Cellular Respiration

Pulling some things together… What did the previous slide represent? Notice that during each energy

transformation, heat is lost! What is this called?

Combustion Reactions

A chemical reaction that involves a hydrocarbon and oxygen. It produces energy (heat) so rapidly that a flame results.

The products of this reaction include carbon dioxide and water.

C(x)H(x)+O2→H2O(g)+CO2(g)

Combustion is commonly called burning.

It is an exothermic reaction.

Cells and Energy

Glycolysis and respiration as source of energy for the cell

How do cells make ATP?Phosphorylation!

Chapter 6

Cells need to generate ATP!

Substrate level phosphorylation Uses enzymes Transfers phosphate

group from an organic substrate to ADP.

X-P + ADP + enzyme X + ATP

Chemiosmotic Phosphorylation

a.k.a. Chemiosmosis

Needs a membrane. Uses the potential

energy to create a concentration gradient of H+

(hydrogen ions) across a membrane.

Uses special enzymes, ATP synthases.

Things to keep in mind... (we are going to go over this…)

• Exergonic or endergonic?

• What is oxidized?

• What is reduced?

• In what form is energy released?

• What is the importance of CO2 in the

atmosphere?

• What is the source of oxygen in the

atmosphere?

Respiration = C6H12O6 + 6O2 6CO2 + 6H2O

Reminder: Endergonic reactions:

have a net absorption of E

Exergonic reactions: have a net release of E.

These reactions are “coupled,” one does not occur without the other!

While cellular respiration, in total, is an exergonic reaction, it is made up of a series of reactions which involve both types!

C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY RELEASED (ATP)

Redox Reactions The movement of electrons from one

molecule to another is an oxidation-reduction reaction. Loss of electrons is oxidation Gain of electrons is reduction

LEO the lion goes GER ex. C4H6O5 + NAD+ C4H4O5 + NADH +

H+ oxidized reduced

The “master” formula…

There are 2 types of cellular respiration

With oxygen: aerobic cellular respiration (What are aerobic exercises?)

Without oxygen: anaerobic cellular respiration a.k.a. fermentation

Eukaryote vs Prokaryote Glycolytic pathways

Overview of Cellular Respiration

A. Glycolysis (anaerobic)

B. Fermentation B. Aerobic Respiration1. Citric Acid Cycle2. Electron Transport Chain

(anaerobic respiration)

Without oxygen With oxygen

Would you like that with or without oxygen?

Aerobic - environments with oxygen

Anaerobic - environments without oxygen

Most organisms need O2 but there are some that can live in either environment and a few that must live in the absence of O2!

Saccharomyces cerevisiae (yeast) images provided by Peter Hollenhorst and Catherine Fox

Obligate Anaerobes

Clostridium botulinum - Gram-positive, endospore-forming, rod prokaryote. Vegetative and spore stages. Note the flagella.

Causes botulism.Magnification*: x2,000Type: SEM

Clostridium tetani - Gram-positive, rod prokaryote; vegetative and spore stages. Note the flagella.

Causes tetanus. SEM |Magnification*: x1,750Type: SEM

Review of Mitochondria Eukaryotic

organisms carry out cellular respiration in the mitochondria (power house of the cell) http://www.sci.sdsu.edu/TFrey/MitoMovies/CrisMitoMovie.htm

Reminder: Possible evolution of mitochondria-endosymbiont

The Mitochondria Double membrane Has it’s own DNA!! Can reproduce in

cell…! Endosymbiont?? Possible evolution?

http://hybridmedicalanimation.com/anim_mitosis_wmVideo.html

Introduction to Cellular Respiration

The process by which food molecules (glucose) are broken down to release energy (ATP)

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

In eukaryotic organisms, this process takes place in the mitochondria. In prokaryotic organisms, this process takes place in the cell membrane.

Overview: Respiration occurs in 4 (5) main stages Glycolysis

Exergonic Occurs in the cytoplasm Splits glucose into 2 molecules of pyruvic

acid Pyruvic acid is modified into Acetyl CoA

as it diffuses into the mitochondria. Each pyruvic acid loses a carbon to CO2

This is a high energy fuel molecule for the next stage

Krebs Cycle Exergonic Occurs in the matrix of the mitochondria Produces CO2 as a waste product ** Main function of first 2 stages: supply

3rd stage with electrons! Electron Transport Chain and

Chemiosmotic Phosphorylation Occurs on the cristae of the mitochondria Uses oxygen Produces the most ATP

Overview of Aerobic Cellular Respiration

Define the four stages of respiration and their location in the cell

Glycolysis Formation of acetyl

coenzyme A

Citric acid cycle

Electron transport

and chemiosm

osis

Glucose

Pyruvate

2 ATP

1 2 3 4

Stage 1: Glycolysis

glyco- : sugar (glucose)-lysis: to split

A. Glycolysis (Overview)

A molecule of glucose (6 carbon compound) is broken apart making 2 pyruvic acid compounds (3 carbons each)

2 ATP and 2 NADH molecules produced

Glycolysis STEP 1 - 2 phosphates are attached to glucose,

forming a new 6-C compound. The phosphate groups come from 2 ATP, which are converted to ADP. (Glucose is phosphorylated!)

STEP 2 - The 6-C compound formed in Step 1 is split into 2 3-C molecules of PGAL.

STEP 3 - The 2 PGAL molecules are oxidized (LEO), and each receives a phosphate group forming 2 new 3-C compounds. The phosphate groups are provided by 2 molecules of NAD+ forming NADH.

STEP 4 - The phosphate groups added in Step 1 and Step 3 are removed from the 3-C compounds.

This reaction produces 2 molecules of Pyruvic Acid.

Each phosphate group combines with a molecule of ADP to make a molecule of ATP.

Because a total of 4 phosphate groups were added, FOUR MOLECULES OF ATP ARE PRODUCED.

Substrate-level phosphorylation

Enzymes in the cytoplasm pass a high energy phosphate to ADP to make ATP.

Not very efficient… FYI: The high energy phosphates

came from the oxidation of BPG, in the presence of an enzyme, forming PGAL (a.k.a. G3P) and ATP.

Keep up with totals:

Summary of

glycolysis:

Don’t panic… you do not need to memorize this, but it will give you a greater appreciation for what really is happening to get from glucose to pyruvate!

How many different enzymes are involved?

Question 1

How much ATP is needed to activate glycolysis?

Energy investment phase andsplitting of glucose

Glucose

2 ATP

2 ADP

Fructose-1,6-bisphosphate

2 X Glyceraldehyde phosphate (G3P)

3 steps

P P

P P

(see next slide)

Question 2

How much ATP/net & ATP is produced in glycolysis?

2 ATP

2 ADP

(G3P)

5 steps

P(G3P)

Pyruvate Pyruvate

NADH

NAD+

P

2 ATP

2 ADP

NADH

NAD+

Energy capture phase

Net yield per glucose:? ATPs and ? NADH

2 X Glyceraldehyde phosphate (G3P)

Question 3

Identify the exergonic and endergonic reactions in the following exergonic coupled enzyme steps in glycolysis:

Energy investment phase:• Glucose + ATP Glucose-6-phosphate + ADP

Energy capture phase:• Phosphoenolpyruvate + ADP Pyruvate + ATP

In summary…. 2 ATP molecules

were used in Step 1, but 4 are produced in Step 4. Therefore, glycolysis has a NET YIELD of 2 ATP molecules for every molecule of glucose that is converted into Pyruvic Acid

http://biology.clc.uc.edu/courses/bio104/atp.htm

Glucose

2 pyruvic acid molecules + 4 H+ + energy

stored in 2 ATP molecules

Glycolysis Facts: Glycolysis is the universal E-

harvesting process of life. Because glycolysis occurs universally,

it is thought to be an ancient metabolic system.

The net gain of two ATP molecules represents only 5% of the E that a cell can harvest from a glucose molecule.

Pyruvic Acid’s 2 Possible Pathways

If O2 is not available Fermentation

alcoholic lactic acid many types of fermentation!

If O2 is available Kreb cycle

2 Possible Paths if no O2 present

Why must pyruvate be converted to either ethyl alcohol or lactate in the absence of oxygen?

Glucose (C6)

2 Pyruvate (C3)

Glycolysis

2 NADH2 NAD+

2 ATP

CO2

2 Ethyl alcohol (C2)

Glucose

2 Pyruvate

Glycolysis

2 NADH2 NAD+

2 ATP

2 Lactate (C3)

Stage 2: The Preparatory Reaction

Acetyl CoA Production

B.O.P. (Breakdown of Pyruvate)

1. The 2 pyruvic acid compounds (3C) are changed into 2 2-carbon compounds and 2 molecules of CO2

2. Occurs in the space between the membranes of the mitochondria

Takes place as pyruvate moves into the matrix of the mitochondria

Production of Acetyl CoA When pyruvic acid enters the

mitochondrial matrix, it reacts with a molecule called coenzyme A to form Acetyl Coenzyme A, abbreviated acetyl CoA. CO2, NADH, and H+ are produced in this reaction.

Remember: There are 2 pyruvic acids formed from 1 glucose!

Question 1

Pyruvate (C3) + CoA + NAD+

Acetyl(C2)CoA + CO2

+NADH

How many of the six carbons of glucose are lost in this way?

Question 2

Considering the transition reaction and the first reaction of the Krebs cycle below, how would you describe the role of Coenzyme A?

Transition reaction:Pyruvate (C3) + CoA Acetyl(C2)CoA + CO2

Krebs cycle first reaction:Oxaloacetate (C4)+ AcetylCoA Citrate (C6) + CoA

Stage 3

Krebs Cycle a.k.a. Critic Acid Cycle

Krebs Cycle Named for German-British

researcher Hans Krebs (1900-1980).

Also called the Citric Acid Cycle

The Krebs cycle is a biochemical pathway that breaks down Acetyl CoA, producing CO2, H+, NADH, FADH2, and ATP.

Step 1 A 2-Carbon

molecule of Acetyl CoA combines with a 4-Carbon compound, OXALOACETIC ACID, to produce a 6-Carbon Compound CITRIC ACID.

Step 2 Citric Acid releases a

CO2 molecule and a H atom to form a 5-Carbon compound. By losing a H atom with its electron , Citric Acid is OXIDIZED. The H atom is transferred to NAD+, REDUCING it to NADH.

Step 3

The 5-Carbon compound releases a CO2 molecule and a H atom, forming a 4-Carbon compound. NAD+ is reduced to NADH. A Molecule of ATP is also synthesized from ADP.

Step 4 The 4-Carbon compound

releases a H atom to form another 4-Carbon compound. The H atom is used to reduce FAD (Flavin Adenine Dinucleotide) to FADH2, a molecule similar to NAD+ that accepts electrons during Redox Reactions.

Step 5 The 4-Carbon

compound releases a H atom to regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The H atom reduces NAD+ to NADH.

Summary

Keeping up with totals:

In Glycolysis 1 glucose molecule produces 2 Pyruvic Acid molecules, which can then form 2 molecules of Acetyl CoA.

1 Glucose molecule causes 2 turns of the Krebs cycle.

The 2 turns produce 6 NADH, 2 FADH2, 2 ATP, and 4 CO2 molecules.

The CO2 is a waste product that diffuses out of the cells and is given off by the organism.

The bulk of the E released by the oxidation of Glucose still has NOT been transferred to ATP. Only 4 molecules of ATP have been generated - 2 from Glycolysis and 2 From the Krebs cycle.

10 molecules of NADH and the 2 FADH2 molecules from the Krebs cycle DRIVE the next stage of Aerobic Respiration - The Electron Transport Chain.

That is where MOST of the E transfer from Glucose to ATP actually occurs.

Stages 4 and 5

Electron Transport Chain (ETC) and Chemiosmosis

Electron Transport Chain The electron transport chain

is a system of electron carrying proteins embedded into the inner membrane of a mitochondrion, the cristae.

These proteins transfer e- from one to another, down the chain, much in the way a bucket brigade passes buckets of water.

Electron Transport Chain (ETC) NADH is oxidized to NAD+ at the first

protein/enzyme complex. 2 H+ are moved across the membrane and the high E electron moves through a series of membrane proteins.

As the e- pass through a second protein/enzyme complex, its E is used to move another 2 H+ across the membrane.

ETC con’t. At protein/enzyme complex 3 another 2

H+ are moved across the membrane. Once the e- has spent all of its E, it joins

oxygen and other H+’s and e- ‘s to make a water molecule.

This process creates a gradient by using the high energy e- and H from NADH (and FADH2).

ETC and FADH2

FADH2 can not enter the ETC at the same point. It must enter at the 2nd protein/enzyme complex. Here it is oxidized to FAD+. Since it only passes through 2 protein/enzyme complexes, it can only move 4 H+ across the membrane.

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

Oxygen: the “ultimate” electron acceptor!

Still no ATP! The ATP is actually produced by a proton

motive force. This force is a store of potential energy created by the gradient formed when hydrogens (protons) are moved across a biological membrane.

Therefore, the electron transport chain merely produces a gradient through which ATP can be made (this is known as chemiosmosis).

2H+

2H+ 2H+ 2H+

2H+ 2H+

→ NAD+

e-

Cytosol

Intermembranespace

Outer mitochondrial membrane

Inner mitochondrial

membrane

Matrix of mitochondrion

Complex IComplex II

Complex III Complex IV

Complex V:ATP synthase

Chemiosmosis A special protein called ATP synthase

provides a channel for H+ ions to move across the cristae. It also contains the enzyme that catalyzes the phosphorylation of ADP to from ATP.

As H+ ions move through the port, their flow drives the synthesis of ATP.

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

Summary

Websites with animations http://www.science.smith.edu/

departments/Biology/Bio231/etc.html http://www.sp.uconn.edu/~terry/

images/anim/ETS.html http://www.sci.uidaho.edu/bionet/

biol115/t4_energy/etc.htm

Total ATP generated:

From the scheme, what is the function of the electron transport stage of respiration?

GlycolysisGlucose

2 Pyruvate

2 ATP

2 ATP

NADH

Transition reaction

Citric acid cycle

Electron transport and chemiosmosis

2 4 – 6 ATP

NADH2 6 ATP

NADH6 18 ATP

FADH22 4 ATP

32 - 34 ATP

Substrate-levelphosphorylation

Oxidativephosphorylation

Substrate-levelphosphorylation

Total Energy Yield

Are carbs. our only option?

Other food… Glucose is not the only material

that can be metabolized to generate energy. Many carbohydrates can be broken down in glycolysis and enter the Krebs Cycle. Proteins can be broken down into amino acids and those can be deaminated and the carbon chains feed into the Krebs Cycle. The very long carbon chains of fatty acids can be chopped into two carbon pieces by a process known as Beta Oxidation. Since the fatty acid chains can be up to 20 carbons long there is a very great deal of energy stored in fats.

Fermentation (a.k.a. anaerobic respiration)

No oxygen required!

Anaerobic RespirationIn some organisms, there are times when cells are without O2

for short periods of time. When this happens, an anaerobic process called fermentation follows glycolysis and provides a means to continue producing ATP until O2 is available again.

Anaerobic Respiration

In the absence of O2, some cells can convert Pyruvic Acid into other compounds through additional biochemical pathways that also occur in the cytosol.

The combination of Glycolysis PLUS these additional pathways are known as FERMENTATION.

During the processes of fermentation NO ADDITIONAL ATP IS SYNTHESIZED.

2 Types of Fermentation Lactic Acid

Fermentation occurs in some

bacteria, in plants, and most animals (including humans)

Alcoholic Fermentation occurs in some

yeast and bacteria

Lactic Acid Fermentation

Pyruvic acid is converted into lactic acid. Lactic acid involves the transfer of 2 H

atoms from NADH and H+ to Pyruvic Acid. In the process, NADH is oxidized to form NAD+ which is needed to keep Glycolysis operating.

Lactic Acid Fermentation

Bacteria can do it!

Lactic acid fermentation by microorganisms plays an essential role in the manufacture of food products such as yogurt and cheese.

So can you!

Certain animal cells, including our muscle cells convert pyruvic acid to lactic acid.

During exercise, breathing cannot provide your body with all the oxygen it needs for aerobic respiration. When muscles run out of O2, the cell switch to lactic acid fermentation.

This process provides your muscles with the energy then need during exercise.

Lactic Acid Fermentation

In L.A.F., the 2 molecules of pyruvic acid formed from glycolysis are used to make 2 molecules of lactic acid and NAD+ which is necessary for glycolysis.

L.A.F allows glycolysis to happen repeatedly for quick energy. Each time glycolysis occurs, 2 ATP are formed.

Alcoholic Fermentation

In alcoholic fermentation, pyruvic acid from glycolysis is changed into ethyl alcohol and CO2. As a result, NAD+ is formed which is needed for glycolysis. Each time glycolsysis occurs, 2 ATP are made.

Alcoholic Fermentation

Alcoholic Fermentation cont.

This process is used in making beer, wine, and bread.

A.F. by the yeast in a bread recipe produces CO2 bubbles that raise the bread dough.

Also, many bacteria carry out A.F. under anaerobic conditions.

Fermentation

Let’s Compare Lactic Acid Fermentation and Alcoholic Fermentation...

Lactic Acid Fermentation:

glucose

glycolysis (pyruvic acid)

lactic acid + NAD+ +2 ATP

Alcoholic Fermentation:

glucose

glycolysis (pyruvic acid)

CO2 + ethyl alcohol + 2 ATP + NAD+

Fermentation Totals:

Comparison of energy from one glucose molecule…

Lactic Acid Fermentation: 2ATP Alcoholic Fermentation: 2 ATP Cellular Respiration: 36 ATP Aerobic Respiration is more

energy efficient than anaerobic respiration!

Let’s Compare Photosynthesis and Cellular Respiration...

Photosynthesis: food accumulated energy from sun

stored in glucose CO2 taken in O2 given off needs sunlight occurs only in

presence of chlorophyll

Cellular Respiration: food broken down energy in glucose

is released CO2 given off O2 taken in does not need

sunlight occurs in all living

cells