Chapter 6: How Cells Harvest Chemical Energy

Muscle Fibers

Fast-twitch• Performs best for sprints• Contract quickly but tire

quickly• Make ATP anaerobically

(not using oxygen

Slow-twitch• Perform best for endurance • Can sustain repeated

contractions• Make ATP aerobically (using

oxygen)

Photosynthesis vs. Cell Respiration

• Photosynthesis uses carbon dioxide to produce high energy carbon molecules and oxygen

• Cellular respiration uses carbon molecules and oxygen to produce energy and carbon dioxide

• The products of photosynthesis are the reactants of cellular respiration

Cellular respiration

• Function: generate ATP to be used for cellular functions

• Can produce up to 38 ATP molecules which is 40% of energy from a glucose molecule, the rest is lost in heat energy

Energy consumption of the body

• The human brain burn about 120 g (1/4 lb.) of glucose per day and uses 15% of oxygen consumption a day

• The average human needs to take in 2200 kcal per day about 1.25 lb. of glucose per day

Reduction vs. oxidation

• Reduction reactions• The addition of

electrons from a substance

• Oxidation reactions• The loss of electrons

from a substance

2 key players in oxidizing glucose

• Dehydrogenase: an enzyme that takes hydrogens from molecules

• NAD+ : Nicotinamide adenine dinucleotide, an organic molecule that cells make from the vitamin niacin and use to shuttle electrons in redox reactions

Stages of cellular respiration

• Stage 1: Glycolysis: cytoplasm: breaks glucose into 2 pyruvates

• Stage 2: Citric Acid Cycle: Mitochondria: Stroma: makes small amounts of ATP and provides ETS with electrons

• Stage 3: oxidative phosphorylation (ETS and chemiosmosis: cristae: makes most ATP

Overview of cell respiration

Glycolysis

• Begins with glucose and ends with 2 pyruvates• Substrate-level phosphorylation: an enzyme transfers

a phosphate group from a molecule directly to an ADP to form ATP. This is used in both glycolysis and citric acid cycle to produce small amounts of ATP

• At the end the molecules of pyruvate still hold most of the energy from glucose and will be oxidized in the citric acid cycle

• The 2 molecules of ATP produced here are only 5% of the glucose molecule

Glycolysis

Pyruvate for the citric acid cycle• Pyruvate loses the

carboxyl group in the for of carbon dioxide (released during respiration)

• 2 C-compound is oxidized and NAD+ becomes NADH

• Coenzyme A joins the 2 C-compound and becomes Acetyl coenzyme A

Citric Acid Cycle

• AKA the Kreb’s Cycle named for Hans Krebs• Takes place in the matrix of the mitochondria• Starts with acetyl Coenzyme A and ends with 2

CO2, 6 NADH and 2 FADH2

Citric Acid Cycle

Oxidative Phosphorylation

• Includes the electron transport chain and chemiosmosis

• Takes place in the cristae (folds in the inner membrane of the mitochondria). The cristae increase the surface area of the membrane so that more reactions can take place

• Exergonic reaction• Chemiosmosis the energy of H+ drives the

synthesis of ATP

Poisons that interrupt Cell Respiration

• Rotenone: binds with an electron carrier at the first protein complex and blocks the movement of electrons through the ETS

• Cyanide and carbon monoxide: bind with an electron carrier at the 4th protein complex blocking the passage of oxygen ceasing the flow of H so no ATP can be formed

• Oligomycin (an antibiotic): used for fungal infections: prevents the flow of H

More poisons

• Uncouplers: causes the mitochondria to leak H

• DNP (DiNitrophenol): produces an enomrous increase in metabolic rate, profuse sweating as the body tries to cope with the excess heat energy produced, collapse and death

TotalsStage where Start

WithATPDir.

ATP Indir.

FADH2 NADH CO2 Other

glycolysis Cyto-plasm

Glucose2 ATP

2 0 0 2 0 2 pyruvates

Pyruvate to Citric Acid Cycle

Cyto to mito.

pyruvate 0 0 0 2 2 (goes to the atm.

None

Citric Acid Cycle (goes through 2x)

Matrix of mito.

Acetyl CoA

2 0 2 6 4 (goes to the atm.)

none

Oxidative Phosphorylation

cristae NADH, FADH2O2

0 0 2x2=4 3X10=30

Total 38 4 34

Totals

Lactic Acid Fermentation

• Can be used by muscle cells to generate NAD+

• Lactate builds up in muscles during strenuous activity, carried back to the liver and converted to pyruvate

• Used in the dairy industry to make cheese

Alcoholic fermentation

• Used in the winemaking industry

Anaerobes

• obligate aerobes: must have oxygen to survive

• Obligate anaerobes: must have no oxygen to survive

• Facultative anaerobe: can survive with or without oxygen

Organic molecules into cell respiration