Discuss the importance of cycles

• The Calvin cycle is very important in generating various products used in the process of photosynthesis. The cycle occurs in the stroma of the chloroplast and produces glucose in the light-independent stage of photosynthesis, which is needed in anaerobic and aerobic respiration, to allow ATP to be released and allows photophosphorylation to occur. In the Calvin cycle, carbon dioxide from the environment reacts with a 5 carbon sugar (ribulose bisphophate) in a carbon fixation reaction, this reaction is catalysed by the Rubisco enzyme.
• As a result ribulose bisphosphate is converted into a 3 carbon sugar glycerate-3-phosphate, which is then reduced by NADPH to form triose phosphate. In the process of this conversion, NADPH is converted into NADP, and the energy produced from the hydrolysis of 2 ATP molecules, then releases 2 ADP and 2 Pi. Both NADPH and ATP are products of the light-dependant stage of photosynthesis. Finally 1 out 6 triose phosphate molecules are converted into useful substances such as glucose. Some glucose molecules are used to regenerate ribulose bisphosphate, however this requires energy from 1 ATP.
• Overall plants depend on this cycle as an energy source and wouldn’t have any without it.
• The Kreb’s cycle is another process which takes place in the matrix of the mitochondria, and is needed to allow organisms to respire aerobically. This first stage of the Kreb’s cycle is the conversion of acetyl coenzyme A to a 6 carbon sugar, releasing coenzyme A so that it can be reused in the link reaction, allowing it to react with acetate again. After this 6 carbon sugar is decarboxylated, releasing another molecule of carbon dioxide. It is then dehydrogenated causing a molecule NAD to be reduced into NADH, after all of these processes it forms a 5 carbon sugar.
• The 5 carbon sugar is decarboxylated releasing another molecule of carbon dioxide. Both molecules of carbon dioxide are released into the environment via expiration as they are a waste product, which must be removed from the lungs. The carbon dioxide released can then be used by plants to photosynthesise, which signifies its importance. The 5 carbon sugar is then dehydrogenated allowing the reduction of 2 molecules of NAD to NADH and 1 molecule of FAD to FADH to take place. During the conversion of the 5 carbon sugar, to the 4 carbon sugar substrate level phosphorylation occurs.
• During substrate level phosphorylation, ADP and Pi are converted into ATP. The remaining products from the cycle which are NADH, FADH and ATP are important as they are used in oxidative phosphorylation. ATP is the energy source for this reaction, and NADH and FADH release high energy electrons which in turn allow 32 to 34 molecules of ATP, to be released. During respiration the waste product released is carbon dioxide which is used in photosynthesis, specifically the light-independent reaction for plants. To add to its importance the ATP produced in the Kreb’s cycle.
• ATP from Kreb’s cycle is useful for: Providing energy for chemiosmosis of hydrogen ions down ATP synthase, which is also in oxidative phosphorylation which allows muscle contractions to take place.