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INTRO to METABOLISM & CELLULAR RESPIRATION/ FERMENTATION (CELLULAR…
INTRO to METABOLISM & CELLULAR RESPIRATION/ FERMENTATION
CELLULAR RESPIRATION/ FERMENTATION
CATABOLIC PATHWAYS AND PRODUCTION of ATP
one catabolic process, fermentation, is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen
the most efficient catabolic pathway is aerobic respiration, in which oxygen is consumed as a reactant along with the organic fuel
most eukaryotic and many prokaryotic organisms can carry out aerobic respiration
cellular respiration includes both aerobic and anaerobic processes
the breakdown of glucose is exergonic
ELECTRON TRANSPORT CHAIN
consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells (and the plasma membrane of respiring prokaryotes)
electrons removed from glucose are shuttled by NADH to the “top,” higher-energy end of the chain
at the “bottom,” lower-energy end, O2 captures these electrons along with hydrogen nuclei (H+), forming water
electron transfer from NADH to oxygen is an exergonic reaction
instead of this energy being released and wasted in a single explosive step, electrons cascade down the chain from one carrier molecule to the next in a series of redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal elec- tron acceptor, which has a very great affinity for electrons
GLYCOLYSIS
occurs in the cytosol
begins the degrada- tion process by breaking glucose into two molecules of a compound called pyruvate
Some of the steps of glycolysis and the citric acid cycle are redox reactions in which dehydrogenases transfer electrons from substrates to NAD+ or the related electron carrier FAD, forming NADH or FADH2
TRANSITION REACTION
location: cytoplasm->mitochondria
no oxygen required
Reactants: 2 pyruvate acid, 2NAD+ from ETS, 2 coenzyme A
Products: 2CO2, 2NADH- go to ETS, 2 Acetyl CoA
KREBS CYCLE
Location: mitochondrial matrix
no oxygen required
Reactants: 2 Acetyl CoA, 6 NAD+ from ETS, 2 FAD fromETS, 2 ADP + 2 P
Products:4 CO2, 6 NADH go to ETS, 2 FADH2 go to ETS, 2 ATP
INTRO TO METABOLISM
TYPES OF PATHWAYS
CATABOLIC PATHWAYS
metabolic pathways release energy by breaking down complex molecules to simpler compounds
major pathway of catabolism is cellular respiration
ANABOLIC PATHWAYS
consume energy to build complicated molecules from simpler ones; they are some- times called biosynthetic pathways
example: the synthesis of an amino acid from a simple molecule to a protein from an amino acid
METABOLIC PATHWAYS
begins with a specific molecule, which is then altered in a series of defined steps, resulting in a certain product
FORMS OF ENERGY
KINETIC ENERGY
energy associated with the relative motion of an object
example:the motion of the cue stick to push the cue ball, which in turn moves the other balls
THERMAL ENERGY
is kinetic energy associated with the random movement of atoms or molecules; thermal energy in transfer from one object to another is called heat
light would be an example
energy is the capacity to cause change
POTENTIAL ENERGY
an object not presently moving may still possess energy
energy is not kinetic
it is energy that matter possesses because of its location or structure
example:Water behind a dam, for instance, possesses energy because of its altitude above sea level
CHEMICAL ENERGY
refers to the potential energy available for release in a chemical reaction
ATP POWERS CELLULAR WORK BY COUPLING EXERGONIC REACTIONS TO ENDERGONIC REACTIONS
cells do chemical, transport, and mechanical work
cells manage their energy resources to do work by energy coupling, the use of an exergonic process to drive an endergonic one
ATP (adenosine triphosphate) is responsible for mediating most energy coupling in cells
STRUCTURE AND HYDROLYSIS OF ATP
ATP contains sugar ribose, with the nitrogenous base adenine and a chain of three phosphate groups (the triphosphate group) bonded to it
with help of some enzymes, cells are able to use energy released by ATP hydrolysis directly to drive chemical reactions
the key to coupling exergonic and endergonic reactions is the formation of as phosphorylated intermediate
during chemical work, the pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers
during transport work, the pumping of substances across membranes against the direction of spontaneous movement
during mechanical work, the contraction of muscle cells, and
the movement of chromosomes during cellular reproduction
ENZYMES SPEED UP METABOLIC REACTIONS BY LOWERING ENERGY BARRIERS
enzymes are a macromolecule that act as a catalyst, a chemical agent that speeds up a reaction without being consumed by the reaction
without enzymes chemical traffic through the pathways of metabolism would become terribly congested because many chemical reactions would take such a long time
enzymes lower the activation energy of a chemical reaction so it will speed up the reaction.
the reactant of an enzyme acts on is referred to as the enzyme’s substrate
enzyme binds to its substrate (or sub- strates, when there are two or more reactants), forming an enzyme-substrate complex
while enzyme and substrate are joined, the catalytic action of the enzyme converts the substrate to the product (or products) of the reaction
Only a restricted region of the enzyme molecule actually binds to the substrate, this region is the active site