Chemiosmotic Hypothesis:

etc-question-and-answer-wordle

The chemiosmotic hypothesis was developed in 1961 by Peter D. Mitchell which suggests that most ATP synthesis in respiring cells comes from the electrochemical gradient across the inner membranes of mitochondria by using the energy of NADH and FADH2 formed from the breaking down of energy-rich molecules, such as glucose.

The diagram below shows the structure of a mitochondria:

mito
Molecules such as glucose are metabolized through glycolysis to produce acetyl CoA as an energy-rich intermediate. The oxidation of acetyl CoA in the mitochondrial matrix is coupled to the reduction of a carrier molecule such as NAD and FAD. The carriers pass electrons to the electron transport chain (ETC) in the inner mitochondrial membrane, which in turn pass them to other proteins in the ETC. The energy available in the electrons is used to pump protons from the matrix across the inner mitochondrial membrane, storing energy in the form of a trans-membrane electrochemical gradient. The protons move back across the inner membrane through the enzyme ATP synthase. The flow of protons back into the matrix of the mitochondrion via ATP synthase provides enough energy for ADP to combine with inorganic phosphate to form ATP. The electrons and protons at the last pump in the ETC are taken up by oxygen to form water.

Diagram showing the structure of mitochodrial ATP synthase (F1F0 ATPase)

atpase                          pi
In all cells, chemiosmosis involves the PROTON-MOTIVE FORCE (PMF) in some step. This can be described as the storing of energy as a combination of a proton and voltage gradient across a membrane. The chemical potential energy refers to the difference in concentration of the protons and the electrical potential energy as a consequence of the charge separation (when the protons move without a counter-ion).
In most cases the proton motive force is generated by an ETC which acts as both an electron and proton pump, pumping electrons in opposite directions, creating a separation of charge. In the mitochondria, free energy released from the electron transport chain is used to move protons from the mitochondrial matrix to the inter-membrane space of the mitochondria. Moving the protons to the outer parts of the mitochondria creates a higher concentration of positively charged particles, resulting in a slightly positive and slightly negative side. This charge difference results in an electro-chemical gradient. This gradient is composed of both the pH gradient and the electrical gradient. The pH gradient is a result of the H+ ion concentration difference. Together the electro-chemical gradient of protons is both a concentration and charge difference and is often called the proton motive force. The PMF needs to be about 50 kJ/mol for the ATP synthase to be able to make ATP.
CHEMIOSMOTIC PHOSPHORYLATION is the third pathway that produces ATP from inorganic phosphate and an ADP molecule. This process is part of OXIDATIVE PHOSPHORYLATION. The complete breakdown of glucose in the presence of oxygen is called cellular respiration. The last steps of this process occur in mitochondria. The reduced molecules NADH and FADH2 are generated by the Krebs cycle and glycolysis. These molecules pass electrons to an electron transport chain, which uses the energy released to create a proton gradient across the inner mitochondrial membrane. ATP synthase then uses the energy stored in this gradient to make ATP. This process is called oxidative phosphorylation because oxygen is the final electron acceptor and the energy released by reducing oxygen to water is used to phosphorylate ADP and generate ATP.
References:
http://www.biologyjunction.com/chemiosmotic_theory.htm
http://www.biophysics.org/LinkClick.aspx?fileticket=_p0bE5R5-mM%3D&tabid=2886

pizap.com13646092333321

Questions to ask when studying cellular respiration:

GLYCOLYSIS

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?

LINKED REACTION

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?

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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.

pyruvate

FERMENTATION IN YEAST

a1

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.

yeastbuds       bread     images (2)

FERMENTATION IN MUSCLE CELLS

lactferm

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.
randy-orton-246        300px-Illu_muscle_structure

References:

http://www.cliffsnotes.com/study_guide/Fermentation.topicArticleId-8741,articleId-8606.html

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookglyc.html

galt_treatment

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.

  • convulsions
  • irritability
  • poor feeding habits where the baby refuses to eat formula containing milk
  • poor weight gain
  • yellow skin and whites of the eyes (jaundice)
  • vomiting

gal 1

gal 3

 

The above photo indicates that the absence of the GALT enzyme leads to health problems as indicated above.

References:

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001405/

http://www.umm.edu/imagepages/17187.htm

Sir had mentioned…

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?

  1. The Cori cycle involves 2 organs, the contracting muscle and the liver.
  2. It functions in anaerobic conditions when the muscles are contracting under reduced oxygen.
  3. The contracting muscles produce lactate (instead of pyruvate proceeding to acetyl CoA to TCA cycle) which is supplied to the liver.
  4. In the liver gluconeogenesis converts lactate to pyruvate and glucose.
  5. 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.

cori1

Cori cycle

cori5

References:

http://www.wiley.com/college/boyer/0470003790/animations/cori_cycle/cori_cycle.htm

Ńέω Țσpїς ―› ●Ģłγςσļγšїš●

Steps in GLYCOLYSIS:

glycolysis_gif

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:

Preparatory Phase

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]

Payoff Phase

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

References:

http://windsor.edu/Assi_model.htm