Membranes Flashcards
What is a lipid raft
A section of the lipid membrane where the average composition of a patch of the membrane is different from the bulk composition
Rich in cholesterol
How can lipids move in a membrane
Lateral diffusion (easily) Rotation ( easily) Transverse diffusion (difficult)
What do translocase enzymes do
They enable the transverse diffusion of the same type of lipids
What do scrambalase enzymes do
They enable the transverse diffusion of the any type of lipids
Why is apoptosis triggered
Cell are not useful and are using unnecessary resources
or
Cells realise that they are infected
What is the process of apoptosis
cell shrinkage and DNA fragmentation -> membrane blebbing -> apoptotic bodies -> phagocytosis of apoptotic bodies
What is dementia
An umbrella term describing a serious deterioration in mental functions such as memory, language, orientation and judgement
What are the main symptoms of Alzheimer’s disease
Amnesia Aphasia Agnosia Apraxia Visuospatial difficulties
What causes Alzheimers disease
Neurons malfunction and die in the brain
Senile plaques of amylase B
What are the treatments of the symptoms of Alzheimers
Cholinesterase inhibitors
NMDA receptor antagonist
What are the three types of membrane proteins
Integral (intrinsic) membrane protein
Lipid-linked membrane protein
Peripheral (extrinsic) membrane proteins
What are integral membrane proteins
Span the membrane with single or multiple transmembrane (TM) segments
Interact with fatty acid chains
TM regions made of hydrophobic side chains
What are lipid-linked membrane proteins
Proteins which contain covalently attached fatty acids that bind the protein to the membrane
What are peripheral membrane proteins
Do not interact with hydrophobic core of bilayer
Interact with lipid head-groups or other proteins
Readily removed by high salt solution
Soluble in aqueous solution
What are examples of peripheral membrane proteins
cytoskeletal proteins
spectrin
actin
What are glycoproteins and glycolipids and where are they found
Carbohydrates attached to proteins and lipids
Extracellular face of membrane
What are the function of membrane carbohydrates
Stability of proteins
Intercellular recognition
What are the symptoms of cholera
Severe diarrhoea
Vomiting
What is the virulence factor of cholera
Cholera toxin
How is cholera treated
Oral rehydration therapy of water salts and glucose
What is a pure lipid bilayer permeable to
Only H2O, small hydrophobic molecules and small uncharged molecules
What is passive transport and what are the two types
Transport which does not require energy
Simple diffusion
Facilitated diffusion
What is active transport and what are the two types
Transport which requires energy as moving molecules against conc gradient
ATP driven
Ion driven
What is simple diffusion
No metabolic energy needed
Small molecules
No specificity
Rate of diffusion proportional to concentration gradient
What is facilitated diffusion
No energy required Occurs down conc gradient Depends on integral membrane proteins Proteins are specific Similar kinetics to enzymes (dependent on temp, pH, saturable, inhibitable)
What are ionophore
Ion carrier
Antibiotic produced by bacteria to kill competing bacteria
Free transport of ions discharges ion gradients of target cell
Two types:
Carrier and channel-forming
What are ion channels
Rapid and gated passage of anions and cations Highly selective Ions flow down conc gradient Osmotic balance maintaining Signal transduction Nerve impulses
What glucose transport facilitated diffusion
Transport of glucose into erythrocytes
Glucose transporter integral membrane protein GLUT1
How is the glucose conc gradient maintained
Hexokinase modifies glucose by adding a phosphate to make glucose-6-phosphate
What are aquaporins
Water channel proteins required for the bulk flow of water across cell membranes
How does the the Na+/K+ gradient work
High [K+], low [Na+] in cell
Controls cell volume
Makes nerve and muscle cells electrically excitable
Facilitates ion-driven active transports of amino acids and sugars
Maintained by Na+/K+ATPase
How does Na+/K+ATPase work
Pumps 3 Na+ ions out and 2 K+ ions into the cell
Polarises the cell membrane
ATP hydrolysis induces conformational changes, allowing pumping of Na+ and K+ against conc gradients
Coupled system
What is ion-driven active transport
Movement of molecule is coupled to ion movement
What are the two types of ion driven active transport
symport
antiport
What are cardiac glycosides
Used in congestive heart failure
Plant steroids
Inhibit Na+/K+ATPase
Therefore decreases Na+ gradient across membrane
So increases conc Ca2+ inside cell
Enhances strength of contraction of heart muscle
What are the characteristics of intestinal epithelial cells
Line the lumen of small intestine
Large surface area for absorption
Absorb nutrients from digested food
Transfer nutrients into the blood
How is glucose moved from intestinal lumen to blood
Glucose moves into intestinal epithelial cell by Na+/glucose symport transporter -> moves out of cell into blood via GLUT2 glucose transporter
What is exocytosis and what are the two types
Secretion of molecules out of the cell
Constitutive: in all cells for secretory proteins
Regulated: in specialised cells when signalled by Ca2+
What is endocytosis and what are the three types
Taking up of molecules into the cell
Phagocytosis: ingestion of large particles by specialised cells
Pinocytosis: uptake of fluid by all cells
Receptor-mediated endocytosis: molecules bound to receptors are taken up into the cells
What are the phagocytes and where are they found
macrophages, neutrophils and dendritic cells
In the immune system
What are the types of intercellular signalling
Paracrine: nearby target cell
Endocrine: transported round blood stream to far away target cell
Autocrine: own target
Neuronal: stimulus detected, converted to electrical signal, released as chemical signal to target cell
Juxtacrine: Physical association of two cells by membrane bound molecules
What are the types of extracellular signalling molecules
Hormones Neuro transmitters Growth factors Cytokines Gasotransmitters
What are the types of receptors
Ligans-gated
G Protein Coupled Receptor
Kinase-linked
Nuclear hormone
Why do cells communicate
To regulate development and organisation into tissues
Control their growth and division
Co-ordinate their functions
How can cell communication go wrong
Signal is lost Signal is no longer sent Target ignores signal Signal doesn't reach the target Too much signal Multiple breakdowns
How can cells communicate
Remote signalling by secreted molecules
Contact signalling by plasma membrane bound molecules or contact signalling via gap junctions
What are the functions of hormones
Regulate: Body's energy needs, Protein and nucleic acid metabolism, Mineral and electrolyte metabolism, Synthesis and release of hormones Activity is regulated by positive and negative feedback
Why are there different receptor subtypes
To allow different cell to respond differently to the same hormone
What is the process of the Renin-angiotensin system
Decrease in renal perfusion causes release of RENIN -> This cleaves ANGIOTENSINOGEN in liver to ANGIOTENSIN I -> ANGIOTENSIN I is converted to ANGIOTENSIN II by enzyme ACE -> This causes the effects which together increase blood pressure -> feedback loop
What are the strategies devised to control RAS activity
Inhibit renin release and/or activity
ACE inhibitors
AT1 receptor antagonists
Aldosterone receptor antagonists
What is the life cycle of a neurotransmitter
Synthesis Storage Release Receptor activation Neurotransmitter inactivation
How do drug act on neurotransmitters
At any stage in the neurotransmitters life cycle to modulate their action
What are the two types of depression
Unipolar
Bipolar
What causes depression
Functional deficit of monoaminergic (noradrenaline, dopamine, serotonin) transmission
What are the treatment options for depression
Monoamine reuptake inhibitors Monoamine oxidase inhibitors Miscellaneous "atypical" antidepressants Electroconvulsive therapy Mood stabilising drugs
What is signal transduction responsible for
Regulating almost every aspect of physiological function at the cellular level
What is hierarchy of signal transduction
Things happen in a certain order
1st messenger -> receptor -> conformational change -> activates G protein -> Effector enzyme -> 2nd messenger -> protein kinases -> target proteins -> cellular response
How many transmembrane domains do GCRPs have
7
What is the amplification of signal
Single molecule signal has a large effect inside the cell
What are the three sites of signal amplification
G-protein
Effector enzyme
Protein Kinase
What is the function G-proteins
Hydrolyse GTP -> GDP
What are the two groups of G-proteins
Receptor associated: heterotrimeric
Small GTPase: monomeric
What are the three alpa G protein subunits
Linked to specificity of signalling
Gia
Gsa
Gqa
What is a 2nd messenger
A short-acting intracellular molecular that is rapidly formed or released as a result of receptor activation
What are the 5 common 2nd messengers
cyclic AMP cyclic GMP Diacylglycerol Inositol 1,4,5-triphosphate Intracellular calcium
What are the three amino acid residues which can be phosphorylated
Serine
Threonine
Tyrosine
What are the functions of lipids
Energy storage Major components of cell membranes Required to solubilise fat soluble vitamins Biosynthetic precursors Signalling molecules
How is fat transported
By a carrier to form a lipoprotein which are particles in plasma
What are the four main classifications of lipoproteins
VLDL (very low density lipids)
LDL (Low density lipids)
HDL (high density lipids) Chylomicrons
What do chylomicrons do
transport dietary fats from intestines to tissues
What do VLDL do
transport lipids made in the liver to the peripheral tissues
What do LDL do
Provide cholesterol for peripheral tissues
Main carrier of cholesterol
What do HDL do
Transport cholesterol to liver from peripheral tissues
What determines the function of each lipoprotein
the specific protein strands embedded in the surface of lipoprotein
What are the major classes of apolipoproteins
ApoA
ApoB
ApoC
ApoE
What is the result of mutations affecting LDL receptors
Cells cannot take up LDL
Circulating LDL in plasma increase so excess cholesterol is deposited in the arteries leading to enhanced risk of developing atherosclerosis
How does an atherosclerotic plaque develop
Normal artery -> fatty streak -> fibrous plaque -> advanced plaque
What is the cholesterol-sythetic pathway
HMG-CoA -> Mevalomate -> IPP -> FPP -> Squalene -> Cholesterol
How is the cholesterol-sythetic pathway regulated
HMG-CoA reductase
What two organs control blood cholesterol levels
Liver
Intestine
How is hypercholesterolaemia controlled pharmacologically
Statins: prevent cholesterol synthesis in the liver
Cholesterol absorption inhibitors: prevent uptake from the intestine
Fibrates: reduce triglycerides and increase HDL
