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

CELLULAR RESPIRATION

● 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

● Oxidation = loss of e-

● Reduction = gain of e-

CELLULAR RESPIRATION

● occurs primarily in mitochondria● catabolic process

organic cmpds. + oxygen --> carbon dioxide + water + energy C

6H

12O

6 + O

2 --> CO

2 + H

2O + ATP

● glucose is oxidized● oxygen is reduced

CELLULAR RESPIRATION

● Some helpful hints:– when you think of electrons, think of hydrogen– electrons start out with food, end up with oxygen– electrons “fall” to oxygen step-by-step,

not all at once– glucose is our example, but fats, proteins and other

sugars work, too– ATP = energy– ATP can donate phosphate group so other

molecules can do work (ATP = ADP + Pi)

CELLULAR RESPIRATION

● Occurs in stages: 1. glycolysis 2. intermediate step 3. Krebs cycle/citric acid cycle 4. electron transport chain & 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)

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 and 2 NADH

GLYCOLYSIS

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

INTERMEDIATE STEP

● Junction between glycolysis and Krebs cycle ● Occurs when pyruvates enter mitochondrial

membrane

● Each pyruvate is converted to acetyl CoA

INTERMEDIATE STEP

● Process: 1. carboxyl group is removed and released as CO

2

2. remaining molecule is oxidized;

NAD+ becomes NADH 3. coenzyme A attaches to remaining molecule

● Benefits of this step??

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)● CO

2 is released

KREBS CYCLE

● EACH acetyl CoA to go through produces: 1 ATP 3 NADH 1 FADH

2

2 CO

2

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

Molecules of the ETC

● Made up mostly of integral proteins– Exception = ubiquinone is lipid

● Most are cytochromes

– Contain heme to transfer e-

Chemiosmosis

● Occurs in mitochondrial membrane

● Uses H+ gradient to power reaction of ADP + Pi

● Requires ATP synthase = integral protein acting as enzyme

Oxidative Phosphorylation

● Coupling of ETC and chemiosmosis

● each NADH = 3 ATP● each FADH

2 = 2 ATP

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?

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