Transcript Cellular Respiration

Chapter 4
Operating a Cell:
Enzymes, Metabolism, and
Cellular Respiration
Fourth Edition
BIOLOGY
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
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Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
Enzymes and Metabolism
 Enzymes
 Proteins that catalyze (speed up) chemical reactions
in a cell
 the enzyme speeds up the reaction BUT IS NOT CONSUMED IN
THE REACTION
 Metabolism: all chemical reactions occurring in the
body
 organized into distinct metabolic pathways
Enzyme 2
Enzyme 1
A
Starting
molecule
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D
C
B
Reaction 1
Enzyme 3
Reaction 2
Reaction 3
Product
Enzymes and Metabolism
 Enzymes
 Enzymes work by lowering the
activation energy needed for a
reaction
 activation energy – initial energy you
need to put into the system to start
the reaction
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Enzymes and Metabolism
 Substrates are the substances being catalyzed by the enzyme
 enzymes bind a substrate at the active site
 active site has a unique shape – fits the substrate specifically
 now know that the binding of the substrate to the active site
causes a shape change to the active site
 called induced fit
 Specificity of the enzyme to the substrate is based on enzyme
shape and active site
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Animation: Enzymes
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Metabolism
Exergonic reaction: energy released, spontaneous
 Types of metabolic reactions
 these reactions release energy into the system
 those exergonic reactions release some of their
energy in the form of heat = exothermic reaction
 those reactions in which the potential energy of the
products is greater than that of the reactants are
called endergonic
Amount of
energy
released
Free energy
 reactions in which the potential energy of the
products is lower than that of the reactants are
called exergonic
Reactants
Energy
Products
Progress of the reaction
Endergonic reaction: energy required, nonspontaneous
 these reactions require energy input
 your metabolism is a combination of exothermic and
endothermic reactions

are coupled together

i.e. the exothermic reactions provide the energy to drive the
endothermic reactions
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Free energy
 those reactions that require the input of heat =
endothermic
Products
Amount of
energy
required
Energy
Reactants
Progress of the reaction
ATP
 running all of your metabolic pathways takes energy
 usually in the form of ATP
 ATP = ribose sugar + adenine base + 3 phosphate groups
 the breaking of one phosphate bond between 2 phosphate groups releases
potential energy into the system
 used by the cell to power the endergonic reactions of metabolism
 as we breakdown food – use the potential energy in food chemicals to
produce ATP

e.g. breakdown glucose to make ATP

160 kg of ATP per day!
ATP  ADP + Pi + energy
phosphate bonds
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ATP
 the energy released from breaking down ATP can power
different kinds of work in the cell
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Metabolism
 we need a way of quantifying the energy required to drive metabolism (i.e. to
perform cellular work)  calorie
 a calorie is the amount of energy required to raise the temperature of 1 gram
of water by 1C.
 1000 calories  1 kilocalorie or Calorie
 the breaking of one phosphate bond between 2 phosphate groups of ATP
releases 7300 calories (7.3 kcal) of energy into the system
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Metabolism
 kilocalorie (kcal) or Calorie:
 unit of energy represented on food labels
 “Calories are consumed by cells to do work”
 cell uses the potential energy in found to do work – by making ATP
 we quantify that potential energy as calories
 Extra calories can be stored as fat
 3,555 Calories = 1 pound of fat
 Metabolic rate: the rate at which the body uses energy
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Enzymes and Metabolism
 metabolic rate = rate at which your body uses energy
 can be measured as the number of calories it takes to power your
metabolism
 Basal Metabolic Rate or BMR = represents the resting energy of a awake,
resting but alert person
 energy used to power the vital organs – 70% of our total energy needs
 70 Calories/hour or 1680 Calories/day for an average male
 Metabolic rate is influenced by many factors:
 Body weight, sex, exercise, genetic makeup, age, and nutritional status
 numerous equations can be used to calculate BMR and the number of
Calories to be taken in per day
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Cellular Respiration
 Cellular respiration is a series of enzymatic reactions that
converts energy from food into energy stored in ATP.
 ATP synthesis is performed in the cytoplasm = fermentation
 also takes place in the mitochondria = aerobic respiration
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Cellular Respiration
 when a phosphate group is transferred from ATP to
another molecule (phosphorylation) - energy
is transferred and ADP is produced.
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Cellular Respiration
 as ATP is used in the cell it must be replenished by cellular
respiration.
 Aerobic cellular respiration occurs in the mitochondria and
requires the presence of oxygen.
 C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP
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Animation: Glucose Metabolism
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Aerobic Respiration
 occurs in four complex steps starting in the cytosol of the cell
and completing in the mitochondria.
 1. Glycolysis – cytosol
 2. Transition step – mitochondria
 3. Kreb’s cycle
 4. Electron Transport Chain (ETC) & ATP synthesis
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Step 1: Glycolysis
 6-carbon glucose molecule is broken down into two 3-carbon pyruvic acid
molecules (i.e. pyruvate)
 Takes place in the cytosol and doesn’t require oxygen and produces 2 ATP
 two molecules of an electron acceptor called NAD+ are used
 these pick up the electrons and hydrogen ions released during glycolysis to
become NADH
 NADH carries 2 electrons and 2 protons
 NADH with its electrons will enter into mitochondria
End result:
2 ATP
2 NADH
2 pyruvates
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Step 2: Transition Step
 pyruvate is brought into the mitochondria and chemically
converted – IF O2 IS PRESENT
End result:
 mitochondria composition
2 CO2
 a. outer membrane
2 NADH
 b. inner membrane folded into cristae
2 acetyl coA

c. center of the mitochondria = matrix
 2 pyruvates are converted into 2 molecules of acetyl coA by the
enzymes of the mitochondrial matrix
 matrix: 2 pyruvate  2 acetyl coA + 2 CO2 + 2NADH
 make 2 more molecules of NADH
Pyruvate
x2
NAD
CO2
CoA
NADH
+ H
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Acetyl CoA
CoA
Step 3: Citric Acid Cycle

Citric acid cycle: series of chemical reactions catalyzed by 8 different enzymes in the
mitochondrial matrix

named this because one product in this cycle is citric acid

also called the Kreb’s cycle

cycle runs twice – once for each molecule of acetyl coA made

the result is the generation of 2 ATP, 6 NADH, 2 FADH2 and the release of 4 molecules
Acetyl CoA
of carbon dioxide
CoA
Citric
acid
cycle
FADH2
3 NAD
FAD
3 NADH
+ 3 H
x2
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2 CO2
ADP + P i
ATP
End result:
2 ATP
6 NADH
2 FADH2
4 CO2
Step 4: Electron Transport and ATP Synthesis

Electron transport chain acts like a conveyor belt, moving electrons through a series of
proteins

three protein complexes in the cristae of the mitochondria

NADH and FADH2 drop off their electrons and hydrogen ions to these complexes

the protein carriers move the electrons through the chain: 1  2  3


turns these complexes into proton pumps

pump the hydrogen into the space between the inner and outer membranes
(intermembrane space)
the concentration of H+ ions increases within the intermembrane space H+ GRADIENT
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Step 4: Electron Transport Chain and ATP Synthesis
 H+ ions are charged, and can’t simply diffuse back across the membrane into
the matrix
 they must pass through a protein channel called ATP synthase – generating
ATP as they do
 as H+ ions diffuse through ATP synthase = ADP + P  ATP
 the ETC generates 34 ATP molecules for every pair of pyruvate that enters the
mitochondria

add this to the 2 ATP made from cytosolic glycolysis = 36 ATP per glucose
 at the end of the chain, the electrons combine with oxygen to produce water.
Ultimate electron acceptor = oxygen
End result:
34 ATP made from NADH and FADH2
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BioFlix: Cellular Respiration
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Cellular Respiration - Metabolism of Other
Nutrients
 Proteins and fats can also provide energy when
carbohydrates are unavailable.
 They are broken down and their subunits feed into
aerobic cellular respiration.
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Cellular Respiration - Metabolism Without Oxygen:
Anaerobic Respiration and Fermentation
 Anaerobic respiration: uses something other
than O2 to accept electrons

done by bacteria
 Fermentation takes place in the cytosol and
does not require O2 to make ATP

first series of reactions in aerobic respiration

produces CO2 and lactic acid – done by
bacteria, yeast and also in animal cells (e.g.
muscle in humans)

C6H12O6  2 pyruvate + 2 ATP  lactate (lactic
acid)

if O2 is present – don’t make lactic acid –
pyruvate is brought into the mitochondria to
finish aerobic respiration
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Cellular Respiration - Metabolism Without Oxygen:
Anaerobic Respiration and Fermentation
 Bacteria in yogurt also
use fermentation to
make lactic acid.
 Yeast cells use
fermentation to convert
glucose to ethanol.
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Body Fat and Health
 Difficult to define “overweight” precisely
 Women need more body fat to maintain fertility than men
do
 Average healthy body fat percentages:
 Women: 22% and Men: 14%
 Body Mass Index (BMI): correlates amount of body fat with
risk of illness and death, using both height and weight
 Healthy range of BMI = 20-25
 Obesity: BMI of 30 or higher
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Body Fat and Health
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Body Fat and Health
 Risk of obesity is influenced by both lifestyle (diet,
exercise) and genetics
 Obesity increases risks of:
 Diabetes
 Hypertension
 Heart disease
 Stroke
 Joint problems
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