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Coursework: Biochemistry

Bolatova Talshyn

Name_______________________________

B

Tutor Group__________________________

Coursework: Biochemistry

Answer all the questions

  Maximum marks Your mark
Q1  
Q2  
Q3  
Q4  
Total Marks  

 

 

Submit a hard copy in the box in front of reception block 2

By Friday November 23rd 13.00

1 The diagram below shows what happens to electrons during part of the light-dependent reactions of photosynthesis. Any excited electrons that are not taken up by electron carriers follow pathway A and release energy as light in a process called fluorescence. The excited electrons that are taken up by electron carriers follow pathway B.

(a) Name the molecules X and Y shown on the diagram.

X...Photosystem 2(PS2)

Y..............NADP+.....................................................................................................................

(2marks)

(b) Explain the importance of reduced Y in the process of photosynthesis.

.NADPH plays crucial role in Calvin cycle, since it together with ATP supplies chemical energy(which is taken from light and converted to ATP and NADPH) and reduces glycerate 3 phosphate to glyceraldehyde 3 phosphate in order to make carbohydrates(nutrients). ........................................................................................

(3marks)

 

(c) A light was shone on a leaf and left switched on.

The graph below shows changes in the amount of light given off as fluorescence by the leaf

 

(i) Suggest an explanation for the increase in fluorescence.

...At the beginning chlorophylls have to be excited, which means that its electrons raises from ground state to higher energy level. In first second all chlorophylls are being excited. However it is unstable, so electrons fell back, releasing energy as heat or light(fluorescence). So within first second chlorophylls are being excited followed by electrons felling again, that is why fluorescence is increasing .............................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................

(2marks)

(ii) Suggest a reason for the fall in fluorescence.

...........All chlorophylls are excited, photosynthesis begins, and it can use fully the energy of light, so it now does not have release much energy as fluorescence, that is why its level decrease................



................................................................................................................................

................................................................................................................................

(1marks)

 

(d) Explain why an inhibitor of carbon dioxide fixation would lead to an increase in

fluorescence.

...If block carbon dioxide fixation via inhibitor, it makes photosynthesis inefficient. Chlorophyll cannot manage to great amount of energy, and this excess energy can damage it. That is why fluorescence is needed; it helps to release unabsorbed energy. Fluorescence is high when low energy is used to photosynthesize, so that is why when photosynthesis is disturbed by inhibitor florescence increase. ....................................................................................................................................

(4marks)

Total 12 marks

 

2. The initial stage of aerobic respiration is glycolysis. The diagram below outlines some of the steps of glycolysis.

Glucose

 

 

Glucose phosphate

 

 

Substance X

(a) (i) Substance X is the final product of glycolysis. Name substance X.

............................................................pyruvate....................................................................

(1mark)

(ii) Explain how glucose is changed into glucose phosphate in the first step of glycolysis.

...........The phosphorylation of glucose occurs through transfer one phosphate group from ATP to glucose, ADP is released, so this stage is energy consuming. Phosphorylation of glucose is catalysed by Hexokinase. Glucose 6 phosphate can be altered to fructose 6 phosphate. Second phosphorylation occurs with consumption of another ATP and the resulting sugar is fructose 1,6 bisphosphate (ADP released). However this sugar I not stable, so it is broken to two 3 carbon sugars: dihydroxyacetone phosphate (then enzymatically also converted to glyceraldehyde 3 phosphate) and glyceraldehyde 3 phosphate. .....................................................................................................................

 

(2marks)

 

 

(b) If oxygen is present, the products of glycolysis undergo further reactions in the Krebs cycle.

Describe what happens in the Krebs cycle.

.............................................Before entering krebs cycle Coa is added to pyruvate molecules and oxidative decarboxylation occurs, acetyl CoA is formed. NAD catches released electrons and becomes NADH, so in this link reaction yield is NADH per each of two pyruvates. During the Krebs cycle firstly oxidation of acetyl CoA(2c) by oxaloacetate(4c) occurs, forming citrate(6c). Citrate goes through series of reactions losing 2 CO2 which forms three NADH and one FADH2.Citrate isomerised to isocitrate, which loses CO2 and forms NADH, product is alfaketogluterate (5c). It also loses CO2 and again NAD is reduced to NADH,remaining compound is added CoA, sucinyl CoA released. Only one molecule of ATP is directly formed in one cycle when GDP catches P group of sucinyl CoA, then gives it to ADP to form ATP, succinate is formed here(4c). Sucinate turns to fumerate,hydrogen is recovered, so FAD+ reduced to FADH2. Water is added, and fumerate becomes malate. Malate reduces NAD to NADH + H, and becomes oxaloacetate, which begins cycle again. There are two molecules of acetyl CoA entered cycle, so yield is 6 NADH 2ATP and 2 FADH2. At the end of each cycle oxaloacetate(4c) is produced and cycle begins again. Theoretical yield of aerobic respiration here is 2ATP 2NADH per glycolysis, 2NADH per link reaction, 6NADH 2FADH 2ATP per Krebs cycle = 38 ATP. ..........................................................................................

.......................................................................................................................................

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.......................................................................................................................................

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(3marks)

(c) The diagram below shows the changes in energy levels during aerobic respiration

Explain what happens to the energy released in aerobic respiration as shown in the

diagram above.

...... ..................... Released energy is retained in bonds between phosphate groups of ATP, when energy is needed ATP is broken down, giving approximately 40 kj. Some energy is released as heat.................................

.......................................................................................................................................

(2marks)

Total 8 marks

 

 

3. (a) The photograph below shows a mitochondrion as seen using an electron microscope.

 

 

(i) Name the parts labelled B and C.

B .......matrix......................................................................................................................

C ......................cristae ......................................................................................................

(2marks)

(ii) Give the letter that represents the location of the electron transport chain.

....................C....

(1mark)

 

 

(b) Antimycin A is an inhibitor of the electron transport chain. It binds to one of the electron carriers in the chain.

An experiment was carried out to investigate the effect of Antimycin A on the respiration of yeast cells. Yeast cells were mixed with a buffer solution containing ADP, phosphate ions and glucose to form a suspension.

This suspension was then placed in a waterbath at 30 C and incubated for 30 minutes. During this time, the oxygen content of the suspension was measured.

The experiment was then repeated with Antimycin A added to the suspension 5 minutes after the start of the incubation.

The results are shown in the table below.

Time of incubation in /minutes Oxygen consumption of suspension / arbitrary units
  Without Antimycin A With Antimycin A added 5 minutes after the start of incubation
6.4 6.4
3.7 3.7
2.4 3.7
1.6 3.7
0.9 3.7
0.5 3.7
0.5 3.7

 

(i) Suggest why the oxygen content of the suspension of cells without Antimycin A did not reach zero.

...........because mitochondria consumed all present glucose and converted all ADP to ATP. As we know in Crebs cycle from glucose NADH is formed, which donates electrons to electron transport chain for reducing the oxygen and forming water. No glucose means no NADH , consequently consumption of oxygen stops, and its concentration will not decrease. As for ADP and phosphate ions, mitochondria also through electron transport chain makes ATP, therefore consumes oxygen. When all ADP converted to ATP, oxygen is not needed. .....................................................................................................................

................................................................................................................................

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................................................................................................................................

................................................................................................................................

................................................................................................................................

(2 marks)

(ii) Explain why the oxygen concentration of the suspension did not decrease after

Antimycin A was added.

.....Antimicyn blocks electron transport in comlex 3, so it will stop electron transport from NADH to oxygen. Consequently, oxygen is not reduced to form water, which means is not used. So, the after adding antimycin the concentration of O2 remained unchanged...........................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................

(2 marks)

(iii) Suggest what effect the addition of Antimycin A will have on the production of ATP.

Give an explanation for your answer.

...Antimicyn through binding to the Q(complex 3) and blocking electron transport, disrupts the formation of H+ gradient. As we know ATP is formed when H+ fells down the gradient and ATP synthase uses its energy to form ATP.(process called chemiosmosis) If there is no gradient protons will not move towards ATP synthase and ATP production will not occur...............................................................................................................................

................................................................................................................................

 

(3 marks)

Total 10 marks

4. Isolated mitochondria in a solution containing inorganic phosphate and an electron donor can be used to study respiration. An electrode is used to record changes in oxygen concentration while mitochondria respire.

The graph below shows changes in oxygen concentration for some isolated mitochondria.

 

 

(a) (i) Describe and explain the trends shown on the graph above.

.....at the beginning the O2 fell gradually because cell respired normally, then it decreased dramatically with addition of ADP because mitochondria started producing ATP , for that great amount of O2 was used.When ADP is run out, the rate of O2 consumption again fell gradually, since production of ATP slowed down. ...........................................................................................................................

................................................................................................................................

(3marks)

 

 

(ii) Name an electron donor used in the electron transport chain in mitochondria.

...................................NADH.............................................................................................

(1marks)

(iii) State the location of the electron transport chain in mitochondria.

........................................inner membrane. H+ goes down the gradient from intermembrane space crossing inner membrane to matrix, to produce the ATP

(1 mark)

Total marks 5

 

 


Date: 2016-01-03; view: 1074


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