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Basic Science Notes
Stimulation of α receptors leads to:
Vasoconstriction
decrease in gut motility
uterus contraction
decrease in pancreatic exocrine secretion
Cholera toxin: activates G protein, which activates adenylate cyclase
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Iron is absorbed in upper small intestine
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The sulfate form contains more elemental iron per dosage unit than gluconate
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Mitochondrial DNA codes for
proteins in the oxidative phosphorylation / electron transport chain
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DNA
Bases are paired with hydrogen bonds but the ribose-phosphate complexes are paired
with covalent bonds
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Coding sequences (exons) are interspersed with introns
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mRNA translation into proteins occur in the cytoplasm
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It has sites for amino-acid attachment and codon (a
particular sequence of 3 bases) recognition
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Each tRNA molecule binds only one type of amino acid, but because the
genetic code is degenerate, more than one codon exists for each amino acid
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Reverse
transcription involves transcription of RNA to DNA (used by retroviruses)
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Multiple codons (triplets of nucleotides) code for the same amino acid
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They bind to RNA and stops it from processsing
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DNA polymerase needs to be stable at high temperatures and hence thermostable
enzyme from T
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The mixture is heated to below 100°C
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HindIII and EcoRI are examples of restriction enzymes
DNA ligase and polymerase are involved in joining and linking DNA together
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They are usually small, consisting of a few thousand base pairs
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A Barr body is an inactivated X chromosome
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Heterochromatin contains mostly inactivated genes
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Northern blotting detects RNA
Southern blotting detects DNA
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3) describes a female with a normal number of
chromosomes but a translocation between the long arm of chromosome 4 (q) and the
short arm of chromosome 8 (p)
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Conditions with genomic imprinting:
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myotonic dystrophy
Beckwith-Wiedemann syndrome
Prader Willi syndrome
Angelman syndrome

Anticipation refers to increase in the number of trinucleotide repeats
The list of trinucleotide repeat disorders are:
Fragile X
Huntington's chorea
Myotonic dystrophy
Friedreich's ataxia
Spinocerebellar ataxia
Spinobulbar muscular atrophy
Diseases which have mitochondrial inheritance (passed on by the mother):
• Kearn Sayre's
• MELAS
• MERRF
• progressive external opthalmoplegia
• Leber's optic atrophy
There are cyclins at various phases of the cell cycle (G1 to S phases) which can bind
to enzymes such as threonine and serine kinases (also known as cyclin dependent
kinases)
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Eukaryotes (higher organisms) have muliple chromosomes in a genome which is
separated from the rest of the cell by a nuclear membranes
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Oncogenes
Proto-oncogenes and oncogenes encode growth factors
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Mutated proto-oncogenes that cause cancer are called oncogenes
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c-myc translocation occurs in Burkitt's lymphoma
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SRC oncogene is associated with sarcoma
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Bax, Bad and Bak are members of the
oncogenes which promote cell death
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Bcl-2 prevents cell death by blocking apoptosis, preventing p53 mediated cell
destruction and prevent cell death
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If a person inherits only one
functional copy of the p53 gene from their parents, they are predisposed to cancer and
usually develop several independent tumors in a variety of tissues in early adulthood
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Li Fraumeni syndrome
predisposes patients to breast cancer and sarcoma
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It has a role in downregulating cell division
and apoptosis
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Phenotypic features are prognathism, long face, high arched
palate, large ears, cryptorchidism, hypotonia and mitral valve prolapse
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Aortic
regurgitation may occur due to aneurysmal dilatation a feature
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Homocystinuria is an autosomal recessive disorder
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Osteoporosis and osteopetrosis are also seen in homocystinuria
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The anion gap is normal (Na + K - Cl - Bicarb) - normal range is 10 - 16
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Myosin is involved in striated muscle contraction
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MRCPASS NOTES

5

Myosin heavy chain mutation is implicated in familial hypertrophic cardiomyopathy
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Enzyme deficiencies
Gaucher’s disease – Glucocerebrosidase deficiency
Tay Sachs disease - Hexosaminidase A deficiency
Niemann Pick disease - Sphingomyelinase deficiency
Metachromatic leukodystrophy - Arylsulphatase A deficiency
Hurler's syndrome - Iduronidase deficiency
Fabry's disease is an X-linked lysosomal storage disorder
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Ceramide accumulation occurs in various organs
including the heart, skin and nerves
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Gaucher's disease is associated with the enzyme glucocerebrosidase
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Maple syrup urine disease (MSUD) is an aminoacidopathy secondary to an enzyme
defect in the catabolic pathway of the branched-chain amino acids leucine, isoleucine,
and valine
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Causes of Retinitis pigmentosa are:
Kearn Sayre's syndrome
Usher's disease
Refsum's disease
Lawrence Moon Biedl syndrome
Alports's syndrome
Friedrich's ataxia
SIGNAL TRANSDUCTION
G protein receptors are 7 transmembrane spanning receptors
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Classical pathway
C1 (q,r,s), C2, C3, C3 are components
C43b cleaves and activates C3
Activated by Ab-Ag complexes
Alternative pathway
C3, factor D, factor B, properdin are components
C3bBb activates C3
Activated by endotoxin, bacterial cell wall
Membrane Attack Complex
Helps to penetrate cell membranes, leading to lysis
Neisseria infection leading to meningococcal meningitis often occurs in patients with
complement deficiencies of C5-9
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C3a - mediates inflammation
C3b - cleaves C5, opsonises, activates alternative pathway
C5a – chemotaxin, mediates inflammation
Cell Adhesion Molecules are important regulatory molecules in inflammation and
cell signalling/migration
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CD94 receptor is located in Natural Killer (NK) cells
and is bound to the cell membrane
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MHC class I proteins are present on all nucleated cells
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MHC class II proteins are only expressed on dendritic cells, macrophages, B-cells as
antigen presenting cells
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B cells are activated in primary
immune response which initially produce IgM
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Most T cell antigens have repetitive epitopes (e
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LPS/endotoxin), which
are able to cross link to B cell surface immunoglobulin to activate these cells
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Recombinant forms of interleukin
receptor antagonists (IL-1Ra) are useful as disease modifying drugs in rheumatoid
arthritis
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Antibody
production is promoted
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Tumour necrosis factor can bind to either p55 or p75 receptors and activates nuclear
factor kappa B (NFkB) transcription factor
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TNF α is procoagulant and can lead to thrombosis
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It enhances dendritic cell migration
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IFN α and IFN β are antiviral cytokines
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IFN α and IFN β (not γ) bind to the same receptor known as type I receptors
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IgG is the commonest antibody in the serum
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It comprises 2 Fab fragments, and is
divalent rather than monovalent
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Systemic Mastocytosis is due to excessive mast cell stimulation
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Mast cells are Ig E mediated but can be triggered by injury, drugs and
complements
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Diagnosis can be confirmed by raised levels of urinary N-methyl imidazole, blood
eosinophilia and thrombocytopenia
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MRCPASS NOTES

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Hypersensitivity reactions
Anaphylaxis is a type I reaction (atopic diseases)
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Serum sickness is a type III reaction (immune complex disease)
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Common Variable Immunodeficiency (CVID) is a disorder characterized by low
levels of serum immunoglobulins and an increased susceptibility to infections
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X linked immunodeficiency include SCID and Bruton's hypogammaglobulinaemia
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Prion proteins are
usually resistant to protease digestion and are not broken down by heat
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CJD, Kuru and scrapie are prion diseases
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Normal prion proteins
are encoded by chromosome 20
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PrPsc proteins are anchored by glycoproteins (GPI)
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MRCPASS NOTES

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