introduction to metabolism. metabolism the sum of the chemical changes that convert nutrients into...

Introduction to Metabolism

Metabolism

The sum of the chemical changes that convert nutrients into energy and the chemically complex products of cells

Hundreds of enzyme reactions organized into discrete pathways

Substrates are transformed to products via many specific intermediates

Metabolic maps portray the reactions

A Common Set of Pathways

Organisms show a marked similarity in their major metabolic pathways

Evidence that all life descended from a common ancestral form

There is also significant diversityAutotrophs use CO2; Heterotrophs use

organic carbon; Phototrophs use light; Chemotrophs use Glc, inorganics use S and obtain chem energy through food generated by phototrophs.

The Sun is Energy for Life

Phototrophs use light to drive synthesis of organic molecules

Heterotrophs use these as building blocks

CO2, O2, and H2O are recycled

Metabolism

Metabolism consists of catabolism and anabolism

Catabolism: degradative pathways Usually energy-yielding! “destructive metabolism” FUELS -> -> CO2 + H2O + useful energy

Anabolism: biosynthetic pathways energy-requiring! “constructive metabolism” Useful energy + small molecules --> complex

molecules

Organization in Pathways

Pathways consist of sequential steps

The enzymes may be: Separate Form a multienzyme complexA membrane-bound system

New research indicates that multienzyme complexes are more common than once thought

Catabolism and Anabolism

Catabolic pathways converge to a few end products

Anabolic pathways diverge to synthesize many biomolecules

Some pathways serve both in catabolism and anabolism and are called amphibolic pathways

Comparing Pathways

Anabolic & catabolic pathways involving the same product are not the same

Some steps may be common to both

Others must be different - to ensure that each pathway is spontaneous

This also allows regulation mechanisms to turn one pathway and the other off

METABOLIC REGULATION

Regulated by controlling:

1. Amounts of enzymes

2. Catalytic activities

3. Accessibility of substrates

Digestion of food polymers: enzyme-catalyzed hydrolysis

Glycolysis: glucose catabolism generate ATP without consuming oxygen (anaerobic)

Citric Acid Cycle: metabolism of acetyl-CoA derived from pyruvate, fatty

acids, and amino acids acetyl oxidized to CO2

operates under aerobic conditions reduction of coenzymes NAD+ and FAD; energy used to

produce ATP

Oxidative phosphorylation: reduction of molecular oxygen by NADH and FADH2

energy of reduced compounds used to pump protons across a cell membrane

potential energy of electrochemical gradient drives phosphorylation of ADP to ATP

The ATP Cycle

ATP is the energy currency of cells In phototrophs, light energy is

transformed into the chemical energy of ATP

In heterotrophs, catabolism produces ATP, which drives activities of cells

ATP cycle carries energy from photosynthesis or catabolism to the energy-requiring processes of cells

Redox in Metabolism

NAD+ collects electrons released in catabolism

Catabolism is oxidative - substrates lose electrons, usually H- ions

Anabolism is reductive - NADPH provides the electrons for anabolic processes, and the substrates gain electrons

WHY ATP?

Free energy is released when ATP is hydrolyzed.

This energy drives reactions that need it (eg. muscle contraction)

Recall coupled reactionsATP has a higher phosphoryl

transfer potential

RECURRING MOTIFS IN METAB

Certain compounds keep on recurring or appearing in metabolic reactions and their functions are the same in the processes

Metab looks complicated but reactions are actually limited and repeating.

ACTIVATED CARRIERS

These species help carry out the metabolic reactions, even nonfavorable ones, at times

Example: ATP (activated carrier of phosphoryl groups)

Activated carriers of electrons for fuel oxidation: e- acceptors!

Aerobic systems: O2 is the

final e- acceptor, but this does not occur directly

Fuels first transfer e- to carriers: pyridine molecules or flavins.

NAD+: nicotinamide adenine dinucleotide

Activated carriers of electrons for fuel oxidation: e- acceptors!

FAD: Flavin adenine dinucleotide

Activated carrier of electrons for reductive biosynthesis: e- donors!

NADPH: common electron donor

R is phosphate group

Activated carrier of carbon fragments

COENZYME A: carrier of acyl groups

Activated carrier of two-carbon fragments

VITAMINS

Many vitamins are "coenzymes" - molecules that bring unusual chemistry to the enzyme active site

Vitamins and coenzymes are classified as "water-soluble" and "fat-soluble"

The water-soluble coenzymes exhibit the most interesting chemistry

Key Reactions in Metabolism

1. REDOX reactions

Electron carriers are needed!

2. LIGATION reactions

Bond formation facilitated by ATP cleavage

3. ISOMERIZATION reactions

4.GROUP TRANSFER

5.HYDROLYTIC reactions

Bond cleavage by addition of H2O

6.ADDITION of functional groups to double bonds or REMOVAL of groups to form double bondsUses lyases