Chapter 9- Cellular Respiration

Monday 11/27

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Test Correction Format

1. Rewrite question 2. Write correct answer 3. Scientifically explain the right answer 4. Scientifically explain why your answer was

incorrect

CELLULAR RESPIRATION

−QUESTION: Why is breathing necessary?

ANSWER: We (heterotrophs) can't make our own food We must break down food made by autotrophs We use oxygen to release energy stored in those organic molecules

Types of Reactions• Catabolic reactions-

Break down substances • Ex. cellular

respiration

• Anabolic reactions- Build up substances

Types of Reactions

● Oxidation-Reduction Reactions (redox) − transfer of electrons from one reactant to another − because one substance loses the electron and

another gains it, redox reactions always go together

OIL RIG ● Oxidation is loss of e-

● Reduction is gain of e-

CELLULAR RESPIRATION

● occurs primarily in mitochondria ● catabolic process

organic cmpds. + oxygen --> carbon dioxide + water + energy C6H12O6 + O2 --> CO2 + H2O + ATP

● glucose is oxidized ● oxygen is reduced

Cellular Respiration

Some helpful hints: − when you think of electrons, think of hydrogen atoms − electrons start out with food, end up with oxygen

− Why oxygen??

− glucose is our example, but fats, proteins and other sugars work, too

CELLULAR RESPIRATION

● Some helpful hints: − electrons “fall” to oxygen step-by-step,

not all at once − ATP = energy − ATP can donate phosphate group so other

molecules can do work (ATP = ADP + Pi)

● Why is this process so in depth? − Energy must be harnessed in steps; too much

would be lost if occurred all at once

CELLULAR RESPIRATION

● Occurs in stages: 1. glycolysis 2. intermediate step (pyruvate oxidation) 3. Kreb's cycle/citric acid cycle 4. electron transport chain (ETC) & chemiosmosis

NAD+

● nicotinamide adenine dinucleotide (no, you do not need to know this!)

● derivative of niacin (vitamin) ● functions as electron acceptor/carrier ● becomes NADH (reduced)

● Gains H atom or electrons! (RIG)

NAD+ —> NADH

First process: Glycolysis

GLYCOLYSIS● “splitting sugar” ● catabolic process ● occurs in cytosol (cytoplasm) ● breaks down glucose (6C) into two molecules of

pyruvate (3C) ● occurs with or without oxygen ● uses 2 ATP ● produces 4 ATP (2 net ATP) and 2 NADH

Glycolysis

Substrate level phosphorylation • Phosphate transferred from substrate to ADP by

enzyme • Forms ATP • 4 created from glycolysis

ATP

GLYCOLYSIS

● IF oxygen is present, pyruvates and NADH can go on to generate more energy ----------->>> INTERMEDIATE STEP

Second process: Intermediate step (pyruvate oxidation)

INTERMEDIATE STEP (pyruvate oxidation)

● Junction between glycolysis and Kreb's cycle ● Occurs when pyruvates enter mitochondrial

membrane (matrix) ● Each pyruvate is converted to acetyl CoA

INTERMEDIATE STEP

● Process: 1. carboxyl group is removed and released as CO2 2. remaining molecule is oxidized; NAD+ becomes NADH 3. coenzyme A attaches to remaining molecule

● Benefits of this step??

Third process: Kreb’s/Citric Acid cycle

KREBS CYCLE

● also known as citric acid cycle ● occurs in mitochondrial matrix ● starts with acetyl CoA (2C) ● acetyl CoA (2C) combines with

oxaloacetate (4C) to make citrate (6C) ● eventually citrate (6C) is decomposed back to

oxaloacetate (4C) ● CO2 is released

KREBS CYCLE

● EACH acetyl CoA to go through produces: 1 ATP (substrate level phosphorylation) 3 NADH 1 FADH2 (electron carrier; INFO 2 CO2

x2 for a glucose molecule!!!

Fourth process: Electron transport chain (ETC) and chemiosmosis

ELECTRON TRANSPORT CHAIN

● Occurs in mitochondrial membrane (cristae) ● Does not directly make ATP

− Coupled with chemiosmosis to produce ATP ● Summary: electrons are transferred from one

molecule to another until reaching oxygen ● NADH inputs electrons at beginning of chain ● FADH2 inputs lower energy electrons at second complex

Molecules of the ETC

● Made up mostly of integral proteins − Exception = ubiquinone is

lipid ● Most are cytochromes

− Contain heme to transfer e-

ETC• As electrons are transferred from carriers, H+

ions pumped into inner membrane space • Effects on pH?

• Creates hydrogen ion gradient

Chemiosmosis

● Occurs in mitochondrial membrane ● Uses H+ gradient to power reaction of ADP + Pi

(CREATES ATP) ● Requires ATP synthase

= integral protein acting as enzyme

Oxidative Phosphorylation

● Coupling of ETC and chemiosmosis ● each NADH = 3 ATP ● each FADH2 = 2 ATP

Fermentation

● What happens if oxygen is not available? ● What becomes the final electron acceptor? ● What phases of cellular respiration still occur? ● How much ATP is produced? ● In what organisms does this commonly occur?