anatomy and physiology i cellular metabolism instructor: mary holman

Anatomy and Physiology I

Cellular Metabolism

Instructor: Mary Holman

Metabolism

• Refers to all the chemical reactions in the body that use or release energy

• It is the energy-balancing between synthesis reactions and decomposition reactions in the body

Anabolism• a synthesis reaction

• the joining of smaller molecules to form larger ones

• requires energy

• dehydration synthesis - removal of water

Fig. 4.1a

CH2OH

H H

OH

O

H OH

Monosaccharide(glucose)

+

HHO

H

OH

H H

OH

O

H OH

Monosaccharide(glucose)

HHO

H

OH

CH2OH

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

Formation of a disaccharide:a molecule of H20 is removed

H20

Fig. 4.1b

H H

OH

O

H OH

Disaccharide(maltose)

H2O

Water+

HHO

H H H

OH

O

H OH

HO

H

OH

CH2OH CH 2OH


An example of Anabolism:A Disaccharide is formed by dehydration synthesis

+

Fig. 4.2a

H C

H

Glycerol 3 fatty acid molecules+

OH HO

H C OH HO

H C

C

C

COH HO

OH

O

O


(CH2)14 CH3

(CH2)14 CH3

(CH2)14 CH3

Dehydration Synthesis of a Fat

Fig. 4.2b

C

C

C

O

O

O

H C

H

Fat molecule (triglyceride) 3 water molecules

+

H C

H C O

O

O

H

H2O


H2O

H2O

(CH2)14 CH3

(CH2)14 CH3

(CH2)14 CH3

+

Fig. 4.3a

Amino acid + Amino acid

N

H

H

C C

H

R H

O

N

H

H

C C

H

R H

O


O

Another example of Anabolism:Two amino acids joined to make a dipeptide

Fig. 4.3b

N

H

H

C

R

Dipeptide molecule +

Peptidebond

H

N

H

OH

H

O

N H2O

Water


O

C CC

R

+

Dipeptide

Catabolism

• a decomposition reaction

• the breaking down of larger

molecules to form smaller ones

• releases energy

• often requires H2O

Fig. 4.2

H C

H

Glycerol 3 fatty acid molecules+

OH HO

H C OH HO

H C

C

C

COH HO

OH

O

O

C

C

C

O

O

O

H C

H

Fat molecule (triglyceride) 3 watermolecules

+

H C

H C O

O

O

H

H2O

(CH2)14 CH3

H2O

H2O


(CH2)14 CH3

(CH2)14 CH3

(CH2)14 CH3

(CH2)14 CH3

(CH2)14 CH3

Anabolism - dehydration synthesis - requires energy

Catabolism - hydrolysis - produces energy

+

Enzymes

• Molecules that speed up chemical reactions

• Are not used up in the reaction

so they can be recycled

• Usually are proteins

• Names often end in -ase

Fig. 4.4

Unalteredenzymemolecule

Enzyme-substratecomplex

Active site

(a) (b) (c)

Enzymemolecule


Product moleculeSubstrate molecules

Action of Enzymes

Fig. 4.5

Substrate1

Enzyme A Substrate2

Enzyme B Substrate3

Enzyme C Substrate4

Enzyme DProduct


Enzyme Specificity

Fig. 4.6

Inhibition

Substrate1

Substrate2

Enzyme B Substrate3

Enzyme C Substrate4

Enzyme DProduct

Rate-limitingEnzyme A


Negative feedback mechanism

Fig. 4.7

Ribose

Adenosine

P P P

Adenine

Phosphates


ATP - Adenosine triphosphate

Fig. 4.8a

Energy transferredfrom cellularrespiration usedto reattachphosphate

P P

P P P

P

ADP

ATP


ADP to ATP

Fig. 4.8b

ADP

ATP

Energy is transferred and utilized bymetabolicreactions whenphosphate bondis brokenP P

P P P


P

Potential energy is stored in the bonds between the outer 2 P groups of ATP

Hi energy bonds

Cellular Respiration or Cellular Metabolism

• The breakdown in the body of high-energy molecules to produce energy

• Catabolism of glucose C6H12O6

produces ATP

• Three steps:– Glycolysis– Citric Acid Cycle– Electron transport chain

Fig. 4.9a

1 Glycolysis

Cyt

oso

l

ATP2

Glucose

High-energy electrons (e–)

Pyruvic acidPyruvic acid

The 6-carbon sugar glucose is broken down in the cytosolinto two 3-carbon pyruvic acid molecules with a net gainof 2 ATP and the release of high-energy electrons.


Glycolysis

Glycolysis

2 ATP used and 4 ATP generated = Net 2 ATP

2 electron pairs released to NAD+

• 1 molecule of glucose (6 carbon)• results in 2 molecules of pyruvic acid (3 carbon)• happens in the cytosol• anaerobic

NAD+ + 2H NADH + H+

NAD+ and FAD Deliver High Energy Hydrogen To the Electron Transport System

When NAD+ accepts 2 hydrogen atoms,the two electrons and a hydrogen nucleus bind to NAD+ to form NADH. The remaining H ion (a hydrogen nucleus or H+ ) is released

FAD + 2H FADH2

Events After Glycolysis

If O2 Adequate If O2 not Adequate

Pyruvic acid is convertedinto lactic acid until thereis adequate oxygenfor the aerobic steps of cellular respiration

Pyruvic acid enters the mitochondrion andis modified to enterthe citric acid cycle

Fig. 4.9b

2High-energy electrons (e–)

CO2


Acetyl Co A

The 3-carbon pyruvic acids generated by glycolysis enterthe mitochondria. Each loses a carbon (generating CO2)and is combined with a coenzyme to form a 2-carbonacetyl coenzyme A (acetyl CoA). More high-energy electrons are released.


Citric Acid Cycle

Preparation for Citric Acid Cycle

• If O2 is adequate, pyruvic acid enters mitochondrion• releases a carbon as CO2

• combines with coenzyme A to form acetyl coenzyme A

One electron pair passed to NAD+

for each molecule of pyruvic acid convertedto Acetyl CoA

Fig. 4.9c

3

Mit

och

on

dri

on


ATP2

Acetyl Co A

Citric acid

Citric acidcycle

Oxaloacetic acidEach acetyl Co A combines with a 4-carbon oxaloaceticacid to form the 6-carbon citric acid, for which the cycleis named. For each citric acid, a series of reactionsremoves 2 carbons (generating 2 CO2’s), synthesizes1 ATP, and releases more high-energy electrons.The figure shows 2 ATP, resulting directly from 2turns of the cycle per glucose molecule that entersglycolysis.

2 CO2

Citric Acid Cycle or Krebs Cycle• Acetyl coenzyme A combines with oxaloacetic acid to form citric acid• CO2 formed as carbons are removed• cycle regenerates oxaloacetic acid• happens aerobically

For each turn of the citric acid cycle:3 electron pairs passed to NAD+1 electron pair passed to FAD1 ATP generated

Fig. 4.91

3

4

2

Glycolysis

Cyt

oso

lM

ito

cho

nd

rio

n

ATP2

Glucose


2e– and 2H+

2

H2OO2

Electrontransport

chain ATP32–34


2 CO2

Acetyl CoA

Citric acid

Citric acidcycle

Oxaloacetic acid



ATP

Glycolysis

The 6-carbon sugar glucose is broken down in the cytosolinto two 3-carbon pyruvic acid molecules with a net gainof 2 ATP and release of high-energy electrons.

Citric Acid Cycle

The 3-carbon pyruvic acids generated by glycolysis enterthe mitochondria. Each loses a carbon (generating CO2

and is combined with a coenzyme to form a 2-carbonacetyl coenzyme A (acetyl CoA). More high-energy electrons are released.

Each acetyl CoA combines with a 4-carbon oxaloaceticacid to form the 6-carbon citric acid, for which the cycleis named. For each citric acid, a series of reactions removes 2 carbons (generating 2 CO2’s), synthesizes1 ATP, and releases more high-energy electrons.The figure shows 2 ATP, resulting directly from 2turns of the cycle per glucose molecule that entersglycolysis.

Electron Transport Chain

The high-energy electrons still contain most of thechemical energy of the original glucose molecule.Special carrier molecules bring the high-energy electronsto a series of enzymes that convert much of the remaining energy to more ATP molecules. The other products areheat and water. The function of oxygen as the final electronacceptor in this last step is why the overall process is calledaerobic respiration.

12

CO2

2 pr

2 pr

3 pr to Nad+/turn1 pr to Fad+/turn

1 ATP/turn

8 pr total

Fig 4.9

Fig. 4.11

Citric acid cycle

ADP +ATP

Pyruvic acid from glycolysis

Citric acid

(start molecule)

Acetyl CoA

(replenish molecule)

Acetic acid

Oxaloacetic acid

(finish molecule)

Isocitric acid

CO2

CO2

Succinyl-CoASuccinic acidFAD

FADH2

Fumaric acid

Malic acid

Cytosol

MitochondrionNADH + H+

NAD+

NADH + H+

NAD+

NADH + H+

NAD+

CoA

CoA

CoA

CoA

P

NADH + H+

NAD+

P

CoA Coenzyme A

Carbon atom

Phosphate

-Ketoglutaric acida

CO2

Citric AcidCycle

Fig. 4.12

ATPADP +ATP synthase

Electron transport chain

Energy

P

2H+ + 2e–

2e-

2H+

NADH + H+

NAD+FADH2

FAD

O2

H2O

Energy

Energy

2H+ + 2e–

Electron Transport Chain• Each NADH carried e- pair creates 3 ATP• Each FADH2 carried e- pair creates 2 ATP• Oxygen serves as final e- acceptor and produces H20

10 e- pairs carried by NADH = 30 ATP*2 e- pairs carried by FAD = 4 ATPGlycolysis = 2 ATPCitric Acid Cycle = 2 ATP

Net ATP from 1 moleculeGlucose = 38 ATP*

From: Principles of A&P Tortora & Grabowsky

Cellular Respiration Overview

Fig. 4.13


ATP2

ATP2

Glucose

Pyruvic acid Pyruvic acid

Acetyl CoA

CO2

2 CO2

Citric acidOxaloacetic

acid

H2O

2e– + 2H+

High energyelectrons (e–) andhydrogen ions (H+)

High energy

electrons (e–) and

hydrogen ions (H+)

Electron transport chain

ATP32-34

Cytosol

Mitochondrion

High energyelectrons (e–) andhydrogen ions (h+)

1/2 O2

Fig. 4.15

High energyelectrons carried

by NADH and FADH2

H2O

2e– and 2H+

Waste products

–NH2

CO2

CO2

Citricacidcycle

Electrontransport

chain

Amino acids

Acetyl coenzyme A

Simple sugars(glucose)

Glycerol Fatty acids

Proteins(egg white)

Carbohydrates(toast, hashbrowns)

Food

Fats(butter)

Pyruvic acid

ATP

ATP

Glycolysis

1

2

3

ATP

© Royalty Free/CORBIS.

½ O2

Fig. 4.15

High energyelectrons carried

by NADH and FADH2

Complete oxidationof acetyl coenzymeA to H2O and CO2

Produces high energy electrons(carried by NADH and FADH2), which yield muchATP via the electrontransport chain

Breakdown of simplemolecules to acetylcoenzyme Aaccompanied byproduction of limitedATP and high energyelectrons

H2O

2e– and 2H+

Waste products

–NH2

CO2

CO2

Citricacidcycle

Electrontransport

chain

Amino acids

Acetyl coenzyme A

Simple sugars(glucose)

Glycerol Fatty acids

Proteins(egg white)

Carbohydrates(toast, hashbrowns)

Food

Fats(butter)

Pyruvic acid

ATP

ATP

Breakdown of largemacromoleculesto simple molecules

Glycolysis

1

2

3

ATP

© Royalty Free/CORBIS.

½ O2

2

1

3

Pg. 134

anatomy and physiology i cellular metabolism instructor: mary holman

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synthesis reactions

larger molecules

energy enzymes molecules

joining of smaller molecules

decomposition reactions

release energy

chemical reactions