Principles Of Medicine Flashcards
Evidence for endosymbiotic theory
Mitochondria contain separate DNA with No associated histones
Mitochondria can only be formed from other mitochondria
Mitochondria contain their own protein synthesising complexes with many similarities to prokaryotic machinery
First amino acid of mitochondrial transcript fMET as is the case in bacteria and not MET as in eukaryotes
A number of antibiotics such as streptomycin will also block protein synthesis is mitochondria, but not in cytoplasm of eukaryotes.
Describe the steps of glycolysis including the types of each reaction
Glucose phosphorylated by hexokinase enzyme at carbon 6
- requires ATP investment
- Group transfer
Phosphoglucose Isomerise enzyme converts 5C ring to 4C, creating an extra side branch and molecular symmetry
- isomerization
- glucose 6 phosphate —> fructose 6 phosphate
Fructose-6-phosphate phosphorylated to fructose 1,6 bisphosphate by phosphofructokinase
- Requires ATP investment
- group transfer
Fructose 1,6 bisphosphate hydrolysed by aldolase to 2 3 carbon molecules including glyceraldehyde 3 phosphate
-hydrolysis
Other 3C molecule converted to glyceraldehyde 3 phosphate by TPI
-Isomerization
Inorganic phosphate added to each G3P to form 2x 1,3 bisphophoglycerate
- NAD+ reduced by dehydrogenase enzyme
- Group transfer
1 phosphate group removed by phosphoglycerate kinase enzyme
-ATP generated
Phosphate group moved from position 3->2 by isomerise enzyme (phosphoglycerate mutase)
-isomerization
Water eliminated to form double bond by enolase enzyme
-group removal
ATP generated by removal of final phosphate group by Pyruvate kinase
-group transfers
Describe formation of Lactate from pyruvate under anaerobic conditions
Catalysed by pyruvate dehydrogenase
NADH oxidised
What is the importance of lactate production in anaerobic conditions
Allow NAD+ to be regenerated so that glycolysis can continue as NAD+ is required for dehydration of gkyceraldehyde-3-phosphate
When rate of NADH formation in glycolysis greater than its rate of oxidation in NADH dehydrogenase complex
Describe the role of Creatine phosphate as a buffer
Acts as buffer for storage of ATP
Creatine phosphate + ADP + H+ creatinine + ATP
Catalysed by creatine kinase
Sustain supply first 4s intense exercise
Describe the platelet plug formation
Platelet binds to Von Willebrand factor or to Glpla receptor
ADP and thromboxane released
Thromboxane causes vasoconstriction
Positive feedback mechanism present
Conformational change In GP11b/111a
Opens fibrinogen binding sites
Mechanism of action of aspirin
Inihibits production of thromboxane A2.
Describe formation of a stable haemostatic plug (secondary haemostats)
FVII bind to TF in extravascular environment
Causes activation of fx->Xa and IX->IXa
Cleaves some prothrombin to thrombin
Causes activation of other cofactors which cleave more fX and IXa
Rapid, sustained generation of thrombin
Thrombin catalyses cleavage of fibrinogen to fibrin
Describe the action of protein C
Thrombin binds to thrombomodulin
Causes conformational change of protein C to APc (activates protein C)
Protein C binds and inhibits fVa and VIIIa in presence of protein S
Describe action of antithrombin
Inhibit thrombin and fxa
Potentiated by heparin
Describe the mechanism of action of heparin
Potentiates antithrombin inhibition of thrombin and fXa
IV drip
Mechanism of action of clopidogrel on platelets
Inhibits ADP binding site (P2Y12) on platelet cell membrane.
Lasts 7 days till new platelets produced
What Is the role of calcium ions in the thrombotic cascade
Help bind activated clotting factors to phospholipid surface of platelets
Mechanism of action of Warfarin
Vitamin K antagonist
Reduces synthesis of clotting cofactors
F(2,3,9,10)
Need to monitor
Several days to take effect
Mechanism of action of direct oral amticoagulants (DOACs)
Inhibit thrombin or fXa
Describe fibrinolysis
Plasminogen activated to plasmin by tPA when bound to lysine residues of fibrin
Plasmin catalyse degradation of fibrin clot
Mechanism of action of transexamic acid
Prevents plasminogen binding to lysine residues of fibrin
Prevents fibrinolysis
Describe how prothrombin time (PT) is measured
Blood collected
Sodium citrate added (prevents Ca2+ activating blood clotting)
Sample centrifuged, plasma taken
TF and phospholipid added
Calcium added and timer started
(Can use thromboplastin recombinant instead of phsopholipid and TF)
INR generated- normalised ratio
Pt patient/ Pt average
Describe how activated thromboplastin test is carried out (APTT)
Contact activator such as glass added to phospholipid after addition of sodium citrate and centrifugation
Ca2+ added and time to clot measured
(fXII activated by surface contact)
Describe three causes of bleeding
Reduction in platelet number
Reduction in platelet function
Reduction in coagulation factors
Describe 3 causes of thrombosis
Reduced anticoagulant proteins
Increased levels clotting factors
Increased platelet levels
What is mitochondrial uncoupling?
Any process which disrupts the proton concentration gradient between the intermembrane space and the mitochondrial matrix. Rate of NADH And FADH2 oxidation not linked to rate of ATP synthesis
Action of cyanide on mitochondria
Block cytochrome oxidase complex
Action of Malonate on mitochondria
Competitive inhibitor of succinate dehydrogenase
Slows flow of electrons to Co enzyme Q
Action of Rotenone on mitochondria
Inhibits transfer of electrons from complex 1 to ubiquinone
Action of oligomycin on mitochondria
Block flow of protons in F0F1 ATP synthase complex
Action of dinitrophenol on mitochondria
Introduce micropores in inner membrane
Causes mitochondrial uncoupling
Decreases proton gradient
Describe formation of a granulocyte from a HSC
Multipotent Hemopoeitc stem cell divides and differentiates to form a common myeloid progenitor.
In presence of G-CSF myeloblast formed
Further differentiate to Basophils, neutrophils and eosinophils
Function of neutrophils
Defence against infection
Phagocytosis
Neutrophil migration associated with infection
Function of eosinophils
Defence against parasitic infection
Function of basophils
Involved in regulation of immune responses
Stores of histamine and heparin and proteolytic enzymes
Function of monocytes
Present antigens to lympohoid cells
Migrate to tissues where they develop into tissue macrophages
Function of tissue macrophages
Phagocytic and scavenging function
Storage and release of iron
Describe formation of a natural killer (NK) cell
HSC differentiates to common lymphoid progenitor via mitosis
CLP further differentiates to NK cell
Function of natural killer (NK) cell
Kill tumour cells
Kill virus infected cells
secrete cytotoxic granules
What is leucocytosis?
An increase in the number of lymphocytes in the blood above the reference range
Different names depending on cell type affected e.g. monocytosis eoisinophilia basophilia lymphocytosis neutrophilia
What is leucopenia?
An decrease in the number of lymphocytes in the blood below the reference range
e.g.
neutropenia
Causes of neutrophilia
Infection,
inflammation
infarction
chronic myeloid leukaemia
Pregnancy
Exercise
Corticosteroids
What is left shift in regards to neutrophilia?
Increase in non-segmented neutrophils or neutrophil precursors in the blood
Causes of neutropenia
Chemotherapy/radiotherapy Autoimmune disorders (Produce antibodies against own neutrophils) Severe bacterial infections Viral infections drugs-e.g. anti-pscycotics
Benign ethnic neutropenia
-African or Afro-Caribbean ancestry
Causes of neutrophil hypersegmentation
Lack of vitamin B12
Folic acid deficiency
(Megaloblastic anaemia)
Causes of lymphocytosis
Viral infection (transient) e.g. whooping cough Leukaemia (persistent)
Histological presentation of lymphocytosis
Atypical lymphocytes
Basophilic cytoplasm
‘Hugging’ of red blood cells
Causes of lymphopenia
HIV
Chemotherapy
Radiotherapy
Corticosteroids
Causes of monocytosis
Infection (chronic)
Chronic inflammation
Histological features of eoisinophils
Granular cytoplasm
lobed nuclei
Histological features of basophils
Purple/blue cytoplasm
granular
Histological features of monocyte
Lobular nucleus
Clear cytoplasm
Histological features of neutrophil
lobed nucleus (5-7) Clear cytoplasm
Histological features of lymphocyte
Blob of cytoplasm with inner blob (purple)
Causes of Eosinophilia
Allergy
Parasitic infection
leukaemia
Causes of Basophilia
leukaemia (uncommon finding)
Describe normal inflammatory pathway after vascular tear.
- Inflammatory signals:
Non apoptotic cell death releases molecular signals
(DAMPS) - Vasodilators released:
Histamine
Nitric oxide - Vascular changes
Increased permeability
reduced flow
Plasma leakage - Immune cell recruitment
Chemokines released causes leukocyte migration to chemokine source - Cytokines causes up regulation of adhesion molecules such as selectins.
Chemokines promote low to high affinity switch in integrins.
Neutrophils bind to selectins
Cytoskeletal rearrangement and extension of pseudopodia causes neutrophil ‘rolling’
Neutrophil function at site of inflammation
Pathogen recognition and clearance (TLR4)
Cytokine secretion promoting recruitment and activation of other immune cells
Phagocytosis
-Destruction by reactive oxygen species (ROS)
Resolution of acute inflammation
Pathogen recognition
Neutrophils have short half life
Macrophages clear apoptotic cells
Repair/wound healing
Pros vs cons of macrophage residency in chronic inflammation
Good:
Phagocytic
Cytotoxic
Anti-inlfmmatory
Bad:
Cytotoxic
Inflammatory
Pro-fibrotic
Consequences of chronic inflammation
Fibrosis- collagen deposition
loss of function
scarring
excessive tissue damage
Describe the structure of collagen I, II and III
3 alpha chains:
type I- heterotrimer (2 genes)
Type II/III- homotrimer (1 gene)
Triple helix
Describe the primary sequence of collagen.
Characteristic glycine X-Y repeat
Glycine only amino acid small enough to fit in helix
X-Y normally hydroxyproline/proline
What does post translational modification of proline lead to?
Hydroxylation of proline allows formation of hydrogen bonds
How does vitamin C deficiency lead to scurvy?
Vitamin C required co factor in enzyme required for collagen cross linking
Unhydroxylated collagens cause tissue weekness
Describe collagen biosynthesis from a secreted protein
Fibril associated collagen
Procollagen converted to tropocollagen after cleavage of end terminals
tropocollagens form collagen fibrils with hydrogen bonds between each
What are non fibril associated collagens
Arrange head to tail or laterally
Form ‘web/grid’
Collagen IV in basement membrane
What is Ehlers-Danlos syndromes (EDS)
Inherited connective tissue disorder resulting in stretchy skin and loose joints
Mutation in collagen gene
Components of a basement membrane:
Collagens
Glycoproteins
Proteoglycans
Consequence of diabetic nephropathy
Accumulation of extracellular matrix- highly thickened basement membrane
-restricts renal function
Cause and effects of Alport syndrome
Mutation in collagen IV Abnormally split and laminated GBM -progressive loss kidney function -proteinuria (proteins in urine) -hearing loss
Describe the structure of elastic fibres
Elastin core
Microfibrils surround which are rich in fibrillin protein
Consequences of Marfan’s syndrome
Predisposition to aortic ruptures
Spider like fingers
Describe the structure and function of laminins
heterotrimic proteins
alpha, beta, gamma chain in cross shape
Multi adhesive proteins
-interact cell surface receptors (integrins, dystroglycan)
Interact with basement matrix components (collagen, proteoglycans)
What disease is caused by an absence of the alpha 2 chain in laminin 2?
Congenital muscular dystrophy
Describe the structure and function of fibronectin
glycoprotein
derived from single gene- alternate splicing mRNA gives rise to different types
Multi adhesive protein
Describe formation of a collagen fibril
Pro alpha chains undergo covalent modifications and 3 form triple helixed procollagen molecule
Procollagen cleaved to collagen
Forms fibrils in parallel direction
What is paracrine signalling?
Hormone acts on an adjacent cell
I.E. Nitric Oxide
What is signalling between membrane proteins?
Plasma proteins on adjacent cells interacting
- Bacterial cell wall components with toll like receptors on haemopoetic cells
What is autocrine signalling?
signalling molecule acts on same cell
- acetylcholine-presynaptic receptors
List and describe the four types of cell signalling receptors
Ionotrophic receptor-
Ligand binding opens ion channel which traverses membrane
G-Protein coupled receptors
ligand binding activates intracellular G-protein complex
and GDP is converted to GTP
Enzyme-linked receptor
Ligand binding to receptor activates internal enzymes
Intracellular receptor
Membrane permeable ligand binds to a receptor inside a cell
Describe action of an ionotrophic receptor
Ligand binds to receptor
Conformational change
opens pore
Ions can move in or out of cells depending on conc gradient
Describe mechanism of a G-protein coupled receptor activating target protein.
Heterotrimic G-protein and receptor are inactive
extracellular ligand binding changes conformation of receptor
Unassociated G-protein can now bind with receptor (receptor increased affinity)
GDP-GTP
G protein dissociates into alpha and a beta-gamma subunit
binds to target protein
Describe the mechanism of a G-protein coupled receptor disassociating from a target protein
Internal GTP-ase dephosphorylates GTP-GDP
alpha subunit dissociates from target protein and rebinds to beta/gamma subunit
Receptor remains active as long as ligand bound and can activate further G-proteins
3 categories of G-protein alpha subunits
G-alpha S (Stimulate)
G-alpha I (inhibitory)
G-alpha q (activates system e.g. muscle contraction)
Describe mechanism of an enzyme-linked receptor
Ligand binding causes receptors to cluster
Receptor clustering activates enzyme activity within cytoplasm
Enzymes phosphorylate receptor
phosphorylation causes binding of signalling proteins to cytoplasmic domain
signalling proteins recruit other signalling proteins
autocrine signalling
Describe mechanism of a type 1 intracellular receptor
Ligand/hormone binds to receptor
Causes Heat Shock Protein (HSP) to dissociate
2 receptors bind together forming homodimer and travel to nucleus
Bind to DNA and cause DNA changes or affect transcription
Describe mechanism of a type 2 intracellular receptor
Hormone/ligand binds to receptor which is bound to DNA within the nucleus
causes changes to DNA/ transcription
Describe the structure of collagen
3 alpha chains, can be homo or heterotrimer
Triple helix
Glycine- X-Y repeat (x-proline) (Y-hydroxyproline) Hydrogen bond cross links (hydroxylated Proline-proline) ((-PTM))
How many chain types does type I collagen have?
How many chain types does type II/III collagen have?
2 chain types, 2 genes, heterotrimer
1 chain type, 1 gene, homotrimer
Consequences of vitamin C deficiency on collagen structure
Results in unhydroxylated collagens, vitamin C required co-factor for enzymes involved
Describe formation of a collagen fibril
Pro alpha chains undergo covalent modifications and 3 form triple helixed procollagen molecule
Procollagen cleaved to collagen
Forms fibrils in parallel direction (troop
