Exam 2 Lecture 4 Flashcards
All living systems
require an ongoing
supply of
energy
energy can be thought of as
the capacity to
cause specific chemical
or physical changes
Cells Need Energy to Drive 6 Different Kinds of
Work which are
- Synthetic work
- Mechanical work
- Concentration work
- Electrical work
- Generation of heat
- Generation of lig
synthetic work
changes in chemical Bonds
formation of Bonds
biosynthesis
The work of biosynthesis
results in the formation of new
chemical bonds and the
synthesis of new molecules
Biosynthesis is required for
growth and maintenance of
cells and cellular structures
Energy that cells require for
biosynthetic work is used to
make energy-rich organic
molecules and incorporate them
into macromolecules
Mechanical Work
Changes in the Location or
Orientation of a Cell or a Subcellular Structure
Mechanical work involves a
physical change in the position
or orientation of a cell or some
part of it
The movement of a cell relative
to its environment often requires
one or more appendages, such
as cilia or flagella
These require energy to move
the cell
Examples of mechanical work
A large number of muscle cells work together in
muscle contraction
Chromosomes move along spindle fibers during
mitosis
Cytoplasmic streaming and movement of
organelles and vesicles along microtubules occur
Ribosomes move along a strand of mRNA
Concentration Work
Concentration work accumulates substances within a cell or
organelle or removes toxic by-products of cellular activity
Examples include the concentration of specific molecules and
enzymes in organelles, digestive enzymes in secretory
vesicles, and the import of sugars and amino acids into cells
Electrical Work
Moving Ions Across a
Membrane Against an Electrochemical Gradient
During electrical work, ions are transported across a
membrane, resulting in differences in both concentration and
electrical potential (or membrane potential)
Every cellular membrane has a characteristic electrical potential
In the case of mitochondria or chloroplasts, the difference is
essential in production of AT
Electrical work in Neurotransmission
Electrical work is important in transmission of nerve
impulses
In this case, a membrane potential is generated by
pumping Na + ions into and K + ions out of the cell
The electric eel (Electrophorus electricus) uses
energy to generate a membrane potential of 150
mV per cell and several hundred volts for the entire
organism
heat
an increase in temperature that is useful to warm-blooded Animals
Living organisms do not use heat as a form of energy as a steam engine does
However, producing heat is a major use of energy in all
homeotherms
Homeotherms: animals that
regulate their body temperature
independent of the environment
Homeotherms:
animals that
regulate their body temperature
independent of the environment
Bioluminescence
the production of Light
Bioluminescence, the
production of light, is important
in a number of organisms, such
as fireflies, certain jellyfish, and
luminous toadstools
Bioluminescence is generated
by the reaction of ATP with
luminescent compounds
Green fluorescent protein (GFP;
from the jellyfish Aequorea
victoria) and its variants are
very useful to cell biologists
Nearly all life on Earth is directly or indirectly
sustained from
sunlight
phototroph
capture light energy from the sun and
transform it into chemical energy, stored as ATP
chemotrophs
obtain energy by oxidizing chemical
bonds in molecules (organic or inorganic)
Autotrophs
an organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide.
Heterotrophs
an organism deriving its nutritional requirements from complex organic substances.
Photoautotrophs
use solar energy to produce all the
carbon compounds they need from CO2
(photosynthesis)
Photoautotrophs include plants, algae,
cyanobacteria, and photosynthetic bacteria
photoheterotrophs
Some bacteria are photoheterotrophs, which harvest
solar energy for some cellular activities but rely on
intake of organic molecules as a source of carbon
chemoautotrophs
A few bacteria are chemoautotrophs, which oxidize
inorganic compounds such as H 2S, H2, or inorganic
ions for energy and use CO 2 as a carbon source
Chemoheterotrophs
ingest and use chemical
compounds (carbohydrates, fats, and proteins) to
provide both energy and carbon for cellular needs
All animals, protozoa, fungi, and many bacteria
are chemoheterotrophs
Energy Flows
Through the Biosphere
Continuously
Oxidation
is the removal of
electrons from a substance,
usually hydrogen atoms (H +
plus one electron)
Oxidation reactions release
energy
reduction
Reduction, the addition of
electrons to a substance
through addition of hydrogen
atoms (and a loss of oxygen
atoms), requires an input of
energy
Phototrophs
the PRODUCERS, use sunlight energy to produce more reduced
cellular compounds through photosynthesis
These compounds are converted to all the materials needed for surviva
Chemotrophs
the CONSUMERS, take in reduced compounds and oxidize
them to release their stored energy
efficiency of Biological Processes
No process in biological systems is
100% efficient; some energy is inevitably released (lost) as heat,
usually dissipated into the
environment
Some of this heat is used
In warm-blooded animals to
maintain body temperature
In plants to attract pollinators or
melt overlying snow
The Flow of Energy Through the Biosphere Is
Accompanied by
a flow of matter
Energy enters the biosphere
as _______________ and leaves as _________ both without _________
Energy enters the biosphere
as photons and leaves as
heat, both without matter
while passing
through the biosphere,
energy exists primarily in the
form of
chemical bond
energies
matter cycles between
phototrophs and
chemotrophs
cyclic flow of matter includes
Carbon, oxygen, nitrogen,
and water all cycle
continuously
They enter the
chemotrophic sphere as
reduced, energy-rich
compounds and leave it as
oxidized, energy-poor
forms
Energy flow is governed by the principles of
Thermodynamics
Thermodynamics
concerns the laws governing
energy transactions that accompany most
physical and chemical processes
Bioenergetics
(applied thermodynamics) applies
principles of thermodynamics to the biological world
Energy can be defined as
the ability to cause
change
The energy under consideration in any particular case is called the
system
the rest of the universe is called
the surrounding
The boundary between the system and
surroundings may be
real or hypothetical
A closed system is
sealed
from its environment and can
neither take in nor release
energy
An open system
can have
energy added to it or
removed from it
Organisms are what type of system
open
systems, capable of uptake
and release of energy
A system is in a specific
state if each of its variable properties is held at a
specified value.
In this situation, the total energy of the system has a unique value.
If the state changes, the total energy change is determined only by the
initial and final states of the system
what are three of the most important variables in biological reactions
Three of the most important variables—temperature, pressure, and
volume—are essentially CONSTANT during biological reactions.
why are temp, pressure, and volume essentially constant during bio rxn
This is because reactions occur in dilute solutions within cells at
approximately the same temperature, pressure, and volume during the
entire reaction.
Oil Rig
Oxidation is losing
reduction is gaining
Exchange of energy between a system and its
surroundings occurs as
Heat or work
is heat a useful energy source for cells?
Heat is not a very useful energy source for cells
because many biological systems are isothermal
(at a fixed temperature)
work is
the use of energy to drive a process other than heat flow
The units for quantifying the energy changes during
chemical reactions are
calories (cal) (1 kilocalorie (kcal)
= 1000 calories).
Physicists prefer the
joule (J); 1 J = 0.239 cal
calorie
the amount of energy required to raise 1 gram of
water by 1 degree centigrade at 1 atmosphere of pressure
first law of thermodynamics
the law of
conservation of energy.
It states that in every physical or chemical change, the
total amount of energy in the universe remains constant.
Energy may be converted from one form to another but
cannot be created or destroyed
In biological systems, the energy that leaves a system
must
equal that which entered it plus the amount
remaining (stored) in the system
Total energy stored within a system is called
internal
energy, or E.
ΔE is the
change in internal energy that occurs during
some process
Calculating ΔE
ΔE is the difference in internal energy of a system before a
process (E1 ) and after it (E2 )
2 1E E E
For a chemical reaction, this can be written as
products reactantsE E E
( see slide)
Enthalpy
change in enthalpy (H),
or heat content, which is related to E, dependent on
pressure (P) and volume (V)
H = E + P V
Enthalpy in biological processes
Enthalpy change of a particular reaction can be
expressed as:
Because pressure and volume change little or not at all in
biological reactions,
ΔH may be either positive or negative
see slide for equation
Exothermic rxn
ΔH is negative
In exothermic reactions, energy is released (e.g., the
burning of gasoline in a car)
If ΔH is positive, a reaction is
endothermic
In endothermic rxn energy is
Absorbed
( melting of an ice cube)
The Second Law of Thermodynamics
States That Reactions Have
directionality
A thermodynamically spontaneous reaction is
one that is a
favorable reaction.
Thermodynamic spontaneity
is a measure of whether or
not a reaction or process can occur
Reactions have directionality, that is
they can proceed
spontaneously only in one direction (e.g., the burning of a
piece of paper).
The second law of thermodynamics is the law of
thermodynamic spontaneity
thermodynamic spontaneity
first law
heat
enthalpy
second law
order
second law explained
in every physical or chemical change, the
universe tends toward greater disorder or randomness
(entropy).
* It allows us to predict what direction a reaction will
proceed under specific conditions, how much energy will
be released, and how changes in conditions will affect it
Entropy and Free Energy Are Two
Alternative Means of Assessing
Thermodynamic Spontaneity
Whether or not a reaction can proceed can be measured
by changes in
entropy or free energy
Entropy (S) is a measure of
randomness or disorder
All processes or reactions that occur spontane (??)
when a system becomes less ordered entropy …
Increases
(e.g., when ice melts or a solvent evaporates)
when a system becomes more ordered
Entropy decreases
ex. when ice forms water
Entropy Change as a Measure of
Thermodynamic Spontaneity
change in S universe is positive for
or every spontaneous process or
reaction (increases the entropy of the universe)
But in the specific system involved, entropy may change
or stay the same.
Expressing the second law in terms of ΔS is not very
useful in predicting the spontaneity of biological
processes.
A measure of spontaneity for a system alone is called
free energy (G)
change in free energy equation
Gproducts - Greactants
ΔG is related to
enthalpy and entropy of a reaction
ΔG = ( in terms of enthalpy and entropy )
ΔG = ΔH − T ΔS (T = temperature of the system in
degrees Kelvin, or C +273)
Free energy is a readily measurable indicator of
spontaneity
Every spontaneous reaction is characterized by a______ in free energy of the system
decrease
So, if ΔG < 0, the reaction is
thermodynamically
spontaneous.
thermodynamically
spontaneous rxn
ΔG < 0
Exergonic rxn are
Exergonic reactions are energy-yielding and occur spontaneously
(ΔG < 0)
endergonic rxn are
Endergonic reactions are energy-requiring and do not occur
spontaneously under the conditions specified (ΔG > 0)
is the oxidation of glucose exergonic or endergonic
the oxidation of glucose (a highly
exergonic process):
6 12 6 2 2 2C H O + 6O 6CO + 6H O + energy
ΔG = −686 kcal/mol
the reverse rxn of glucose oxidation is exergonic or endergonic ?
The reverse reaction is endergonic ( input of energy)
ΔG = +686 kcal/mole
6CO + 6H O + energy C H O + 6O2
The term spontaneous tells us that
a reaction can take
place, not that it will
Whether an exergonic reaction will proceed depends on
on a
favorable (negative) ΔG but also on the availability of a
mechanism.
Usually an input of activation energy is required as well
equilibrium constant
Keq
Keq
is the ratio of product
concentrations to reactant concentration at equilibrium.
At equilibrium, there is no net change in the
concentrations of reactants or products
keq equation
keq = [B]/[A]
what can the equilibrium constant tell you about a mixture
If you know the equilibrium constant for a reaction, you
can tell whether a particular mixture of products and
reactants is in equilibrium.
If the mixture is not at equilibrium, you can tell in what
direction it must proceed to reach equilibrium
what is the concentration ratio
the ratio of products to reactants
what does it mean when the concentration is less than Keq ?
A concentration ratio (products to reactants) less than Keq
means that the reaction will proceed to the right to
generate more product
what does it mean when the concentration is MORE than Keq ?
A concentration ratio greater than Keq means that the
reaction will proceed to the left ( toward reactants)
