Transcript You will need to read on the aging process in your textbook

Chapter 6
Metabolism
• You will need to read on the aging process in
your textbook
• Metabolism: refers to the cell’s capacity to
acquire energy and use it to build, store, break
apart, and eliminate substance in controlled
ways
Energy
• Potential energy: is the capacity to make
things happen, to do work
– Measured in kilocalories
– Also called chemical energy
• Kinetic Energy: is the energy of motion
– Heat energy
• Heat: transfer of energy from ATP also
resulted in the release of another form of
energy
What can cells do with energy?
• Energy from the sun or from organic
substances becomes coupled to thousands of
energy-requiring processes in cells
• Cells use the energy to perform chemical,
mechanical, and electrochemical work.
How much energy is available?
• First law of thermodynamics: states that the
total amount of energy in the universe is
constant; it can’t be created nor destroyed, it
can only change forms
– Energy can not be produced by the cell- it can only
be borrowed from someplace else
– High quality energy is usable
– Low quality (such as heat) is released into the
universe
One way flow energy
• Second law of thermodynamics: states that
the spontaneous direction of energy flow is
from high to low quality forms
– Each conversion produces energy (usually heat)
that is unavailable for work
– Entropy: the measure of disorder
Cells and Energy Hills
• Energy changes in living cells tend to proceed
spontaneously in the direction that results in a
decrease in usable energy
• Endergonic (“energy in”) reactions require
input resulting in products with more energy
than reactants
– Example: Photosynthesis
Continue…
• Exergonic (“energy out”) reactions release
energy such that the products have less
energy than the reactants had
– Example: Cellular Respiration
ATP couples energy inputs with outputs
• ATP is composed of adenine, ribose, and three
phosphates
– Energy input links phosphate to ADP to produce
ATP (phosphorlyation phosphate transfer)
– ATP can in turn donate a phosphate group to
another molecule, which then becomes primed
and energized for specific reactions
Continue…
• ATP is like currency in an economy
– Earning ATP is an exergonic reaction and spending
(using) ATP is a endergonic reaction
– ADP can be recycled to ATP very rapidly in the
ATP/ADP cycle
Electrons transfer drive ATP formation
• Electrons are transferred in nearly every reaction
that harnesses energy for use in the formation of
ATP (Oxidation-Reduction Reaction)
• In plant cells sunlight energy drives electrons
from water molecules to initiate the reactions
that will eventually produce carbohydrates
• In aerobic respiration, the degradation of glucose
release energy that can be transferred to ATP
– This actually makes more ATP
Participants in Metabolic Reactions
• Reactants: are substances that enter a
reaction
• Products: what is produced from a reaction
• Intermediates: are compounds that are
formed between the reactant and product.
• Energy Carriers: are mainly ATP- usually
activate enzymes and other factors
Continue…
• Cofactors: are small molecules and metal ions
that help enzymes by carrying atoms or
electrons (EXAMPLE: NAD+)
• Transport Proteins: are membrane bound
proteins that participate in adjusting
concentration gradients that will influence the
direction of metabolic reactions
What are Metabolic Pathways?
• Metabolic Pathways form series of reactions
that regulate the concentration of
substanceds within cells by enzyme-mediated
linear and circular sequences
• Biosynthetic pathways, small molecules are
assembled into large molecules without the
need for energy
– Example: Simple sugars assembled into larger
complex carbohydrates
Continue…
• Degradative pathways: large molecules such
as carbohydrates,lipids, and proteins, are
broken down to form products fo lower
energy.
– Released energy can be used for cellular work
Are Reactions Reversible?
• Chemical reactions can proceed from
reactants to products, which if they are
allowed to accumulate, will be convert back to
reactants
• The direction of concentrations and the
collision of molecules
Continue..
• When reaction approaches chemical
equilibrium, the forward and reverse raction
proceed at equal rates
– No net change in concentration
– Every reaction has it own ratio of products to
reactants at equilibrium
No vanishing atoms at the end of the run
• The law of conservation of mass states that
the total mass of all substances entering a
reaction equals the total mass of all products.
– This is why we must “BALANCE” a chemical
equation by having equal number of atoms of
each element on both sides of the arrow.
C02 + H20  C6H12O6 + O2
Balance the equation
Electron Transfer Chains in the
Main Metabolic Pathways
• Energy is released from storage molecules
(such as glucose) in controlled steps via a
series of intermediate molecules
– Electrons released during bond breaking are
transferred stepwise through the components of
electron transport systems located on various cells
membranes
– Oxidized: Electrons are donated
– Reduced: Electrons are gained
Continue…
• Coenzymes: are large organic molecules such
as NAD+, FAD, and NADP+ that transfer
protons and electrons from one substrate to
another.
• Electrons are similar to staircases where the
electrons flow down the steps from the top
(most energy available) to the bottom (least
amount of energy)
• The energy is harnessed to move H+ ions
which turns establish pH and electric gradient
Enzymes
• Enzymes helps organisms exist through
speeding up chemical reactions
• Without enzymes could not process food,
build new cells, get rid of old cells, keep your
brain working, and to contract muscles
• Enzymes increases the rate of reaction by
lowering the activation energy (the amount of
energy needed to get a reaction going)
Enzymes have four features:
• 1- speed up a chemical reaction
• 2- can be reused
• 3- at least some of them, can recognize both
reactants and products in order to catalyze a
reaction in both directions
• 4- very selective about substrates
How do enzymes lower energy hills?
• Active Site: pockets or crevices where
substrates are bound and specific reaction are
catalyzed
– Increases the rate of reaction by creating a
microenvironment that is energetically more
favorable for the reaction
Transition at the Top of the Hill
• Activation Energy brings the reactive chemical
groups into alignment so that chemical bonds
can be broken, created, and rearranged.
• The substrate is brought to its transition
state– point where the reaction takes place
How Enzyme Work?
• Binding energy: energy released from all of the
weak interactions
• Which helps bring about transition state by
four mechanisms:
– 1. helping substrate get together
– 2. orienting substrate in position to favor a
reaction
– 3. shutting out water
– 4. inducing changes in enzyme shape (induced-fit
model)
About those cofactors
• Cofactors are nonprotein groups that bind to
many enzymes and make them more reactive
• Inorganic metal ions such as Fe++ also serve as
cofactors when assisting membrane
cytochrome proteins in their electron transfer
in chloroplast and mitochondria
Why are enzymes so big?
• A large molecule affords structural stability
• Extensive folding of polypeptide chains puts
amino acids and functional groups in location
and orientations that favor interactions with
water and substrate
How Enzymes Activity Controlled?
• Some controls regulate the number of enzyme
molecules available by speeding up/slowing
down their synthesis
• Sometimes enzymes bind to other sites than
their active site
Continue…
• Allosteric enzymes (in addition to active site)
regulatory sites where control substances can
bind to alter enzyme activity; I fthis control
substance is the end product in the enzyme’s
metabolic pathway, the feedback inhibition
occurs (shutdown)
Do Temperature and pH affect
Enzymes?
• Enzymes operate best within defined
temperature ranges
– High temperature decreases reaction rate by
disrupting the bond that maintain 3-D shape
(denaturation occurs)
– Most enzymes function best at the pH range of 6
to 8
• Exception: stomach enzyme: Pepsin
– Higher or lower pH can disrupt the shape and
function
Light Up the Night
• Fireflies use enzymes (luciferase) to produce
light by bioluminescence
• Researchers transferred genes for
bioluminescence into strains of Salmonella so
that the course of infection could be tracked
by visualization