metabolism - nwaccfaculty.nwacc.edu/gbates/mbio2014/lectures/microch8.pdf · 2 types of metabolism...
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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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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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