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