A Quick Guide to pH, pKa and pI - Bitesize Bio
pH describes the acidity of a solution. pKa and pKb are the logarithmic acid and base dissociation constants, respectively. Ka and Kb are the acid and base. This pA2 value then equates to the pKB value. . A symbiotic relationship in which the symbiont (parasite) benefits at the expense of the host by .. Phase IV consists of post marketing surveillance studies conducted to learn more about the .. Just like the pH, the pKa tells you of the acid or basic properties of a substance. pKa tells us how acidic (or not) a given hydrogen atom in a compound is. This is useful because . Since the scale is logarithmic, a pH difference of 1 corresponds to a factor of 10 in stronger the acid, in the basic pKB scale, the lower the. pKB, the stronger .. to its launch on the market took thirteen years. This enormous.
If we multiply both sides of this equation by HA over H plus, on the left-hand side we get Ka times the inverse of this. So you have your HA over H plus is equal to your concentration of your conjugate base. And let's do the same thing here. Solve for A minus. So to solve for A minus here, we might have to do 2 steps.
So if we take the inverse of both sides, you get 1 over Kb is equal to A minus over H, the concentration of my conjugate acid times the concentration of hydroxide. Multiply both sides by this. And I get A minus is equal to my concentration of my conjugate acid times concentration of hydroxide. All of that over my base equilibrium constant. Now, these are the same reactions. In either reaction for given concentrations, I'm going to end up with the same concentration.
This is going to equal that. These are two different ways of writing the exact same reaction. So let's set them equal to each other. So let me copy and paste it, actually. So I'm saying that this thing, copy, is equal to this thing right here.
So this is equal to-- let me copy and paste this-- that. That's equal to that. So let's see if we can find a relationship between Ka and Kb. Well, one thing we can do is we can divide both sides by HA.
So if we divide both sides by HA. Actually, I could probably have that earlier on to the whole thing. If we ignore this part right here, this is equal to that. Let me erase all of this. I'm using the wrong tool. So we could say that they both equal the concentration of A minus. So that's equal to that. We can divide both sides by HA. This over here will cancel with this over here.
And we're getting pretty close to a neat relationship. And so we get Ka over our hydrogen proton concentration is equal to our hydroxide concentration divided by Kb.Ph and Pka Concept
You can just cross-multiply this. So we get Ka, our acidic equilibrium concentration, times Kb is equal to our hydrogen concentration times our hydroxide concentration. Remember, this is all in an aqueous solution. What do we know about this?
What do we know about our hydrogen times our hydroxide concentration in an aqueous solution? For example, let me review just to make sure I'm jogging your memory properly.
We could have H2O. It can autoionize into H plus. And this has an equilibrium. You just put the products. So the concentration of the hydrogen protons times the concentration of the hydroxide ions. And you don't divide by this because it's the solvent. And we already figured out what this was.
If we have just completely neutral water, this is 10 to the minus 7. And this is 10 to the minus 7. So this is equal to 10 to the minus Now, these two things could change. I can add more hydrogen, I could add more hydroxide. And everything we've talked about so far, that's what we've been doing. That's what acids and bases do.
They either increase this or they increase that. But the fact that this is an equilibrium constant means that, look, I don't care what you do to this. At the end of the day, this will adjust for your new reality of hydrogen protons.
And this will always be a constant. As long as we're in an aqueous solution, a solution of water where water is a solvent at 25 degrees. I mean, in just pure water it's 10 to the minus 7. But no matter what we do to this and this in an aqueous solution, the product is always going to be 10 to the minus 14th power. So that's the answer to this question. This is always going to be 10 to the minus If you multiply hydrogen concentration times OH concentration. Now they won't each be 10 to the minus 7 anymore, because we're dealing with a weak acid or a weak base.
So they're actually going to change these things. But when you multiply them, you're still going to get 10 to the minus And let's just take the minus log of both sides of that. Let me erase all this stuff I did down here. I'll need the space. Let's say we take the minus logs of both sides of this equation. So you get the-- let me do a different color-- minus log, of course it's base 10, of Ka. Let me do it in the colors. Ka times Kb is going to be equal to the minus log of 10 to the minus So what is this equal to?
The log of 10 to the minus 14 is minus 14, because 10 to minus 14th power is equal to 10 to the minus You take the negative of that, so this becomes So the right-hand side of your equation just becomes And this one, we could use log properties.
This is same thing as the minus log of Ka. We use the colors. Ka plus the minus log of Kb. Or, though you could think of this-- this is your pKa, this is your pKb. So you can say, this is pKa plus pKb.
Oh, I wanted to use blue. Plus pKb, and all of that's going to be equal to Now why is this useful? Well, if you know the pKa for a weak acid-- For example, let's say we have NH4 plus. Pepsin cleaves the 44 amino acids from pepsinogen to create more pepsin. It will not cleave at bonds containing valine, alanine or glycine.
Peptides may be further digested by other proteases in the duodenum and eventually absorbed by the body. Pepsin is stored as pepsinogen so it will only be released when needed, and does not digest the body's own proteins in the stomach's lining.
Pepsin functions best in acidic environments, particularly those in a pH of 3. Pepsin denatures if the pH is more than 5. Pepsin is potently inhibited by the peptide inhibitor pepstatin. Peptide A large molecule macromolecule made up of amino acids. Peptides are the building blocks of proteins. Peptide bond A covalent bond joining two amino acids, formed by condensation synthesis. Peptidoglycan A type of polymer in bacterial cell walls consisting of modified sugars cross-linked by short polypeptides.
Peptidyl site The site on the ribosome occupied by the peptidyl- tRNA just before peptide bond formation. Peptidyl transferase The enzymatic centre in the ribosome responsible for peptide bond formation during translation. Perception The interpretation of sensations by the brain; The ability to make sense of what one sees, hears, feels, tastes or smells.
Percent A fraction in which the denominator is assumed to be Percolation The movement of water through the openings in a substance, e. Perfect number A number that is the sum of all its factors except itself. Perfusion Sometimes used synonymously with blood flow, although perfusion can be applicable to the flow of a solution other than blood. Pericardium The sac that contains the heart and produces fluid which allows the heart to move easily.
Pericentric inversion A chromosomal inversion that involves the centromere.
A Quick Guide to pH, pKa and pI
Pericentromere The region around or near the centromere also known as kinetochore of a nuclear chromosome. Perimeter The sum of the lengths of the sides of a polygon. Period The measure of how often a function repeats its same values. Periodic function A function that keeps repeating the same values. Periosteum A fibrous membrane that covers the surface of bone except at the end of the bones where it is covered with cartilage as part of a joint.
In children, periosteum is involved in forming new bone and molding the configuration of bone; and in the adult, the periosteum forms new bone secondary to injury or infection. Peripheral membrane protein Proteins loosely attached or adhering to a membrane. They do not span the lipid bilayer of the membrane, but attach indirectly, typically by binding to integral membrane proteins, or by interactions with the lipid polar head of the lipid bilayer of the cell mambrane.
Peripheral nervous system The sensory and motor neurons that connect the body to the central nervous system. Peripheral neuropathy Damage to the neurons that carry sensory information from the arms and legs. Peripheral pain pathways Pain perception is initiated by excitation of unmyelinated C-fibre or thinly myelinated Adelta primary afferent neurons nociceptors with cell bodies in spinal dorsal root ganglia DRG.
The DRGs also contain temperature sensors, itch sensors, cutaneous mechanoreceptors and mechanosensitive afferents from the musculature, none of which is normally nociceptive. Nociceptors can be divided into subclasses defined by their receptive properties, neurochemical profiles and central projections. Each subclass of nociceptive neurons responds to a characteristic range of acute stimuli, such as tissue damage, extreme temperature, or chemical insult.
For reasons that remain poorly known, peripheral nerve damage can lead to neuropathic pain: Further differentiation of nociceptors establishes different subclasses defined by their receptive properties, neurochemical profiles and central projections.
However, for reasons that remain poorly known, peripheral nerve damage can lead to neuropathic pain: Periplast The entire assemblage of scales, spines and spicules which encase some heliozoa, chrysomonads, etc.
Peristalsis Regular contractions of a body or part of a body. Mostly said of the intestinal system of vertebrates: Also applied to the squirming behaviour of some euglenids. Peristome The region of the body around, and external to, the mouth. To deserve application of this term, the region must be modified to favour the acquisition of food.
Peritoneum A membrane that lines the body cavity and forms the external covering of the visceral organs. Peritonitis Inflammation of the lining of the abdominal cavity. Indications of peritonitis are called "peritoneal signs": The peritoneal membrane is very sensitive to exposure to foreign substances.
Contact with blood, bile, urine, pus will cause peritoneal signs. Before antibiotics, people would die from peritonitis if an inflamed appendix burst. Peritubular capillaries In the vertebrate kidney, the capillaries that surround the renal tubule.
Water and solutes are reabsorbed into the bloodstream through the peritubular capillaries and some substances are secreted from them into the renal tubule Periventricular leukomalacia The most common ischemic brain injury in premature infants, characterized by the death of white matter near the cerebral ventricles. The lesion results from decreased cerebral blood flow to the periventricular white matter surrounding the lateral ventricles in the brain.
The associated neurologic deficit is spastic dylegra. Frequently results in Cerebral Palsy. Permeability A measure of the ease with which a substance can penetrate through a membrane. An Ideal semi-permeable membrane is permeable only to solvent, usually water, ie. A Selectively permeable membrane is permeable to some substances and impermeable to others, i. This definition applies to a biological membrane. Permutation The permutation of n things taken j at a time is: Peroxidase An enzyme which catalyzes the transfer of oxygen from hydrogen peroxide to a suitable substrate and thus brings about oxidation of the substrate.
Peroxide Value PV Measures the amount of peroxides and hydroperoxides in a sample of fat produced in the oxidation process. Peroxisome A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide. Perpendicular Two lines are perpendicular if the angle between them is 90 degees. The tendency to continue an activity once it has been started and to be unable to modify or stop the activity even though it is acknowledged to have become inappropriate.
Persistent repetition of words, ideas of subjects so that, once an individual begins speaking about a particular subject or uses a particular word, it continually recurs. Perseveration differs from the repetitive use of "stock words" or interjections such as "you know" or "like".
The inappropriate persistence of a response in a current task which may have been appropriate for a former task. Perseverations may be verbal or motoric. Perseveration is most commonly seen in organic mental disorders, schizophrenia and other psychotic disorders. Persistent Vegetative State PVS A long-standing condition in which the patient utters no words and does not follow commands or make any response that is meaningful.
Pertussis Acute infectious disease characterized by a cough that has a "whoop" sound; also called whooping cough A serious respiratory infection which can cause pneumonia, brain damage, or death. Pervasive developmental disorder PDD 1. Extreme distortions or delays in the development of social behavior and language.
A term used to describe drug exposure to children while in the womb. Results of this exposure can cause extremely short attention spans. PET scan positron emission tomography scan A procedure in which a small amount of radioactive glucose is injected into a vein, and a scanner is used to make detailed, computerized pictures of areas inside the body where the glucose is used. Because cancer cells often use more glucose than normal cells as they more metabolically active than normal cellsthe pictures can be used to find cancer cells in the body.
After receiving the radioactive drug, the patient lies still for about 45 minutes while the drug circulates throughout the body. If a tumor is present, the radioactive sugar will accumulate in the tumor. The patient then lies on a table, which gradually moves through the PET scanner 6 to 7 times during a minute period. The PET scanner is used to detect the radiation.
A computer translates this information into the images that are interpreted by a radiologist. They may also detect cancer when other imaging techniques show normal results. PET scans may be helpful in evaluating and staging recurrent disease. Petit mal attacks Epileptic seizures characterized by brief periods of fixed stare, unconsciousness, unresponsiveness, and lack of activity.
A measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions. See pH scale Phage A virus for which the natural host is a bacterial cell i. Also called a bacteriophage. Phagemid A type of plasmid which carries within its sequence a bacteriophage replication origin. When the host bacterium is infected with "helper" phage, the phagemid is replicated along with the phage DNA and packaged into phage capsids.
Phagocytes Large white blood cells that contribute to the immune defenses by ingesting microbes, other cells, cell debris, microorganisms, and foreign particles. The two principal phagocytes are neutrophils and monocytes. They emigrate out of the blood and into tissues in which an infection has developed. After phagocytosis the ingested material is then degraded via enzymes.
Biomedical Sciences Glossary - P
Phagocytosis A type of endocytosis internalization into the cell involving large, particulate substances; The ingestion of visible particles of food by enclosing them with a membrane to form a food vacuole. Phagotroph An organism which feeds by phagocytosis. Pharmacokinetics Examines the effects on the body of a drug, specifically the study of the intake of drugs in the body including absorbtion, distribution, transformation and excretion.
Examines issues such as how quickly a drug is absorbed into the blood and how different dosages affect the absorption, how the drug is distributed into organs or tissues the body, how the body metabolizes the drug and whether what the drug is changed into by the body is active, as well how long it takes the body to metabolize half of the drug the drug's half-lifeand how long it takes the drug to clear the body and be excreted Pharmacotyping The individualized drug selection and dosage profiling by a doctor based on patient's genotyping and haplotyping data for genes involved in pharmacodynamic and pharmacokinetic drug actions in the body.
Pharyngeal arches Also known as branchial arches, gill arches, or visceral arches Columns of mesenchyme found in the neck of the developing vertebrate embryo derived from cranial neural crest. In lower vertebrates, blood vessels formed here become part of the gills; in higher vertebrates derivatives include portions of the jaw and middle ear. Pharynx An area in the vertebrate throat where air and food passages cross. A region of the ingestion apparatus lying internal to the mouth of a metazoan organism or internal to the cytostome of a protist.
Involved in the swallowing process.
pH, pKa, Ka, pKb, Kb - Organic Chemistry | Socratic
Stage of drug research development, undertaken prior to the administration of the drug to humans. Consists of in vitro and in vivo screening, pharmacokinetics, toxicology, and chemical upscaling. If preclinical toxicity studies in animals reveal no harmful effects, a phase I study is usually then performed on a limited number of healthy human volunteers.
These studies are designed on a small scale to show that the drug is safe in humans and set to determine the highest tolerated dose and to explore the safety, kinetics, interactions, and pharmacological effects of various doses.
They seek to gain early evidence of effectiveness. Ultimately, all the information gleaned from a well designed Phase I trial will aid in developing a well designed Phase II trial.
Phase Ia studies examine how the body reacts to a single, one-time dose of the drug in a monitored situation, usually involving healthy volunteers without the condition that the drug will be indicated for. As each dose is tested in a predetermined number of people, the trial progresses to the next dosing level with a different group of volunteers.
Phase Ib trials examine how the body reacts to multiple doses of the drug over a period of time, from a few days to a few weeks. The average length of time that a compound is in Phase I testing is about one year. Phase II testing looks at the efficacy of a drug, provided that it has proven safe in Phase I testing. Phase II testing is conducted in a relatively small number of patients having the condition the drug is indicated for, using several doses that, based on the data obtained in Phase I, are hypothesized to be efficacious doses.
A placebo is also tested to obtain a baseline value for the comparison of drug effectiveness. Phase II testing takes from several months to 3 years. In clinical phase IIa studies, efficacy is tested on a limited group of patients, and the optimal administration regimen dose, frequency is determined. Here efficacy and safety of a single or a limited number of drug regimens are evaluated by applying them in a sufficiently large number of patients usually a few hundredwho are more representative of the population as a whole.
Efficacy and safety of the new treatment are compared with a placebo or with the existing standard treatment or to other approved drugs. Usually, several complementary phase III studies are performed simultaneously. The reports of the phase I to III studies are part of the drug registration file. Studies commenced after closing the registration file but before the product is released on the market are sometimes grouped under the name phase IIIb studies.
Testing takes on average 24 months, with the FDA requiring a longer period for drugs to treat some indications. Once the FDA has reviewed all the data from clinical testing, it can approve the NDA for the drug to be marketed and sold, or it can schedule a hearing to bring experts together to comment on the clinical data and the drug to be reviewed. Sometimes an additional study is requested to clarify the scientific data to show more proof that the drug works, or to compare the drug to existing medications for treating the disease.
Begins when the product is approved for release on the market. Phase IV consists of post marketing surveillance studies conducted to learn more about the drug's risks, benefits, optimal use, and how it compares to competitors. Studies on large numbers of people may be helpful after a product is brought into circulation, for instance, in order to trace rare side effects. Phencyclidine hydrochloride PCP An anesthetic agent used in veterinary medicine.
Also an illegal hallucinogenic street drug, "angel dust. An environmentally induced phenotype that resembles the phenotype produced by a mutation. Phenetics An approach to taxonomy based entirely on measurable similarities and differences in phenotypic characters, without consideration of homology, analogy, or phylogeny.
Phenotype The physical and physiological traits of an organism ; Observable manifestation of a genetic trait, resulting from a specific genotype the set of genes it possesses and its interaction with the environment. The term for the appearance of an organism with respect to a particular character or group of characters physical, biochemical, and physiologicas a result of the interaction of its genotype and its environment.