Post on 02-Jan-2016
Chapter 5
Cell Respiration & Metabolism
Remon Wahba, MD
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Chapter 5 OutlineGlycolysis
Lactic Acid Pathway
Aerobic Respiration
Fat & Protein Metabolism
5-2
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Metabolism
All reactions in the body that involve
Energy Transformations
5-3
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Metabolism Divided into 2 categories:
Catabolism Breaking down of molecules to Release
Energy Is primary source of energy for making ATPATP
Anabolism Formation (synthesis) of larger molecules Requires EnergySource of body’s large energy-storage
compounds
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Metabolism continued
5-4
Glycolysis
5-4
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Glycolysis Breaking down of Glucose Molecules
Does not require Oxygen (Anaerobic)
Occurs in the Cytoplasm
Glucose Molecules split into 2 Molecules of Pyruvate
Small amount of Energy is liberated 2 ATP ( Adenosine Tri Phosphate) 2 NADH ( Nicotinamide Adenine Di Nucleotide
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Glycolysis (cont)
Glycolysis is Exergonic Produces net of 2ATPs & 2NADHs
However, glucose must be activated with 2ATPs (phosphorylation) before energy can be obtainedPhosphorylation traps glucose inside cell
So 2 ATPs are used & 4 ATPs are produced (net gain of 2 ATP)
5-6
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Glycolysis (cont)
Fig 5.2
5-7
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Lactic Acid Pathway For Glycolysis to continue, NADHs produced
need to give its Hs away In absence of O2,
NADH gives its Hs to pyruvate creating Lactic acid (Anaerobic Respiration)
In the presence of O2, NADH gives its Hs to O2 forming Water
(Aerobic Respiration)
5-8
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Lactic Acid Pathway
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Lactic Acid Pathway continued
Also called Lactic Acid Fermentation
Occurs in SkeletalSkeletal & HeartHeart muscles when oxygen supply falls below critical levelDuring Heavy Exercise or Vascular
Blockage
Occurs in RBCsRBCs Don't have mitochondriaUse only lactic acid pathway
5-9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Glycogenesis & Glycogenolysis
For osmotic reasons cells can't store many free Glucose moleculesGlycogenesis
Storage of Glucose as GlycogenSkeletal Muscles & Liver store lots of
Glycogen
Glycogenolysis Breaking down of Glycogen to release
Glucose as glucose 6-phosphatePhosphate groups trap Glucose molecules
inside cells 5-10
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Skeletal muscles use trapped glucose-6-phosphate for their own energy needs
Liver has glucose-6-phosphatase that removes phosphate groups So glucose can be released into the
blood stream to be used by All Body Cells
Glycogenesis & Glycogenolysis continued
5-11
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Cori CycleSome Lactic Acid produced in skeletal
muscle goes to LiverWhere it is converted back into Pyruvate then to Glucose & GlycogenThis process is called:
GluconeogenesisGluconeogenesis(Formation of new glucose)(Formation of new glucose)
5-12
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Cori Cycle
Helps to: Restore Skeletal Muscle Glycogen which was consumed during exercise
Remove Lactic Acid from the Blood
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Cori Cycle
Aerobic Respiration
5-13
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Aerobic Respiration Occurs in the Mitochondria
Requires the presence of Oxygen (aerobic)
Pyruvates are broken down and CO2 is produced
Large amount of Energy is Produced (34-36 ATP)
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Aerobic RespirationBegins when Pyruvate formed by
Glycolysis enters MitochondriaC02 is removed from Pyruvate forming Acetyl CoA (Coenzyme A is a carrier for acetic acid)
C02 goes to lungs to be excreted
Energy in Acetyl CoA is extracted during Aerobic respiration in mitochondria 5-14
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Aerobic Respiration
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Krebs Cycle Begins with Acetyl CoA combins with
Oxaloacetic Acid to form Citric Acid
In a series of reactions Citric Acid is converted back to Oxaloacetic Acid to complete the pathway
Two ATP molecules are produced in the Krebs Cycle from every glucose molecule
Large amount of ATP is produced by Electron Transport Chain (ETC) from NADH and FADH
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Electron Transport Chain
Chain of molecules in inner mitochondrial membrane
Molecules undergo Oxidation / Reduction reactions and Energy is released.
Energy released is used to synthesize ATP by Oxidative Phosphorylation
O2 is the Last electron acceptor
and water is formed
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Krebs Cycle
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Krebs Cycle continued
Fig 5.8
5-17
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Function of Oxygen Allows Electron Transport to continue by acting as
The Final Electron Acceptor
O2 accepts these electrons & combines with 4H+s to form 2 water molecules O2 + 4 e- + 4 H+ 2 H20
In the absence of O2, the Kreb’s cycle would stop and Respiration becomes Anaerobic
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ATP Formation ATP can be made by 2 ways:
Direct (substrate-level) phosphorylationWhere ATP is generated when bonds break2 ATPs in Glycolysis are made this way2 ATPs / glucose in Kreb's made this way
Oxidative Phosphorylation Where ATP is generated by ETC (Electron
Transport Chain)30 - 32 ATPs are produced this way (some
are used to pump ATP out of the Mitochondria)
5-23
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Net Production of ATP
2 from Glycolysis
2 from Direct Phosphorylation in Krebs Cycle
26 from Oxidative Phosphorylation in ETC
A total of 30 ATPs are produced from
each Glucose Molecule
Fat & Protein Metabolism
5-28
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Fats are hydrolyzed to Glycerol & Fatty acidsThese can be modified to run through Kreb's
Proteins are broken down to Amino AcidsWhich can be Deaminated & run through
Kreb's
These pathways can be used to interconvert Carbohydrates, Fats, & Proteins
5-29
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Figure 3.30
Fatty acids Glycerol Pyruvate Carbonbackbone
NH3Urea (waste)
Preparatorystep
AcetylCoA
Citric acidcycle
Electrontransportsystem
(2) many
Glucose Amino acids
Fats Glycogen Protein
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When more energy is taken in than consumed, ATP synthesis is inhibited
Glucose is converted into: Glycogen
& Fat
Energy Storage
5-30
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Acetyl CoA
Is a common Substrate for energy & synthetic pathways
Fig 5.12
5-31
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Fat Synthesis (Lipogenesis)
Acetyl CoAs Can be linked together to form fatty acids
Fatty acids + glycerol = Fat (Triglycerides)Occurs mainly in:
Adipose Tissue &
Liver
5-32
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Fat Synthesis (Lipogenesis)
Fat is a major form of energy storage in bodyYields 9 kilocalories/gramCarbs & proteins yield only 4 Kilocalories/g
Most Energy stored in the body is in the form of
TriglyceridesTriglycerides
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Lipolysis
Is breakdown of fat into Fatty Acids & GlycerolVia hydrolysis by Lipase
Acetyl CoAs from free fatty acids serve as major energy source for many tissues
5-33
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Ketone Bodies Triglycerides are continually broken down &
resynthesizedEnsures blood will contain fatty acids for
Aerobic Respiration During Fasting, Severe Dieting & in Severe
Diabetes large amount of fat is broken downCauses high levels of Free Fatty AcidsSome are converted by the Liver into ketone
bodiesGive breath an Acetone smell
5-36
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Nitrogen (N) ingested primarily as ProteinWhich is used in body as Amino Acids
Excess is excreted mainly as Urea
5-37
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Nitrogen (N) BalanceNitrogen balance = N ingested Vs. N
excretedPositive N balance:
N ingested is more than excretedNegative N balance:
N ingested is less than excreted
In Healthy Adults: Amount of N excreted = Amount ingested 5-38
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Nitrogen (N) Balance
Excess amino acids are not stored in the body
Can be converted into:
Carbs (Gluconeogenesis)
Fat (Lipogenesis)
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20 amino acids used to build proteins:12 can be produced by body (Non-essential)
8 must come from diet (Essential Amino Acids)
5-39
Proteins of Animal Origin are rich in Essential Amino Acids
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Essential & Non-essential Amino Acids
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Transamination Transfer of Amine Group from one Amino Acid
to create another one New Amino Acids can be produced
Addition of -NH2 group to pyruvate or Kreb's cycle Acids (Keto Acids) to make a new amino acid
Catalyzed by Transaminase5-40
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Oxidative Deamination Is process by which excess Amino Acids are
eliminated -NH2 (Amine group) is removed from Glutamic
acid, forming keto acid & AmmoniaAmmonia is converted to urea & excretedKeto acid goes to Kreb’s or to Fat or Glucose
5-42
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Gluconeogenesis
The formation of new Glucose from Non- Carbohydrate molecules.
During Prolonged Fasting most of Blood Glucose is produced in the Liver by
GluconeogenesisGluconeogenesis
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Gluconeogenesis New glucose can be formed from:
Amino AcidsAmino Acids are converted to Keto Acids,
then Pyruvate, then GlucoseGlycerol
From the breakdown of LipidsLactate
Lactates are first converted into Pyruvates then to Glucose (Cori Cycle)(Cori Cycle)
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Uses of Different Energy Sources
Different cells have different preferred energy substrates
Brain uses glucose as its major source of Energy
5-44
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Uses of Different Energy Sources
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Terms to RememberGlycolysis
Breakdown of Glucose into 2 Pyrovate
Glycogenesis Formation of Glycogen from Glucose
GlycogenolysisBreaking down of Glycogen to release
Glucose
GluconeogenesisFormation of Glucose from
Noncarbohydrate
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Terms to Remember
LipolysisBreakdown of Lipids into Fatty Acids &
Glycerol
LipogenesisFormation of Lipids for storage
Ketogenesis:Formation of Ketone Bodies from Fatty
AcidsOccurs in the Liver