Question

Question 2 a (800 words)

i) When yeast metabolises glucose under anaerobic conditions, it produces ethanol and CO2 as end products of glycolysis but under aerobic conditions, pyruvate is the end-product of the glycolytic pathway. What is the physiological rationale for producing ethanol and CO2 under anaerobic conditions? Fully explain your answer.

ii) The standard free energy change for the oxidation of glucose to CO2 is shown below: Glucose + 6 O2 → 6 H2O + 6 CO2 ∆G’o = - 2840 kJ mol-1 If the free energy change (∆G’o) for the hydrolysis of ATP (ATP + H2O → ADP + Pi) is - 30.5 kJ mol-1, what is the overall percentage efficiency of glycolysis in terms of the free energy “captured” in the form of ATP? Make sure you fully explain your calculations and take care to include units and give your answer to three significant figures.

iii) Clearly explain in your own words the differences between substratelevel phosphorylation and oxidative phosphorylation. iv) What is the physiological rationale for the inhibitory effect of ATP on Phosphofructokinase?

Question 2b

In 800 words, Describe the process of receptor activation in Cell Signalling pathways. Illustrate your answer with a Cell Signalling system of your choice making sure to include the pathway(s) of receptor activation, the second messenger(s) involved and the downstream cellular response(s).

Answer 1

Question 2b

In 800 words, Describe the process of receptor activation in Cell Signalling pathways. Illustrate your answer with a Cell Signalling system of your choice making sure to include the pathway(s) of receptor activation, the second messenger(s) involved and the downstream cellular response(s). (100 marks)

ANS

cells must be able to receive and process signals in order to responde in their environmental condition. signals originate outside borders of cells. Individual cells often receive many signals simultaneously, and they then integrate the information they received from outside. also they send out messages to other cells both near and far. to make this communication easy. most of the signals that cells receives are chemical in nature.

the cells have a receptor it is a protein.signal molecules are bind with this protein receptor and start physiological response. there are specific receptor present for specific molecules and only bind with that molecule. there are hundreds of receptor types present  in cells, and different cell types have different populations of receptors. for example insulin receptor only bind with insulin. generally receptors are transmembrane proteins, which bind to signaling molecules outside the cell and subsequently transmit the signal through a sequence of molecular switches to internal signaling pathways.

mambrane receptors have 3 classes.B the name of the receptors is based on mechanism by which the receptors transform external signals into internal ones.

1.G-protein-coupled receptors, (via protein action)

2.ion channel receptors, (via ion channel opening)

3. enzyme-linked receptors. (via enzyme activation)

also some receptor exist deep inside the cell or in side the nucleus.

FIG: example of ion channel activation.signal molecule bind with recetopr and activate chennel.

in figure it can shows as cell receive the signal its configuration become changed. that starts biochemical reactions within the cell. These intracellular signaling pathways called as signal transduction cascades, typically amplify the message, producing multiple intracellular signals for every one receptor that is bound. Activation of receptors start to synthesis of small molecules called second messengers. that second messenger start to coordinate with intracellular signaling pathways.

EXAMPLE OF SINGNALING PATHWAY:

A common second messenger involved in signal transduction cascades is a cyclic AMP (cAMP) . adenylyl cyclase is an enzyme present in membrane that synthesize cAMP from ATP. Then cAMP molecules activate the enzyme protein kinase A (PKA), which allow to  phosphorylation of multiple protein substrates by attaching phosphate groups to them. Phosphorylation allows for intricate control of protein function and control activity of many enzymes involved in intracellular signaling pathways.then protein kinases can enter the nucleus and affect transcription. the signal stops after the transcription by degradedation of phoshoralated protein by the enzyme phosphodiesterase.

FIG:An example of a signal transduction cascade involving cAMP.

Conclusion

Cells are receive signals in the chemical form via various signaling molecules. then  signaling molecule are joins to the appropriate receptor on a cell surface. binding of signaling molecule with recetor triggers the chain of events that carries the signal to the cell interior and also amplifies it as well. Cells can also send signaling molecules to other cells.

THANK YOU.