Y do some enzymes need to be stored at really low temperatures? Also, i find it difficult to understand cellular aerobic respiration. Anyone got an analogy?
Enzymes are typically stored at low temperatures whilst they are being transported or not in use because we know that most enzymes get denatured and this is irreversible at high temperatures, so to prevent this from happening, by storing in really low temperatures, the enzymes don't denature but they simply 'freeze', and when stored at their optimal/room temperature, their specific functionality resumes. So in short, freezing them basically retains their enzymatic shape and hence they will not get denatured.
Aerobic cellular respiration is respiration that requires the addition of oxygen molecules. If there are no oxygen molecules present, then the pyruvate molecules that result from glycolysis will simply enter the fermentation cycle, producing ethanol (in plants and yeast) and lactic acid (in humans and other animals). Anyway, aerobic respiration has two main steps that you need to know, the Citric Acid Cycle (Krebs Cycle) and the Electron Transport Chain (ETC).
Here is what happens in:
- Citric Acid Cycle: So the two resultant products, the 2 pyruvate molecules from glycolysis enter the mitochondrial matrix (which is the mitochondial 'juice' inside the inner membrane). Once these molecules are there, they undergo reactions with Coenzyme A, and during this reaction, a NADH and a CO2 and Acetyl CoA molecules are produced, PER pyruvate. So, when this occurs, the Acetyl CoA undergoes further reactions, yielding 3 NADH molecules, 1 FADH2, 2CO2 and an ATP molecule. So, when both the pyruvates finalise their reactions during the Krebs cycle, there is a result of: 8 NADH, 2 FADH2, 2ATP and 6 CO2 molecules produced. Now just keep in mind that the ATP molecules are energy, the whole point of the process (respiration), and the CO2 is expelled as waste product, that is what we breathe out and what plants consume for photosynthesis. The NADH and FADH2 molecules are called 'carrier' molecules, they carry the 'H' atoms as well as electrons to the 'Electron' Transport Chain.
Inputs: 2 Pyruvate, 8NAD+, 2FAD, 2ADP+2Pi
Outputs: 2ATP, 6CO2, 2FADH2, 8NADH
ETC: You do not need to know much about this process at all for VCE. Just know that its a 'chain', that is, electrons are passed along cytochromes (protein molecules) that are embedded within the cristae (inner projections of the inner membrane of mitochondria) and until they reach an oxygen molecule, where they are accepted as well as Hydrogen atoms that are carried by the NADH and FADH2 molecules, to produce water. Also, whilst this occurs, note that ATP is synthesised in a great amount, approximately 32-34 (depending on which type of cell, for example, a muscle cell would need more energy compared to skin cells) ATP molecules are produced PER glucose molecule.
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