 ARHOLIADAU EXAMINATIONS SEMESTER 1 EXAMINATIONS 2010 IBERS (BIOLOGICAL SCIENCES) BS21920 UNDERSTANDING PROTEINS AND ENZYMES TIME ALLOWED: TWO HOURS ANSWER ALL QUESTIONS FROM SECTION A IN THE SPACE PROVIDED ON THE QUESTION PAPER, AND ONE QUESTION FROM SECTION B IN THE SEPARATE ANSWER BOOK Rhif Cyfeirio’r Myfyriwr/ Student Reference Number: …………………………………………… Dyddiad/Date ……………………………………………… Ystafell Arholiad/Examination Room ……………………………………………… Rhif y Sedd/Seat Number ……………………………………………… 1. Please give the information requested above and enter your name in the space provided at the top right of this page. If your answers are to be marked under a scheme approved by the College whereby the examiners will not know your identity, fold over and seal down the top right-hand corner (using the gummed slip provided) in order to conceal your name. 2. The answers must be legibly written. The Examiners can either ignore illegible script or have it typed and the expense of typing charged to the candidate. 3. Write your answers in ink. 4. This paper must be handed in complete. 5. If you leave the examination early, please do so quietly so as not to disturb other candidates. 1. Rhowch y wybodaeth angenrheidiol yn y blychau uchod a rhowch eich enw yn y man gwag ar dop y tudalen ar y dde. Plygwch a seliwch y cornel ochr dde ar dop y tudalen (gan ddefnyddio’r slip gludiog a ddarperir) er mwyn cuddio eich enw. 2. Rhaid i’r atebion fod wedi eu hysgrifennu’n glir. Gall yr Arholwyr nail ai anwybyddu sgript annealladwy, neu drefnu i’w theipio a chael yr ymgeisydd i gwrdd â chost y gwaith. 3. Ysgrifennwch eich atebion mewn inc. 4. Ni ddylid torri allan unrhyw ran o’r llyfr hwn; rhaid ei ddychwelyd mewn ffurf gyflawn. 5. Os ymadewch â’r ystafell arholi yn gynnar, gwnewch hynny’n dawel os gwelwch yn dda rhag aflonyddu ar ymgeiswyr eraill. Fold over and stick down/plygwch y gornel drosodd Cyfenw/Surname ............................................. Enwau Cyntaf/ Forenames ...................................................... ........................................................................ Page 2 of 7 SECTION A (50 Marks) 1. What are the names of the following amino acids: (3 marks) 2. Give the names of two amino acids that are formed by post-translational modification of proteins (2 marks) .................................................................................................................... .................................................................................................................... and the name of one amino acid coded for by what is normally a stop codon. .................................................................................................................... (1 mark) Page 5 of 7 11. Briefly outline with the aid of a diagram how a bitopic arrangement for an integral protein is brought about. (5 marks) 12. Complete the enzymatic reactions, which occur in the duodenum to catabolise ingested nutrients. (5 marks) (Lipolytic acyl hydrolase) Triacylglycerol → .................. (α-glucosidase) Maltose → .................. (Oligo 1,6-glucosidase) Amylopectin → .................. (Ribonuclease) .................. → Nucleotides (Trypsin) Protein → .................. Page 6 of 7 13. This is a protein purification table of a hypothetical enzyme. Fill in the gaps in the table. (7 marks) Purification step Volume (ml) Total Protein (mg) Enzyme activity (units) Specific Activity (units/mg) Purification (fold) Yield (%) Crude extract 1000 10,000 100,000 - 100 Ammonium sulphate precipitation 200 2000 75,000 37.5 75 Ion exchange chromatography 100 500 50,000 50 Sephadex gel filtration 50 100 25,000 25 Affinity chromatography 5 5 10,000 2000 10 Page 7 of 7 SECTION B (50 Marks) ANSWER ONE QUESTION IN THE SEPARATE ANSWER BOOK 1. Describe how a polypeptide synthesised in the cytoplasm of a eukaryotic cell is targeted, modified and correctly folded in the lumen of the endoplasmic reticulum. What determines the ultimate destination of the protein? 2. Describe in detail how different types of bonding are important in conferring protein structure. Also, explain how protein structure is affected by changing pH, temperature, and redox potential. 3. Below is the data acquired from a series of kinetic experiments on a purified enzyme -galactosidase. A series of tubes were prepared which contained a constant amount of enzyme, but with varying concentrations of a substrate (ONPG). - galactosidase hydrolyses ONPG to give a yellow compound, which absorbs light at 420 nm. Tubes were incubated for 60 minutes, and the absorbance at 420 nm measured in a spectrophotometer. Explain whether -galactosidase exhibits Michaelis-Menten kinetics. Transform the data and plot it as a Lineweaver-Burk plot. From the plot, extract the Km and Vmax values of -galactosidase. Rate (A420 / hour) ONPG concentration (mM) 0.991 10 0.982 9 0.959 8 0.935 7 0.891 6 0.832 5 0.748 4 0.657 3 0.509 2 0.311 1 0.000 0 END