ECM/epithelium/membrane transport Flashcards
What is the ECM
which assemble into a 3 dimensional extracellular structure with structural, and often other, functions
How is the ECM structurally complex
fibrous framework embedded in a gel-like background matrix
Structure of the plant ECM
Polysaccharide fibres (cellulose, hemicellulose + proteins) embedded in a gel of highly negative charged pectin polymers. Cellulose cross linked by thin hemicellulose fibres.
Structure of the animal ECM
fibrous protein fibres (e.g. collagens) embedded in matrix of highly charged glycosaminoglycans
Specialised ECM example in plants
cell wall
What does the cell wall prvide
ridgity and strength
What does the cell wall work in association with
turgor pressure from it’s cell osmosis draws water in; cell wall resists this and becomes stretched in the process –has high tensile strength Analogy with tyre – useless without pressure from inside
Cell wall 3 structures
middle lamella, primary cell wall, secondary cell wall
Middle lamella
first component secreted after cell division, glues cell together, allows plasmodesmata to form
when is the primary and secondary cell wall synthesised
primary - synthesised second
secondary - last but only after cell wall no longer divide
ECM composition - what is the middle lamella
uniform and continuous layer between adjacent cell walls
ECM composition - what is the middle lamella made from
Mostly pectcic acid, some pectin: polysaccharides (polymer of about 100 galactouronic acid molecules. Highly charged and hydrated, forms gel with Ca2+ and Mg2+
First cell wall effect on the middle lamella
pushes the middle lamella away from the plasma membrane
Properties of the primary cell wall
expandable, to allow for cell growth and semi permeable; nutrition and respiration
components of the cell wall
cellulose, hemicellulose and pectin
cellulose in the primary cell wall
straight chain glucose polymer; polymer chains held together with hydrogen bonds to form larger assemblies, fibrils and fibres. Form on the outside of the plasma membrane and arranged in to highly ordered structure
Hemicellulose in the primary cell wall
made of many different sugar monomers, branching chains. Cross-link cellulose fibrils together, increasing tensile strength of the wall
Pectin in the primary cell wall
gel contains fibres and gives compression resistance to wall
Small quantity proteins in the cell wall
some alter mechanical properties of wall structure e.g. stretching in cell growt. Other enzymes – formation, remodelling, breakdown of wall components – fruit ripening, leaf fall etc…
Where does the secondary cell wall form
between plasma membrane and primary cell wall
What is the secondary cell wall made from
Mostly fibres – cellulose, lignin (wood), pectins not always present, no proteins
Thickness of the secondary cell wall
very thick - gives the region of the plant very high tensile and compressive strength
Animal ECM - fibrous component
collagen and/or elastic fibres
Ground substances of the animal ECM
glycosaminoglycans (polysaccharides), proetoglycans, glycoproteins
Fibres: stretch resistance and elastic recoil
Function of the ground substance
hold water, jelly
what does the ECM do the job of
connective tissue
What can prevent spread of infection
compression resistance
type 1 collagen
the single most common protein in the body – most connective tissues
Type II collagen
cartilage
Type III collagen
prominent in embryonic tissues. Also repairs tissues, some specific distributions in adults as well
Type IV collagen
basal lamina
What do the individual gene products (alpha chain) form - collagen
assemble in threes to form tropocollagen
What does tropocollagen assemble into
fibrils – laterally but in quarter – stagger arrangement to make long structures, with a clear banding pattern
What do fibrils form
Fibrils associate to form fibres – typical of types 1,2 and 3 collagens
How is type 4 collagen formed
subunits assemble into planar sheets sit beneath epithelia, endothelia and on muscle cell surfaces
properties of collagen
Has high tensile strength and little stretch
Gene products that from collagen
Gene product: alpha chains (x3) -> tropocollagen -> fibril formation -> banding pattern
What does type 4 collagen form that the others don’t
Type IV collagen forms mats, not fibres. All basement membranes.
What is elastin made from
Made from tropoelastin protein subunits, and the glycoprotein fibrillin.
What is ehler danloss syndrome
mutation in type I collagen. Elastin works but collagen doesn’t causing hyper elasticity of skin ligaments etc - considerable variation in extent of condition person to person.
What are glycosaminoglycans
Long unbranched polysaccharide chains.
Repeating disaccharide, some with sulphate groups: Hyaluronan, chondroitin sulphate, dermatan sulphate, keratan sulphate, heparan sulphate (sulphated GAGs)
What do sulphated GAGs assemble into
arger structures: proteoglycans
What does hyaluronan function with
proteoglycans or on its own
important characteristics of sulphated GAGs and hyaluronan
highly polar (charged) attract water into their molecular structure.
Function of sulpahted GAGs and hyaluronan
Compression resistance and lubrication
what does hyaluronan do which GAGs don’t
Gel formation, lubrication
What do GAGs do to proteoglycans
draw water into structure due to charge: generate ‘swelling pressure’
What does lots of aggrecan (GAG side chain) in cartilage do
provides stiffness and compression resistance
What may be the function of the proteoglycan
Others may only have a dew, or indeed just one, GAG chain: may be involved in water uptake but also in interactions with collagen, cells, signalling molecules etc: e.g. decorin, biglycan, fibromodulin
What can aggrecan associate with
hyaluronan to form huge macromolecular aggregates – megadaltons
What diseases can the degradation of proteoglycans lead to
arthritis, intervertebral disc degeneration
What are glycoproteins
Proteins with glycosilations, but not as extensive as the proteoglycans
What is fibronectin
Multidomain glycoprotein: domains bind to different substrates
Fibronectin function
Link cell surfaces to a wide range of other molecules and molecules to each other. Cell adhesion, migration and signalling
Laminin structure
3 chains, form a cross shape binding regions to: one another, Other ECM molecules e.g. type IV collagen, proteoglycans to form planar. And to other cells (anchors cells to basal lamina)
What is the epithelial layer
: completely cellular layer, avascular, sits on top of a basement membrane, usually over a vascular connective tissue
What do epithelia control
the entry and exit of all materials to and from the body tissues
Classification of epithelia - number of layers
1 layer - simple
more than 1 - stratified
classification of epithelia - shape of top layer
squamos, cuboidal, columnar
Structure of epithelial cell
cilia, basal body, columnar cell, basal cell, basement membrane
how may epithelia not fit the classification
if its transitional causing it to be stretched/collapsed e.g., epithelium that lines the bladder shifts between collapsed and stretched as the bladder empties and fills
Features of epithelium - cellularity
entirely cellular - separate internal and external environments. Cellular monitoring of transfer
Features of epithelium - specialised intercellular contact
desmosomes, adherens junctions, tight junctions, gap junctions
Features of epithelium - polarity
top surface is different to bottom surface. Top contacts external environment, whereas the bottom contacts the basement membrane and the body. May be modified – cilia, microvilli; basal striations
Features of epithelium - basement membrane
2 parts. Basal lamina – form epithelium. Reticular fibres (= collagen) - from connective tissue
Stratified epithelium function
Provide protection from damage, the surface cells can be lost and replaced from underneath
Stratified squamos keratinised epithelium
toughest. The surface cells are filled up with keratin, lose nuclei. Tough, dead, waterproof covering.
Stratified squamos non-keratinised epithelium
Second toughest. These cells are alive all the way to the surface. Inner body surfaces: oral cavity, oesophagus, vagina. Kept moist by glandular secretions.
Stratified cuboidal columnar
uncommon – ducts of sweat glands lachrymal glands (same functional principle)net
Where is simple epithelia found
Occur where substances must be transported across the epithelium
Squamos cell function
very thin – act as filters. Lets water and ions through, hold back bigger molecules
Columnar and cuboidal cell function
ole in active transport and modification of materials that pass through them – e.g. gut cells. Plenty of cell ‘machinery’ - mitochondria, lysosomes and golgi etc.
Where are goblet cells found
in simple columnar pseudostratified columnar
What is gating of ion channels
fluctuation between open and closed.
How do ion channels work out what to transport
by measuring the intracellular and extracellular fluid
What does the single-channel conductance of a typical ion channels range from
0.1 to 100 pS
What factors control gating
Membrane voltage (e.g., depolaristaion), Extracellular agonists or antagonists (e.g., ligand gated), Intracellular messengers (e.g., Ca2+), Mechanical stretch of the plasma membrane (physical mechanisms)
What are ligand-gated ion channels made from
3,4 or 5 protein subunits that together form an ion-conducting pore in the center of the receptor (multiple subunits)
What does activation of receptor on ion channel cause
a pore to open through which ions can pass (conformational change)
What does metabotropic receptor activation initiate
an intracellular signaling mechanism (ions do not pass through the receptor protein) - allows another channel to open
Example of metabotropic receptor
adrenergic receptors of the autonomic nervous system (e.g., beta-adrenergic receptors in heart)
Speed of response from metabotropic receptor
a slower prolonged response compared to a metabotropic receptor
What type of receptor is a metabotropic receptor
A G-protein coupled receptor
Metabotropic receptor response to signals
Can amplify or dampen signals: Gs – stimulatory. Gi – inhibitory
Intracellular and extracellular fluids of the cell membrane
primarily water (in which solutes such as ions, glucose and amino acids are dissolved).
Which substances can diffuse across the bilayer
Gases (e.g., O2 and CO2) and ethanol
What are water channels called
aquaporins
What are water channels called
aquaporins
What are water channels called
aquaporins
Where are there large number of aquapor5ins
in the kidney - to regulate how dilute the urine is
How is water influx/efflux regulated
by altering number of AQPs in the membrane (membrane protein trafficking) - changing their permeability
What do uniporters do
transport one substance
what do symporters do
transport more than one substance in the same direction (co-transpor)
What do antiporters do
transport substances in different directions
Uniporters example
GLUT2 (brings glucose into the cell0. Mutation can cause diabetes as ability to transport glucose is affected.
Symporter example
NKCC2 found in the kidneys. 1Na+, 1K+, 2Cl- symporter. Critically important for diluting and concentrating urine.
Antiporter example
Na+, H+ antiporter. Found in all cells. Important in regulating intracellular pH
ATP dependent ion transporter example
Na+, K+ ATPase (also called the Na+K+ pump)
ATP dependent ion transporter structure
Three subunits (alpha, beta and gamma). Alpha subunit has binding sites for: NA+, K+, ATP and Ouabain (inhibitory – used to treat hypotension)
Where is vacuolar H+-ATPase found
in membranes of many intracellular organelles (e.g., lysosomes)
Plasma membrane H+-ATPase importance
has a role in urinary acidification
Example of ATP-binding cassette (ABC) transporters
e.g., cystic fibrosis transmembrane regulator (CFTR) - affects Cl- transporting
What is primary active transport
transport is directly couples to ATP hydrolysis (to move substances against their concentration gradient)
What is secondary active transport
energy for the transport comes from the electrochemical gradient. The energy from one molecule is used to move another molecule(s) against its electrochemical gradient e.g., 3NA+-Ca2+ antiporter.
