Ch7: Microbial Metabolism

SPR26 OSU MICROBIO

Why does life need energy?

To build complex cells and molecules from simpler ones.

Define metabolism.

The total of all chemical reactions in the cell that provide energy and build cellular components.

Define catabolism vs. anabolism.

• Catabolism = breaks molecules down, releases energy, supplies electrons & precursors.
  Anabolism = builds complex molecules, consumes energy, requires electrons.

What is a metabolite?

Any product or substrate of metabolism.

What are the major metabolic energy strategies?

• Phototrophy = light as energy source

• Chemotrophy = chemical energy

• Organotrophy = organic molecules

• Lithotrophy = inorganic molecules

Source of Energy: Light, Organic, and Inorganic, and how energy is transferred in each

• Light: Energy is transferred from photons to electrons

• Organic sources: Energy is transferred from high energy organic sources (electron E)

• Inorganic sources: Energy (electrons) is transferred from inorganic molecules

Why is ATP called the cell’s energy currency?

It stores and transfers energy from catabolism to cellular work (anabolism, transport, etc.).

What is ATP made from?

Adenosine (adenine + ribose) + three phosphates.

What happens when ATP is hydrolyzed?

ATP → ADP + Pi + energy (used for cellular work).

Name the three mechanisms of ATP synthesis.

• Substrate-level phosphorylation

• Oxidative phosphorylation

• Photophosphorylation

Define substrate-level phosphorylation.

Direct transfer of a phosphate from a metabolic intermediate to ADP to form ATP.

Where does substrate-level phosphorylation occur?

Glycolysis and the Krebs (TCA) cycle.

Define oxidative phosphorylation.

ATP made using energy from oxidation of nutrients → proton motive force → ATP synthase (respiration).

Define photophosphorylation.

ATP made using light energy to generate a proton motive force (photosynthesis).

Define oxidation and reduction.

• Oxidation = loss of electrons, add O, remove H

• Reduction = gain of electrons, remove O, add H

What always happens together in redox reactions?

One molecule is oxidized while another is reduced.

Why are electron carriers important?

They transfer electron energy in controlled steps instead of all at once.

Name major electron carriers and their reduced forms.

• NAD⁺ → NADH

• FAD → FADH₂

• NADP⁺ → NADPH

What is the role of electron carriers in metabolism?

They move electron energy from catabolic reactions to pathways like the ETC.

Why do cells use multi-step metabolic pathways?

To control energy release and allow regulation and branching of reactions.

What is the role of enzymes?

They are catalysts that speed up reactions by lowering activation energy.

Do enzymes change ΔG of a reaction?

No — they only affect reaction rate, not free energy change.

What does lowering activation energy mean?

Making it easier for reactants to reach the transition state.

What factors affect enzyme activity?

Temperature, pH, salt concentration, cofactors, and coenzymes.

What is feedback inhibition?

When the end product of a pathway inhibits an earlier enzyme in that pathway.

What happens when enzymes denature?

They lose their shape and can no longer function.

Carbon sources (like glucose) are chemically _____. Glucose → CO2: Reactions are ______.

• broken down

• oxidative

Energy is released and transferred to _____ and_________ (reduction).

• ATP

• electron carriers

_________are used as carbon building blocks for biosynthesis pathways

Intermediates

Central catabolism can be completed via _____or _______.

• Respiration

• Fermentation

Glycolysis: Oxidation of Glucose to Pyruvate — Can occur regardless of whether _______ is present!

oxygen (O2)

Glycolysis: Investment Phase INPUT

INPUT:

• 1 Glucose

• 2 ATP

Glycolysis: Pay-Off Phase OUTPUT

OUTPUT (possible):

• 4 ATP (Net 2 ATP) – Substrate-Level Phosphorylation (SLP)

• 2 NADH (reduction, electron energy)

• 2 Pyruvate (oxidation)

• Substrates for Biosynthesis (Intermediates)

Glycolysis: Oxidation of Glucose to Pyruvate pathway

6-Carbon Glucose → Two 3-Carbon Pyruvate molecules (No carbon loss)

Glycolysis: Substrates for Biosynthesis

• Carbohydrates

• Nucleotides

• Lipids (glycerol)

• Amino Acids

Other Enzymatic Pathways exist to Catabolize _____

Sugar

Other Enzymatic Pathways can be sources of ________ for Biosynthesis

NADPH and other Metabolites

In other Enzymatic Pathways, some steps/enzymes overlap with _______

Glycolysis (G3P is common intermediate)

NADPH and other Metabolites can occur in the presence or absence of ______

Oxygen (O2)

Pentose Phosphate (PP) Pathway YIELD

• ~2 NADPH

• 1 ATP

can vary; intermediates needed for biosynthesis of nucleic acids & amino acids

Entner-Doudoroff (ED) Pathway YIELD

• 1 NADPH

• 1 NADH

• 1 ATP

• 2 pyruvate

Microorganisms might have one or several enzymatic pathways, therefore, they can be used to _________

ID microbes

Preparatory (aka Intermediate) Step: Oxidation of Pyruvate to Acetyl-CoA INPUT

Per 1 molecule of Glucose…

• 2 Pyruvate

Preparatory (aka Intermediate) Step: Oxidation of Pyruvate to Acetyl-CoA OUTPUT

• 2 NADH (reduction, electron energy)

• 2 CO2

• 2 Acetyl-CoA

• Substrates for Biosynthesis (Intermediates)

Oxidation of Pyruvate to Acetyl-CoA Overall Pathway

3-Carbon Pyruvate → 2-Carbon Acetyl-CoA

(Carbon loss to CO2)

TCA (aka Krebs) Cycle: Oxidation of Acetyl-CoA → CO2 INPUT

Per 1 glucose molecule…(2 turns of the cycle)

• 2 Acetyl-CoA

TCA (aka Krebs) Cycle: Oxidation of Acetyl-CoA → CO2 OUTPUT

Per 1 glucose molecule…(2 turns of the cycle)

• 4 CO2

• 6 NADH (e- energy reduction)

• 2 FADH2 (e- energy reduction)

• 2 ATP → Substrate-Level Phosphorylation (SLP)

• Substrates for Biosynthesis(intermediates)

TCA (aka Krebs) Cycle: Oxidation of Acetyl-CoA → CO2: OVERALL PATHWAY

2-Carbon Acetyl-CoA→ No organic carbon product

(Carbon loss to CO2 and Glucose is fully Oxidized at this point)