Aerobic Harvesting of Cellular Energy

CELLULAR RESPIRATION: AEROBIC HARVESTING OF CELLULAR ENERGY

. In chemo heterotrophs, eukaryotes perform cellular respiration That harvests energy from food which yields large amounts of ATP, that allows for cellular work.

 To reduce entropy and perform work, life requires energy.  In almost all ecosystems, energy ultimately comes from the sun, which is why we studied photosynthesis first!  Key to remember……  glucose and oxygen are produced, so that’s what we have to work with!

 The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules.

 An important question is how do cells extract this energy?

Where Have we Seen something Like this Before??!!

Final metabolic pathway is the Electron Transport Chain

We can harvest electrons from atoms to control the proton energy that follows them around.

Have to be VERY careful to control these ions or acids can build up!

We can do this with a semi-permeable membrane, enzymes to control (transport) the electrons and resulting protons

Final, stable electron and proton acceptors. Figure 6.5C NADH

NAD ATP 2 Controlled H release of energy for synthesis of ATP

 1 O 2 H 2 2

H2O Semi-permeable membrane-crista Enzymes-to control (transport) the electrons and resulting protons –mobile enzymes: Cytochrome Q and Cytochrome C Non-mobile enzymes; NADH Reductase, Ubiquinone, (Collectively called “complexes”) and then ATP Synthase used to place electrons on their final acceptor in a process called “chemiosmosis”.

Ultimately, Cells tap energy from electrons “falling” from organic fuels to oxygen

 When the carbon-hydrogen bonds of organic compounds are broken, electrons are created and then transferred to a “final electron/proton” acceptor.

 An electron loses potential energy when it “falls” to oxygen.

 What will use all this harvested electron/proton energy as it “falls” to create?

 Think about what you know and come up with a substance who can donate Hydrogen?

 Think about what you know and come up with a substance who can accept Hydrogen? How is this done? By shuttling the electrons and protons found in hydrogen!

 Cellular respiration is the changes in hydrogen atom distribution.

 Glucose

 loses its hydrogen atoms and

 becomes oxidized to CO2.  Oxygen

 gains hydrogen atoms and

 becomes reduced to H2O.

 Cellular respiration consists of a sequence of steps that can be divided into three stages.  Stage 1 – Glycolysis-Cytosol  Stage 2 – Pyruvate processing-Bridge between cytosol and mitochondrion  Stage 3- Citric acid cycle-Mitochondrion  Stage 4 – Oxidative phosphorylation with chemiosmosis- Cristae

Cellular respiration

 Stage 1: Glycolysis  occurs in the cytoplasm and is anaerobic, it  begins cellular respiration, and  breaks down glucose into two molecules of a three- carbon compound called pyruvate/pyruvic acid  Goal, break sugar to collect hydrogens  Net versus Gross ATP gains

 C6H12O6+ 4 ADP +4 Pi + 2 ATP + 2 NAD  2 C3H5O3+ 4ATP+ 2 NADH+ 2 ADP + 2 Pi Pyruvate/Pyruvic Acid has lots more bond energy that can be extracted!

We need to stabilize the citric acid and make it permeable to the outer mitochondrial membrane. This second stage of cell respiration is a “bridge reaction” because Nothing is produced, but we get the task done! The first substance encountered in the mitochondria by The acetyl-Coa is oxaloacetate.

Together they form a stable 6 carbon compound called “citrate/citric acid”

Hence the next main stage of cell respiration is called The “Citric acid cycle”.

Stage 2: The citric acid cycle takes place in mitochondria, breaks pyruvate to carbon dioxide, and supply the next stage with electrons (NAD/FAD) recycle pyruvic acid/pyruvate stabilizer (Co-A) regenerate Acetyl –CoA acceptor-oxaloacetate Goal is to collect hydrogens, make some ATP (substrate) and release waste

Fourth and final stage of Cellular respiration

 Stage 3: Oxidative phosphorylation  involves electrons carried by NADH and

FADH2,  They shuttle H e- to the electron transport chain embedded in the inner mitochondrial membrane, (cristae)  involves chemiosmosis which is passing H e- and H+ through ATP synthase (chemiosmosis)  together, they generate ATP through oxidative phosphorylation. Figure 6.10_1

   H H H H   Mobile H  Protein H H H  electron H ATP complex carriers of electron synthase carriers III IV I

Electron FADH2 FAD flow 1 2 H O H O NADH NAD 2 2 2 H ADP P ATP H

Electron Transport Chain Chemiosmosis

Oxidative Phosphorylation Most ATP production occurs by oxidative phosphorylation

 Oxidative phosphorylation

 involves electron transport and chemiosmosis and

 requires an adequate supply of oxygen.

 Electrons from NADH and FADH2 travel down the electron transport chain to from one enzyme to another using mobile enzymes to assist in the electron moving properly.

 Finally, in chemiosmosis, ATP synthase channels the H e- and following

H+ to O2 waiting in the matrix.

CYTOPLASM Electron shuttles Mitochondrion across membrane 2 NADH 2 NADH or

2 FADH2 6 2 2 NADH NADH FADH2

Glycolysis Pyruvate Oxidative 2 Oxidation Citric Acid Phosphorylation Glucose Pyruvate 2 Acetyl Cycle (electron transport CoA and chemiosmosis)

Maximum per glucose:

 2  2  about ATP ATP 28 ATP About 32 ATP by substrate-level by substrate-level by oxidative phosphorylation phosphorylation phosphorylation ALL ROADS! CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effects

 Three categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisons

1. block the electron transport chain (for example, rotenone, cyanide, and carbon monoxide),

2. inhibit ATP synthase (for example, the antibiotic oligomycin), or

3. make the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol). Figure 6.11

Cyanide, Oligomycin Rotenone H H carbon monoxide H H ATP synthase H H H

DNP

FADH2 FAD 1 O 2 H NADH NAD 2 2

H H2O ADP P ATP But once we are past glycolysis, what is the major reactant needed to complete the remaining steps of cellular respiration?

HINT:

FERMENTATION: ANAEROBIC HARVESTING OF ENERGY

 Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation

 takes advantage of glycolysis,

 produces two ATP molecules per glucose, and

 reduces NAD+ to NADH.

 The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.

 Then, since we can’t effectively catabolize pyruvates, the animal cell does what it can and produces Lactic acid and CO2.

 Fully anaerobic creatures like fungi, convert glucose to ethanol and CO2 Fermentation enables cells to produce ATP without oxygen

 Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.

 The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt.

 Other types of microbial fermentation turn

 soybeans into soy sauce and

 cabbage into sauerkraut. Figure 6.13B Glucose

2 ADP 2 NAD

2 P Glycolysis 2 ATP 2 NADH

2 Pyruvate

2 NADH

2 CO2

2 NAD

2 Ethanol Fermentation enables cells to produce ATP without oxygen

 Obligate anaerobes-archae bacteria

 are poisoned by oxygen, requiring anaerobic conditions, and

 live in stagnant ponds and deep soils.

 Facultative anaerobes

 include yeasts and many bacteria, and

 can make ATP by fermentation 6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on

 GlycolysisEarth is the universal energy-harvesting process of life.

 The role of glycolysis in fermentation and respiration dates back to

 life long before oxygen was present,

 when only prokaryotes inhabited the Earth,

 about 3.5 billion years ago.