Bioenergetics and cellular respiration

Question 1

Bioenergetics is:

Answer 1

It is the study of energy transformation within an organism, the making and breaking of
chemical bonds in molecules within the body. It is a multistep enzymatic reaction that is aimed to produce 𝐴𝑇𝑃. 𝐴𝑇𝑃 is a molecule that stores energy in the cell. The energy is stored in a highly energetic, unstable
phosphoric anhydride chemical bond.
When 𝐴𝑇𝑃 becomes 𝐴𝐷𝑃, energy is released, and then can be used by the cell for anabolic processes.

Terminology:

1. Anabolism – building of molecules (requires energy). 2. Catabolism – breaking down of molecules (release energy).
2. Metabolism – sum of anabolic and catabolic processes in the body.

Question 2

Aims of Bioenergetics:

Answer 2

1. Production of 𝐴𝑇𝑃.
2. Production of heat – by product of bioenergetics processes. Bioenergetics accord for constant
   body temperature. When bonds in molecules break down, energy and heat is emitted.
3. Production of water – during bioenergetics process, we produce approximately 1.5 𝑙𝑖𝑡𝑒𝑟 of water
   a day.

Question 3

Enzymes

Answer 3

Bioenergetics is a multi-enzymatic process. Enzymes are proteins that catalyze chemical reactions. All
enzymes have an active site in which substrate becomes product. Some enzymes have regulatory sites, in
which enzymes activity can be enhanced or inhibited. Enzymes that have a regulatory site (allosteric site)
are called regulatory enzymes.

Question 4

Enzyme properties:

Answer 4

• They do not change the equilibrium constant. They only increase the rate of the reaction.
• They need optimal 𝑝𝐻 and temperature to be active (proteins).
• They are not changed or consumed in the reaction.
• The allosteric site has regulatory capacity that can stop or activate the enzyme activity.

Question 5

Enzymes in Bioenergtics:

Answer 5

In bioenergetics 𝐴𝑇𝑃 inhibit the regulatory enzymes (negative feedback mechanism) and 𝐴𝐷𝑃 activates
the regulatory enzymes.
*Coenzymes – these are organic molecules (usually vitamins) that are needed by enzymes to catalyze a
reaction.

The cellular respiration uses two coenzymes:

1. 𝑁𝐴𝐷 + (vitamin 𝐵3) – carrying electron to 𝑁𝐴𝐷𝐻 and produced 3 𝐴𝑇𝑃𝑠 per molecule.
2. 𝐹𝐴𝐷 (vitamin 𝐵2) – carrying electron to 𝐹𝐴𝐷𝐻2 and produced 2 𝐴𝑇𝑃𝑠 per molecule.

Question 6

Cellular respiration is

Answer 6

Type of bioenergetics. A metabolism process that takes place in the cells of an organism to convert chemical energy from nutrients into 𝐴𝑇𝑃 and a byproduct of water. Humans depend on this process to survive. The production of water in this process is also very important.

Question 7

Types of bioenergetics:

Answer 7

*Aerobic respiration – up to 18 times better then anaerobic respiration because of the process with
oxygen that needs mitochondria in the cell. Cells that mostly do aerobic respiration:
- Cardiac muscles.
- Red skeletal muscles.
- Brain cells.

*Anaerobic respiration – less efficient than aerobic respiration, due to the process that doesn’t use
oxygen (because of luck or shortage of mitochondria in the cells). Cells that mostly preform
anaerobic respiration:
- White skeletal muscles – due to shortage of mitochondria.
- 𝑅𝐵𝐶 - anaerobic respiration only, due to lack of mitochondria in the cells.
- Kidney’s medulla.

• • When oxygen is involved in the respiration of the cell, more 𝐴𝑇𝑃 will be produced.
• • Anaerobic respiration will produce lactic acids, alcohol and more molecules in its process.

Question 8

Stage 1 of Cellular respiration

Answer 8

Called Glycolysis and it occurs in the cytoplasm. It doesn’t require oxygen. It is made of 10 enzymatic steps. The first 5
steps are called reparatory phase, and the remaining 5 steps are called payoff phase.
During the preparatory phase, glucose is broken down into two molecules of three carbons each (glyceraldehyde 3 phosphate). Two molecules of 𝐴𝑇𝑃 are invested in the process.
During the payoff phase, these molecules are converted into pyruvate (3 carbon molecule). It is called payoff phase, because we gain 4 molecules of 𝐴𝑇𝑃 and 2 molecule of reduced 𝑁𝐴𝐷𝐻 +𝐻+. The net gain of glycolysis is 2 molecules of 𝐴𝑇𝑃 per glucose.

**Cori’s cycle (fermentation) – during anaerobic conditions (oxygen is not present), pyruvate is converted into lactic acid (𝑁𝐴𝐷𝐻 is oxidized to 𝑁𝐴𝐷+), then lactic acid is transported to the liver where 2
molecule of lactic acid are recycled to become glucose

Question 9

Stage 2 of cellular respiration

Answer 9

Is called 𝑷𝑫𝑯 Complex (Pyruvate Dehydrogenate Complex):
𝑃𝐷𝐻 complex is made of three enzymes. During this process pyruvate is converted to acetyl co-enzyme 𝐴. One carbon is excreted in the form of 𝐶𝑂2 and the molecule is activated. The energy gain is reduced 𝑁𝐴𝐷𝐻 +𝐻+ per pyruvate (2 per glucose). Activated acetyl co-enzyme 𝐴 can continue to the next phase.

Question 10

Stage 3 of cellular respiration

Answer 10

Called Citric Acid Cycle:
Acetyl co-enzyme 𝐴 is feeding the cycle (2 carbon molecule). It initially reacts with oxaloacetate (4 carbon
molecule) to produce citric acid (6 carbon molecule). The remaining 7 steps (of this stage) are aimed to produce energy and to excrete two carbons in the form of 𝐶𝑂2. The energy gain is 3 molecules of 𝑁𝐴𝐷𝐻 + 𝐻+, 1 of 𝐹𝐴𝐷𝐻2 and 1 of 𝐴𝑇𝑃 (multiply all by 2 for 1 glucose).

Question 11

Stage 4 of cellular respiration

Answer 11

Called Electron transport chain:
Electron transport chain is made of 5 complexes (proteins with metal) that are imbedded within the inner mitochondrial membrane. The aim is to convert reduced vitamins into electron flow and then into 𝐴𝑇𝑃
synthesis.

Question 12

The complexes in stage 4

Answer 12

The 1st complex binds 𝑁𝐴𝐷𝐻 +𝐻+. It accepts the electrons (reduction) and then transports the electron to a chaperon. The electrons are transported into the 3rd complex and then to 4th complex. From there,
they bind to oxygen. Oxygen is the final acceptor of electrons. It waits to bind with 4 electrons, then it takes
4 protons from the matrix to form water.
𝑂2 +4𝑒′ +4𝐻 = 2𝐻2𝑂
Electron flow results in opening of the channels in complexes 1,3 and 4. Protons are pumped from the
matrix to the intramembranous space. A proton motive force is building a concentration gradient. Protons can return to the matrix only via 𝐴𝑇𝑃synthase (the 5th protein). Energy is released and used for the chemical reaction to form 𝐴𝑇𝑃.
𝐴𝐷𝑃 +𝑃 = 𝐴𝑇𝑃
From each binding of 𝑁𝐴𝐷𝐻 +𝐻+ to the 1st complex, we gain 2 molecule of 𝐴𝑇𝑃.
𝐹𝐴𝐷𝐻2 bind to the 2nd complex (named succinate dehydrogenase), and then it sends electrons to the 3rd and then to the 4th complexes, and from there to bind with oxygen (just like 𝑁𝐴𝐷𝐻 +𝐻+).
From each binding of 𝐹𝐴𝐷𝐻2 to the 2nd complex we gain 2 molecules of 𝐴𝑇𝑃.

• • The 2nd complex is a peripheral complex, while the others are integral ones in the mitochondria’s inner
    membrane.

** The 2nd complex does not pump protons like the other complexes

Question 13

Overall 𝐴𝑇𝑃 production:

Answer 13

From one molecule of glucose, the cell produces between 36-38 (depends on what was entered from the outside of the cell 𝐹𝐴𝐷 or 𝑁𝐴𝐷) of 𝐴𝑇𝑃𝑠 in aerobic respiration, while in an anaerobic we get only 2 𝐴𝑇𝑃𝑠.

Question 14

Toxics in cellular respiration

Answer 14

Carbon monoxide- CO - and Cyanide - 𝐶𝑁− are irreversibly binding to the 4th complex instead of oxygen. Therefore, there is no final acceptor of electrons. The level of 𝐴𝐷𝑃 in the mitochondria increases and bioenergetics is
activated (full gas in neutral). The cell suffocates and also produces heat. The body temperature rises and
causes death. Treatment – 100% oxygen.

Question 15

Uncoupling in cellular repiration

Answer 15

Uncoupling are proteins that inhibit the 𝐴𝑇𝑃 synthesis by enabling free passage of proton into the 
mitochondria matrix (thus ruining the proton gradients between the mitochondria’s membranes). Uncoupling usually have a role in normal physiology like hibernation, because the energy from the 𝐸𝑇𝐶 is used to generate heat instead of producing 𝐴𝑇𝑃.