Transcript Ch 8 Notes

2.a.1 – All living systems require constant
input of free energy (8.1-8.3).
 4.b.1 – Interactions between molecules
affect their structure and function (8.4 &
8.5).

The totality of an organism’s chemical
processes
 Concerned with managing the material
and energy resources of the cell

Pathways that break down complex
molecules into smaller ones, releasing
energy
 Example: Cellular respiration
 DOWNHILL!

Pathways that consume energy, building
complex molecules from smaller ones
 Example: Photosynthesis, condensation
synthesis
 UPHILL!

Energy cannot be created or destroyed
 It can be converted from one form to
another
 The sum of the energy before the
conversion is equal to the sum of the
energy after the conversion

Some usable energy dissipates during
transformations and is lost
 During changes from one form of energy
to another, some usable energy
dissipates, usually as heat
 The amount of usable energy therefore
decreases

Ability to do work
 The ability to rearrange a collection of
matter
 Forms of energy:
› Kinetic
› Potential
› Activation


Kinetic:
› Energy of action or motion
› Ex: heat/thermal energy

Potential:
› Stored energy or the capacity to do work
› Ex: chemical energy

Energy needed to convert potential
energy into kinetic energy
Activation Energy
Potential Energy
The portion of a system's energy that can
perform work
 Known as ΔG

ΔG = Δ H - T Δ S
Δ = change (final-initial)
ΔG = free energy of a system
ΔH = total energy of a system
(enthalpy)
T = temperature in oK
ΔS = entropy of a system
 If
the system has:
› more free energy=less stable (greater
work capacity)
› less free energy=more stable (less work
capacity)
› As rxn moves towards equilibrium, ΔG
will decrease
These are the source of energy for living
systems
 They are based on free energy changes
 Two types: exergonic and endergonic

 Exergonic:
› chemical reactions with a net
release of free energy
› Ex: cellular respiration
› - ΔG , energy out, spontaneous
 Endergonic:
› chemical reactions that absorb free
energy from the surroundings
› Ex: Photosynthesis
› + ΔG , energy in, non-spontaneous
- ΔG
+ΔG
Couples an exergonic process to drive
an endergonic one
 ATP is used to couple the reactions
together
 Types: mechanical, transport, chemical

 Adenosine
Triphosphate
 Made of:
1. Adenine (nitrogenous base)
2. Ribose (pentose sugar)
3. 3 phosphate groups*
*bonds can be broken to make ADP
Three phosphate groups and the energy
they contain
 Negative charges repel each other and
makes the phosphates unstable

› Tail is unstable = more free energy = more
instability
Works by energizing other molecules by
transferring phosphate groups
 Hydrolysis of ATP = free energy is released
as heat (can be adv or not adv)

Energy released from ATP drives
anabolic reactions
 Energy from catabolic reactions
“recharges” ATP
 Very fast cycle

› 10 million made per second
Coupled
RXN
Takes place in
cytoplasm and
mitochondria
 Using special
process called
substrate-level
phosphorylation

› Energy from a high-
energy substrate is
used to transfer a
phosphate group to
ADP to form ATP
Biological catalysts made of protein
 Speeds up rxn without being consumed
 Cause the speed/rate of a chemical rxn
to increase

› By lowering activation energy
AB + CD
AC + BD
*AB and CD are “reactants”
*AC and BD are “products”
*Involves bond forming/breaking
*Transition state: can be unstable
Unstable
state
Energy is
released
as heat
 Lower
the activation energy for a
chemical reaction to take place
 Why do we need enzymes?
› Cells can’t rely on heat to kick start rxns
› Why? Denaturation, heat can’t decipher
between rxns
› Enzymes are selective! Can only operate
on a given chemical rxn

Substrate –
› the material the enzyme works on

Enzyme names:
› Ex. Sucrase
› “- ase” name of an enzyme
› 1st part tells what the substrate is (i.e. Sucrose)
Some older known enzymes don't fit this
naming pattern
 Examples: pepsin, trypsin

The area of an enzyme that binds to
the substrate
 Structure is designed to fit the
molecular shape of the substrate
 Therefore, each enzyme is substrate
specific

Enzyme +
Subtrate
EnzymeSub complex
Enzyme +
Product
Notice: Complex becomes product, but
enzyme stays the same! Enzyme is NOT
CONSUMED!
Lock and Key model
2. Induced Fit model
1.
Reminder: Enzymes and substrates are
usually held together by weak
chemical interactions (H/ionic bonds)

Substrate (key) fits to the active site
(lock) which provides a
microenvironment for the specific
reaction

Substrate “almost” fits into the active site,
causing a strain on the chemical bonds,
allowing the reaction
Usually specific to one substrate
 Each chemical reaction in a cell requires
its own enzyme
 Don’t change during rxn
 Always catalyze in direction towards
equilibrium

1)
2)
3)
4)
Active site is template for enzyme
Enzymes may break/stretch bonds
needed to be broken/stretched
Active site is microenvironment
Active site directly participates in
chemical rxn
 Environment
 Cofactors
 Coenzymes
 Inhibitors
 Allosteric
Sites
Factors that change protein structure
will affect an enzyme.
 Examples:

› pH shifts (6-8 optimal)
› Temperature (up, inc activity)
› Salt concentrations

Cofactors:
› Non-protein helpers for catalytic
activity
› Examples: Iron, Zinc, Copper

Coenzymes:
› Organic molecules that affect
catalytic activity
› Examples: Vitamins, Minerals, usually
proteins
Inhibitor
video
 Competitive
› mimic the substrate and bind to the active
site (compete for active site)
› Toxins/poisons – Ex: DDT
› Can be used in medicine – painkillers,
antibiotics

Noncompetitive
› bind to some other part of the enzyme
› Causes active site to change shape











Identify forms of energy and energy transformations.
Recognize the Laws of Thermodynamics.
Recognize that organisms live at the expense of free energy.
Relate free-energy to metabolism.
Identify exergonic and endergonic reactions.
Identify the structure and hydrolysis of ATP.
Recognize how ATP works and is coupled to metabolism.
Recognize the ATP cycle
Relate enzymes and activation energy.
Recognize factors that affect enzymes specificity and
enzyme activity..
Recognize factors that control metabolism.