Microbial Metabolism: The Chemical Crossroads of Life Chapter 8.
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Transcript of Microbial Metabolism: The Chemical Crossroads of Life Chapter 8.
2 types of metabolism
• Anabolism - biosynthesis– building complex molecules from simple ones– requires energy (ATP)
• 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– apoenzyme –protein portion– cofactors – nonprotein portion• metallic cofactors – iron, copper, magnesium • coenzymes -organic molecules - vitamins
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• Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, 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 substrate; 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, 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
3. Phosphotransferases – transfer phosphate groups, involved in energy transfer
4. Methyltransferases – move methyl groups from one molecule to another
5. Decarboxylases – remove carbon dioxide from organic acids
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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 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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Energy –capacity to do work or cause change
• Endergonic reactions – consume energy• Exergonic reactions – release energy
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Redox reactions
• always occur in pairs• There is an electron donor and electron
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, NADP, coenzyme A & compounds of the respiratory chain
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ATP
• 3 part molecule consisting of– adenine – a nitrogenous base– ribose – a 5-carbon sugar– 3 phosphate groups
• Removal of the terminal phosphate releases energy
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Formation of ATP
1. substrate-level phosphorylation2. oxidative phosphorylation3. photophosphorylation
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Catabolism of glucose
1. Glycolysis2. Tricarboxylic acid cycle, Kreb’s cycle3. Respiratory chain, electron transport
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Metabolic strategies
Pathwaysinvolved
Final e- acceptor ATP yield
Aerobic respiration
Glycolysis, TCA, ET
O2 38
Anaerobic respiration
Glycolysis, TCA, ET
NO3-, So4
-2, CO3
-3
variable
Fermentation Glycolysis Organic molecules
2
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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 3 CO2 molecules
• Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation
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Fermentation
• Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen
• Uses organic compounds as terminal electron 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
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• Many pathways of metabolism are bi-directional or amphibolic
• Metabolites can serve as building blocks or 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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