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ENERGY AND MOVEMENT
I. Energy
A. Organisms are ordered states of matter and a constant
supply of energy is required to maintain life
B.
Energy = capacity to do work, may be chemical, mechanical, electrical or
heat
1. Energy is usually measured in calories:
a. 1 calorie = amount of energy required to heat 1 gm of water from
14.5oC to 15.5oC at standard pressure
b. Note that the public uses the "capital C" Calorie =
kilocalorie (1,000 "small c" calories)
C. Virtually all energy on earth comes from sunlight
1. Plants use energy from the sun
to make the bonds which hold organic molecules together
D. Chemical reactions:
1. Exergonic reactions yield energy
2. Endergonic
reactions require energy
II. Laws of thermodynamics
A. First law - energy can neither be created nor destroyed, it can only be
redistributed
1. This means there is a finite amount of energy in the universe but it can
change form
B. Second law - physical and chemical processes proceed in such a way that the
entropy of the universe increases
1. Entropy = disorder or randomness
C. Since organisms are ordered states of matter, it takes a constant input of
energy to keep them together
D. However, as a consequence of the second law energy
transformations can not be 100% efficient because energy is lost to the
environment
1. Only perhaps 25% of potential energy in gasoline is converted to move a
car; rest is lost as heat
2. In
living organisms the energy loss is most often as heat, e.g. when
muscles convert chemical energy in ATP to mechanical energy, some is lost as
heat
III. Redox reactions
A. Energy transformations in living systems involve the transfer of electrons
and protons [H+] from one energy level to another,
or from one atom or molecule to another
B. Reactions involving electron transfer(s) are called reduction or oxidation (REDOX)
reactions:
1. Oxidation = loss of electrons, e.g. Na to Na+
2. Reduction = gain of electrons, e.g. Cl to Cl-
IV. ATP (adenosine triphosphate)
A. Virtually all energy on earth comes from sunlight
B.
Plants use energy from the sun to make the bonds which hold organic molecules
together
C.
When these bonds are broken the energy is transferred to ATP
D. The ATP is
then moved about cells and organisms to power their needs
E. Structure of ATP
1. Adenine
2. Ribose
3. Three phosphate
F. The terminal (3rd) phosphate bond is a special high
energy bond
G. Recall that mitochondria are cellular powerhouses
1. Glucose from the foods you eat
enter the mitochondria
2. When the glucose bonds are broken their energy is used to add the
third phosphate to ADP (adenosine diphosphate) converting it to ATP
3. Since a phosphate is added this is called phosphorylation
4. The ATP is moved to where energy is needed and the terminal phosphate is
cleaved off to provide energy
5. The resulting ADP then goes back to the mitochondria to be "recharged" into
ATP
a. ATP is like a portable rechargeable battery
b. It is estimated that the human body cycles an average of 40 kg (88 lb.) of ATP
into ADP per day!
V. Enzymes
A. In living organisms some chemical reactions take place in which energy is passed
from one molecule to another via metabolic pathways
1. Metabolic pathway = ordered series of
chemical reactions, each generally mediated by a specific enzyme
2.
Metabolism = the sum total of the chemical reactions within an organism
a. Anabolic
reactions build molecules
b. Catabolic reactions break down molecules
B. Virtually all chemical reactions within organisms are mediated by enzymes
1. Enzymes = large globular proteins from 12,000 to 1 million
molecular weights that act as catalysts
a. Catalysts = substances that accelerate chemical reactions but
which remain unchanged or unused in the
process
C. How enzymes work
1. To go from reactants to products the chemical bonds in the reactants must be
broken so that new ones can be formed in the product. E.g. a condensation reaction to make a
polymer
2. Before this can happen the reactants must collide with each other sufficiently to
distort their bonds to form an intermediate spring-like transition state
3. Activation energy = the energy required to
make a collision sufficient enough to form the transition state
4. Enzymes function by lowering the activation energy necessary for a reaction
to take place
5. Enzymes have an active site into which the
substrates fit, forming an enzyme-substrate complex
6. The active site orients the substrates near each other and subtly changes their
shapes, straining their bonds and helping them reach the transition state. This lowers the
energy of activation making it easier for the reactants to form products
D. Enzyme reactions are greatly influenced by both temperature
and pH
1. Most enzymes only function within
very narrow ranges of temperature or pH
2. This is because their shape is distorted so they
don’t function
a. Siamese cats have dark ears, nose, paws and tails because those parts are colder
than rest of the body. The enzyme responsible for the dark pigment melanin only functions
at lower temperatures
VI. Diffusion
A. Cells are ordered states of matter, mostly in water solutions, separated from
their environment via selectively permeable membranes. Some substances can pass
through them and some can not
B. The movement of substances is the result of internal energy which keeps them in
constant motion and concentration gradients
1. Concentration gradient = differences in the concentration
or pressure of materials in one part of a contained area compared to another
C. Because of entropy materials tend to move down concentration gradients,
i.e. from regions of higher concentrations to regions of lower concentrations,
e.g.
cream in coffee
D. Materials move down concentration gradients because under high concentrations
molecules collide with each other more than they would if spread over a
larger area
E. Diffusion = tendency of materials to move from areas of high
concentration to areas of low concentrations
F. Many materials, particularly water, enter and leave cells via simple
diffusion due to a concentration gradient on either side of the membrane
G.
Passive transport = the movement of a substance into or out of a cell due to a
concentration gradient. It is passive because it spontaneously happens with no input of
energy
VI. Osmosis and Tonicity
A. Biological membranes are usually selectively permeable, permeable
to many small molecules but not larger or electrically charged molecules
B.
Osmosis = the movement of water through a selectively permeable membrane in
response to a concentration or pressure gradient
1. Water moves from regions of higher concentration (high water potential) or pressure to where it is
present in lower concentrations
C. Tonicity = relative concentrations of solutes in two
solutions
1. Solute = a substance dissolved in a solvent. E.g. throw some salt
into water - the water is the solvent and the salt is the solute
2. Tonicity is usually used to refer to concentration differences between cells and their
environment
3. There are three types of solutions:
a. Isotonic solution = solute concentration inside and outside cells is equal.
Therefore there is no net movement of water into or out of cell
b. Hypotonic (low) solution = low in solutes (high in water molecules).
Therefore water moves into cell
c. Hypertonic (high) solution = high in solutes (low in water
molecules). Therefore water moves out of cell
D. When water moves into a cell via osmosis it can create osmotic pressure,
eventually causing it or its plasma membrane to burst
1. Lysis = bursting of a cell or plasma membrane
E. Recall that plants have a large central vacuole. Osmotic pressure is what keeps
plant cells turgid (rigid)
1. Turgor pressure = the pressure that develops in plant cells as a
result of osmosis
VII. Transport across membranes
A. Often cells must transport materials against a concentration gradient, this takes energy
so it is called active transport
B. Recall that the lipid bilayer also contains embedded proteins
C. Active transport
across membranes is usually accomplished by these membrane transport proteins
1. With an input of energy these proteins may change shape and act as carriers
by bringing molecules inside the cell
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