Introduction to Metabolism Cell Structure and Function

Introduction to Metabolism Cell Structure and Function

Cells can be divided into two primary types

prokaryotes - Almost all prokaryotes are bacteria

eukaryotes - Eukaryotes include all cells of multicellular organisms, and many single-celled organisms such as the yeasts and the protists.

Introduction to Metabolism - Origin of Eukaryotes

Introduction to Metabolism - Cell Structure and Function

Anatomy of a Typical Eukaryotic Cell

The d i f f e re nce s be t w e e n p r o k a r y o t e s a n d eukaryotes l ie in their internal organization and modes of reproduction.

In eukaryotic cells, many of the cellular macromolecules a r e p a c k a g e d i n t o o r g a n e l l e s , s u b c e l l u l a r structures surrounded by their o w n m e m b r a n e s . P r o k a r y o t e s l a c k t h i s internal organization.

Introduction to Metabolism - Cell Structure and Function

General Functions of Metabolism

Obtain energy in a chemical form by degradation of nutrients

Convert a wide variety of nutrient molecules into the central precursor molecules needed to build proteins,

carbohydrates, nucleic acids, and lipids

Synthesize cell molecules.

Modify and repair the biomolecules necessary for specific functions in specialized cells or both.

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Catabolism vs Anabolism

Catabolism Biochemical Degradation of Energy-Containing Compounds

1 Capture of the Energy in New Chemical Forms

(ATP, GTP, NADH, NADPH, FADH2) 2

Conversion of Energy-Containing Compounds into a small number of simple molecules

(Pyruvate, Acetate, Krebs Cycle Intermediates)

Catabolism vs Anabolism

Anabolism

Biosynthesis of Molecules from Simple Components 1

Glucose → Other Monosaccharides and Polysaccharides 2

Acetate → Fatty Acids 3

Glycerol + Fatty Acids → Triglycerides 4

Lipids + Polar Components → Cell Membranes 5

Amino acids → Proteins, Hormones, Neurotransmitters 6

Nucleotides → ATP, Coenzymes, Nucleic Acids

Transport of Substances Across Membranes

Stages of Catabolism

Nutrient molecules are degraded to lower-molecular mass components.

The products of stage 1 are converted into one simple molecule: Acetyl-S-CoA.

Acetyl-S-coenzyme A is oxidized to CO2 and H2O by the Citric Acid Cycle.

Reduced coenzymes are oxidized through the Electron Transport Chain to yield ATP.

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Stages of Catabolism

Stages of Catabolism

Stages of Catabolism

Stages of Catabolism

Stages of Catabolism Acetyl-CoA

Citric Acid Cycle

ATP Production

Stages of Catabolism

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Stages of Catabolism

Nutrients New Forms of Energy

During the second and third stages of catabolism, important compounds are formed that fuel anabolism:

Adenosine triphosphate (ATP) Carrier of energy.

Nicotinamide adenine dinucleotide (NADH) Carrier of reducing power

Nicotinamide adenine dinucleotide phosphate (NADPH) Carrier of reducing power

Flavin adenine dinucleotide (FAD) Carrier of reducing power

Flavin adenine mononucleotide (FMN) Carrier of reducing power

NAD(P) +

ATP

Synthesis of ATP

Adenosine-O--P--P Adenosine-O--P--P--P

R--PNutrients

Substrate level phosphorylation: Direct transfer of a phosphate group from a high energy phosphate

compound to adenosine diphosphate

Synthesis of ATP

Adenosine-O--P--P Adenosine-O--P--P--P

PEnergy

High energy electrons

Oxidative phosphorylation: Direct addition of inorganic phosphate to ADP during the simultaneous oxidation of reduced

cofactors by the electron transport chain

ATP

ADP

AMP

PO43-

PO43-

Energy

Energy

H2O

H2O

Energy is used to Fuel Anabolic Processes: Biosynthesis Active transport Muscle contraction Transcription, translation

Use of ATP

Forms of Hydrogen in Oxidation/Reduction Reactions

H H

H H

H H+-

hydrogen molecule

hydrogen atoms

hydrogen ionhydride ion

The carriers of energy in oxidation-reduction reactions are actually the electrons, but the

hydrogens tell us where the electrons are.

Reduction and Oxidation of Coenzymes

Certain cofactors link metabolic oxidations to metabolic reductions. These oxidations and reductions are better described as dehydrogenations and hydrogenations, the removal and addition of hydrogen ions and electrons.

Coenzyme(oxidized)

Coenzyme-H2(oxidized)

BH2

BA

AH2

( reduced )

Metabolic intermediates

Metabolic intermediates

Coenzyme(oxidized)

Coenzyme-H2(oxidized)

BH2

BA

AH2

Coenzyme As an oxidizing agent As a reducing agent

Nicotinamide adenine dinucleotide NAD+ NADH/H+

Nicotinamide adenine dinucleotide phosphate NADP+ NADPH/H+

Flavin adenine dinucleotide FAD FADH2

Flavin adenine mononucleotide FMN FMNH2

Reduction and Oxidation of Coenzymes

( reduced )

Metabolic intermediates

Metabolic intermediates

Reduction and Oxidation of Nicotinamide Cofactors

+ H +

NAD+ serves as an oxidant by accepting a hydride ion (H:-) from a reductant to form NADH.

NAD+

NADH/H+

H:- , H+

H+

H

This reduced form is later reoxidized by passing its electrons to molecular oxygen through the electron transport chain in the mitochondria.

+ H+

Reduction and Oxidation of Nicotinamide Cofactors

NAD+ serves as an oxidant by accepting a hydride ion (H:-) and a H+ from a reductant to form NADH.

This reduced form is later reoxidized by passing its electrons to m o l e c u l a r o x y g e n through the electron transport chain in the mitochondria.

Reduction and Oxidation of Flavin Cofactors

FADH2

--

OHCH2

FAD

H H,

FAD serves as an oxidant by accepting two hydrogen atoms from a reductant to form FADH2.

This reduced form is later reoxidized by passing its electrons to molecular oxygen through the electron transport chain in the

mitochondria

H H,

Reduction and Oxidation of Flavin Cofactors

FAD serves as an oxidant by accepting two hydrogen atoms from a reductant to form FADH2.

This reduced form is later reoxidized by passing its

electrons to molecular oxygen through the electron

transport chain in the mitochondria

C CH CH C

H H O

O

O

O

C CH CH C

O

O

O

O

FAD FADH2

Succinate

Fumaratesuccinate

dehydrogenase

The Electron Transport System

pyruvate

Acetyl CoA

glycerolderivatives

fats carbohydrates proteins

DIETARY CARBON

fatty acids monosaccharides amino acids

TCA CYCLE

CO2

CO2

NADH/H+

FADH2

ATP

ATP