Amino Acids & Proteins Flashcards
basic structure of amino acid
at least one amino group (NH2) and one carboxyl functional group (COOH) bonded to an alpha-carbon
amphoteric
molecule that is both an acid and a base
peptide bond
a covalent bond formed between the amino group of one amino acid and the carboxyl group of another amino acid
how are amino acids amphoteric?
- amino group can accept a proton to form NH3+ (basic)
- carboxyl group can donate a proton to form COO- (acidic)
polypeptide
a chain of amino acids linked together by peptide bonds
how does the body obtain amino acids?
- half of amino acids cannot be produced in vivo at a rapid enough rate to support growth
- essential amino acids supplied by diet in form of proteins
metabolism of amino acids
- stomach: gastrin stimulates secretion of HCl and proteolytic enzymes to promote denaturation of proteins and to catalyze hydrolysis into polypeptides
- small intestine: HCl is neutralized by sodium bicarbonate secreted from the pancreas because of secretin to protect the intestinal lining
- secretin and cholecystokinin stimulate the release of proteolytic enzymes which continue the process of digestion by hydrolyzing polypeptides into constituent amino acids
essential amino acids
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
difference between essential and nonessential amino acids
- essential: cannot be synthesized in vivo at a fast enough rate and must be acquired through dietary intake
- nonessential: body can synthesize adequate amounts and additional dietary intake is unnecessary
nonessential amino acids
alanine, asparagine, aspartic acid, glutamic acid, selenocysteine, serine
aminoacidopathies
- inborn errors of metabolism that inhibit the body’s ability to metabolize specific amino acids
- can cause severe medical complications (brain damage) due to accumulation of toxic amino acids or their by-products in the tissue
maple syrup urine disease
- deficiency in branched chain keto acid decarboxylase
- leads to excess branched chain amino acids which causes metabolic acidosis
- maple syrup scented urine
- amino acids involved: valine, leucine, isoleucine
phenylketonuria
- phenylalanine hydroxylase is reduce or absent which impedes abnormal cerebral development
- leads to loss of interest, mental retardation, restlessness, irritability
cystinuria
- defect in renal tubule transport protein affecting dibasic amino acids
- causes cystine kidney stones and crystalluria
alkaptonuria
- black urine disease
- defect in homogentisic acid
- causes black cartilage and arthritis
primary protein structure
number, type, sequence of amino acids in polypeptide chain
secondary protein structure
commonly formed arrangements stabilized by hydrogen bonds between nearby amino acids within a protein; alpha-helix and beta-pleated sheets
tertiary protein structure
overall shape or conformation of protein molecule; fold
quaternary protein structure
shape or structure that results from interaction of more than one protein molecule that functions as a single unit
what does the basic structure of protein include?
carbon, oxygen, hydrogen, nitrogen, sulfur
where are plasma proteins predominantly synthesized?
synthesized in liver and secreted into circulation
**immunoglobulins are synthesized by b lymphocytes
what are the main physiologic functions of plasma proteins?
energy source, maintaining water distribution through compartments of body, role in maintaining acid-base balance by serving as buffers to maintain pH, involved in hemostasis by participating in formation and dissolution of blood clots; catabolism, nitrogen balance, hormone regulation
what are the chemical properties of proteins?
- amino acid chain changes properties
- can be positively or negatively charged due to n- or c- terminal ends
isoelectric point
pH at which an amino acid or protein has no net charge
- pH > isoelectric point = net negative charge
- pH < isoelectric point = net positive charge
protein synthesis
- amino acid sequence determined by corresponding sequence of nitrogenous bases in DNA
- genetic code is a set of three-nucleotide combination (codon) standing for a specific amino acid
- double-stranded DNA unfolds in nucleus, one strand is used as a template for the formation of a complementary strand
- DNA to mRNA to tRNA to CODON to PROTEIN
- transcription, translation, initiation, elongation, termination
isoelectric point
pH at which a substance has a net neutral charge
- pH > isoelectric point = net negative charge
- pH < isoelectric point = net positive charge
transcription
process where double-stranded DNA unfolds in nucleus and one strand is used as template for the formation of a complementary strand of mRNA; occurs in cell nucleus
translation
mRNA is translocated across nuclear membrane into cytoplasm; occurs in cytoplasm
why do proteins have no designated storage?
because are repetitively synthesized (anabolism) and degraded (catabolism) so amino acids are always recycled
protein catabolism
nitrogen balance is maintained by equal intake and excretion of amino acids
what conditions are associated with when more nitrogen is excreted than incorporated?
excessive tissue destruction, burns, starvation
what can be done when nitrogen is in excess?
amino acids can be converted to urea for kidney excretion and into glucose or ketones for energy
how are proteins classified?
based on structure, composition, function
simple proteins
peptide chains composed of only amino acids and may be globular or fibrous in shape
complex/conjugated proteins
protein that consists of amino acids and a nonprotein prosthetic group; prosthetic group is what defines characteristics of proteins
- ie. enzymes, hormones, immunoglobulins
what plasma proteins are commonly analyzed?
albumin or globulin
what does a routine analysis of blood specimens typically include?
measurement of total protein and albumin, and calculation of albumin-to-globulin ratio
prealbumin
- migrates before albumin in classic serum protein electrophoresis
- transport protein for thyroid hormones, thyroxine and triiodothyronine
- forms a complex with retinol-binding protein to transport retinol (vitamin a) and is rich in amino acid tryptophan
why could prealbumin have decreased serum or plasma concentrations?
hepatic damage due to decreased protein synthesis, during an inflammatory response, result of tissue necrosis, poor nutritional status
why could prealbumin have an increased serum or plasma concentration?
steroid therapy, alcohol abuse, chronic renal failure
negative acute-phase reactant
substance that decreases in the presence of an acute disease state
what are decreased blood concentrations of albumin commonly associated with?
acute inflammatory response, liver/kidney disease, damage to hepatocytes, malnutrition, malabsorption
albumin
- negative acute-phase reactant
- most abundant plasma protein and found in significant amounts in extravascular space
- responsible for nearly 80% of colloid osmotic pressure; involved in maintaining fluid balance
- maintains a homeostatic pH by serving as buffer in circulation
- binds and transports large variety of substances throughout the body
what are increased blood concentrations of albumin commonly associated with?
dehydration
positive acute-phase reactant
substance that increases markedly in presence of an acute onset of a disease state
what are the alpha-1 globulins?
antitrypsin, fetoprotein, acid glycoprotein
antitrypsin
- glycoprotein synthesized predominantly in the liver
- function: to inhibit neutrophil elastase, a protease released from neutrophils and macrophages during an infection
- positive acute-phase reactant
when is antitrypsin increased?
inflammation, infections, injuries, pregnancy, contraceptive use
when is antitrypsin decreased?
lung damage, emphysema
fetoprotein
- synthesized in utero by developing embryo and then by fetal liver and gastrointestinal tract
- positive acute-phase reactant
when are increases of fetoprotein seen?
inflammatory conditions, increased likelihood of spina bifida, neural tube defects, abdominal wall defects, anencephaly, general fetal distress, presence of multiple gestation
when are decreases of fetoprotein seen?
increased risk for Down Syndrome, Edwards Syndrome
acid glycoprotein
- produced primarily by liver
- physiological functions include maintaining barrier function of capillaries, regulating immunity, meditating sphingomyelin metabolism, acting as a transport protein
- positive acute-phase reactant
when is acid glycoprotein elevated?
stress, inflammation, tissue damage, acute myocardial infarction, trauma, pregnancy, cancer, pneumonia, rheumatoid arthritis, surgery
what are the alpha-2 globulins?
haptoglobin, ceruloplasmin, macroglobulin
haptoglobin
- synthesized in the liver as a tetrameter consisting of two alpha and two beta chains
- primary function is to bind free hemoglobin to prevent loss of iron into urine
- positive acute-phase reactant
when does haptoglobin increase?
inflammation, ulcerative colitis, acute rheumatic disease, acute myocardial infarction, severe infection
when does haptoglobin decrease?
hemolytic anemia, decreased liver synthesis
ceruloplasmin
- copper-containing glycoprotein synthesized in liver
- primary function is to serve as transport protein for copper
- primarily measured along with blood and urine copper concentrations to aid in diagnosis of Wilson’s
- Kayser Fleischer Rings
- positive acute-phase reactant
when can ceruloplasmin be increased?
inflammation, severe infection, tissue damage, some cancer, pregnancy, patients taking estrogen, oral contraceptives, medications
when can ceruloplasmin be decreased?
Wilson’s, malnutrition, malabsorption, severe liver disease, nephrotic
macroglobulin
- tetramer of four identical subunits synthesized by liver
- protease inhibitor, reducing accessibility of protease functional sites but does not fully inactivate them
- regulation of growth factors and cytokines as well as chaperoning misfolded proteins
when do macroglobulins appear increased?
- nephrotic syndrome, pregnancy, using hormoned-based contraceptives, patients with renal disease secondary to diabetes mellitus or hepatorenal syndromes
when do macroglobulins appear decreased?
pancreatitis, liver disease
what are the beta globulins?
transferrin, microglobulin, fibrinogen, c-reactive protein
transferrin
- synthesized by liver
- major component of beta globulin fraction in protein electrophoresis
- primary function: bind and transport iron to and from storage sites and to prevent iron from being inappropriately deposited in other tissues
- negative acute-phase reactant
when could transferrin be decreased?
liver disease, malnutrition, nephrotic syndrome, infection, inflammation, malignancy
what is associated with an increase in transferrin?
iron deficiency anemia
microglobulin
- light chain component of major histocompatibility complex of human leukocyte antigen
- found on surface of most nucleated cells and is present in high concentrations on lymphocytes
- filtered by the renal glomeruli but is almost completely reabsorbed and catabolized in proximal tubules
what does an elevated plasma concentration of microglobulin reflect?
impaired renal clearance, rheumatoid arthritis, systemic lupus erythematosus
fibrinogen
- largest proteins in blood plasma
- synthesized in the liver and classified as a glycoprotein because of its considerable carbohydrate content
- function: form a fibrin clot when activated by thrombin, meaning all fibrinogen should be removed in clotting process and leaving none present in serum specimens
- increases significantly during an inflammatory response
- positive acute-phase reactant
when do fibrinogen levels rise?
pregnancy, oral contraceptive
when do fibrinogen levels decrease?
extensive coagulation
complement c3
- synthesized in the liver as single polypeptide chains and circulate in blood as non-functional precursors
- most abundant complement protein in human plasma
what are increased levels of complement c3 linked to?
acute inflammatory disease, tissue inflammation
what are decreased levels of complement c3 linked to?
autoimmune disease, neonatal respiratory distress syndrome, bacteremia, tissue injury, chronic hepatitis
c-reactive protein
- synthesized in the liver
- first acute phase reactant to increase
- non-specific inflammation indicator
when does c-reactive protein rise?
tissue inflammation, active coagulation or complement, rheumatic fever, bacterial infection, gout
what are the gamma globulins?
immunoglobulins including IgG, IgA, IgM, IgD, IgE
immunoglobulins
- glycoproteins composed predominantly with a small percentage of carbohydrate
- produced by b lymphocytes that confer humoral immunity
- consists of two identical heavy chains and two identical light chains linked by two disulfide bonds
IgG
- most abundant class of antibodies found in blood plasma and lymph
- act on bacteria, fungi, viruses, and foreign particles by agglutination, opsonization, and complement activation by neutralizing toxins
- can cross the placenta
what is increased IgG associated with?
liver disease, infections, IgG myeloma, parasitic disease, rheumatic diseases
what is decreased IgG associated with?
acquired immunodeficiency, increased susceptibility to infection
IgA
- found in mucus secretions
- secretory IgA is resistant to enzyme degradation and remains active in digestive and respiratory tracts to provide antibody protection in body secretions
when do you see increases in IgA?
liver disease, infections, autoimmune diseases nutritional hepatic cirrhosis
when do you see decreases in IgA?
impaired protein synthesis, immunodeficiency
IgM
- first antibody to respond to antigenic stimulation
- cannot cross the placenta
- only immunoglobulin synthesized by neonate
what conditions present an increased IgM concentration?
bacterial infections, toxoplasmosis, primary biliary cirrhosis, cytomegalovirus, rubella, herpes, fungal diseases, Waldenstrom’s
what conditions present a decreased IgM concentration?
protein-losing conditions, hereditary immunodeficiencies
IgD
- present on surface of most b lymphocytes
- very little is released into circulation
- helps regulate b lymphocyte function
when is IgD concentration typically increased?
infections, liver disease, connective tissue disorders
IgE
- associated with allergic and anaphylactic reactions, autoimmune processes, parasitic infections
- concentration in circulation is very low
- elevated concentration observed in many inflammatory and infectious diseases
troponin
- specific to cardiac muscle
- considered the gold standard for diagnosis of acute coronary syndrome, in which blood supply to heart muscle is impeded
b-type natriuretic peptide
- produced initially as prohormone which is cleaved by enzymes corin and furin
- found in greatest concentration in left ventricular myocardium
- neurohormones that affect body fluid homeostasis
what are elevated concentrations of b-type natriuretic peptides associated with?
congestive heart failure, acute coronary syndrome
hypoproteinemia
conditions in which serum or plasma total protein concentration is below the reference range
what are the general causes of hypoproteinemia?
excessive loss, decreased synthesis, increased protein catabolism
hyperproteinemia
increase in total plasma proteins
what are the general causes of hyperproteinemia?
dehydration caused by vomiting, diarrhea, excessive sweating, diabetic acidosis, hypoaldosteronism, excessive production of proteins
biuret method
- used to determine total protein concentrations in serum or plasma
- an alkaline medium and the presence of at least two peptide bonds, cupric ions (Cu2+) will complex with groups involved in peptide bond to form violet-colored chelate
- color and absorbance are proportional to number of peptide bonds present and reflect total protein concentration of specimen
turbidimetry and nephelometry
- used to measure concentration of solution with particles
- measuring amount of light transmitted through particulate solution or light scattered by particles
dye binding
- based on ability of most proteins to bind dyes, causing a spectral shift in absorbance maximum
ultraviolet absorption
- concentration of protein can be estimated by ultraviolet absorption at 280 nm
- used to estimate protein concentration in a solution
- utilization of ultraviolet absorption to measure peptide bonds is limited to peptide fragments
hemoglobin
- transport protein
- role: transport oxygen from lungs to tissues and transport carbon dioxide back to lungs
- measured in peripheral blood as part of complete blood count
- decreased hemoglobin is indicative of anemia
hemoglobinopathies
qualitative defects caused by mutations in DNA of globin chain that produce a structurally different form leading to a decrease in red blood cell survival
thalassemias
quantitative defects due to mutations that reduce the synthesis of normal hemoglobin
myoglobin
- primary oxygen-carrying protein found in striated skeletal and cardiac muscle
- can reversibly bind oxygen and requires a very low oxygen tension to release bound oxygen
- transports oxygen from muscle cell membrane to mitochondria
- serves as extra reserve of oxygen to help exercising muscle maintain activity longer
