Energy transformations and Enzymes Flashcards
1st law of thermodynamics
Energy is not created or destroyed in a closed system but it can be transformed
Energy is…
the capacity to do work
Potential energy
Energy stored as chemical bonds, concentration gradients, etc.
Kinetic energy
The energy of movement
Metabolism
Sum total of all chemical reactions occurring in a biological system at a given time
Anabolic metabolism
Complex molecules are made from simple molecules; energy is required
Catabolic metabolism
Complex molecules are broken down to smaller ones; energy is released
2nd law of thermodynamics
When energy is converted from one form to another, some of that energy becomes unavailable to do work
Entropy (S)
A measure of the disorder in a system
Enthalpy (H)
Total energy
Free energy (G)
The usable energy that can do work
Unusable energy is represented by entropy multiplied by the absolute temperature
H=G+TS
If change in G is -
free energy is released
If change in G is +
free energy is required
If free energy is not available
the reaction does not occur
Exergonic reaction
release free energy
Catabolism
Complexity decreases (generates disorder)
Endergonic reaction
Consume free energy
Anabolism
Complexity (order) increases
ATP can be ______ to ADP and P
Hydrolyzed
ATP ____ and ____ free energy
Captures; transfers
ATP can also ______
Phosphorylate; donate a phosphate group to other molecules
When ATP hydrolysis releases so much energy
- 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
How many cycles of synthesis and hydrolysis does each ATP molecule go through everyday?
10,000
Energy is released by hydrolysis of ATP can be used to drive an _______
Endergonic reaction
Metabolic pathways
Chemical reactions in cells are organized in metabolic pathways that are interconnected
The complex pathways are modeled using computer algorithms
Systems biology
Enzymes help ____ and ______ metabolic pathways
organize and regulate
Most biological catalysts are enzymes (proteins)
Act as a framework in which reactions can take place
Catalysts
Increase rates of chemical reactions
Activation energy
The amount of energy required to start the reaction
Activation energy puts the reactants in a reactive model called the
transition state
Transition state intermediates
Activation energy changes the reactants into unstable forms with higher free energy
Activation energy can come from___
heating the system
Enzymes ____ the energy barrier by bringing reactants together
lower
Enzymes are _____
highly specific
Reactants are called ____
substrates
Substrate molecules bind to the ____ of the enzyme
active site
The 3D shape of the enzyme determines the ____
specificity
The enzyme substrate complex is held together by
hydrogen bonds, electrical attraction, or covalent bonds
Enzymes ____ the energy barrier for reactions
lower
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
Enzyme specifity depends on
precise interlocking of molecular shapes
interactions of chemical groups at the active site of
Induced fit
some enzymes change shape when it binds the substrate, which alters the shape of the active site
Rate of catalyzed reaction depends on
substrate concentration
Concentration of an enzyme is usually much _____ than the substrate
lower
At saturation
all enzyme is bound to substrate; it is working at maximum rate
Enzyme activity can be controlled in two ways
Regulation of gene expression and regulation of enzyme activity
Enzyme inhibitors
Molecules that bind to the enzyme and slow reaction rates
Naturally occurring inhibitors
regulate metabolism
Artificial inhibitors
Can be used to treat disease, kill pets, or study how enzymes work
Reversible inhibition
Inhibitor bonds noncovalently to the active site and prevents substrate from binding
Competitive inhibitors
Compete with the natural substrate for binding sites
Uncompetitive inhibitors
bind to the enzyme-substrate complex, preventing release of products
Noncompetitive inhibitors
bind to enzyme at a different site (not the active site)
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
Most allosteric enzymes are proteins with
quaternary structure
Inhibitors and activators bind to other polypeptides called
regulatory subunits, at regulatory sites (allosteric sites)
Feedback inhibition
the final product acts as a noncompetitive inhibitor of the first enzyme, which shuts down the pathway
Reversible phosphorylation
Regulates many enzymes
By being heated
enzymes can lose tertiary structure and become denatured
Every enzyme is most active at a particular Ph which ____
Influences ionization of functional groups
At low Ph (high H+) COO- may react with H+ to form
COOH (no longer charged); this affects folding and thus enzyme function
Cells harvest chemical energy from
glucose oxidation
Metabolic pathways
a coordinated series of biological reactions catalyzed by enzymes that convert molecules into other molecules
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
Three catabolic processes harvest energy from glucose
glycolysis (anaerobic)
cellular respiration (aerobic)
fermentation ( anaerobic)
Oxidation-reduced (redox) reactions
one substance transfers electrons to another substance
Reduction
gain of electrons
Oxidation
Loss of electrons
If a carbon containing molecule gains H or loses O, its likely been ____ (gained electrons or electron density) and its an oxidizing agent
reduced
If a carbon containing molecule lose H or gains O, its likely been ______ (lost electrons or electron density) and is a reducing agent
oxidized
Conversions of C-C bonds to C=O bonds is _____
oxidation because there is a net movement of electrons away from C
Coenzyme NAD+ is a key electron carrier in
biological redox reactions
Glycolysis
takes place in cytoplasm
converts glucose into 2 molecules of pyruvate
produces 2 ATP and 2 NADH
occurs in 10 steps
step 1-5 requires ____
ATP; 2 ATP input
Steps 6-10 yield
NADH and ATP; yields 4 ATP and 2 NADH
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
What is the starting point for the citric acid cycle?
Acetyl CoA
Acetyl CoA donates its acetyl group to ______, forming citrate
oxaloacetate
8 reactions completely oxidize the acetyl group to ____
2 molecules of CO2
Energy released is captured by
GDP
NAD+
FAD+
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
Electron transport
electrons from NADH and FADH2 pass thru the respiratory chain of membrane-associated electron carriers in the mitochondria
Chemiosmosis
protons flow back across the membrane thru a channel protein, ATP synthase, which couples diffusion with ATP synthesis
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)
Lactic acid fermentation
pyruvate is the electron acceptor; lactate is the product
lactate dehydrogenase catalyzes fermentation
Alcoholic fermentation
yeast and some plant cells
requires two enzymes to metabolize pyruvate to ethanol
products are CO2, ethanol, and 2 ATP
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
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
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
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
Glycolysis and citric acid cycle are subject to
allosteric regulation of key enzymes
The main control point in glycolysis is
phosphofructokinase which inhibited by ATP
The main control point in the citric acid cycle is
isocitrate dehydrogenase
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
Irreversible inhibition
inhibitor covalently bonds to side chains in the active site and permanently inactivates the enzyme
