CELLULAR RESPIRATION How Cells Obtain Energy To Sustain Life

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CELLULAR RESPIRATION How Cells Obtain Energy To
Sustain Life
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ENERGETICS

• Life Requires Energy!
• Growth Development
• Muscle Contraction
• Cell Division
• Immune Responses

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ORIGIN OF ENERGY

• Nearly all energy for life on earth comes from
  sunlight
• Energy in sunlight is captured by photosynthesis

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THE BIG PICTURE
6CO2 6H20 ENERGY ? C6H1206 6O2
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RESPIRATION
Oxygen
INHALATION
EXHALATION
Diaphragm
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FOOD
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CELLULAR RESPIRATION

• Sum Of All Chemical Reactions Taking Place Within
  A Living Cell
• C6H1206 6O2 ? 6CO2 6H20 ENERGY
• Glucose Oxygen ? Carbon Water Energy
• dioxide

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METABOLIC PATHWAYS
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OVERVIEW

• Aerobic Cellular Respiration
• 3 steps
• Glycolysis
• Krebs cycle
• Electron Transport Chain

C6H1206 6O2 ? 6CO2 6H20 ENERGY
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REQUIREMENTS OF METABOLISM

• Metabolism Requires
• Input of energy
• Starting materials
• Catalysts
• Helper molecules

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MANY REACTIONS REQUIRE AN INPUT OF ENERGY

• Many Rxns In the Cell Are Non Spontaneous
• Require energy

Products
AB C
Reactants
Potential energy
DE
A BC
Time
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ATP PROVIDES ENERGY TO MAKE A REACTION GO

• What is ATP?
• Nucleotide
• Adenosine Triphosphate

P
P-PP
Adenine
Ribose sugar (5 C sugar)
O
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Adenosine triphosphate (ATP)
Adenine
Adenine
Phosphate groups
Ribose
Ribose
ATP consists of adenine, ribose, and three
phosphate groups.
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HYDROLYSIS OF ATP RELEASES ENERGY
Pi
P
P
P
P
P
H2O
Energy
Water
Inorganic phosphate



ATP
ADP
7.3 kcal/mol ATP
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RATES OF REACTION

• Even with enough energy, there is no guarantee
  rxns will proceed at a suitable speed
• Catalysts help

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LOCK KEY MODEL OF ENZYME AND SUBSTRATE
Substrate (glucose)
Enzyme (hexokinase)
Substrate (Key)
A
BC
A
B
C
A B
C
Enzyme (Lock)
Shape change
Shape change
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ENZYMES SPEED REACTION RATES

• Enzymes
• Are specific for the molecules they react with
• Lower activation energy (Ea)
• Speed rxns
• Recycled after reaction

Transition state
Ea without enzyme
Potential energy
Ea with enzyme
A BC
Reactants
AB C
Products
Time
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MOLECULAR HELPERS

• Two Molecules Help the Process Along
• NAD
• FAD

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REDUCTION of NAD
NADH (electron carrier)
Reduction
Oxidation
Reduced form (high energy)
Oxidized form (low energy)
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OXIDATION-REDUCTION REACTIONS(oil rig)
Reduction Gain of electrons Energy Oxidation
Loss of electrons Loss of Energy
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REDUCTION OXIDATION REACTIONS (REDOX)

• Reduction Always Coupled to Oxidation
• Redox Rxns Allow Slow Release of Energy From
  Glucose

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CELLULAR RESPIRATION IS A SERIES OF REDOX
REACTIONS

• In
• Cellular
• Respiration
• C in glucose is oxidized by way of breaking it
  down to CO2
• Oxidation of C is tied to reduction of other
  molecules
• (ex NAD)

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WHERE DO CELLS GET ENERGY TO MAKE ATP?

• From glucose.

Many steps
P-PP
glucose
ATP
O
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Glucose
H
O
1
C
6
CH2OH
2
H
OH
C
5
H
H
C
O
3
C
H
HO
1
4
H
C
C
4
OH
OH
H
C
H
HO
OH
2
3
C
C
5
H
C
OH
H
OH
6
C
H
OH
H
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ENERGY IN GLUCOSE

• All cells must break C-bonds in glucose to
  release energy
• Energy stored in bonds is called chemical
  energy

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CELLULAR RESPIRATION BEGINS IN THE CYTOPLASM

• Glucose Metabolism (first part of respiration)
• Starts in cytoplasm of cells of all organisms
• Glycolosis
• Glucose metabolism is part of larger process
  called cellular respiration

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THE GLYCOLYTIC PATHWAY
1
2
3
4
5
ATP
ATP
ADP
ADP
FRUCTOSE
GLUCOSE
FRUCTOSE
GLUCOSE
6-PHOSPHATE
6-PHOSPHATE
1,6--BISPHOSPHATE
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THE GLYCOLYTIC PATHWAY
6
7
8
9
10
Pyruvate
2 ADP
2 ADP
2 NAD
2 ATP
2 NADH
2 ATP
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SUMMARY OF GLYCOLYSIS

• Enzyme Mediated Rxns Yield
• Two 3-carbon molecules (pyruvate)
• Two ATP molecules (net)

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SUMMARY OF GLYCOLYSIS

• Additionally
• Two NAD ? Two NADH molecules
• (oxidized) (reduced)
• (2NAD 2H 2e- ? 2 NADH)

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ADDITION OF A HYDROGEN ATOM REDUCES A MOLECULE
Addition of a Hydrogen Atom to a Molecule Reduces
It! Hydrogen atom (H) H (ion) 1
electron (e-)
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Bathroom Break!
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TWO PATHWAYS AFTER GLYCOLYSIS

• In Absence of Oxygen
• Anaerobic Respiration
• Occurs in cytoplasm

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ALCOHOLIC FERMENTATION BY YEAST

• In absence of oxygen, energy production can occur
  through Fermentation
• Yields max 2 ATP/ glucose
• Yeast modify pyruvate to
• produce ethanol
• NAD must be regenerated

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LACTIC ACID FERMENTATION OCCURS IN HUMANS
No intermediate Pyruvate accepts electrons from
NADH
2 NAD
2 Lactate
2 NADH
Glucose
2 ATP
2 Pyruvate
2 ADP
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TWO PATHWAYS AFTER GLYCOLYSIS

• In Presence of Oxygen
• Aerobic Respiration

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AEROBIC RESPIRATION OCCURS IN MITOCHONDRIA

• Transition reaction
• Krebs cycle
• Electron Transport Chain

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MITOCHONDRIA
Outer membrane
Intermembrane space
Inner membrane
Matrix
424 nm
424 nm
Cristae
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GLYCOLYSIS THE KREB CYCLE
6 NADH
2 NADH
2 NADH
2 FADH2
4 CO2
2 Pyruvate
Glucose
Krebs cycle
2 Acetyl CoA
2 CO2
2 ATP
2 ATP
Cytoplasm
Mitochondrion
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TRANSITION REACTION

• 2 Pyruvate oxidized to 2 acetyl-CoA
• 2 NAD reduced to
• 2 NADH
• 2 CO2 produced

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From Transition Rxn to Beginning of Krebs Cycle
NADH
Coenzyme A
NAD
Oxaloacetate
Pyruvate
Acetyl CoA
Citrate
Pyruvate is oxidized to acetyl CoA, which
reacts with oxaloacetate to begin Krebs cycle
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Krebs proposed that the reactions occur in a
cycle.
NADH
NAD
NAD
NADH
Isocitrate
?Ketoglutarate
Citrate
Succinyl CoA
KREBS CYCLE
ADP
GDP
GTP
Pyruvate
ATP
Oxaloacetate
Succinate
FAD
NADH
NAD
FADH2
Fumarate
Malate
H2O
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A series of carboxylic acids is oxidized during
Krebs Cycle.
Isocitrate
Succinyl CoA
Fumarate
Oxaloacetate
?Ketoglutarate
Malate
Citrate
Succinate
More reduced
More oxidized
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Summary of Transition Reaction and Krebs cycle

• Each glucose that enters glycolysis is converted
  into 2 Pyruvate molecules
• Transition Reaction
• 2 pyruvate are converted
• to acetyl CoA
• 2 NADH produced
• 2 CO2 produced
• Krebs Cycle
• 2 Acetyl CoA produce
• 6 NADH
• 2 FADH2
• 2 ATP
• 4 CO2

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Two of the early reactions are regulated.
Citrate
Pyruvate
Acetyl CoA
Oxaloacetate
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What is product inhibition?
X
Inter- mediate
Inter- mediate
Start of pathway
Product
Enzyme 1
Enzyme 3
Enzyme 2
Presence of product inhibits enzyme 1
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SUMMARY OF AEROBIC RESPIRATION
GLYCOLYSIS
KREBS CYCLE
ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION
NADH
NADH
NADH
FADH2
Electron transport chain...
Krebs Cycle
CO2
Glucose
Pyruvate
H2O
CO2
ATP
ATP
ATP
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METABOLISM OF ALL MACROMOLECULES IS TIED TO
CELLULAR RESPIRATION

• Stored carbohydrates (besides glucose) can be
  broken down and used in glycolysis and the Krebs
  cycle.

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Sucrose
CH2OH
O
O
HOCH2
H
H
H
H
OH
HO
H
H
O
CH2OH
HO
H
OH
HO
H
Fructose subunit
Glucose subunit
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Starch
CH2OH
CH2OH
CH2OH
O
O
O
H
H
H
H
H
H
Up to 1000or moremonomers
H
H
H
OH
H
H
OH
H
OH
O
O
O
O
OH
H
H
OH
OH
H
Glucosesubunit
Glucosesubunit
Glucosesubunit
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• Other molecules can also be used to produce
  chemical energy
• Proteins
• Fats

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Energy Sources Other than Glucose
Fatty acids
Fats
Glycerol
Carbs
Acetyl CoA
Sugars
Glucose
Pyruvate
Proteins
Amino acids
NH3
PROTEINS, CARBOHYDRATES AND FATS CAN ALL FURNISH
SUBSTRATES FOR CELLULAR RESPIRATION
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METABOLISM OF ALL MACROMOLECULES IS TIED TO
CELLULAR RESPIRATION

• Inversely, excess intermediates of glycolysis and
  the Krebs Cycle can be converted and stored as
• Carbohydrate
• Fat
• Proteins

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Intermediates in Carbohydrate Metabolism Can Be
Drawn Off a Synthesize Cell Components
Pathway for synthesis of RNA, DNA
Phospholipids
Fats
Fatty acids
Several intermediaries used as substrates in
amino acid synthesis
Glycogen or starch
Glucose
Pyruvate
Acetyl CoA
Krebs cycle
Lactate (from fermentation)