Chemiosmotic Hypothesis:


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:

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.



1. Which stage in the metabolic pathway is ATP generated as  a NET gain for the call?

a. glucose to glucose 6-phosphate

b. fructose 6-phosphate to fructose 1,6-bisphosphate

c. fructose 1,6-bisphosphate to glyceraldhyde 3-phosphate

d. 1,3-bisphosphoglycerate to 3-phosphoglycerate

e. phosphoenolpyruvate to pyruvate

2. Phosphorylation of glucose and its conversion to glyceraldhyde 3-phosphate refers to:?

a. energy generation phase

b. pay off phase

c. energy conservation phase

d. preparatory phase

e. energy splitting phase

3. Which of the following enzymes does not have a delta G that is close to zero (0) where it is not in equilibrium?

a. hexokinase

b. aldolase

c. enolase

d. pyruvate kinase

e. phosphoglycerate kinase

4. What is the  name of the enzyme that catlyses the only oxidation reaction in glycolysis?

a. phosphoglycerate kinase

b. glyceraldehyde 3-phosphate dehydrogenase

c. triose phosphate immerase

d. aldolase

e. phosphoglycerate mutase

5. Converting one molecule of glucose to two molecules of pyruvate yields a total of ____ ATP?

a. 1

b. 2


d. 4

e. 5

6. Glucolysis occurs in the __________ ?

a. mitochondria

b. nucleus

c. cytoplasm

d. cytosol

e. golgi apparatus

7. Which of the follwing enzyme is the most regulated in glycolysis and controls the second priming effect ?

a.  aldose

b. hexokinase

c. phosphohexose isomerase

d. phosphofructokinase

e. pyruvate kinase

8. Why is glucose 6-phosphate more important than glucose molecules itself?

a. no transporters for the form

b. only glucose is transported across

c. phosphorous is attached to ATP

d. becomes unstable and promotes the reaction

e. all of the above


More quizzes are available in the page entitled ‘βï¤čħḝмḯşŗŷ ξxåღ ტմεșțΐǿŋŝ’. Do enjoy! 🙂

By biochemist01 Posted in Quiz


Lysine has three ionizable functional groups with the following pKa values:

α-amino group = 9.04

α-carboxylic group = 2.17

R group = 12.48

The R group for lysine is –CH2CH2CH2CH2NH2

(i) Write the equilibrium equations for its three ionizations and assign the proper pKa for each ionization. Show the net charge on the lysine molecule at each ionization stage.

lysine tit

(ii) Calculate the Isoelectric Point (pI):

The pI is the pH at which two amino acid has a net charge of zero (0).

1. Write out equations to show ionisation. Start with the amino acid in its fully protonated form. The pK values increase as you loose H-atoms so start the ionization using the group with the lowest pK value and then you increase as ionization continues.

2. Ensure that pk values are placed above reversible arrows.

3. Calculate the net charge of each molecule by adding the positive charges and subtracting the negative ones.

4. Calculate the pI using the equation below: ( pK1 value is the pk value to the left of the zero net charge and pK2 value is to the right of the net charge of zero).

pI = pk1 + pk2 ⁄ 2

pI = 9.04+12.48/2

pI = 10.76

All my Biochem Bloggers please note this titration steps for exam. It has been confirmed that it is going to come!!! Don’t say I didn’t warn

Amino acids & Proteins Quiz

You have 15 minutes to complete 20 questions:



  1. All proteins have both a primary and secondary structure.
  2. Denaturing proteins disrupts their primary structures only.
  3. Urea is a chaotrope which disrupts the hydrophobic interactions causing the protein to loose its tertiary structure.
  4. A typical amino acid has an amino group, a hydrogen atom and a carbonyl group bonded to a central carbon.
  5. The biuret test is only done to determine the presence of proteins not amino acids in a solution.


1. How many different types of amino acids are present?

a. 3

b. 20

c. 100

d. 120

e. none of the above

2. Which of the following forces is the most unfavorable for protein folding?

a. Covalent bonding

b. Vander Waals interactions

c. Conformational entropy

d. Hydrophobic interactions

e. Electrostatic interactions

3. An essential amino acid is one that:

a. readily available in the body

b. the body can synthesize

c. is essentially easy to synthesize

d. the body cannot synthesize

e. none of the above

4. The sequence of letters ‘KNQG’ will represent:

a. alanine, cysteine, proline, glycine

b. lysine, asparagine, glutamine, glycine

c. asparagine, lysine, glycine, glutamine

d. histidine, glycine, asparagine, valine

e. asparagine, glutamine, histidine, glycine,

5. The sulphur containing chain of cysteine is:

a. hydrophobic, highly reactive and capable of reacting with another cysteine

b. hydrophillc, highly reactive and capable of reacting with another cysteine

c. amphiphilic, not reactive with another cysteine

d. amphiphilic, highly reactive and capable of reacting with another cysteine

e. none of the above

6. Which amino acid when exposed to Ninhydrin produces a brown colour?

a.  alanine

b. valine

c. asparagine

d. proline

e. glycine

7. Beta pleated sheets are examples of protein’s:

a. primary structure

b. secondary structure

c. tertiary structure

d. quaternary structure

e. α – helix configuration

8. Sickle cell disease is due to:

a. a mutation in the beta chain of hemoglobin

b. mutation in the secondary structure between Glu and Val residues

c. a mutation in the alpha chain of hemoglobin

d. infection with a parasite

e. none of the above

9. Which one of the following is an essential amino acid?

a. alanine

b. cysteine

c. asparagine

d. glycine

e. valine

10. If an egg white protein of albumin is denatured into a hard boiled egg then which of the following is least affected?

a. the primary structure of ovalbumin

b. the secondary structure of ovalbumin

c. the tertiary structure of ovalbumin

d. the quaternary structure of ovalbumin

e. none of the above

11. Disulphide bonds are formed between:

a. between two cysteine residues

b. between two cystine residues

c. between a alanine and asparagine residue

d. between two glycine residues

e. none of the above

12. Alpha helicies in the secondary structure of proteins are affected by:

a. the interactions between R groups spaced 3 or 4 residues apart

b. the electrostatic repulsion or attraction between successive amino acid residues with charged R groups

c. the bulkiness of adjacent R groups

d. the occurrence of Pro and Gly

e. all of the above

13. The four subunits of hemoglobin represents:

a. primary structure

b. secondary structure

c. tertiary structure

d. quaternary structure

e. none of the above

14. The α-amino acids have a carboxyl group with a pK around __________ , and an amino group with a pK near __________ .

a. 7.0 and 9.0

b. 5.5 and 12.1

c. 2.2 and 9.4

d. 1.0 and 6.3

e. 0.5 and 11.0

15. Refer to the diagram below. Choose the correct answer:Image

a. parallel beta pleated sheet & anti parallel alpha pleated sheet

b. parallel beta pleated sheet & anti parallel beta pleated sheet

c. anti parallel beta pleated sheet & parallel alpha pleated sheet

d. anti parallel beta pleated sheet & parallel beta pleated sheet

e. none of the above


Quiz on Carbohydrates:

Multiple Choice Questions:

1) Why is it that sucrose is the only non-reducing sugar while maltose and lactose which are also disaccharides are reducing sugars?

a.  sucrose is made up of glucose and fructose

b.  sucrose bonding is an alpha (1-2) linkage

c.  sucrose has only one free anomeric carbon

d.  sucrose comprises of glycosidic bonds between C1 and C2

e.  sucrose anomeric carbons are both involve d in bonding

2) The polysaccharides that contain alpha linkages are:

a.  starch

b. sucrose

c.  cellulose

d.  glycogen

e. cellobiose

Select the correct multiple answer using ONE of the keys A, B, C, D or E as follows:
A. 1, 2 and 3 are correct
B. 1 and 4 are correct
C. 2 and 5 are correct
D. only 4 is correct
E. all are correct