From Snickers to ATP

Review ATP Cellular Respiration

◦ Glycolysis◦ Pyruvate oxidation◦ Krebs cycle◦ Electron Transport chain

Fermentation

All of our energy comes from? This energy is the form of? Plants convert this energy to? The energy is potential (stored) energy

stored in? The energy is released by? Most living organisms require energy in the

form of?

Oxidation of sugars, primarily glucose. Key chemical reactions = REDOX reactions,

transfer of electrons and H+ from one substance to another.

Energy is harvested from electrons and used to produce ATP.

ATP is stored in small quantities in cells but is primarily produced on demand by cellular respiration.

ATP consists of three phosphate groups, ribose, and adenine.

Phosphate groups

Ribose

Adenine

ATP production: ADP + P → ATP; 2 types◦ Substrate level phosphorylation

◦ Oxidative phosphorylation

2 types of Cellular Respiration◦ Aerobic - oxygen is used as the final electron

acceptor.◦ Anaerobic – final electron acceptor is an inorganic

molecule; some bacteria and archaea. Fermentation – is also an anaerobic process.

Summary of aerobic respiration using glucose: C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + energy (ATP)

4 Steps, fig 9.8:

In the cytosol, 10 reactions, 3 stages, fig 9.13◦ Glucose (6 C) is primed, using 2 ATP’s, and

converted to fructose 1,6 – bisphosphate.◦ Fructose is split into two 3-C molecules,

glyceraldehyde 3-phosphate (G3P)◦ Energy extraction: electrons and H+ transferred

to 2NAD+ and 4 ATPs produced. Final product – 2 pyruvate molecules (3 C).

Glycolysis begins with an energy-investment phase of 2 ATP

All 10 reactions ofglycolysis occurin cytosol

GLYCOLYSIS

What goes in:

What comes out:

Glucose

Glucose-6-phosphate

Fructose-6-phosphate Fructose-

1,6-bisphosphate

Pyruvate

The “2” indicates that glucosehas been split into two 3-carbon sugars

During the energy payoff phase, 4 ATP are produced for a netgain of 2 ATP

Figure 9-7Figure 9-7

NAD+

Reduction

Oxidation

Oxidized

Oxidized

Nicotinamide

Phosphate

Ribose

Phosphate

Ribose

Adenine Phosphate

Phosphate

Ribose

Ribose

Adenine

Reduced

Nicotinamide

NADH(electron carrier)

Reduced

Summary: Glucose + 2 NAD+ + 4ADP → 2 pyruvate + 2 NADH + 4ATP.

Note: each G3P is oxidized to produce 1 NADH and 2 ATP by substrate level phosphoylation.

2 ATP are used to pay back 2 used at the beginning.

Net Production: Glucose + 2 NAD+ + 4ADP → 2 pyruvate + 2 NADH + **2ATP.

Fig 9.14. What inhibits glycolysis?Fig 9.14. What inhibits glycolysis?

Takes place in the outer membrane of the mitochondria, fig 9.16 and 9.17.

Each pyruvate (3 C) is oxidized to an acetyl group (2 C).

Each acetyl group is combined with Coenzyme A (CoA) and feeds into the Kreb’s Cycle.

Summary: 2 Pyruvate + 2 CoA + 2 NAD+ → 2CO2 + 2acetyl CoA + 2NADH

Figure 9-17Figure 9-17

Takes place in the matrix of the mitochondria, 9 reactions, 2 stages, fig 9.19.◦ Priming:

Each acetyl CoA (2 C) combines with oxaloacetate (4 C) in Kreb’s cycle to form citrate (6 C).

CoA removed and recycled.

2 stages cont’d◦ Energy Extraction:

Oxidation reactions transfer electrons and H+ to NAD+ and FADH. Each acetyl group that enters produces 3 NADH and 2 FADH2.

ATP produced by substrate level phosphorylation. Each acetyl group produces 2 ATP.

Figure 9-19Figure 9-19

Oxaloacetate

Malate

FumarateSuccinate

Succinyl CoA

-Ketoglutarate

Citrate Isocitrate

Pyruvate

Acetyl CoA

THE KREBS CYCLE

In each turn of thecycle, the twoblue carbons areconverted to CO2

The two redcarbons enterthe cycle viaacetyl CoA

All 8 reactions of theKrebs cycle occur in themitochondrial matrix,outside the cristae

In the next cycle, thisred carbon becomesa blue carbon

Summary: 2 acetyl CoA + 2 oxaloacetate + 6NAD+ +

2FADH + 2ADP → 4CO2 + 6NADH + 2FADH2 + **2 ATP + 2

oxaloacetate (remains in Kreb’s Cycle). Regulation, fig 9.20.

These steps arealso regulated viafeedback inhibition,by ATP and NADHThis step

is regulatedby ATP

OxaloacetateAcetyl CoA

Citrate

Figure 9-21Figure 9-21

So far we have 4ATP and a bunch of electrons (energy) and H+ carried by NADH and FADH2.

NADH and FADH2 transfer electrons to the transport chain (ETC) on the cristae of the mitochondria, fig 9.24.

The ETC “harvests” the energy from the electrons as they pass down the chain.

The energy harvested from the electrons is used to “pump” H+ from the matrix to the intermembrane space of the mitochondria (energy is stored in the H+).

This produces a concentration gradient for H+.

Occurs in the inner membraneof the mitochondrion

H+ reenter the matrix through the enzyme, ATP synthase.

ATP synthase recovers the energy and produces ATP via oxidative phosphorylation.

Using the H+ gradient to produce ATP is called chemiosmosis.

Figure 9.25

H+ transferred to O2 to produce H2O. Summary: 10 NADH + 2 FADH2 + 3O2 →

**26 ATP + 6H2O. Add the 2 from glycolysis and 2 from the Kreb’s

cycle brings the total to 30 ATPs produced from every glucose molecule.

Fate of pyruvate in the absence of oxygen. Allows for ATP production on a small scale

by recycling NAD+ for glycolysis. 2 types:

Lactic acid fermentation:

Ethanol fermentation:

Figure 9-27bFigure 9-27b

Lactic acid fermentation occurs in humans.

2 Pyruvate

2 Lactate

No intermediate;pyruvate acceptselectrons from NADH

Figure 9-27cFigure 9-27c

Alcohol fermentation occurs in yeast.

2 Pyruvate

2 Acetylaldehyde2 Ethanol

Metabolism = all of the chemical reactions in an organism◦ Catabolism

◦ Anabolism

In the absence of available glucose, fats and proteins can feed into glycolysis and the Kreb’s Cycle, fig 9.29.

Products of glycolysis and the Kreb’s cycle can be used to produce RNA/DNA, proteins and fats, fig 9.30.

Figure 9.29

Figure 9.30