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CELLULAR RESPIRATIONCHAPTER 9
9-1 Chemical Pathways
Chemical Energy and Food
The two equations are exact opposites! BUT…
Energy is in a different form!
PHOTOSYNTHESIS
___________ + _________ + ___________ →_______________ + __________6 CO2 6 H2O C6H12O6 6O2
_____________ + _________ →________ + __________ + __________
CELLULAR RESPIRATION
C6H12O6 6O26 CO2 6 H2O
Discovery School - The Mitochondria (2:44)
LIGHT
ATP
Comparing Photosynthesis &
Cellular Respiration:
• Which type(s) of organisms carry out
photosynthesis?
Autotroph Heterotroph
• Which type(s) of organisms carry out cellular
respiration?
Autotroph Heterotroph
Overview of Cellular Respiration
• Cellular respiration is the process that releases energy from food in the presence of oxygen.
• If oxygen is available, organisms can obtain energy from food by a process called cellular respiration.
• The summary of cellular respiration is presented below.
6 O2 + C6H12O6 6 CO2 + 6 H2O + Energy (ATP)
Structure of the Mitochondria:
How Mitochondria Create Energy (1:42)
Chemical Energy and Food
• Cellular respiration happens
slowly and in many steps.
• If all the energy was release in
one step… Most would be lost as
light and heat!
• Cellular respiration breaks down glucose
molecules and banks their energy in ATP
Chemical Energy and Food
•Amount of heat it takes to raise 1 gram of water 1oC = calorie
•Amount of heat it takes to raise 1 kilogram of water 1oC = Calorie
•Unit for measuring energy in food = Calorie
1 Calorie = 1 kilocalorie = 1,000 calories
Energy Consumption - Virtual Cell Animation (4:41)
Comparing Photosynthesis & Cellular Respiration
Photosynthesis Cellular Respiration
Function
Location
Reactants
Products
Produces food (chemical
energy) for the plant
(glucose C6H
12O
6)
Produces chemical energy
(ATP) for the cell
Chloroplast Mitochondria
Water (H2O),
Carbon dioxide (CO2)
and sunlight
Oxygen (O2) and
Glucose (C6H
12O
6)
Oxygen (O2) and
Glucose (C6H
12O
6)
Water (H2O),
Carbon dioxide (CO2)
and energy (ATP)
NADH
NADH FADH2
GLYCOLYSISGlucose Pyruvate
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
Substrate-level
phosphorylation
Oxidative
phosphorylation
Mitochondrion
and
High-energy
electrons
carried by
NADH
ATPATPATP
CO2 CO2
Cytoplasm
Substrate-level
phosphorylation
Compare
Photosynthesis
to Cellular
Respiration
Light Energy
CO2H2O
Chloroplast
LIGHT
REACTIONS
(in thylakoids)
CALVIN
CYCLE
(in stroma)
NADP+
ADP + P
ATP
NADPH
O2 Sugar (C6H12O6)
How Cells Obtain Energy (14 min)Cell respiration up to 8:30
An Overview
of Cellular
Respiration:
Stages of Cellular Respiration
The three main
stages of cellular
respiration are
1. Glycolysis
2. Krebs cycle
3. Electron transport
chain.
Oxygen and Energy
• Glycolysis takes place in the
cytoplasm of a cell.
• Glycolysis is an ANAEROBIC
processes. It does not directly
require oxygen, nor does it rely
on an oxygen-requiring process
to run.
• Only a small amount of energy is
captured to produce ATP
• 90% of the chemical energy that
was available in glucose is still
unused (locked in bonds of
pyruvic acid)
Oxygen and Energy
• Pathways of cellular respiration
that require oxygen are called
AEROBIC.
• The Krebs cycle and electron
transport chain are both aerobic
processes.
• Both processes take place inside
the mitochondria.
Overview of Cellular Respiration
Occurs in three main stages:Stage 1: Glycolysis
• Occurs in the cytoplasm• Breaks down glucose into
pyruvate, producing a small amount of ATP
Stage 2: The Citric Acid Cycle (Krebs cycle)
• Takes place in the mitochondria• Completes breakdown of
glucose, produces a small amount of ATP
• Provides third stage of cell respiration with electrons
Stage 1
Stage 2
Stage 3
Overview of Cellular Respiration
Stage 3: Oxidative phosphorylation (ETC)• Occurs in the
mitochondria• Uses the energy
released by “falling” electrons to pump H+
across a membrane• Harnesses the energy of
the H+ gradient through chemiosmosis, producing ATP
Stage 3
Understanding Oxidation and Reduction
•Oxidation is the loss of electrons; electrons are removed
from hydrogen atoms contained in glucose.
•Reduction is the gain of electrons; oxygen atoms accept
hydrogen and electrons forming water H2O.
• Hydrogen is a source of electrons.
• Remember:• OIL RIG (Oxidation Is Loss, Reduction Is Gain)
• LEO the lion goes GER (Lose Electrons – Oxidation)
(Gain Electrons – Reduce)
In cellular respiration, glucose is
oxidized and oxygen is reduced.
Electron Carriers (enzymes) Involved
•NAD+ (Nicotinamide adenine dinucleotide)
Accepts H+ to become NADH
•FAD (Flavin adenine dinucleotide)
Accepts 2H+ to become FADH2
NADH vs NADPH
NADH – cell respiration NADPH - photosynthesis
Overview of Cellular Respiration
NADH
NADH FADH2
GLYCOLYSIS
Glucose Pyruvate CITRIC ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
Substrate-level
phosphorylationOxidative
phosphorylation
Mitochondrion
and
High-energy electrons
carried by NADH
ATP
ATPATPCO2 CO2
Cytoplasm
Substrate-level
phosphorylation
Stage 1Stage 2
Stage 3
Krebs
How Cells Obtain Energy (14 min)Cell respiration up to 8:30
9.2 Glycolysis
“sugar breaking” glykos = sweet, lysis = split apart
• The first step in cellular respiration = Glycolysis
• Occurs in the CYTOPLASM outside the mitochondria
• Does not require oxygen, BUT it needs some energy to get it started.
• What molecule is going to supply the energy?
ATP
Glycolysis Overview - Virtual Cell Animation (3:00)
Glycolysis
Put in 2 ATP and get back 4 ATP
Net gain of 2 ATP and 2 NADH
________
↓
___________ → → _____________
↓
____________________ + _______________
GLUCOSE
ATP ATP ATP ATP NADH NADH
2 PYRUVIC ACID
Glycolysis
• Produces pyruvic acid (pyruvate = 3-carbon compound)
• Cell needs to invest some energy to get a higher return (2 ATP gained)
• Occurs quickly, in milliseconds to respond to increased energy demand
Glycolysis Reactions - Virtual Cell Animation (5:00)
Pyruvate vs Pyruvic acid
The Advantages of Glycolysis
• Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase.
• Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.
How Efficient is Glycolysis?
• Complete oxidation of glucose releases 686 kcal
• Production of a standard amount of ATP from ADP absorbs 12 kcal
• 2 ATP are produced from every glucose molecule broken down by glycolysis
Energy required to make ATP
Efficiency of == --------------------------------------------
Glycolysis Energy released by oxidation of glucose
• Efficiency of glycolysis = 3.5%
9-2 The Krebs Cycle and
Electron Transport
Bill Nye Greatest Discoveries - Krebs Cycle (5:38)
Mitochondria Structure
•Has a double membrane, with an intermembrane space between the two layers.
•Cristae are folds of the inner membrane
•The matrix is the innermost compartment, which is filled with a gel-like fluid.
•Krebs Cycle occurs in the matrix of the mitochondria.
The Krebs Cycle
Carbon dioxide is lost to the atmosphere as waste
ATP can be used directly to supply energy for the cell
High energy electron carriers move into the ELECTRON TRANSPORT CHAIN
The Krebs Cycle
• During the Krebs cycle, the 2nd
stage of cellular respiration, pyruvic acid produced in glycolysis is broken down into carbon dioxide in a series of energy-extracting reactions.
• The Krebs Cycle is also known as the Citric Acid Cyclebecause citric acid is the first compound formed in this series of reactions.
Citric Acid Cycle An Overview (3:17)
The Krebs Cycle
• Pyruvic acid enters the mitochondria matrix
• Pyruvic acid is converted into an intermediate 2 carbon molecule called Acetyl-CoA before entering the Krebs Cycle.
• The Krebs cycle breaks down carbon compounds into carbon dioxide (waste), ATP, NADH, and FADH2
The Citric Acid Cycle The Reactions (4:13)
The Krebs Cycle
• Pyruvic acid from glycolysis enters the matrix, the innermost compartment of the mitochondrion.
Kreb’s Cycle
• Pyruvic acid from glycolysis enters the matrix
• NAD+ accepts 2 high-energy electrons to form NADH.
• One molecule of CO2 is also produced.
• The remaining 2 carbon atoms react to form acetyl-CoA.
Diagram by Riedell
The Krebs Cycle
The Citric Acid Cycle The Reactions (4:13)
• Acetyl-CoA combines with a 4-carbon molecule (oxaloacetic acid) to produce citric acid.
Diagram by Riedell
The Krebs Cycle
• Citric acid is broken down into a 5-carbon compound and then a 4-carbon compound.
• Two molecules of CO2 are released.
• The 4-carbon compound can then start the cycle again by combining with acetyl-CoA.
The Citric Acid Cycle The Reactions (4:13)
KREBS CYCLE
PRODUCES
____
____
____
____
KREBS CYCLE
Krebs Cycle Animation
3
1
1
4
The Krebs Cycle
• Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.
• For each turn of the cycle, 1 ADP molecule is converted into ATP.• ATP can directly power the cell’s
activities.
• NADH and FADH2 are used in the electron transport chain to generate ATP.
Energy Extraction
• Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in 2 complete “turns” of the Krebs cycle.
• Therefore, for each glucose molecule, 6 CO2 molecules, 2 ATP molecules, 8 NADH molecules, and 2 FADH2
molecules are produced.
Summary Sheet
• Glycolysis of 1 glucose = 2 Pyruvic acid molecules= 2 molecules of acetyl CoA
• Causes 2 turns of the Krebs Cycle
• 8 NADH (4 per Turn)
• 2 FADH2 (1 per Turn)
• 2 ATP (+ 2ATP from glycolysis)= 4 ATP thus far
• 6 CO2 molecules (3 per turn)
Summary Sheet Continued
• The bulk of energy released by the oxidation of glucose still has not been transferred to ATP.
Requires NADH and FADH2
10 NADH: 2 from Glycolysis
2 from pyruvic acid to acetyl CoA
6 from Krebs Cycle
2 FADH2
THESE MOLECULES DRIVE THE NEXT STAGE OF AEROBIC RESPIRATION!!!
Electron Transport Chain
• Enzymes (protein complexes) for the electron transport chain are located on the inner mitochondrial membrane.
• Several complexes are called cytochromes.
Electron Transport Chain (3:48)
Electron Transport Chain
• Electrons from NADH and
FADH2 travel down the
ELECTRON TRANSPORT CHAIN,
between protein complexes, to
oxygen (final electron
acceptor), which picks up H+
to form water
• Energy released by the redox
reactions is used to pump H+
into the space between the
mitochondrial membranes
(inter membrane).
H2O
NAD+
NADH
ATP
H+
H+
Controlled
release of
energy for
synthesis of
ATP
2 O2
2e
2e+
1
2
Electron Transport Chain (2:00)
Chemiosmosis
•In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes.
•Drives the synthesis of ATP!
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
Protein
complex
Electron
flow
Electron
carrier
NADH NAD+
FADH2 FAD
H2OATPADP
ATP
synthase
H+ H+ H+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
+ P
O2
Electron Transport Chain Chemiosmosis
.
OXIDATIVE PHOSPHORYLATION
+21
2
© Pearson Education
High energy electrons and ATP
• Every time a pair of high energy electrons moves down the ETC the energy is used to move H+ ions across the membrane.
• These ions rush back across the membrane with enough force to spin the ATP synthase and generate enormous amounts of ATP
• On average, each pair of high energy electrons that moves down the full length of the ETC provides enough energy to produce 3 molecules of ATP
Electron Transport Chain
Electron Transport Chain
• High energy e- from NADH and FADH2 are passed along a series of molecules
• As they pass e- lose some energy to pump protons from the matrix
• This builds up a concentration gradient between the inner and outer mitochondrial membrane (intermembrane)
• The gradient drives the synthesis of ATP by chemiosmosis
The Role of Oxygen
• Oxygen (O2) serves as the final electron acceptor of the ETC
• O2 also accepts the protons H+
• O2 is essential for getting rid of low E e- and H+
• Without O2 the ETC cannot function
• The combination of protons, electrons, and oxygen produces water
O2 + 4 e- + 4 H+ 2 H2O
Site of the
Electron
Transport
Chain and
ATP
Synthesis
ATP
Synthase
Overview of Cellular Respiration
Energy Yield
• Each NADH in the
E.T.C. = 3 ATP
• Each FADH2 in the
E.T.C.= 2 ATP
Cellular Respiration - Glycolysis, Krebs Cycle, ETC (6:00)
Cellular Respiration Glycolysis,
Krebs cycle, Electron Transport (6:01)
Energy Yield
• In most eukaryotes, the NADH made in the cytoplasm during glycolysis cannot diffuse through the inner membrane of the mitochondria.
• It must be transported via active transport.
• Consumes 2 ATP:
38 ATP – 2 ATP = 36 ATP• In the presence of oxygen, the complete
breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.
• This represents about 36% of the total energy of glucose.
• The remaining 64% is released as heat.
Fermentation
•When pyruvic acid moves to the next step,
• if there is no oxygen = anaerobic
• if there is oxygen = aerobic
Fermentation
• Fermentation – process by which cells release energy in the absence of oxygen• Glycolysis produces ATP quickly and does not require O2
• Without O2 the ETC does not run – no where for NADH to deposit its electrons
• Without NAD+ the cell cannot keep glycolysis going and ATP production stops.
Two types of fermentation:• Alcoholic Fermentation
• Lactic Acid Fermentation
Alcoholic Fermentation
Occurs in yeast cells:
• Yeast is added to bread– CO2 produced in fermentation make air spaces in bread and therefore bread rises.
• Alcohol evaporates during cooking
• Alcohol is toxic to cells. If too much fermentation occurs, alcohol will kill yeast cells.
• Happens when:• Yeast make beer
• Bacteria make wine
How Stuff Works - Bread (2:35)
How Stuff Works - Whiskey (2:32)
Lactic Acid Fermentation
• Happens in muscles during exercise when body can’t get oxygen to tissues fast enough.
• Lactic acid builds up in muscles causing soreness.
• Bacteria use lactic acid fermentation to make: yogurt, cheese, sour cream, pickles, sauerkraut
The Totals
• Cellular Respiration (aerobic: with oxygen)
1 glucose → 36 ATP
• Fermentation (anaerobic: without oxygen)
1 glucose → 2 ATP
