Membreme Flashcards
Amphipathic
Comprising hydrophilic and hydrophobicregions
Three major till type of membrane lipid?
Glycerophospholipids
Sphingolipids
Sterols
Glycerophospholipids
Phosphorylated head group
Three-carbon glycerol backbone and hydrocarbon fatty acid chain
-M group include, choline or serine
Amphopathic various derivatives present in varying amounts in membrane of all cell
Fatty acid tail can be saturated or unsaturated cone or more double bond
Sphingolipids
Phosphorylated head group•
Sphigosine backbone and 2 hydrocarbon fatty acid chairs one of the latter acid chains is’ he sphingosine
Polar group includes choline or can be a sugar
Amphipathic a present in most cellsbut most abundant in myelin sheath surrounding nerve cells
Sterols
Cholesterol in animals(ergosterol in fungi, hoponoid, in bacteria)
Present in varying amounts and influences membrane in varying amounts and influences membrane fluidity rigidity
Unsaturated, double bonds in fatty acid tails create space to s terol to sit in the membrane
Composed n and properties of membrane
The outer and inner layers can have different compositions
Clustering of lipid molecules to give domains or rafts
Different cells and organelles can have different membrane compositions also can be single bi layer or double bilayer the study of a membrane
Membranes are self-sealing- ensuresthe cell remains intact and not damaged of killed
Key processes like cell division,endobutosis) exocytosis
Selectively permeable
Separating the inside environment of the cell
From the out side
Maintenance of pH and ionic composition
Regulation of cell volume
Concentration of metabolites and extrusion of waste substances and toxin
Generation of ion gradients for excitable tissues (muscle and nerve )
Channel/ cores/transporters
Allow compounds to enter or leave thecell either
Along their concentration passive transport 1 diffusion lfacilitated diffusion by
By extending energy to move against their concentration gradient - active transport
Are integral membrane protein and require several polypeptide subunits arranged to creat a structure with central equal us channel
Allow movement of molecules across the membrane and controlled by opening or closing by the subunits
Receptors and adesión molecules
Bind extracellular molecules without necessarily transporting across the membrane
Allow cells to sense their environment and to adhere to their tissue
Many other prodien and enzyme are present in /on membrane
Selective permanbily
Water, gaser(O2, CO 2, No) - urea compass through the belayer unaided
Rate of movement of water might not be sufficient for cell function
Gases dirt use rapidly due to concentration gradient
Although water passes throughfacilitated transport by (aqua) poring is required
Ion sugar amino acid can not pass through the membrane unaided and require integral membrane protein do
Passive transport - diffusioni facilitated diffuse
Active transport requiring expenditure of energy
Transport be diffusion is driven by difference on either side of the melane can be
Chemical electrical
Diffusion process is influenced by what
Steepness of the concentration gradient
Temperature
Size or mass of diffusing substance
Surface area
Diffusion distance
Numbers of channels/transporters on the surface of the cell
How transporters help
Allow accumulation against a concentration gradient
Higher specific for one molecule ion or class or molecules sugars amino acid
Require expenditure- energy and there are several key sources
ATP hydrolysis
Dissipation of proton/ sodium gradient
Examples of transports
Uniporters, symporters, antiporters (involve ATP hydrolysis; secondary proton or sodium gradients)
ATP-binding cassette (ABC) system (ATP hydrolysis)
Transporters (active)
Transporters move compounds in and out of cells against their concentration gradients
This requires energy, which can be supplied by ATP hydrolysis (ATPases) e.g.,
Sodium-potassium pump, calcium pump
Mitochondrial ATP synthase
ATP- Binding Cassette (ABC transporters)
Secondary active transport
Secondary active transport / co-transport of a molecule along its concentration gradient (co-transporters); uses energy of ATP hydrolysis indirectly to establish proton or sodium gradients
e.g., Na+ – K+ ATPase or Na+ pump is a membrane transporter that maintains gradients of Na+ and K+ across the membrane.
For each ATP hydrolyzed 3 Na+ ions are removed from the cell and 2 K+ are brought in; by keeping this Na+ gradient, it creates a secondary ‘energy’ source to drive secondary active transport
Proton gradients are also used to drive activity of mitochondrial ATP synthase and generation of ATP
Channels?
Channels, carriers (facilitated) allow diffusion of specific molecules down a gradient
Gated ion channels are highly selective for specific ions and open and close in response to a particular signal
ligand-gated (e.g., acetylcholine binding its receptor – see figure below)
voltage gated (e.g., potential difference across a membrane – depolarization)
Gap junctions are channels that connect directly with neighbouring cells
Prominent in cells like cardiomyocytes where there is rapid communication and movement of ions across the heart to mediate contractile forces
The atp-binding cassette (ABC) tranpotter
Over 200 different ABC systems
Present in pro- and eukaryotic cells
Transport best studied in Gram negative bacteria
In human cells ABC transporters are involved in;
Cystic fibrosis (Cystic Fibrosis Transmembrane Conductance Receptor - CFTR) – is a Cl- transporter, that is mutated in conditions like CF
Multi-drug resistance – pumping drugs out of a cell, notably cancer cells
Requires energy generated by hydrolysis of ATP – active transport
Receptors?
Most receptors bind extracellular molecules without transporting them across the membrane and allow cells to sense their environment
Receptors detect extracellular signals, called ligands such as hormones and growth factors or molecules
Most receptor ligands do not move across the membrane, but cause a change in the cytoplasmic domain of the receptor protein, either through clustering of the receptors or through inducing a conformational change of the receptor protein
They usually initiate a cascade of signalling molecules – second messengers such as cAMP or cGMP – see pharmacology lectures
What are main principles of passive and active transport
Outline the processes of active and secondary active transport
Exocytosis
Exocytosis; secretion of proteins out, across the cytoplasmic membrane
Packaged into secretory vesicles by Golgi apparatus and targeted to cytoplasmic membrane;
Vesicles fuse with cytoplasmic membrane and release their contents extracellularly; may involve clathrin-coated pits (see endocytosis)
Constitutive and active processes
Bacteria have dedicated transporter systems called translocases; constraints of the cell wall means exocytosis, endocytosis etc might be as possible compared to animal cells
Endocytosis
Endocytosis; Uptake of macromolecules from extra-cellular space, across the cytoplasmic membrane; occurs continuously in all animal cells
Pinoctosis
Pinocytosis is a constitutive and continuous process involving uptake of extra-cellular fluid via small membrane vesicles
Phagocytosis
is a specialized form of endocytosis in macrophages and neutrophils to ingest bacteria and cell debris
Receptor mediated endocytos is
involves the protein clathrin forming clathrin-coated pits and vesicles; protein has a distinctive 3-legged structure called a triskelion, which assemble to form a basket-like structure to stabilize the endocytic vesicle; uptake of cholesterol most studied process
Key facet of cell function
Signaling
To able the drag interact membrane
Drugs must also ‘negotiate’ the cell membrane and need to interact with and follow the various membrane transport and signalling mechanisms and principles
Agonists
activate the target as a ligand e.g., Insulin
Antagonists
block the activation of the target by ligand e.g., Beta blockers block the adrenaline receptor (treating hypertension and arrhythmia)
Signal transduction blockers
Kinase inhibitors are being developed as cancer treatments
