Plant Cell Wall & Cell Membrane

Question 1

Plant cell structures: basic parts

Answer 1

Cell wall
Protoplasm

Question 2

Cell wall

Answer 2

Almost all plant cells have a cell wall (except some sperm cells of seed plants)
The shape of a plant cell is constrained by its cell wall
Impart rigidity - cellular exoskeleton.
The plant cell wall is a highly organized composite of many different polysaccharides, proteins, and aromatic substances.

Question 3

Cell wall composition

Answer 3

Most are transparent/translucent
Contains cellulose as the principal scaffolding component
polymer of B-glucose units arranged as microfibril units
Cellulosic microfibrils are synthesized to the cell surface by cellulose synthase complexes.
Different layers of the cell wall may have different patterns due to microtubule’s depolymerization & repolymerization

Question 4

Cell wall types

Answer 4

Primary cell wall - thin (<1um) and characteristic of young, growing cells.
Offers physical support during time of growth an din herbaceous tissues

Secondary cell wall - thicker and stronger than primary cell wall;
It owes its strength and toughness to lignin for added support and protection.
Lignified secondary cell wall is requirement for terrestrial colonization and vertical growth

Question 5

Primary cell walls

Answer 5

Composed of multiple compounds formed in a complex assemblages:
Carbohydrates:
Cellulose
Cross-linking glycans
Pectins

Structural Proteins:
Hydroxyproline
Proline
Glycine
Arabinogalactan

Aromatic
Hydroxycinnamates

Question 6

Primary

Answer 6

Cell walls of some cell types may also contain polymeric lipids such as waxes, cutins, and suberins.

Cell walls of neighboring palnt cells are held together by middle lamella, which are made up of pectin:
2 adjacnet cell walls cemented by middle lamella: compound middle lamella (CML)

Maceration - process of separating middle lamella

Question 7

Protoplasm

Answer 7

Protoplasm - substance of the cell;
Protoplast - substance of a single cell

Refers to the mass of proteins, lipids, nucleic acid, and water w/n the cell
Components:
Cell membrane
Cytoplasmic elements
Nucleus
Cytoskeleton

Question 8

Cell Membrane

Answer 8

A remarkable boundary of all living cells.

In eukaryotic cells, membranes:
Enshroud the genetic material.
Delimit boundaries of other internal structures
Regulates fluxes of ions and metabolites

Question 9

Fluid mosaic membrane

Answer 9

All biological membranes have the same basic molecular organization:
Bilayer of lipids > spontaneous assembly
Embedded proteins > selective traffic of solutes

Question 10

Membrane lipids

Answer 10

Common membrane lipids (plants):
Phospholipids
Glycosylglycerides ~ galactolipids
Glucocerobrosides
Sterols

Question 11

Phospholipids

Answer 11

Individual molecules are free to move; can slide past each other.
It can assume any shape.
Have the ability of self-assembly
Studies revealed the movement of individual molecules (ex. Flip-flop)

Question 12

Membrane proteins

Answer 12

Provide enzymatic and structural functions.
Proteins associated with lipid bilayer:
Integral proteins - embedded in the bilayer
peripheral proteins - bound to the bilayer by non-covalent bonds
Anchored proteins- bound to covalently to the bilayer via lipid molecules