The Working Cell
I.
Energy is the capacity to perform work
a. ENERGY  the capacity to do work; to move matter in a
direction it would not move if left alone
b. KINETIC ENERGY  energy actually doing work
i. HEAT  the movement of molecules in a body of matter
1. A type of Kinetic Energy
c. POTENTIAL ENERGY  the capacity to perform work due to
location or arrangement
d. CHEMICAL ENERGY  the potential energy of molecules
II.
Two laws govern energy conversion
a. THERMODYNAMICS  the study of energy transformations
that occur in a collection of matter
i. THE FIRST LAW OF THERMODYNAMICS
1. The total amount of energy in the universe is
constant
2. Energy can be transferred or transformed, but
never created or destroyed
ii. THE SECOND LAW OF THERMODYNAMICS
1. Energy conversions reduce the order in the
universe
2. An increase in ENTROPY
a. ENTROPY  the amount of disorder in a
system
III.
Chemical reactions either store or release energy
a. Two types of chemical reactions
i. ENDERGONIC REACTIONS  require a net input of
energy
1. Produce products rich in potential energy (PE)
ii. EXERGONIC REACTIONS  releases energy
1. Uses reactants with high potential energy (PE)
2. Cellular respiration  exergonic process that
releases energy in sugar
b. CELLULAR METABOLISM  all the endergonic and
exergonic reactions in a cell
IV.
ATP shuttles chemical energy within the cell
a. ATP  Adenosine Tri Phosphate
i. Powers near all cellular work
b. ENERGY COUPLING  using energy from exergonic
reactions to drive essential endergonic reactions
c. ATP has 3 parts
i. Adenine (a nitrogenous base)
ii. Ribose (a 5-carbon sugar)
iii. 3 phosphate groups
d. Hydrolyzing the phosphate groups is what releases energy
i. ATP + H20  ADP + ENERGY
e. PHOSPHORYLATION  the transfer of a phosphate group
i. The transfer of the phosphate group is key as substances
acquire energy from phosphate to do work
f. ATP is recycled
V.
Enzymes speed up the cell’s chemical reactions by lowering
energy barriers
a. Reactions require some energy in order to get started
b. ENERGY OF ACTIVATION  amount of energy that
reactants must absorb to start a chemical reaction
c. ENZYME  a protein molecule that serves as a biological
catalyst; speeds up a chemical reaction by lowering the
activation energy
VI.
A specific enzyme catalyzes each cellular reaction
a. Enzymes have unique 3-D shape and shape denotes function
b. Shape determines what reaction an enzyme will catalyze
c. SUBSTARE  reactant from chemical reaction the enzyme is
catalyzing
d. Enzymes only recognize specific substrates
e. ACTIVE SITE  part of enzyme that actually binds to enzyme
f. INDUCED FIT vs LOCK AND KEY
g. INDUCED FIT  molds to substrate; ALLOWS FOR
MULTIPLE ROLES FOR ENZYMES
h. LOCK AND KEY  Rigid shape
i. Enzymes named by substrate they are acting/binding
i. Example  sucrase acts on sucrose
VII. The cellular environment affects enzyme activity
a. Temperature can alter enzyme shape, limiting its ability to
function
b. Salt concentration and pH can also affect enzyme function
c. COFACTORS  non-protein helpers that aid in enzyme
function
i. COENZYME  an organic cofactor, such as vitamins
VIII. Enzyme inhibitors block enzyme action
a. INHIBITOR  a chemical that interferes with enzyme action
b. 2 types
i. Competitive Inhibitor  resembles substrate, competes
for active site
ii. Non-competitive Inhibitor  binds directly to enzyme to
change its shape
c. NEGATIVE FEEDBACK  type of inhibition; products of a
reaction inhibit enzyme action
IX.
Some pesticides and antibiotics inhibit enzymes
a. Use inhibition to our benefit by making pesticides and
antibiotics
X.
Membranes organize the chemical activities of cells
a. CELL MEMBRANE  separates internal environment from
external
b. SELECTIVE PERMEABILITY  allows some substances to
cross more easily and blocks passage of some substances
altogether
XI.
Membrane phospholipids form a bilayer
a. Membrane composed of phospholipids that from a bilayer in
aqueous solution
b. NONPOLAR, HYDROPHOBIC molecules are soluble in lipids
and can easily pass through membranes
c. POLAR, HYDROPHILLIC are not soluble in lipids and
CAN’T pass through
d. Rely on membrane proteins to pass through
XII. The membrane is a fluid mosaic of phospholipids and proteins
a. FLUID MOSAIC  common description of the plasma
membrane
i. Membrane pieces are not rigid, may change position in
membrane
ii. Membrane has proteins embedded within the
phospholipids
b. Bent tails of phospholipids keep distance between adjacent
lipids and allow fluidity
c. Cholesterol molecules add to stability of fluidity @ various
temperatures
d. GLYCOPROTEIN  proteins with carbohydrate chains
attached
e. GLYCOLIPID  lipids with carbohydrate chains attached
XIII. Proteins make the membrane a mosaic of function
a. Proteins serve many functions
i.
ii.
iii.
iv.
Attach membrane to cytoskeleton
ID’s cell
Forms junctions between cells
Receptors for chemical messengers with specific shape to
catch that messenger
1. SIGNAL TRANSDUCTION  catching a
messenger then causing a chain reaction chemical
pathway
v. Help move substances across the membrane
XIV. Passive transport is diffusion across a membrane
a. DIFFUSION  the tendency for particles of any kind to spread
out spontaneously to regions where they are less concentrated
i. DOES NOT REQUIRE ENERGY
b. PASSIVE TRANSPORT  the diffusion of a substance across
a biological membrane
c. CONCENTRATION GRADIENT  amount of substance on
one side of membrane versus opposing side
XV. Osmosis is the passive transport of water
a. OSMOSIS  a special case of passive transport involving the
diffusion of water across a selectively permeable membrane
b. HYPERTONIC  higher concentration of solute
c. HYPOTONIC  lower solute concentration
d. ISOTONIC  same concentration of solute
XVI. Water balance between cells and their surroundings is crucial to
organisms
a. OSMOREGULATION  the control of water balance
b. Cells places in different solutions will have various responses
i. Cells in
1. Isotonic  stay normal
2. Hypotonic  cell will lyse
3. Hypertonic  cell with shrivel
XVII. Transport proteins facilitate diffusion across membranes
a. FACILITATED DIFFUSION  a membrane protein aids a
molecule that can’t naturally diffuse across the membrane
i. TYPE OF PASSIVE TRANSPORT
XVIII. Cells expend energy for active transport
a. ACTIVE TRANSPORT  the use of energy to move a
molecule across a membrane against its concentration gradient
b. Usually use ATP as energy source
i. Active transport begins when solute binds to protein
ii. After binding a phosphate group from ATP, attaches to
protein giving it energy to change shape and transport
solute across membrane
iii. Phosphate stays attached to allow transport of another
solute in opposite direction
iv. *Very important for sodium-potassium pump*
XIX. Exocytosis and endocytosis transport large molecules
a. Large molecules can’t easily pass through membrane
b. EXOCYTOSIS  process used by cell to export bulky
materials
c. ENDOCYTOSIS  a cell takes in macromolecules or other
particles by forming vesicles or vacuoles from its plasma
membrane
i. 3 types of endocytosis
1. PHAGOCYTOSIS  cell eating
2. PINOCYTOSIS  cell drinking
3. RECEPTOR-MEDIATED ENDOCYTOSIS 
substance binds to receptor on membrane
XX. Faulty membranes can overload the blood with cholesterol
a. Normally the liver removes excess cholesterol
b. Cholesterol circulates in the blood as LDL’s which bind to liver
cell membranes (receptor-mediated endocytosis) to be removed
c. Excess cholesterol can’t be removed fast enough
d. HYPERCHOLESTEROLEMIA  disease of infants where
they lack the receptor molecules on liver cell membranes for
LDL’s
XXI. Chloroplasts and mitochondria make energy available for cellular
work
a. Chloroplasts convert light energy to chemical energy
b. Mitochondria convert chemical energy to ATP
c. Energy is not totally recycled; some is lost to environment as
heat