Energy, Metabolism, and Enzymes
Ch 6 Baboon
Ch 5.1-5.8 Bat
- Energy: the ability to do work
- Two major types of energy
1. Kinetic - energy of motion
- EX: movement, heat, electrical, radiant
2. Potential - stored energy
- EX: positional, chemical bonds, gravitational, charge
potential (battery)
- Energy is constantly being transformed from one
type to another
- EX: radiant energy from sunlight transformed into the
energy of chemical bonds (kinetic to potential)
1st and 2nd Law of Thermodynamics
- 1st Law - Law of Conservation of Energy
- Energy can be transformed or transferred but it can't be
or destroyed
created
- 2nd Law - Law of Entropy
- When energy is is transformed or transferred, some will be
"lost", usually as heat
- Every change in Energy results in the world becoming
disordered (chaotic)
- Entropy - the quantitative measure of disorder
more
Systems
- Open - when energy and matter can be transferred back
and forth between the system and its surroundings
EX: human body
- Closed - when energy and/or matter can NOT be
transferred back and forth between the system and its
surroundings
Energy of Life
- Living organisms require a constant supply of energy to perform
work that must take place in cells (powered by ATP)
- Mechanical work - cell division, muscle
contraction, cilia movement, etc...
- Transport work - pumping substances across membranes
- Chemical work - breaking and forming chemical bonds
- Energy flows from the non-living world into living organisms and
back
- Conversion of Radiant Energy to Chemical Energy
- Photosynthesis (makes glucose)
- Chemical Energy is transferred between organisms
- Energy is "lost" as heat along the way
Metabolism
- Metabolism is the sum total of all chemical reactions in
an organism (transformation of energy)
- Two types of reactions1. Catabolic reactions release energy by breaking
chemical bonds (complex ⇒ simple)
- also known as exergonic reactions because
they release
energy
- EX: Cellular respiration
2. Anabolic reactions use energy to make chemical bonds
(simple ⇒ complex)
- also known as endergonic reactions because
they
require energy
- EX: Photosynthesis
Exergonic
(Catabolic)
ΔG is negative, energy is given off
vs.
Endergonic
(Anabolic)
ΔG is positive, energy is absorbed
ΔG = amount of free energy in a system
These reactions are usually coupled in living things
- E released in exergonic is used to power endergonic
Enzymes
- Enzymes: proteins that act as catalysts for reactions
without being permanently altered or destroyed
- Catalyst: increases efficiency of reactions
- Enzymes frequently have the suffix "ase"
- Substrate: substance the enzyme acts on
- EX: enzyme salivary amylase breaks down starch
(substrate) in the food you eat
- EX: enzyme glycogen synthase that builds glucose into
glycogen
Enzyme - Substrate Relationships
- Enzyme - substrate relationships are specific
- Active site - point where substrate and enzyme interact (bind)
- Induced Fit Theory – active site is a crevice on the enzymes
surface which interacts with the substrate. Enzyme folds around
the substrate like a tight fitting glove
Enzymes and Chemical Reactions
- Reversibility - enzymes can break substances
down (catabolic) or help put them together
(anabolic)
Enzymes and Chemical Reactions
- Catabolic (exergonic)
- Enzymes weaken bonds of substrate so
less energy is needed to break it down
- lowers activation energy
- Anabolic (endergonic)
- Enzymes chemically align angles of
molecules to make bonding easier
Catabolic
Substrates
(reactants)
Enzyme
---------------->
Products
(sucrase enzyme)
Sucrose
---------------->
Fructose + Glucose
Enzymes and Chemical Reactions
- Activation energy: initial energy required to break chemical
bonds during an exergonic (catabolic) reaction
- i.e. Need to put a little E in before you can release some
Enzymes and Chemical Reactions
- Enzymes act as catalysts
- lower the activation energy required
Exergonic rx
Environmental Conditions
- Temperature
- higher temperature result in increased molecular motion
and higher kinetic energy. More collisions between
molecules lead to faster reactions
- in general an increase of 10°C doubles the rate of reactions
- too much heat can, however, can cause denaturation
Environmental Conditions
- pH
- most enzymes require a neutral pH
- Exceptions:
- Pepsin (stomach) needs pH 2
- Trypsin (intestine) needs pH 7
- Concentration of substrate and product
- Lots of substrate and little product = more product formed
- Lots of product and little substrate = more substrate formed
Cofactors
- Non-protein molecules that are necessary for
some enzymes to work
- Usually vitamins that must be ingested
by organisms
because the body does not naturally produce them
- EX: iron or zinc
- Sometimes called co-enzymes
Enzyme Inhibitors
1. Competitive inhibitors
- molecule binds to the active site, preventing substrate from
binding
- usually reversible
- EX: pesticides, drugs
2. Non-competitive inhibitors
- molecule binds to a region other than the active site
shape change in the enzyme
- EX: penicillin
- prevents enzymes used by bacteria to assemble the
from working
causing a
cell wall
Cooperativity
- Cooperativity
- Enzyme becomes more receptive to
substrate
molecules once one substrate
molecule has attached
- EX: once one molecule of oxygen binds to
hemoglobin
it encourages the molecule to
bind to several more
molecules of oxygen
Allosteric Regulation
- Allosteric enzymes
- enzymes have 2 kinds of binding sites
1. one site for the substrate (the active site)
2. one site called the allosteric site that allows the
be controlled
enzyme to
- Allosteric inhibitors: bind to the allosteric site and stop the
enzyme from functioning
- Allosteric activators: bind to the allosteric site and turn the
enzyme on.