Grade 12 Biology Unit 2

Aerobic Cellular Respiration

C6H12O6 + 6O2 → 6CO2 + 6H2O + 36ATP

Metabolism

The sum of all chemical reactions in a cell or organism (continuous series of endergonic and exergonic reactions)

Energy

The ability to do work

Forms of Energy

Potential E:

Gravitational

Chemical

Elastic

Kinetic E:

Light

Sound

Thermal

Thermodynamics

The study of E (or flow of E) through living and non-living matter

First Law of Thermodynamics (Principle of Conservation of E)

Energy cannot be created or destroyed, instead converted from one form to another

Bond Energy

Measure of the stability of bonds, measured in kJ/mol (E required to break the bond)

The closer the e- is to the nuclei, the less...

Potential E it has

Breaking bonds=

E is absorbed

Forming bonds=

E is released

EA (subscript A)

Activation E

Transition State

Temporary unstable condition between old bonds breaking and new ones forming

E required to break bonds > E released when forming bonds

Endothermic (Photosynthesis, +▲H)

E required to break bonds < E released when forming bonds

Exothermic (Cellular respiration, -▲H)

Endothermic reaction

Photosynthesis

Exothermic reaction

Cellular Respiration

Enthalpy

Change in E of the products and reactants (▲H)

Second Law of Thermodynamics

In every energy transfer, some useful E in the system becomes unusable and randomness increases (mostly as heat)

Entropy

A measure of disorder in a system. (Natural tendency of the universe is towards increasing entropy)

Spontaneous reactions

Able to proceed on their own once enough E has been applied to get it started

Non-spontaneous reactions

Not able to proceed on their own, needs a constant supply of E

Gibbs Free Energy

Remaining useful E that can do work (G)

▲G < 0

Spontaneous, exergonic

▲G > 0

Non-spontaneous, endergonic

Excess E from an exergonic reaction can be used to...

Drive an endergonic reaction

Catabolic reactions

The breaking down of molecules (exergonic)

Anabolic reactions

The building up of molecules (endergonic)

1P -> 2P -> 3P

AMP -> ADP -> ATP

ATP

Energy currency of the cell

Dephosphorylation

Release of E to do work, exergonic (breaking apart phosphates, ATP -> ADP + Pi)

Phosphorylation

Absorbing of E to form bonds, endergonic (adding phosphates, ADP + Pi -> ATP)

Activation energy of enzyme graph

How do enzymes speed up reactions?

1) Bring substrates closer for rxn

2) Stress the bonds on the mlcl with ionic forces on enzyme, stressed bonds break more easily (induced-fit model)

When one mlcl is oxidised...

Another must be reduced (Oxygen is often involved)

Oxidation is...

A series of enzyme-catalysed reactions that release a small amount of E that can be transferred to E carrying mlcls (like NAD+)

Why is the E from oxidation released in small bursts?

To prevent a big, destructive burst of energy (allowing it to be captured and stored in a usable form)

NAD+ is a...

Coenzyme

In the oxidation of glucose, NAD+...

Is reduced (NAD+ + 2H+ + 2e- -> NADH + H+)

Flow of energy

Obligate aerobes

Requires oxygen for survival

The transfer of G to produce ATP from the oxidation of glucose can occur in two ways:

1) Substrate-Level Phosphorylation

-ATP formed by a series of enzyme-catalyzed reactions

2) Oxidative Phosphorylation

-NAD+ and FAD reduced

-NADH and FADH2 transfer E to ATP indirectly through a series of redox runs (electron transport chain)

4 Stages os Cellular Respiration

1) Glycolysis

2) Pyruvate Oxidation

3) Citric Acid/Krebs Cycle

4) Electron Transport Chain

Glycolysis consists of...

10 enzyme-catalysed reactions in the cytoplasm (does not require oxygen)

Pyruvate Oxidation

-Oxygen is required for pyruvate (3C) to enter the matrix through a transport protein in the inner mitochondrial membrane

1) Decarboxylation reaction of Pyruvate Oxidation

-Pyruvate undergoes oxidative decarboxylation

-Carboxyl group is removed as a CO2 mlcl

2) Dehydrogenation reaction of Pyruvate Oxidation

-Remaining 2C is oxidized

-NAD+ is reduced to NADH + H+

3) End Result of Pyruvate Oxidation

Resulting acetate (2C) combines with CoA to form the 2C mlcl Acetyl CoA

Citric Acid Cycle consists of...

8 enzyme-catalysed reactions in the matrix where citrate is decarboxylated and dehydrogenated (oxidised with reduction of NAD+ and FAD)

Substrate-level phosphorylation in the Citric Acid Cycle

Dephosphorylation of GTP -> GDP, converts ADP -> ATP

Citric Acid Cycle Steps

1) Oxaloacetate -> Citrate

2)

3) NAD+ -> NADH, -> CO2

4) NAD+ -> NADH, -> CO2

5) GTP -> GDP, ADP -> ATP

6) FAD -> FADH2

7)

8) NAD+ -> NADH

Products of Citric Acid Cycle with 2 mlcl of Acetyl CoA

-6NADH

-2FADH2

-2ATP

-4CO2

Electron Transport Chain transfers electrons, which...

-Releases G, causing H+ in the matrix to be pumped into the intermembrane space

-This creates a concentration gradient of H+

-This creates the proton-motive force, which is from the potential energy of the electrochemical gradient, harnessed to do work

-Which leads to chemiosmosis, the ability of cells to use the proton-motive force to do work, thus synthesising ATP

Concentration gradient

Concentration of one side is higher than the other

Proton-motive force

The potential energy of the electrochemical gradient used to do work

Chemiosmosis

Ability of cells to use the proton-motive force to drive ATP synthesis

UnCouPler (UCP) protein

Embedded in the inner mitochondrial membrane that allows passage of H+ without going though ATP synthase

Thermogenesis

E is dissipated as heat instead of ATP, maintaining body temp in babies and helping revive animals from hibernation

Ionophores

Lipid-soluble chemicals that reversibly bind ions, to transport them across the membrane

NADH produces...

3 ATP

FADH2 produces...

2 ATP

Net ATP in Glycolysis

2 ATP

Net ATP in Pyruvate Oxidation

2NADH from glycolysis -> 2FADH2 -> 4 ATP

2NADH from pyruvate oxidation -> 6 ATP

Net ATP in Citric Acid Cycle

6 NADH -> 18 ATP

2FADH2 -> 4ATP

2 ATP

Net ATP of Cellular Respiration

36 ATP

% Efficiency of Cellular Respiration Formula

mol ATP made x E in kJ/mol of ATP

÷

total E in glucose

Regulation of ATP

-ATP inhibits (allosteric inhibition-reversible non-competitive inhibitor) phosphofructokinase

-Also inhibits the citric acid cycle

Regulation of NADH + Citrate

NADH and citrate allosterically inhibits (reversible non-competitive inhibitor) phosphofructokinase

Activation of ATP synthesis

Breaking down of ATP to AMP allosterically activates phosphofructokinase

Fat (Extra E for Cellular Resp.) enters cell as...

Glycerol -> Glyceraldehyde 3 phosphate (G3P)

Fatty Acids -> Acetyl CoA

Protein (Extra E for Cellular Resp.) enters cell as...

Amino Acids -> Pyruvate, Acetyl CoA, in Citric Acid Cycle

Sucrose (Extra E for Cellular Resp.) enters cell as...

Glucose -> Glucose

Fructose -> Fructose-6-phosphate -> Glucose

Starch (Extra E for Cellular Resp.) enters cell as...

Glucose -> Glucose

Glycogen (Extra E for Cellular Resp.) enters cell as...

Glucose-1-phosphate -> Glucose

Fermentation occurs when...

Oxygen is not available

Fermentation is a means of...

Regenerating NAD+ so that glycolysis can continue on in the absence of oxygen (to produce ATP)

Lactic Acid Fermentation (humans)

Glucose -> (ADP -> ATP) (NAD+ -> NADH) 2 Pyruvate -> (NADH -> NAD+) Lactic Acid

Lactate Threshold

The point at which lactate production is too high for transport out of muscles to keep up (can be improved with endurance training)

Oxygen Debt

The amount of oxygen your body needs after intense exercise to return to its resting state

Alcoholic Fermentation

Occurs in yeast in anaerobic conditions to produce ethanol and CO2 to regenerate NAD+

Glucose -> (ADP -> ATP) (NAD+ -> NADH) 2 Pyruvate -> (-> CO2) (-> CO2) 2 Acetaldehyde -> (NADH -> NAD+) Lactic Acid