Cellular Respiration: Oxidative Phosphorylation

The below diagram is a good summary of what happens during oxidative phosphorylation (including the electron transport chain and ATP synthesis)

During this process, electrons are passed to a series of enzymes via electron carriers.
It is first given to NADH dehydrogenase, then carried to the cytochrome b-c complex by ubiquinone, then carried to the cytochrome oxidase complex by cytochrome c. Here, oxygen acts as the final electron acceptor. These enzymes are in order of increasing electron affinity.
For every electron passed at each of the enzymes, energy obtained is used to transport a H+ ion into the inner membrane space of the mitochondria.
This creates potential energy in the form of positive charge build up.
Finally, these protons enter the matrix through the ATP synthase structure creating one ATP molecule for every H+ that was pumped out.

Why is the net ATP production of cellular respiration 36-38?
This is because, as can be seen from the overall diagram of cellular respiration on the right, the NADHs that are produced during glycolysis must be brought into the matrix of the mitochondria. Passage through the outer membrane is simple, however, they cannot pass through the inner membrane without some help.
There are 2 ways this occurs: through aspartate or glycerate phosphate.
When aspartate is used, the NADH passes through as NADH.
When glycerate phosphate is used, the electron passes through and attaches to FAD to make FADH2.

RECALL:
NADH enters at first enzyme of ETC pumping 3 electrons, creating 3 ATPS.
NADH enters at second enzyme of ETC pumping 2 electrons, creating 2 ATPS.

This is why there may be slight variations.

Reactants: 6NADH (from Krebs), 2NADH (from pyruvate oxidation), 2FADH2 (from Krebs), 2FADH2 OR 2NADH (from Glycolysis), 32-34 ADP, 32-34 phosphate groups, 6Oxygen molecules, 12H+
Products: 8-10NAD+, 2-4FAD+, 24H+, 32-34 ATP, 6Water molecules
Location: Inner membrane of the mitochondria
Net ATP: 32-34

Cellular Respiration: Krebs Cycle

The bellow diagram serves as a good summary for what occurs during the Krebs Cycle.

By the end of the Krebs cycle, all the carbons from the initial glucose molecule have been expelled as carbon dioxide. (2 during pyruvate oxidation, and 4 during the krebs cycle)

Energy that has been stored in the electron carrier molecules (NADH and FADH2) can now proceed to the electron transport chain where they can be used to synthesize ATP; the for of usable energy in cells.

Reactants: 2Acetyl-CoA, 6NAD+, 2ADP, 2 phosphate groups, 2FAD
Products: 2CoA, 4carbon dioxide, 6NADH, 6H+, 2FADH2, 2ATP
Location: Mitochondrial matrix
Net ATP: 2

Cellular Respiration: Pyruvate oxidation

During pyruvate oxidation, the two pyruvates are transported into the matrix of the mitochondria. A transport protein is required to allow for its passage through the inner membrane.

First, a low energy carboxyl group is removed as carbon dioxide.
*This is a decarboxylation reaction catalyzed by the enzyme: pyruvate decarboxylase.
Secondly, NAD+ oxidizes the 2 carbon compound forming NADH.
Thirdly, sulfur containing CoA attaches to the acetate component.

The acetyl-CoA is now ready for the Krebs Cycle!

Reactants: 2 pyruvate, 2NAD+, 2CoA
Products: 2 acetyl-CoA, 2NADH, 2H+, 2Carbon dioxide molecules
Location: Mitochondrial Matrix
Net ATP: none

This video also illustrates the electron transport chain discussed in the next blog as well!

Cellular Respiration: Glycolysis

The first phase of cellular respiration is called glycolysis. Only 2.2% of the energy from cellular respiration is attained through glycolysis.

The above image illustrates the process of glycolysis in detail. It includes the names of the enzymes responsible for catalyzing each individual reaction. It also included the names and structural diagrams of the intermediate reactions.

In general, gylcolysis can be divided into 2 phases: energy investment (Step#1-3) and energy payoff (Step#4-10). During the energy investment phase, 2 ATP molecules are used. In the energy payoff phase, 4 ATPs in addition to 2 NADHs are synthesized.

Reactants: glucose, 2ATP, 2NAD+, 4ADP, 2 phosphate groups
Products: 2 pyruvate, 4ATP, 2ADP, 2H+, 2NADH
Location: Cytosol
Net ATP: 2

This video explores glycolysis with particular focus on the enzymes involved.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions within the body without being consumed. They can be used over and over again.

All reactions require an initial input of energy, called activation energy. Enzymes lower this activation energy as shown in the diagram to the left.

Key terms:
Substrate - the reactants which the enzyme acts on.
Enzyme-substrate complex - the complex formed when the substrate molecules bind to the enzyme.
Active site - where the substrates bond to the enzymes
Cofactors - non-organic enzyme helpers
Coenzymes - organic enzyme helpers
Allosteric site - another region on the enzyme where materials can bond to the enzyme locking it in either its active or inactive shape.
Feedback inhibition - when the product of the reaction bonds to the allosteric site of an enzyme locking it into its inactive form.

The cycle:
The below image is a good summary of how the catalytic cycle works.

Inhibition:
There are two types of inhibition: competitive and non competitive.
Competitive - inhibitor competes with substrate to bind to the active site of the enzyme.
Non-competitive - inhibitor binds to the allosteric region of enzyme.

Here is a video showing the importance of enzymes in out body.

Methods of Transport: Active

Active transport in cells requires the use of energy to transport products against the concentration gradient. 30-40% of all energy within a cell is used for transport.

Individual molecules:
Transport proteins actively pump molecules in/out of the cell using energy.
An example of such a pump would include the sodium-potassium pump. Three sodium ions within the cytosol bind to the protein causing it to change shape. The protein can then attain a phosphate group from ATP causing another change in shape that releases the sodium ions outside the cell, and allowed potassium ions to bond to the protein. The phosphate group then dislocates making the protein return to its original shape releasing the potassium ions within the cell.

Cells like to have a high concentration of potassium ions within them, and a low sodium ion concentration. To allow this to work,


In Bulk:
In bulk, material is moved into/out of a cell using endocytosis and exocytosis.

Endocytosis:
Involves the movement of material into the cell through the creation of new vesicles from the cell membrane.
When liquids are brought in, it is called, pinocytosis.
When solids are brought in, it is called, phagocytosis.

Exocytosis:
Involves the movement of material out of the cell through fusing vesicles with the plasma membrane.

Methods of Transport: Passive

Passive transport does not require the use of energy to move material into/out of the cell.
There are two types of passive transport: osmosis and diffusion

Osmosis:

Osmosis is a special type of diffusion; Movement of water along a concentration gradient until equilibrium is established.
In isotonic solutions, the concentration of solute is equal in both the inside and out side of the cell. Therefore, there is no net change in movement of water. This environment is ideal for animal cells. When plant cells are placed in isotonic solutions, however, they are called 'flaccid' and are not as supported by the cell wall.
In hypertonic solutions, the concentration of solute outside the cell is greater. Therefore, solvent moves out of the cell causing it to shrivel. Animal cells become shriveled and plant cells become plasmolyzed.
In hypotonic solutions, the concentration of solute less than inside the cell. Therefore, solvent moves into the cell causing it to swell. This is ideal for plant cells as they become turgid. But animal cells may become lysed and burst.

Diffusion:

Diffusion is defined as the movement of solute molecules from an area of high concentration to an area of low concentration (along a concentration gradient) until equilibrium is established.

Diffusion in cells can be facilitated. This involves the use of transport proteins to move these solute molecules across the membrane. It is still considered passive transport because the particles are moving without the use of energy according to the concentration gradient.