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

“Induced fit”Active site

Enzyme - structure

Simple enzymes – consist of protein aloneConjugated 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 activity1. _________________ inhibition –

substance that resembles normal substrate competes with substrate for active site

2. _________________ 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, pressureEnzymes have optimal T and pH for

activityCan 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

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Figure 8.7 Constitutive and regulated enzymes

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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

Transfer reactions by enzymes

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

2. Phosphotransferases – transfer phosphate groups, involved in energy transfer

3. Methyltransferases – move methyl groups from one molecule to another

4. Decarboxylases – remove carbon dioxide from organic acids

5. 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 transfersO 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

NOTE: electron transfers involve a hydrogen atom (proton + electron) = ____________________ and involves an electron carrier

Redox reactions

REMEMBER: Cellular respiration is one big _________________ !

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Metabolic Pathways

Electron carriers resemble __________ that are loaded and

unloaded with electrons and hydrogen most carriers are __________, NAD, FAD, NADP,

coenzyme A & compounds of the respiratory chain

donor acceptorshuttle

Redox reactions

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

The path that electrons take on their way down from glucose to oxygen involves many stops

NADH

Figure 6.6

1/2

(from food via NADH)

2 H 2 e

Energy forsynthesis

of

Electro

n tran

spo

rt chain

2 e

2 H

1/2

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

How is ATP regenerated?ATP used for Energy must be regenerated (ADP + Pi)

1. substrate-level phosphorylation

2. oxidative phosphorylation

3. 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).