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energy
the capacity to do work
2 types of energy
kinetic and potential
kinetic energy
energy of motion
potential energy
stored energy
how do we get energy?
light energy absorbed by chloroplasts in plant cells
plants photosynthesize glucose
animals/humans consume glucose, breaking it down into water and CO2
energy stored in the bonds between carbon atoms, ATP released when these bonds are broken
what happens to energy between transitions
some energy is lost as heat
the laws of thermodynamics
energy cannot be created or destroyed, only converted
energy transformation creates disorder outside of the cell
entropy
a measure of disorder - heat released that is unavailable to do work
oxidation-reduction reactions (redox reactions)
transfers energy; often involves hydrogen
oxidation
atom or molecule loses an electron (gains positive charge)
reduction
atom or molecule gains an electron (gains negative charge)
metabolism
all chemical reactions of a cell or organism
metabolic pathway
series of biochemical reactions that converts one or more substrates (reactants) into a final product
catabolic reactions
breaks down larger molecules - releases energy
examples of catabolic reactions
hydrolysis, cellular respiration
anabolic reactions
synthesizes larger molecules - uses energy
examples of anabolic reactions
dehydration synthesis, photosynthesis
free energy
the amount of energy available to do work; also known as G
Gibb’s free energy (G)
all chemical reactions affect G
ΔG (delta G)
abbreviation for a change in G after a reaction
free energy formula
ΔG = ΔH - TΔS
chemical reactions can be predicted based on…
…changes in free energy
positive ΔG
products have more free energy than reactants
nonspontaneous; requires input of energy
endergonic
anabolic
negative ΔG
products have less free energy than reactants
spontaneous
exergonic
catabolic
exergonic reaction
net release of free energy
spontaneous
negative ΔG
if energy is released in a chemical reaction…
…ΔG < 0 - products of these reactions will have less free energy than the reactants
endergonic reaction
absorbs free energy from its surroundings; requires energy
nonspontaneous
positive ΔG
if a chemical reaction requires an input of energy…
…ΔG G > 0 - products of these reactions will have more free energy than the reactants
activation energy
the energy required for a reaction to proceed
“transition state”
reactant(s) become contorted and unstable, which allows the bond(s) to be broken or made
reaction rate can be increased by:
increasing energy of reacting molecules (heating) or lowering activation energy (catalyst)
ATP (adenosine triphosphate)
bonds that link the 3 phosphate groups are high-energy bonds - when they are broken, the products have lower free energy than reactants
ADP
adenosine diphosphate - 2 phosphates
ATP cycle
energy released from splitting ATP is used during anabolic reactions, ATP is created during anabolic reactions
ATP is not used for ____
long-term energy storage
enzymes
protein catalysts that speed up reactions by lowering the required activation energy
enzymes bind with ___ ___
reactant molecules
enzyme-substrate specificity
enzymes catalyze a single reaction
what determines enzyme-substrate specificity?
the 3D shape of the enzyme and reactants (substrates) - substrate molecules interact at the enzyme’s active site
2 parts of enzyme’s active site
binding and catalytic sites
binding sites
bind and orient substrate(s)
catalytic sites
reduce chemical activation energy
what determines the active site?
the proteins primary sequence and tertiary structure; protein folding brings specific amino acids close to each other to form the active site
induced fit
a slight change in enzyme chape maximizes catalysis
changes in pH on enzyme activity
can reduce substrate-enzyme binding
changes in temp on enzyme activity
can denature the enzyme (loss of shape)
enzymes lower activity rate by:
helping the substrate reach its transition state
enzymes help the substrate reach transition state by either:
positioning 2 substrates to they align for the reaction
provide an optimal environment within the active site for the reaction
contort/stress the substrate so it’s less stable and more likely to react
temporarily react with the substrate (chemically change it) making it less stable and more likely to react
what happens after a catalyzed reaction?
the product is released and the enzyme becomes available to catalyze another reaction
enzyme activity regulation
helps cells control their environment to meet their specific needs
enzyme activity can be regulated by:
modifications in temp or pH
production of molecules that inhibit or promote enzyme function
availability of coenzymes or cofactors
coenzymes
organic molecules - including ATP, NADH+, vitamins
cofactors
inorganic ions
how are coenzymes/cofactors provided?
from diet
2 forms of enzyme inhibition
competitive and allosteric (noncompetitive) inhibitors
competitive inhibitor
binds to active site to block substrate
slows reactions rates
does not effect maximal rate
allosteric (noncompetitive) inhibitor
binds in a separate site to change 3D shape of enzyme and therefore active site, so the substrate cannot fit
slows reaction rates
reduces maximal rate
maximal rate
speed of a reaction when substrate is not limited
feedback inhibition
where the end product of the metabolic pathway inhibits an upstream step; one reaction along pathway can inhibit another reaction