Chapter 5 Cell Respiration & Metabolism Remon Wahba, MD.

Chapter 5

Cell Respiration & Metabolism

Remon Wahba, MD

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 5 OutlineGlycolysis

Lactic Acid Pathway

Aerobic Respiration

Fat & Protein Metabolism

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Metabolism

All reactions in the body that involve

Energy Transformations

5-3


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


Metabolism continued

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Glycolysis

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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


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)

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Glycolysis (cont)

Fig 5.2

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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


Lactic Acid Pathway


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


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

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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)

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Cori Cycle

Helps to: Restore Skeletal Muscle Glycogen which was consumed during exercise

Remove Lactic Acid from the Blood


Cori Cycle

Aerobic Respiration

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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)


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


Aerobic Respiration


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


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


Krebs Cycle


Krebs Cycle continued

Fig 5.8

5-17


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


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


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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Fats & Proteins as Energy Sources

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

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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


When more energy is taken in than consumed, ATP synthesis is inhibited

Glucose is converted into: Glycogen

& Fat

Energy Storage

5-30


Acetyl CoA

Is a common Substrate for energy & synthetic pathways

Fig 5.12

5-31


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


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


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


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

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Amino Acid Metabolism

Nitrogen (N) ingested primarily as ProteinWhich is used in body as Amino Acids

Excess is excreted mainly as Urea

5-37


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


Nitrogen (N) Balance

Excess amino acids are not stored in the body

Can be converted into:

Carbs (Gluconeogenesis)

Fat (Lipogenesis)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Essential & Non-essential Amino Acids

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


Essential & Non-essential Amino Acids


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


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


Gluconeogenesis

The formation of new Glucose from Non- Carbohydrate molecules.

During Prolonged Fasting most of Blood Glucose is produced in the Liver by

GluconeogenesisGluconeogenesis


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)


Uses of Different Energy Sources

Different cells have different preferred energy substrates

Brain uses glucose as its major source of Energy

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Uses of Different Energy Sources


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


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

Chapter 5 Cell Respiration & Metabolism Remon Wahba, MD.

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