harvesting chemical energy chapter 9. n n objectives f f describe how covalent bonds serve as an...
TRANSCRIPT
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