ICPP Flashcards
(153 cards)
Describe main features of fluid mosaic model of the cell membrane
Amphipathic
Fluid - lipids are in motion within the bilayer
Affected by temp and molecular mass.
Mosaic - many membrane proteins embedded in bilayer
Lipid motions:
Intra chain
Fast axial rotation
Lateral diffusion
Recognise the main membrane lipids - 4
Recognise their head and tail
2 types of phospholipids:
1) Glycerophospholipids (normal). Can have different heads attached to phosphate group that are polar and charged.
2) Sphingomyelin - is a sphingosine combine with a fatty acid chain joined to a phosphate group. Can also have choline or ethanolamine attached.
Glycolipids - are sphingomyelin without the phosphate group. Have sugar group attached(head). Can be cerebrosides (monosaccharide) or gangliosides (oligosaccharide with Sialic acid residues).
Cholesterol - hydrophobic tail (steroid rings) and hydrophilic head (OH group).
Main lipid membrane properties
Glycerophospholipids- acyl chains can be saturated or not. Can have diff lengths. Thermodynamically most stable arrangement.
Sphingomyelin- mostly saturated acyl chain and unsaturated are trans so no kink so close packing.
Glycolipids - sugar groups extends extend reach of membrane so used for cell recognition and important in immune system for this.
Cholesterol - polar head binds to carbonyl group on fatty acid chain which limits movement and rigid steroid rings interfere with crystalline structure so reduce mobility and inc stability.
how do amphipathic molecules behave in aqueous
environments and how does this leads to the formation of lipid bilayers
The amphipathic molecules form one of two structures in water, micelles and bilayers.
The bilayer formation is spontaneous in water and is thermodynamically driven. Tail and head optimally energetically stable.
Extensive non- polar attractive forces between the hydrophobic tails and electrostatic and hydrogen bonding of head with water.
Discuss the influence of unsaturated fatty acids and
cholesterol on membrane fluidity
Adding unsaturated phospholipid goes from gel to more fluid as it cannot closely pack. Downwards shift of temp at which membrane is fluid.
Cholesterol allows fluid nature to be maintained over a wider temp range. Buffer.
At higher temp - Polar head interacts with acyl group of PL head – limits movement.
At lower temp - interferes with crystalline packing.
Understand how sphingolipids and cholesterol regions of
the membrane form rafts
Congregation of sphingolipids and cholesterol, which have reduced mobility compared to rest of membrane, allows selective hosting of specific proteins.
Inc tight packing. Can have GLs.
Reduced mobility of raft optimises signalling stability and limits random drift of proteins.
Act as organising domains for
receptors and signalling molecules
Optimise kinetic interaction for
signal transduction
Recognise the key role of hydration in maintenance of
physiological membrane structure and function
Allows it to form bilayer as it interacts with head.
Variation by 10% affects function.
Water interacts with polar regions stabilises the lipid head regions.
Understand the importance of flexibility and elasticity in the
cell membrane
Cell membranes need to be able to transmit forces:
Throughout own cell structures In synchrony with other cells tissues–organs – body
The elasticity of the bilayer is essential when forces act upon the membrane and distort its shape. When the force is removed it can then ‘bounce’ back into shape.
Appreciate Major Functions of the Cell Membrane
Continuous, highly selective permeability barrier
Control of the enclosed electrochemical environment
Communication
1 - Recognition 2 - Signalling
3 - Adhesion proteins 4- Immune Surveillance
Signal generation in response to stimuli (electrical, chemical)
Recognise proteins are flexible and elastic – a key
structural feature that enables function
Proteins direct forces throughout its chains and active sites to change structure to perform specific roles.
Peptide chains can flex through single bond structure.
Can store and release energy when acted upon by a force.
Changes in conformation require specific biological signal.
Phoshatidyl
Choline most common
Inositol - key signalling role
Know that hydration is essential to both protein structure and function
Need to incorporate water as an essential part of their biological structure.
Can enter hydrophilic crevices within protein if accessible
Water stays away from hydrophobic regions - this still
contributes to shaping of the functioning protein.
Recognise proteins exhibit varying degrees of mobility
within the membrane bilayer
Look at notion
Lateral diffusion
Rotational - F 1 /F0 ATPase
Conformational change
Understand conformational changes in proteins
underpin protein function
They are adopted following interactions with specific molecular or bioelectric signals.
These conformational states contribute to conveying further signals within the cell for example via G-proteins. They can also contribute to directed molecular movements as part of a larger task eg actin/myosin mediated contraction.
Recognise the different categories of the relationship of
proteins with the membrane
Look at notion
2 major groups - peripheral and integral
Peripheral proteins- external and internal membrane face
Integral:
Allow molecules to interact eg receptor kinases, transporters etc.
Not removed by ionic change.
non-polar bonding occurs within the hydrophobic interior of the lipid bilayer. Peptide chains on external and internal membrane face have
mainly polar residuals to interact with polar head, water, ions, peripheral proteins etc.
internal:
provides flexibility and elasticity of whole cell membrane
enzymes and important regulatory subunits of receptors, ion channels and transporters.
Disperses forces throughout network to protect cell integrity from mechanical disruption
External:
Essential for transmission of mechanical force generated
enzymes, antigens and adhesive molecules that attach the extracellular matrix.
Lipid Anchored Proteins
covalent link via fatty acid/lipid group within bilayer
Functional protein is outside membrane – can move laterally eg G proteins
Describe restrictions on protein movement in the
membrane - exemplified by integral and peripheral
protein cell - cell interaction
Aggregation - lipid rafts
Tethering - Extracellular and Intracellular - integrin
Cell – Cell Interaction - cadherins
Describe cytoskeletal elements in RBCs - 3 groups, 7 proteins
Look at notion
1.Transmembrane proteins
2. Intermediate Anchoring Proteins connecting 1 & 3
3. Long flexible/elastic force carrying proteins
1 -2 -3 interact via electrostatic non-covalent bonds
Trans - band 3.1 and glycophorin
Band 3.1 - essential transporter in carriage of CO2
Glycophorin - antigen – reduces adhesive/friction forces
Also shape biconcave and enable forces to be distributed through whole structure.
Intermediate- Ankyrin
Anchors Band 3.1 to Spectrin
Adducin – Actin – Band 4.1
Band 4.1 anchors Glycophorin Adducin Stabilises Assembly
Interact via polar bonds
Flexible - spectrin - double helix - Transmits forces throughout whole RBC
Describe how cytoskeleton imparts great structural
flexibility exemplified by RBCs
RBC has immense flexibility and elasticity • (ie stores Potential Energy - Releases Kinetic energy) due to weak but large number of electrostatic forces.
• Cortical cytoskeleton extends lifespan ≈ 120 days.
Example loss of cytoskeletal integrity in Disease and
Drug Therapy
Cytoskeleletal protein mutations - loss of RBC structural integrity
Hereditary Spherocytosis - rigid, Forces cause pinched off microvesicles - loss of O2
carrying capacity
Cytochalasin in chemotherapy Inhibits polymerisation of actin filaments in cancer cells so incorrect anchoring of spectrin with glycophorin in RBCs
Cortical cytoskeleton
Cell cortex - layer of actin beneath membrane
Ses 2
What is the membrane to permeable to? How is it measured.
Look at notion for coefficient diagram
extremely permeable to small uncharged gas molecules such as O2, CO2 and N2.
Then Small Uncharged Polar Molecules - This includes water, urea and NH3.
Large Polar Molecules - This includes sugars and amino acids.
Inorganic/Organic Ions
Permeability coefficient scale is cm/sec
Describe the general factors in Fick’s Law determining the rate of passive diffusion for lipid soluble solutes. No need to know equation.
J = P (C1-C2)
Diffusion coefficient = factors affecting permeability x diff in concs
What are impermeable solutes selectively transported via?
membrane proteins classed as: Pores; Channels; Carriers