Catalysts
�Increase rate of reactions �Remain unchanged by the reaction �Do not change the nature of the reaction or the
final result (the same reaction would have occurred in absence of enzyme but at slower rate)
Generally enzymes are_____
Proteins; exception= ribozymes
enzymes
decrease activation energy required for rxn
Substrate
molecule or reactant the enzyme changes
How do enzymes decrease activation energy?
-Bring rxt close @ active site
-formation of an enzyme-substrate complex that has more energy than the individual rxts
Lock and key model
-Substreate and active site fit together like a lock and key
-models of the enzyme active site
Induced Fit model
-interaction btw enzyme nd substrate conformation of the active site, inducing the binding of the substrate
-models of the enzyme active site
Isoforms
same enzyme, tissue specific acid sequence
-plasma enzymes
creatine phosphokinase(CPK, CK Isoforms)
MM-Skeletal Muscle
BB-Brain
MB-Heart
Tissue-specific isoforms
released by damaged or diseased tissue
Measurment of isoforms
using monoclonal antibodies aids in diagnosis of disease
Physiological enzyme activity is controlled by
-temperature
-pH
-cofactors
-coenzymes
-zymogens
-phosphorylation
-substrate concentration
-reversability
Temp
- physio enzymes optimum temp @ or near 37oC
- 0oC = immeasurable activity
-40oC and +++ most enzymes inactive
-tertiary structure destabilized
pH
-pH optima spans pH scale
-pepsin ph=2
-trypsin ph=8
-optima of purified enzymes in test tube =/= physiologically relevant pH
Cofactors
-Metal ions -Ca2+, Mg2+, Zn2+, Nb2+, Cu2+, selenium
- induce a conformational change in the active site of the enzyme to enhance formation of the ES complex
Coenzymes
-subcategory of cofactors. organic moecules, not necessarily an enzyme per se
-derived from water soluble vitamins such as niacin, riboflavin, pyridoxine
-transport small moloecules such as hydrogen atoms to active site of enzyme
zymogens
-enzymes produced in the inactive form
-proteolytic cleavage (hydrolysis of the peptide chain @ a specific location) converts enzyme to the active form
-pancreatic enzymes, insulin
Phosphorylation
-addition of a phosphate group
Protein Kinases
enzymes that add phosphate groups
Addition of a phosphate group can:
-activate an enzyme
-deactivate an enzyme
-increase or decrease activity
Phosphatases
removes phosphate groups
Phosphorylation/dephosphorylation Cascades
complex phosphorylation cascades are common to physiological regulation
Substrate concentration
-enzyme activity increases as substrate concentration increases to a plateau
-@ plateau phase, all available enzymes are function @ maximum velocity
-increase in substrate concentration produces no change in rxn rate
-@ this point enzyme is saturated
Substrate inhibition (end product inhibition, negative feedback inhibition)
-the concentration of a final product in a metabolic pathway inhibits an enzyme earlier in the sequence
-prevent over-accumulation of final product
-can shift pathway to production of another intermediate
Allosteric Inhibition
-the mechanism by which an endproduct inhibits an enzyme
-binding induces a conformational change in the enzyme which inhibits its activity
-
Allosteric inhibitor(endproduct)
binds to a site on the enzyme, separate from the active site
allosteric inhibition
is directed by concentration of the allosteric inhibitor
allosteric binding site
What products bind to if product is too high
-site not active unless concentration of product exceeds a certain level
Reversible rxns
-some enzymes catalyze forward and reverse rxns
-carbonic anhydrase
h2c03<=> h2o+co2
Law of mass action
rxn is driven from the side of the equation where product concentration is higher, to side where concentration is lower
metabolic pathways
formed when enzymes are linked in sequences of rxns
inborn errors of metabolism
-each enzyme in a metabolic pathway is controlled by a separate gene
-intermediate upstream of the defect accumilate
-intermediates downstream of the defect decrease
- results in a disease state
(properties of the) Plasma Membrane
-separates intra and extracellular environments
-selectively permeable
-hydrophobic molecules readily penetrate the membrane
-small inorganic ions pass through channels in memnbrane
Categories of transport
-passive transport
-active transport
Passive Transport
-net movement of ions down concentration gradient (from higher to lower conc.)
-doesnt require energy
-types
simple diffusion
osmosis
facilitated diffusion
Diffusion
movement of a molecule or ion to a lower conc. (down conc. gradient)
-random motion
-eliminates a conc. gradietn; distributes evenly
permeable
-gas xchange occurs by diffusion
Osmosis
-when a membrane isnt permeable (selectively impermeable) to solute
-net diffusion of h2o
-simple diffusion of solvent instead of solute
Aquaporins
...
Osmotic pressure
-the force that would have to be exerted to prevent osmosis
Fluid compartments
-plasma
-interstitial fluid-fluid that lies btw cells in tissues (interstitial space- space btw cells)
-intracellular fluids- fluid in the cytoplasm
osmotically active
- a solute that cant cross a membrane barrier
-promotes osmosis or movement of h2o
-ex: plasma proteins(cant move from capillaries to interstital fluid. draw h2o out of interstitial space in2 plasma)
-low plasma protein- excessive tissue fluid accumulatio
osmolality
-total molality of a solution based on sum of all solutes
-ex 1m glucose & 1m frucose = 2osm
-ex 1m glucose +1 m fructose + 1m nacl= 4osm
Intravenous Fluids
-5% dextrose- 5g glucose/100ml; 0.3m; 0.3osm
-normal saline-0.9g nacl/100ml; 0.15;0.3osm
-5% dextrose & normal saline have the same osm as plasma=isotonic to plasma
Tonocity of solutions
-conc. of osmotically active solutes
isotonic
solutions w/same osmo active solutes as plasma
hypertonic
solutions w/higher osmo active solutes than plasma
hypotonic
solutions w/lower osmo active solutes than plasma
Facilliated Diffusion
-Carrier-mediated transport
-Passive=no energy
-movement from high to low conc. requires a carrier, usually a protein
-characteristivcs= specificity, competition, saturation
Glucose transport
-glucose enters cell by facillitated diffusion
-transporters called
GLUT
-isoforms= GLUT1,GLUT2,etc. Tissue specific
GLUT4
-skeletal muscle isoform
-stored in cytoplasmic vesicles
-inserted in membrane in response to insulin stimulation or exercise
Active transport
-occurs against a conc. gradient (lower to higher conc.)
-requires input of energy ATP
-Ca-100nM intra; 1mM extracellular
-requires specific transport proteins
-primary
-secondary
Primary Active Transport
-hydrolysis of ATP is directly coupled to the action of the transporter
Primary active transport
�Sequence of events �Molecule to be transported binds to a recognition
site
�ATP is used to phosphorylate the transporter protein
�Phosphorylation causes a conformational change in the transporter
�Molecule is released on opposite side of membrane, using
The Na+/K+ ATPase
-one of the most important active transport mechanism in the body
-maintains ionic balance and can be used to perform work
Na+ higher extra, K+ is higher intra
The Na+/K+ ATPase
an ion pump composed of several protein subunits
-regulated by phosphorylation
-
important membrane proteins
Secondary active transport (coupled transport)
-diffusion of Na+ down its conc. gradient powers the movement of another ion, against its conc. gradient
-ATP hydrolysis= indirect
-energy rquird for movement of a molecule against a conc. gradient obtained from NA+ gradient
types of secondary active transport
-cotransport or symport
-antiport of countertransport
cotransport or symport
he molecule to be transported is moved in the same direction as Na+ (into the cell)
antiport of countertransport
A molecule is transported in the opposite direction of Na+ (out of the cell).
The Na+/Ca2+ Exchanger
-countertransport
-signal transduction elevate intracellular free ca2+
-prolonged high ca2+=damaged cells
Using The Na+/Ca2+ Exchanger
-cells pump ca2+ out and allow na2+ in
�The energy created by the Na+ gradient fuels Ca2+ extrusion by the cell
�Excess Na+ is removed by the Na+/K+ ATPase.
Membrane Potential
Unequal distribution of charge results in a charge difference or membrane potential, measured in voltage
voltage across the plasma membran
-theoretical approx.
-based on k+
-membrane is motst permeable to k+
-approx based on k+ alone
Resting Membrane Potentia
-In reality, the membrane potential fluctuates between -90 and +60, particularly during cell signaling.
-The membrane potential of an unstimulated cell
-The RMP of most cells in the body is close to the K+ equilibrium potential, -65 - -85 mV.
RMP
The permeability of a specific ions
�The concentration of the ion in the intracellular and extracellular environment
-A change in the concentration of any ion on either side of the membrane will change the membrane potential.
RMP & signal transduction
Changes in RMP are used in cell signaling.
� In neurotransmission, RMP increases, due to influx of Na+
� Similar changes occur in muscle contraction.
depolarization
movement of membrane potential in the positive direction
hyperpolarization
Movement of membrane potential in the negative direction
RMP maintained by
Na+/K+ ATPase
metabolism
all rxns in body involved in energy transfer
catabolic rxns
break down glucose, fatty acids, and proteins for use as an energy source
anabolic rxns
fueled by atp and synthesize new cellular marcromolecules
energy transfer
-energy contained in glucose, fatty acids, and amino acids is transferred to chemical bond energy,
ATP
-transfer involves REDOX rxns
Glycolysis
-breakdown of glucose for energy
-pyruvic acid can be used to generate additional ATP as can NADH
- Glucose + 2 NAD + 2ATP + 2Pi yields 2 pyruvic acid + 2NADH + 2ATP
-a. Pyruvic acid + acetyl coA (aerobic)
b. Conversion to lactic acid (anaerobic)
lactic acid pathway (anaerobic respiration)
-conversion of glucose to lactic acid by reduction of pyruvate (as opposed to O2)
-occurs when O2 is lacking
-end products are lactic acid w/a net gain of 2ATP per glucose
-most relevant in red blood cells and skeletal muscle cells
Glycogenesis and Glycogenolysis
-due to osmotic & permeability q's, cells dnt store glucose
-the storage form of glucose is glycogen
Glycogenesis
formation of glycogen from glucose is called (skeletal muscle and liver)
Glycogenoslysis
is the breakdown of glycogen to glucose-6-phosphate, which enters the glycolytic cycle
The cori Cycle
-G-6-P can be converted to glucose and released to the blood, via the enzyme g-6-phospatase. This rxn occurs in the liver b/c cells in the liver make the enzyme.
-lactic acid, amino acids, & glycerol can also be converted to G-6-P and glucose by the liver
Energy sources
-several alternative energy sources in body
-glucose (all cells)
-glycogen (liver)
-triglycerides (stored in adipose)
-proteins (breakdown of muscle)
-all forms of energy storage can be interconverted