How Cells Make ATP

by PHOSPHORYLATION... adding a phosphate to ADP ADP + P ------> ATP

a) substrate level phosphorylation... where a substrate molecule ( X-p ) donates its P to ADP making ATP b) chemiosmosis - [Oxidative Phosphorylation via Electron Transfer Chain]... food substrates donate e- & protons to acceptor molecules [NADH], i.e., oxidation. NADH gives up electrons & protons are pumped out of mitochondria (or the chloroplasts in photosynthesis); protons diffuse back into mito thru an enzyme - ATP synthase, the ATP synthase enzyme makes ADP + P --> ATP figure * c) photophosphorylation.... e- of light energy, instead of food covalent bonds, are captured by chlorophylls to make a proton gradient across the chloroplast membranes... figure* protons move through a chloroplast ATP synthase enzyme to make ATP

Oxidative Metabolism... (cell respiration)
occurs in heterotrophic organisms that consume foods
... we say organisms oxidize (consume) foods (often glucose) to make energy
because they remove & capture electrons...
... where is energy in foods? it's in the covalent bonds (e-)
Thus - METABOLISM is cells capturing e- via REDOX reactions.


REDOX REACTION...
e- passed from one molecule to another [PGAL --> NAD⁺] in a chemical rx
energy is transferred into the new molecule (a redox couple) by holding e-

OXIDATION = removal of electron &/or proton from food covalent bond

REDUCTION = gaining electron &/or proton; adds an electron to an acceptor molecule

a model redox reaction...

A-H + B-O <---> A + B-O-H
donor acceptor (:H) acceptor donor
PGAL NAD+ 1,3-bisphosphoglycerate NADH

reducing oxidizing becomes becomes
agent agent oxidized reduced

Oxidation state* and energy relationship --> the more reduced = the more energy it holds

an example using acceptor coenzyme (redox couple) NAD⁺ <--> NADH*

Thus : metabolism becomes the stepwise oxidation of foods

if aerobic - requires oxygen as electron acceptor

if anaerobic - requires no oxygen (uses other e- acceptors)

Cell RESPIRATION... is Concept Activity 9.1 - Overview of Cellular Respiration
Investigation chapter 9.1 - How Rate of Respiration is Measured

1. oxidation of GLUCOSE --> CO₂ + H₂O
& 2. reduction O₂ to H₂O

C₆H₁₂O₆ + 6O₂ <----> 6 CO₂ + 6 H₂0 + e- ---> 36-38 ATP
DG = -686 Kc/mole 263Kc = 38%

called oxidation... because e- are removed from glucose

called reduction... because e- passed to O₂ making water
& 3. phosphorylation of ADP (thus oxidative phosphorylation)

a more complete definition of cell respiration :

- series of enzyme rx's (biochemical pathways) in the cytoplasm & mitochondria that,

- remove e- (oxidation) from covalent bonds of substrates (as glucose), and

- pass e- to acceptor molecules [coenzymes] such as NAD⁺ & FAD*
which become reduced [ NADH & FADH₂ ]

- the reduced coenzymes [ NADH & FADH₂ ] pass e- to other acceptors...
a series of protein electron carriers called cytochromes,

- the electron carriers [cytochromes] pass e- to O₂ --reduction--> H₂O

- cytochromes also pump protons [H⁺] out of mitochondria into peri-mito space,

- protons move back into mito thru a special enzyme (ATP synthase*) & make ATP

the Enzyme Pathways* of Cell Respiration...
Glyco-lysis : converts 1 glucose (C6) to 2 pyruvate (C3) produces : 2 pyruvate, 2 NADH, & 2 ATP (net) occurs in : cytoplasm [anaerobic] may include : alcoholic fermentation = glucose --> alcohol lactic acid fermentation = glucose --> lactic acid
KREBS Cycle : oxidizes : 2 pyruvate to CO2 + H2O produces : 8 NADH, 2 ATP, 2 FADH2 releases : 6 CO2 occurs in the mitochondria [aerobic]
ETC - Electron Transport Chain : uses carrier proteins (cytochromes, etc...) and passes e- & H+ from NADH & FADH2 to O2 to make H2O generates a proton gradient (chemiosmosis) across the inner mitochondria membranes
& ATPsynthase : the enzyme of the inner mitochondrial membrane end that lets H+ back into mitoplasm & makes ATP directly

Glycolysis... don't memorize the pathway, but learn the...
KEY REACTIONS of GLYCOLYSIS... Concept Activity 9.2 - Glycolysis
1. substrate level phosphorylation* [occurs twice in glycolysis]
2. redox reaction step 6* involving NAD⁺
3. reactions --> investment phase* & payoff phase* - Summary of glycolysis*
Quicktime movie animation of glycolysis*^{view for homework}

FATE of NADH - need to regenerate NAD+: mito membranes is impermeable to NADH alcoholic fermentation* "history of wines" lactic acid fermentation* also called anaerobic respiration shuttles* malate shuttle (liver, kidney, heart) = NADH c --> NADH m glycerol-P shuttle (muscle/brain) = NADH c --> FADH2m Purpose: to move electrons captured in cytosolic NADH c into mitochondria
FATES of PYRUVATE (figure*) Concept Activity 9.5 - Fermentation if anaerobic alcoholic fermentation & lactic acid respiration if aerobic pyruvate dehydrogenase + Krebs Cycle

SUMMARY GLYCOLYSIS figure*

- 2 ATP to initiate

- 2 substrate level phosphorylation steps = 4 ATP gross

thus Glycolysis makes: what goes in & come out*
2 ATP (net),
2 NADH, and
2 PYRUVATES

remember the role of the ... Fermentations & Shuttles

Heterotrophic Metabolism in Aerobic Organisms...
Krebs Cycle [Sir Hans Krebs] the Fate of Pyruvate*

PYRUVATE DEHYDROGENASE Reaction... in mitoplasm (Fig 9.10)* oxidizes PYR --> acetyl-CoA a multienzyme complex of 60 proteins and 5 coenzymes involves CoASH* -----> acetyl coenzyme A [Fritz Lippman] reactions: 1. decarboxylation (-CO2), 2. reduction of NAD+ --> NADH, 3. acylation & synthesis of AcoA*
KEY Reactions of KREBS CYCLE 1. NAD+ is reduced (NADH) and FAD is also reduced (FADH2) 2. substrate level phosphorylation occurs (GTP <--> ATP) 3. decarboxylation occurs [-COOH] 4.* an acylation reaction via coenzyme-A (forms Acetyl-coA) SUMMARY Reactions: [Krebs Cycle Quicktime Movie*] Summary figure* full cycle
--> how many actual ATP have we made so far? Activity 9.3- The Citric Acid (Krebs) Cycle

OXIDATIVE PHOSPHORYLATION & ELECTRON TRANSFER CHAIN...
Concept Activity 9.4 - Electron Transport*
the coupling of oxidation of substrates (-e) to the phosphorylation of ADP to make ATP
µ remember, most of the energy of glucose's bonds is now carried in NADH & FADH₂
e- passed from NADH/FADH₂ to O₂ via "carrier molecules"* names*
these series of electron carrier proteins occur in 4 membrane subunits fig 9.16*
I) NADH Reductase, II) Succinate Dehydrogenase
III) Cytochrome Reductase, IV) Cytochrome Oxidase
Virtual Cell - ETC animation*


CHEMIOSMOSIS (fig 9.16*) & ATP Synthase (fig 9.14* & EM)
creation of a hydrogen ion gradient (H⁺) by e- flow thru the ETC
- some e- carriers release protons to outside (into perimitochondrial space)
- H⁺ diffuse back into mitoplasm thru ATP synthase ---> ATP via a molecular motor*
- Boyer hypothesis* & animation of ATP synthase of mechanism by D. Nicholson*
- bacteriorhodopsin* provides experimental proof of H⁺ gradient making ATP