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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
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
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!
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
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
36
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.
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
Copyright © Cengage Learning. All rights reserved
48
• 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