Cellular Membranes Flashcards
Why are cellular membranes called ‘amphiphillic’
Both hydrophobic and hydrophilic regions
Give the 3 functions of plasma membranes
For receiving info from other cells eg using glycoproteins
A barrier to extra cellular molecules eg ions
For movement and expansion of a cell
What can pass though membranes via simple diffusion
Very small polar molecules like H2O
Hydrophobic (non polar) molecules like co2 and 02 , urea
What can’t pass through lipid membrane
Charged ions like NA, ca2+ (polar)
Large molecules like glucose and amino acids
Explain the 3 parts to cholesterol structure
A hydroxyl OH head which is hydrophilic
Steroid rings (carbon)
And a fatty acid hydrophobic tail
Explain cholesterols function and how it performs it and why is it important
Cholesterol interferes with movement of fatty acid tails vis their rigid steroid rings
This is important as it reduces permeability which some transporters and enzymes depend on less fluidity
Name the 4 major phospholipids
Phosphatadyl ethanolamine
Phosphatadylserine
Phosphatadylcholine
Sphingomyosin
What is sphingomyosin made of
A sphingosine with a phosphate and choline attached
Which side of the membrane are glycolipids found
Apical (extra cellular side)
Name the 2 main types of glycolipids and their differences
Galactocerebroside - 2 fatty tails, glycerol, and 1 GALactose
Ganglioside - same structure but 3X GAL , GLU, NANA(cialic acid) , 1x GAL nac
Name the 4 types of membrane proteins
1- transporters - move nutrients and metabolites
2- linkers - link extra/intra molecules to the membrane eg cytoskeleton
3- receptors
4- enzymes
What are the 3 groups of proteins on membranes showing diversity
1- integral - permanently attached eg transporters
2- lipid anchored proteins - covalently bonded to lipids in membrane EG GPI PROTEINS
3- PERIPHERAL - only associated temporarily to a specific membrane protein (dissociate eg when extreme ph)
How are lipid anchored proteins attached to each other
By covalent bond
What are the 2 modes of passive transport
Transporter mediated (transporter/carrier)
Channel mediated (channel protein)
3 types of active transport / energy driven
1- coupled/cotransport
2- atp driven (hydrolysis of atp used)
3- light or redox driven - eg in chloroplasts
What is the glycoxalyx
A cell coat which is formed by glycolipids and glycoproteins
Made of oligosaccharides
Why are glycoproteins very important
N glycans - allow protein folding no aggregation
Mucins production- lubrications for cell signalling
Proteoglycans-
Cell to cell adhesion in matrix
Growth factor binding (proliferation)
GAG to provide a gel for connecting joints
4 functions of the glycocalyx
Protection - from unwanted interactions
Storage - of proteins like growth factors which then are released (why glycoproteins promote metastasis)
Adhesion - carbohydrates and proteins/lipids
Recognition- cells have specific glycolysation
Why is glycocalyx used as recognition of cells
Different cells have specific glycolysation patterns
Name the 3 types of glycoproteins and the amino acid they bind to
N- glycans. Bind to asp(N)
O glycans - bind to serine or threonine via a oxygen bond
Proteoglycans - bind to serine
What oligosaccharide to all glycans have in common
Acetyl glucosamine
Either N or O
What is the repeated units attached to proteoglycans called and made of
Glycosaminoglycans (GAG)
Amino acid sugar
Uronic sugar
Which experiment first found that membrane proteins had ability to move around membrane
FRAP - flurescent recovery after photobleaching
What did frap find
That proteins differ in diffusion ability
In a tight stack of cells some proteins are separated in either apical or basal membrane sides. Why is this
Tight junctions between cells mean polarisation of proteins
Why is the polarity of proteins in membranes important for co transport
At the apical side, the na+ co transporter is needed to carry glucose from lumen
At the basal membrane the na pump and the glucose transporter is needed
There are 4 ways of constructing protein mobility , what are they
1- self assemble together (aggregation)
2) macromolecules tether proteins outside of the cell (extracellular)
3) macromolecules tether proteins on basal side in cytosol
4) cell to cell protein interaction (joining of cells)
How is the cytoskeleton an example of the protein mobility restrictions in the red blood cells
Proteins are associated with the cytoskeleton network (spectrin protein) which restricts their movement
Free protein membranes eg trans membranes are also restricted in the cytoskeletoncomplex
There are 3 ways proteins can be membrane bending - explain
1) proteins can bind to large phospholipid heads to cluster them = bending
2) rigid bent proteins attach to the membrane
3) hydrophobic protein domains are attached into the membrane bending it
Why is bending of membranes important (3 ways)
Membrane trafficking (exo and endo)
Cell division
What are GPI proteins an example of and what kind of roles do they have
GPI are lipid anchored proteins
Attached to phosphatidylionisitol lipids
Can act as receptors etc
How did FRAP work
Proteins were modified to be GFP proteins that bound to membrane proteins
Found difference in diffusion in different proteins on membrane
How do gangliosides act as entering points for cholera
Cholera binds to the cell surface receptor ganglioside and enters cells. This causes devastating impact
Why does protein kinases in signalling need phosphatidylserine on the basal side?
(Showing importance of asymmetrical bilayer)
Negative charged phosphate is needed to activate proteins in cellular response
What are mucins needed for produced by n glycans
For protection at epithelial cells
And for lubrications for cell signalling
Why is n glycans in particular important for viruses to survive
Their spike proteins are glycosylated which prevents binding of antibodies and they can bind to surface receptors
What are glycolipids made of and name the 2 major types and charges they have
They are made up of sphingosine and also attached covalently to oligosaccharides such as galactose
Galatocerebrosides are neutral with a galactose
Gangliosides are negative in charge and have a sialic acid
Explain the 3 functions of the glycolipids
1- they determine blood group by their saccharides. Eg antigen A is a gal nac is added by glycosyltransferases and B antigen is just gal
2- they are entry points for some bacteria and toxins such as cholera has gangliosides as a receptor
3- they are involved in cell to cell interaction eg the inflammatory response. They attach to lectin proteins which allow for wbc to enter inflamed tissues
What are the main functions of n glycan glycoproteins
1- they produce mucins important for lubrication for cell signalling
2- they allow folding of proteins correctly
3- they are important for viruses as they coat spike proteins to stop antibodies
What is the structure of a proteoglycan
Serine attached protein to a tetrasacharide and gag (uronic acid and amino acid sugar)
Why are GAGs important making proteoglycans important
They form gel mesh in the matrix which can withstand compression eg in joints such as knees
How can mutation to proteoglycans cause metastasis
They are growth receptor factors = cell proliferation
How can proteoglycans also help in inflammatory response / cell cell interaction aswell as glycolipids
They can bind to lectin proteins
What are aggrins and their job?
They are proteoglycans which act as receptors on NMJ and on Tcells
They allow lipid clustering - acH and Tcells receptors cluster which allows for Tcells activation in immunity and also for muscle contraction
Why would mutation to proteoglycans stop immune system
Aggrins needed to cluster Tcells receptors for a response from the antigen presenting cell
Name the 2 aggrins types
Musk
LRP4
Why are transmembrane proteins called amphipillic
Both a hydrophilic region (polar side chain not inside membrane)
Hydrophobic region inserted in the membrane eg valine side chain
Why do unsaturated cis fatty acids cause fluidity
Became shorter and less tightly packed due to kinks
What do linker proteins do
Link cytoskeletal filaments like actin IF and microtubules and nuclear lamins
