Week 6: Cell Structure and Function in Bacteria and Archaea

= removal of electrons from an atom or molecule

Oxidation

= addition of one or more electrons to a molecule

Reduction

= substance that is oxidized

Electron donor

= substance that is reduced

Electron acceptor

Cells generate ____ to store energy and fuel processes

adenosine triphosphate (ATP)

The change in free energy during a reaction is referred
to as

G0

Reactions with -G0 release free energy.

Exergonic

Reactions with +G0 require energy

endergonic

exergonic cellular processes that generate free energy

Catabolic pathways

endergonic cellular processes in which cellular synthesis requires energy

Anabolic pathways

ability to donate electrons during electron transfer reactions (redox reactions)

Reducing power

Photorophs obtain energy from___? Do not require _____as an energy source? and
Oxygenic2(O produced) and anoxygenic (no2O produced) photosynthesisthesis

light
chemicals

Chemotrophs obtain energy from___?

• Aerobic reactions require o2 as electron acceptor

• Anaerobic reactions use anything other than o2 as electron acceptor

• Respiration or fermentation

• Energy source can be organic (containing carbon with some
  exceptions) or inorganic

chemical reactions

obtain energy and reducing power from organics

Chemoorganotrophs

obtain energy and reducing power from inorganics

Chemolithotrophs

obtain carbon from organics

Heterotrophs

obtain carbon from CO2

• Also called primary producers: synthesize organic
  matter from inorganic carbon

Autotrophs

How are redox reactions and half-reactions written?

• When two half-reactions combine, the electron donor is actually oxidized, so its half-reaction is reversed.

What do reduction potentials tell us?

• They predict whether a substance will act as an electron donor or electron acceptor.

• Greater difference in reduction potentials = more energy released during the redox reaction.

What happens during a redox reaction?

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• The first half-reaction produces electrons that the second half-reaction consumes.

• Electron donor (oxidized reactant): donates electrons.

• Electron acceptor (reduced reactant): accepts electrons.

What does the reduction potential (E°′) indicate?

• Measures a substance's tendency to gain or donate electrons (units: volts, V).

• Negative E°′: reduced substance is a strong electron donor (e.g., glucose/CO₂ couple).

• Positive E°′: oxidized substance is a strong electron acceptor (e.g., O₂/H₂O couple).

ATP, Phosphenolpyruvate, Glucose-6-phosphate,
Acetyl-CoA, Acetyl phosphate are?

Energy-rich compounds

Most important energy-rich compound in the cell
– Formation of ATP allows the cell to store
potential energy

ATP generation:

Phosphorylation =

addition of P to a chemical compound

Fermentation (Glycolysis)
– ATP generated following a high-energy P transfer from a phosphorylated substrate to ADP

Substrate-level phosphorylation:

ATP produced from proton motive force (PMF) formed by transport of electrons
– Higher ATP yield than fermentations

Oxidative (or Photo) Phosphorylation:(or Photo) Phosphorylation:

– Occurs in the absence of terminal electron acceptors
– ATP generated following a high-energy P transfer from a phosphorylated substrate to ADP
– ATP directly synthesized

26
1. Substrate-level phosphorylation:a

26
1. Substrate-level phosphorylation:-fermentation

– Chemoorganotrophs
– Anaerobic process
– Glycolysis is most common pathway for catabolism of glucose (Embden-Meyerhof-Parnas pathway = three stages)

– Nearly universal pathway for glucose catabolism that oxidizes glucose to pyruvate
– Can participate in multiple forms of catabolism
(fermentation, aerobic respiration, anaerobic
respiration

Glycolysis (Embden–Meyerhof–Parnas pathway)

What is photophosphorylation?

• Occurs only in photosynthetic cells.

• Light energy → ATP + NADPH via an electron transport chain (ETC).

• Light energy creates a proton motive force (PMF), which drives ATP synthase to produce ATP.

• Like oxidative phosphorylation, it relies on electron transfer reactions to generate the PMF.

What is oxidative phosphorylation?

• Uses an electron transport chain (ETC) with inorganic electron acceptors to generate a proton motive force (PMF).

• Breakdown of organic molecules (e.g., carbohydrates) produces NADH/FADH₂, which donate electrons to fuel the ETC.

• The PMF powers ATP synthase to make ATP.

In oxidative phosphorylation the movement of electrons from an electron donor to an electron acceptor generates a____?

proton motive force (PMF).

The ____ is an electrochemical gradient formed by energy-conserving reactions that transport protons outside the cytoplasmiic membrane

PMF

PMF electrochemical gradient ultimately synthesizes what?

ATP

electrons transferred from reduced electron donors to external electron acceptors

respiration

____ and ____Produced in glycolysis and citric acid cycle must be re-oxidized for redox balance

NADH and FADH2

In respiration, reoxidation occurs when?

electron transport

active site binds NADH,
accept two electrons and two protons that are
transferred to flavoproteins, regenerating NAD+

NADH dehydrongenases

contain derivative riboflavin as prosthetic group that accepts two electrons and two protons but only donate electrons

Flavoproteins

— small hydrophonic nonprotein redox molecules

• can move within membrane

• accept two electrons and twp protons but transfer electrons only

• typically link iron0sulfer proteins and cytochromes

• ubiquinone (coenzyme Q) and menaquinone most common

Cytochromes, other Iron proteins, and quinones

ATP Synthase

Use uses nergy from pmf to form atp

• pmf generates a torwque; mechanical energy catalyzes ADP + Pi to ATP

what can reverse ATP synthase activity and transport protons out of cytoplasm generating instead of dissipating PMF

ATP hydrolysis

What are the two pathways for glucose utilization?

Fermentation: Glucose → pyruvate (stops after glycolysis).

• Respiration: Pyruvate enters the citric acid cycle, producing NADH & FADH₂ to power the electron transport chain

What is the net yield of the Citric Acid Cycle per pyruvate?

• 3 NADH

• 1 FADH₂

• 1 ATP (or GTP)

• 2 CO₂

• Oxaloacetate is regenerated

Why is the Citric Acid Cycle important?

• Produces NADH & FADH₂ to fuel the electron transport chain.

• 2 pyruvate (from 1 glucose) enter the cycle.

• Provides intermediates for the biosynthesis of many biomolecules.

• Redox balance is maintained through respiration.

How are lipids utilized for energy production?

• Lipases break down lipids into fatty acids + glycerol.

• Glycerol and fatty acids are oxidized and enter pathways connected to the Citric Acid Cycle (CAC).

• Beta-oxidation breaks down fatty acids, producing energy carriers (NADH & FADH₂) for the electron transport chain.

• Lipid oxidation generates large amounts of energy for cellular respiration.

How are proteins used for energy production?

• Extracellular proteases break proteins into amino acids.

• Amino acids enter cells but require conversion before catabolism through processes like:

  • Deamination (removal of amino group)

  • Decarboxylation (removal of carboxyl group)

  • Dehydrogenation (removal of hydrogen/electrons)

• In extreme conditions (e.g., starvation), cells can break down their own proteins for energy.