Molecular Flashcards
Nucleotides: Position of phosphodiester bond.
Links a 5’ triphosphate with a 3’ hydroxyl group.
Direction of polymerization of nucleic acids.
5’ to 3’.
Nucleotides:
A. Which are purines? Pyrimidines?
B. Which have one ring? Two rings?
Purines are adenine and guanine (2 rings); pyrimidines are cytosine and thymine (1 ring).
Nucleotides: Numbers of hydrogen bonds in pairings.
Cytosine-guanine: 3 bonds.
Adenine-thymine: 2 bonds.
How hydrogen-bonding between nucleotides affects the melting temperature of DNA.
Segments of DNA that are rich in C-G pairs melt at a higher temperature than those with mostly A-G.
Dimensions of a typical molecule of DNA:
A. Diameter.
B. Length of turn.
C. Number of nucleotides per turn.
A. 2 nm.
B. 3.4 nm.
C. 10.
Micro-RNAs.
Short segments of RNA that regulate levels of messenger RNA.
Heterogenous nuclear RNAs (hnRNAs).
Include micro-RNAs and messenger RNAs.
Structural difference between
A. Adenine and guanine.
B. Cytosine and thymine.
C. Thymine and uracil.
A. Adenine has no carbonyl group.
B. Thymine has two carbonyl groups.
C. Thymine has an extra methyl group.
RNA polymerases: Direction of action.
5’ to 3’.
RNA polymerases: Products.
RNA polymerase I: Ribosomal RNA.
RNA polymerase II: Messenger RNA.
RNA polymerase III: Transfer RNA.
Nucleases:
A. Function.
B. Types.
A. To cleave phosphodiester bonds.
B. Exonucleases require a free end; endonucleases do not.
Mitochondrial genome:
A. Number of copies per mitochondrion.
B. Number of genes.
C. Products of genes.
A. One or more.
B. 37.
C. Oxidative proteins, tRNAs, rRNAs.
Heteroplasmy: Definition.
Heterogeneity of mitochondrial genomes within one cell (antonym: homoplasmy).
Epigenetic regulation: Types (2).
Methylation.
Acetylation.
CpG islands:
A. Definition.
B. Significance.
A. Regions of cytosine-phosphate-guanine sequences.
B. Methylation of the cytosine molecules turns off transcription of adjacent genes.
Effect of acetylation on DNA transcription.
Acetylation of histones increases transcription of DNA; deacetylation decreases it.
Splicing of mRNA:
A. Mediators.
B. Causes of alternative splicing.
A. Small nuclear ribonucleoproteins (snRNP).
B. Mutation in site of splice acceptor, splice donor, or branching.
Protein structure:
A. Primary.
B. Secondary.
C. Tertiary.
D. Quaternary.
A. The sequence of amino acids.
B. The coiling of the polypeptide (e.g. α helix).
C. The 3-dimensional structure of a polypeptide.
D. The combining of polypeptides to make a protein.
DNA replication:
A. Stage of cell cycle.
B. Place in the DNA molecule where it begins.
A. S phase.
B. At AT-rich “origins”.
DNA polymerase: Direction of action.
5’ to 3’.
Parts of the cell cycle.
G1 phase: Diploid.
S phase: Duplication of chromosomes.
G2 phase: Tetraploid.
M phase: Mitosis.
Phase of mitosis in which
A. The centrioles move to opposite poles of the cell.
B. The nuclear envelope disappears.
C. The chromosomes are aligned in the middle of the cell.
A. Prophase.
B. Metaphase.
C. Metaphase.
Period of meiosis in which
A. Recombination occurs.
B. Nondisjunction occurs.
A. Prophase I.
B. Meiosis I (mostly) or meiosis II.
Periods of meiosis in which the oocyte pauses, and how long these pauses last.
Dictyotene stage (after prophase I): Until puberty.
Metaphase II: Until fertilization.
Definition of polymorphism.
A genetic change that causes no harm and occurs in at least 1% of the population.
Point mutation: Types (5) and their consequences.
Nonsense: Termination codon.
Missense: Different amino acid.
Silent: Same amino acid.
Splice mutation: Different donor or acceptor site.
Frameshift: Different reading frame.
Histones: Charge.
Positive.
Nucleosome: Structure.
A sequence of 146 base pairs of DNA wrapped around an octamer of histone proteins (two each of H2A, H2B, H3, H4).
Nucleosome: What connects one to the next.
20-50 bases and a linking histone, H1.
Packing of DNA into chromosomes.
The chain of nucleosomes is coiled into the 30-nm chromatin fiber, which then forms loops; the loops are formed into minibands, the minibands into chromosomes.
Shortest chromosome.
21 (not 22).
Classification of chromosomes by location of centromere.
Metacentric: p ≈ q.
Submetacentric: p < q.
Acrocentric: p ≈ 0 and is frequently involved in translocation.
Meaning of “22q12.3”.
Chromosome 22, long arm, region 1 (nearest to the centromere), band 2, subband 3.
Techniques of staining of chromosomes for karyotypes.
G (Giemsa) banding.
Q (quinacrine) banding.
R (reverse-Giemsa) banding.
G banding: Areas that take up the stain.
AT-rich areas > GC-rich areas.
How to assess the purity of extracted DNA.
Calculate the ratio of absorbance at 260 nm (DNA) to that at 280 nm (protein).
A value <1.8 corresponds with relative purity.
PCR: Components (6).
Heat-stable polymerase. Template DNA. Primers. Deoxynucleotides. Divalent cation. pH buffer.
PCR: Steps.
Denaturation of DNA at 95 degrees.
Annealing at about 65 degrees.
Extension (polymerization) at 72 degrees.
Return to 95 degrees.
PCR: Formula for estimating the number of copies at a particular cycle.
Number of copies = 2^n.
Methylation-specific PCR: Purpose.
To detect methylated sequences for amplification.
Methylation-specific PCR: Procedure.
Sodium metabisulfate converts methylated cytosine bases to uracil.
Uracil-specific PCR primers are used to amplify the methylated sequence.
Reverse-transcription PCR: Purpose.
To detect specific sequences of RNA.
Reverse-transcriptase PCR: Procedure.
Reverse transcriptase is used to make a cDNA copy of the RNA; the DNA can then be amplified by PCR.
Real-time PCR.
Use of a fluorescent dye to measure the quantity of DNA as it forms.
Melting point of DNA: How to measure it.
Incorporate non-hydrolyzable probes or dyes into the DNA.
Measure the fluorescence while incrementally increasing the temperature.
Melting point of DNA: Definition (2).
The point at which half the DNA is single stranded.
The point of maximal change in the rate of melting (on a plot of fluorescence vs. temperature).
Multiplex PCR: Purpose.
To permit simultaneous identification of multiple PCR products.
Multiplex PCR:
A. Procedure.
B. Limitation.
A. Many templates and primers are added to one tube and allowed to react at the same time.
B. Reactions may be affected by competition for limited resources within the system.
Transcription-mediated amplification:
A. Purpose.
B. Application.
A. Isothermal amplification of RNA.
B. Mainly in the study of infectious agents.
Types of blotting (3).
Southern: DNA.
Northern: RNA.
Western: Protein.
Sanger sequencing: Principle.
Incorporation of dideoxy-bases to cause termination of strand elongation.
The different strands can be analyzed by electrophoresis.
Sanger sequencing: Modern adaptation.
The dideoxy-bases are labeled with different fluorochromes and incorporated in one reaction. The products are analyzed by capillary electrophoresis and detection of fluorescence.
Pyrosequencing: Principle.
A molecule of pyrophosphate is released upon the formation of a phosphodiester bond. The amount of pyrophosphate can be used to determine the sequence of DNA.
Chromosome-enumeration probes: Target.
Conserved, highly repetitive sequences of satellite DNA, often near the centromeres.
Locus-specific probes: Types (2).
Fusion probes: Used for well-defined translocations with conserved breakpoints or fusion points.
Breakapart probes: Used when a gene may have various translocation partners.
Comparative genomic hybridization: Procedure.
Various probes are applied in metaphase in order to count copies of chromosomes or regions thereof.
Comparative genomic hybridization:
A. Application.
B. Limitation.
A. To characterize inherited and acquired (neoplastic) chromosomal abnormalities.
B. Cannot detect unbalanced translocations.
Array comparative genomic hybridization:
A. Advantage over conventional CGH.
B. Application.
A. Array CGH has higher resolution.
B. Investigation of a developmentally delayed child with an apparently normal karyotype.
Short tandem repeats:
A. Definition.
B. Applications (3).
A. Normally occurring sequences of 2-5 repeated oligonucleotides.
B. Determination of parentage, identification of remains, assessment of chimerism in transplant recipients.
Short tandem repeats: Disorders (2).
Unstably inherited: Trinucleotide repeats.
Unstable within an individual: Disorders of mismatch repair.
Single-nucleotide polymorphisms:
A. Definition.
B. Frequency in genome.
C. SNP haplotype.
A. Polymorphism of single base-pairs.
B. 1 in 1000 bases.
C. Total of an individual’s polymorphisms.
Single-nucleotide polymorphisms: Applications (3).
DNA fingerprinting for forensics.
Forming a genetic family tree.
Determining predisposition to diseases, responses to medications, and other traits.
Sequencing of whole genomes:
A. Methods (2).
B. Variation.
A. Next-generation sequencing, high-throughput sequencing.
B. Sequencing of whole exomes (exons).
Cytochrome P450: Nomenclature.
Example: CYP2D6*1.
Superfamily: CYP. Family: 2. Subfamily: D. Isoenzyme: 6. Allele: 1.
Drugs whose metabolism is affected by:
A. CYP2D6 (2).
B. CYP2C9 (4).
A. Codeine, tricyclic antidepressants.
B. Warfarin, phenytoin, omeprazole, diazepam.
VKORC1.
Vitamin K epoxide reductase: Involved in the metabolism of vitamin K and inhibited by warfarin.
Enzymes in which polymorphisms can alter the effect of isoniazid.
N-acetyltransferase.
Some genetic disorders are not inherited: How so?
Some are acquired during gametogenesis or early in embryogenesis (germline).
Some are acquired in differentiated cells (somatic).
Autosomal-dominant inheritance:
A. Appearance of pedigree.
B. Probability of transmitting the trait.
A. Disease is present in every generation.
B. 50% for each offspring.
Autosomal-dominant inheritance: Typical products of affected genes.
Structural proteins, receptor proteins, transmembrane channels.
Autosomal-recessive disorders:
A. Appearance of pedigree.
B. Probability of transmitting the trait.
A. Disease may skip generations.
B. 25% per offspring (if both parents are carriers).
Autosomal-recessive disorders: Typical product of affected genes.
Enzymes.
For which type of Mendelian inheritance are penetrance and expressivity most relevant?
Autosomal-dominant inheritance.
How X-linked-recessive disorders may be expressed in females (3).
Homozygosity.
Asymmetric lyonization.
Turner’s syndrome.
Types of inherited nephritic syndrome (3).
Mild: Benign familial hematuria, thin-basement-membrane disease.
Severe: Alport’s syndrome.
Penetrance vs. expressivity:
Penetrance: How many who have the mutation express the disease.
Expressivity: Degree to which they express it.
Alport’s syndrome:
A. Clinical triad.
B. Course.
A. Glomerulonephritis, sensorineural hearing loss, ocular lesions.
B. Hematuria initially; progression to end-stage renal disease.
Alport’s syndrome:
A. Inheritance.
B. Effect on carriers.
A. X-linked recessive.
B. Asymptomatic hematuria in some.
Alport’s syndrome:
A. Diagnosis.
B. Appearance on electron microscopy.
A. IHC of biopsy of skin or kidney shows lack of α₅ chain of type IV collagen.
B. Thin or disrupted lamina densa.
Congenital nephrotic syndrome: Definition.
Nephrotic syndrome before 3 months of age.
Congenital nephrotic syndrome: Differential diagnosis (2).
TORCH infection.
Inherited nephrotic syndrome.
Congenital nephrotic syndrome of the Finnish type: Clinical features (3).
Markedly enlarged placenta.
Massive proteinuria in utero.
Nephrotic syndrome by 1 month of age.
Congenital nephrotic syndrome of the Finnish type: Electron microscopy.
Abnormal variation in size of slit pores.
Rarefaction of slit diaphragms.
Congenital nephrotic syndrome of the Finnish type: Gene, location, and product.
NPHS1 on 19q13.1 encodes nephrin, a key component of the glomerular slit diaphragm.
Pierson’s syndrome: Clinical associations (2).
Microcoria, death within several months.
Pierson’s syndrome: Renal biopsy.
Mesangial sclerosis and crescents.
Pierson’s syndrome: Gene, location, and product.
LAMB2 on 3p21 encodes β₂-laminin, a component of the glomerular basement membrane.
Alport’s syndrome: Gene and its location.
COL4A5 on Xp22.3.
Nail-patella syndrome: Clinical manifestations.
Abnormalities of nails, skeleton, and eyes.
Variable renal disease.
Nail-patella syndrome: Renal biopsy.
Basement membrane expanded by fibrillary collagen deposits.
Nail-patella syndrome: Inheritance.
Autosomal dominant.
Nail-patella syndrome: Gene, location, and product.
LMX1B on 9q34.1 encodes a factor that regulates the transcription of COL4A3.
Denys-Drash syndrome: Clinical manifestations (3).
Wilms’ tumor, male pseudohermaphroditism, rapidly progressive renal failure.
Denys-Drash syndrome: Renal biopsy.
Mesangial sclerosis.
Denys-Drash syndrome: Gene and its location.
WT1 on 11p13.
Denys-Drash syndrome: Variant.
Frasier’s syndrome: Less severe; associated with gonadoblastoma.
Familial autosomal-dominant focal-segmental glomerulosclerosis: Clinical presentation.
Onset of the nephrotic syndrome in adolescence or young adulthood.
Familial autosomal-dominant focal-segmental glomerulosclerosis: Genes and their products.
ACTN4: α-Actinin.
TRPC6: Transient receptor potential cation channel 6.
Familial autosomal-recessive corticosteroid-resistant nephrotic syndrome: Clinical presentation.
Onset of proteinuria in early childhood.
Familial autosomal-recessive corticosteroid-resistant nephrotic syndrome: Renal biopsy.
Initially resembles minimal-change disease but transforms to FSGS.
Familial autosomal-recessive corticosteroid-resistant nephrotic syndrome: Gene and its product.
NPHS2: Podicin.
Renal Fanconi’s syndrome: Definition.
Proximal-tubular dysfunction with various causes.
Renal Fanconi’s syndrome: Chemical abnormalities.
Glycosuria, aminoaciduria, phosphaturia, hypokalemia, bicarbonate wasting with subsequent metabolic acidosis.
Renal Fanconi’s syndrome: Inherited metabolic causes (6).
Cystinosis, tyrosinemia, galactosemia, hereditary fructose intolerance, glycogen-storage diseases, Wilson’s disease.
Renal Fanconi’s syndrome: Acquired causes.
Myeloma kidney, amyloidosis, urate nephropathy, heavy metals, others.
Renal Fanconi’s syndrome: Other inherited causes (2).
Idiopathic.
Dent’s disease: X-linked recessive mutation in CLCN5, which encodes a chloride channel.
Autosomal-recessive polycystic-kidney disease: Clinical presentation.
Oligohydramnios with pulmonary hypoplasia.
Autosomal-recessive polycystic-kidney disease: Gross pathology.
Kidneys remain reniform but have radially oriented cysts that consist of ectatic, elongated collecting ducts.
Autosomal-recessive polycystic-kidney disease: Extrarenal manifestation.
Malformations of biliary plates.
Autosomal-recessive polycystic-kidney disease: Gene and its location.
PKHD1 on 6p.
Autosomal-dominant polycystic-kidney disease:
A. Incidence.
B. Time of presentation.
C. Penetrance.
A. 1 in 500 live births.
B. Adulthood.
C. 100% by the 5th decade.
Autosomal-dominant polycystic-kidney disease:
A. Initial presentation.
B. Gross pathology.
A. Isosthenuria and hypertension.
B. Cortical and medullary cysts.
Autosomal-dominant polycystic-kidney disease: Extrarenal manifestations (4).
Cysts in pancreas and liver.
Mitral-valve prolapse.
Intracranial berry aneurysms.
Autosomal-dominant polycystic-kidney disease: Gene and its location.
PKD1 on 16p13 in 85% of cases.
Cystic renal dysplasia:
A. Inheritance.
B. Gross pathology.
A. Not inherited; may result from ureteral obstruction in utero.
B. Kidneys are not reniform; mixture of cysts and loose mesenchyme; usually unilateral.
Cystic renal dysplasia: Associated syndrome.
Meckel-Gruber: Kidney disease, polydactyly, occipital encephalocele.
Glomerulocystic kidney disease:
A. Time of presentation.
B. Histology (2).
A. Neonatal period.
B. Dilation of Bowman’s capsule; renal dysplasia.
Brugada’s syndrome:
A. Epidemiology.
B. Typical presentation.
C. Genetic basis.
A. Southeast Asia.
B. Healthy young man dying in his sleep.
C. Mutations in various genes that encode ion-channel proteins.
Arrhythmogenic right-ventricular dysplasia:
A. Presentation.
B. Histology.
A. Sudden cardiac death in young adult during physical activity.
B. Fibrous and fatty replacement of myocardium.
Arrhythmogenic right-ventricular dysplasia:
A. Genetic defects.
B. Variant.
A. Various.
B. Naxos disease: Heart disease, abnormal skin, woolly hair.
Prolonged QT interval: Significance.
Can lead to ventricular arrhythmias.
Prolonged QT interval: Inherited syndromes (3).
Romano-Ward (AD, no hearing loss).
Jervell Lange-Nielsen (AR, hearing loss).
Andersen-Tawil.
Prolonged QT interval: Metabolic causes.
Hypokalemia.
Hypercalcemia.
Hypomagnesemia.
Genes associated with a prolonged QT interval: Most commonly mutated.
LQT1.
Which gene is mutated in inherited syndromes of long QT interval in which arrhythmias are induced by ____?
A. sleep
B. auditory or emotional stimulus
A. LQT3.
B. LQT2.
Prolonged QT interval: Pharmacological causes (5).
Tricyclic antidepressants.
Phenothiazines.
Macrolides.
Antiarrhythmics, classes IA and III.
Andersen-Tawil syndrome:
A. Clinical triad.
B. Gene.
A. Episodic paralysis, long QT interval, dysmorphism.
B. LQT7.
Inherited syndromes of long QT interval: Penetrance.
Twice as great in females.
Dilated cardiomyopathy: What fraction of cases is genetic?
About one third.
Dilated cardiomyopathy, X-linked: Gene.
The gene that encodes dystrophin. Also implicated in Duchenne’s muscular dystrophy and Becker’s muscular dystrophy.
Dilated cardiomyopathy, autosomal dominant: Most common gene.
MYH7, which encodes the β heavy chain of myosin.
Hypertrophic cardiomyopathy:
A. Incidence.
B. Gross pathology.
A. Approaches 1 in 500.
B. Thick interventricular septum.
Hypertrophic cardiomyopathy: Histology (3).
Hypertrophy of myocytes.
Disarray of myofibers.
Interstitial fibrosis.
Hypertrophic cardiomyopathy:
A. Most common mutation.
B. Inheritance.
A. R403Q in MYH7.
Familial isolated cardiac amyloidosis:
A. Inheritance.
B. Geographic distribution.
A. Autosomal dominant.
B. High prevalence in Portugal, Sweden, Japan, and parts of Africa.
Familial isolated cardiac amyloidosis:
A. Gene.
B. Clinical associations (2).
A. TTR, which encodes transthyretin.
B. Peripheral neuropathy, leptomeningeal amyloidosis.
Gene that encodes a very early transcription in cardiogenesis.
NKX2-5.
Cardiac defects associated with mutations in GATA-4.
Septal defects (mostly atrial).
Holt-Oram syndrome:
A. Cardiac defects.
B. Other clinical feature.
A. Septal defects (atrial or ventricular).
B. Malformations of upper limb(s).
Holt-Oram syndrome:
A. Inheritance.
B. Gene.
A. Autosomal dominant.
B. TBX-5.
DiGeorge’s syndrome: Most common cardiac defects (4).
Tetralogy of Fallot.
Interrupted aortic arch.
Ventricular septal defects.
Truncus arteriosus.
DiGeorge’s syndrome:
A. Gene implicated in cardiac defects.
B. Type of mutation.
A. TBX-1 on 22q.
B. Microdeletion.
Noonan’s syndrome:
A. Most common cardiac defects (2).
B. Other clinical features (2).
A. Right-sided defects, esp. pulmonic stenosis; hypertrophic cardiomyopathy.
B. Lymphatic malformations, prolonged coagulation times.
Noonan’s syndrome: Gene.
PTPN11.
Alagille’s syndrome:
A. Most common cardiac defect.
B. Gene.
C. Inheritance.
A. Pulmonic stenosis.
B. JAG1.
C. Autosomal dominant.
Trisomy 21: Most common cardiac defect.
Malformation of the endocardial cushion leading to ventricular septal defect.
Turner’s syndrome: Most common cardiac defects (4).
Bicuspid aortic valve.
Coarctation of the aorta.
Dilatation of the aortic root, which predisposes to aortic dissection.
Williams’ syndrome:
A. Most common cardiac defect.
B. Other clinical manifestations (4).
A. Supravalvular aortic (hourglass) stenosis.
B. Dysmorphic facies, mental retardation, hypercalcemia, defects of connective tissue.
Williams’ syndrome:
A. Gene responsible for most of the features.
B. Type of mutation.
A. Elastin gene.
B. Microdeletion.
Genes associated with a prolonged QT interval: Potassium channels (2).
LQT1, LQT2.
True hermaphroditism: Definition.
Presence of both ovarian and testicular tissue, whether separately or together in one organ.
True hermaphroditism: Karyotype.
Usually 46,XX, albeit almost always with transposed genetic material that includes the SRY gene.
Sometimes a mosaic of 46,XX and 46,XY.
Never 46,XY.
Pseudohermaphroditism:
A. Definition.
B. Leading causes.
A. Discordance between genotypic/gonadal sex and phenotypic (external genital) sex.
B. Males: Androgen insensitivity; females: congenital adrenal hyperplasia.
Androgen-insensitivity syndrome:
A. Inheritance.
B. Hormone levels.
A. X-linked.
B. Normal or high testosterone and LH.
Kallmann’s syndrome:
A. Clinical features.
B. Most common pattern of inheritance.
C. Most commonly affected gene and its location.
A. Hypogonadism due to decreased gonadotropins; anosmia.
B. X-linked.
C. KAL1 on Xp22.3.
McCune-Albright syndrome: Classic clinical features (4).
Polyostotic fibrous dysplasia.
Café-au-lait spots.
Precocious puberty.
Other endocrine abnormalities.
McCune-Albright syndrome: Reason for variable expression.
All cases are somatic mosaics, the germline mutation being incompatible with life.
Familial hypocalciuric hypercalcemia:
A. Inheritance.
B. Chemical findings (2).
A. Autosomal dominant.
B. Hypercalcemia; normal PTH (and normal parathyroid glands).
Congenital hypothyroidism: Clinical features.
Normal fetal development due to maternal thyroid hormone.
Postnatal deficiency can impair development of brain.
Congenital hypothyroidism: Causes.
Most common: Maternal autoantibodies.
Rare: Genetic; may be related to defects in PAX8 or TSHR.
Diabetes mellitus, type 1: Relevance of HLA type.
Relative with for those with HLA-DR3 or -DR4:
2-3 in heterozygotes.
10 in homozygotes.
Maturity-onset diabetes of the young:
A. Inheritance.
B. Clinical presentation.
A. Autosomal dominant.
B. Insulin-independent; similar to type 2, but with onset before the age of 25.
Hirschsprung’s disease:
A. Histology.
B. Associated structural chromosomal abnormality.
A. Absence of ganglion cells; axons are hypertrophic.
B. Trisomy 21 is found in 10% of children with HD.
Hirschsprung’s disease: Associated syndromes (6).
Neurofibromatosis, type 1. Multiple endocrine neoplasia, type 2a. Waardenburg's syndrome. Congenital central hypoventilation. Familial dysautonomia. Smith-Lemli-Opitz syndrome.
Hirschsprung’s disease: Related single-gene defects.
RET, GDNF, EDNRB are rarely mutated.
Osler-Weber-Rendu syndrome: Relevance of clinical presentation to age.
Children: Epistaxis.
Adolescents: Skin lesions.
Older adults: Gastrointestinal bleeding.
Microvillus-inclusion disease:
A. Importance.
B. Inheritance.
A. Leading cause of malabsorption in neonates.
B. Autosomal recessive.