Cellular Respiration

What we will cover Adenosine triphosphate ATP is the immediate source of energy for most cellular processes ATP breaks down to ADP and releases energy ATP is generated in the aerobic breakdown of carbohydrate In anaerobic respiration ethanol and lactate are produced and NAD (a coenzyme) is regenerated and can be used to make ATP

C N NH2 HC CH H O OH CH2 O- P Ribose Phosphates Adenine Adenosine Triphosphate In cells ATP is converted to ADP; energy is released when the bond connecting the phosphates is broken.

ATP to ADP +Pi Releases Energy

Aerobic Respiration

There are three phases to Aerobic Respiration ... they are: 1. Glycolysis (same as the glycolysis of anaerobic respiration) 2. Krebs cycle (AKA - Citric Acid cycle) 3. Oxidative Phosphorylation and The Electron Transport Chain

The Separate Biochemical Steps GLYCOLYSIS LINK REACTION TRICARBOXYLIC ACID OR KREBS CYCLE ELECTRON TRANSPORT SYSTEM OR OXIDATIVE PHOSPHORYLATION

Phase One: Glycolysis (takes place in the cytoplasm) Glucose (6 carbons) Pyruvic Acid (3C) 2 ATP’s supply the activation energy 4 ATP’s are produced 2 NAD+ + 2 e- 2 NADH 4 ATP Yield = 2 ATP Net Gain

The First Stage of Respiration for ALL living organisms, anaerobes or aerobes, is called Glycolysis and takes place in the Cytosol.

Glycolysis glyco means “glucose/sugar”, and lysis means “to split”. Therefore, glycolysis means “to split glucose” This process was likely used to supply energy for the ancient forms of bacteria.

Glycolysis Function - to split glucose and produce NADH, ATP and Pyruvate (pyruvic acid). Location - Cytosol

Reactants for Glycolysis Glucose 2 ATP…. As activation energy 4 ADP and 4P Enzymes 2 NAD+ (Nicotinamide Adenine Dinucleotide, an energy carrier)

2 ATP’s supply the activation energy Glycolysis 4 ATP’s are produced Pyruvic Acid (3 Carbons) Glucose (6 carbons) 2 ATP’s supply the activation energy Pyruvic Acid (3 Carbons) 2 NAD+ + 2 e- 2 NADH 4 ATP Yield = 2 ATP Net Gain

Products of Glycolysis 2 Pyruvic Acids (a 3C acid) 4 ATP 2 NADH

Net Result 2 Pyruvic Acid 2 ATP per glucose (4 – 2 = 2) 2 NADH In summary, glycolysis takes one glucose and turns it into 2 pyruvates (molecules of pyruvic acid), 2 NADH and a net of 2 ATP.

Recap phase 1 - Glycolysis Phase 2 – Krebs Cycle Cellular Respiration Recap phase 1 - Glycolysis Phase 2 – Krebs Cycle

Glycolysis Function - Split down the glucose molecules so they are small enough to enter the Mitochondria Products: 2 Pyruvic Acids (a 3 Carbon acid) 4 ATP 2 NADH ATP – is the immediate source of energy for most cellular processes NADH – carries electrons to the Electron Transport Chain

2 molecules of triose phosphate Glycolysis 1 molecule of glucose (What you need to know) 6 2ATP 2ADP phosphorylation 2 molecules of triose phosphate 3 3 4ADP 4ATP 2NAD Reduced 2NAD 2 molecules of pyruvate What is the net production of ATP? 3 3

The story so far

NADH and FADH NAD = Nicotinamide Adenine Dinucleotide FAD = Flavin Adenine Dinucleotide NADH and FADH are Coenzymes which carry energy in the form of electrons NADH = reduced NAD FADH = FADH2 = reduced FAD

Oxidation and Reduction Oxidation describes the loss of electrons / hydrogen or gain of oxygen (NAD/ FAD) Reduction describes the gain of electrons / hydrogen or a loss of oxygen. (NADH/ FADH)

The Link Reaction In order for Aerobic Respiration to continue the Pyruvic acid is first converted to Acetic Acid by losing a carbon atom and 2 oxygens as CO2. The Acetic acid then must enter the matrix region of the mitochondria. The CO2 produced is the CO2 animals exhale when they breathe.

Phase Two: The Krebs Cycle (AKA the Citric Acid Cycle) Once the Acetic Acid enters the Matrix it combines with Coenzyme A to form a new molecule called Acetyl-CoA. The Acetyl-CoA then enters the Krebs Cycle. CoA breaks off to gather more acetic acid. The Acetic acid is broken down. Sir Hans Adolf Krebs Produces most of the cell's energy in the form of NADH and FADH2… not ATP Does NOT require O2

The Link reaction Mitochondrion Citric Acid Production

Link Reaction 3 2 pyruvate coenzyme A NAD Reduced NAD NAD Reduced NAD Carbon dioxide acetyl coenzyme A 2

The Krebs cycle 27

 The Krebs Cycle Citric Acid Production Mitochondrion

Reduced co enzymes 3NADH Krebs Cycle 2 acetyl coA citrate oxaloacetate 6 4 2 Carbon dioxide ATP Reduced co enzymes 3NADH 1 FADH

As a result of one turn of the Krebs cycle the cell makes: Summary As a result of one turn of the Krebs cycle the cell makes: 1 FADH2 3 NADH 1 ATP However, each glucose produces two pyruvic acid molecules…. So the total outcome is: 2 FADH2 6 NADH 2 ATP The key function of the Krebs cycle is to provide electrons for the Electron Transport Chain, the production of ATP is a bonus.

The story so far

Phase Three: Oxidative Phosphorylation Function: Extract energy (in the form of electrons) from NADH and FADH2 in order to add a phosphate group to ADP to make ATP. Location: Mitochondria cristae.

Oxidative Phosphorylation Requires NADH or FADH2 ADP and P O2

Electron Transport Chain Uses NADH During the electron transport chain, H+ is moved against a gradient. The energy needed to do this is supplied by electrons carried by NADH

What happens along the inner membrane of the mitochondria? The loss of electrons from NADH result in the addition of energy to protein pumps in the membrane resulting in a H+ being moved from the inside to the outside of the inner membrane This happens many times creating an imbalance (gradient) of H+. Oxygen pulls electrons to keep them moving.

What happens along the inner membrane of the mitochondria? ATP is made as H+ ions are allowed back into the matrix of the mitochondria by a different protein (ATP synthase). The energy released by the “rush” of H+ is used by this enzyme to make ATP (kind of like a rush of water in a stream being used to turn a water wheel). Ultimately, aerobic respiration produces ~36 ATP molecules from each individual glucose molecule.

The Electron Transport Chain

Cytochrome c Cytochrome c: is one of the proteins of the electron transport chain; exists in all living organisms; is often used by geneticists to determine relatedness.

Chemiosmotic Hypothesis Biologists still don’t know exactly how ATP is made. The best theory we have is called the Chemiosmotic Hypothesis.

The Chemiosmotic Hypothesis proposes that the Electron Transport Chain energy is used to move H+ (protons) across the cristae membrane, and that ATP is generated as the H+ diffuse back into the matrix through ATP Synthase.

Electron Transport Chain FAD enters here so 2 ATP produced Reduced Carrier 3 Carrier 2 Carrier 4 Reduced NAD Water NAD ATP ATP ATP Oxygen Reduced Carrier 2 Carrier 3 Reduced Carrier 4

ATP Sum 10 NADH x 3 = 30 ATPs 2 FADH2 x 2 = 4 ATPs 2 ATPs (Gly) = 2 ATPs 2 ATPs (Krebs) = 2 ATPs Max = 38 ATPs per glucose

However... Some energy (2 ATP’s) is used to shuttle the NADH from Glycolysis into the mitochondria…..So, some biologists teach there is an actual ATP yield of 36 ATP’s per glucose.

The Final story