Harvesting Chemical EnergyChapter 9

Objectives Describe how covalent bonds serve as an energy

store Describe the relationship between form and function Relate the caloric requirements of humans to the

energy requirements for cellular reactions Describe the workings of each phase of cellular

respiration with emphasis on the reactants, the products, the net production of ATP and the cellular locations

Explain how alcoholic fermentation and lactic acid fermentation can be used to generate ATP in the absence of oxygen

Introduction

Harvesting chemical energy involves mitochondria

generates ATP With adequate O2 supplies food is “burnt”

(aerobic respiration) In absence of O2 food molecules are

“fermented”

Overview of Cellular Respiration

Glucose is broken down yielding energy

Breakdown is catabolic

Synthesis or build –up is anabolic

Overview of Cell Respiration

Cell respiration stores energy in ATP molecules overall equation:

C6H12O6 + 6O2 ----> 6CO2 + 6H2O + energy

efficiency ~40% compared with car ~25% Energy is used for body maintenance and voluntary

activity average human needs ~2200kcal/day

Molecular Basics

Energy obtained by transferring electrons (Hydrogens) from organic molecules to oxygen

movement of H+ represents electron movement

involves series of steps coupling endergonic and exergonic reactions

Molecular Basics

Hydrogen carriers (like NAD+) shuttle electrons paired endergonic-exergonic reactions are known as

redox (reduction-oxidation) reactions

oxidation-loss of electron, exergonic reduction-gain of electron, endergonic

breakdown of glucose involves series of redox reactions

at each step breakdown portion oxidized and NAD+ reduced to NADH

Molecular Basics

Energy released when electrons “fall” from hydrogen carrier to oxygen NADH releases energetic electrons, regenerating

NAD+

electrons enter electron transport chain series of redox reactions, passes electrons from one

molecule to next

ultimate electron acceptor is oxygen small amounts of energy released to make ATP

Molecular Basics: Two mechs to make ATP

Two mechanisms for making ATP 1. Chemiosmosis

involves electron transport chain and ATP synthase

uses potential energy of H+ gradient produced by electron transport chain to generate ATP

Two mechs to make ATP cont.

2. Substrate-level phosphorylation

does not involve either electron transport chain or ATP synthase

ADP phosphorylated by enzyme using PO4-

group from phosphorylated substrate

When an electron or hydrogen is lost, this is known as:

A.A. OxidationOxidation

B.B. ReductionReduction

Three Stages of Respiration

Glycolysis- in the cytoplasm

Kreb’s cycle-in the mitochondrial matrix

Electron transport chain-in the inner mitochondrial membrane …..

Glycolysis

Harvests energy by oxidizing glucose to pyruvic acid in cytoplasm ten steps involved

separate enzyme for each stepalso requires ADP, phosphate and NAD+

ATP required to form initial intermediates

Summary of Glycolysis broken into two phases:

steps 1-5 are endergonic = require ATP input

steps 6-10 are energy-releasing= exergonic; make ATP and NADH

net energy gain is 2 ATP and 2 NADH for each glucose

2 Pyruvate are also made

Pyruvate is processed to Acetyl Co A

Pyruvate is chemically processed before entering Kreb’s cycle NAD+ is reduced to to NADH Pyruvate is stripped of a carbon, releases CO2

complexed with coenzyme A (CoA) forming acetyl CoA

net energy gain is 2 NADH for each glucose

Kreb’s Cycle Completes oxidation of organic molecules,

releasing many NADH and FADH occurs in mitochondrial matrix

involves eight steps which results in production of CO2 as waste product

requires ADP, phosphate, NAD+, FAD, and oxaloacetate

eighth step regenerates oxaloacetate

Krebs Cycle Summary

net energy gain from Krebs is 2 ATP, 6 NADH and 2 FADH2 for each glucose that started the process of cellular meatbolism

SO.. For each Acetyl CoA that enters the Krebs Cycle how many ATP, FADH2 and NADH are made

From Glycolysis FADH is made?

A.A. TrueTrue

B.B. FalseFalse

Electron Transport Chain

The The Electron Transport ChainElectron Transport Chain is imbedded in the is imbedded in the mitochondrial cristaemitochondrial cristae

There are many proteins involved that transfer hydrogens There are many proteins involved that transfer hydrogens to generate a hydrogen gradientto generate a hydrogen gradient

Chemiosmosis Chemiosmosis = the process in which energy stored in the = the process in which energy stored in the form of a hydrogen gradient is used to power ATP form of a hydrogen gradient is used to power ATP synthesissynthesis

The greatest amount of energy is produced via this methodThe greatest amount of energy is produced via this method

Electron Transport Chain: Gradient Is Generated

electron transport chain is series of protein complexes in the inner mitochondrial membrane (cristae)

complexes oscillate between reduced and oxidized state

H+ transported from inside cristae to intermembrane space as redox occurs

Chemiosmosis: ATP is Generated

H+ gradient drives ATP synthesis in matrix as H+ transported through ATP synthase

net energy gain is 34 ATP for each glucose

Oxygen is the final hydrogen( electron) acceptor

Water is the “waste” product

Electron Transport Chain: Issues Some poisons function by interrupting critical

events in respiration

rotenone, cyanide and carbon monoxide block various parts of electron transport chain

oligomycin blocks passage of H+ through ATP synthase

Uncouplers, like dinitrophenol (DNP), cause cristae to leak H+, cannot maintain H+ gradient

Cellular Respiration: Summary Each glucose molecule yields 38 ATP

glycolysis in cytoplasm yields 2 ATP in absence of O2, but mostly prepares for mitochondrial steps that require O2

Kreb’s cycle in mitochondrial matrix produces some 2 ATP, but mostly strips out CO2 and produces energy shuttles

Electron transport chain produces 34 ATP but only if O2 present

Cellular Respiration: Summary cont.

3 ATP produced for each NADH and 2 ATP produced for each FADH2

Don’t try to derive each one, there is still scientific controvery about this issue

The transporters of the Electron Transport Chain are antiports:

A.A. TrueTrue

B.B. FalseFalse

Some things to consider ???????????

Why do you breathe oxygen?Why do you breathe oxygen?

When you diet where do those “lost” When you diet where do those “lost” pounds go and how do they do it?pounds go and how do they do it?

Where does the COWhere does the CO2 2 you exhale come you exhale come

from?from?

Fermentation Energy-releasing reactions in absence of oxygen Recharges NAD+ pool so glycolysis can

continue in absence of oxygen alcoholic fermentation in yeast and bacteria results in

2C ethanol; product is toxic lactic acid fermentation in many animals and bacteria

results in 3C lactic acid; causes muscle fatigue

pyruvate represents decision point in respiratory pathway for organisms capable of carrying out either aerobic respiration or fermentation strict anaerobes live in environments that lack

oxygen; only glycolysis facultative anaerobes, e.g. yeast and certain bacteria,

live in environments that either lack or contain oxygen

Molecular Fuel for Respiration

Free glucose not common in animal diets Each basic food type can be molecular

energy source carbohydrates hydrolyzed to glucose; enters

glycolysis proteins hydrolyzed to amino acids

amino group stripped and eliminated in urine carbon backbone enters middle of glycolysis or

Kreb’s cycle

lipids hydrolyzed to glycerol and fatty acidsglycerol enters middle of glycolysisfatty acids converted to acetyl CoA;

enters Kreb’s cycle

Raw Materials for Biosynthesis

Cells obtain raw materials directly from digestion of macromolecules

Assembly of new molecules often reversal of breakdown during respiration

ATP required for biosynthesis and produced by degradation

All cells can harvest molecular energy Storage of molecular energy restricted