CP BIO Chapter 9 Cellular Respiration How Cells Harvest Chemical Energy

All life activities need energy a. Maintain homeostasis; do life functions breathe, circulate blood active transport, synthesize molecules regulate temperature, etc. b. Physical and mental activity c. Cells use energy in ATP molecules CP BIO: Ch. 9 Cell Respiration

Basics of Cellular Respiration Breaks down glucose in many small steps a biochemical pathway Energy released is stored in molecules of ATP –Each ATP has enough energy for one cell task One glucose molecule yields 36 ATP

Cells use ATP for energy ATP - adenosine triphosphate High-energy bond between phosphate groups - breaks easily, bond energy is released Energy is used by cell to do work

All organisms do respiration Need oxygen - aerobic No oxygen - anaerobic Energy flow is one-way - sun  plants  ATP Chemicals recycle

Oxygen and Energy Aerobic respiration harvests the most ATP from glucose Aerobic Anaerobic Breaks down glucose completely Glucose partly broken down Yields max amount of ATP Yields only 2 ATP/glucose Most organisms Only a few microorganisms Products: CO 2, H 2 OProducts: depends 3 stages of breakdown 2 stages of breakdown Glycolysis Glycolysis Krebs cycle Fermentation Electron Transport Chain

Mitochondria – “power house” Compartments - for different stages Inner membrane –Deep folds for more surface –Many reactions at the same time Cristae - folds in membrane Matrix –Space enclosed by inner membrane Intermembrane space –Between inner and outer membrane

Cells need oxygen for cell respiration

Cells use O 2 for respiration, make CO 2 In lungs: O 2 goes into blood; CO 2 out In cells: O 2 goes into cells; CO 2 out

Electron Acceptors Help in reaction pathway, re-used 2 in respiration: NAD and FAD Accept hydrogen ions and electrons from glucose as it breaks down Transfer them to another molecule later in pathway –makes ATP

3 Stages in Respiration 1.Glycolysis In cytoplasm Splits glucose in half 2.Krebs Cycle In mitochondria Finishes glucose breakdown 3. Electron Transport Chain In mitochondria Generates the most ATP

3 Stages of Cell Respiration

Glycolysis 1 st stage Glycolysis = “sugar splits” Glucose 2 smaller molecules - makes 2 ATP Need ATP to start a. Two ATP attach to glucose b. glucose splits in two c. forms 3-carbon PGAL d PGAL becomes pyruvic acid

2 ATP invested Energized glucose splits Hydrogen ions and electrons removed 4 ATP made Net yield 2 Final carbon compound

Glycolysis – splits glucose 1) NAD takes H from glucose – makes NADH 2) PGAL changes to pyruvic acid 3) 4 ATP are produced, but net yield is 2 Products of glycolysis: 2 ATP 2 NADH 2 pyruvic acid

All organisms do glycolysis Need no oxygen or special organelles Probably evolved very early in history of life Can meet energy needs of some simple organisms

Sir Hans Krebs German chemist, 1930s Described the cycle of reactions that make energy in cells Received Nobel in 1953 “Krebs Cycle” or “Citric Acid Cycle”

IF OXYGEN IS PRESENT, pyruvic acid moves into mitochondrion PREPARES pyruvic acid for Kreb’s cycle NOT a separate stage More H go to NAD CO 2 comes off Forms Acetyl-CoA Ready for Krebs Cycle

Krebs Citric Acid Cycle Stage 2 in aerobic respiration In MATRIX Completes breakdown of glucose to CO 2 Makes many molecules of NADH and FADH 2 (make ATP in Stage 3)

Why is it a “Cycle”? Carbon compound in matrix is used and returned -”recycled” Citric Acid is first carbon compound to form in cycle Each cycle makes 1 ATP Acetyl CoA starts the “cycle”

Products of Krebs Cycle 2 ATP/glucose molecule (one each “turn”) Several molecules of NADH and FADH 2 – These will yield energy in stage 3 Last carbons in glucose form CO 2 and diffuse out of cell

Stage 3 - Electron Transport Chain SAME AS ETC IN PHOTOSYNTHESIS Chain of proteins in inner membrane Take electrons from NADH, FADH Electron energy makes ATP MOST ATP made in this stage

ETC in Respiration

Only happens if oxygen is available to take electrons at end of chain and form WATER O + 2 H e -  H 2 O

Electrons power ATP synthesis Total ATP yield per glucose: Glycolysis – 2 ATP Krebs – 2 ATP ETC - 32 ATP Total = 36 ATP

Summary of Aerobic Respiration PathwayReactantsProducts# ATPLocation GlycolysisGlucose + Pyruvic Acid NADH 2cytoplasm Krebs Cycle Acetyl CoACO 2 NADH FADH 2 2 Mitochondrial matrix Electron Transport Chain NADH, FADH 2 O 2 H 2 O32 Mitochondrial cristae Total ATP36-38

Anaerobic Respiration FERMENTATION follows glycolysis –Needs NO oxygen –Makes NO additional ATP after glycolysis –NAD is reused –Pyruvic acid is changed into a final product

Fermentation: two kinds Alcohollactic acid

Alcohol Fermentation Some yeasts pyruvic acid  ethyl alcohol + CO 2 Baking, brewing beer and wine CO 2 gas makes bread dough rise, bubbles in beer and champagne No more ATP made

Lactic Acid Fermentation Pyruvic acid  lactic acid Anaerobic bacteria -make lactic (and other) acids Commercial uses: cheese, yogurt, soy products, sauerkraut, vinegars Muscle cells – can do fermentation only temporarily lactic acids builds up  “oxygen debt” Muscles fatigue, cramp With fresh oxygen: Lactic acid  blood  liver, changed back to pyruvic acid  Kreb’s cycle

Other foods in respiration Carbs are #1 choice for cell energy: 4 cal/g Fats: twice the calorie store: 9cal/g Proteins: LAST choice: – needed for many important roles 4 cal/g -Fats and proteins are also broken down in many small steps -Amount of ATP depends on molecule