Week 2 - Glycolysis Flashcards
What are the three essential features of the glycolysis pathway?
Reduction of NAD+
Production of ATP
Production of pyruvate
What is cellular respiration and what does it involve?
It is is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. It includes glycolysis (Acetyl-CoA production), the TCA cycle (Acetyl-CoA oxidation), and the electron transport chain (electron transfer and oxidative phosphorylation). It’s a process in which cells consume O2 and produce CO2, and provides energy in the form of ATP.
Where do the three stages of cellular respiration occur inside the cell?
Glycolysis (Acetyl-CoA production) occurs in the cytoplasm.
The TCA cycle (Acetyl-CoA oxidation) occurs in the mitochondrial matrix.
The electron transport chain (oxidative phosphorylation) occurs in the inner mitochondrial membrane.
Where, overall, are the three CO2 molecules lost in cellular respiration?
One molecule in glycolysis, and two molecules in the TCA cycle.
What are the four possible fates of glucose?
Storage as glycogen.
2 x equivalents of pyruvate molecules (oxidation via glycolysis).
Ribose 5-phosphate (via pentose phosphate pathway).
Synthesis of structural polymers in bacteria and plant cells eg. cellulose.
Chronic Niacin deficiency (Vitamin B3) leads to what disease?
Pellagra
In the absence of oxygen (anaerobic conditions), what happens to pyruvate after glycolysis?
It is reduced to lactate through oxidation of NADH to NAD+, a process termed ‘lactic acid fermentation’.
In the presence of oxygen (aerobic conditions), what happens to pyruvate that results from glycolysis?
The pyruvate is oxidised (with loss of the carboxyl group as CO2), and the remaining two carbon unit becomes the acetyl group of Acetyl-CoA. This acetyl group is metabolised in the TCA cycle and fully oxidised to yield CO2.
The main product of glycolysis?
Pyruvate.
Pyruvate in microorganisms and plant tissues
It can be reduced to ethanol, again with oxidation of NADH to NAD+, i.e. alcoholic fermentation.
First step of glycolysis?
Phosphorylation of glucose, i.e. Glucose to glucose 6-phosphate. It is catalysed by the enzyme Hexokinase, and requires ATP to proceed (part of the investment phase). It also requires Mg2+ as a cofactor. This enzyme completely encloses the substrate to exclude water, i.e. an exapmle of an ‘induced fit’ interaction. It is an irreversible reaction, but it not the first ‘committed step’ of glycolysis, as it can go and do other things.
In general, what is a kinase?
An enzyme that uses ATP and phosphorylates something.
Third step of glycolysis?
Phosphorylation of fructose-6-phosphate (F-6-P)
to fructose-1,6-bisphosphate (F-1,6-BP). Catalysed by a very important regulatory enzyme, the ‘gatekeeper of glycolysis’, Phosphofructokinase-1 (PFK-1). We consume another ATP, and we gain another phosphate group on our substrate. Irreversible reaction, and also known as the first ‘committed step’ of glycolysis, because once it has occurred, the molecule is more or less committed to going all the way through glycolysis.
Phosphofructokinase-1 (PFK-1) and bacteria
The bacterial enzyme has 4 identical subunits. The active site binds to the sugar and ATP. The enzyme also has regulatory binding sites at the top and bottom.
Step 10 in glycolysis?
Transfer of phosphoryl group from phosphoenolpyruvate (PEP) to ADP. It is catalysed by pyruvate kinase. The name is backwards though, as it implies using ATP to phosphorylate something. But what’s happening here is we are transferring a phosphate from phosphoenolpyruvate onto ADP to form ATP, which we have to multiply by 2, due to having 2 x 3 carbon chains, rather than the original single 6-carbon chain molecule.
