Download Harvesting Chemical Energy

Harvesting Chemical Energy
Chapter 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
each step breakdown portion oxidized and NAD+
reduced to NADH
 at
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
phosphorylated by enzyme using PO4group from phosphorylated substrate
ADP
When an electron or hydrogen is
lost, this is known as:
A.
B.
Oxidation
Reduction
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 step
also requires ADP, phosphate and NAD+
ATP required to form initial intermediates
Summary of Glycolysis
broken
steps
into two phases:
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
ADP, phosphate, NAD+, FAD, and
oxaloacetate
eighth step regenerates oxaloacetate
requires
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.
B.
True
False
Electron Transport Chain

The Electron Transport Chain is imbedded in the
mitochondrial cristae

There are many proteins involved that transfer hydrogens
to generate a hydrogen gradient

Chemiosmosis = the process in which energy stored in the
form of a hydrogen gradient is used to power ATP
synthesis

The 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
present
transport chain produces 34 ATP but only if O2
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.
B.
True
False
Some things to consider ???????????

Why do you breathe oxygen?

When you diet where do those “lost”
pounds go and how do they do it?

Where does the CO2 you exhale come
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
acids
glycerol enters middle of glycolysis
fatty 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
