Download Chapter 5: The Working Cell

Chapter 5: The Working Cell
Energy and Work
 Thousands of chemical reactions taking place inside
cells and organisms.
o Many of these reactions require an investment of
energy.
 Energy – the capacity to perform work.
o Work – when an object is moved against an
opposing force: gravity, friction, rearrange
atoms in matter.
 Two Types of Energy
o Kinetic Energy – Energy of motion
 Moving objects perform work by
transferring motion to other matter.
o Potential Energy – Energy of position or stored
energy
 Based on location or structure.
http://www.youtube.com/watch?v=vl4g7T5gw1M
http://www.schooltube.com/video/f147084ab011fc64a890/
Kinetic vs. Potential: Circle Potential and Box Kinetic (Both?)
Questions:
Quiz Yourself
1. Which letter shows the ball when it has the maximum
kinetic energy?
D
2. Which letter shows the ball when it has the maximum
potential energy?
A
3. Which letter shows the ball when it has just a little more
kinetic energy than A?
G
4. Which letter shows the ball when it has the least
potential energy?
D
5. Which letter shows the ball when it has just a little less
potential energy than letter F?
C
6. Which sequence correctly shows an increase in kinetic
energy?
A. E, F, B, G
B. B, F, E, C
C. D, E, B, F
D. A, G, F, C
D
Types of Potential Energy






Gravitation potential energy
Elastic potential energy
Electric potential energy
Magnetic potential energy
Nuclear potential energy
Chemical potential energy
o Molecules have potential energy because ….
of the stored energy in the covalent bonds between
atoms.
Types of Kinetic Energy
 Thermal energy
 Light energy
THERMODYNAMICS
The study of energy transformations that occur in a
collection of matter.
 Matter – “system” could be 1 cell or the whole planet
 All else – “surrounding”
Living organisms are open systems
 Exchange both energy and matter with their
surroundings.
1st Law of Thermodynamics
Total amount of energy in the universe is constant.
Energy is not created or destroyed, it is transformed and
transferred.
 Convert sun energy into chemical energy (energy
stored in the bonds between a molecule’s atoms)
2nd Law of Thermodynamics
Energy conversions reduce the order of the universe and
increase Entropy.
Entropy – the amount of disorder in a system.
During energy conversions some energy becomes unusable
(not used for work). This is usually in the form of heat.
 Heat is a “low” form of energy.
Cells use energy to form ordered structures from less
organized starting materials.
Where does the energy come from?
Cells convert “high” ordered forms of energy into “lower”
ordered energy and molecules. The difference in energy is
used to form ordered structures.
Ex: Cellular Respiration
Glucose + O2  ATP + CO2 + H2O + Heat
(High energy) (Usable energy) (Low energy)
Chemical Reactions Store/Release Energy
Two types of energy reactions:
1. Endergonic Reactions – Chemical reactions that
require a net investment/input of energy.
 Molecules with low potential absorb energy from the
surroundings producing products that have greater
stored potential energy.
o Energy stored in the covalent bonds between
atoms.
2. Exergonic Reactions – Chemical reactions that release
energy.
 Reactants start with high potential energy in their
bonds. Products have less potential energy.
 Energy is released when bonds are broken.
o Energy released is used for survival, growth and
reproduction.
 Δ G of a Reaction = Change in Free Energy
(Energy of Products – Energy of Reactants)
 Endergonic Reactions have positive Δ G.
 Exergonic Reactions have negative Δ G.
Photosynthesis – uses the energy from sunlight to convert
inorganic molecules into high energy organic molecules.
Cellular Respiration – uses organic molecules and oxygen
to convert stored chemical potential energy in food to
“usable” potential chemical energy - ATP.
Cellular Metabolism – the sum total of all the chemical
reactions (endergonic and exergonic) taking place in an
organism.
Energy Coupling
the use of energy released
from exergonic reactions is
necessary for endergonic
reactions.
ATP – Adenosine Triphosphate
Adenine
Ribose
Phosphate Groups (3)
Hydrolysis of ATP into ADP and P
ATP – ADP + P Cycle
Exergonic Reaction:
 Releases Energy
 Energy used to
synthesize ATP
from ADP and P
Endergonic Reaction:
 Require Energy
 Energy used for
cellular work
(chemical,
mechanical and
transport)
Three Types of Cellular Work:
1. Chemical Work – Phosphorylation of a reactant
molecule drives an endergonic reaction that produces a
high energy product molecule.
2. Mechanical Work –
Phosphorylation of a motor
protein in muscle cells cause
the proteins to change shape,
pull on microfilaments (actin),
causing the cell to contract.
3. Transport Work –
Phosphorylation of proteins
pumps (transport proteins)
embedded in the plasma
membrane allows molecules to
move from areas of low
concentration to areas of high concentration.
Enzymes and Chemical Reactions
Cells must invest energy to start chemical reactions.
 This prevents the spontaneous breakdown of
molecules with high potential energy.
 Energy of Activation (EA) or Activation Energy - the
energy that must be absorbed to start a chemical
reaction.
o What does the energy do?
 Contorts or weaken bonds before the
reaction forms new bonds.
If cells need certain chemical reactions to happen quickly,
why not increase kinetic energy (heat)?
 Speed up all chemical reactions (not good)
 Denature proteins
Why use enzymes (special enzyme catalysts)?
 Speed up specific chemical reactions by
lowering the Energy of Activation.
o How do they work?
 Position molecules for bonding or
weaken bonds before breaking.
Enzymes are proteins. Remember protein shape is
important to function.
Enzymes generally end in –ase and are named after the
substrate they bind.
Enzymes Are Specific
Enzymes are proteins whose 3-D shape determines their
function/role in a chemical reaction.
The reactant(s) that a specific enzymes acts upon is called
the substrate.
The specific region on the enzyme where the substrate
binds is called the active site.
 Enzymes catalyze specific reactions because only certain
substrate molecules fit into the active site.
o When the substrate binds to the active site, the
shape changes (induced fit) to weaken bonds for
breaking or positions molecules close together for
bonding.
Enzyme hydrolysis of sucrose
Enzymes and Environmental Conditions
An enzyme’s shape determines its function, and the shape
can be affected by the environment.
Enzymes are most effective under specific conditions.
Temperature – close to normal cell/body temperature
Salinity – high salt ions interfere with chemical bonds
pH – close to neutral, H+ interfere with bonding
Cofactors (inorganic) and Coenzymes (organic) are ions
or molecules that help enzymes function.
Enzyme Inhibitors
An enzyme’s ability to bond with its substrate can be
interfered with by chemicals called inhibitors.
Two types of inhibitors:
Competitive Inhibitors – have structures like the substrate
and bind to the enzyme’s active site before the substrate.
Add more substrate to increase productivity.
Noncompetitive Inhibitors – bind to a secondary location
on the enzyme (allosteric site) that changes the shape of the
active site preventing the substrate from binding.
http://www.youtube.com/watch?v=PILzvT3spCQ
Inhibition
 Hydrogen bonded inhibitors are weakly held
o Reversible
 Covalently bonded inhibitors are strongly held
o Irreversible
Enzyme inhibition is not always bad.
 Some chemical reactions require multiple steps.
Products can inhibit further steps if in excess. This is
called feedback inhibition.
 Beneficial drug
o Ibuprofen and aspirin – pain inhibition
o Protease – HIV inhibitors
o Cancer drugs – cell division inhibitors
Harmful inhibition
 Toxins and poisons
o Cyanide – ATP inhibition
o Sarin gas – nerve impulse inhibition
o Pesticides – nerve impulse inhibition
o Antibiotics – cell wall inhibition