Lecture 12

Electron carriers

Energy released during nutrient breakdown is captured by reducing NAD+, NADP+, and FAD to NADH, NADPH, and FADH2, which transport high energy electrons

Energy currency

ATP stores usable energy in high-energy phosphate bonds and releases it through dephosphorylation to power energy-requiring cellular reactions

Apoenzyme

The inactive protein portion of an enzyme without its required helper

Cofactor/coenzyme binding

The helper binds to the apoenzyme and enables the correct structure or chemical activity

Holoenzyme

The complete, active enzyme formed by the apoenzyme plus its cofactor or coenzyme

Catalysts

speed up chemical reactions without being consumed or pemanently changed

Enzymes are usually…

proteins that catalyze biochemical reactions in cells

Enzymes lower the…

activation energy, allowing reactions to occur more rapidly

Activation energy

the energy required to break or form chemical binds and convert reactants into products

The reactants that bind to an enzyme are called…

substrates

The substrate binding region is the…

enzyme’s active site

Enzymes show high specificity because…

the active site has a complementary shape and chemical environment

Activation energy

the minimum amount of energy required for reactant molecules to undergo a chemical reaction

Enzymes lower activation energy…

allowing the reaction to occur faster without being consumed

Glycolysis is the most common pathway…

to carry out glucose catabolism

Glycolysis is a ten-steps process govered by…

different enzymes

The ATP Molecules formed in Glycolysis are formed by…

substrate-level phosphorylation

In Glycolysis, step 3 is a…

rate limiting step (increase in ATP or Citric acid can slow FFK)

Glycolysis step 1,3, and 10 are…

irreversible

Net gain from glycolysis

• 2 ATP

• 2 NADH

• 2 Pyruvate molecule

The energy investment phase of the Embden-Meyerhof-Parnas glycolysis pathway uses…

2 ATP molecules to phosphorylate glucose, forming two glyceraldehyde 3-phopshate (G3P) molecules

The energy payoff phase harnesses the energy in the…

G3P molecules, producing four ATP molecules, two NADH molecules, and two pyruvates

Entener-Doudoroff (ED) Pathway

An alternate pathway for the breakdown of glucose into pyruvate

Entener-Doudoroff (ED) Pathway occurs mainly in

certain Gram-negative bacteria, although some archaea and Gram-positive bacteria also use it

Entener-Doudoroff (ED) Pathway occurs in the

cytoplasm

Entener-Doudoroff (ED) Pathway converts

one glucose molecule into two pyruvate molecules

Entener-Doudoroff (ED) Pathway uses

fewer ATP molecules than glycolysis

Entener-Doudoroff (ED) Pathway produces

NADPH, which can support biosynthesis reactions

Entener-Doudoroff (ED) Pathway produces a net gain of:

• 1 ATP

• 1 NADH

• 1 NADPH

• 2 PYRUVATE

The intermediates from the Pentose Phosphate (PP) Pathway are used for the…

biosynthesis of nucleotides and amino acids → may be favored when the cell has a need for nucleic acid and or protein synthesis, respectively

The PPP does not directly produce…

ATP

Major products of PPP

• NADPH

• 3-7 C biomolecules

• Other sugar phosphates for metabolism

During pyruvate oxidation, the 3-carbon pyruvate…

loses one carbon as CO2 → leaves a 2-carbon acetyl group → transferred to coenzyme A (CoA-SH) → forms acetyl-CoA through a high-energy thioester bond

Kreb Cycle/Citric acid cycle/TCA per turn of the cycle

• 2x CO2

• 3x NADH

• 1x FADH2

• 1X ATP (or GTP)

The TCA cycle is both catabolic and anabolic

• Catabolic: generates NADH, FADH2, and GTP/ATP

• Anabolic: supplies intermediates for the synthesis of amino acids, nitrigenous bases, heme, and lipids

The overall process of catabolism from substrate breakdown to reduction of a terminal electron acceptor (such as O2) is called…

respiration

Cellular respiration begins when…

electrons are transferred from NADH and FADH2 (made in glycolysis reaction, and the Krebs cycle) through a series of chemical reactions to a final inorganic electron acceptor

Most ATPs are generated during…

oxidative phosphorylation which occurs during cellular respiration

Redox potential/ Reduction potential

A measure of a substance’s tendency to gain electrons (be reduced)

Electron acceptors - Cytochromes

Heme-containing proteins that transfer electrons through reversible oxidation and reduction of an iron atom

Electron acceptors - Flavoproteins

Proteins that contain a flavin nucleotide cofactor and participate in oxidation-reduction reactions

Electron acceptors - Iron-sulfur proteins

Proteins with iron and inorganic sulfur atoms arranged in clusters

Electron acceptors - Quinones

Small, lipid-soluble electron carriers that freely diffuse within membranes

Electron transport system (ETS)

• Last component involved in the process of cellular respiration

• Compromises a series of membrane-associated protein complexes and associated mobile accessory electron carriers

The electrons from NADH and FADH2 are passed rapidly from one ETS electron carrier to the next. These carriers can pass electrons along in the ETS because of their…

redox potential

ETS complexes contain multiple redox centers such as:

• Flavins

• Iron-sulfur clusters

• Heme groups

• Copper centers

The electrochemical gradient formed by the accumulation of H+ (also known as a proton) on one side of the membrane compared with the other is referred to as the…

Proton motive force (PMF)

This flow of hydrogen ions across the membrane, called chemiosmosis, must occur through a channel in the membrane via a membrane-bound enzyme complex called…

ATP synthase

One possible alternative to aerobic respiration is…

anaerbic respiration, using an inorganic molecule other than oxygen as a final electron acceptor such as Nitrate or Nitrite