Bioenergetics

Metabolism: Basic Concepts

Light energy

ECOSYSTEM

CO2 + H2O

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

Organicmolecules

+ O2

ATP

powers most cellular work

Heatenergy

Catabolic pathways•Break down complex molecules into simpler compounds•Release energy

Anabolic pathways•Build complicated molecules from simpler ones•Consume energy

MetabolismThe sum total of all the chemical reactions cell needs to carry out to survive, grow, and reproduce. This control is central to the chemistry of life.

Amino acids

Sugars Glycerol Fattyacids

GlycolysisGlucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

NH3

Citricacidcycle

Oxidativephosphorylation

FatsProteins Carbohydrates

Cells obtain energy by the oxidation of organic Molecules

Not all of a system's energy is available to do work. The amount of energy that is available to do work is described by the concept of free energy.Significance of Free Energy:•Indicates the maximum amount of a system's energy which is available to do work.•Indicates whether a reaction will occur spontaneously or not.Free Energy and MetabolismReactions can be classified based upon their free energy changes:•Exergonic reaction= A reaction that proceeds with a net release of free energy and is spontaneous.•Endergonic reaction= An energy-requiring reaction that proceeds with a net gain of free energy; a reaction that absorbs free energy from its surroundings and non spontaneous.

Organisms live at the expense of free energy

Reactants

Products

Energy

Progress of the reaction

Amount ofenergyreleased (∆G <0)

Fre

e e

ne

rgy

(a) Exergonic reaction: energy released

Energy

Products

Amount ofenergyreleased (∆G>0)

Reactants

Progress of the reaction

Fre

e e

ne

rgy

(b) Endergonic reaction: energy required

•If a chemical process is exergonic, the reverse process must be endergonic.•In cellular metabolism, endergonic reactions are driven by coupling them to reactions with exergonic reactions.•ATP plays a critical role in this energy coupling.

ATP is the immediate source of energy that drives most cellular work, which includes:

•Mechanical work

•Transport work

•Chemical work

(c) Chemical work: ATP phosphorylates key reactants

P

Membraneprotein

Motor protein

P i

Protein moved

(a) Mechanical work: ATP phosphorylates motor proteins

ATP

(b) Transport work: ATP phosphorylates transport proteins

Solute

P P i

transportedSolute

GluGlu

NH3

NH2

P i

P i

+ +

Reactants: Glutamic acid and ammonia

Product (glutamine)made

ADP

+

P

ATP powers cellular work by coupling exergonic to endergonic reactions

•Renewable resource by adding phosphate to ADP•The free energy required for the phosphorylation of ADP comes from the exergonic reactions(catabolism) in the cells.•Shuttling of inorganic phosphate and energy is called the ATP cycle

ATP AS A METABOLIC ENERGY STORAG

NADPH is an important carrier of electrons.

•The hydrogen gradient across the membrane created by ATP synthaseis used to drive cellular work of ATP synthesis

•It couples the electron transport chain to the ATP synthesis

Chemiosmosis: The energy coupling mechanism.

Kyoto Encyclopedia of Gene and Genomes

Major pathways of glucose utilization

Glycolysis

The Citric acid cycle coupled withOxidative phosphorylation

Electronscarried

via NADH

Glycolsis

Glucose Pyruvate

ATP

Substrate-levelphosphorylation

Electrons carried via NADH and

FADH2

Citric acid cycle

Oxidativephosphorylation:

electron transport andchemiosmosis

ATPATP

Substrate-levelphosphorylation

Oxidativephosphorylation

MitochondrionCytosol

An overview of cellular respiration

The glyoxylate cycle

Glyoxylate cycle

Cori cycle

General scheme of the pentose phosphate pathway

Glycolate pathway

Photorespiration adjacent to the calvin cycle

C2 pathway

Stoichiometry of Co2 assimilation in the Calvin cycle

C3 pathway

Carbon assimilation in C4 plants

•Co₂ is fixed at the cost of 3 ATPs where as C2 takes 5 ATPs

•Useful for the plants growing under reduced Co ₂ conditions

CAM pathway

Fatty acid biosynthesis

Oxidation of fatty acidsin mitochondria and peroxisomes

Overview of amino acid catabolism

Links between the urea cycle and citric acid cycle

Aspartate-Arginino shunt

Summary of amino acidcatabolism.

Biosynthesis of Amino Acids

Nucleic acid metabolism

http://seqcore.brcf.med.umich.edu/mcb500/na/purdegr.html

Inosine Monophosphate Oratidine-5’monophosphate

•They are controlled, often by modulation of key regulatory enzymes.

•They are compartmentalized within cells. some processes are associated with regions on the inner face of the cell membrane.

•They usually involve coenzymes, molecules that are second substrates in a number of different reactions.

•The pathways that break particular molecules down are different from those used to synthesize them. This allows them to be controlled separately

Regulation of Metabolic pathways

References

•Lehninger-Principles of biochemisty (forth edition)Authors-D.Nelson, M. Cox•Biochemistry (fifth edition)Authors-J.berg, J.Tymoczko, L.Styer•Biology(seventh edition)Authors-N.Campbell J.Reece•Harper’s Illustrated Biochemistry(26th edition)Authors-R.Murray, D.Granner, V.Rodwell•Biochemistry(second edition)Authors-Garrett and Grisham•Molecular biology of the cellAuthor-Bruce Albert•Molecular cell biology(fifth edition)Authors-Lodish, Berk