Metabolism

And a little on enzymes too!

Enzyme Summary

– Most enzymes are proteins.

– Speed up reactions by lowering the EA

– Enzymes are substrate specific – Enzymes are not permanently changed in the

reaction.• Enzymes can be used over and over again.

– A single enzyme may act on thousands or millions of substrate molecules per second!

Enzyme availablewith empty activesite

Active site

Glucose

Fructose

Products arereleased

Enzyme(sucrase)

Substrate(sucrose)

H2O

Substrate isconverted toproducts

Substrate bindsto enzyme withinduced fit

Enzyme Terms

• Simple enzyme – protein only

• Conjugated enzyme – protein and nonprotein components– Protein = apoenzyme– Nonprotein = cofactor

• Add additional functional groups to those of the amino acids

– Holoenzyme = protein and cofactor together• Biologically active

Cofactors

• Organic cofactors are called coenzymes– Many vitamins serve as coenzymes

• Minerals often serve as inorganic co-factors– Typically have 2+ charge– Ca+2 Mg+2 Fe+2 Zn+2

Enzyme Inhibitors

• Inhibitors are substances that interfere with an enzyme’s ability to function – Many toxins/poisons are enzyme inhibitors

• For example: Mercury binds to sulfur groups on enzymes and cause the enzyme to change shape and lose function

Enzyme Inhibitors

• Inhibitors may bind to the enzyme with covalent bonds or H bonds– Covalent bonding inhibitors irreversible

inhibition

– H bonding inhibitors reversible inhibition

More on Enzyme Inhibitors

• Irreversible enzyme inhibitors have many uses.– Some inhibitors are deadly

• Cyanide – inhibits an enzyme needed to make ATP

• Sarin – inhibits an enzyme needed for nerve transmission

• Pesticides and herbicides – bind to key enzymes in insects and plants

Types of Inhibitors

• Competitive inhibitors – compete with the substrate for binding at the active site– Competitive inhibitors are similar in structure

to the “real” substrate

Types of Inhibitors

• Noncompetitive inhibitors – bind to the enzyme at a location other than the active site– Binding changes the shape of the active site

so that the substrate cannot bind• Called allosteric control

– Release of the inhibitor returns the active site to its proper shape

Substrate

Enzyme

Active site

Normal binding of substrate

Competitiveinhibitor

NoncompetitiveInhibitor -- also called an allostericinhibitor

Enzyme inhibition

Key Players in Metabolism

ATP – cell’s primary energy carrier

FAD and NAD+

Synthesis of FADH2 and NADH

• Oxidation – loss of electrons

• Reduction – gain of electrons

o Reduction often involves adding H+ to a substance.

o The reactions shown are ______ reactions.

FAD+ 2 H+ + 2e FADH2

NAD+ + 2H + + 2e NADH + H +

oThese reactions are coupled with _________ reactions

Co-Enzyme A

Co-Enzyme A binds an acetyl group at the –SH group, an acetyl replaces the H and a thioester forms

Common Metabolic Pathways

• Citric Acid Cycle– Also called the Krebs Cycle

• Electron Transport Chain

• Oxidative Phosphorylation

• All occur in the mitochondria

Fats, Carbohydrates, Proteins

• See board for an overview of how the 3 energy-yielding nutrients enter the common metabolic pathways.

Carbohydrate Metabolism

• Our focus will be on the metabolism of carbohydrates.– Metabolic pathway called glycolysis

prepares carbohydrates for entry into the common metabolic pathways

Mitochondrion

CO2 CO2

NADH

ATP

High-energy electronscarried by NADH

NADH

CITRIC ACID

CYCLE

GLYCOLYSIS

PyruvateGlucose

andFADH2

Substrate-levelphosphorylation

Substrate-levelphosphorylation

OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)

Oxidativephosphorylation

ATPATP

CytoplasmInnermitochondrialmembrane

Carbohydrate Metabolism

• Glucose is the cell’s primary source of energy.

• Glucose needs to be converted to acetyl groups to enter the citric acid cycle. This requires 2 pathways:

1. Glycolysis – does not require oxygen.

2. Preparatory step (your text doesn’t name this step).– This step requires aerobic conditions

Glycolysis

• In a series of biochemical reactions glucose is converted into: 2 pyruvate– 3 C carboxylic acids

• In the process:– 2 NADH are made– 2 ATP are converted to ADP– 4 ATP are made

• Net gain of _____ 2 ATP

Glucose

NAD+

+2

2 ADP

NADH2

P2

2

ATP2 +

H+

2 Pyruvate

Glycolysis

simple form

(Net)

Steps – ATP and pyruvateare produced.

Step A redox reactiongenerates NADH.

Step A six-carbon intermediate splitsInto two three-carbon intermediates.

Steps – A fuel molecule is energized,using ATP.

ENERGY INVESTMENTPHASEGlucose

Glucose-6-phosphate

1

Fructose-6-phosphate

Step

ADP

ATP

P

3

ADP

ATP

P

2

P

4

P Fructose-1,6-bisphosphate

5 5

PP

P

P

P

P

NAD+

PP

ENERGY PAYOFF PHASE

Glyceraldehyde-3-phosphate(G3P)

1,3-Bisphosphoglycerate

NADH

NAD+

NADH

+ H+ + H+

ADP ADP

ATP ATP6 6

3-Phosphoglycerate

2-Phosphoglycerate

7 7

8 8

P P

P P

P P

H2O H2O

ADP ADP

ATP ATP

9 9

Phosphoenolpyruvate(PEP)

Pyruvate

1 3

4

5

6 9

Glycolysis

Not so simple form!

Glycolysis

Glycolysis, cont’d

Fates of Pyruvate

• What happens to the pyruvates made during glycolysis depends upon:– Cell conditions.

• Is O2 present or not?

– Type of organism

Anaerobic Conditions - Fermentation

• Under anaerobic conditions the pyruvate remain in the cytoplasm and are converted to either lactate or ethanol– Which depends on the organism– Called fermentation

• NADH are converted back to NAD+ during the fermentation reaction(s)– NAD+ is used to keep glycolysis going

Alcoholic Fermentation

Alcoholic fermentation occurs in yeast and other organisms.

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Lactate Fermentation

• Lactate fermentation occurs in animals and other organisms.

Cori Cycle - Glucogenesis

Gert and Carl Cori

Aerobic Conditions

• Under aerobic conditions the pyruvate are converted into acetyl Co-A as they enter the matrix of the mitochondria.– The acetyl Co-A then enter into the Citric Acid

Cycle– The NADH made in glycolysis deliver their

electrons and hydrogen ions to the ETC

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Aerobic Conditions

Pyruvate is converted to acetyl CoA and enters the citric acid cycle O

||

CH3–C –COO- + NAD+ + CoA

pyruvate

O

||

CH3–C –CoA + CO2 + NADH + H+

acetyl CoA

Citric Acid Cycle

• Citric acid cycle is a series of reactions in which acetyl (2C) groups are oxidized to form:– 2 CO2

– 3 NADH

– 1 FADH2

– 1 GTP which is used to make ATP• many texts show as ATP

Citric Acid Cycle Reaction Types

• Isomerization – rearranges atoms in molecule

• Hydration – adds water

• Decarboxylation reaction CO2

• Oxidation/reduction reactions NADH and FADH2

• Phosphorylation reaction GTP (ATP)– Called substrate-level phosphorylation

Citric Acid Cycle

• Citric acid cycle is a series of reactions in which acetyl (2C) groups are oxidized to form:– 2 CO2

– 3 NADH

– 1 FADH2

– 1 GTP which is used to make ATP• many texts show as ATP

NADH and FADH2

• NADH and FADH2 deliver H+ and electrons to the Electron Transport Chain (ETC).

• The ETC is a series of electron carriers and enzymes located on the inner membrane of the mitochondria.

Electron Transport Chain

ETC – Proton Pumps

ETC

• The pumping of protons (H+) into the intermembrane space creates a chemical gradient.

• This gradient is a form of potential energy.

• The more protons pumped into the space, the more potential energy.

– Therefore ______ creates more potential energy than _______.

ATP Synthesis at ATP Synthase

• 1 ATP is made for every 4 H+ that pass through ATP synthase– Each NADH results in 10 H+ being pumped

out of the matrix 2.5 ATP/NADH

– Each FADH2 results in 6 H+ being pumped out of the matrix 1.5 ATP/NADH

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• Ten molecules of ATP are produced for each acetyl CoA catabolized

– 3 NADH 7.5 ATP– 1 FADH2 1.5 ATP– 1 GTP 1 ATP

Total 10 ATP per Acetyl CoA

ATP Summary/Glucose• Glycolysis

– 2 ATP net– 2 NADH 3 or 5 ATP depending on cell type

• Pyruvate Acetyl Co-A– 2 NADH 5 ATP

• Citric Acid Cycle– 2 GTP 2 ATP– 6 NADH 15 ATP

– 2 FADH2 3 ATP TOTAL: 30 (32) ATP