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Chapter 6
The Tour of the Cell
The Fundamental Units of Life
• All living things composed of cells
• Cell structure correlated to cell function
• All cells descend from existing cells
Microscopy
• Light microscope = visible light passes through specimen magnified by lenses
– Up to 1000X
Electron microscope to view organelles
pollen
H1N1 virus
• Electron microscopes (EMs)
• Scanning EM (SEM) focus beam of electrons onto surface 3-D image
• Transmission EM (TEM)
• focus beam of electrons through specimen
• internal structures
Cell Fractionation
centrifuge
separates cell components
Homogenization
Homogenate
Differential centrifugation
Tissuecells
TECHNIQUE
Supernatant poured into next tube
TECHNIQUE (cont.)
Homogenate
Pellet
Supernatant
1000 g 10 min
20,000g 20 min
80,000g 60 min
150,000g 3 hr
Nuclei, debris mitochondria membranes ribosomes
• Prokaryotic cells= Archaea and Bacteria• No nucleus, no membrane-bounded organelles
• DNA in nucleoid region
0.5 µm
Eukaryotic cells = Plants, Animals, Fungi, Protista
•DNA in nucleus•Organelles
•Membrane bounded•Cytoplasm = fluid-like interior+ organellesCytosol = fluid
• The plasma membrane = selective barrier allows passage of oxygen, nutrients, waste etc
• Composed of phospholipid bilayer
Features of cells
• Surface to Volume ratio high
• Small cells have greater surface area relative to volume
• Larger organisms do not have larger cells than smaller organisms
Human Rat
The Eukaryotic Cell
• Plant and animal cells have most of the same organelles
1. The Nucleus
Nuclear envelope– double membrane; each a lipid bilayer
– Pores regulate entry and exit of molecules from nucleus
• Chromatin = DNA + proteins
• Chromosomes = strands of chromatin
• Nucleolus
– within nucleus
– rRNA synthesis
2. Ribosomes: Protein Factories
• Composed of rRNA and protein
• Protein synthesis in two locations:
– cytosol (free ribosomes)
– ER or the nuclear envelope (bound ribosomes)
3. The Endomembrane System
• Components– Nuclear envelope
– Endoplasmic reticulum (ER)
– Golgi apparatus
– Lysosomes
– Vacuoles
– *Plasma membrane
The Endoplasmic Reticulum
• >half of total membrane
• continuous with the nuclear envelope
– Smooth ER lacks ribosomes
1. Synthesizes lipids
• Rough ER (RER)
– Ribosomes assemble proteins thread through ER lumen
transport vesicles
– Membrane factory
The Golgi Apparatus
• flattened membranous sacs called cisternae
• cis and trans face
trans face(“shipping” side of Golgi apparatus)
• Functions of the Golgi apparatus:
– Modifies proteins from ER
– Manufactures polysaccharides
– Packages into transport vesicles
Smooth ER
Nucleus
Rough ER
Plasma membrane
cis Golgi
trans Golgi
Lysosomes
• membranous sac of enzymes that digest macromolecules
• recycle cell components (autophagy)
Lysosome
• phagocytosis A cell engulfs another cell to form a food vacuole
• A lysosome fuses with food vacuole and digests molecules
– Central vacuoles
• found in many plant cells
• hold organic compounds and water
4. Mitochondria
• cellular respiration generates ATP (energy)
• contain mtDNA
• all eukaryotic cells have mt
– Some have 1, some 1000sOuter membrane
Cristae
Mitochondria
• outer membrane and inner membrane fold into cristae– large surface area for enzymes that synthesize ATP
5. Chloroplasts (plastid)• found in plants and algae
• sites of photosynthesis
– green pigment chlorophyll, enzymes, other molecules
6. Peroxisomes
• metabolic compartments bounded by a single membrane
• detoxify
catalase
2 H2O2 2H2O + O2
(toxic)
7. Cytoskeleton
• Network of protein fibers organize structures and activities in cell
• Anchors organelles
• Maintains cell shape
Components of the Cytoskeleton
• types of fibers :
– Microtubules
• thickest
– Microfilaments
• actin filaments
• thinnest
8. Centrosomes and Centrioles
• Centrosome
– “microtubule-organizing center”
Centrosome
Microtubule
Centrioles0.25 µm
Longitudinal section of one centriole
Cross sectionof the other centriole
– centrioles
• animal cells
• centrosome has pair
centrosome
9. Cilia and Flagella
• Locomotor appendages of some cells
• Movement pattern controlled by microtubules
10. Extracellular materials
• Cells secrete materials external to plasma membrane
A. Cell Walls of PlantsAlso, prokaryotes, fungi, some protists
• protects, maintains shape, prevents excessive uptake of water
• cellulose fibers
• Plasmodesmata -channels between adjacent plant cells for water, nutrients…..
B. Extracellular Matrix (ECM) of Animal Cells
• No cell walls
• Functions :Support, Adhesion, Movement, Regulation
Integrins “glue cytoskeleton to ECM
Chapter 7
Membrane Structure and Function
Overview: Life at the Edge
• The plasma membrane exhibits selective permeability
– some substances to cross more easily than others
Cellular membranes are fluid mosaics of lipids and proteins
• Phospholipids
• - most abundant lipids in the plasma membrane
• - amphipathic = contain hydrophobic and hydrophilic regions
• fluid mosaic model = membrane is fluid structure with a “mosaic” of proteins embedded
Hydrophilichead
WATER
Hydrophobictail
WATER
Membrane Models: Scientific Inquiry
Note hydrophilic heads and hydrophobic tails in bilayer
Phospholipid
bilayer
Hydrophobic regionsof protein
Hydrophilicregions of protein
The Fluidity of Membranes
Phospholipids in membrane move within bilayer, rarely flip flop
• Lipids, proteins, may move laterally
(a) Movement of phospholipids
Lateral movement
( 107 times per second)
Flip-flop
( once per month)
• Membrane fluidity affected by:
– Type of phospholipid/hydrocarbon saturation
– Cholesterol
– Temperature
• Temperature and membrane fluidity
• cool = fluid gel
– Tightly packed hydrocarbons
• warm (37oC) fluid
Cholesterol
• Stabilizes membrane fluidity with changing temperature
Cholesterol
(c) Cholesterol within the animal cell membrane
Membrane Proteins and Their Functions
• mosaic of proteins embedded in lipid bilayer
• Proteins determine most of membrane’s functions
Membrane Proteins
1. Peripheral proteins
– bound to surface of membrane
2. Integral proteins
– penetrate hydrophobic core
– Transmembrane proteins
• span membrane
• Channel proteins have a hydrophilic channel
Fibers ofextracellularmatrix (ECM)
Glyco-protein
Microfilamentsof cytoskeleton
Cholesterol
Peripheralproteins
Integralprotein
CYTOPLASMIC SIDEOF MEMBRANE
GlycolipidEXTRACELLULARSIDE OFMEMBRANE
Carbohydrate
N-terminus
C-terminus
Helix
CYTOPLASMICSIDE
EXTRACELLULARSIDE
– Transport
– Enzymatic activity
– Signal transduction
– Cell-cell recognition
– Intercellular joining
– Attachment to the cytoskeleton and extracellular matrix (ECM)
Six major functions of membrane proteins:
Cell-Cell Recognition: Carbohydrates
• Cells recognize each other by binding to surface molecules on membrane
Permeability of Lipid Bilayer
• Hydrophobic molecules dissolve in bilayer and pass through membrane rapidly
– O2, CO2, Hydrocarbons
• Hydrophilic (polar) molecules do not cross easily
– Sugar, water, ions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Transport Proteins
Integral membrane proteins (transmembrane) Specific for substance moved
1. channel proteins = hydrophilic channel
Ex. aquaporins channel for water Ex. ion channels
2. carrier proteins, bind to molecules and change shape to shuttle across membrane
Ex. glucose transporter
Passive transport = no energy used
1. Diffusion = molecules spread out evenly into available space
• molecules move randomly
• Molecules diffuse down their concentration gradient from high to lower concentration until equilibrium
Molecules of dye
WATER
Net diffusion Net diffusion
(a) Diffusion of one solute
Equilibrium
• 2. Osmosis is diffusion of water across a selectively permeable membrane
• Water diffuses across a membrane from region of higher water (lower solute) concentration to the region of lower water (higher solute) concentration until equilbrium
Lower
concentrationof sugar)
H2O
Higher
Concentrationof sugar
Selectivelypermeable
membrane
Same concentration
of sugar
Osmosis
Water Balance of Cells Without Walls
• Tonicity =ability of solution to cause cell to gain or lose water
• Isotonic solution: Solute concentration same as that the cell; no net water movement across membrane
• Hypertonic solution: Solute concentration greater than inside cell; cell loses water
• Hypotonic solution: Solute concentration is less than inside cell; cell gains water
Hypotonic solution
(a) Animal
cell
H2O
Lysed
H2O H2O
Normal
Isotonic solution
H2O
Shriveled
Hypertonic solution
Solution type? Isotonic, hypotonic, hypertonic?
• Osmoregulation, control of water balance, is necessary adaptation for life in different environments
Filling vacuole50 µm
(a) A contractile vacuole fills with fluid that enters froma system of canals radiating throughout the cytoplasm.
Contracting vacuole
(b) When full, the vacuole and canals contract, expelling
fluid from the cell.
Water Balance of Cells with Walls (ex. plants)
• Hypotonic solution cell swells turgid(firm)
• Isotonic no net movement of water into cell flaccid (limp)
• Hypertonic cells lose water; membrane pulls away from the wall plasmolysis (lethal)
Hypotonic solution
(b) Plant
cell
H2O
Turgid (normal)
H2O H2O
Isotonic solution
Flaccid
H2O
Plasmolyzed
Hypertonic solution
3. Facilitated Diffusion: Passive Transport Aided by Proteins
• Channel proteins
• Carrier proteins
EXTRACELLULARFLUID
Channel protein
(a) A channel protein
SoluteCYTOPLASM
SoluteCarrier protein
(b) A carrier protein
Active transport
• Energy (ATP) required to move solutes againsttheir gradients
• Membrane proteins!
1. Pumps Ex. sodium-potassium pump
EXTRACELLULAR
FLUID [Na+] high
[K+] low
Na+
Na+
Na+[Na+] low
[K+] high CYTOPLASM
Cytoplasmic Na+ binds to
the sodium-potassium pump.1
Na+ high outside cellK+ low
Na+ low inside cellK+ high
According to diffusion?
• 1. Cytoplasmic Na+ binds to pump protein
Na+ binding stimulatesphosphorylation by ATP.
Na+
Na+
Na+
ATP P
ADP
2
2. ADP is phosphorylated to ATP
Phosphorylation causesthe protein to change its
shape. Na+ is expelled tothe outside.
Na+
P
Na+
Na+
3 Phosphorylation causesthe protein to change its
shape. Na+ is expelled tothe outside.
Na+
P
Na+
Na+
3
3. Na+ out of cell
K+ binds on theextracellular side andtriggers release of thephosphate group.
PP
4
4. K+ binds to pump and P released from ATP (energy used)
Loss of the phosphaterestores the protein’s original
shape.
5 + 6 K+ inside cell Pump animation
6. K+ released
Passive transport
Diffusion Facilitated diffusion
Active transport
ATP
Ion Pumps And Membrane Potential
• Membrane potential = voltage difference across membrane
• Due to differences in distribution of + and - ions
• Inside of cell more electronegative than out
• Electrochemical gradient drives diffusion of ions across membrane:
– chemical = concentration gradient
– electrical = membrane potential and ion’s movement
3. Bulk transport
• Exocytosis
– To secrete products from cell
– Vesicles fuse with membrane
2. Endocytosis
cell takes in macromolecules by forming vesicles from membrane
a. Phagocytosis – for large
particle
Vesicle fuses with lysosome
to digest particle
b. Pinocytosis – for fluids/small molecules
PINOCYTOSIS
Plasmamembrane
Vesicle
0.5 µm
Pinocytosis vesicles
forming (arrows) in
a cell lining a small
blood vessel (TEM)
Chapter 8
An Introduction to Metabolism
METABOLISM
• All of an organism’s chemical reactions• Thousands of reactions in a cell
• Example: digest starch use sugar for energy and to build new molecules
•
Metabolic Pathways
• Begin with starting molecule chemical reactions product(s)
• Each step catalyzed by specific enzyme
Enzyme 1 Enzyme 2 Enzyme 3
DCBAReaction 1 Reaction 3Reaction 2
Startingmolecule
Product
• Catabolic pathways -
– break down complex molecules into simpler compounds
– releases energy for cells to use
• Ex. Glucose metabolism produces ATP
• Anabolic pathways - use energy to build complex molecules from simpler ones
• Ex. Protein synthesis from amino acids
Energy
• Energy
– capacity of a system to do work– can be converted from one form to another
• Kinetic energy = energy of motion A moving object can do work on anything it hits
Potential energy = energy stored within system (ex. water behind a dam). Chemical energy = PE available for release in chemical reaction
Ex. Glucose has high CE
The Laws of Energy Transformation
• Thermodynamics – study of energy transformation
• In open system (organisms), energy and matter can be transferred between system and surroundings
First Law of Thermodynamics
• The energy of the universe is constant: • Energy can be transferred and transformed, but it
cannot be created or destroyed.
• Total energy is conserved
• This is the principle of conservation of energy
Second Law of Thermodynamics
• Every energy transfer or transformation increases entropy (disorder) of the universe
• Living systems are open systems and increase entropy in the environment
• During energy transfer some energy is unusable, often released as heat
(a) First law of thermodynamics (b) Second law of thermodynamics
Chemicalenergy
Heat CO2
H2O
+
First Law: chemical E in
food converted to kinetic E
Second Law: disorder is entered into
environment as heat, CO2
• Spontaneous processes occur without energy input;
– ex. explosion, rusting of a car
– releases energy, usually heat
Glycerol and potassium permanganate
Iron and oxygen into iron oxide
Biological Order and Disorder
• Cells create ordered structures from less ordered materials
Example: proteins built from amino acids
• Organisms replace ordered forms of matter and energy with less ordered forms
Example: catabolism breaks down molecules, releases heat
• Energy flows into an ecosystem in the form of light and exits in the form of heat
Free-energy and metabolism
• Free energy (G) = amount of energy available to do work under conditions of a biochemical reaction
Δ G = change in free energy, unstable systems tend to change to stable equilibrium
• Spontaneous reaction = gives up free energy• Negative Δ G
• Moves towards stability, equilibrium• System at equilibrium does no work (low Δ G)
•
• -Δ G = exergonic reaction
– releases energy
– spontaneous
– “downhill”
Exergonic reaction
• Cellular respiration (1 mole glucose = 180g)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
ΔG = -686kcal/mol available for work
Starch has high free energy
• positive Δ G = endergonic rxn
– Absorbs free energy from surroundings
– Nonspontaneous
• Endergonic example:
• Photosynthesis
6CO2 + 6H2O (+ light energy) C6H12O6 + 6O2
686kcal/mol
Equilibrium and Metabolism
• Reactions in closed system eventually reach equilibrium and then do no work
(a) An isolated hydroelectric system
∆G < 0 ∆G = 0
Equilibrium and Metabolism
• Cells are open systems
– constant flow of materials
– not in equilibrium
(b) An open hydroelectric system
∆G < 0
Equilibrium and Metabolism
• catabolic pathway releases free energy in series of reactions
(c) A multistep open hydroelectric system
∆G < 0
∆G < 0
∆G < 0
ATP powers cellular work
• Coupling = Use exergonic reactions to drive endergonic rxns (overall exergonic)
• Chemical potential energy stored in ATP drives cell activities
– Build proteins, active transport, muscle contraction………..
ATP
• ATP =adenosine triphosphate
Energy released when terminal phosphate bond broken by hydrolysis
Energy
Adenosine triphosphate (ATP)
P P
P P P
P ++
H2O
i
ATP --- ADP + PΔ G = -7.3kcal/mol
phosphorylation
• Transfer P from ATP to another molecule to phosphorylate it
• The phosphorylated molecule is less stable
Phosphorylation opens an aquaporin(spinach)
http://www.sciencedaily.com/releases/2005/12/051222085140.htm
Regeneration of ATP
• Add phosphate group to ADP
• Ex. muscle cell 10 million ATP per second
ADP + P ATPΔ G = 7.3kcal/mol
Energy to regenerate ATP from? (catabolism)
P iADP +
Energy fromcatabolism (exergonic,energy-releasingprocesses)
Energy for cellularwork (endergonic,energy-consumingprocesses)
ATP + H2O
Enzymes speed up metabolic reactions by lowering energy barriers
• catalyst =chemical agent that speeds up a reaction
– Unchanged by reaction
• enzyme = catalytic protein (organic)
• Ex. Hydrolysis of sucrose by sucrase
Activation Energy Barrier
• chemical reaction = bonds broken/formed
• free energy of activation = activation energy (EA) = energy to start chemical reaction
• EA contorts molecule makes bonds unstable
How Enzymes Lower the EA
• 37oC reactants do not reach EA
• Enzymes do not affect ∆G • Enzymes speed rxn rate by lowering EA
• Transition state– Reactants most unstable– EA has been reached
Progress of the reaction
Products
Reactants
∆G < O
Transition state
EA
DC
BA
D
D
C
C
B
B
A
A
Substrate Specificity of enzymes
• Substrate = reactant
• Enzyme-substrate complex
• Product(s)
Sucrose Glucose
Sucrase E-S complex Fructose
Water Sucrase
• Active site region on enzyme where substrate binds
• Induced fit - enzyme shape changes to fit to substrateSubstrate
Active site
Enzyme Enzyme-substratecomplex
(b)(a)
Progress of the reaction
Products
Reactants
∆G is unaffectedby enzyme
Course ofreactionwithoutenzyme
EA
without
enzyme EA withenzymeis lower
Course ofreactionwith enzyme
Catalysis in Active Site
• 1000 – 1,000,000 rxns/sec
• Can catalyze forward or reverse rxn
• Active site can lower an EA barrier by– Orient substrates
– Contort substrate bonds
– Provide microenvironment
– Covalently bond to substrate
Local Conditions
• activity affected by
– temperature , pH (each has optimal)
– chemicals
Cofactors
• Nonprotein
• Assist enzyme
• inorganic cofactor
Metal ion (trace elements)
• Coenzyme = organic cofactor
Vitamins
Enzyme Inhibitors
• Competitive inhibitors – bind to active site of enzyme– compete with substrate at active site
• Noncompetitive inhibitors – bind to another part of enzyme– change shape of active site– May not be reversible
• toxins, poisons, pesticides, and antibiotics
• Substrate and enzyme activity – competitive and non-competitive
(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition
Noncompetitive inhibitor
Active site
Competitive inhibitor
Substrate
Enzyme
Regulation of enzyme activity helps control metabolism
• metabolic pathways are tightly regulated
Allosteric Regulation
• Regulatory molecule binds to enzyme but not at the active site!
• Normal regulation of enzyme activity
• Activator
– Stabilizes shape of active site
– Ex. ADP speeds enzymes of catabolism
• Inhibitor
– Stabilizes inactive form of enzyme
Allosteric inhibition flash
Allosteric activation
(a) Allosteric activators and inhibitors
InhibitorNon-functionalactivesite
Stabilized inactiveform
Inactive form
Oscillation
Activator
Active form Stabilized active form
Regulatorysite (oneof four)
Allosteric enzymewith four subunits
Active site(one of four)
This enzyme has subunits
The activator has stabilized the active enzyme form
The inhibitor has stabilized the inactive form
• Cooperativity =type of allosteric regulation that boosts enzyme activity
• substrate binds to one active site stabilizes favorable shape changes at other subunits
Substrate
Feedback Inhibition
• end product of metabolic pathway turns off pathway
• prevents cell from wasting chemical resources by synthesizing more product than is needed
Intermediate C
Feedbackinhibition
Isoleucineused up bycell
Enzyme 1(threoninedeaminase)
End product
(isoleucine)
Enzyme 5
Intermediate D
Intermediate B
Intermediate A
Enzyme 4
Enzyme 2
Enzyme 3
Initial substrate(threonine)
Threoninein active site
Active siteavailable
Active site ofenzyme 1 nolonger bindsthreonine;pathway isswitched off.
Isoleucinebinds toallostericsite
Chapter 9
Cellular Respiration: Harvesting Chemical Energy
Life Is Work
• Living cells require energy from outside sources
• Plants E from ?
• Animals E from ? And ?
Build a chemical cycling system activity Ch 8 Overview
Lightenergy
ECOSYSTEM
Photosynthesisin chloroplasts
CO2 + H2O
Cellular respirationin mitochondria
Organicmolecules
+ O2
ATP powers most cellular work
Heatenergy
ATP
Energy flows into ecosystem as sunlight
Energy leaves as heat
ATP powers work
• Photosynthesis
– Organelle = chloroplasts
– Generates O2 and organic molecules
• Cellular respiration
– Organelle = mitochondria
– Uses organic molecules to generate ATP
Catabolic Pathways
• Organic molecules have potential (chemical) energy
• Exergonic rxns break down organic molecules energy (and heat)
Cellular Respiration
• Aerobic respiration – Uses O2
– ATP produced
Fuel = organic molecules (carbohydrates, fats, proteins)
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP+ heat)
• Anaerobic respiration – Uses organic molecules
– Does not use O2
– ATP produced
– Glycolysis and fermentation
Cellular respiration 1. Glycolysis (“split sugar”)Occurs in the cytoplasm
Anaerobic
Glucose + 2NAD+ + 2ATP 2 pyruvate+ 2NADH + 4ATP
• Net gain of 2ATP per glucose molecule
• 1 glucose 2 ATP and 2 pyruvate
• Glucose oxidized to pyruvate
• NAD+ reduced to NADH
• No O2 required, no CO2 produced
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Glycolysis Glucose + 2NAD + 2ATP 2 pyruvate+ 2NADH + 4ATP
CYTOSOL
Glycolysis
• Energy investment phase uses 2 ATP
• Energy payoff phase
– 4 ATP
– 2NAD+ reduced to 2NADH
– 1 glucose split to 2 pyruvate
Cellular Respiration: Bioflix animationActivity: Glycolysis
Animation BIO231
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2OGlucoseNet
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2. Citric acid cycle (Krebs) (mitochondrial matrix)
2Pyruvate + NAD+ + FADH 2ATP + NADH +
FADH2 + CO2 + H2O
– 2 ATP per 1 glucose
– CO2 generated
– NADH and FADH2 (electron donors)
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Citricacidcycle
Citric Acid CYCLE: PYRUVATE 2ATP + NADH and FADH2
MITCHONDRION
Before citric acid cycle
• Formation of acetyl CoA from 2 pyruvate
• Acetyl CoA links glycolysis to cycle
BIO 231 TCA cycle animation: Acetyl CoA formation
Pyruvate
NAD+
NADH
+ H+Acetyl CoA
CO2
CoA
CoA
CoA
Citricacidcycle
FADH2
FAD
CO22
3
3 NAD+
+ 3 H+
ADP + P i
ATP
NADH
8 enzymatic steps
Pyruvate
NAD+
NADH
+ H+Acetyl CoA
CO2
CoA
CoA
CoA
Citricacidcycle
FADH2
FAD
CO22
3
3 NAD+
+ 3 H+
ADP + P i
ATP
NADH
Summary of citric acid cycle
• Per molecule glucose (2 pyruvate)
– NADH and FADH2 (electron donors)
– 2 ATP (1 per turn) per glucose
• CO 2 produced (2 per turn)
• Occurs in mitochondrial matrix
• Does not directly require O2, but electron transport chain requires oxygen.
• So, cycle is aerobic.
Krebs Animation BIO 231
Text Activity: The Citric Acid Cycle
• 3. oxidative phosphorylation mitochondria cristae
– NADH and FADH2 donate electrons to electron transport chain is series of steps
– Oxygen , H+
– ~34 ATP per glucose
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Oxidativephosphorylation
ATP
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
Oxidative phosphorylation: NADH, FADH2, O2 34 ATP
Electron Transport Chain = linked steps in oxidative phosphorylation
• BIO 231 Electron transport animation
Note:NADH and FADH2 transfer electronsOxygen requiredH+ gradientATP synthesized
Stepwise Energy Harvest via Electron Transport Chain
• Controlled rxns
(a) Uncontrolled reaction
H2 + 1/2
O2
Explosiverelease ofheat and
lightenergy
(b) Cellular respiration
Controlledrelease ofenergy forsynthesis
ofATP
2 H+ + 2 e–
2 H 1/2
O2(from food via NADH)
1/2
O2
NADH
NAD+2FADH2
2 FADMultiproteincomplexesFAD
Fe•S
FMN
Fe•S
Q
Fe•S
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
IV
50
40
30
20
10 2
(from NADHor FADH2)
0 2 H+ + 1/2 O2
H2O
e–
e–
e–
Electron Transport:Fall in free energy during each step to control release of fuel energy
Chemiosmosis couples energy of electron transport to ATP synthesis
• Wiley animation: chemiosmosis
• Note:
– proteins of electron transport/cytochromes
– NADH, FADH2
– Oxygen
– H+ ions pumped out/H+ gradient
– ATP
H+ gradient, a proton motive force• Electron transport chain e- used to pump H+
across mt membrane
• H+ gradient drives ATP production
Virtual Cell: Electron Transport Chain animation
• ATP synthase
– Many polypeptides and subunits
– H+ ion enters for one turn
– ADP + P ATP
INTERMEMBRANE SPACE
Rotor
H+
Stator
Internalrod
Catalyticknob
ADP+
P ATPi
MITOCHONDRIAL MATRIX
Protein complexof electroncarriers
H+
H+H+
Cyt c
QV
FADH2 FAD
NAD+NADH
(carrying electronsfrom food)
Electron transport chain
2 H+ + 1/2O2 H2O
ADP + P i
Chemiosmosis
Oxidative phosphorylation
H+
H+
ATP synthase
ATP
21
An Accounting of ATP Production by Cellular Respiration
• Most energy:
glucose NADH electron transport chain proton-motive force ATP
= ~38 ATP total
Maximum per glucose: About36 or 38 ATP
+2 ATP +2ATP + about 32 or 34 ATP
Oxidativephosphorylation:electron transport
andchemiosmosis
Citricacidcycle
2Acetyl
CoA
Glycolysis
Glucose2
Pyruvate
2 NADH 2 NADH 6 NADH 2 FADH2
2 FADH2
2 NADHCYTOSOL Electron shuttlesspan membrane
or
MITOCHONDRION
Glycolysis Citric Acid Cycle Ox. Phos.Cytosol mt mt
Anaerobic respiration (no O2)
Prokaryotes
Eukaryotes
Generate ATP without O2
1. Glycolysis
2. Fermentation
Anaerobic respiration (cytoplasm)
Fermentation
No electron transport chain
NAD+ reused in glycolysis (way to keep generating ATP without O2)
Alcohol fermentation
• Pyruvate + NADH ethanol + NAD+ + CO2
• Bacteria
• Yeast
2 ADP + 2 P i 2 ATP
Glucose Glycolysis
2 Pyruvate
2 NADH2 NAD+
+ 2 H+CO2
2 Acetaldehyde2 Ethanol
(a) Alcohol fermentation
2
Lactic acid fermentation
Pyruvate + NADH lactate + NAD+
• Bacteria, fungi in cheese making
• Human muscle cells use lactic acid fermentation to generate Pyruvate + NADH lactate + NAD+
• ATP when O2 is low.
Glucose
2 ADP + 2 P i 2 ATP
Glycolysis
2 NAD+ 2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Fermentation (no O2) vs. Aerobic Respiration
• Both use glycolysis to oxidize glucose (and other organic fuels ) to pyruvate
• ATP
– Cellular respiration 38 ATP per glucose
– Fermentation 2 ATP per glucose
• Obligate anaerobes – fermentation – cannot survive in the presence of O2
– Ex. clostridium botulinum
• Facultative anaerobes – Yeast and many bacteria – can survive using either fermentation or cellular
respiration (pyruvate can be used either way)– Ex. E. coli, Streptococcus
Glucose
Glycolysis
Pyruvate
CYTOSOL
No O2 present:Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRIONAcetyl CoAEthanol
orlactate
Citricacidcycle
Facultative anaerobe
The Evolutionary Significance of Glycolysis
• Glycolysis occurs in nearly all organisms
• Glycolysis probably evolved in ancient prokaryotes before O2 on planet
Glycolysis and the citric acid cycle connect to other metabolic pathways
The Versatility of Catabolism
• Glycolysis and fuel
– Carbohydrates – many accepted
– Proteins amino acids; glycolysis or the citric acid cycle
– Fats glycerol glycolysis
– Fatty acids acetyl CoA
– An oxidized gram of fat produces >2X ATP as oxidized gram of carbohydrate
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