Ch 6 Cellular Respiration Harvesting Chemical Energy Cellular

Ch. 6: Cellular Respiration Harvesting Chemical Energy

Cellular Respiration: An Overview A cellular process that breaks down nutrient molecules with the production of ATP � Consumes (CO 2) oxygen and produces carbon dioxide ◦ Cellular respiration is an aerobic process. � Usually involves the complete breakdown of glucose to CO 2 and H 2 O � Occurs in 3 steps

Overview �Cellular respiration is an exergonic ◦ produces up to 32 ATP molecules from each glucose molecule ◦ captures only about 34% of the energy originally stored in glucose Other foods (organic molecules) can also be used as a source of energy.

Figure 6. 2 O 2 Breathing CO 2 Lungs CO 2 Bloodstream O 2 Muscle cells carrying out Cellular Respiration Glucose O 2 CO 2 H 2 O ATP

Cellular Respiration: An Overview

Cellular Respiration: An Overview �Terms to Know… ◦ Oxidation = the loss of electrons �Compound becomes more positive ◦ Reduction = the gain of electrons �Compound becomes more negative ◦ Electrons and protons (H+) travel TOGETHER

Oxidation C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + energy glucose Reduction l l Electrons are removed from substrates and received by oxygen, which combines with H+ to become water. Glucose is oxidized and O 2 is reduced

Important enzymes NAD+ ◦ A coenzyme of oxidation-reduction. ◦ Each NAD+ molecule is used over and over again ◦ Reduced into NADH �Accepts 2 electrons plus a hydrogen ion (H+) �FAD ◦ Also a coenzyme of oxidation-reduction ◦ Sometimes used instead of NAD+ ◦ Reduced into FADH 2 �Accepts two electrons and two hydrogen ions (H+)

Respiration �Respiration is a cumulative function of 3 metabolic stages ◦ Glycolysis �Only reactions that takes place outside of mitochondria and doesn’t require O 2 ◦ Citric acid cycle (Krebs Cycle) ◦ Oxidative Phosphorylation �Electron transport chain (ETC)

Cellular Respiration Glucose Glycolysis Oxygen Absent ATP Oxygen Present Anaerobic Respiration Aerobic Respiration (Fermentation) (Krebs Cycle & ETC) ATP

Glycolysis �“glucose-splitting” �Big Picture: ◦ Glucose (6 -C) is broken down into 2 molecules of pyruvate (3 -C) �Occurs in the cytoplasm �Occurs without oxygen �Oxidation results in NADH �Made up of 2 phases: and 2 ATP ◦ Energy investment phase ◦ Energy yielding (payoff) phase

Glycolysis: Energy Investment Phase �Glucose is converted into 2 G 3 P (Glyceraldehyde-3 phosphate) �Requires 2 ATP

Glycolysis: Energy-Yielding Phase ◦ 2 G 3 P are converted into 2 Pyruvate (3 C) molecules. ◦ Dehydrogenase enzymes remove H from intermediate compounds and attach them to 2 NAD to produce 2 NADH

Substrate-Level Phosphorylation �An enzyme transfers a phosphate group directly from an organic molecule to ADP to form ATP �The ATP produced in Glycolysis & the Krebs Cycle is produced by this method.

enzyme P ADP P BPG ATP P 3 PG

Net Gain in Glycolysis � 2 ATP - 2 ATP (Energy investment phase) + 4 ATP (Energy yielding phase) + 2 ATP � 2 NADH ◦ Electron carriers ◦ Will be used to make ATP later

Choices, Choices! �If oxygen is absent, anaerobic respiration occurs ◦ Fermentation �Yeast & some bacteria alcoholic fermentation �Animal muscle lactic acid fermentation �If oxygen is present, aerobic respiration occurs ◦ Krebs Cycle and Electron Transport Chain

Cellular Respiration Glucose Glycolysis Oxygen Absent Anaerobic Respiration ATP Oxygen Present Aerobic Respiration (Fermentation) ATP

Fermentation �Fermentation is an anaerobic process that reduces pyruvate to either lactate or alcohol and CO 2 � 2 major types: ◦ Alcoholic and lactic acid fermentation �NAD+ acts as a hydrogen acceptor during glycolysis ◦ If the supply of NAD+ runs out, then glycolysis would have to stop. ◦ Fermentation occurs as simply a means of recycling the NAD+, so that glycolysis can occur again.

Alcoholic Fermentation � Occurs in some BACTERIA and YEAST � 2 step process: ◦ Carbon dioxide is released from pyruvate (3 -C), forming acetaldehyde (2 -C) ◦ Acetaldehyde is reduced by NADH forming ethanol ◦ NAD+ is regenerated � Used wine to produce beer and

Lactic Acid Fermentation � Occurs in ANIMALS � 1 step process: ◦ Pyruvate is reduced by NADH forming lactic acid � NAD+ is regenerated � Occurs in muscle cells, causing muscle pain and fatigue � Used to make yogurt and cheese

Cellular Respiration Glucose Glycolysis Oxygen Absent Anaerobic Respiration ATP Oxygen Present Aerobic Respiration (Fermentation) ATP

Aerobic Respiration � After glycolysis, most of the energy from glucose remains “locked” in 2 molecules of pyruvate � If oxygen is present, the pyruvate enters the mitochondrial matrix to complete the Krebs Cycle Preparatory Phase: � Pyruvate (3 -C) is converted to Acetyl Co. A (2 -C) ◦ CO 2 is released as a waste product ◦ NADH is produced

The Krebs Cycle �Yield per pyruvate molecule (two turns): ◦ 3 NADH ◦ 1 FADH 2 ◦ 1 ATP �(produced via substrate level phosphorylation) ◦ 2 CO 2 �CO 2 released as ◦ We exhale this a waste product

Figure 6. 9 A Acetyl Co. A 2 CO 2 Citric Acid Cycle 3 NAD FADH 2 3 NADH FAD 3 H ATP ADP P

Electron Transport Chain (ETC) �Collection of cytochrome molecules embedded in the cristae membrane ◦ 4 reactions plus ATP synthase �Occurs in inner membrane of mitochondrion �Proton pump that produces a proton gradient that will be used to create ATP

ETC �Electrons from NADH and FADH 2 from glycolysis and the Krebs Cycle lose electrons, proton gradient �The energy in each NADH molecule moves enough protons (H+) into the mitochondrial matrix to create 3 ATP � 1 FADH 2 2 ATP

ETC �The electrons from NADH and FADH 2 are passed from one electron acceptor molecule to another. �Each electron acceptor is more electronegative than the last. �Oxygen is the final electron acceptor, producing water e- oxygen

Steps of the ETC �I- NADH reductase oxidizes NADH to NAD+ resulting in high energy electron �II- high energy electron transfers through coenzyme Q to cytochrome reductase �III- travels through the cytochrome c �IV- travels into cytochrome oxidase where it is now low energy and binds to oxygen to form water

Chemiosmosis �the energy the electrons lose along the way moves H+ out of the matrix and into the intermembrane space of the mitochondria �As H+ ions diffuse through the membrane, ATP synthase uses the energy to join ADP and a phosphate group ATP

Oxidative Phosphorylation: ETC & Chemiosmosis

Figure 6. 12 CYTOPLASM Electron shuttles across membrane 2 NADH Mitochondrion 2 NADH or 2 FADH 2 6 NADH 2 NADH Glycolysis 2 Pyruvate Glucose Pyruvate Oxidation 2 Acetyl Co. A Citric Acid Cycle 2 FADH 2 Oxidative Phosphorylation (electron transport and chemiosmosis) Maximum per glucose: 2 ATP by substrate-level phosphorylation about 28 ATP by oxidative phosphorylation About 32 ATP