AP Biology

Lecture #18Cellular Respiration

Carbon dioxide, water are required

Carbon dioxide, water are released

Oxygen is released

Oxygen is required

1) Water is split by light energy. Oxygen escapes. Coenzymes pick up electrons, H+.

2) ATP energy drives synthesis of glucose from hydrogen and electrons, plus carbon and oxygen (from CO2).

ATP is available to drive cellular tasks

1) Glucose is degraded to CO2 and water. Coenzymes pick up electrons, hydrogen.

2) Coenzymes give up electrons, hydrogen to oxygen-requiring transfer chains that release energy to drive ATP formation.

Figure 7.2Page 112

Linked Processes

Photosynthesis

• Anabolic Pathway

• Energy-storing pathway

• Releases oxygen

• Requires carbon dioxide

Aerobic Respiration

• Catabolic Pathway

• Energy-releasing pathway

• Requires oxygen

• Releases carbon dioxide

What is Cellular Respiration?

• The process of converting food energy into ATP energy

• C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP

Why are both Photosynthesis and Cell Respiration important to Ecosystems?

• Light is the ultimate source of energy for all ecosystems

• Chemicals cycle and Energy flows

• Photosynthesis and cellular respiration are opposite reactions

Why do plants need both chloroplasts and mitochondria?

• Chloroplasts use energy from the sun to make glucose

• Mitochondria convert glucose to ATP—the energy currency of the cell

What is ATP?• Adenosine Triphosphate

– 5-Carbon sugar (Ribose)– Nitrogenous base (Adenine)– 3 Phosphate groups

• Energy currency of the cell

• The chemical bonds that link the phosphate groups together are high energy bonds

• When a phosphate group is removed to form ADP and P, small packets of energy are released

How is ATP used?• As ATP is broken down, it gives

off usable energy to power chemical work and gives off some nonusable energy as heat.

• Synthesizing molecules for growth and reproduction

• Transport work – active transport, endocytosis, and exocytosis

• Mechanical work – muscle contraction, cilia and flagella movement, organelle movement

Why use ATP energy and not energy from glucose?

• Breaking down glucose yields too much energy for cellular reactions and most of the energy would be wasted as heat.

• 1 Glucose = 686 kcal• 1 ATP = 7.3 kcal• 1 Glucose → 36 ATP

• How efficient are cells at converting glucose into ATP?– 38% of the energy from glucose yields ATP,

therefore 62% wasted as heat.

Cellular Respiration is a Redox Reaction • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

• Oxidation is the loss of electrons or H+

• Reduction is the gain of electrons or H+

• Glucose is oxidized when electrons and H+ are passed to coenzymes NAD+ and FAD before reducing or passing them to oxygen.

• Glucose is oxidized by a series of smaller steps so that smaller packets of energy are released to make ATP, rather than one large explosion of energy.

(Oxidation)

(Reduction)

Cell Respiration can be divided into 4 Parts:

1) Glycolysis2) Oxidation of Pyruvate / Transition Reaction3) The Krebs Cycle4) The Electron Transport Chain and Chemiosmotic Phosphorylation

Where do the 4 parts of Cellular Respiration take place?

• Glycolysis: – Cytosol

• Oxidation of Pyruvate:– Matrix

• The Krebs Cycled:– Matrix

• Electron Transport Chain and Cheimiosmotic Phosphorylation:– Cristae

Parts of the Mitochondria

Anaerobic Respiration (no oxygen required, cytoplasm)

1. Glycolysis(substrate level)

Glucose 4 ATP (Net 2 ATP)2 ATP 2 NADH

2 Pyruvate

Aerobic Respiration (oxygen required, mitochondria)

2. OxidationofPyruvate

2 Pyruvate 2 CO2

2 NADH2 Acetyl CoA

3. Krebs Cycle(substrate level)

2 Acetyl CoA 4 CO2

2 ATP6 NADH2 FADH2

4. ElectronTransportChain

(chemiosmotic)

10 NADH 32 ATP2 FADH2 6 H2O6 O2

Total: 36 ATP produced

ATP is made in two ways:1) Substrate Level Phosphorylation

(glycolysis & Krebs cycle)2) Chemiosmotic Phosphorylation

(electron transport chain)

• Substrate-Level Phosphorylation:• Energy and phosphate are

transferred to ADP using an enzyme, to form ATP. Phosphate comes from one of the intermediate molecules produced from the breakdown of glucose.

Glycolysis

Glucose (C6) is split to make 2 Pyruvates (C3)– 1st: ATP energy used to phosphorylate glucose

(stored energy)– 2nd: phosphorylated glucose broken down into

two C3 sugar phosphates– 3rd: the sugar phosphates are oxidized to yield

electrons and H+ ions which are donated to 2 NAD+ → 2 NADH (stored electron and hydrogen for the Electron Transport Chain)

– 4th: The energy from oxidation is used to make 4 ATP molecules (net 2 ATP)

• This is substrate level phosphorylation because an enzyme transfers phosphate to ADP making ATP

• Glycolysis produces very little ATP energy, most energy is still stored in Pyruvate molecules.

Glucose 2 Pyruvate2 ATP 4 ATP (Net 2 ATP)

2 NADH

Oxidation of Pyruvate /Transition Reaction

• When Oxygen is present, 2 Pyruvates go to the matrix where they are converted into 2 Acetyl CoA (C2).

• Multienzyme complex: – 1st: each Pyruvate releases CO2 to

form Acetate. – 2nd: Acetate is oxidized and gives

electrons and H+ ions to 2 NAD+ → 2 NADH.

– 3rd Acetate is combined with Coenzyme A to produce 2 Acetyl CoA molecules.

• 2 NADH’s carry electrons and hydrogens to the Electron Transport Chain.

2 Pyruvate 2 CO2

2 NADH2 Acetyl CoA

The Krebs Cycle / Citric Acid Cycle

8 Enzymatic Steps in Matrix of Mitochondria: Break down and Oxidize each Acetyl CoA (2-C’s) to release 2 CO2 and yield electrons and H+ ions to 3 NAD+ + 1 FAD → 3 NADH + FADH2. This yields energy to produce ATP by substrate level phosphorylation.

The first step of the Krebs cycle combines Oxaloacetate (4 C’s) with Acetyl CoA to form Citric Acid, then the remaining 7 steps ultimately recycle oxalacetate.

Two Turns of the Krebs Cycle are required to break down both Acetyl Coenzyme A molecules.

The Krebs cycle produces some chemical energy in the form of ATP but most of the chemical energy is in the form of NADH and FADH2 which then go on to the Electron Transport Chain.

2 Acetyl CoA 4 CO2

2 ATP6 NADH2 FADH2

The Electron Transport Chain

• NADH and FADH2 produced earlier, go to the Electron Transport Chain.

• NADH and FADH2 release electrons to carriers/proteins embedded in the membrane of the cristae. As the electrons are transferred, H+ ions are pumped from the matrix to the intermembrane space up the concentration gradient. Electrons are passed along a series of 9 carriers until they are ultimately donated to an Oxygen molecule.

• ½ O2 + 2 electrons + 2 H+ (from NADH and FADH2) → H2O.

10 NADH 32 ATP2 FADH2 H2OOxygen

http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

Chemiosmotic Phosphorylation

• Hydrogen ions travel down their concentration gradient through a channel protein coupled with an enzyme called ATP Synthase.

• As H+ ions move into the matrix, energy is released and used to combine ADP + P → ATP.• Hydrogens are recycled and pumped back across the cristae using the Electron Transport

Chain.• ATP diffuses out of the mitochondria through channel proteins to be used by the cell.

http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

ATP Synthase• Multisubunit complex with

4 parts:– Rotor – spins as H+ ions flow– Stator – holds the rotor and knob

complex together in the cristae– Internal Rod – extends between rotor

and knob, spins when rotor spins which then turns the knob

– Knob – contains 3 catalytic sites that when turned change shape and activate the enzyme used to make ATP

Review ATP Production:1) Glycolysis → 2 ATP2) Oxidation of Pyruvate → No ATP3) The Krebs Cycle → 2 ATP4) The Electron Transport Chain and Chemiosmotic

Phosphorylation: – Each NADH produces 2-3 ATP so 10 NADH →

28 ATP– Each FADH2 produces 2 ATP so 2 FADH2 →

4 ATP Total = 36 ATP

• 1 Glucose = 686 kcal• 1 ATP = 7.3 kcal• 1 Glucose → 36 ATP• How efficient are cells at converting glucose into

ATP?– 38% of the energy from glucose yields ATP,

therefore 62% wasted as heat (used to maintain body temperature or is dissipated)

– Ex. Most efficient Cars: only 25% of the energy from gasoline is used to move the car, 75% heat.

All Types of Molecules can be used to form ATP by Cell

Respiration:• Proteins, Carbohydrates, and

Lipids must first be broken down into their monomers and absorbed in the small intestine.

• Monomers may be further broken down into intermediate molecules before entering different parts of Cell respiration to ultimately form ATP.

Anaerobic Respiration: Fermentation• If there is NO oxygen, then cells can make ATP by Fermentation• Without oxygen, Oxidation of Pyruvate and the Electron Transport Chain do not

operate.

• Glucose → Pyruvate → Lactate NAD+ Glycolysis 2 NADH Reduction Rxn or

2 ATP Alcohol + CO2

Fermentation yields a net gain of 2 ATP by substrate level phosphorylation for every 1 Glucose. (Inefficient)

Two Forms of Fermentation: Lactic Acid Fermentation (animals)Alcohol Fermentation (yeast)