Polypeptides {protein, peptide}| {polypeptide} are 50% of body solids. Polypeptide has 5 to 4000 amino acids.
nitrogen
Protein is the only nitrogen source in diet. Nitrogen leaves body as urea in urine.
metabolism
Conjugated protein can bind to another molecule. Peptide-bond breaking, phosphorylation, dephosphorylation, amidation, methylation, and glycosylation alter protein structure and function.
structure
Protein has four structure levels: primary, secondary, tertiary, and quaternary.
functions
Most proteins are enzymes. Proteins are also for transport, structure, storage, hormones, movement, toxins, protection, and clotting. Proteins maintain water balance, because soluble cell proteins cause higher water pressure inside cell, by osmosis. Proteins buffer water solution inside cells, because soluble proteins have weak acid and weak base groups.
functions: storage
Proteins {storage protein} can be for storage. Ferritin stores iron. Casein stores carbohydrate. Ovalbumin stores fat and carbohydrate.
functions: structures
Fibrous proteins {structural protein} are for body structure.
Alpha-keratin is in skin, hair, wool, horn, and nails. Alpha-keratin has three to seven amino acid chains in bundle, cross-linked by disulfide bonds, which then bundle again.
Scales, claws, beaks, silk, and feathers have beta-keratin. Beta-keratin is mostly glycine, alanine, and serine.
Collagen covers organs and bones. Collagen has three amino-acid chains twisted into left-handed helix. It is mostly glycine, alanine, proline, and hydroxyproline. It has lysine-bond cross-links. Boiled collagen is gelatin.
Elastin is in ligaments and stretchable connective tissue such as blood vessel walls.
Resilin is in flea-leg ligaments, fly-wing ligaments, and cicada-song vibrating tissue.
Glycoprotein is in membranes and cell walls.
Mucoprotein is in membranes and cell walls.
Wing joints have resilen, which is elastic.
Insect skeletons have sclerotin.
Viruses have protein coats.
functions: transport
Proteins {transport protein} can transport small molecules {protein transport}.
Ceruloplasmin carries copper.
Ferritin carries iron.
Hemoglobin carries oxygen and carbon dioxide.
Lipoprotein carries fats and cholesterol.
Myoglobin carries oxygen and carbon dioxide.
Serum albumin carries fatty acids and many other substances.
Proteins can also carry calcium and heavy metals.
Cell has 30,000 organelles {proteasome}| that are 100 times bigger than proteins, are tubes, and have proteases that fragment poorly folded or poorly working proteins. Cytoplasm free proteases split protein fragments into amino acids.
enzymes
E1 enzyme activates ubiquitin, which can bind to E2 enzyme, which can then bind to E3 enzyme. E3 enzyme has various possible F-box regions that recognize different protein-end regions. E2-E3 complex (SCF complex) can bind protein at F-box, attach ubiquitins to protein, and release.
proteasome
If several ubiquitins attach to protein, ubiquitin chain attaches to proteasome and activates enzymes that unfold protein and pull protein chain into proteasome tube.
First amino acids can make sequence {signal sequence} that lets protein go through membrane channels.
Amino-acid catabolysis makes energy {amino-acid oxidation}. Liver mitochondria have amino-acid oxidation. Protein-hormone, purine, pyrimidine, vitamin, and porphyrin metabolism involves amino-acid oxidation. Transamination, to make alpha-ketoacid, or deamination, through oxidation by NAD+ to make carbohydrate, removes amino group. Oxidation removes amino acid side chains. Oxidized amino acids become pyruvate, acetyl-CoA, alpha-ketoglutarate, succinyl-CoA, fumarate, or oxaloacetate, for use in TCA cycle.
After release through membranes, membrane-protein complex {calcium pump} restores calcium ions to inside membrane.
Protein chains can have cross connections {cross-linking, protein}|. Two nearby cysteines, which form a spontaneous disulfide bond, can have strong cross-linking. Protein side chains can form hydrogen bonds with oxygens on other amino acids, such as glycine, cysteine, tyrosine, serine, threonine, asparagine, and glutamine.
Proteins above 37 C can lose three-dimensional structure {denaturation, protein}|. If protein has less than 100 amino acids, folding is subcritical after denaturation. If protein has more than 100 amino acids, folding is critical after denaturation.
Proteins can catalyze reactions {enzymatic reaction}|.
types
Enzymes can catalyze hydrogen-ion interactions. They can catalyze anion and cation formation. They can catalyze chelation. They can catalyze charge-transfer coupling. They can catalyze organic-acid formation and breakdown. They can catalyze proton abstractions. They can catalyze Schiff-base reactions.
They can catalyze configuration inversion.
They can catalyze phosphate transfer. They can catalyze pyrophosphate incorporation. Adenylate cyclase can catalyze cAMP-mediated reactions. They {guanylate cyclase} can catalyze cGMP-mediated reactions. They can catalyze transfers.
They can catalyze oxidation. They can catalyze reduction.
They can catalyze metal-bridge formation. They can catalyze metal binding.
They can catalyze acetylation. They can catalyze acylation.
They can catalyze free-radical reactions.
They can catalyze ring breaking and forming.
They metabolize amines, amides, aldehydes, histidines, imidazoles, ketones, nitroxides, oxides, serines, thiols, and thiol esters. They metabolize lipoproteins, carbohydrates, membranes, ion channels, enzyme proteins, lipids, and nucleic acids.
process
Enzymatic reactions can involve active-site directed agents, induced fit, steric effects, and molecular vibrations.
process: reversible
In enzyme-catalyzed chemical reaction, substrate and enzyme quickly and reversibly bind together to make transition state {enzyme-substrate complex}. The reversible reaction has forward and backward reaction rates {Michaelis-Menten rate equation, enzymatic reaction}.
process: irreversible
Transition state slowly and irreversibly separates to reform enzyme and make product. The irreversible reaction has only forward reaction rate.
process: overall
Reaction first part reaches equilibrium quickly, and intermediate concentration quickly becomes constant {steady state, equilibrium}. At steady state, intermediate concentration change over time is zero, free-enzyme concentration is much less than substrate concentration, and intermediate concentration equals total enzyme concentration.
d[ES]/dt = 0 = f1*[E]*[S] - b1*[ES] - f2*[ES]. [E] = [ET] - [ES]. [E] << [S], so [ES] = [ET]. [ES] is enzyme-substrate-complex concentration. [ET] is total-enzyme concentration. [E] is enzyme concentration. f1 is reversible-reaction forward rate. b1 is reversible-reaction backward rate. f2 is irreversible-reaction forward rate.
process: rate
Substrate depletion rate equals product creation rate: product amount divided by time in seconds. Rate is reaction velocity. Rate depends on forward rate, of making product from intermediate, times intermediate concentration.
Reaction rate can be constant {constitutive reaction rate}. Reaction rate can depend on another-molecule concentration {induced reaction rate}.
Product formation rate depends on maximum possible rate, substrate concentration, and forward and back reaction rate constants.
Maximum velocity depends on enzyme concentration and rate constant. Maximum rate {maximum velocity} {Vmax} equals forward reaction rate times total enzyme concentration.
Rate constant for whole Michaelis-Menten equation depends on all three rates: Km = (b1 + f2) / f1. Reaction velocity v depends on rate constant Km, substrate concentration S, and maximum velocity Vmax: v = (Vmax * [S]) / (Km + [S]).
After formation, proteins spontaneously rotate around single bonds, under electric forces, to make three-dimensional structures {protein folding}|.
process: forces
Amino-acid side chains have polarity. Amino acids can be more polarized, dissolve in water, and tend to be at protein surface. Electric forces are greatest at protein surface, where water interacts with amino-acid side chains. Protein ends polarize and are always at protein surface.
Amino acids can be non-polar and tend to be in protein interior. Protein middle has no water, and side chains there interact among themselves.
process: time
It takes 0.2 second to fold protein.
process: misfolding
One-third of proteins misfold {misfolding, protein}. Rotenone pesticide increases misfolding.
structure
In protein structure, all torques equal zero, and all angular accelerations equal zero. Peptide bonds have no rotation. Typically, all amino acids contribute to structure.
structure: globular
Protein typically becomes globular, because amino-acid chain folds back on itself. Globular proteins have 3.5 to 7.5 loops, with 16 to 24 amino acids each. Loop almost touches ends. Loop goes in same direction as alpha helix coil. Loop follows right-hand rule, with loop going around fingers and thumb in forward-motion direction along sequence.
structure: peptide bond
Peptide bond has N[H2]-Calpha[HR]-Ccarboxy[O]-N[H]-Calpha[HR]-Ccarboxy[O] (2 is subscript).
Bond lengths are the following. C-C for sp^3 = 0.1524 nanometers. C-H for sp^3 = 0.1090 nanometers. C-S = 0.1810 nanometers. S-S = 0.2036 nanometers. C-O peptide bond = 0.123 nanometers. N-H peptide bond = 0.100 nm. Calpha-N = 0.146 nanometers. Calpha-Csidechain = 0.153 nanometers. Calpha-Hsidechain = 0.100 nanometers. Calpha-Ccarboxy = 0.152 nanometers. C-N peptide bond = 0.132 nanometers. Ccarboxy-Cnextalpha = 0.243 nanometers. N-Cnextcarboxy = 0.246 nanometers. Calpha-Nnext = 0.241 nanometers. Ccarboxy-Cnextcarboxy = 0.372 nanometers. N-Nnext = 0.368 nanometers. Calpha-Cnextalpha = 0.381 nanometer.
Bond angles in degrees are the following. C-C-C for sp^3 = 113.0, C-C-H for sp^3 = 109.3, H-C-H for sp^3 = 107.2, C-S-C = 100.4, and C-S-S = 104.5.
Distance between alpha carbons can be 0.381 nanometers {beta sheet, protein}, 0.250 nanometers {alpha helix, protein}, 0.090 nanometers {beta turn, protein}, or random {random coil, protein}.
Protein structure descriptions can use phi angle around N-Calpha axis and psi angle around Calpha-C axis, at all Calphas. One angle has highest probability.
Right-handed alpha helix has phi angle = -57 degrees and psi angle = -47 degrees. Range can be -180 to +180 degrees. Normal range is -180 to +60 degrees. -120 degrees is normal. For proline, angle is always 0 or 110 degrees.
Beta sheet has phi angle -120 and psi angle +120. Range can be -180 to +180 degrees. Normal range is -60 to +120 degrees. Normal is 0 degrees.
technique
To study protein folding, place start position for first amino acid nonexistent alpha carbon at 0,0,0. Pick phi angle. Make new k-axis vector be N-Calpha bond. New i-axis direction is from k-axis line to Ccarboxy. j axis is cross product of k with i. Pick psi angle. Make k-axis vector be Calpha-Ccarboxy bond. New i axis is direction from bond to previous N. j axis is cross product of k with i.
Translate polar coordinates to Cartesian coordinates as necessary. Use many known structures to get actual side-chain coordinates from actual values. Use these to find conditional probabilities for amino acids and nearest, second nearest, and so on, amino acid, to make large table. Do not use alpha helix, beta sheet, or beta turn for values. Just find best parameter set and number.
Transition state slowly and irreversibly separates to reform enzyme and make product {Michaelis-Menten rate equation, enzyme}. The irreversible reaction has only forward reaction rate.
Amide bonds {peptide bond}| can form between amino-acid carboxyl groups and amino-acid amino groups. Peptide bonds resonate, are planar, have no rotation, and have hydrogen in trans configuration to oxygen. Peptide bonds do not allow branching.
Trypsin in stomach acid normally cleaves proteins, using water. If body water is low, trypsin ligates amino acids, forming water {plastein reaction}.
Cell-membrane proteins {sodium-potassium pump} can use one-third of all ATP, keep cell volume constant, make membrane excitability possible, and drive amino-acid and sugar active transport. If sodium is present, ATPase phosphorylates. Conformational change carries sodium ion from cell inside to outside, and potassium ion from outside to cell inside, against concentration gradients. Digitalis affects sodium-potassium pumps.
In muscle and microtubule contraction {muscle contraction}|, protein slides along another protein by grabbing and pulling, using ATP.
process
Calcium ions are in muscle-cell sarcoplasmic reticulum. Calcium-ion release initiates sliding. If calcium ion is present, tropomyosin goes into actin helix groove, and calcium opens binding sites, so actin can bind. Then ATPase globule tilts 45 degrees, pulling actin along. Then actin releases. After contraction, tissue elasticity passively returns muscle to normal length.
myosin
Myosin has four light chains and two long alpha-helix chains, which make two beads at myosin end. Beads are ATPases, connect actin to myosin, and are where calcium ions act. Three thick myosins surround each thin actin.
actin
Actin is globular protein that polymerizes into globule helix. Six thin actin proteins surround each thick myosin protein.
tropomyosin
Tropomyosin molecule helically wraps around actin.
troponin
Troponin molecule has binding sites for calcium, tropomyosin, and actin.
Transverse tubules are adjacent to sarcoplasmic reticulum at structures {triad junction}.
Muscle fibers have fine-tube {tubule} networks on cell surfaces and insides.
Skeletal muscle has parallel protein filaments {myofibril} lined up along elongated muscle-cell axis. Dark A bands have overlapping actin and myosin. Light I bands have actin, tropomysin, and troponin.
Repeating units {sarcomere} can have alternating dark A bands and light I bands. Dark Z line is in light I-band middle, where actins connect. Light H zone is in dark A-band middle and has thick myosin. Light H zone has middle dark M line, where myosins meet.
Proteins can have hydrogen bonds between every fourth peptide bond, with hydrogen-bond plane parallel to helical axis and side chains perpendicular to helical axis {alpha helix, protein structure}. Big or charged amino acids disrupt alpha helix. Proline stops alpha helix, because it is imino acid and does not make regular peptide bond.
Proteins can have hydrogen bonds between amino-acid chains lying in opposite directions, with side chains perpendicular to hydrogen bonds {beta sheet, protein structure}. Large amino acids interfere with hydrogen bonding and disrupt beta sheets.
The charged amino acids serine, isoleucine, and proline can make amino-acid-chain turn {beta turn, protein structure}. Proline is imino acid and makes irregular peptide bond at different angle.
Proteins {fibrous protein} can be elongated amino-acid chains. Fibrous proteins are for structure.
Proteins {globular protein} can have polar side chains on surface and non-polar side chains inside, with sharp bends at proline, serine, or isoleucine. Most proteins, such as enzymes, are globular.
Proteins {oligomer} can have multiple amino-acid chains.
Amino acid sequence {primary structure} determines protein properties.
Amino-acid-sequence three-dimensional alignment can be irregular, alpha helix, beta sheet, or beta turn {secondary structure} {conformation, protein}. Heat or chemicals can disrupt secondary structure and change protein conformation {denaturation, protein structure}.
Overall amino-acid-chain shape can be globular or fibrous {tertiary structure}.
Protein oligomers can have multiple amino-acid chains {quaternary structure}. Hydrogen bonds hold chains together. Hemoglobin has two "alpha" chains and two "beta" chains.
Carbon atoms can attach to carboxyl group and amino group {amino acid}|. The carbon atom also attaches to hydrogen atom and functional group {side chain, amino acid}. Cells can have 150 different amino acids.
asymmetry
Central carbon is asymmetric, because it has four different groups. It can rotate light clockwise (R) or counterclockwise (L).
groups
Amino acids have groups. Alkyl amino acids are glycine, alanine, valine, leucine, and isoleucine. Aromatic amino acids are phenylalanine, tryptophan, and tyrosine. Sulfur amino acids are cysteine, which is thiol, and methionine, which is thioether. Hydroxyl amino acids are the alcohols serine and threonine and the phenol tyrosine. Acidic amino acids have charge -1 in solution: aspartic acid and glutamic acid. Amide amino acids are asparagine and glutamine.
Lysine and arginine, which have amino group, are basic amino acids and have charge +1 in solution. Histidine is basic amino acid, is secondary amine, has aryl ring with two nitrogens, has charge +0.5 in solution, and has smaller charge in solution because it is weak base.
Imino acid is proline, which is secondary amine. Non-polar amino acids are alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, and proline.
polymerization
Amino acids can polymerize to make protein. Twenty different amino acids are in protein. Proteins have only L-amino acids, not R-amino acids. Amino acids that are fewest in proteins are methionine, then histidine, and then tryptophan. Methionine is first amino acid in protein chain. Free amino acid to dipeptide ratio is 10:1.
absorption
Intestine absorbs 92% of amino acids.
types
Delta-aminolevulinic acid comes from glycine and succinyl-CoA. Epinephrine comes from tyrosine. Melanin comes from tyrosine. Phenylalanine makes tyrosine. Serotonin comes from tryptophan. Amino acids can make folic acid, S-adenosylmethionine, thyroxine, histamine, sphingosine, and NAD+. Amino acids can lose amino group to become carboxylic acids in TCA cycle. Carboxylic acids in TCA cycle can gain amino group to become amino acids. Amino acids can break down to ammonia and urea.
Fibrinogen, thrombin, and blood-factor proteins participate in blood clotting {blood clotting}|.
Proteins {conjugated protein} can bind to other molecules.
Cysteine can bind to another cysteine {cystine} by disulfide bond.
Glutamic acid {glutamate, protein} builds purines and pyrimidines.
Cell proteins {heat-shock protein} can increase during stress. HSP40 carries newly folded amino-acid chains. HSP60 chaperone covers proteins as they fold, to prevent partly folded proteins from hitting others, and binds to misfolded intermediates to restart folding. HSP70 holds ATP, but when ATP leaves, it binds peptide and so aids protein conformation and assembly. HSP90, such as gp96, organizes proteins from other chaperones into receptors and other multiprotein structures. HSP70 and HSP90 carry antigens to antigen-presenting-cell CD91 receptors.
Small proteins {interferon}| can bind to plasma membranes and can protect against viruses that degrade mRNA and block protein-synthesis initiation. After viral-gene expression starts, interferon can stop all viral-gene expression {interferon response}. In humans, viruses that make long double-stranded RNAs trigger PKR enzyme production, which stops mRNA translation to protein. RNAse L breaks down mRNA. Interferon cytokine secreted by virus-infected cells enhances both these responses.
Alpha-keratin {keratin}| is in skin, hair, wool, horn, and nails. Alpha-keratin has three to seven amino acid chains in bundle, cross-linked by disulfide bonds, which then bundle again. Scales, claws, beaks, silk, and feathers have beta-keratin. Beta-keratin is mostly glycine, alanine, and serine.
Amino acids can link by peptide bonds {peptide}|. Peptides do not branch. Peptides are transmitters and hormones.
Proteins {protein hormone}, such as insulin, growth hormone, and adrenocorticotropin, can be hormones.
Protofibrils {protofibril} are soluble, have 4 to 30 misfolded proteins that clump together, and do not break down quickly enough in disease, later forming fibrils and {amyloid} plaque.
Urea processing uses the following steps {urea cycle}. Ammonia builds up in cells from various deaminations. Ammonia is toxic, because it blocks TCA cycle. In mitochondria, ammonia reacts with two ATP, carbon dioxide, and water molecule to make one carbamyl phosphate. In cytoplasm, carbamyl phosphate reacts with ornithine to make citrulline. Citrulline diffuses to cytosol and reacts with aspartic acid, which splits to give arginine and fumarate. Water reacts with arginine to make nitrogen compounds {urea}| {ornithine}. Urea is not toxic, can cross membranes, and excretes in urine.
Proteins, such as snake venoms, can be poisons {toxin}|. Bacteria make diphtheria toxin. Cobra venom and banded kait venom bind to acetylcholine receptor. Tetanus toxin and black-widow-spider toxin affect acetylcholine vesicle release. Tetanus toxin prevents glycine release. Benzodiazepines, phencyclidine, and strychnine are toxins. Poisons can stay inside cells {endotoxin} or secrete to outside {exotoxin}. LAL chemical, from horseshoe crab blood, tests for endotoxins in drugs and implants.
Botulinus toxin {botulism}| affects acetylcholine vesicle release.
Proteins {enzyme}| can be catalysts. Enzyme and ribozyme catalysts regulate biochemical reactions. Coenzymes can bind to or assist enzymes.
history
Schwann discovered pepsin [1825], which cuts proteins. Robiquet and Boutron discovered emulsin [1830]. Leuchs discovered ptyalin [1831]. Payen and Persoz discovered amylase [1833], which cuts starches. Corvisart discovered trypsin [1856], which cuts proteins. Kuhne invented the word enzyme [1878]. Bertrand discovered need for coenzymes [1897]. Arthur Harden and William John Young discovered coenzyme for zymase [1906]. Henri studied enzyme kinetics and proposed enzyme-substrate complex [1903]. Barger and Stedman discovered that physostigmine inhibited cholinesterase [1923], which metabolizes choline. Jones and Perkins discovered ribonuclease [1923], which cuts RNA. Enzymes are proteins [1925]. Briggs and Haldane used steady state for enzyme kinetics [1925]. Sumner discovered urease [1926], which metabolizes urea. Stedman discovered acetylcholinesterase [1932], which metabolizes acetylcholine. Aeschlimann discovered that neostigmine inhibited cholinesterase [1931]. Hellerman hypothesized need for thiol groups in enzymes, as did Bersin and Logemann [1933]. Hellerman hypothesized need for metal bridges in enzymes [1937]. Mann and Keilin discovered that sulfanilamide inhibited carbonic anhydrase [1940]. Sanger and Tuppy found insulin amino-acid sequence [1951]. Sutherland discovered cyclic AMP in animal cells [1956]. Koshland hypothesized enzyme conformation changes upon binding [1958]. Kendrew used x-ray crystallography on myoglobin [1958]. Merrifield developed solid-phase peptide synthesis and built insulin and ribonuclease [1963].
types
Chymotrypsin, cytochrome, diastase, flavin, lipase, lysozyme, nuclease, RNA polymerase, thermolysin, and DNA polymerase are enzymes.
transition states
About 100,000,000 transition-state shapes exist for enzymes.
In competitive inhibition, inhibitor shape can be similar to substrate shape, so inhibitor can bind to enzyme at substrate site {active site}.
In non-competitive inhibition, inhibitors can bind to enzymes at other sites {allosteric site} to alter active sites.
Molecules {coenzyme}| can bind to enzymes to activate them. Michaelis and Wollman discovered that free radicals formed from alpha-tocopherol [1950]. Lipmann isolated coenzyme A [1945]. Mitchell, Snell, and Williams isolated folic acid [1941]. O'Kane and Gunsalus isolated lipoic acid [1948]. Metals can be coenzymes [1930]. Jansen and Donath isolated thiamine [1926]. Fildes hypothesized that molecules similar to natural substrates or coenzymes compete and are therapeutic. Methotrexate treats leukemia (Farber) [1946].
Post-transcription, enzymes {proteolytic enzyme} can cleave terminal amino acids and break peptide chains into pieces: proteinase, peptidase, pepsin, trypsin, chymotrypsin, carboxypeptidase, amino peptidase, dipeptidase, endopeptidase, and exopeptidase.
Reagents {substrate} can bind to enzymes at active sites.
Enzyme precursors {zymogen} can split or react to create enzymes.
Molecules {inhibitor} can bind to enzyme to reduce reaction rate {enzyme inhibition}.
Inhibitor shape can be similar to substrate shape, so inhibitor can bind to enzyme at active site {competitive inhibition}.
Inhibitor can bind to enzyme at allosteric site to alter active site {non-competitive inhibition}.
Inhibitor can bind directly to enzyme-substrate complex to change activation energy {uncompetitive inhibition}.
Heat-shock proteins {foldase}, such as HSP60, envelope proteins as they fold to prevent partly folded proteins from hitting others.
Heat-shock proteins {chaperone} bind to misfolded intermediates to restart folding.
Molecules {ubiquitin, protein}| can bind misfolded proteins and go to proteosomes to break peptide bonds.
Proteins can be for protection {immunity}|. Antigen binding to beta-lymphocyte surface triggers process that creates plasma cells. Plasma cells specialize to make antibody to antigen.
Antigens can enter body. Immunoglobulin proteins {antibody}| bind antigens, so body can remove foreign molecules. Antibodies bind to antigens by hydrogen bonds, van der Waals forces, and ionic bonds. Antibody-connecting subunits can cross plasma membrane and bind to cells.
structure
Antibodies have three subunits. Two subunits can bind to one antigen each. One subunit connects two binding subunits to make Y-shaped structure. Antibodies have two light protein chains and two heavy protein chains, linked by disulfide bonds. Light chains are at Y tips. All antibodies have kappa or lambda light chain but different heavy-chain constant regions. Heavy chains are in arms and base of Y. Light and heavy chains have variable end and constant end. Several hundred genes code variable regions, making millions of different antibodies. About 100,000,000 different antibody shapes can exist.
precipitation
When one antibody binds to two antigens, complex becomes insoluble. Bound molecules precipitate from solution, and then cell phagocytes eat them.
Five proteins {immunoglobin}| affect immunity. IgA is in secretions. Immune system makes IgM first. IgG increases as IgM decreases. IgE is for allergies. IgD is another immunoglobin.
Large molecules {antigen}| can enter body from outside.
Antigens have regions {epitope}| where other molecules can bind.
Small molecules {hapten} can bind to epitope.
Protein groups {complement, protein} can lyse cells if antibodies bind to cells.
Genes {joint gene} {J gene} can code for connections between light and heavy chains.
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Date Modified: 2022.0225