Metabolism Flashcards
Metabolic pathways
Metabolic reactions are organized into pathways, each step being catalyzed by an enzyme.
Starting molecule -> B -> C -> Product
Metabolism
Sum of all of an organism’s chemical processes.
What are the two types of metabolic pathways?
Catabolic and anabolic
Catabolic pathways
-Release energy
-Break down complex molecules into simpler ones
Eg. cellular respiration: breaks down glucose into CO2 and water, provides energy for the production of ATP.
Anabolic pathways
-Consume energy
-Build complex molecules from simpler ones
Eg. photosynthesis: synthesizes glucose from CO2 & water.
-Synthesis of macromolecules: released energy by catabolic pathways is used to drive anabolic pathways.
Energy
- Ability to do work
- Kinetic or potential
- Can be transformed from one type to another
Kinetic energy
Energy of motion
Potential energy
Stored energy that matter possesses due to location or structure
eg. chemical reaction, diffusion, concentration (active transport)
Thermodynamics
Study of energy transformation
First law of thermodynamics
Energy can be transferred or transformed but it cannot be created or destroyed
Second law of thermodynamics
Every energy transformation makes the world more disordered.
-Heat is the most random energy.
Free energy
Portion of a system's energy that can do work. G=H-TS H, total energy of the system (enthalpy) T, temperature S, entropy (measure of disorder)
Chemical reactions and energy
Change in free energy
delta G = delta H - T delta S
delta G = Gproducts - Greactants
Two kinda of chemical reactions
Spontaneous & nonspontaneous
Spontaneous chemical reactions
Exergonic (energy coming off system), delta G is negative.
Net release of energy (products have less energy)
Nonspontaneous chemical reactions
Endergonic, delta G is positive
Requires input of energy
If a chemical reaction is endergonic, then the reverse must be exergonic
Equilibrium
A+B↔️C+D
System cannot do work, cells at equilibrium are dead.
Metabolic disequilibrium
Product is removed, prevents equilibrium from occurring.
The product becomes reactant for other metabolic pathways.
Adenosine triphosphate (ATP)
Powers cellular work:
- Mechanical: breaking of cilia, muscle contraction, chromosome movements.
- Intracellular transport: Na, k-ATPase
- Chemical: polymerization
- Within the cell: hydrolysis of ATP is coupled to endergonic reactions, transfers phosphate group from ATP to another molecule.
Structure of ATP
- Adenine (nitrogen base)
- Ribose (a five-carbon sugar)
- Three phosphate groups
(phosphate bonds are unstable, negative energy)
ATP+H2O->ADP+Pi+energy
Enzymology
- Enzymes are biological catalysts
- Most are proteins
- Not consumed by the reaction
- Speed up the metabolic rate of reactions by lowering energy barriers
Chemical reactions
Involve bond breaking and bond making.
1) Transition state: molecules are unstable, reactants must absorb energy to reach this state (activation energy Ea)
2) Reaction occurs and energy is released as new bonds are formed
Enzymes
Catalyze the conversion of substrate (reactants) to products.
E+substrate-> ESubstrate -> E + products
Active site
- Pocket or groove in the protein’s surface, formed by a few amino acids.
- Binding of substrate causes a change in enzyme structure (induced fit)
Allosteric enzymes
- Involved in regulation of metabolic pathways
- Comprised of two or more polypeptides, each with its own active site.
- Allosteric site (is not the active site) usually located where the polypeptides join.
- Two conformations: active and inactive.
Allosteric enzyme Activation & inhibition
- Binding of the regulator stabilizes active form
- Binding of the regulator stabilizes inactive form
Regulators
- Molecules that bind weakly to the allosteric site.
- Behave like reversible noncompetitive inhibitors.
- Often inhibitors & activators are similar in shape and compete for allosteric site.
Phosphofructokinase
- Found in pathway of glycolysis.
- ATP is inhibitor (feedback: what is produced goes back to beginning of the chain and stops it).
- AMP activation
- Both bind at allosteric site
Threonine deaminase
- Involved in production of isoleucine (amino acid)
- Feedback: end product acts as inhibitor (of activity and the pathway)
- Isoleucine binds allosterically
Cooperativity
- Activation if enzyme activity
- Enzymes are comprised of more than one polypeptide
- Substrate binding to the active site of one subunit induces a conformational change in all subunits
Mechanism to lower activation energy (4)
- Correct orientation of substrates
- Induced fit may distort the substrate’s chemical bonds
- Active site may provide a microenvironment for a specific reaction
- Side chains of the amino acid at the site may participate directly in the reaction.
Rate of reaction
Dependent on concentration of the substate (if low, rate is low). If high, all active sites are engaged (saturation)
Cofactors or coenzyme
Require additional, nonprotein molecules to function.
-Coenzymes: organic molecules, derived from vitamins.
Enzyme inhibition
- Competitive: resemble substrate, bind at active site. overcome by increasing substrate concentration
- Non competitive: bind to another part, changes shape.
