dr. laurie solis. extra cellular components and connections between cells help coordinate cellular...
TRANSCRIPT
Cell Walls of Plants
Cell walls are an ‘extra cellular’ structure of plant cells that distinguishes them from animal cells
Cell walls
Protects the plant cell Maintains the cells shape Prevents excessive uptake of water On the whole the cell wall holds up
the plant against the forces of gravity
The story of the cell wall… Once upon a time…
There was a baby plant…
A young plant cell first secretes a relatively thin and flexible wall called the ‘primary cell wall’
The story of the cell wall… In actively growing cells, the cellulose fibrils are oriented at ‘right angles’ to the direction of cell expansion
This affects the growth pattern and can be seen under a microscope.
Cell wall… As a result, it is
believed microtubules in the cell cortex guide cellulose and deposits the fibrils
The cellulose is oriented in the way of growth
Thereby, microtubules affect the growth pattern.
The cytoskeleton is both a:• muscle• and a skeleton,• and is responsible for • cell movement, • cytokinesis, • and the organization of the organelles within the cell.
Cytoskeleton
Middle Lamella
Middle lamella Thin layer rich in sticky
polysaccharides called pectins
Located between primary walls of adjacent cells
This glues adjacent cells together
When the cell matures and stops growing it strengthens its wall
Middle Lamella
Middle lamella The glue the
middle lamella uses is called: pectin
Pectin is used as a thickening agent in jams and jellies
Secondary wall
Some plant cells have a secondary wall
Deposited between the plasma membrane and the primary wall
Deposited in several layers
Strong and durable matrix
Strong cell protection and support
Wood is composed mainly of secondary layers
Extracellular Matrix-Animal Cells
Animal cells do not have cell walls
Instead, they have an extracellular matrix (ECM)
ECM
ECM Main ingredients
are: Glycoproteins
secreted by the cell
Glycoproteins are proteins with covalently bonded carbohydrates, usually short chains of sugars
ECM
There are different types of glycoproteins
The most common in animal cells is collagen
Collagen forms strong fibers outside of the cell
Collagen accounts for 50% of the total protein in the human body!
Collagen
Because collagen is fibrous it is embedded in a woven web from proteoglycans
Proteoglycans consist of a core protein with many carbohydrate chains attached.
Often it is 95% carbohydrate
ECM-Fibroconectin/Integrin
Fibroconectin is also part of the ECM
Binds (and other proteins) to surface receptor proteins of the cell called integrins (inside the plasma membrane)
Integrin transmits signals between the ECM and the cytoskeleton and integrate changes occurring outside and inside the cell
ECM research
New research on the ECM indicates that the role of the ECM, fibroconectins and integrins affect what goes on in the cell
Cells – collective operation Even though we look
at cells individually, remember that: Cells act collectively Cells make up tissue,
organs, and organisms
Cells interact, adhere, and communicate through direct physical contact
Cell Walls - Plasmodesmata
So far we’ve learned that plant cells have a strong exterior wall
However, cell walls are perforated with channels called plasmodesmata
Cell Walls - Plasmodesmata
Plasmodesmata, allows cytosol to pass through so it can connect the physical environments of the adjacent cells
Plasma membranes line each channel
Water and small solutes can pass easily through
Animal Cells/Junctions
Animal cells have three types of intercellular junctions Tight junctions Desmosomes And gap junctioins
Occur in the epithelial tissue (external and internal surfaces of the body)
Animal Cells/Junctions Tight Junction Plasma membranes
are tightly pressed together
Bound by specific proteins
Form continuous seals Tight seal, prevents
leakages of cellular fluid (that is why sweat leaks out of our body and not into another cell)
Animal Cells/Junctions Desmosomes Function like rivets,
and fasten cells together in strong sheets
Contains filaments made of keratin proteins
Creates tissue and muscle!
Muscle tears are really tears in desmosomes!
Animal Cells/Junctions Gap junctions Provide
cytoplasmic channels from one cell to an adjacent cell
Contain membrane proteins
Necessary for communication between cells
Conclusion – Cells are integrated Remember that Cells are
integrated! That means they
work together! The cell is a living
unit greater than the sum of its parts!