Energy and the Cell
What are energy and the laws that govern energy?
I. Energy is the capacity to perform work
A. Energy – The ability to do work – to accelerate (change
speed of direction) matter over some distance.
1. Kinetic Energy – The energy of motion – any thing
moving has kinetic energy
a) A moving car, person riding a bike, a pencil
falling, etc…
b) Heat is a type of kinetic energy – moving molecules
2. Potential Energy – the ability to do work due to
location or arrangement, but not doing so at the moment
– stored energy
a) Grav. PE - Location – boulder on a mountain
b) Chem PE – Arrangement of atoms – stick of
dynomite, ATP, Glucose
II. Two Laws Govern Energy Conversion
A. Thermodynamics – the study of energy transformations
in matter
1. 1st law of thermodynamics – energy cannot be created
of destroyed and thus all of the energy in the universe is
constant – it just changes forms!!
2. 2nd law of thermodynamics (entropy of Universe
increases)
a) when energy changes form (PE to KE, PE to PE,
etc…) – there is always an increase in disorder
(entropy) of the universe
(1) entropy – measure of disorder,
(a) higher entropy = more disorder.
(2) Heat – random motion of molecules – a form of
disorder.
(a) More heat generated, higher the entropy of
system.
b) Since all energy is slowly turned into heat energy,
Energy goes from useful to less useful, concentrated to
dispersed
(1) Ex) Gasoline car – chemical PE converted to KE
to heat – useful to less useful, concentrated to
dispersed
c) So how are we so ordered?
(1) We use energy (from sun ultimately) to create
ordered structures from less ordered structures
(a) Increase or decrease in entropy??
(2) If we are creating order, our surroundings must
become more disordered – our chemical reactions
generate a lot of heat!
(a) we are islands of low entropy in an increasingly
random universe.
d) No chemical reaction can be 100% efficient
III.Chemical Reactions Either Store of Release Energy
A. Two types of chemical reactions
1. Endergonic “energy in” reactions – require an input of
energy
a) Photosynthesis: 6CO2 + 6H2O  C6H12O6 + 6O2
b) reactants absorb energy yielding products rich in
PE
2. Exergonic “energy out” reactions – energy is released
– reactants rich in PE yielding products low in PE –
burning wood
a) Cellular Resp: 6O2 + C6H12O6  6CO2 + 6H2O
b) How do we go from reactants to products?
c) Energy needed to break bonds, energy released
when bonds form.
d) Bond energy slide
(1) Bonds store energy
(2) What’s a calorie? 1 gram of water by
1 °C = 4.184Joules
(3) Takes 10 J (2.2 cal) to lift a
small book one meter off the ground
(4) How about a light bulb? 40Watts = 40J/s
(5) What’s a mole?
(6) Which is harder to break C-H or O-H? Why do
you think that is?
(7) higher the bond energy, harder it is to break and
the more stable the bond is!! – they are stuck tighter
together, can’t pull apart
(8) Energy flows from unstable to stable – ball rolling
down a hill. From weak bonds to strong bonds.
e) calculate G = -686 kcal per mol of
glucose (gives of 686 kcal of energy)
f) Cellular respiration – like burning wood to release
energy
(1) burning wood is one step – heat and light
(2) cell resp – many steps, “slow burn” of fuel
molecules (glucose) – capture energy
3. Couple an exergonic reaction to an endergonic one:
a) 6O2 + C6H12O6  6CO2 + 6H2O G = -686
kcal per mole (releases 686 kcal of
energy)
b) ADP + P  ATP G = +7.3kcal/mol (absorbs 7.3
kcal of energy)
c) So how many ATP can we make from one glucose
in theory? (94) We only make about 36 = 424 kcal lost
to heat. Why? Only ~40% efficient.
d) How many ATP will it take to lift a small book off
the ground (2.2 calories)? 1.81x10^20!!
e) our cells can use 10,000,000 molecules of ATP per
cell per second
B. Cellular Metabolism – all of the exergonic and
endergonic reactions of the cell
IV.
ATP shuttles chemical energy within the cell
A. Most endergonic Rxs in cell require small amts of
energy - glucose and triglyceride have large amounts
1. Like powering your ipod with a car battery
2. Solution – use car battery to charge 100 ipod batteries!
B. Take one glucose and make 36 ATP (calculate)
C. or 1 triglyceride and make 330 ATP
D. ATP – energy rich, cellular fuel
1. ATP  ADP + P G = -7.3kcal/mol
2. Couple with endergonic reactions – unwinding DNA,
active transport, any many, many, many more
E. Where’s the energy in ATP?
1. Adenine
2. Ribose
3. 3 phosphate groups
F. Covalent bonds connecting 2nd and 3rd P groups are
unstable - easily hydrolyzed:
1. Phosphates don’t like to be next to each other, they
want to POP off…
2. ATP + H2O  ADP + P + Energy
3. ADP + H2O  AMP + P + Energy (not as much as a)
4. Exergonic or endergonic?
G. How is the energy transferred?
1. Phosphorylation – transfer of a phosphate group to a
molecule – form bond, energy released
a) P pops off from ATP to other molecules like
proteins, transferring energy – charge and shape of P
causes protein to change shape.
b) P would rather be on protein (lower energy) than
on ATP (higher energy) – ball would rather be on
floor than on desk
H. What happens to the used up ATP?
1. The AMP and ADP are recycled back (reloaded) to ATP
by burning more glucose – working cell uses up and
remakes all its ATP in about 1 minute!
2. ATP is like a rechargeable battery.
3. 10,000,000 ATP made per cell per second
I. Review
1. ATP is fuel of the cell
2. P on ATP wants off (high energy), jumps off and
attaches to other molecules (low energy) to make them
move (phosphorylation)
How Enzymes Work
V. Enzymes speed up the cells chemical reactions by
lowering energy barriers
A. What and where?
1. Enzymes – protein catalysts (chemical that speeds up
reaction without being consumed).
2. Names end in –ase and named after substrates
3. Activation energy (lighting a match).
a) orientation to each other, time
4. Enzymes lower energy of activation barriers by forcing
orientation over a specific time
VI.
A specific enzyme catalyzes a specific reaction
A. Enzyme shape denotes function – the reaction it will
catalyze
B. Specific enzymes recognize specific substrates
C. Enzymes bind (grab) substrate in active site – holds
substrate in a specific position for a specific time
D. E + S  E-S complex  E-P complex  E + P
E. Induced fit vs. lock and key
VII. The cellular environment affects enzyme activity
A. Temperature, [Salt], pH – alter structure, alter function
B. Cofactors – nonprotein helpers needed by some
enzymes to function (“molecular tools” – people need
tools!!)
1. inorganic – ex) zinc, iron, copper (now you know why
you need to eat these things!)
2. organic = coenzyme – made from vitamins in your cells
or are vitamins
VIII. Enzyme inhibitors block enzyme action
A. Inhibitor – chemical that interferes with a protein’s
function
B. 2 major types of enzyme inhibitors
1. competitive – competes with substrate for active site
2. non-competitive – bind to enzyme, not active site, to
change its shape, substrate no longer fits in active site
C. Negative Feedback – products of a reaction inhibit the
enzyme action (thermostat analogy) – extremely important
in regulation
D. Pesticides and Antibiotics – some inhibit enzymes –
give examples. Malathion (pesticide) inhibits
acetylcholinesterase (nerve transmission). Penicillin
blocks enzyme involved in building bacterial cell wall.
Membrane Structure and Function
IX.
Cell Membranes
A. Separate outside from inside
B. phospholipids, cholesterol and proteins
C. Selectively permeable
1. Some substances to easily enter than others
2. completely blocks certain substances
D. compartmentalize eukaryotic cells
1. different metabolic environments simultaneously
E. Provide a reaction surface
1. membrane embedded enzymes
F. ~3nm thickness
X. Membrane phospholipids form a bilayer
A. Phospholipids form lipid bilayer
B. Hydrophobic interior blocks many hydrophilic
molecules
C. Hydrophobic (non-polar) molecules cross easily
D. Hydrophilic molecules need membrane proteins to help
enter cell.
XI.
Fluid Mosaic Model
1. Mosaic = many small pieces
a) Proteins embedded in membrane amongst many
kinds of phospholipids and cholesterol
2. Fluid = most proteins and phospholipids can move
freely (some attached to cytoskeleton)
B. Bent tails of PL (unsaturated) keep distance and allow
fluidity
C. Glycoproteins – proteins with attached carbohydrate
chains
D. Glycolipids – lipids with attached carbohydrate chains
E. Cholesterol stabilized fluidity of membrane at various
temperatures
XII. Membrane Proteins
A. Cell Junctions – attach to other cells, extracellular
matrix and/or cytoskeleton
B. Identification Tags – sugars of glycoproteins and
glyolipids
C. Enzymes
D. Receptors
1. specific shape of receptor binds to chemical
messenger molecule,
2. signal sent into cell
3. triggers chain reaction involving other proteins =
signal transduction.
E. Transporters – shuttle hydrophilic substances in and
out
XIII. Passive transport is diffusion across a membrane
A. Diffusion – tendency for particles to spread out to
places where they are less concentrated along a
concentration gradient
1. concentration gradient – a smooth decrease in
concentration from high to low
2. no input of energy required
B. Passive Transport – diffusion of a substance across a
biological membrane until equilibrium
C. Equilibrium – substance goes back and forth equally, no
net change in concentration
D. Different molecules diffuse independently of each other
E. Very important in organisms – O2 and CO2 in lungs
XIV. Osmosis is the passive transport of water
A. PM is permeable to water (proteins)
B. Osmosis – special name given for the passive diffusion
of water across a selectively permeable membrane
C. Hypertonic – higher concentration of solute
D. Hypotonic – lower solute concentration
1. Terms are relative - depends what you are comparing
to
E. Water will move from hypotonic (higher water conc.) to
hypertonic (lower water concentration) solution (down
water concentration gradient from high to low) until the
concentrations are equal = isotonic
XV. Water balance between cells and their surroundings
is crucial to organisms
A. Cell membrane is a semipermeable membrane
B. Osmoregulation – the control of water balance
C. Cells placed in different solutions will have different
reactions:
1. Isotonic solution – stay the same – plants will wilt –
need pressure in their cells to stand up.
2. Hypotonic (higher water concentration) solution –
animal cell will fill with water, and burst (lysis) – plant cell
will also fill, but cell wall protects from popping – plant
stand upright
3. Hypertonic (lower water conc) – water will leave the
animal cell and cell will shrivel. In plants, cell wall will pull
away from membrane – turgor pressure lost
XVI. Transport proteins facilitate (aide in) diffusion
across membranes
A. Facilitated diffusion – A protein with a pore that spans
the membrane bilayer allows a substance (solute) to
diffuse down its conc. gradient into the cell. (solute
physically can’t get through membrane otherwise)
1. No energy required – diffusion
2. Rate depends on # of transport proteins and steepness
of gradient (dam analogy)
XVII. Cells expend energy for active transport
A. Active transport – using a transport protein to move a
molecule across a membrane AGAINST its concentration
gradient.
1. These proteins are like mechanical pumps – pumps
need electricity
2. Requires energy (ATP mediated phosphorylation) –
allows protein to change shape in order to “pump” the
solute molecule
a) Solute binds to protein
b) Phosphate from ATP attached to protein
c) Protein changes shape and solute pumped across
3. Some couple the passage of different solutes in
opposite directions across the membrane
a) Important example = Na+ - K+ pump
XVIII.
Exocytosis and endocytosis transport large
molecules
A. Large molecules are too big to pass through membrane
B. Exocytosis – membrane bound vesicles with large
molecules fuse with membrane and release contents
outside
C. Endocytosis – plasma membrane pinches in,
surrounding material from outside, and closes forming a
membrane-bound vesicle with material within – 3 flavors
1. pinocytosis – cell drinking
2. phagocytosis – cell eating
3. receptor-mediated endocytosis – substance binds to
receptor and triggers uptake
XIX. Faulty membranes can overload the blood with
cholesterol
A. Liver normally removes excess cholesterol from blood
by RM endocytosis
B. Cholesterol circulates in blood as LDLs
C. Hypercholesterolemia – 1 in 500 – inherited – few or no
(1 in 1,000,000) LDL receptors.
D. LDL levels rise and cholesterol is deposited on lining of
blood vessels
XX. Chloroplasts and mitochondria make energy
available for cellular work
A. Energy, enzymes, and membranes are important players
in mitochondria and chloroplasts
B. Photosynthesis and cellular respiration are linked
1. Chloroplasts – light energy used in endergonic
reactions to build energy rich molecules in chloroplasts
2. The energy in these molecules is put into ATP in
mitochondria
3. Chemicals involved as the reactants in chloroplasts
are the products in mitochondria and vice versa.