Metabolism - NWACCfaculty.nwacc.edu/gbates/mbio2014/lectures/Microch8.pdf · 2 types of metabolism • Anabolism - biosynthesis – building complex molecules from simple ones –

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Microbial Metabolism: The Chemical Crossroads of Life

Chapter 8

Metabolism

The sum total of all chemical reactions & physical workings

occurring in a cell

2 types of metabolism

• Anabolism - biosynthesis– building complex molecules from simple ones– requires energy (ATP)

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• Catabolism - degradation– breaking down complex molecules into simple

ones– generates energy (ATP)

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Enzyme structure

• Simple enzymes – consist of protein alone• Conjugated enzymes or holoenzymes –

contain protein and nonprotein molecules

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contain protein and nonprotein molecules– apoenzyme –protein portion– cofactors – nonprotein portion

• metallic cofactors – iron, copper, magnesium • coenzymes -organic molecules - vitamins

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Enzyme-substrate interactions

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• Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase,

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; ,amylase, penicillinase

• Endoenzymes – retained intracellularly & function there

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• Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of

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q , gsubstrate; enzymes involved in glucose metabolism

• Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources

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• Synthesis or condensation reactions –anabolic reactions to form covalent bonds between smaller substrate molecules,

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,require ATP, release one molecule of water for each bond

• Hydrolysis reactions– catabolic reactions that break down substrates into small molecules, requires the input of water

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Transfer reactions by enzymes

1. Oxidation-reduction reactions – transfer of electrons

2. Aminotransferases – convert one type of amino acid to another by transferring an amino group

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acid to another by transferring an amino group3. Phosphotransferases – transfer phosphate groups,

involved in energy transfer4. Methyltransferases – move methyl groups from

one molecule to another5. Decarboxylases – remove carbon dioxide from

organic acids

Metabolic pathways

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Control of enzyme activity

1. Competitive inhibition – substance that resembles normal substrate competes with substrate for active site

2 Feedback inhibition concentration of product at

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2. Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme

3. Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes

4. Enzyme induction – enzymes are made only when suitable substrates are present

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Competitive inhibition

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Energy –capacity to do work or cause change

• Endergonic reactions – consume energy• Exergonic reactions – release energy

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e go c e c o s e e se e e gy

Redox reactions

• always occur in pairs• There is an electron donor and electron

acceptor which constitute a redox pair

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acceptor which constitute a redox pair• The process salvages electrons & their

energy.• released energy can be captured to

phosphorylate ADP or another compound

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Electron carriers

• resemble shuttles that are loaded and unloaded with electrons and hydrogen

• most carriers are coenzymes NAD FAD

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most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain

NAD reduction

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Electron carriers

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ATP

• 3 part molecule consisting of– adenine – a nitrogenous base– ribose – a 5-carbon sugar

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ribose a 5 carbon sugar– 3 phosphate groups

• Removal of the terminal phosphate releases energy

ATP

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Phosphorylation of glucose by ATP

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Formation of ATP

1. substrate-level phosphorylation2. oxidative phosphorylation3 photophosphorylation

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3. photophosphorylation

substrate-level phosphorylation

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Catabolism of glucose

1. Glycolysis2. Tricarboxylic acid cycle, Kreb’s cycle3 Respiratory chain electron transport

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3. Respiratory chain, electron transport

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Metabolic strategies

Pathwaysinvolved

Final e-acceptor ATP yield

Aerobic Glycolysis, O2 38

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respiration y y ,

TCA, ET2

Anaerobic respiration

Glycolysis, TCA, ET

NO3-, So4

-2, CO3

-3variable

Fermentation Glycolysis Organic molecules

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Overview of aerobic respiration

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Overview of aerobic respiration

• Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C)

• TCA – processes pyruvic acid and generates

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p py g3 CO2 molecules

• Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation

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Glycolysis

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TCA cycle

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Electron transport system

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Chemiosmosis

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Fermentation

• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen

• Uses organic compounds as terminal electron acceptors

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acceptors• Yields a small amount of ATP• Production of ethyl alcohol by yeasts acting on

glucose• Formation of acid, gas & other products by the

action of various bacteria on pyruvic acid

Fermentation

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Products of fermentation

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• Many pathways of metabolism are bi-directional or amphibolic

• Metabolites can serve as building blocks or sources of energy

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sources of energy– Pyruvic acid can be converted into amino acids through

amination– Amino acids can be converted into energy sources

through deamination– Glyceraldehyde-3-phosphate can be converted into

precursors for amino acids, carbohydrates and fats

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