CHAPTER 9

CELLULAR RESPIRATION

Oxygen,

Carbondioxide,

Glucose

Water

Mitochondria

C6H12O6 + O2 CO2 + H2O WHY????? + 36 ATP

Digestion of food

Breathing In

Breathing

Out/ Urine

Cell resp is so….. engaging even to canines….if Buddy gets it - oh … so will you!

Fig. 9.1

Cellular respiration and photosynthesis are opposite pathways (so .. ATP is made during and used during cell resp

photosynthesis

Gasoline Combustion Cell Respiration

Organic compounds + O2 -> CO2 + H2O + Energy

C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)

Carbs, Protein, Lipids

• Couples cell resp. to Anabolic reactions

• Bonds between PO4 groups can be broken to release energy (ADP/AMP is made).

ATP: Adenosine Triphosphate

ATP: Adenosine Triphosphate

http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/metabolism/energy/adpan.html

• PO 4 released from ATP is tagged to a substrate that will not normally react

• Substrate is phosphorylated and now able to undergo the chemical reaction

• *ATP can be regenerated *

ATP: How it works…. review

ATP Banks the Energy Released in Multiple Steps

From Glucose

C6H12O6 + 6O2 -> 6CO2 + 6H2O

CATABOLIC

PATHWAY

Food has electrons

Electrons can be removed and moved

This releases ENERGY!

The loss of electrons is called oxidation (also addition of O)

The addition of electrons is called reduction (also addition of H)

Chemistry basics for cell respiration (NOT AGAIN!!)

Redox reaction – involves oxidation + reduction

Na + Cl -> Na+ + Cl-

• Na the electron donor, is the reducing agent and reduces Cl.

• Cl the electron acceptor, is the oxidizing agent and oxidizes Na.

Redox reactions require both a donor and acceptor

An electron looses energy as it shifts from a less electronegative atom to a more electronegative one

In the cell, electron moves from macromolecules (via a H reservoir) to oxygen

A redox reaction that relocates electrons closer to oxygen

releases chemical energy (ATP)

C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)

Oxidized

Reduced

2H (food) + NAD+ -> NADH + H+

Electrons from glucose/food are carried by NAD+ (high energy electron carrier)

- Nicotinamide Adenine Dinucleotide

(NADH) – is the cells’ H reservoir

- Dehydrogenase - enzyme

+2e-

+2H+

+2e-

+2H+ Released in solution

1P

Electrons “fall” from organic molecules to oxygen during cellular respiration in a stepwise manner Hydrogen atoms in Glucose give up these Electrons. Energy is released at each step ….. as ATP

Electron Transport Chain

C6H12O6

http://www.chem.purdue.edu/courses/chm333/oxidative_phosphorylation.swfhttp://www.youtube.com/watch?v=MMB2VR0087w

Fig. 9.5

Electrons are passed by increasingly electronegative

molecules in the chain until they are caught by oxygen.

Oxygen is the FINAL ELECTRON ACCEPTOR - why? Oxygen is the most electronegative acceptor in the Electron Transport

Chain. It accepts the electrons (flowing from food) to make WATER

G = -53Kcal/mole of NADH

The Process of Aerobic Cellular Respiration

1. Respiration involves Glycolysis, the Krebs cycle and Electron Transport Chain

2. Glycolysis - breaks glucose (6Carbon) into two pyruvates (3Carbon). Packages

Hydrogen Electrons into NADH.

Glycolysis Gain - 2 ATP + 2NADH

3. Shuttle - takes pyruvate from cytoplasm to mitochondria. Gain 2NADH.

4. Krebs cycle - takes the two 3 Carbon compounds from Glycolysis and extracts

all Carbons and Oxygens as CO2 and Hydrogen electrons are transported by

NADH/FADH2. Gain - 2 ATP + 6NADH + 2FADH2

5. Electron Transport Chain and Oxidative Phosphorylation: Move electrons

through redox reactions, create a H+ (proton) gradient, and use the power of

proton gradient to make ATP

Gain - 10 NADH to 30 ATP and 2FADH2 to 4 ATP

Aerobic Cellular respiration generates 38 ATP molecules for each sugar molecule it

oxidizes. Shuttle may not be as efficient and produce less energy - so 36 ATP!

C6H12O6 + 6O2 -> 6CO2 + 6H2O + 38ATP

Energy flows from glucose -> NADH -> electron transport chain -> proton-motive force -> ATP

Making ATP: Substrate level phosphorylation - (ATP made from substrates) & Oxidative Phosphorylation - (ATP made via Electon transport Chain)

Fig. 9.6

Shuttle

ATP

4 ATP in Substrate level

phosphorylation Vs 34 ATP

In Oxidative Phosphorylation

2 2 34

1) Substrate-level

phosphorylation

(4/38 ATP)

• Here an enzyme

transfers a phosphate

group from an

organic molecule

(the substrate)

to ADP, forming

ATP.

Fig. 9.7

Remember that Electrons are REMOVED from HYDROGEN and they are PASSED DOWN the Electron Transport Chain along Redox Reactions

What will be left if Electron is Removed from a Hydrogen Atom

1P

H+ (proton)

http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

Coupling of the redox reactions of the electron

transport chain to ATP synthesis is called chemiosmosis

Electron Transport Chain (ETC)

Does not make ATP!!

Chemiosmosis couples ETC to

Oxidative Phosphorylation

http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

2H (food) + NAD+

2) Oxidative

Phosphorylation (90%

ATP – 34/38):

ATP synthase in the cristae

makes ATP from ADP and

Pi.

• ATPsynthase used the

energy of an existing proton

gradient to power ATP

synthesis. (H+ motive force)

• This proton gradient

develops between the

intermembrane space

and the matrix. Fig. 9.14

http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn1.swf

What’s happening in different locations of the cell? Cytoplasm - Glycolysis (End product

is Pyruvate)

Shuttle - Cytoplasm into Mitochondria

Kreb’s Cycle - Matrix of Mitochondria (fluid inside mitochondria)

Electron Transport Chain - Enzymes located all along the inner mitochondrial membrane; Electrons ferried from NADH to Oxygen

H+ ions moved from Matrix to

Space between Inner and Outer Membrane

Oxidative phosphorylation:

H+ ions move back into Matrix ATP Synthase is in the Inner

Mitochondial Membrane (Cristae - folds)

ATP is made in the Matrix

Fluid with Enzymes

For Glycolysis

Inter

Membrane

Space ATP

Glycolysis Krebs cycle

Cytoplasm Mitochondrial Matrix

No Oxygen Needed Needs Oxygen

Glycolysis Krebs cycle

Input = Acetyl Co A

Output = 2 Pyruvate, 4ATP, 2NADH

Input = Glucose, 2ATP

Output = 4CO2, 6NADH, 2FADH2, 2ATP

S- COA

C = O

CH3 2CO2

Fig. 9.8

Glycolysis

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 9.9a

Glycolysis

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 9.9b

Glycolysis

CO2

Glycolysis Krebs cycle Shuttle

◊ The Krebs cycle consists of eight steps

Fig. 9.11

Fig. 9.12

◊ The Krebs cycle

◊ Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein (multiprotein complex I). • The electrons continue

along the chain which includes several cytochrome proteins and one lipid carrier - Ubiquinone

• The final electron acceptor is: OXYGEN because it is MOST electronegative

• The product is WATER and ……. (its not over) Fig. 9.13

I II

III

IV

ELECTRON TRANSPORT CHAIN

http://www.chem.purdue.edu/courses/chm333/oxidative_phosphorylation.swf

◊ Read this for Understanding: ◊ Electrons from NADH or FADH2

ultimately pass to oxygen. • one O2 molecule is reduced to two molecules

of water.

◊ The electron transport chain generates no ATP directly.

◊ Its function is to break the large free energy drop from food to oxygen into a series of smaller steps that release energy in manageable amounts.

◊ The movement of electrons along the electron transport chain does contribute to chemiosmosis and ATP synthesis.

◊ A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi.

◊ ATP used the energy of an existing proton gradient to power ATP synthesis. • This proton gradient

develops between the intermembrane space and the matrix. Fig. 9.14

http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn1.swf

Fig. 9.15

◊ Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work. • In the mitochondrion, chemiosmosis

generates ATP. • Chemiosmosis in chloroplasts also generates

ATP, but light drives the electron flow down an electron transport chain and H+ gradient formation.

• Prokaryotes generate H+ gradients across their plasma membrane. ◊ They can use this proton-motive force not only to

generate ATP but also to pump nutrients and waste products across the membrane and to rotate their flagella.

Fig. 9.16

◊ Fermentation: partial degradation of sugars in the absence of oxygen (Anaerobic)

◊ Cellular respiration: complete breakdwn of sugars in the presence of oxygen (Aerobic Respiration)

Fermentation Cellular Respiration

Anaerobic (No O) Aerobic (+ O)

Input: Glucose, Output: ATP

1st Process: Glycolysis

Electron Carrier: NAD+

Electron Acceptor: Pyruvate/Acetaldehyde

(incomplete oxidation of food)

Electron Acceptor:Oxygen

(Complete oxidation of food)

End products: ATP = 2, Lactic Acid CH3CH2OHCOOH/Ethanol (C2H5OH)

ATP =36, CO2 and H20

Cytoplasm Cytoplasm + Mitochondria

Fermentation enables some cells to produce ATP without the help of oxygen

Anaerobic catabolism of sugars can occur by fermentation.

In alcohol fermentation, pyruvate is converted to ethanol in two steps

◊ During lactic acid fermentation (muscle cells, bacteria) pyruvate is reduced directly by NADH

to form lactate (ionized form of lactic acid).

◊ Some organisms (facultative anaerobes), including yeast and many bacteria, muscle cells can survive using either fermentation or respiration.

◊ Obligate anerobes = sorry, no choice have to be anerobic!

◊ Pure aerobes = neuron/brain cell!

.

◊ Supply and demand regulates it

Feedback mechanisms control cellular respiration

◊ Allosteric regulation of phosphofructokinase sets the pace of respiration.

• This enzyme is inhibited by ATP and stimulated by AMP (derived from ADP).

◊ It responds to shifts in balance between production and degradation of ATP: ATP ADP + Pi AMP + Pi.

• Thus, when ATP levels are high, inhibition of this enzyme slows glycolysis.

• When ATP levels drop and ADP and AMP levels rise, the enzyme is active again and glycolysis speeds up.

◊ Citrate, the first product of the Krebs cycle, is also an inhibitor of phosphofructokinase.

• This synchronizes the rate of glycolysis and the Krebs cycle.

• Also, if intermediaries from the Krebs cycle are diverted to other uses (e.g., amino acid synthesis), glycolysis speeds up to replace these molecules.

◊ Metabolic balance is augmented by the control of other enzymes at other key locations in glycolysis and the Krebs cycle.

◊ Cells are thrifty, expedient, and responsive in their metabolism.