Chapter 13 (glycolysis and kreb cycle)

Cell respiration

Process by which cells harvest and energy stored in food molecules; usually accompanied by the uptake of O2 and the release of CO2

ADP

Nucleoside diphosphate produced by hydrolysis of the terminal phosphate of ATP

ATP

Activated carrier that serves as the principle carrier of energy in cells. Made of adenine, ribose and 3 phosphate groups

Catabolism

Set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with release of energyG

Glucose

Six carbon sugar that plays major role in metabolism of living cells. Stored as glycogen in animal cells and starch in plant cells G

Glycolysis

Series of enzyme-catalyzed oxidation reactions in which sugars are partially degraded and their energy is captured by activated carriers ATP and NADH (sugar splitting reaction). Located in the cytosol.

Pyruvate

Three carbon metabolite that is the end product of the glycolytic breakdown of glucose. Provides link to the citric acid cycle and other pathways S

Substrate-level phosphorylation

Process by which ATP is formed by the transfer of a phosphate group from a substrate molecule to ATP. Substrates that participate in this form of ATP synthesis must carry phosphate group linked via a “high energy” covalent bond.

NADH

Activated carrier of electrons widely used in energy producing breakdown of sugar molecules

Fermentataion

The breakdown of organic molecules without the involvement of molecular oxygen. Form of oxidation that yields less energy than aerobic cell respiration.

Acetyl CoA

An activated carrier that donates carbon atoms in its readily transferable acetyl group to many metabolic reactions including citric acid cycle. Acetyl group linked to coenzyme A (CoA ) by thioester bond that release large amount of energy when hydrolyzed.

Fat

Type of lipid used by living cells to store metabolic energy. Typically composed of triacylglycerols.

Citric acid cycle (TCA)

Series of reactions that generate large amounts of NADH by oxidizing acetyl groups derived from food molecules to CO2. In eukaryotic cells, occurs in mitochondrial matrix with enzymatic coupled reactions

FAD

A molecule that accepts electron and hydrogen atoms from electron donor

GDP

Nucleoside diphosphate that is produced by the hydrolysis of the terminal phosphate of GTP, a reaction that produces inorganic phosphate

Anabolic pathway

Series of enzyme-catalyzed reactions by which large biological molecules are synthesized from smaller subunits, usually requiring an input in energy

Oxidative phosphorylation

Membrane-based process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons derived from food molecules to molecular oxygen

Electron-transport chain

A series of membrane-embedded electron carrier molecules that facilitate the movement of electrons from a higher to a lower energy level, as in oxidative phosphorylation and photosynthesis

NAD+

A molecule that accepts a hydride ion (H-) from a donor molecule, thereby producing the activated carrier NADHFa. Widely used in energy-producing breakdown of sugar molecules

FADH2

A high energy electron carrier produced by reduction of FAD during the breakdown of molecules derived from food including fatty acids and acetyl CoA.G

GTP

Nucleoside triphosphate used in the synthesis of RNA and DNA. Like the closely related ATP, serves as an activated carrier in some energy transfer reactions.

Hydride Ions

A hydrogen atom carrying an electron that is transferred during key redox reaction (step 6 of glycolysis with glyceraldehyde-3-phosphate dehydrogenase) Transferred from substrate to carrier molecules NAD+ or FADH (oxidized) to form NADH or FADH2 (reduced form)

Glucose reaction

glucose (C6H12O6) + O2 → CO2 + H2O

ΔG = −2880 kJ/mole which is highly favorable

Glycolysis step 1

Glucose phosphorylated by ATP with hexokinase to form a sugar phosphate (glucose 6-phosphate). Phosphates negative charge prevents sugar phosphate passage through plasma membrane, trapping glucose in cell. Hexokinase will be competitively by own product (G6P)

Glycolysis step 3

The new hydroxyl group on carbon 1 of fructose 6-phosphate is phosphorylated by ATP. The entry of glycolysis is allosterically inhibited by enzyme phosphofructokinase (PFK)

Glycolysis step 6

Two molecules of glyceraldehyde 3-phosphate (G3P) from steps 4 and 5 are oxidized, beginning energy generation phase of glycolysis. NADH is formed and phosphate is linked to G3P. Harvest high energy electron as NAD+ is reduced to NADH

Glycolysis step 7

Transfer of ADP of high energy phosphate group in step 6 forms ATP. There are 2 G3P molecules produced after step 4 so there are 2 ATP molecules formed in this step.

Glycolysis step 10

The high energy phosphate group generated in step 9 (phosphoenolpyruvate) with ADP forms ATP. As there are 2 pyruvates after cleavage, 2 ATP is formed along with 2 pyruvates again.

Inputs and outputs of glycolysis

• 2 ATP consumed per glucose in steps 1 to 3

• Generates 4 ATP total (2 at step 7 and step 10)

• Harvest pair of high energy electron at step 6 (NAD+ reduced to NADH)

Phosphofructokinase (PFK)

A regulatory enzyme in glycolysis catalyzing irreversible phosphorylation of fructose 6-phosphate to fructose 1-6 biphosphate using ATP. Used in 3rd step of glycolysis. Extremely regulated enzyme that is stimulated when bound to AMP and allosterically inhibited when bound to downstream products: ATP, lactate or citrate.

Allosteric inhibition

A regulatory mechanism where inhibitor molecule binds to secondary site on enzyme called the allosteric site which is different than the active site that causes a conformational change in the enzyme shape.

Citric acid cycle step 1

An enzyme removes proton from CH3 group on acetyl CoA. The negatively charged CH2- forms a bond to a carbonyl carbon of oxaloacetate to form citrate

Citric acid cycle step 2

Citrate undergoes an isomerization reaction where water is removed then added back to form isocitrate.

Citric acid cycle step 3

The isocitrate loses Co2 while NAD+ is oxidized to form NADH and producing an unstable product called α-ketoglutarate

Citric acid cycle step 4

α-ketoglutarate dehydrogenase complex catalyzes an oxidation that produces a NADH by reducing NAD+ one CO2 and thioester bond to form succinyl CoA

Citric acid cycle step 5

Succinyl CoA has inorganic phosphate that displaces CoA to form high energy linkage to succinate. The phosphate is then passed to GDP to form GTP and succinate forms

Citric acid cycle step 6

FAD accepts 2 hydrogens from succinate and oxidizes into FADH2 and creates fumarate

Citric acid cycle step 7

Fumarate has water added to it and places a hydroxyl group next to carbonyl to form malate

Citric acid cycle step 8

The carbon carrying hydroxyl group on malate is converted into a carbonyl group forming oxaloacetate while yielding a pair of electrons used by NAD+ to make NADH.

Inputs and outputs of glycolysis per glucose molecule (2 turns)

Inputs: 2 Acetyl-CoA, 6 NAD+, 2 FAD, 2 GDP+Pi, 2 oxaloacetate (regenerated each turn), 2 H20

Outputs: 4 CO2, 6 NADH + 6H+, 2 FADH2, 2 GTP, 2 coenzyme A, 2 oxaloacetate

Energy yielding reaction

A reaction where electrons are transferred from one molecule to another, releasing stored energy to cells can capture. The amount of energy released depends on the difference in electron affinity between both molecules.