ECM & Cell Wall Flashcards
What are the four major tissue types in the body?
- Connective
- Epithelial
- Nervous
- Muscular
What is the main component of connective tissue?
Extracellular matrix (ECM)
What percentage of collagen mass in humans is collagen I?
90%
What are the mechanical properties of tissues determined by?
Specific protein composition of the ECM
What are the properties of collagen I related to?
Tissue stiffness
What are the main components of the basal lamina?
- Laminin
- Collagen IV
What are integrins?
Trans-membrane proteins that link ECM to the cell’s cytoskeleton
What is the role of integrins in cell migration?
They facilitate adhesion of protrusions to the surface
What is the precursor form of collagen called?
Procollagen
Procollagen cannot assemble into fibrils until it is cleaved by a protease and that mainly happens outside the cell
What is required for the trimerisation of procollagen?
Ascorbic acid (vitamin C)
What is the function of glycosaminoglycans (GAGs)?
They resist compression and occupy a large volume relative to their mass
- large negatively charged polysaccharides
- strongly hydrophilic (take up large volume)
- occupy a huge volume relative to their mass
What is the role of proteoglycans in connective tissue?
They are extracellular proteins with covalently-linked GAGs
Fill in the blank: Collagen resists _______.
Tension
What is the primary component of the plant cell wall?
Cellulose
What gives the plant cell wall its tensile strength?
Cellulose fibers
How are cellulose fibers synthesized?
At the cell membrane
What is the primary function of pectin in the plant cell wall?
Resists compression
What do cells use to control the composition of the secondary cell wall?
Their genetic programming
What happens to integrins during mitosis?
They are phosphorylated and weaken their grip on the ECM
True or False: Hyaluronan is a polysaccharide that contains protein.
False
What connects the ECM to the cytoskeleton in epithelial cells?
Integrins
What is the role of fibroblasts in connective tissue?
They secrete and organize collagen filaments using focal contacts containing integrins
What are the two types of cell-cell junctions in epithelia?
- Tight junctions
- Desmosomes
Fill in the blank: The _______ matrix provides strength in connective tissues.
Extracellular
What type of proteins are laminin and collagen IV?
Components of the basal lamina
What does the organization of cellulose fibers affect?
Cell and tissue structure
Their orientation determines the axis of cell growth
What is the consequence of genetic changes in the ECM?
Abnormal conditions like brittle bone disease
What is the structural role of collagen in connective tissue?
It provides tensile strength
What is the function of the mucus matrix?
Provides lubrication and protection
What determines the orientation of cellulose deposition in plant cell walls?
Microtubules inside the cell
What is the significance of integrins in cell adhesion?
They mediate the attachment of cells to the ECM
What is the effect of turgor pressure on plant cells?
It drives cell expansion
What is a key feature of the primary cell wall in plants?
Relatively thin and allows cell growth
Tissue structure of the skin
- Epithelial, muscle and nervous tissues —> have little ECM & IFs and cell-cell junctions provide strength
- Connective tissues —> has few cells & lots of ECM that provides strength
What doe the ECM control?
The mechanical properties of tissues which is determined by the specific protein composition of the ECM
For example :
- tough & flexible = skin, tendon
- hard & dense = bone
- shock-absorbing = cartilage
- soft & transparent = in the eye
Importance of collagen
Is a key component of connective tissue
40 different collagen genes in humans but 90% of collagen mass is collagen I
What is collagen I?
A key component of bone
Osteoblasts deposit ECM in the bone and the light and dark rings are collagen I
Calcium phosphate fills the gaps and provides rigidity
What is collagen made from?
Made by connective tissues
Osteoblasts (bone) and fibroblasts (skin and tendons)
Organisation of collagen
- procollagen polypeptide chain
- triple-stranded helical procollagen molecule
- trimerisation of procollagen occurs in the ER and needs absorbic acid (vitamin C)
- collagen fibrils and collagen fibres OUTSIDE the cell
Importance of collagen organisation
- collagen fibres must be properly aligned
- cells deposit collagen in an organised way
- cells rearrange the fibres after secretion by pulling on them = needs integrins in focal contacts
Genetic conditions of the ECM
- abnormally stretchable skin
- brittle bone disease
- skeletal changes = short bones, altered bone structure
How do fibroblasts attach to the ECM?
Via integrins in focal contacts
Linker proteins
Help cells bind to the ECM
- fibronectin in focal adhesions
- laminin in the basal lamina
How does cartilage resist compression?
- GAGs generate swelling pressure (because they bind water molecules)
- This pressure is resisted by the collagen fibres —> supports pressures of hundreds of kilos per cm2
How are proteoglycans synthesised?
- protein component is made in the ER where glycosylation starts
- glycosylation is completed in the Golgi apparatus
- delivered to the plasma membrane by constitutive secretion
What is hyaluronan?
Made only of carbohydrates = contains no protein at all
It is synthesised by hyaluronan synthase at the plasma membrane and is extruded directly into the extracellular space
Features of the plant ECM
- plants have tough external cell walls to give cells strength
- cell wall resists turgor pressure and compression & tension
- long fibres are oriented along the lines of stress
- the primary cell wall is laid down first
What properties are determined in the secondary cell wall composition?
- hard and thick in wood
- thin, flexible and waxy in leaves
What is cellulose?
- polysaccharide of D glucose
- long fibres containing 16 strands are held together by hydrogen bonds
Structure of cellulose
Cellulose fibres are interwoven with other polysaccharides
- pectin forms a gel that resists compression
- cross linked by other polysaccharides for strength
Role of pectin
Sticks neighbouring cells together
Fills spaces
Resists compression
Where are cellulose fibres synthesised?
At the cell membrane by cellulose synthase
Cellulose synthase is made in the ER and transported via the Golgi apparatus to the plasma membrane
Oriented deposition of cellulose in the plant cell wall
- Cellulose fibrils are synthesised at and extruded through the plasma membrane by cellulose synthase
- Microtubules inside the cell determine the orientation of fibre deposition outside the cell
- Cellulose synthase is a plasma membrane protein that is synthesised at the ER and transported via the Golgi apparatus to the plasma membrane
