AP BIOLOGY 6.7Dr. Laurie Solis

Extra cellular components and connections between cells help coordinate cellular activities.

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!