Questions to ask when studying cellular respiration:
1. where is glycolysis occurring?
2. what are the 10 enzyme involved?
3. what are the reactants and products formed?
4. is there any gain of loss at the end of glycolysis?
5. what does this process require in order to continue?
6. is there any cofactors necessary for the catalyzed reactions to continue?
1. what is the reactant and product involved?
2. what is the enzyme involved?
3. is there any cofactors needed for this process to continue?
4. at the end of this reaction what happens to the products formed (Acetyl-CoA)?
5. where in the cell does this process occur?
CITRIC ACID CYCLE
1. how many ATP, NADH and FADH2 is generated?
2. is ATP used in this process?
3. what product of respiration is formed at this stage through the metabolism of Acety-CoA?
hint- Glucose + Oxygen —-> Carbon Dioxide + Water + Energy
C6H12O6 + 6O2 —-> 6CO2 + 6H2O + Energy
4. where in the cell does this process occur?
ELECTRON TRANSPORT CHAIN- CHEMIOSMOSIS
1. what do you understand by the chemiosmosis theory?
2. where in the cell is the ETC located?
3. what is the product of respiration formed at this stage?
4. how is ATP generated by this process?
5. what do you understand by the terms ATP synthase, Complexes 1, 2, 3 and 4?
6. how do protons and electrons flow across and along the organelle’s membrane?
Fermentation is an anaerobic process in which energy is released from glucose in the absence of oxygen. It occurs in yeast cells, erythrocytes, bacteria and in the muscle cells of animals.
FERMENTATION IN YEAST
In yeast cells glucose is metabolized through cellular respiration as in other cells. However, when oxygen is lacking glucose is still metabolized to pyruvic acid (pyruvate) via glycolysis. The pyruvate is first converted to acetaldehyde by the enzyme pyruvate decarboxylase and then to ethyl alcohol by the enzymic process of alcohol dehydrogenase. There is no net gain or loss just regeneration of NAD+. This process is essential because it removes electrons and hydrogen ions from NADH during glycolysis. The effect is to free the NAD so it can participate in future reactions of glycolysis.
Yeast is used in bread and alcohol production. Alcohol fermentation is the process that yields beer, wine, and other spirits. The carbon dioxide given off during fermentation supplements the carbon dioxide given off during the Krebs cycle and causes bread to rise.
FERMENTATION IN MUSCLE CELLS
When muscles contract too frequently (as in strenuous exercise) they rapidly use up their oxygen supply. As a result, the electron transport system and Krebs cycle slows down as well as ATP production. However, muscle cells have the ability to produce a small amount of ATP through glycolysis in the absence of oxygen. The muscle cells convert glucose to pyruvate. Then the enzyme lactate dehydrogenase in the muscle cells converts the pyruvic acid to lactic acid. This reaction regenerates NAD+. Eventually the lactic acid buildup causes intense fatigue and the muscle cell stops contracting.
It is a rare genetic metabolic disorder that affects an individual’s ability to metabolize the sugar galactose properly. There are three forms of this disease Galactose-1-phosphate uridyl transferase deficiency, Galactokinase deficiency or Galactose-6-phosphate epimerase deficiency.
Infants with galactosemia can develop symptoms in the first few days of life if they eat formula or breast milk that contains lactose. The symptoms may be due to a serious blood infection with the bacteria E. coli.
- poor feeding habits where the baby refuses to eat formula containing milk
- poor weight gain
- yellow skin and whites of the eyes (jaundice)
The above photo indicates that the absence of the GALT enzyme leads to health problems as indicated above.
What is the Cori Cycle?
It is also known as the Lactic acid cycle. It is a metabolic pathway in carbohydrate metabolism that links anaerobic glycolysis in muscle tissue to gluconeogenesis in the liver.
How is it important to metabolism?
- The Cori cycle involves 2 organs, the contracting muscle and the liver.
- It functions in anaerobic conditions when the muscles are contracting under reduced oxygen.
- The contracting muscles produce lactate (instead of pyruvate proceeding to acetyl CoA to TCA cycle) which is supplied to the liver.
- In the liver gluconeogenesis converts lactate to pyruvate and glucose.
- Glucose is then metabolised by contracting muscle via glycolysis, to pyruvate and acetyl CoA under aerobic condition (sufficient oxygen), and acetyl CoA enters TCA cycle. Otherwise the glucose goes through anaerobic glycolysis and the Cori cycle goes on till oxygen is sufficient.
Steps in GLYCOLYSIS:
From this week the new topic to be investigated by this blogger is…can you guess? Yes it is Glycolysis. First let me start with a definition of glycolysis: it is a metabolic pathway which takes place in every single cell in its cytosol. It does not have any specific organelle to take place in but uses the cell’s cytosol for its purpose.
There are ten reactions which takes place in this pathway involving the use of 3 irreversible and 7 reversible reactions. It is divided into two stages:
STEP 1. glucose is converted to glucose 6-phosphate by the enzyme hexokinase which is an irreversible reaction. One molecule of ATP is used for this conversion.
[Irreversible reaction is where delta G – activation energy has a high negative value therefore if it was to go in the opposite direction it would require a high positive activation energy]
STEP 2. glucose 6-phosphate is converted to fructose 6-phosphate with the use of the enzyme phosphohexose immerase which is a reversible reaction.
[Reversible reaction is where the delta G is close to zero and it can go in both directions]
STEP 3. fructose 6-phosphate is converted to fructose 1,6 bisphosphate by the aid of the enzyme phosphofructokinase-1 (PFK-1). Another molecule of ATP is used for this conversion.
[Did you know? PFK-1 is the most regulated enzyme in glycolysis]
STEP 4. fructose 1,6 bisphosphate is then converted to glyceraldehyde 3-phosphate (G3P) and dihydroxy acetone phosphate (DHAP) by the enzymic reactions of aldolase.
[DHAP does not enter the second phase of glycolysis]
STEP 5. the enzyme triose phosphate isomerase comes into play to convert DHAP to a molecule of G3P.
[G3P and DHAP are isomers of each other]
STEP 6. glyceraldehyde 3-phosphate (2 molecules) is converted to 1,3 -bisphosphoglycerate (1,3- BPG) (2 molecules) by glyceraldehyde 3- phosphate dehydrogenase. Both and oxidation and phosphorylation reaction occurs at this step.
[Oxidation= 2NAD+ → 2NADH]
[Phosphorylation= 2Pi inorganic phosphates are added to carbon 3 on 1,3 BPG]
STEP 7. 1,3 -bisphosphoglycerate (2) is converted to 3-phosphoglycerate (2) by phosphoglycerate kinase. Two molecules of ATP is generated from this conversion and is broken even since ATP used in the first phase is compensated at this point.
[Substrate level phosphorylation- generation of ATP in glycolysis]
STEP 8. 3-phosphoglycerate (2) is converted to 2-phosphoglycerate (2) by phosphoglycerate mutase. The phosphate group is moved from carbon 3 to carbon 2.
STEP 9. 2-phosphoglycerate (2) is converted to phosphoenolpyruvate (2) by the enzymic reaction of enolase. It is a dehydrtion reaction since 2 molecules of water is lost.
STEP 10. phosphoenolpyruvate (2) is converted to pyruvate by pyruvate kinase. Two molecules of ATP is formed.
For every glucose molecule entering glycolysis 2ATP and 2NAP+ is used and 4 ATP and 4 NADH generated.
NET GAIN:- 2 ATP and 2 NADH