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Cellular Respiration What we do with the glucose from photosynthesis to release the energy stored in it

Cellular Respiration What we do with the glucose from photosynthesis to release the energy stored in it

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Cellular Respiration

What we do with the glucose from

photosynthesis to release the energy stored in it

Stored Energy

• The amount of energy available in a molecule is measured in calories: the amount of energy needed to warm 1 gram of water by 1 degree C.

• In food, this energy is measured as kilocalories (kilo =?), or Calories.

• A gram of carbohydrates has 4 Calories; a gram of fat has 9.

GlucoseGlycolysis

Cytoplasm

Pyruvic acid

Electrons carried in NADH

Krebs Cycle

Electrons carried in

NADH and FADH2 Electron

Transport Chain

Mitochondrion

Cellular respiration

Glucose(C6H1206)

+Oxygen

(02)

GlycolysisKrebsCycle

ElectronTransport

Chain

Carbon Dioxide

(CO2)+

Water(H2O)

Cellular Respiration

Glucose

To the electron transport chain

2 Pyruvic acid

Glycolysis

What if there is no O2?

• One round of glycolysis doesn’t make much ATP, but it happens really fast and is done by thousands sets of enzymes per second in a cell.

• Problem: lots of NAD+ is needed to pick up electrons and H+. It will run out very quickly.

• Usually aerobic respiration recycles it.

Aerobic and anaerobic pathways

Glucose

Glycolysis Krebs cycle

Electrontransport

Fermentation (without oxygen)

Alcohol or lactic acid

Lactic acid fermentation

Glucose Pyruvic acidLactic acid

The point of fermentation

• Fermentation produces no more ATP, but returns NADH to the low energy form NAD+; this allows glycolysis to continue working.

• Humans appreciate the products of alcohol fermentation and use them to produce alcohol and to make bread rise.

Good, but not great

• Glycolysis and fermentation provide enough ATP for single celled organisms, or to power larger organisms for a short time.

• Bigger organisms need to take advantage of the remaining energy in pyruvic acid.

Why Do We Need So Much ATP?

Number of molecules

per cell

Molecules synthesized per

second

Molecules of ATP required per second for

synthesis

DNA 1 0.00083 60,000

RNA 15,000 12.5 75,000

Polysaccharid

es39,000 32.5 65,000

Lipids 15,000,000 12,500.0 87,000

Proteins

1,700,000 1,400.0 2,120,000

Aerobic respiration

• Happens in the mitochondrion.

• 2 Sets of reactions:

– Krebs Cycle in mitochondrial matrix

– Electron transport chain and chemiosmosis in cristae.

Citric Acid Production

The Krebs Cycle

Krebs cycle

• From each pyruvic acid, a set of chemical reactions produces– 2 ATP– NADH

– FADH2

– CO2 as a byproduct

• Since we started with 2 pyruvic acids, the cycle runs twice for each glucose.

On to electron transport…

• The NADH and FADH2 will be used in the electron transport chain.– H ions will be released from them and

electrons will pump the ions – chemiosmosis – just like in

photosynthesis!

Electron TransportHydrogen Ion Movement

ATP Production

ATP synthase

Channel

Inner Membrane

Matrix

Intermembrane Space

Electron Transport Chain

Aerobic exercise

• Aerobic respiration gives us more ATP, but it takes longer to get started.

• Conditioning increases the number of mitochondria in cells and the number of red blood cells so we are better at carrying oxygen.

• These factors make aerobic respiration work more efficiently.

Anaerobic exercise?

• At the beginning of exercise, we rely on glycolysis and fermentation to provide ATP. Lasts about 90 seconds.

• After long periods of exercise (breathing hard!) we start to run out of oxygen and have to switch back to fermentation for a bit.

• Lactic acid accumulates in muscles – what happens?