Chapter 8: How Cells Release Stored Energy. Overview of Carbohydrate Metabolism Glucose + 6 O 2 6 CO 2 + 6 H 2 O The overall reaction is exergonic

Chapter 8: How Cells Release Stored Energy

Overview of Carbohydrate Metabolism

Glucose + 6 O2 6 CO2 + 6 H2O

The overall reaction is exergonic.

The energy given off is used to make ATP.


• The first step of carbohydrate metabolism is called glycolysis.– Glucose is the starting material for glycolysis.

• What happens to the end-products of glycolysis depends upon conditions in the cell.


GLYCOLYSIS

ANAEROBIC Conditions

No oxygen present

AEROBIC RESPIRATIONOxygen present

OR


GLYCOLYSIS


Occurs in Cytoplasm

AEROBIC RESPIRATION

Occurs in Mitochondria

OR


GLYCOLYSIS


Net gain of 2 ATP

AEROBIC RESPIRATION

Net gain of 36-38 ATP

OR


GLYCOLYSIS

ANAEROBIC Conditions• Fermentation• Type depends upon cell type

AEROBIC RESPIRATION• Preparatory step• Krebs Cycle• Electron Transport System

OR

Energy Releasing Pathways

• Carbohydrate metabolism begins in the cytoplasm with the glycolysis pathway

– The first steps of glycolysis are endergonic and require the input of 2 ATP

Glycolysis

• In the first step glucose is converted to glucose-6-phosphate in a phosphorylation reaction– Reaction is endergonic– Reaction requires an input of ATP

• A rearrangement reaction occurs to make fructose-6-phosphate

Glycolysis

• Another phosphorylation reaction occurs to made fructose-1,6-phosphate– Reaction is endergonic– Reaction requires an input of ATP

• 5 more reactions occur

Glycolysis

• In the glycolysis reactions the following are made– A total of 4 ATP

• Made by substrate level phosphorylation

• Direct transfer of a P to ADP ATP

– 2 NADH from NAD+, 2e, H+

– 2 pyruvate (3 carbon each)

Glycolysis Summary

• Where it occurs:• First substrate: (starting “material”)

• Organic end product:

• Also made:– net gain of ____ ATP (why net?, how made?)– _____ NADH (made from?)

Glycolysis Summary

• Where it occurs: Cytoplasm

• First Substrate: Glucose (6C)

• Organic end product: 2 Pyruvate (3C)

Glycolysis Summary

• Also made– net gain of 2 ATP made by substrate-

level phosphorylation

• Pathway requires an input of 2 ATP to start and makes a total of 4 ATP

– 2 NADH – each made from NAD+ ,2e and H+

Energy Releasing Pathways

• What happens to the products of glycolysis depends upon cell conditions.

Aerobic conditions• Preparatory step and Krebs cycle• Electron transport system

Anaerobic conditions• Fermentation

Aerobic Respiration

• Preparatory Step– Reaction that occurs as the pyruvate enter

the matrix of the mitochondria

Aerobic Respiration

• Preparatory Step– As the pyruvate enter the mitochondria

each has a carbon removed and co-enzyme A added

– Produced in the Prep. Step• 2 NADH (go to ETS)

• 2 CO2 (diffuse out of mitochondria and cell)

Aerobic Respiration

• Preparatory Step– Produced in the Prep. Step

• 2 NADH (go to ETS)

• 2 CO2 (diffuse out of mitochondria and cell)

• 2 Acetyl Co-A (enter into Krebs cycle)

Preparatory Step Summary

• Where and when it occurs:

• Substrate:

• Organic Product:

• Also made:– ___________– ___________

Preparatory Step Summary

• Where and when it occurs: Occurs as pyruvate enter mitochondria, occurs under aerobic conditions

• Substrate: 2 Pyruvate (3C)• Organic Product: 2 Acetyl-CoA (2C)• Also made:

– 2 CO2

– 2 NADH

Aerobic Respiration

• Krebs Cycle – Each Acetyl-CoA (2C) joins with an

oxaloacetate (4C) to form a citrate (6C)

– Rest of Krebs cycle reactions occur• Last reaction produces oxaloacetate

(4C) which joins with the next available acetyl-co A…….

Aerobic Respiration

• The metabolism of 2 pyruvates in the the Krebs Cycle reactions produces:– 2 ATP (by substrate-level phosphorylation)

– 6 NADH (go to ETS)

– 2 FADH2 (go to ETS)

– 4 CO2 (diffuse out of mito. and cell)

Krebs Cycle Summary

• Where it occurs:• Starting substrates:• Last product of pathway:• Also made (in total for 2 acetyl-CoA entering)

____ CO2

____ ATP (method made by?)

____ NADH

____ FADH2

Krebs Cycle Summary

• Where it occurs: matrix of mito.• Starting substrates: acetyl-CoA, oxaloacetate• Last product of pathway: oxaloacetate• Also made (in total for 2 acetyl-CoA)

4 CO2

2 ATP (by substrate level phophorylation)

6 NADH

2 FADH2

Electron Transport System (ETS)

• ETS is also known as Electron Transfer Phosphorylation

• ETS occurs at proteins located on the inner membrane of the mitochondria

Electron Transport System (ETS)

• ETS Proteins– Some of the ETS proteins are called

cytochromes

– Some of the ETS proteins are proton (H+) pumps

– ATP is made by the enzyme ATP synthase

ETS

• NADH and FADH2 proceed to the ETS

– Process starts when they give up 2e and H+ to a specific ETS protein

– In the process NADH and FADH2 are

• ? Oxidized or reduced?

ETS

• H+ from the matrix follow the electrons into proton pumps (complex I, III, IV) and the H+ are pumped out of the matrix

ETS

• The electrons continue to be passed from ETS protein to ETS protein

– At each proton pump, H + from the matrix pumped out of the matrix

ETS

• This creates an electrical & chemical gradient

– Form of _________ energy

ETS

• Electron transfer stops when the last ETS protein transfers the 2e to oxygen which:– Joins with H+ to form water

ETS and ATP Synthesis

• Back to the H+ ions pumped into the outer compartment

– Potential energy of their electrical/chemical gradient is used to make ATP at ATP synthase


• The enzyme ATP synthase is also embedded in the inner membrane of the mitochondria

• The flow of H+ through this enzyme releases energy and ATP is made.– called oxidative phosphorylation

4


• The more H+ pumped out of the matrix, the more potential energy, and the more ATP that can be made by ATP synthase


• Each NADH made in the mito. results in enough H+ being pumped out of the matrix to make 3 ATP.

• Each FADH2 results in enough H+ being pumped out of the matrix to make 2 ATP.

NADH from Glycolysis

• The NADH made in glycolysis must enter the matrix in order to deliver their electrons to the ETS

• How they “enter” the mitochondria depends upon the cell type.


• In most cells the 2 NADH made in glycolysis pass their electrons and H+ to FAD in the matrix making:– 2 NAD+ -- remain in the cytoplasm and are reused in

glycolysis

– 2 FADH2 -- take the electrons and H+ to the ETS where a total of ____ ATP are made


• In liver, heart, and kidney cells the 2 NADH are able to enter the matrix.– The 2 NADH take their electrons and H+ to the ETS

where a total of ____ ATP are made

ATP Synthesis Summary

• Glycolysis– ____ ATP (net) (method?)– ____ NADH ____ ATP (most cells)

• Preparatory step– ____ ATP– _____ NADH ____ ATP (method?)

ATP Synthesis Summary

• Krebs Cycle____ ATP (method?)

____ NADH ____ ATP (method?)

____ FADH2 ____ ATP (method?)

Fermentation

• Under anaerobic conditions the products of glycolysis enter fermentation reactions.

• All fermentation reactions occur in the cytoplasm.

Fermentation

• The purpose of all fermentation is to regenerate NAD+ so that glycolysis can continue.– Cell’s have a limited supply of NAD +

– The cell’s major source of NAD+ is the first step of the ETS

– Under anaerobic conditions the Krebs cycle and ETS stop….

Fermentation

• The two most common forms of fermentation are:– Lacate fermentation– Alcoholic fermentation

• Which type of fermentation occurs depends upon the organism.

Lactate Fermentation

• Lactate fermentation occurs in:– Humans and all other animals– Many bacteria

• including those used to make many cheeses


2 Pyruvate* (3C)

2 Lactate* (3C)

* Also called: pyruvic acid and lactic acid

2 NADH

2 NAD+ glycolysis


• Lactate build up in the cell results in:– Increased blood supply to the area

• Blood brings oxygen

• Blood “washes” out the lactate– Lactate is taken to the liver where it is converted back to

pyruvate (called the Cori cycle)

– Lactate in the blood can cause acidosis

– If the lactate levels get too high cramping occurs• Painful

Alcoholic Fermentation

• Alcoholic fermentation occurs in:– Yeast (a fungus)

• used in making alcoholic beverages and “yeast” breads

– Many bacteria• Including those used to make Swiss cheese


2 Pyruvate (3C)

2 Acetaldehyde (2C)

2 Ethanol (2C)

__________

2 NADH

2 NAD+ - reused in glycolysis


• Ethanol build up in the cell ultimately denatures the cell’s proteins.– This results in cell death!– Wild yeasts die at 4% alcohol, wine making

yeasts die at 14% alcohol.


Reactions cannot be reversed.– Remember, the lactate fermentation reaction is

reversible • Lactate can be converted back to pyruvate in the

liver, not in the cell it’s made in

Documents

Chapter 8: How Cells Release Stored Energy. Overview of Carbohydrate Metabolism Glucose + 6 O 2 6 CO 2 + 6 H 2 O The overall reaction is exergonic