Lecture 15: ECM and plant cell wall Flashcards
What is the role of the extracellular matrix in animal tissues?
The architectural basis
Controls mechanical properties
How does the ECM control mechanical properties of animal tissues?
Through its protein composition
What type of collagen is in connective tissue?
90% is collagen 1
The amount of collagen 1 correlates to tissue stiffness
What is the composition of bone?
Collagen 1 which are dark and light rings
Osteoblasts that deposit ECM in bone are black dots
Gaps are calcium phosphate
What is collagen made by in bone?
Osteoblasts
What is collagen made by in skin and tendons?
Fibroblasts
What are the four stages of collagen composition?
- Procollagen polypeptide chain
- Triple stranded helical procollagen molecule
- Collagen fibril
- Collagen fibres
What is procollagen?
Collagen is secreted as procollagen
It can’t form fibrils until its cleaved
What is the organisation of procollagen?
Cells deposit it in an oriented way
They rearrange fibres after secretion using integrins in focal contacts
What are the results of genetic conditions affecting the ECM?
Abnormally stretchy skin
Brittle bone disease
Skeletal abnormalities
What is the role of integrins?
Attach the cell’s cytoskeleton to ECM
What determines cytoskeleton linkage?
The type of cell
What type of cytoskeleton linkage is in migrating cells?
Focal adhesions
What type of cytoskeleton linkage is in epithelial monolayers?
Hemi desmosomes
How to fibroblasts attach to the ECM?
Using integrins in focal contacts
How do cells bind to collagen?
Using a linker protein
What is the linker protein in focal adhesions?
Fibronectin
What is the linker protein in the basal lamina?
Laminin
In what ways do integrins change during animal cell mitosis?
They are phosphorylated
Weaken their grip on ECM
What is the role of the spaces in between collagen?
Filled by gels of polysaccharide and protein
Resist compression
What are GAGs?
Large negative polysaccharides
Hydrophilic
What are proteoglycans?
Extracellular proteins with covalently linked GAGs
What is the process of proteoglycan synthesis?
- Protein component made in ER
- Glycosylation starts
- Glycosylation completed in golgi
- Delivered to plasma membrane by constitutive secretion
What is cartilage?
Tough and resists compression
GAGs generate swelling pressure
Pressure resisted by collagen fibres
What is hyalyronan?
Made of carbohydrate and no protein
Where does hyaluronan synthesis happen?
Plasma membrane
Extruded into extracellular space
What are the properties of the plant ECM?
Tough external walls for strength
Cell wall resists turgor pressure
Resists compression and tension
Long fibres oriented along stress lines
What are the properties of the primary cell wall?
Laid down first
Relatively thin
Allows the cell to grow
What are the properties of the secondary cell wall?
Composition controlled by cell to determine its properties
Hard in wood and flexible in leaves
What are the purpose of cellulose fibres in the plant cell wall?
Tensile strength
What is the structure of cellulose fibres?
Polysaccharide of D glucose
Long fibres with 16 strands
Held together with H bonds
What is the arrangement of cellulose fibres?
Interwoven with other polysaccharides
What is the role of pectin?
Sticks neighbouring cells together
Fills spaces and resists compression
What is determined by the organisation of cellulose fibres?
The axis of cell growth
Tissue structure
What is the process of synthesis of cellulose fibres?
- Cellulose synthase made at ER
- Transported by golgi to PM to synthesis cellulose
What drives the movement of cellulose?
Cellulose synthesis
What is the process of cellulose deposition in the plant cell wall?
- Cellulose fibrils synthesised and extruded through PM by cellulose synthase
- Microtubules in cell determine orientation of deposition outside of cell
