Unit 8 Flashcards
Explain the principal functions of glycolysis. Hint: pathways can be described in different ways and produce products other than directmetabolites.
- important in metabolism and as energy source
- multi-step sequence referred to as pathway
- product of rxn is turned into substrate of another rxn
- pathways are catabolic (degradative) or anabolic (synthetic)
How many chemical reactions are used in glycolysis when converting glucose to pyruvate and what is the essential purpose of this series of reactions?
- 10 reactions
- energy release happens to rapid for cell cannot capture it
- allows for gradual decrease in free energy
Compare and contrast the general features of anaerobic glycolysis (fermentation) and aerobic glycolysis. Your explanation should include a discussion of the role of NADH in the reaction(s).
Anaerobic- production of ATP in cells that do not have mitochondria
Aerobic- formation of acetyl coA which is important in Citric acid cycle. reoxidized the NADH that is formed during oxidation of glyceraledehyde 3-phosphate.
Explain what is meant by the phrase ‘Three stages of catabolism”. Hint: in your answer give at least one example of the type of molecules expected at
each stage.
1) hydrolysis of complex molecules (proteins to amino acids, polysach to mono sach)
2) conversin of building blocks to simple intermediates (amino/polysach convered into CoA and other simple molecules)
3) oxidation of acetyl CoA (TCA cyle leads to oxidation which makes large amounts of ATP)
Which two essential biomolecules are considered to be end products of glycolysis (aerobic and anaerobic) and how are they essential? Hint: Anessential molecule is one that is needed by the cell in other important chemical
processes. Your answer should mention these important processes
.
Aerobic glycolysis end product is pyruvate.
Anaerobic glycolysis end product is lactate
Pyruvate is important because of the TCA cyle to make ATP
Lactate is important as a substrate in gluconeogensis to produce new glucose in muscle cells
List the three principal enzymes that are regulated in glycolysis. What makes these enzymes suitable for regulation?
Hexokinase, phosphofructokinase, pyruvate kinase
Hexo- low km (high affinity for glucose) allows glycolysis to occur even when blood glucose levels are low
Phos- allosterically inhibited by ATP so it slows down glycolysis
Pyruv- allosteric effectors can regulate by phosphorylation
(a) Could fructose 2, bisphosphate be considered a metabolic intermediate of glycolysis? (b) What action does fructose 2,6 bisphosphate have on glycolysis and gluconeogenesis and how is this important?
- no, it is a regulator of the process so therefore it would not be considered a metabolic intermediate
- Activator of phosphofructokinase-1 which phosphorylates in glycolysis. Controls both reciprocally. Important because it prevents glycolysis and gluconeogensis from running at the same time.
What is the function of the enzyme phosphofructokinase 2 (PFK2) and how may this enzyme be considered different from what we may usually assume for the function of an
- acts as a regulator
- different because it doesnt speed up chemical reactions
There are a variety of fairly common human genetic diseases in which
enzymes required for the breakdown of fructose, lactose, or
sucrose are
defective. However, there are very few cases of people having a genetic
disease in which one of the enzymes of glycolysis is severely defective.
Why do you suppose such mutations are seen so rarely?
They are very rare because they are important for survival of an organism. They would die.
Glycolysis has two reactions that require one ATP each and two reactions that produce one ATP each. This being the case, how can fermentation of glucose to lactate lead to the net production of two ATP molecules per glucose?
-The ATP yield for triose reactions therefore has to be doubled in order to suffice stoichiometrically with the ATPs consumed in hexose phosphorylation.
Some textbooks use the phrases ‘Investment Phase’ (also known as ‘Preparatory Phase’) or ‘Generation Phase’ (also known as ‘Payoff Phase’) to describe two particular aspects of glycolysis
. What
do
these
phrases
refer
to
?
- Investment (1st phase of glycolysis energy invest of 2ATP per glucose is necessary)
- Payoff (2nd phase) due to 3 carbon sugars modified in such a way that 2ATP are produced
Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans, and explain the circumstances that favour each.
- Used as acetyle-C-A in the krebs cycle (used to increase ATP stock in mitochondria)
- End up as oxaloacetate to be used in kreb cycle to produce ATP (beneficial for long aerobic activity where prolonged supply of ATP is needed)
- End up as lactate (benefits in muscle due to it regenerating NAD+ which is used in glycolysis)
The conversion of glucose into glucose 6 phosphate, which must occur in glycolysis, is thermodynamically unfavourable (endergonic) with a ΔG o’ =
13.8kJ/mol. How do cells overcome this problem?
Hint : review Unit 6
- Products are removed in very next step of pathway
- Causes very low steady state concentration of products which causes actual free-energy change negative
Explain how a deficiency of pyruvate kinase may cause haemolytic anaemia.
- result of reduced rate of glycolysis which leads to decreased ATP production
- Makes RBC change shape which leads to phagocytosis
- premature death leads to this anemia
List all the nonglycolysis reactions of gluconeogenesis
(starting from pyruvate)
and include enzyme names, reactants and products.
- Carboxylation of pyruvate
- Enzyme= pyruvate carboxylase
- Reactant=Pyruvate
- Products=OAA
Decarboxylation of cytosilic oxaloacetate
- Enzyme= PEP carboxykinase
- Reactants= oxaloacetate
- Products= PEP
Dephosphorylation of fructose 1,6-bisphosphate
- Enzyme= fructose 1,6-bisphosphotase
- Reactants= fructose 1,6- bisphosphate
- Products= fructose 6-phosphate
Dephosphorylation of glucose 6-phosphate
- Enzyme= glucose 6-phosphotase
- Reactant= glucose 6-phosphate
- Products= glucose
