Proteins and Amino Acids
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| What are proteins? | covalently linked polymers of amino acids; linked head to tail with carboxyl group of one amino acid combining with amino group of another amino acid
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| Name the four structures of proteins and their characteristics. | Primary structure-number and types of amino acids and their sequence in polypeptide chain; Secondary structure-winding of polypeptide chain (alpha-helixor beta-pleated sheet); Tertiary structure-way the twisted chain folds back on itself to form 3 dimensi
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| What component makes proteins different from carbohydrates and lipids? It is also used in the reference method for testing for proteins. | nitrogen content; average content is 16%
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| General characteristics of pre-albumin | synthesized by liver; migrates ahead of albumin in routine electrophoresis; rarely seen on cellulose acetate (unless CSF); decreased in hepatic damage, burns, salicylate ingestion, and tissue necrosis; good marker for poor protein nutrition
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| General characteristics of albumin | present in highest concentration in serum; synthesized in liver;
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| Earliest method for total protein testing | Kjeldahl method tests for nitrogen content; Biuret method measures peptide bonds
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| Present method for total protein testing | dye-binding and shift in color: Coomassie blue, Ponceau S, Amino Blue; Direct photometric: absorbed at UV @ 200, 225, or 280nm; turbidimetric & nephelometric methods
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| Albumin reference range | 35 - 55 g/L or 3.5 - 5.5 g/dL
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| Quantitative method for albumin | electrophoresis - calculate albumin as % of total protein
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| What are the functions of albumin? | contributes to osmotic pressure of vascular fluid (maintains appropriate fluid in tissues); binds various substances in blood, transports and stores these substances in an inactive form
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| What is bisalbuminemia? | presence of albumin that has unusual molecular characteristics -two bands on electrophoresis
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| What is analbuminemia? | genetic abnormality, causes absence of albumin, asymptomatic except for slight edema
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| What is hypoalbuminemia? | decreased albumin, caused by either impaired synthesis or protein loss
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| What is hyperalbuminemia? | increased albumin, dehydration
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| Alpha-1-Globulins: Name the proteins in this fraction | alpha1antitrypsin, alpha1fetoprotein, alpha1lipoprotein (HDL)
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| What is the function of alpha1antitrypsin? | neutralizes trypsin-like enzymes that can cause hydrolytic damage to structural protein; migrates directly following albumin
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| Deficiency of alpha1antitrypsin linked to | pulmonary diseases and juvenile hepatic cirrhosis
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| Increased level of alpha1antitrypsin evidenced in | inflammatory reactions, pregnancy, and oral contraceptive use
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| What is the function of alpha1fetoprotein? | protects fetus from immunolytic attack by mother
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| Increased level of alpha1fetoprotein evidenced in | spina bifida and neural tube defects also increased in presence of twins
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| Decreased level of alpha1fetoprotein evidenced in | Down’s syndrome;
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| Marked increased level of alpha1fetoprotein evidenced in | in hepatocellular carcinoma and some gonadonaltumors in adults
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| Alpha2Globulins: What are the proteins found in this fraction? | haptoglobin, ceruloplasmin, alpha2macroglobulin
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| What is the function of haptoglobin? | binds free hemoglobin by its alpha chain-prevents loss of hemoglobin and its iron into the urine
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| Where is haptoglobin synthesized? | hepatocytes, composed of 2 types of polypeptide chains the beta chain contains the site where the molecule bind hgb
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| Haptoglobin increased in: | inflammatory conditions, burns and nephrotic syndrome
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| Haptoglobin decreased in: | intravascular hemolysis (transfusion reactions, HDN and malaria)
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| What is ceruloplasmin and where is it synthesized? | copper containing alpha2glycoprotein, synthesized in liver
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| What is ceruloplasmin function(s)? | function may be antioxidant
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| Ceruloplasmin decreased level in: | Wilson’s disease (decrease in serum copper but increase in tissues) andMenkes’ Kinky hair syndrome (decrease in copper absorption)
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| What is the function of alpha2macroglobulin? | inhibits proteases such as trypsin, pepsin, and plasmin (also contributes to thrombin inhibition in blood) and binds to some hormones such as insulin
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| Increased level of alpha2macroglobulin seen in: | nephrosis, diabetes, and liver disease
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| Beta globulins: name the protein found in the beta fraction | transferrin, hemopexin, complement, fibrinogen, CRP
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| What is the function of transferrin? | transport of iron to its storage sites, and transports iron to cells that synthesize hemoglobin and other iron containing compounds
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| Transferrin defienciency: | accumulation of iron in apoferritin or histiocytes may precipitate in tissues as hemosiderin-hypochromic anemia
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| Hemochromatosis | increased iron, decreased transferrin (hereditary disorder of iron metabolism
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| What is fibrinogen and where is it synthesized? | forms fibrin clot when activate by thrombin; synthesized in liver; one of largest proteins in plasma
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| What is CRP? | an acute phase reactant synthesized in liver; when bound to bacteria and fungi, promotes the binding of complement (which facilitates their uptake by phagocytes)
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| Increased CRP seen in: | increased in acute rheumatic fever, bacterial infections, MI, RA,carcinomatosis, gout, viral infections
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| What is the function of hemopexin? | removes circulating heme; synthesized by the liver
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| What is complement? | proteins that participate in immune reactions
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| Complement classical pathway activation begins with? | when C1q binds to Ag-Ab complex final result is lysis of cell
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| Complement alternate pathway activation begins with? | process begins with C3, final result is lysis of cell; alternate path does not require Ab; early components are bypassed
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| Name the proteins in the gamma globulin fraction. | Immunoglobulins: IgM, IgG, IgD, IgE, IgA and Human Ventricular Myosin Light Chain
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| Gamma globulins synthesized by? | plasma cells and B lymphocytes
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| Describe the composition of immunoglobulins | 2 heavy chains and 2 light chains joined by disulfide bonds
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| What is a monoclonal immunoglobulin and when are they seen? | immunoglobulins that are derived from one plasma cell; found in plasma cell malignancy (myelomas)
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| How do monoclonal gammopathies appear on electrophoresis? | spikes in the gamma region
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| IgA is found where and is unique because of what? | serum and secretions; in secretions it contains a J piece
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| Polyclonal increases of IgA are seen in which disease states? | liver disease, infections, and autoimmune diseases
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| Which immunoglobulin is the first to appear in response to antigen stimulation? | IgM
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| Monoclonal increases in IgM are seen in what disease? | Waldenstrom’s macroglobulinemia
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| Which immunoglobulin class is found in association with allergic and anaphylactic reactions? | IgE
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| What protein is found in the serum 30 minutes after initial chest pain and confirms myocardial ischemia? | Human Ventricular Myosin Light Chain
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| Define hypoproteinemia and its cause. | decreased levels of protein associated with negative nitrogen balance; excessive loss due to renal disease, leakage into GI tract, bleeding; decreased intake due to malnutrition and malabsorption
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| What is hyperproteinemia and what can cause it? | increased proteins; seen in dehydration due to vomiting, diarrhea, diabetic acidosis, hypoaldosteronism; excessive protein production usually gamma globulins example multiple myeloma — Bence Jones proteins in urine
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| What is the reference/classic method for total protein determination and what principle is it based on. | Kjeldahl technique; based on nitrogen content of 16%
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| How does refractometry work? | velocity of light is changed as it passes the boundary between 2 transparent layers causing light to be bent
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| The biuret method for protein analysis is based on what properties? | presence of at least 2 peptide bonds in proteins; measure a change in color, the more peptide bonds the darker the color change
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| Dye binding is based on what principle? | most proteins will bind to dyes
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| UV absorption is based on what principle? | protein absorbs light at 210 nm (peptide bonds) and 280 nm (tyrosine, tryptophan, phenylalanine)
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| Salt fractionation was used for determining what protein? | albumin; globulins were precipitated out in high salt concentration
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| Albumin concentrations are commonly determined by what method and how does it work? | dye-binding; pH of solution adjusted to give albumin a positive charge, attracted to anionic dye, measure based on different absorptive maximum of bound vs free dye
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| The principle of electrophoresis is what? | separates protein on basis of electrical charge
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| At a pH of 8.6 what charge to proteins have? | negative
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| List the five bands that proteins will separate into on routine electrophoresis. | albumin, alpha1, alpha2, beta, and gamma
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| How does radial immunodiffusion work? | precipitin reaction of protein (Ag) with its specific Ab incorporated in an agar gel, the diameter of the ring is proportional to the concentration of protein
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| What is immunoelectrophoresis? | electrophoretic separation followed by diffusion of separated proteins and antiserum to one or more of the proteins
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| What is immunofixation? | protein is separated by electrophoresis then monospecific antisera are laid over the electrophretic pattern, the antisera will precipitate the protein of interest and trap it on the support medium, it can then be stained and visualized
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| What is electroimmuno difffusion? | electrophores proteins into a gel containing monospecific antibody; appears as a rocket shape
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| How does isoelectric focusing work? | pH gradient is fixed, protein is electrophoresed into gel and migrates to its isoelectric point and stops
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| How can you distinguish between glomerular and tubular proteinuria? | glomerular= large proteins in urine; tubular =small proteins in urine
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| Define overload and post-renal proteinuria. | overabundance of proteins from serum tubules are overwhelmed and cannot absorb them; protein coming from urinary tract below kidneys (inflammation or malignancy)
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| In the qualitative detection of urine protein, what is the method based on? | response of dye indicator to pH in presence of protein
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| What is the proper collection procedure for quantitative dectection of urine protein? | collect 24 hour specimen, void complete upon beginning then collect all voids for 24 hours completely void at end of collection; reported as protein/24 hours
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| List the methods for determining quantitative urine proteins. | Refractometer; turbidity – uses sulfasalicylic acid; Folin-Ciocalteau-changes color from yellow to blue during rxn. with tyrosine, tryptophan, and histidine; Modified Biuret; Dye-binding; Electrophoresis; Immunochemistry
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| List the routine tests normally ordered on a CSF. | protein, glucose, cell count and differential, culture and sensitivity
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| Name the bands seen in CSF electrophoresis. | pre-albumin, albumin, alpha1, alpha2, beta1 and beta2
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| In what disease state do you find oligoclonal banding in the globulin fraction of CSF electrophoresis? | multiple sclerosis
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| What are myelin basic proteins? | constituents of myelin, provide an index of active demyelination in diseases such as multiple sclerosis
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