CELLULAR RESPIRATION How do cells harvest and access chemical energy?

How is energy released from food? Food molecules are slowly metabolized through various pathways to generate units of ATP These pathways take place in the cytoplasm (glycolysis) and mitochondria (Kreb’s Citric Acid Cycle and ETS)

Cellular Respiration Equation C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + 36ATP

How do cells “tap” energy? Energy is contained in electron arrangement in the chemical bonds of organic fuels (e.g. glucose) Cellular respiration basically shuttles electrons through a series of reactions and releases energy in form of ATP

How much ATP does a human muscle cell need? 10 million molecules of ATP per second!!

Two basic ways to break down sugar to make ATP Aerobically Needs oxygen In slow-twitch muscle fibers Anaerobically Does not need oxygen In fast-twitch muscle fibers

Connection between breathing and cellular respiration

Oxygen Need Breathing brings in oxygen from outside the body to our lungs (gas exchange) Blood carries oxygen to our cells to carry out cellular respiration Carbon dioxide is removed from cells and exhaled through lungs (gas exchange)

Cellular Respiration Overview

3 Stages of cellular respiration 1.Glycolysis (in cytoplasm) 2.Citric acid cycle (in mitochondrial matrix) 3.Oxidative phosphorylation – Electron transport chain and chemiosmosis (on inner mitochondrial membrane)

Glucose is oxidized to form carbon dioxide Produces CO2; Uses O2 ATP and other energy molecules power cell respiration Krebs Citric Acid Cycle = Matrix of Mitochondria 3 Reactions Glycolysis = cytoplasm Kreb’s Citric Acid Cycle = matrix mitochondria ETS = Inner membrane cristae

Glycolysis = substrate level phosphorylation 2 ATP Pay  Glycolysis  4 ATP Net Gain 2 ATP 2C 3 H 6 O 3 or 2 pyruvate 2 NADH

Kreb’s Citric Acid Cycle 2 pyruvate Mitochondria Outer membrane Acetyl COA CO 2 2 ATP Substrate level phosphorylation 2FADH 2 6NADH 2NADH

e- OxygenH2OH2O Proteins In Membrane ATP Oxidative Phosphorylation Electron Transfer

Glycolysis Citric Acid Cycle Fatty Acid Oxidative Phosphorylation ETS Oxidative Phosphorylation Oxidative Phosphorylation ATP Synthase Chemiosmosis

Sprinter vs. marathon runner Sprinting requires quick bursts of energy and intense action Long distance running requires endurance and slow, steady action Have more “fast-twitch” muscle fibers which contract quickly and powerfully Good for short bursts of intense activity Have more “slow-twitch” muscle fibers (80% in quadriceps) which contract slowly and continuously Don’t tire as quickly

Connection between photosynthesis and cellular respiration

C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + 36ATP Loss H atoms Gain H atoms

Oxidation-Reduction Reaction Oxidation : loss of electrons from a molecule “ LEO the lion says Loss of Electrons is Oxidation Reduction: gain of electrons from a molecule GER!” Gain of Electrons is Reduction

Redox reactions NAD+ + 2H  NADH + H+ Reduction OHHO + 2H Oxidation Dehydrogenase Carries 2 e-- 2H+ + 2e--

Redox reactions Oxidation and reduction reactions are always coupled together One molecule loses electron(s) to the other molecule Energy is released when electrons are passed from molecule to molecule in a cascade (electron transport chain)

Redox Reactions Oxidation reactions are exergonic Reduction reactions are endergonic Breaking down glucose involves a series of redox reactions with the help of a dehydrogenase enzyme and its coenzyme NAD+

NAD + is a hydrogen carrier A coenzyme molecule made from niacin (a B vitamin) Shuttles electrons in redox reactions Removes hydrogen atoms (with their electrons) from molecules (i.e. they become oxidized) NAD+ then becomes reduced to NADH

Electron carriers NADH delivers electrons to a series of electron carriers in a cascade In this cascade, electrons “fall” down an energy “hill” and release energy for making ATP along the way Oxygen is at the bottom of the “hill” and is the final electron acceptor

Glycolysis (rxn 1: cytosol) “Sugar-splitting” One glucose molecule is split into two pyruvic acid molecules through 9 steps Reactants: glucose, ADP, phosphate, NAD+ and ATP Net yield (Products): 2 ATP molecules, 2 NADH and 2 pyruvic acids

2ATP 2P 2ADP + 2 NAD+2 NADH 2 pyruvate Glucose 2H+ +

Substrate-Level Phosphorylation Adenosine P P P PP ATP Organic Substrate ADP Enzyme

NAD+NADHH+ + pyruvate CO 2 Coenzyme A CoA Acetyl CoA “Bridge” Reaction: Pyruvic Acid is converted to Acetyl CoA

Citric Acid Cycle (Rxn 2: Matrix) Acetyl CoA molecule is broken down into 2 carbon dioxides (CO 2 ) Reactants: Acetyl CoA, ADP, phosphate, NAD+, FAD and oxaloacetic acid Net yield: Two ATP, six NADH, two CO 2 and two FADH 2 molecules Oxygen must be available (needs aerobic conditions)

Oxidative phosphorylation (Rxn 3 Cristae) A series of protein complexes in a row that become alternately oxidized and reduced, as electrons from NADH and FADH 2 molecules pass through Hydrogen ions actively transported to intermembrane space and result in 34 ATP molecules being produced

Oxidative Phosphorylation

Inhibitors

ATP yield from Cellular Respiration Glycolysis Substrate Level Phosphorylation 2 ATP Krebs Citric Acid Cycle Substrate Level Phosphorylation 2 ATP ETS Chemiosmosis Oxidative Phosphorylation ~ 34 ATP

The energy in glucose is released by many exergonic reactions a little bit at a time is used to make ATP molecules by endergonic reactions

Aerobic cellular respiration Requires oxygen Complete breakdown of glucose into CO 2 Involves citric acid cycle and oxidative phosphorylation

Anaerobic Respiration No oxygen required Involves the conversion of glucose to pyruvic acid Alcoholic fermentation: conversion of pyruvic acid to alcohol Lactic acid fermentation: conversion of pyruvic acid to lactic acid

Fermentation

Lactic acid fermentation Making yogurt and cheese from lactose sugar in milk by using anaerobic bacteria Overexertion of human muscles from strenuous exercise results in lactic acid buildup sore muscle “burn” -ATP and oxygen -supplies depleted