Energy transformations and Enzymes Flashcards
(97 cards)
1
Q
1st law of thermodynamics
A
Energy is not created or destroyed in a closed system but it can be transformed
2
Q
Energy is…
A
the capacity to do work
3
Q
Potential energy
A
Energy stored as chemical bonds, concentration gradients, etc.
4
Q
Kinetic energy
A
The energy of movement
5
Q
Metabolism
A
Sum total of all chemical reactions occurring in a biological system at a given time
6
Q
Anabolic metabolism
A
Complex molecules are made from simple molecules; energy is required
7
Q
Catabolic metabolism
A
Complex molecules are broken down to smaller ones; energy is released
8
Q
2nd law of thermodynamics
A
When energy is converted from one form to another, some of that energy becomes unavailable to do work
9
Q
Entropy (S)
A
A measure of the disorder in a system
10
Q
Enthalpy (H)
A
Total energy
11
Q
Free energy (G)
A
The usable energy that can do work
12
Q
Unusable energy is represented by entropy multiplied by the absolute temperature
A
H=G+TS
13
Q
If change in G is -
A
free energy is released
14
Q
If change in G is +
A
free energy is required
15
Q
If free energy is not available
A
the reaction does not occur
16
Q
Exergonic reaction
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release free energy
17
Q
Catabolism
A
Complexity decreases (generates disorder)
18
Q
Endergonic reaction
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Consume free energy
19
Q
Anabolism
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Complexity (order) increases
20
Q
ATP can be ______ to ADP and P
A
Hydrolyzed
21
Q
ATP ____ and ____ free energy
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Captures; transfers
22
Q
ATP can also ______
A
Phosphorylate; donate a phosphate group to other molecules
23
Q
When ATP hydrolysis releases so much energy
A
- Phosphate groups have negative charges and repel each other- the energy needed to get them close enough to bond is stored in the P-O bond
- The free energy of the P-O bond is much higher than the energy of the O-H bond that forms after hydrolysis
24
Q
How many cycles of synthesis and hydrolysis does each ATP molecule go through everyday?
A
10,000
25
Energy is released by hydrolysis of ATP can be used to drive an _______
Endergonic reaction
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Metabolic pathways
Chemical reactions in cells are organized in metabolic pathways that are interconnected
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The complex pathways are modeled using computer algorithms
Systems biology
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Enzymes help ____ and ______ metabolic pathways
organize and regulate
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Most biological catalysts are enzymes (proteins)
Act as a framework in which reactions can take place
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Catalysts
Increase rates of chemical reactions
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Activation energy
The amount of energy required to start the reaction
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Activation energy puts the reactants in a reactive model called the
transition state
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Transition state intermediates
Activation energy changes the reactants into unstable forms with higher free energy
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Activation energy can come from___
heating the system
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Enzymes ____ the energy barrier by bringing reactants together
lower
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Enzymes are _____
highly specific
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Reactants are called ____
substrates
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Substrate molecules bind to the ____ of the enzyme
active site
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The 3D shape of the enzyme determines the ____
specificity
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The enzyme substrate complex is held together by
hydrogen bonds, electrical attraction, or covalent bonds
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Enzymes ____ the energy barrier for reactions
lower
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An enzyme may use one or more mechanisms to catalyze a reaction
Orient substrates so they can react
Induce strain by stretching the substrate-makes the bonds unstable and more reactive to other substates
Temporarily add chemical group
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Enzyme specifity depends on
precise interlocking of molecular shapes
interactions of chemical groups at the active site of
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Induced fit
some enzymes change shape when it binds the substrate, which alters the shape of the active site
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Rate of catalyzed reaction depends on
substrate concentration
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Concentration of an enzyme is usually much _____ than the substrate
lower
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At saturation
all enzyme is bound to substrate; it is working at maximum rate
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Enzyme activity can be controlled in two ways
Regulation of gene expression and regulation of enzyme activity
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Enzyme inhibitors
Molecules that bind to the enzyme and slow reaction rates
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Naturally occurring inhibitors
regulate metabolism
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Artificial inhibitors
Can be used to treat disease, kill pets, or study how enzymes work
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Reversible inhibition
Inhibitor bonds noncovalently to the active site and prevents substrate from binding
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Competitive inhibitors
Compete with the natural substrate for binding sites
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Uncompetitive inhibitors
bind to the enzyme-substrate complex, preventing release of products
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Noncompetitive inhibitors
bind to enzyme at a different site (not the active site)
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Allosteric regulation
A non-substrate molecule binds enzyme at a site different than the active site, which changes enzyme shape
Active form-cannot bind substrate
Inactive form- cannot bind substrate
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Most allosteric enzymes are proteins with
quaternary structure
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Inhibitors and activators bind to other polypeptides called
regulatory subunits, at regulatory sites (allosteric sites)
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Feedback inhibition
the final product acts as a noncompetitive inhibitor of the first enzyme, which shuts down the pathway
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Reversible phosphorylation
Regulates many enzymes
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By being heated
enzymes can lose tertiary structure and become denatured
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Every enzyme is most active at a particular Ph which ____
Influences ionization of functional groups
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At low Ph (high H+) COO- may react with H+ to form
COOH (no longer charged); this affects folding and thus enzyme function
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Cells harvest chemical energy from
glucose oxidation
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Metabolic pathways
a coordinated series of biological reactions catalyzed by enzymes that convert molecules into other molecules
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5 principles
complex transformations occur in a series of seperate reactions
each reaction is catalyze by a specific enzyme
many metabolic pathways are similar in all organisms
In eukaryotes, metabolic pathways are compartmentalized in specific organelles
Key enzymes can be inhibited or activated to alter the rate of the pathway
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Three catabolic processes harvest energy from glucose
glycolysis (anaerobic)
cellular respiration (aerobic)
fermentation ( anaerobic)
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Oxidation-reduced (redox) reactions
one substance transfers electrons to another substance
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Reduction
gain of electrons
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Oxidation
Loss of electrons
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If a carbon containing molecule gains H or loses O, its likely been ____ (gained electrons or electron density) and its an oxidizing agent
reduced
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If a carbon containing molecule lose H or gains O, its likely been ______ (lost electrons or electron density) and is a reducing agent
oxidized
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Conversions of C-C bonds to C=O bonds is _____
oxidation because there is a net movement of electrons away from C
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Coenzyme NAD+ is a key electron carrier in
biological redox reactions
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Glycolysis
takes place in cytoplasm
converts glucose into 2 molecules of pyruvate
produces 2 ATP and 2 NADH
occurs in 10 steps
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step 1-5 requires ____
ATP; 2 ATP input
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Steps 6-10 yield
NADH and ATP; yields 4 ATP and 2 NADH
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Pyruvate oxidation
Occurs in the mitochondrial matrix
Pyruvate is oxidized to acetate and CO2
Acetate bonds with coenzyme A to form acetyl CoA
One NAD+ is reduced to NADH
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What is the starting point for the citric acid cycle?
Acetyl CoA
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Acetyl CoA donates its acetyl group to ______, forming citrate
oxaloacetate
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8 reactions completely oxidize the acetyl group to ____
2 molecules of CO2
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Energy released is captured by
GDP
NAD+
FAD+
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Oxidative phosphorylation
The reason our cells need oxygen
ATP synthesized by reoxidation of electron carriers in the presence of O2
Two componets: electron transport and chemiosmosis
Occurs in the mitochondrial inner membrane
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Electron transport
electrons from NADH and FADH2 pass thru the respiratory chain of membrane-associated electron carriers in the mitochondria
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Chemiosmosis
protons flow back across the membrane thru a channel protein, ATP synthase, which couples diffusion with ATP synthesis
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When H+ diffuse in chemiosmosis, potential energy is converted into _____, rotating the central polypeptide and transferring energy to the FI subunit
Kinetic enery
Energy used to make ATP (about 28)
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Lactic acid fermentation
pyruvate is the electron acceptor; lactate is the product
lactate dehydrogenase catalyzes fermentation
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Alcoholic fermentation
yeast and some plant cells
requires two enzymes to metabolize pyruvate to ethanol
products are CO2, ethanol, and 2 ATP
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Catabolic interconversions
polysaccharides are hydrolyzed to glucose and enters glycolysis
lips are broken down
proteins are hydrolyzed to amino acids-> glycolysis or citric acid cycle
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Anabolic interconversions
glucogenesis- citric acid cycle and glycolysis intermediates are reduced to form glucose
acetyl CoA can be used to form fatty acids
citric acid cycle intermediates can be use to synthesize nucleic acid componets
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How do cells decide which pathway to use?
Levels of substrates in the metabolic pool are quite constant
Organisms regulate enzymes to maintain balance between catabolism and anabolism
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Mechanisms that regulate rates of each step in a metabolic pathway
change the amount of active enzyme by regulating gene expression
change enzyme activity by covalent modifications
feedback inhibition by allosteric enzymes
substrate availability
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Glycolysis and citric acid cycle are subject to
allosteric regulation of key enzymes
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The main control point in glycolysis is
phosphofructokinase which inhibited by ATP
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The main control point in the citric acid cycle is
isocitrate dehydrogenase
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Acetyl CoA is another control point
if ATP levels are high and the citric acid cycle shuts down, the accumulation of citrate activates fatty acid synthesis from acetyl CoA, diverting it to storage
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Irreversible inhibition
inhibitor covalently bonds to side chains in the active site and permanently inactivates the enzyme
