Cellular Respiration:Energy for Life!

Living is work. To perform their many

tasks, cells require transfusions of energy from outside sources. In most ecosystems,

energy enters as sunlight which is trapped and converted to organic molecules by photosynthesis.

Respiration converts the energy of organic molecules into usable energy (ATP).

A. Introduction

There are two types of metabolic pathways that release the energy stored in complex organic molecules:

Fermentation (aka anaerobic respiration), leads to the partial breakdown of sugars in the absence of oxygen. Occurs in the cytoplasm.

A more efficient and widespread catabolic process, cellular respiration (aka aerobic respiration) uses oxygen as a reactant to complete the breakdown of a variety of organic molecules. Most of the processes in cellular

respiration occur in mitochondria.

Comparing Fermentation and Aerobic Cellular Respiration

Fermentation

Aerobic Cellular Respiration

Use oxygen?Level of breakdown of sugar?Location in cell?

No Yes

Partial- Less efficent

Complete- More efficient

Cytoplasm Cytoplasm & Mitochondria

Cellular respiration is similar to the combustion of gasoline in an automobile engine.

The overall process is: Organic compounds + O2 -> CO2 + H2O +

Energy Carbohydrates, fats, and proteins can

all be used as the fuel, but it is traditional to start learning with glucose. C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP

+ heat) The catabolism of glucose is exergonic

with a delta G of - 686 kcal per mole of glucose. Some of this energy is used to produce ATP

that will perform cellular work.

A cell does three main kinds of work: Mechanical work, beating of cilia,

contraction of muscle cells, and movement of chromosomes

Transport work, pumping substances across membranes against the gradient (ie. Na+K+pump)

Chemical work, driving reactions like dehydration synthesis of DNA, RNA and proteins.

In most cases, the immediate source of energy that powers cellular work is ATP.

B. ATP powers cellular work !

The transfer of the terminal phosphate group from ATP to another molecule is called phosphorylation. This changes the shape of the

receiving molecule, performing work (transport, mechanical, or chemical).

When the phosphate groups leaves the molecule, the molecule returns to its alternate shape.

ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.

What does ATP look like- simply…

PO4- PO4

- PO4-

adenine base

ribose    high-energy bonds

The bonds between phosphate groups can be broken by hydrolysis. Hydrolysis of the end phosphate group

forms adenosine diphosphate [ATP -> ADP + Pi] and releases 7.3 kcal of energy per mole of ATP under standard conditions.

ATP is a renewable resource that is continually regenerated by adding a phosphate group to ADP. In a working muscle cell the entire pool of

ATP is recycled once each minute, over 10 million ATP consumed and regenerated per second per cell.

ATP, adenosine triphosphate, is the chemical equivalent of a loaded spring. The close packing of three negatively-

charged phosphate groups is an unstable, energy-storing arrangement.

Loss of the end phosphate group “relaxes” the “spring”.

The price of most cellular work is the conversion of ATP to ADP and inorganic phosphate (Pi).

An animal cell regenerates ATP from ADP and Pi by the catabolism of organic molecules like glucose.

C. Cells recycle the ATP they use for work

Click here for animation

Respiratory pathways relocate the electrons stored in food molecules, releasing energy that is used to synthesize ATP.

Reactions that result in the transfer of one or more electrons from one reactant to another are oxidation-reduction reactions, or redox reactions. The loss of electrons is called oxidation. The addition of electrons is called

reduction.

D. Respiration is a “redox” reaction

“Redox” can be defined in many ways…

Reduction

Oxidation

Electrons Gain of electrons

Loss of electrons

Hydrogen Gain of hydrogen

Loss of hydrogen

Oxygen Loss of oxygen

Gain of oxygen

Energy? Storage of energy

Release of energy

GER!! GER!!!Remember:

“LEO” the lion says “GER”

Lost electrons means oxidizedGained electrons means reduced

In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy.

In the summary equation of cellular respiration: C6H12O6 + 6O2 + 6 H2O-> 6CO2 + 12H2O + 36 ATP

Glucose is oxidized, oxygen is reduced, and electrons lose potential energy.

E. Electrons get transferred from organic molecules to oxygen during cellular respiration

Cellular respiration does not oxidize glucose in a single step.

Rather, glucose and other organic molecules are broken down gradually in a series of steps, each catalyzed by a specific enzyme.

At key steps, hydrogen atoms are stripped from glucose and passed first to a coenzyme, like NAD+ (nicotinamide adenine dinucleotide).

F. NAD and FAD are important electron carrier molecules in respiration.

• This changes the oxidized form, NAD+, to the reduced form NADH.

•NAD + functions as the oxidizing agent in many of the redox steps during the breakdown of glucose.

Therefore, NADH which is reduced is a temporary electron-energy storage molecule.

FADH2 is another reduced coenzyme.

This energy is tapped to synthesize ATP as electrons “fall” from NADH to oxygen.

Glucose NADH and FADH2 O2

Cellular respiration uses an electron transport chain to break the fall of electrons to O2 into several steps.

Otherwise, if all of the energy were released from glucose at once, the cell would explode!

Respiration occurs in five metabolic stages:

1. Glycolysis2. The oxidation of pyruvic acid to

acetyl CoA (The Link Reaction)3. The Krebs-citric acid cycle4. The electron transport chain 5. The chemiosmotic synthesis of ATP.

G. Respiration -an overview

During glycolysis, glucose, a six carbon-sugar, is split into two, three-carbon sugars.(Lysis means to split)

These smaller sugars are oxidized and rearranged to form two molecules of pyruvate.(3 carbons compounds)

Each of the ten steps in glycolysis is catalyzed by a specific enzyme.

H. Glycolysis is the first stage of any kind of respiration (both anerobic and aerobic)

In the energy investment phase, ATP provides activation energy by phosphorylating glucose. This requires 2 ATP per glucose.

In the energy payoff phase, ATP is

produced by substrate-level phosphorylation and NAD+ is reduced to NADH.

2 ATP (net) and 2 NADH are produced per glucose.

• The ATP produced in glycolysis is an example

of substrate-level phosphorylation.

•Here, an enzyme transfers a phosphate group from an organic molecule (the substrate) directlyto ADP, forming ATP.

The process starts with 1 glucose. The net yield from glycolysis is 2

ATP and 2 NADH per glucose. No CO2 is produced during glycolysis.

Glycolysis occurs whether O2 is present or not.

Glycolysis takes place in the cytoplasm of the cells (this makes sense since all cells have cytoplasm)

What Do You Really Need to Remember About Glycolysis?

Cellular respiration can occur in the presence or absence of OXYGEN (O2)

I. Types of Cellular Respiration

With oxygen = Without oxygen = AEROBIC ANAEROBIC

Overall reaction for aerobic respirationC6H12O6

+ 6 O2 6 CO2+ 6 H2O + energy

NOTE: the reverse of this equation is the equation forPHOTOSYNTHESIS

12 H2O+

ANAEROBIC- starting with glycolysis

Which came first: aerobic or anaerobic respiration?

Why? Because there was no free oxygen

present in the early earth’s atmosphere when organisms first evolved.

FREE OXYGEN

AEROBIC & ANAEROBIC RESPIRATION

Anaerobic net gain = Aerobic overall net gain =

GLUCOSE(C6H12O6)

2 PYRUVIC ACID( 2 C3H4O3 )

2 ALCOHOL +2 CO2

( 2 C2H3OH +2CO2)

2 LACTIC ACID( 2 CH3CHOHCOOH)

ANAEROBIC PHASE AEROBIC PHASE

2 ATP

2 ADP

CO2 + H2O

O2

34 ADP 34 ATP

36 ATP

2 ATP

4 ADP

4 ATP

Glycolysis

2 NAD+

2 NADH

2NAD+

2NAD+

AEROBIC & ANAEROBIC RESPIRATION GLYCOLYSIS (glucose

pyruvic acid (a.k.a. pyruvate)) IN CYTOSOL

Pyruvate can then pass through three different pathways: alcoholic fermentation (in cytosol) lactic acid fermentation (in cytosol) oxidation of pyruvate followed by Krebs cycle

(in matrix of mitochondria) and the electron transport chain (in inner membrane of mitochondria)

ANAEROBIC PROCESSES

AEROBIC PROCESS

In glycolysis, glucose is oxidized to two pyruvate molecules with NAD+ as the oxidizing agent, not O2.

Some energy from this oxidation produces 2 ATP (net).

Glycolysis generates 2 ATP whether oxygen is present (aerobic) or not (anaerobic).

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

Fermentation can generate ATP from glucose by substrate-level phosphorylation as long as there is a supply of NAD+ to accept electrons.

Under anaerobic conditions, various fermentation pathways generate ATP by glycolysis and recycle NAD+ by transferring electrons from NADH to pyruvate.

Why anaerobic? When a short burst of ATP is

needed When oxygen supplies run out

in respiring cells In environments that are

deficient in oxygen, such as water-logged soils.

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

1. Pyruvate is converted to a two-carbon compound, acetaldehyde, by the removal of CO2. 2. Acetaldehyde is reduced by NADH to ethanol.

1

2

Fermentation tanks producing wine

Alcohol fermentation by yeast is used in brewing and baking industries.

Bioethanol is a renewable source of energy using alcoholic fermentation

Pros and Cons of Biofuels?Positive effect of biofuels

May limit greenhouse gases compared to burning petrol sources

(considered carbon neutral since carbon made and carbon used is about equal)

May reduce dependence on foreign sources of fuel

Renewable source of energy unlike burning fossil fuels

Negative effect of biofuels Certain sources of biofuels

can be costly to grow Growing sources could put

pressure on local water supplies

Using corn or soybeans for fuel could put pressure on food supply availability

Consequences of growing biofuel plants deforestation and use of fertilizers may hurt the ecosystem

During lactic acid fermentation, pyruvate is reduced directly by NADH to form lactate (ionized form of lactic acid). Lactic acid fermentation by some

fungi and bacteria is used to make cheese and yogurt.

Muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP when O2 is scarce. The waste product, lactate, may cause muscle fatigue, but ultimately it is converted back to pyruvate in the liver.

Products of lactic acid fermentation

REVIEW: Fermentation and cellular

respiration are anaerobic and aerobic alternatives, respectively, for producing ATP from sugars. Both use glycolysis to oxidize sugars

to pyruvate with a net production of 2 ATP by substrate-level phosphorylation.

Both use NAD+ as an electron acceptor.

In fermentation, the electrons of NADH are passed to an organic molecule, regenerating NAD+. Q: Has NADH been oxidized or reduced?OXIDIZED

In respiration, the electrons of NADH are ultimately passed to O2, generating ATP

In addition, even more ATP is generated from the oxidation of pyruvate in the Krebs cycle (net gain=36 ATP)

Without oxygen, the energy still stored in pyruvate is unavailable to the cell (Only 2 ATP are made from glycolysis pathway)

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

At a cellular level, human muscle cells can behave as facultative anaerobes, but nerve cells cannot.

For facultative anaerobes, pyruvate is a fork in the metabolic road that leads to two alternative routes.

Review1. What waste products do yeast make

as a result of fermentation?2. What happens when our muscles are

low in oxygen?3. Why do anaerobes need to continue

reactions beyond glycolysis when all of their ATP that they can make has already been produced?

4. What is the net gain of ATP as a result of lactic acid and alcoholic fermentation?

5. Why are anaerobes not able to produce as much ATP as aerobes?

If O2 is present, pyruvate moves to the Krebs cycle and the energy stored in NADH can be converted to ATP by the electron transport system and oxidative phosphorylation.

More than three quarters of the original energy in glucose is still present in two molecules of pyruvate.

If oxygen is present, pyruvate enters the aerobic pathway in the mitochondria in eukaryotes where the oxidation of the organic fuel to carbon dioxide occurs.

Note: some aerobic bacteria exist. Which organelle in prokaryotes takes the place of the mitochondria?

ANSWER: The plasma membrane is used for the necessary enzymatic reactions (ETC)

K. Stage 2 of Aerobic Respiration: Oxidation of Pyruvic Acid- The Link Reaction

As pyruvate enters the mitochondrion, pyruvate is

converted to acetyl CoA which enters the Krebs cycle in the matrix.

Carboxyl group is removed as CO2.

A pair of electrons is transferred from the remaining two-carbon fragment to NAD+ to form NADH.

The oxidized fragment combines with coenzyme A to form acetyl CoA.

What is important to remember about this stage? Per glucose,

Two 3-carbon pyruvate molecules are the reactants and are converted to acetyl compounds.

2 acetyl-CoA (coenzyme A) molecules are formed

(two 2 carbon compounds) 2 carbon dioxide molecules are formed since

pyruvate is decarboxylated. (How many more are yet to come?) 2 NADH molecules are formed since pyruvate is

oxidized. (How many so far is that?)

L. STAGE 3- THE KREBS/CITRIC ACID CYCLE:

The Krebs cycle is named after Hans Krebs who was largely responsible for elucidating its pathways in the 1930’s.

Acetyl-CoA (2 carbon molecule) is the starting point of the cycle.

Overview of cycle: Oxidation of acetyl-CoA is coupled with the

reduction of electron carrier molecules, NADH FADH2

Decarboxylation which liberates carbon dioxide

The production of ATP (substrate-level phosphorylation.

animation

This cycle begins when acetate from acetyl CoA combines with oxaloacetate (OAA) to form citrate.Ultimately, the oxaloacetate is recycled.Each cycle produces one ATP by substrate-level phosphorylation, two carbon dioxides, three NADH, and one FADH2 (another electron carrier) per acetyl CoA.Since there are 2 acetyl-CoA molecules produced from stage 2, there are two turns of the Krebs cycle which doubles the numbers of the products made.

The conversion of pyruvate and the Krebs cycle produces large quantities of electron carriers.

How many do we have at this point per glucose?

NADH? FADH2?

8 from pyruvate oxidation & Krebs

2 from Krebs

What do you really need to remember about the Krebs cycle?

2 acetyl Co-A are the initial reactants The cycle begins when a 2-carbon acetyl-

CoA joins with a 4 carbon oxaloacetic acid to form a 6 carbon citrate.

There are two “spins” of the cycle per original glucose molecule

With 2 turns…4 carbon dioxide molecules, 2 ATP, 6 NADH and 2FADH are made!

The cycle occurs in the mitochondrial matrix

Draw a picture of the mitochondria and label where the Krebs Cycle occurs

Only 4 of 36 ATP ultimately produced by respiration of glucose are derived from substrate-level phosphorylation.

The vast majority of the ATP comes from the energy in the electrons carried by NADH and FADH2.

The energy in these electrons is used in the electron transport system to power ATP synthesis.

M. Oxidative Phosphorylation includes The Electron Transport Chain and Chemiosmosis

What does oxidative phosphorylation mean?

The final stages of aerobic respiration: including the electron transport chain

and the chemiosmosis of ATP. (coupled reactions)

This is where the most amount of ADP is phosphorylated to ATP (the phosphate is added back on to ATP)

Oxygen is used to accept electrons from NADH and FADH2 in this process.

N. Stage 4 – The Electron Transport Chain

• As hydrogens come off of NADH and FADH2, these molecules become oxidized.

• The electrons from hydrogen travel down a chain of electron carrier molecules like “HOT POTATO”.

• Oxygen has diffused into the matrix and accepts the electrons

The ETC takes place on the cristae (inner membrane)

Role of Oxygen in the ETC?

• Oxygen is the final acceptor of electron on the ETC

• Oxygen is needed to bind with the free protons in the mitochondrial matrix to maintain the hydrogen gradient, resulting in the formation of water.

Thousands of copies of the electron transport chain are found in the extensive surface of the cristae, the inner membrane of the mitochondrion. Most components of the chain are

proteins that can alternate between reduced and oxidized states as they accept and donate electrons.

Electrons drop in free energy as they pass down the electron transport chain.

animation

animation

Electrons carried by NADH are transferred to the first molecule in the electron transport chain, flavoprotein. The electrons continue along the

chain which includes several cytochrome proteins and one lipid carrier.

The electrons carried by FADH2 have lower free energy and are added to a later point in the chain.

Electrons from NADH or FADH2 ultimately pass to oxygen. For every two electron carriers

(four electrons), one O2 molecule is reduced to two molecules of water.

The electron transport chain generates no ATP directly but aids in the chemiosmotic synthesis of ATP.

A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi. H+ ions are pumped

into the intermembrane space of the mitochondria as the electron transport chain occurs. These come from NADH and FADH2 hydrogens.

This creates a proton gradient on either side of the cristae.

animation

The proton gradient is produced by the movement of electrons along the electron transport chain. This high concentration of H+ in

the intermembranal space sets up facilitated diffusion along the F1 complex (ATP synthase)

The energy from this diffusion process allows ADP to gain a phosphate to form ATP.

The ATP synthase molecules are the only place that will allow H+ to diffuse back to the matrix.

This exergonic flow of H+ is used by the enzyme to generate ATP.

32 more ATP molecules are formed from this phase of respiration.

This coupling of the redox reactions of the electron transport chain to ATP synthesis is called chemiosmosis.

The mechanism of ATP generation by ATP synthase is still an area of active investigation.

movie

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 it’s used to power the production of food.

Prokaryotes generate H+ gradients across their plasma membrane since they don’t have mitochondria.

A Closer Look at Mitochondria Structure

Sketch a mitochondria labeling all structures seen in an electron micrograph.

Annotate your drawing by describing which reactions of the aerobic pathway occur in each section of your drawing.

Structure vs. Function? Highly infolded cristae allows for more

surface area for reactions (ETC) to occur to generate maximum ATP

Compartmentalization of organelle (matrix vs. intermembranal space) allows for proton gradient to be established which is key to making ATP

Matrix is fluid filled area for reactions to occur (e.g. Krebs) and where many enzymes are stored.

During respiration, most energy flows from glucose -> NADH & FADH2-> electron transport chain and proton-gradient -> ATP.

Considering the fate of carbon, one six-carbon glucose molecule is oxidized to six CO2 molecules.

Some ATP is produced by substrate-level phosphorylation during glycolysis and the Krebs cycle, but most comes from oxidative phosphorylation.

P. Cellular respiration generates many ATP molecules for each sugar molecule it oxidizes: a review

Click here for a cool rap on respiration

animation

Each NADH from the Krebs cycle and the conversion of pyruvate contributes enough energy to generate a maximum of 3 ATP (rounding up).

Each FADH2 from the Krebs cycle can be used to generate about 2ATP.

In some eukaryotic cells, NADH produced in the cytosol by glycolysis may be worth only 2 ATP. The electrons must be shuttled to

the mitochondrion.

34 ATP are produced by oxidative phosphorylation

This plus the 4 ATP (total) from substrate-level phosphorylation gives a bottom line of 38 ATP

Considering 2 ATP are put in for activation energy during glycolysis, the total ATP made aerobically is

36 ATP

Animation on the mitochondria in action- by Biovisions

How efficient is respiration in generating ATP? Complete oxidation of glucose

releases 686 kcal per mole. Formation of each ATP requires at

least 7.3 kcal/mole. Efficiency of respiration is 7.3

kcal/mole x 38 ATP/glucose/686 kcal/mole glucose = 40%.

The other approximately 60% is lost as heat.

Cellular respiration is remarkably efficient in energy conversion.

Q.Body temperature and Metabolic Rate Most of the energy from glucose is

released as heat. What do animals do with this heat?

Cold-blooded (aka ectothermic or poikilothermic) animals cannot retain this heat. Their body temperature fluctuates with the environmental temperature.

Warm-blooded (aka endothermic or homeothermic) animals retain part of this heat to regulate their internal body temperatures.

• What does this graph show about homeotherms & ectotherms?

• How would the metabolic rate compare in each at different temperatures?

How do poikilotherms regulate their body temperatures? These organisms must adapt to changes

in temperature by changing their position, body orientation, location or time of day that they are active.

For example, butterflies vibrate their wings to increase muscle temperature needed for flying.

Turtles bask in the sun to warm up on a hot day.

Desert animals may be nocturnal to avoid extreme daily temperatures.

How do Homeotherms regulate their body temperature? Mammals and birds are the only two

groups of homeotherms. To maintain a constant body

temperature, these animals have adaptations like having effective insulation (ie. fat, fur, feathers), having the ability to shunt blood towards or away from blood vessels, shivering, sweating or panting.

Metabolic rate is inversely proportional to body size In homeotherms, smaller animals

have greater surface-to-volume ratios and therefore larger heat loss.

These animals must oxidize food at a high rate and have a greater metabolism to survive.

Shrews must eat constantly to stay alive while an elephant may eat a meal periodically throughout the day.

Glycolysis can accept a wide range of carbohydrates. Polysaccharides, like starch or

glycogen, can be hydrolyzed to glucose monomers that enter glycolysis.

Other hexose sugars, like galactose and fructose, can also be modified to undergo glycolysis.

The other two major fuels, proteins and fats, can also enter the respiratory pathways, including glycolysis and the Krebs cycle, used by carbohydrates.

R. Glycolysis and the Krebs cycle connect to many other metabolic pathways

Proteins must first be digested to individual amino acids.

Amino acids that will be catabolized must have their amino groups removed via deamination. The nitrogenous waste is excreted as

ammonia, urea, or another waste product.

The carbon skeletons are modified by enzymes and enter as intermediaries into glycolysis or the Krebs cycle depending on their structure.

The energy of fats can also be accessed via catabolic pathways.

Fats must be digested to glycerol and fatty acids. Glycerol can be converted to

glyceraldehyde phosphate, an intermediate of glycolysis.

The rich energy of fatty acids is accessed as fatty acids are split into two-carbon fragments.

These molecules enter the Krebs cycle as acetyl CoA.

In fact, a gram of fat will generate twice as much ATP as a gram of carbohydrate via aerobic respiration.

Reactions of fats entering the aerobic pathway are REVERSIBLE!

If you eat too many cookies or potato chips which are mostly carbohydrates, your cells cannot process all of the glucose for energy.

Therefore, some of these carbohydrates can follow reversible reactions within the mitochondria and end up forming FAT!

Check this out

Carbohydrates, fats, and proteins can all be catabolized through the same pathways.

S. Negative feedback mechanisms control cellular respiration Basic principles of supply and demand

regulate the metabolic economy. If a cell has an excess of a certain amino

acid, it typically uses feedback inhibition to prevent synthesis pathway of that amino acid.

The rate of catabolism is also regulated, typically by the level of ATP in the cell. If ATP levels drop, catabolism speeds up

to produce more ATP.

Be able to answer the following review questions

1. Compare reduction and oxidation.2. How many ATP’s are needed to begin glycolysis?3. What happens in Phosphorylation?4. What are the products of lysis in glycolysis5. Relate the structures of the mitochondrion to their functions.6. What are the three major stages of cellular respiration?7. What is the net gain of ATP from glycolysis per glucose molecule? 8. When does the link reaction occur?9. What is the exact location where the Krebs cycle occurs?10. During one rotation of the Krebs cycle, how many molecules of carbon dioxide

are produced?11. How many molecules of ATP are produced with each turn of the Krebs cycle?12. What happens to the pH of the inter-membrane space as electrons move along

the ETC?13. Of what value is the folding of the inner-mitochondrial membrane?14. What is the enzyme called through which protons pass when going from the

inter-membrane space to the matrix?

More questions to answer Explain what, in general, happens in cell respiration.  What are the products of glucose breakdown when it occurs

in the cytoplasm?  What are the products of glucose breakdown when it occurs

in the mitochondria?  What are the products of anaerobic respiration in plants and

yeast (fungi)?  What are the products of anaerobic respiration in animals?  What organelle must be present for aerobic respiration?

More review questions to consider:

What is the form of energy used by cells to carry out life processes?

Write out the balanced equation for cellular respiration

Explain the difference between anaerobic and aerobic respiration.

Compare ATP production in aerobic and anaerobic respiration.

Where does glycolysis occur? What stage is common to all types of respiration? What gas is a waste to both aerobic respiration

and alcoholic fermentation.

Finally…. What are the products of glycolysis? Which type of respiration do prokaryotes carry

out? Where in the cell do lactic acid and alcoholic

fermentation occur? How many carbons does each pyruvate molecule

produced by glycolysis have? When does decarboxylation occur in aerobic

respiration and what usually forms as a result? What is the link reaction? Give at least 3 examples of when oxidation

reactions occur in aerobic respiration. What gets reduced?

Review…facts you need to know! 1. Cellular respiration includes

glycolysis, anaerobic respiration, and aerobic respiration. The link reaction, the Krebs cycle, and oxidative phosphorylation occur in aerobic respiration with the mitochondrion. Glycolysis and anaerobic respiration occur in the cytosol.

2. The ETC and chemiosmosis is the process by which most ATPs are produced. These processes occur on the inner mitochondrial membrane and on the membranes of the cristae. FADH2 and NADH bring the energy rich electrons to the ETC. oxygen is the final acceptor of the chain’s energy rich electrons to form “water of metabolism”.

Review…facts you need to know!

3. The final ATP net gain of aerobic cellular respiration is 36. the cell is most efficient at breaking down the carbohydrate glucose; however, other organic compounds are commonly broken down by respiration.

Review…facts you need to know!

4. Oil/rig = oxidation is loss/reduction is gain. In oxidation, there is loss of electrons and hydrogen. In reduction, there is gain of electrons and hydrogen. Oxidation results in C-O bonds. Reduction results in C-H bonds. Photosynthesis is, in general, a reduction process. Cellular respiration, in general, is an oxidation process.

Review…facts you need to know!

5. Summary of glycolysis: 2 ATPs are used to start A total of 4 ATPs are produced- a net gain of 2 ATPs 2 molecules of NADH are produced Involves substrate level phosphorylation, lysis, and

oxidation and ATP formation Occurs in the cell cytoplasm Whenever ATP levels in the cell are high, feedback

inhibition will block the first enzyme of the pathway. Thus, slowing or stopping the production of more ATPs

Review…facts you need to know!

Summary of glycolysis continued: 2 pyruvate molecules are present at the end of the

pathway Glycolysis produces ATPs by substrate level

phosphorylation since the phosphate groups are transferred directly to ADP from the original phosphate-bearing molecule

Review…facts you need to know!

6. Once pyruvate is produced in glycolysis, the next pathway is determined by the presence or absence of oxygen. If oxygen is present, pyruvate will go through the link reaction and enter the mitochondrion. If oxygen is not present, pyruvate will remain in the cytoplasm and go through the process of anaerobic respiration.

Review…facts you need to know!

7. In the link reaction, pyruvate is converted into acetyl CoA, which is the compound that enters the Krebs cycle. During this link reaction, each pyruvate also results in the formation of 1 NADH and 1 carbon dioxide. This acetyl CoA can also be produced from other carbohydrates and lipids, not just a hexose, usually glucose.

Review…facts you need to know!

8. The Krebs cycle begins and ends with the 4C compound called oxaloacetate. This cycle results in the formation of the following from 1 molecule of glucose:

2 ATP molecules 6 molecules of energy-rich NADH and 2 molecules of

energy-rich FADH2 move to the ETC 4 molecules of carbon dioxide which are released from

the cell as waste

Review…facts you need to know!

9. Most of the ATP produced from glucose catabolism occurs in the ETC, the last phase of cellular respiration. This reaction involves inner mitochondrial membrane of the cristae and the space between the inner and outer membranes of the mitochondrion.

The inner membrane includes proteins called electron carriers These electron carriers pick up the energy-rich electrons from

NADH and FADH2 and pass them from one another in a series of oxidations and reductions

Review…facts you need to know!

At each exchange at these proteins, small amounts of energy are released. This energy is used to transport hydrogen ions into the inter-membrane space.

These hydrogen ions, protons, then passively move from the inner-membrane space back into the matrix through a large protein that includes ATP synthase

The ATP synthase is an enzyme which allows the attachment of a phosphate group to ADP to make ATP

This overall process is also called chemiosmosis. The chemi-portion means that electrons, not water, are passively moving through a selectively permeable membrane

Review…facts you need to know!

10. Chemiosmosis is called oxidative phosphorylation because it uses the energy released by oxidation to add phosphate to ADP to produce ATP. Remember, substrate-level phosphorylation did not involve electron flow.

Review…facts you need to know!

11. Theoretically, 36 ATPs are produced by cellular respiration involving 1 molecule of glucose.

4 ATPs are produced in glycolysis (net gain of 2) 2 ATPs are produced in the Krebs cycle 32 ATPs are produced in the ETC by chemiosmosis

Review…facts you need to know!

12. Overall, respiration equation: C6H12O6 6CO2 + 6H20 + energy

(heat or ATP)

Review…facts you need to know!

13. Mitochondrial parts versus functions: Outer membrane: separates the mitochondrion from the

remainder of the cell Matrix: inner cytosol like area which contains the enzymes for

the link reaction and the Krebs cycle Cristae: shelf-like membranes with inner space allowing for

oxidative phosphorylation Inner mitochondrial membrane: contains the carriers for the ETC

and ATP synthase for chemiosmosis Space between inner and outer membranes: space for the

accumulation of protons (hydrogen ions) so that chemiosmosis can occur

Review…facts you need to know!