exam

Question 1

pepsin

Answer 1

Biochem: Pepsin is involved in the hydrolysis of proteins into peptides and amino acids by breaking them down into peptide bonds and is a zymogen called pepsinogen - an inactive substance that is converted into an enzyme with the presence of HCl acid. Secretion of zymogens protects the stomach wall, primarily the chief cells that secrete it, from auto-digestion. If pepsin was secreted in the active form, it would break down the mucosal barrier and expose the underlying tissue to corrosion by HCl and the digestive enzymes, leading to ulcer formation.

Question 2

Pyruvate Dehydrogenase Complex

Answer 2

Respiration: Pyruvate Dehydrogenase Complex is multi enzyme complex in its quatenerary structure that can carry out 3 reactions at once and is responsible for converting pyruvate into acetyl-CoA by pyruvate decarboxylation. As a result of this complex, energy is saved as fewer side reactions and fewer enzymes are needed.

Question 3

RuBISCO

Answer 3

Photosynthesis: RuBISCO is involved in the first major step of carbon fixation. It has active site where CO2 or O2 can bind, but it has a higher affinity for CO2. When it picks up O2 it initiates photorespiration, where instead of carbon fixing happening it leads to the loss of already-fixed carbon as CO2. Photorespiration wastes energy and decreases the production of glucose

Question 4

GCPR

Answer 4

Regulation: GCPR is transmembrane domain receptor as it is embedded in a cells plasma membrane. GPCRs interact with G proteins in the plasma membrane and binds on the extracellular side. When an external signalling molecule binds to a GPCR, it causes a conformational change in the GPCR. This change then triggers the interaction between the GPCR and a nearby G protein. Whenever a G protein is active, both its GTP-bound alpha subunit and its beta-gamma dimer can relay messages in the cell by interacting with other membrane proteins involved in signal transduction.

Question 5

-ve feedback ADH

Answer 5

Stimulus: dehydration
Receptor: hypothalamus
Processor: hypothalamus or posterior pituitary gland
Effector: kidney collecting ducts
Response: aqua porins move to join membrane in collecting duct
-ve feedback: more water reabsorption, less ADH production

Question 6

ADH Water

Answer 6

ADH causes the walls of the distal convoluted tubule and collecting ducts in the kidneys to become more permeable to water. Water channels called aquaporins are contained within the membranes of intracellular vesicles in the epithelium of the distal convoluted tubule and collecting ducts. ADH stimulates the fusion of the vesicle membrane with the plasma membrane, like exocytosis. The aquaporins are now in place and allow water to flow out of the tubules and ducts in response to the hypertonic condition of the renal medulla. This water is reabsorbed in the blood stream.

Question 7

ADH Signalling

Answer 7

When ADH binds to g-protein couples receptor, the g protein subunit alpha displaces GDP and attaches GTP turning it on. The activated g protein travels and binds to membrane bound adenylyl cyclase which then uses ATP to produce cAMP, a secondary messenger. After this, the GTP will dissociate adenylyl cyclase and turn back into GDP. cAMP activates protein kinase which enables it to phosphorylate and pass along the single through a series of enzyme cascade reactions going. As a result, a signal is sent for the vesicle with the aquaporins to merge with the collecting duct membrane.