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ATP: Adenosine Triphosphate

ATP         ADP + Pi (Hydrolysis, energy release)

ADP + Pi         ATP (Condensation)

Properties of ATP:

-Small and soluble (easily transported in cells)

-Easily hydrolysed (instantaneous release)

-Remade easily (condensation, regeneration)

-Makes molecules reactive (phosphorylation)

-Cannot pass out of the cell

ATP used in active process e.g. active transport

Made up of adenine, ribose and 3 x phosphates

ATP is made by:

-Respiration in animals and plants

-Photosynthesis in plants

Glycolysis overview:

Glycolysis splits glucose into smaller molecules of pyruvate and occurs in the cytoplasm of cells. It is split into two stages:

Phosphorylation: 

-Glucose is phosphorylated using a phosphate taken from an ATP molecule.

-Another phosphate is added making hexose bisphosphate.

-Hexose phosphate is then split to form two molecules of triose phosphate.

Oxidation:

-Triose phosphate(s) oxidised to pyruvate(s), regenerating 4 x ATP per glucose, as well as 2 molecules of reduced NAD.

*Net gain of 2 x ATP, 2 x NADH and 2 x pyruvate

Link reaction explained:

-Pyruvate decarboxylated then oxidised by NAD.

-This forms acetate, which then combines with coenzyme A to form acetyl-CoA.

-No ATP produced

Anaerobic respiration: 

Decarboxylation: Where a carboxyl (CO2) group is removed from a compound.

Dehydrogenation: Removal of hydrogen

Oxidation: Where a species loses electrons

Reduction: Where a species gains electrons

Substrate-level phosphorylation: Where a phosphate group is transferred from an intermediate compound to a species.

Oxidative phosphorylation: 

The purpose of oxidative phosphorylation is to use the energy carried by the electrons in NADH and FADH2 to generate ATP through a condensation reaction. It occurs across the inner mitochondrial membrane (double-membrane bound).

-Various protein complexes span the IMM. 

-Reduced NAD and FAD are oxidised at one of these protein complexes. This oxidation releases electrons and hydrogen ions (H+/protons).

-The electrons move down an ETC (electron transport chain) across the protein complexes.

-The movement of electrons is coupled to the pumping of H+ ions into the inter-membrane space, building an electrochemical gradient (H+ gradient)

-H+ ions move back down their electrochemical gradient through ATP synthase, which combines Pi to ADP through rotary motion, forming ATP.

-Oxygen acts as the terminal electron acceptor in the ETC. It combines with H+ ions and electrons to form water (H2O).

-This process is known as chemiosmosis.

C6H12O6 + 6O2                    6CO2 + 6H2O (+ATP also made)

Mitochondria

Structure and function:

Mitochondria are double-membrane bound organelles responsible for carrying out respiration. They share similarities to bacteria in shape and structure, and also have their own DNA.

Matrix: The aqueous medium inside a mitochondrion. This is where the electrochemical gradient is established to drive ATP synthesis.

Cristae: Folds in the inner membrane of the mitochondrion. This helps the inner membrane to have a large surface area, for an increased amount of reactions to occur on (chemiosmosis)

Glucose

Glucose phosphate

Hexose bisphosphate

2 x Triose phosphate

2 x Pyruvate

Anaerobic respiration: 

-Pyruvate in glycolysis converted to lactate (animals) or ethanol (plants) using reduced NAD.

-Regeneration of NAD allows glycolysis to continue and therefore making ATP

-Lactate turns to lactic acid which causes muscle fatigue. It is overcome by repaying oxygen debt.

Krebs cycle explained:

The purpose of the Krebs cycle is to use the acetyl CoA (formed from the link reaction), a 4C compound and a series of redox reactions to release ATP and reduced coenzymes (NADH, FADH2 for oxidative phosphorylation). This occurs in the matrix.

Combination + dissociation:

-Acetyl CoA combines with oxaloacetate (4C) to form a 6C citrate compound. CoA leaves here and is returned to the link reaction.

Decarboxylation + Dehydrogenation:

-A primary decarboxylation event shortens the 6C to a 5C compound. Here another NAD is reduced to NADH.

-This reduction is driven by dehydrogenation.

-A secondary decarboxylation event shortens the 5C to the 4C oxaloacetate initially used (regeneration).

-Here another  2 NAD are reduced to NADH, and a FAD is reduced to FADH2. ATP is also made via condensation of ADP + Pi

-The reduction of NAD and FAD involves another dehydrogenation step.

-ATP production is driven by a phosphate transfer from one of the intermediates. This is known as substrate level phosphorylation.

ATP Synthase

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