Ch 07

Microbial

Metabolism

SLOs • Differentiate between metabolism, catabolism, and anabolism.

• Fully describe the structure and function of enzymes.

• Differentiate between constitutive and regulated enzymes.

• Describe how enzymes are controlled.

• Name the chemical in which energy is stored in cells.

• Create a general diagram of a redox reaction.

• Identify electron carriers used by cells.

• List three basic catabolic pathways and the estimated ATP yield for each.

• Construct a paragraph summarizing glycolysis.

• Describe the Krebs cycle, and compare the process between bacteria and eukaryotes.

• Discuss the location and the significance of the ETC.

• Compare and contrast aerobic and anaerobic respiration.

• Summarize the steps of microbial fermentation, and list three useful products it can create.

• Describe how other COHs and how proteins are catabolized.

Metabolism and the Role of Enzymes

• Metabolism: Def?

• Catabolism: Provides __________ and

_________________ for anabolism.

• Anabolism: Uses __________ and

_________________ to build large molecules

Big Picture

Compare to Fig 7.1

Enzymes: Biological _________

Increase reaction rate by ______________

Do not become part of the products

Are unchanged in the process

Simple enzymes consist of protein alone

Conjugated enzymes = Holoenzymes

contain protein and nonprotein molecules

Fig 7.2

Enzyme Substrate Interaction

Active site highly specific

Model:

Common cofactors: Fe, Mg, Mn Zn ……

Many coenzymes are Vitamin derivatives

Oxidoreductases and dehydrogenases, transferases, Hydrolases, Ligases …

Fig 7.3

Regulation of Enzyme Action

• Constitutive enzymes, e.g.: ?

• Regulated enzymes Induction and

repression

• Enzyme function is dependent on

temperature, pH, osmotic pressure

?

Fig 7.4

Metabolic Pathways

Fig 7.5

Terminology: Intermediate products, common

intermediates, branching points

Metabolic Pathways of Energy Production:

COH Catabolism

• Cellular respiration – Aerobic respiration – Anaerobic respiration

• Fermentation

The three steps of aerobic respiration 1. Glycolysis (oxidation of _____ to ______) 2. Krebs cycle (oxidation of acetyl CoA to ___) 3. Oxidative phosphorylation (e- transport chain)

Control of Enzyme Action: Inhibitors

Competitive

inhibitors

Noncompetitive – allosteric inhibitors

Compare to Fig 7.6

vs.

Sulfa drugs

Example:

Feedback

Inhibition

Also known as end-

product inhibition

Controls amount of

substance produced

by a cell

Mechanism is

allosteric inhibition

Enzyme repression

– Protein expression

– Response time longer

than for feedback

inhibition

Control of Enzyme Synthesis

Enzyme induction

– Protein expression

when suitable

substrates present

Fig 7.7 – E.g.: lactase induction in E. coli

Utilization of Energy • Energy is needed to do work.

• Energy comes directly from the sun, or is

contained in chemical bonds.

Exergonic vs. Endergonic reactions

Exergonic and endergonic rxs. often coupled

released energy immediately put to work.

Energy Production:

Oxidation-Reduction Reactions

• Oxidation = loss of e-

• Reduction = gain of e-

Redox reaction: Oxidation reaction paired with reduction reaction.

When a compound

loses electrons, it is

oxidized.

When a compound

gains electrons, it is

reduced.

Rredox reactions are

common in cell and

indispensable to the

required energy

transformations.

Fig. 7.8

Oxidation-Reduction cont.

In biological systems, the electrons are

often associated with hydrogen atoms.

Biological oxidations are often

dehydrogenations.

Electron Carriers

• NAD and FAD are molecular shuttles for e-.

• They are coenzymes for Oxidoreductases

(= enzymes that remove electrons from one

substrate and add them to another)

Fig. 7.9

ATP hydrolysis

powers biosynthesis.

Input of energy is

required to replenish

ATP.

In heterotrophs,

catabolic pathways

provide the energy

that generates ATP

from ADP.

ATP

Fig. 7.10

Catabolism

• Enzymes catabolize organic molecules to

precursor molecules and/or energy that cells

then use for anabolism.

• Energy is stored in

– electrons available in NADH and FADH2

– bonds of ATP

• Both are are produced during __________

and needed in large quantities for

__________ metabolism.

3 Catabolic Pathways

Glycolysis

Multi – step breakdown of glucose into pyruvate

Part of which catabolic pathways (s)?

Generates • small amount of ATP (how many?)

• small amount of reducing power – (?)

The Steps of

Glycolysis

Compare to Fig 7.2

Pyruvate to Acetyl CoA

Acetyl group of acetyl-CoA enters TCA

cycle

Krebs cycle generates ATP and reducing

power Precursor metabolites

Other names for Krebs cycle?

Transition step generates Acetyl-CoA from Pyruvate (decarboxylation)

The Krebs Cycle:

A Carbon and Energy Wheel

Takes place where?

Compare to

Fig 5.13

Krebs

Cycle

Electron Transport Chain • Formed by series of electron carriers located in

....

• Oxidation/Reduction reactions. Reduced electron

carriers from glycolysis and TCA cycle transfer

their electrons to the electron transport chain

• Allows transport of protons (H+) outside of the

membrane Generates proton gradient or

proton motive force (pmf)

• In final step, O2 accepts electrons and hydrogen,

forming water.

Principal Compounds in the e- Transport Chain

NADH dehydrogenase, Flavoproteins, Coenzyme Q,

Cytochromes

The Generation of ATP

Phosphorylation:

Oxidative phosphorylation: ATP synthesis

coupled to electron transport.

– NADH entering electron transport chain gives

rise to 3 ATP

– FADH2 enter electron transport chain at later

point less energy released and only 2 ATP

produced

Substrate level phosphorylation:

ATP synthesis via direct transfer of

a high-energy PO4

– to ADP.

The Terminal Step

• Catalyzed by cytochrome aa3, also known as cytochrome oxidase.

2H+ + 2e- + ½ O2 H20

• Potential side reaction of respiratory chain: Incomplete reduction of O2 to superoxide ion (O2

-) and hydrogen peroxide (H2O2)

• Aerobes produce enzymes to deal with these toxic oxygen products:

– Superoxide dismutase

– Catalase

– Streptococcus lacks these enzymes but still grow well in O2 due to the production of peroxidase.

Inorganic O2-containing molecules, other than free oxygen is final e- acceptor,

e.g.: NO3-

Terminal step utilizes Nitrate reductase

NO3- + NADH NO2

- + H2O + NAD+

Examples for other final e- acceptors: SO42-, CO3

3-

Strict anaerobes and facultative anaerobes

Involves glycolysis, Krebs cycle, and ETC

ATP yield lower than in aerobic resp. because only part of TCA operates under anaerobic conditions.

Anaerobic Respiration

Anaerobic Respiration cont.: Denitrification

• Further reduction of nitrite to nitric oxide

(NO), nitrous oxide (N2O), or N2

• Some species of Pseudomonas and

Bacillus

• INSERT Denitrifying rx from

Nitrogen reduction lab

Fermentation

- Incomplete oxidation of glucose. Does not

involve Krebs cycle or ETC

- Organic molecules are final electron acceptors.

- Some organisms can repress production of ETC

proteins when no O2

• Energy yield low

• Great diversity of end products: …

Alcohol and Lactic Acid Fermentation

Catabolism of other Compounds

• Polysaccharides and disaccharides

– Amylases for digestion of ___________

(very common)

– Cellulase for digestion of __________

(only bacteria and fungi have this enzyme)

– Disaccharidases: Sucrase, Lactase, etc.

• Proteins are broken down into amino acids by

proteases:

- Amino groups are removed through

deamination.

- Remaining carbon compounds are converted

into Krebs cycle intermediates.

In Lab: Biochemical Tests for Bacterial

Identification: Fermentation Tests

Different bacterial species produce different

enzymes Test detects presence of

enzyme

Example:

Lactose

Fermentation

Protein Amino acids Extracellular proteases

Krebs cycle

Deamination, decarboxylation,

dehydrogenation, desulfurylation Organic acid

Protein Catabolism

Decarboxylation

Overview of

COH

Catabolism

Summary of

Aerobic

Respiration in

Prokaryotes

Pathway Eukaryote Prokaryote

Glycolysis

Preparatory step

Krebs cycle

ETC

Location of Carbohydrate

Catabolism

Pathway By Substrate-Level Phosphorylation

By Oxidative Phosphorylation

From NADH From FADH

Glycolysis

Intermediate step

Krebs cycle

Total

ATP produced from complete

oxidation of one glucose using

aerobic respiration

Case File: Not so sweet

Inside the Clinic:

Vitamin D Deficiency

Anabolic Pathways not covered,

except for protein and DNA

biosynthesis, which will be covered

in Ch 8.