Bioenergetics
How Do Organisms Acquire and
Use Energy?
Metabolism
• All of the chemical reactions that occur in
cells.
– Organic substances are converted to other
organic molecules and energy is transformed.
• Energy
– Anything that can do work.
• Example: move a muscle, make a protein
Laws of Thermodynamics
• First Law:
– Energy may change forms, but it is neither
created nor destroyed.
• Second Law:
– Energy changes always occur in the direction
in which the energy of the universe becomes
more disordered.
Entropy
• The amount of disorder or randomness in the
universe.
– Without the input of energy from outside the system,
all systems are spontaneously moving closer to
equilibrium at all times.
Uphill Struggle For Living Things
• Living things must do biological work to
keep the forces of the universe from
dismantling their highly ordered bodies.
• To do this, organisms need a constant
supply of energy.
• Autotrophs and heterotrophs either
produce or obtain energy to overcome this
struggle.
Animal Respiration, Like Fire, Is
Oxidation
• Joseph Priestly
– Championed the idea
of “phlogistron”
• Phlogistron is the
substance that
flowed into the air
when substances
were burned.
Animal Respiration, Like Fire, Is
Oxidation
• Antoine Laurent Lavoisier
– Disproved theory of phlogistron.
• Hypothesized if burning substance releases
phlogistron, then as the substance burns, its weight
should decrease.
• Found the total weight had increased.
– He reasoned burning doesn’t add something to
the air, it takes something out of the air.
– First to recognize fire and breathing both require
oxygen.
Animal Respiration, Like Fire, Is
Oxidation
• Types of energy:
– Kinetic
• Energy that is doing
work
– Potential
• Stored or inactive
energy
Metabolism is Efficient and Highly
Specific
• Can’t burn glucose as
you would wood.
• Need the process to
be controlled to
minimize the energy
loss (entropy).
• Also need it to be
specific.
• Need enzymes.
Metabolism is Efficient and Highly
Specific
• Enzymes
– A class of proteins that catalyze, or speed up,
the steps of metabolism
– Cannot force a reaction to go in a direction
that is not consistent with the laws of
thermodynamics
How Do Enzymes Work?
• They overcome the
activation energy.
– Barrier that prevents
molecules from
undergoing otherwise
favorable reactions
Hallmarks of Enzyme-Catalyzed
Reactions
• Metabolic efficiency:
– Cellular metabolism is characterized by
metabolic pathways.
• Sequences of enzyme-catalyzed reactions in
which the product of one reaction serves as the
reactant for the next.
Hallmarks of Enzyme-Catalyzed
Reactions
• Metabolic specificity
– A given enzyme only
binds to a specific kind
of molecule, called its
substrate
Metabolic Specificity
ATP: Energy Currency of Life
• Adenosine
Triphosphate:
– Assembled by energyyielding metabolic
pathways.
– “Used” to drive
energy-consuming
pathways.
– A nucleotide.
Central
Role of
ATP
Other Nucleotide-Based Compounds
Shuttle Hydrogen
• These molecules
shuttle hydrogen
atoms from one place
to another and from
one compound to
another.
– NAD+/NADH,
– NAD+/FADH2,
– NADP+/ NADPH
• Play central role in
metabolism.
How Do Organisms Use Energy?
• Cellular Respiration
– Metabolic pathways in
which cells harvest the
energy from the
metabolism of food
molecules
– Occurs in three stages
• Glycolysis
• Krebs Cycle
• Electron Transport Chain
Glycolysis
• Occurs in the cytoplasm
• Net reaction:
2 ADP
2 ATP
2 C3H16O3
Pyruvic Acid
C6H12O6
Glucose
2 NAD+
2 NADH
When Oxygen is Limited
• Two problems with anaerobic cellular
respiration:
– 2 ATPs / glucose molecule will not sustain
activity for long periods.
– In the absence of oxygen, glycolysis converts
all of the limited NAD+ to NADH.
• With no more available NAD+, glycolysis ceases.
Lactic Acid Fermentation
• H atoms are removed
from NADH and
added to pyruvic acid
forming lactic acid.
– Regenerates NAD+ in
order for glycolysis to
continue
With Oxygen Present
• Transitional step before Krebs Cycle:
– Accomplishes 3 things
• 1. Hydrogen atoms removed from pyruvic acid
and added to NAD+ making NADH
• 2. Carbon atom is removed from pyruvic acid and
lost as CO2
• 3. Resulting two-carbon molecule is attached to
carrier molecule (coenzyme A) forming acetyl-CoA
– Performed by large enzyme in the in
mitochondria
Krebs Cycle
• Occurs in
mitochondria:
• Entering cycle:
– 1 acetyl-CoA, 3 NAD+,
1 FAD, 1ADP + Pi
• Exiting the cycle:
– 3 NADH, 1 FADH2, 1
ATP, 2 CO2
Electron Transport Chain
• Occurs in
mitochondria:
– Have cristae
• Folds of inner
mitochondrial
membrane
• Contains energy
transforming
machinery needed to
convert the energy
stored in NADH and
FADH2 to ATP
Electron Transport Chain
• Components of the chain
are enzymes
– Grouped into 4 large
complexes
• On inner mitochondrial
membrane
• End products of the
chain
– Gradient of protons across
the inner mitochondrial
membrane
– water
ATP is Made Using Energy From
Proton Gradient
• Proton gradient
similar to dam
– Hold water back until
you need it to do work
– As water rushes down
its gradient toward
equilibrium,
• Use a coupling
mechanism –a
waterwheel or turbineto put that energy to
work for you.
ATP is Made Using Energy From
Proton Gradient
• The basic components
of a dam are:
– 1. Potential energy in
the form of a water
gradient
– 2. An opening that
directs the water flow in
a specific path
– 3. A coupling
mechanism to do the
work
ATP is Made Using Energy From
Proton Gradient
• Synthesis of mitochondria
uses same basic
components.
– Protons moving down their
gradient fuels the synthesis
of ATP by
• Mitochondrial ATP
synthase
• This mechanism of ATP
synthesis is called
chemiosmosis.
Net Overall Yield of Cellular Respiration
• Net yield of ATP production from one
glucose molecule
– Glycolysis: 2 ATP
– Krebs Cycle: 2 ATP
– Electron Transport Chain
• Converting the energy stored in NADH and FADH2
to ATP: 32 ATP
– Total: 36 ATP
How Do Organisms Acquire Energy?
• Only photosynthetic organisms can make
organic molecules from sunlight, CO2 and
H2O.
– Heterotrophic organisms obtain organic
molecules by consuming photosynthetic
organisms.
Pigments absorb the Energy of Light
• Light is a form of energy called electromagnetic
radiation.
– Occurs in a vast spectrum of size and energy
• Shorter wavelength radiation has more energy than long
wavelength radiation.
Pigments absorb the Energy of Light
• Photosynthetic tissues appear green
because they contain pigments.
– Molecules that absorb some wavelength of
light and reflect others.
• Green plants have the pigment chlorophyll
– Absorbs red and blue parts of the spectrum
and reflects the green wavelength.
Pigments absorb the Energy of Light
• If a beam of blue light is aimed at a test tube
containing chlorophyll, the solution fluoresces.
– Light is briefly absorbed and emitted at a different
wavelength.
Photosynthesis
• Consists of two types of reactions:
– Light-dependent reactions
• Produce ATP and NADPH
– Light-independent reactions
• Also known as the Calvin-Benson Cycle.
• Use ATP and NADPH to produce carbohydrates.
Light Reactions Make ATP and NADPH
• Chloroplasts
– Large, green,
membrane-bound
organelles.
– Site of photosynthesis
– Thylakoids
• Contain the lightharvesting pigments.
– Stroma
• Internal space of
chloroplast.
Steps of Light-dependent Reactions
Noncyclic vs. Cyclic Phosphorylation
• Noncyclic:
– Flow of electrons follow a linear noncyclic
pathway:
Light energy
2 H2O + 2 NADP+ + ADP + Phosphate
O2 + 2 NADPH + ATP
– Produce more NADPH than ATP.
– Problem: Calvin–Benson cycle requires 3
ATP for every 2 NADPH to make
carbohydrate.
Noncyclic vs. Cyclic Phosphorylation
• Cyclic:
– Depending on the
need for ATP,
electrons can bypass
the NADP+ and be
passed back to the
chlorophyll molecule
from which they
originally came.
– Still creates proton
gradient.
Calvin-Benson Cycle
• Discovered in late
1940s-1950s
– Used paper
chromatography and
radioactive carbon.
• Depicted carbonfixation in green algae
• Sugar-producing
process of
photosynthesis.
What Do Humans Need to Eat?
• Macronutrients supply energy for our
metabolism.
– Macronutrients: dietary components that are
needed in relatively large quantities for proper
body function.
– Three kinds:
• Protein
• Fats
• Carbohydrates
Proteins
• Make up the main structural components of our
bodies.
• Made of 20 amino acids.
– Our body can produce 12 from fats and
carbohydrates
– The other 8, essential amino acids, have to be
obtained from our diet
– Dietary proteins that provide all of the essential amino
acids in the proper proportions are called complete
proteins or high-quality proteins.
Fats
• Main structural component of cell
membranes
• Two groups of essential fats:
– Omega-3 and omega-6 fatty acids must be
obtained from diet.
• Healthiest way to to obtain fat is to avoid
foods rich in saturated fat (butter, lard) and
cholesterol and concentrate on foods with
unsaturated fats (vegetable oils).
Carbohydrates
• Main source of calories is most diets.
– Not all are equally healthy.
• Healthy carbohydrates are those not
heavily processed.
– Examples: fruits, vegetable, whole grains
• Highly processed carbohydrates cause
drastic spikes in insulin levels.
– Followed by unstable blood glucose levels
and sensations of false hunger.
Micronutrients
• Include vitamins and minerals.
• Needed as cofactors for many enzymes.
– In order for enzymes to catalyze cellular
reactions.
• Serve as building materials for bone and
blood.
• Required in small amounts.
• Crucial for health and well-being.