An Introduction to Microbial Metabolism Chapter 8

energy The capacity to do work or cause change Kinetic energy is actively performing work, Potential energy is stored (ability to perform work based on location/arrangement) 1st law of thermodynamics – energy conservation Endergonic reactions – consume energy Exergonic reactions – release energy

Endergonic: X + Y + energy  Z Exergonic: X + Y  Z + energy

Energy conversions Cell takes PE of chemicals (in electrons/bonds) and eventually converts them to cellular work (KE) Endergonic/exergonic reactions are usually coupled so that the energy can either be used immediately or stored (ATP) for later use

Metabolism The sum total of all chemical reactions & physical workings occurring in a cell

2 types of metabolism _________________ - biosynthesis building complex molecules from simple ones requires energy (ATP) - endergonic _________________ - degradation breaking down complex molecules into simple ones generates energy (stored as ATP) - exergonic Example - glycolysis

Enzymes Needed to keep pace (speed up reactions) Reaction involves either breaking a molecule apart or brining one together Catalyze reactions without becoming products or being consumed in the reaction Act upon ______________ to form _________________ Lower _________________ so reaction rate increases

Enzyme-substrate interactions – lock and key fit Active site “Induced fit”

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

How enzymes work: example - sucrase

Role of coenzyme: Transfer functional group from one substrate to another

Control of enzyme activity _________________ inhibition – substance that resembles normal substrate competes with substrate for active site _________________ inhibition – enzymes are regulated by the binding of molecules other than the substrate on the active site Enzyme _____________– inhibits at the genetic level by controlling synthesis of key enzymes Enzyme _____________– enzymes are made only when suitable substrates are present

Enzyme repression

Enzyme induction

Things that affect enzymes Temperature, pH, pressure Enzymes have optimal T and pH for activity Can be denatured by extreme temperatures or pH (changes protein structure)

Roles of enzymes: Pathogenesis Produced by pathogenic microbes--make microbe a better pathogen (evade host response, destroy host tissues) Examples: Hemolytic enzymes (hemolysins) Elastase, collagenase (destroy connective tissue) Lecithinase C (destroys cells) Penicillinase (inactivates penicillin – antibiotic resistance) Note: names end in -________

Types of enzymes (location, quantity) _______enzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase ________enzymes – retained intracellularly & function there _________________– always present regardless of substrate concentration (glycolysis enzymes) _________________– produced in presence of substrate, prevents cell from wasting resources

Figure 8.6 Types of enzymes 27 27

Figure 8.7 Constitutive and regulated enzymes 28 28

Types of reactions catalyzed by enzymes Synthesis or _________________ reactions – _________________ reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond _________________ reactions– _________________ reactions that break down substrates into small molecules, requires the input of water

Figure 8.8 Enzyme-catalyzed synthesis and hydrolysis reactions 30

Transfer reactions by enzymes Aminotransferases – convert one type of amino acid to another by transferring an amino group Phosphotransferases – transfer phosphate groups, involved in energy transfer Methyltransferases – move methyl groups from one molecule to another Decarboxylases – remove carbon dioxide from organic acids Oxidation-reduction (redox)reactions – transfer of electrons (may involve _________________ )

REDOX reactions The process by which electrons are transferred between atoms is called an oxidation/reduction reaction (redox) – we can track movement of e- by following H transfers _________________ = loses e- (donor becomes oxidized; reducing agent) _________________ = gains e- (acceptor becomes reduced; oxidizing agent) Occurs as a paired reaction “LEO says GER” or “OIL RIG”

Cellular respiration is one big redox reaction! Redox reactions involve electron transfers O I L R I G (Oxidation is Losing; Reduction is Gaining)

Redox reactions Involve electron transfers (energy transfers) always occur in pairs electron donor + electron acceptor = redox pair process salvages electrons & their energy. released energy can be captured to _________________ ADP or another compound

Electron donor + Electron acceptor Redox reactions Electron donor + Electron acceptor NOTE: electron transfers involve a hydrogen atom (proton + electron) = ____________________ and involves an electron carrier

REMEMBER: Cellular respiration is one big _________________ !

Metabolic Pathways 37 37

Electron carriers Redox reactions resemble __________ that are loaded and unloaded with electrons and hydrogen most carriers are __________, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain donor shuttle acceptor

NAD reduction (carries 2 e- ) Redox reactions

Electron carriers – coupled reaction

Overview of cell respiration – electrons are removed from glucose and eventually used to make ATP _____________________________

NADH 1/2 The path that electrons take on their way down from glucose to oxygen involves many stops (from food via NADH) Energy for synthesis of 2 H 2 e Electron transport chain 2 e 1/2 2 H Figure 6.6

ATP – the energy shuttle 3 part molecule consisting of adenine – a nitrogenous base ribose – a 5-carbon sugar 3 phosphate groups _________________ _________________ _________________

_____________ of glucose by ATP How does ATP “give” energy? ATP transfers energy to compounds that are going to be catabolized (or going to do work) by donating the high energy phosphate _____________ of glucose by ATP

How is ATP regenerated? ATP used for Energy must be regenerated (ADP + Pi) substrate-level phosphorylation oxidative phosphorylation photophosphorylation

1. substrate-level phosphorylation

Other ways of making ATP 2. Oxidative phosphorylation: Used by aerobes. series of redox reactions (electron transport system). Involves chemiosmosis. 3. Photophosphorylation – used in photosynthetic organsims. Driven by sunlight (series of reactions).