HB1: Cellular Function and Medical Genetics
*What is vitamin E also known as? What does it participate in? Food sources? Involved in what type of syndromes?
Alpha-tocopherol Non-specific chain-breaking antioxidant **intercepts destructive free radicals vegetable oils, whole grains, nuts, eggs, fruits, vegetables Fat-malabsorption syndromes-cystic fibrosis, cholestatic liver dz
*What does a deficiency in biotin cause?
Alopecia (sudden hair loss) Dermatitis Paresthesia Depapillation of tongue (slick tongue) <img src="paste-440968587247617.jpg" />
*T or F:Î"G depends only on the initial and final states of the chemicals involved in a reaction
TRUE, does NOT depend on the path it takes **known as a state function
*Deficiency in calcium can lead to what?
rickets osteomalacia osteoporosis tetany
*What is vitamin C also known as? What does it participate in?
Ascorbic acid Antioxidant Cofactor in hydroxylation reactions Absorption of iron
*How can hemoglobin participate in CO2 transport?
1) Direct transport by covalently attaching CO2 to N-termini of globin chains 2) Isohydric transport (indirect) - HCO3- transported in plasma at constant pH
*In what forms is CO2 carried in the blood?
1) Dissolved CO2: 9% 2) Carbamino-Hb: 13% 3) HCO3-: 78%
*Differentiate between the oxygen binding curves of hemoglobin vs. myoglobin
1) Hemoglobin = sigmoidal (cooperative binding, positive heme-heme interaction) 2) Myoglobin = hyperbolic (independent binding) <img src="paste-255473244700673.jpg" />
*WhenÎ"G° < 0, what is Keq? WhenÎ"G° = 0, what is Keq? WhenÎ"G° > 0, what is Keq?
1) Keq >1 (products more than reactants) 2) Keq =1 (products = reactants) 3) Keq <1 (reactants more than products)
*_________ is a condition of chronic caloric deficiency _________ is a condition of combined edema and emaciation associated with acute or chronic protein deficiency and chronic energy deficit
1) Marasmus <img src="paste-435831806361601.jpg" /> 2)Marasmic kwashiorkor
*The _________ form of hemoglobin is the oxygenated form The _________ form is the deoxygenated form
1) relaxed = oxygenated 2) taut = deoxygenated <img src="paste-256070245154817.jpg" />
*How does 2,3-bisphosphoglycerate (2,3-BPG) affect oxygen binding to hemoglobin? Why does it do this? How does this shift the O2 saturation curve?
2,3-BPG promotes release of O2 from Hb **shifts curve to right <img src="paste-260820478984193.jpg" /> 2,3-BPG is synthesized in RBC from intermediate in glycolysis (1,3-BPG) **2,3-BPG binds ONLY to dexoyHb and facilitates release of O2 <img src="paste-260846248787969.jpg" />
*What is the normal concentration of proteins in plasma?
6-8 g/dL
*What are the fat soluble vitamins?
A, D, E, K
What are some laboratory exam findings of a patient with an IEM?
Acidosis Alkalosis Low blood nitrogen Hyperammonemia Inappropriate ketosis Liver and pancreas function enzymes Radiologica findings such as rickets
*Deficiency in zinc can lead to what?
Acro-orificial dermatitis (e.g. diaper rash) Poor wound healing Diarrhea Inadequate growth Dysguesia Alopecia Anorexia Impaired reproductive development
*What are the two classifications of carbohydrates?
Available: digested, absorbed, and utilized **includes mono-, di-, oligo-, and polysaccharides Unavailable: dietary fiber **nondigested **provides bulk to diet **aids in elimination
*What are the compenents of total energy expenditure (TEE)?
Basal metabolic rate (BMR) = largest contribution Thermogenesis of feeding (TEF) = energy expended for digestion, absorption, transport, metabolization, and storage of nutrients External work (Physical activity, PA) = varies considerablly TEE = BMR + TEF + PA
CYP3A4 is the most commonly used Cytochrome P450 enzyme in Phase I metabolism reactions. However, it is rarely used clinically. Why?
Because it has very few polymorphisms (alleles) that rarely occur Makes it difficult to stratify metabolizers (e.g. slow, intermediate, ultra-rapid) based on genotype
*What condition is related to thiamine deficiency?
Beriberi, which has 2 forms: 1) Dry -polyneuropathy -Ataxia, apathy -Decreased attention -Ophthalmoplegia (cannot follow light with eyes) -Paresthesia -Foot drop 2) Wet -High output cardiac failure -Edema
*Describe the cooperative binding of O2 to hemoglobin
Binding of O2 to one of the Hb subunits causes conformational change that will positively influence the binding of O2 to the other subunits Induces change in shape of molecule to promote O2 binding <img src="paste-255902741430273.jpg" />
*What is vitamin B7 also known as? What does it participate in? Food sources?
Biotin Coenzyme in bicarbonate-dependent carboxylation reactions egg yolk, liver, whole grain rice
*What are common energy-depleted end products (waste) of catabolic reactions?
CO2 H2O NH3
CYP2C19 is a gene that is part of the cytochrom P450 superfamily. What does this abbreviation mean?
CYP = Cytochrome P450 superfamily Family 2 Subfamily C Polypeptide 19
_________ is the cytochrome P450 enzyme that catabolizes the drug warfarin. What are the two common variants of this gene? Do they increase or decrease enzyme activity?
CYP2C9 Two variants: CYP2C9*1 = reduces to 12% of normal activity CYP2C9*3 = reduces to 5% of normal activity **reduced activity leads to increased risk of hemorrhage due to increased time need for Warfarin metabolism
The antidepressant amitriptyline is metabolized by what Cytochrome P450 enzymes?
CYP2D6 CYP2C19 CYP1A2
Over 90% of phase I drug reactions are catalyzed by 5 Chytochrome P450 enzymes. What are these 5 enzymes?
CYP3A4: 40-45% CYP2D6: 20-30% CYP2C9: 10% CYP2C19: 5% CYP1A2: 5%
*What is vitamin D also known as? What does it participate in?
Calciferol Maintence of calcium levels within a narrow range
*What is the recommended calorie distribution for each macromolecule?
Carbohydrate: 55-60% Protein: 10-15% Fat: 30% -Saturated: <10 -Monounsaturated: 10 -Polyunsaturated: 10
*What is the most important source of dietary energy?
Carbohydrates
*Differentiate between catabolic and anabolic pathways
Catabolic = degradative -Oxidative (extract electrons from intermediates) -Break bonds -Release energy Anabolic = synthetic -Reductive (add electrons to intermediates) -Form bonds -Require energy
*What is vitamin B12 also known as? What does it participate in? Food sources?
Cobalamin Normal blood formation and neurological functions. coenzyme for 2 critical reactions: 1. synthesis of methionine from homocysteine 2. isomerization of methylmalonyl coA to succinyl coA Found naturally in foods of animal orign
*Vitamin A is derived from __________ and exists in what 3 forms?
Derived from carotenoids <img src="paste-109173773697025.jpg" />
*What does iodine deficiency lead to?
Enlarged thyroid gland (goider)
How can genetic variations of the CYP2D6 enzyme be used clinically?
Enzyme activity of CYP2D6 can vary based on genotype: 1) Inactivating mutations/deletions --> lower activity --> patients may fail to metabolize and excrete drug --> high levels of drug remain in system 2) Duplication of gene --> increase metabolism --> metabolizes drug to quickly --> extensive or rapid metabolizers <img src="paste-47772921233409.jpg" /> <img src="paste-48159468290049.jpg" />
*T or F: 2,3-BPG binds to oxyHb to facilitate its release of O2
FALSE, it binds only to deoxygenated Hb Decreases affinity of beta subunits for O2 **allosterically promotes release of remaining O2 molecules bound to Hb **thus 2,3-BPG is an allosteric effector
*T or F: For children and adolescents, underweight, overweight, and obesity are determined by their BMI
FALSE, it is determined by their BMI percentiles **For adults, it is determined by their BMI
*T or F:Î"H (enthalpy) andÎ"S (entropy) can predict whether a reaction can occur
FALSE, neither can predict the spontaneity of a reaction on their own Must be used together to findÎ"G, which can determine if a reaction will occur
*What are some general properties of structural proteins?
Fibrous, asymmetric Relatively simple structures (mainly secondary structure) Frequent structural repeats in polypeptide chain Stability often related to properties of peptide (H-bonding, steric hindrance) **Insoluble in water
*An overdoes of niacin can lead to what?
Flushing Nausea Vomitting Glucose intolerance Liver toxicity
*What is vitamin B9 also known as? What does it participate in?
Folate **active form methyletrahydrofolate Hematopoetic Coenzyme in metabolism of nucleic acid and amino acids Participates in 1-Carbon transfers
Pompe (GSD-II)disease is a lysosomal storage disease. What gene is mutated? Inheritance pattern? Symptoms?
GAA gene is mutated (codes for Lysosomalα-(1,4)-glucosidase) --> accumulation in glycogen in organs and tissues (esp. muscles) Autosomal recessive Muscle weakess (myopathy), poor muscle tone (hypotonia) Hepatomegaly Heart defects
Gaucher's disease is a lysosomal storage disease. What gene is mutated? Inheritance pattern? Symptoms?
GBA gene is mutated (codes for glucocerebrosidase) --> accumulation of glucocerebroside in cells Autosomal recessive Hepatosplenomegaly Epitaxis, bone pain, Anemia, thrombocytopenia Bruising and fatigue
*What is vitamin K involved in? Food sources?
Gamma carboxylation (post-translational modification) of clotting factors (2,7,9,10) and proteins C, S, Z Dark green vegetables
*What is the hemoglobin variant HbA1c?
Glycated hemoglobin (α2β2-glucose) = used to identify average plasma glucose concetration over prolonged periods of time Formed in non-enzymatic glycation pathway by exposing HbA to glucose Important diagnostic tool for diabetes
*How does fetal hemoglobin (HbF) compare to adult hemoglobin (HbA)?
HbA = α2β2 HbF =α2γ2 <img src="paste-262851998515201.jpg" /> HbF has: -Decreased affinity for 2,3-BPG -Higher affinity for O2
*Defeciency in chromium can lead to what?
Hyperglycemia Hyperlipidemia Weight loss Peripheral neuropathy (involved in insulin signaling)
Some genes for Cytochrome P450 enzymes can have polymorphisms. How can this be used clinically?
If gene is polymorphic enough, can result in wide variations of metabolic capabilities of patient Can identify clinically useful variants such as: -Amino acid changes that inactivate gene expression -Multiple copies or deletions **CYP gene must have enough polymorphisms to stratify different metabolizers
Functional domains are crucial to the protein function as they often are involved in interactions with other molecules. What is the function of the following functional domains: 1) Ig Domain 2) Leucine zipper 3) Tyrosine kinase
Ig domain = protein-protein recognition Leucine zipper = DNA recognition Tyrosine kinase domain = phosphorylate tyrposine residues on adjacent proteins
*A deficiency in vitamin K results in what?
Impaired blood clotting Easy bruising and bleeding Nosebleeds, bleeding gums, hematuria, hematochezia Heavy menstrual periods
____________ is a large class of genetic diseases involving congenital disorders of metabolism Gene vaiant alters function of protein which functions as enzyme, mediates transport, etc.
Inborn errors of metabolism
*According to Bohr Effect, how does pH/CO2affect O2 release from hemoglobin? Why does it do this? What two equilibria occur within the cell to explain this?
Increase in CO2 leads to increase in [H+] --> shifts equilibrium to the right <img src="paste-258724534943745.jpg" /> An increase in [H+], such as in tissues, leads to deoxygenation --> shifts equilibrium to the left <img src="paste-258737419845633.jpg" />
What are the consequences of a "blocked" metabolic pathway (such as in inborn errors of metabolism)?
Increase of compounds which are normally present (toxic in excess) **EX: ammonia, methyl malonic acid, etc. Absences of others which are physiologically necessary **glucose, ATP, etc. Uses an alternative pathway, but produces a toxic metabolite that is not normally present
*Deficiency in selenium can lead to what?
Increased plasma glutathione levels Oxidative injury Altered thyroid hormone Cordiomyopathy Keshan Disease
*_________ is a condition of inadequate protein intake in presence of adequate calories. What are its symptoms (5)
Kwashiorkor Hypoproteinemia, pitting edema (results from decreased albumin), wasting/shunting, dermatosis, fatty infiltration of liver <img src="paste-435363654926337.jpg" />
Describe the protein L1CAM (part of a superfamily). How can it be used for various functions?
L1 Cell adhesion moleculeNeuronal cell adhesion molecule, involved in axon guidance, neuronal migration and differentiation Contains Ig domains, fibronectin domains, and akryin-binding domains **can be alternatively spliced to be used for various functions <img src="paste-271643796570113.jpg" />
*Where are most plasma proteins are synthesized?
Liver **except antibodies, which are synthesized in B-cells
*What causes HbS to sickle? What are the effects of this happening?
Low O2 tension --> HbS becomes deoxygenated **solubility of deoxyHbS decreases Polymerization occurs in capillaries of peripheral tissues where O2 pressure is low -Polymers distort shape of RBC -Blood flow through capillaries may cease --> O2 deprivation --> necrosis and lysis of RBC <img src="paste-268083268681729.jpg" />
*A deficiency in folate can lead to what? Food source?
Megaloblastic anemiaNeural tube defects (in developing fetuses) Coexisting B12 deficiency Dark green vegetables, fortified greens, legumes <img src="paste-442149703254017.jpg" />
How can misalignment cause alpha-thalassemia?
Misalignment between alpha and beta hemoglobin genes on homologous chromosomes during homologous pairing and recombination leads to deletion or duplication of alpha globin genes.
Fabry's disease is a lysosomal storage disease. What gene is mutated? Inheritance pattern? Symptoms?
Mutation in GLA gene (codes for α-galactosidase A) --> buildup of globotriaosylceramide/ceramide trihexoside in cells (esp. vessels in skin and cells in kidneys, heart, and nervous system) X-linked recessive Cloudiness in front part of eye (corneal opacity) Ringing in ears (tinnitus) or hearing loss Decreased ability to sweat Pain in hands and feet Clusters of small, dark red spots on skin
What enzymes are involved in Phase II drug metabolism?
NAT1 and NAT2 N-acetyltransferases (acetylate the drug) NAT1 = genetically conserved NAT2 = polymorphic **slow acetylator variants = low levels of NAT2 **rapid acetylator variants = high levels of NAT2
What are some physical exam findings of a patient an IEM?
Neurological: altered consciousness, seizures, ataxia, hypotonia Sun sensitivity Specific odors: sweety, musty, or rotten fish smells Developmental delay Unusual diet preferences History of consanguinity Dysmorphic features, cataracts, unusual hair (course and kinky)
*Defeciency in phosphorus can lead to what?
Neuromuscular, skeletal, hematologic and cardiac manifestations Cardiac arrhythmias
*What is vitamin B3 also known as? What does it participate in?
Niacin Active forms: NAD and NADP Involved in intracellular respiration and fatty acid synthesis Equivalent (nicotinamide) be made from tryptophan
*Can HbH (B4 hemoglobin) effectively transport O2? Why or why not?
No, Hb must have NON-identical subunits to effectively transport O2 and participate in regulatory effects of CO2, pH, and BPG **lacks cooperativity and Bohr effect advantages HbH is composed ofβ4 (present in α-thalassemias) **O2 saturation curve looks more like Mb than HbA
*How is HbF oxygenated in utero?
O2 flows from maternal oxyhemoglobin (HbA of mother) to fetal deoxyhemoglobin <img src="paste-263702402039809.jpg" />
*What does the value P50 indicate? What is the P50 of hemoglobin and myoglobin?
P50 = partial pressure of gas required to achieve 50% enzyme saturation **lower the value, higher the affinity Hb P50 = 26 torr Mb P50 = 3-5 torr <img src="paste-255468949733377.jpg" />
*What is vitamin B5 also known as? What does it participate in? Food sources?
Panthothenic acid Precurosor of Coenzyme A (CoA) and Acy carrier protein (ACP) Involved in fatty acid synthesis, acyl group transfers Lipid, carb, and AA metabolism **deficiency occurs with other B complex vitamin deficiency Meats, whole grain cereals
*A deficiency in Niacin can lead to what? Symptoms (4)?
Pellagra Dementia Dermatitis Diarrhea Death
*What does a deficiency in vitamin E cause? 5
Peripheral neuropathy Muscle weakness Impaired balance Coordination **may result in hemolytic anemia
*What can a deficiency in vitamin B12 cause?
Pernicious anemia (may also be due to missing intrinsic factor); accumulation and incorporation of abnormal FAs into cell membranes -Sore tongue -Paresthesia extremities -Weakness -Megaloblastic anemia
*A deficiency in Vitamin B2 can lead to what?
Pharyngeal/oral hyperemia (increased blood flow) Angular stomatitis (inflammation of corners of mouth), cheilosis (scaling skin around mouth) <img src="paste-438868348239873.jpg" />
__________ is an inborn error in metabolism in which the patient is unable to metabolize phenylalanine
Phenylketonuria (PKU)
*What does the Bohr effect state?
Physiological phenomenon describing hemoglobin binding to O2:1) An increase in CO2 promotes O2 release 2) An increase in [H+] promotes O2 release 3) Both shift Hb saturation curve to the right <img src="paste-256147554566145.jpg" />
*What is serum?
Plasma when clotting factor are removed Yellow in color due to bilirubin
*Describe the principle of isohydric transport. How does hemoglobin play a role in this?
Principle whereby CO2 and HCO3-in solution remain in equalibrium with one another, tied by their common reagent: H+ ions (pH) Hb acts as a buffer to bind to excess H+ (and release O2), to keep plasma pH constant (or at least try to) <img src="paste-265579302748161.jpg" />
*What is vitamin B6 also known as? What does it participate in? Food sources? Treatment of tuberculosis?
Pyridoxine **active form pyridoxal phosphate, pyridoxamine phosphate Coenzyme in numerous protein metabolism pathways **transamination, deamination, decarboxylation liver, fortified cereals, fish, poultry, starchy vegetables Isoniazid
*Standard free energy change (Î"G°) is the change in free energy under standard conditions. What are these conditions? Why is this useful?
Reactants and products are present at 1M 25°C Used to compare two reactions at similar conditions Is relate to Keq by the following equation Î"G° = -RTln(Keq)
*What is the function of Vitamin A in epithelial tissues?
Retinol and retinoic acid: bind to transcription factors and control rate of keratin gene expression **downregulates keratin expression Required for maintenance of epithelial tissues
*What is vitamin A also known as?What does it participate in?
Retinol, retinal, retinoic acid Vision Gene expression Immune function Reproduction Growth
*What is vitamin B2 also known as? What does it participate in? Food sources?
Riboflavin Precursor to coenzymes FAD and FMN **participate in oxidation reduction reactions Milk, bread, fortified cereal
*What does a deficiency in Vitamin D cause? Food sources?
Rickets in children Osteomalacia in adults Fatty fish, fish liver oils, liver, eggs, milk, cereal <img src="paste-446045238591489.jpg" />
Warfarin is used to prevent blood clots (thrombosis). What are the two isomers of this drug? Which is more potent? What Cytochrome P450 enzyme metabolizes this drug?
S and R isomers S is 5x more potent with a shorter half-life CYP2C9
*What are the classifications of fatty acids?
Saturated (no double bonds) Cis-monosaturated Cis polysaturated (includes omega-3 and -6) Trans fats
*What can a deficiency in ascorbic acid cause? Food sources?
Scurvy -perifollicular hemmorhage -corkscrew hair -impaired wound healing -tooth formation -impaired collagen synthesis -cofactor in hydroxylation reactions -biosynthesis of carnitine -modulates absorption of iron Citrus fruit, green vegetables, tomatoes, potatoes
*What can a deficiency in pyridoxine lead to? 6
Seborrheic dermatitis Microcytic anemia Depression Neuropathies EEG abnormalities Seizures
*What is the shape of the oxygen saturation curve of hemoglobin? why is this?
Sigmoidal due to positive cooperativity between O2 binding sites <img src="paste-256151849533441.jpg" />
*What happens during carbon monoxide toxicity? What is the treatment?
Symptoms: cherry red skin and nails Impaired ATP synthesis by oxidative phosphorylation Also affects heme in mitochondria Treatement: Oxygen <img src="paste-266562850258945.jpg" />
*T or F: None of the regulatory effects (CO2, pH, and 2,3-BPG) in Hb are seen in Myoglobin
TRUE Such regulation effects depond on quarternary structure So information can be transmitted between heme sites via contact residues between subunits Hb is tetrameric, while Mb is monomeric (i.e. only has one subunit)
*T or F: CO binds to heme stronger than O2 does
TRUE, binds 200x more tightly than O2 Leads to CO toxicity
How do the Alu repeat sequences affect the Low-Density Lipoprotein Receptor (LDLR)?
The sequence in the LDLR genes is subject to large insertions, deletions, and/or rearrangements via the SINE retrotransposon activity. This mutation in the LDLR is associated with familial hypercholesterolemia (FH).
*Alcoholics are at risk of what vitamin deficiency? What is this condition known as? Symptoms?
Thiamin (B1) deficiency Wernicke-Korsakoff -Ataxia -Ophthalmoplegia -Disorientation -Impaired memory -Nystagmus (eye twitching) -Conflabulation (fabricated memories)
*What is vitamin B1 also known as? What does it participate in? Food sources?
Thiamin **active form is thiamine pyrophosphate (TPP) Coenzyme in metabolism of carbs and branched chain AAs Oxidative decarboxylation of pyruvate, alpha-ketoglutarate Required by transketolase enzyme in pentose phosphate pathway Whole grain, legumes, and pork
*What is the basic structure of collagen? How does this contribute to its function?
Triple helical structure Provides high tensile strength Withstands severe stress on joints and bones without stretching
Other than the necessary cytochrome P450 enzyme, what other gene varaiant also impacts Warfarin metabolism in patient? What does this gene do?
Vitamin K epoxide reductase complex subunit 1 (VKORC1) VKORC1 reduces Vitamin K (cofactor for enzymatic conversion to create clotting factors) to active form, which is needed to create clotting factors **drug target of warfarin
*What are the essential amino acids (10)? Which ones are needed only during periods of growth?
WTF MV LIK HR -tryptophan threonine phenylalanine -methionine valine -leucine isoleucine lysine -histidine arginine R and H are needed only during development
*What affinity does HbF have for 2,3-BPG compared to HbA? Why
Weaker affinity for 2,3-BPG Due to less positive charge in 2,3-BPG binding site, because of: 1) 143-His inβ-chain is replaced by neutral aa 2) ~15-20% of HbF is acetylated at N-terminus
Individual drugs can be substrates for more than one Cytochrome P450 enzyme. How can this be a problem?
Wide and overlapping specificities makes it difficult to correlate metabolism of a drug with patient genotype Makes it hard to predict what type of metabolizer they will be
*What is the relationship betweenÎ"G° and the actualÎ"G of a reaction?
Î"G =Î"G° + RT ln [B]/[A] **can be manipulated by changing the concentrations of A and B **increase in reactant A or decrease in product will decreaseÎ"G
