B MCAT - Bio, Biochem II Flashcards
Osmosis
Osmosis is the movement of water across permeable membranes from areas of lower solute concentration to areas of higher solute concentration.
Osmolarity
When separated by a semipermeable membrane, how will water move?
Osmolarity describes concentration of solute/solution. Low osmolarity = small amount of solute compared to solution. High osmolarity = large amount of solute compared to solution. When separated by a semipermeable membrane, water will move from areas of lower solute concentration to areas of higher solute concentration.
Otolithic organs
The otolithic organs are the saccule and utricle in the inner ear, related to vestibular sense. There are CA crystals adjacent to hair cells in a gel that are sensitive to gravity–they move with gravity when you stand up vs. lay down.
endolymph fluid
fluid that fills the semicircular canals in inner ear to facilitate vestibular sense.
mechanoreceptors
mechanoreceptors sense PRESSURE.
tonicity
the ability of an extra-cellular solution to move water in or out of the cell.
If a cell is placed in a hypertonic solution, there will be a net flow of water out of the cell, and the cell will lose volume. A solution will be hypertonic to a cell if its solute concentration is higher than that inside the cell, and the solutes cannot cross the membrane.
If a cell is placed in a hypotonic solution, there will be a net flow of water into the cell, and the cell will gain volume. If the solute concentration outside the cell is lower than inside the cell, and the solutes cannot cross the membrane, then that solution is hypotonic to the cell.
If a cell is placed in an isotonic solution, there will be no net flow of water into or out of the cell, and the cell’s volume will remain stable. If the solute concentration outside the cell is the same as inside the cell, and the solutes cannot cross the membrane, then that solution is isotonic to the cell.
hydrostatic pressure
Hydrostatic pressure is the pressure a liquid exerts on its container, and reflects the volume of liquid in a space.
P=density x g x h
congenital disorder
present since birth
receptor tyrosine kinases
Receptor tyrosine kinases are integral membrane proteins that relay a “message” from the extracellular side of the cell to the intracellular side of the cell.
hydrostatic vs. oncotic pressure in the capillaries
Hydrostatic pressure is the force that pushes blood out of the capillaries.
Oncotic pressure is the force that pushes blood into the capillaries.
Together, they determine fluid flow from the capillaries to surrounding tissue.
heterocycllic
a compound whose molecule contains a ring of atoms of at least two elements (one of which is generally carbon).
alveoli
tiny air sacs of the lungs which allow for rapid gaseous exchange.
genetic recombination
Genetic recombination leads to the creation of an organism with DNA that differs from its parent organism.
viral replication–lytic vs. lysogenic
lytic virus replication = immediately take over host’s machinery, replicates itself, lyse (destroy) host, and spread to new hosts. “impatient”
lysogenic = (prophage) repressed/latent to start, host doesn’t know it is there until activated, then replicated with host DNA. “hitch a ride”
With a lysogenic virus, the new daughter cells are infected with the virus, eventually leading to a neoplasm, also known as tumor.
retrovirus
(not quite lytic or lysogenic)
MAKES DNA FROM RNA.
Infect animals, not bacteria.
A retrovirus is an enveloped virus with 3 unique proteins.
Enters host through endocytosis or similar mechanism.
Replicates its RNA strand to DNA.
Then replicates again to double stranded DNA with “sticky” ends.
Then travels to host DNA and integrates. Host can’t tell it is foreign and it is transcribed like normal DNA.
Self assembly of new viruses–they bud off from cell membrane.
Prion
A prion is similar to a virus but does NOT contain genetic material.
Two ways to cleave peptide bonds
1) Acid hydrolysis–add water and heat and peptide bonds will cleave. Non-specific.
2) Proteolysis–Use protease enzymes to target specific bonds in the polypeptide chain.
Ex. protease enzyme trypsin. Only cleaves on the carboxyl side (C-terminal) of basic amino acids like arginine and lysine. (trypsin also used by our pancreas to digest food).
Catalytic functions of enzymes
Enzymes can be proton carriers; speed up transfer of H to help lower Ea for rxn.
E+S>ES>E+P
Covalent catalysis–enzymes can carry electrons (be an “electron sink”) as they move around, for example in decarboxylation.
Electrostatic catalysis–enzymes can stabilize charge. For example, DNA is a very negatively-charged polymer because of all the phosphate groups. DNA polymerase includes metal Mg^2+ to stabilize the DNA’s neg charge.
Proximity and orientation effects–enzymes can help make sure that molecules are positioned to collide and react. Increase frequency of collisions.
Cofactors and coenzymes
Help an enzyme along by carrying electrons or participating in a reaction.
Many coenzymes and cofactors come from our diet in form of vitamins and minerals.
Vitamins are organic cofactors and coenzymes. B3, or niacin, is a precursor to NAD and B12 is a precursor to CoA.
Minerals are inorganic (no C) cofactors. Mg^2+ is used by DNA polymerase. Ca can BOTH act as a cofactor, and is a critical molecule itself as well.
Induced fit model of enzyme binding
(vs. active site model)
A substrate for an enzyme is the reactant of the reaction that the enzyme catalyzes.
An enzyme and a substrate must come into close physical proximity for binding to occur, and such proximity can introduce physical forces that alter the shape of the enzyme.
The induced fit model of enzyme binding states that the substrate itself alters the enzyme active site.
Km
Km is the substrate concentration [s] where the enzyme rate V is at 1/2 of the maximum possible rate Vmax.
moles per liter (M)
Lower Km = more efficient enzyme.
Kcat
The turnover number; how many reactions an enzyme can turn over in a second. sec^-1
Higher Kcat = more efficient enzyme.
catalytic efficiency of an enzyme =
catalytic efficiency of an enzyme = Kcat/Km
Higher Kcat = more efficient
Lower Km = more efficient
homotropic vs. heterotropic in enzyme feedback loops
In enzyme feedback loops, a homotropic regulator acts as both the substrate and the regulator (eg. Abundance of ATP in cell says, “we have ATP” and inhibits glycolysis) .
A heterotropic regulator acts only as the regulator, and is not the substrate (eg. Abundance of AMP says, “we need ATP” and activates glycolysis).
Ligand
The ligand is a chemical messenger released by one cell to signal either itself or a different cell. The binding results in a cellular effect, which manifests as any number of changes in that cell, including altering gene transcription or translation or changing cell morphology.
Protein functions
Enzymes can be proteins (though not all enzymes are proteins).
Proteins also function as:
Receptors/ion channel proteins. Eg. insulin is a ligand that binds to a protein receptor on the cell membrane when glucose is abundant to trigger the absorption of glucose.
Transport proteins–Bind small molecules and transport them. Must have high affinity for their ligand when the ligand is in high concentration, and low affinity when the ligand is in low concentration. Eg. hemoglobin.
Motor proteins–myosin (generating contracted muscles), kinesin (intracellular transport), and dynien (intracellular transport and motility of cilia).
Antibodies–protein components of the adaptive immune system. The antigen is the antibody’s ligand.
Enzyme categories
Some enzymes are proteins (made up of primary, secondary, tertiary, and quaternary structures).
Enzymes can also be small inorganic molecules (eg. Mg^2+
Enzymes can be small organic substances that act as coenzymes (eg. flavin).
