Composition of cell wall, Biology


Cell wall composed of cellulose, hemicellulose, pectin, lignin, cutin & chitin.

Cell wall consists of 3 parts -

1. Matrix

  • Highly cross-linked amorphous gel-like ground substances.
  • Water = 30-60%, forms dispersion medium, hydration.
  • Pectin = 2-8%, heteropolysaccaride, helps in cross-linking, determines hydration of cell wall, elasticity, growth.
  • Hemicellulose = 5-15%,     Lipid = 0.5-3%, Protein = 1-2%

2. Microfibrils

  • Structural elements of cell wall. Provide rigidity of cell wall.
  • In plants microfibrils are formed of cellulose.
  • They are 10-25 mm in thickness, 0.5-0.7 mm in length.
  • Cellulose forms the backbone of the plant cell.
  • Cellulose polymer of b-D-glucose.
  • A cellulose microfibril consists of about 3000 glucose molecules.
  • Many chains of cellulose molecules lie parallel to each other to form the bundles.
  • A bundles of 100 molecules of cellulose forms the one elementary fibril known as the micelle.
  • The 20 micelle when get arraged parallely, form the fibrils of 250Å thick, known as microfibrils.
  • Microfibril forms large size bundle of cellulose fibres to form the macrofibrils. (macrofibril form skeletal of cell wall).
  • Microfibrils are loose & wavy in primary wall.
  • Microfibrils are close & parallel arrangement in secondary wall.
  • The hemicellulose is composed of monosaccharide units like arabinose, xylose, mammose & galactose.
  • The pectin chemically composed of glucuronic and galacturonic acid.
  • The lignin chemically composed of confieryl alcohol.
  • The cutin composed of many fatty acids.
  • In fugal cell wall formed of chitin material.
  • The chitin is a polymer of b (1® 4) acetyl glucosamine.
  • Chitin also occurs in Exoskeleton of Arthropods (insects + crustaceans)
  • Chitin is second most abundant organic material.
  • In bacterial cell wall made up of peptidoglycan mucopeptide (murein).
  • Murein is made of N-acetyl glucosamine, acetyl muramic acid and small peptide chains.
  • i.e. Murein is polymer of NAG and NAM

3. Deposition on the cell wall

(a) Lignin

  • Deposition of lignin on cell wall is called lignification.
  • After lignification cell becomes dead & impermeable to water.
  • It provides hardness to the wall.
  • Lignification commonly occur in seconday cell wall.
  • Lignin is the derivative of cellulose.
  • Lignification developed with evolution of land plants.

(b) Cutin

  • Depostion of cutin is called cutinization.
  • Cutin derivative of lipid. Polymer of Hydroxy fatty acids.
  • Deposition on epidermal cells of leaf.
  • Epidermal layer form a layer "cuticle" outside the cell wall.
  • Formation of cuticle layer is called "Cuticularisation".
  • Cutin reduces the rate of transpiration. (Loss of water in vapour form)

(c) Suberin

  • Deposition of suberin is called Suberization.
  • Suberin derivative of fatty acids. Consists of Phellonic acid and Glycerol.
  • After suberization cell becomes dead and impermeable to water.
  • It occurs in cork cells and endodermal cells.
  • Commercial cork is obtained from Quercus suber (Spanish oak)

(d) Silica

  • Deposition occur in Atropa, Grasses, Equisetum, Diatoms.
  • It provides stiffness to wall. Protects the plants from fungal attack. Irritation to grazing animals.

(e) Nonsiliceous Minerals

  • Deposition of Fe and Cu occurs in aquatic habitat plants, e.g. Chara

(f) Wax

  • Polymer of fatty acid and alcohol.
  • Wax occurs as component of cuticle and surface bloom.
  • Water repellent and control transpiration.
Posted Date: 10/5/2012 3:38:45 AM | Location : United States

Related Discussions:- Composition of cell wall, Assignment Help, Ask Question on Composition of cell wall, Get Answer, Expert's Help, Composition of cell wall Discussions

Write discussion on Composition of cell wall
Your posts are moderated
Related Questions
While explaining the concept of natural selection, we have stressed the fact that natural selection is synonymous with differential or non-random reproduction. Natural selection ai

Determine Causes of Iron Deficiency Anaemia? Dietary Inadequacy Poor bioavailability of iron Presence of absorption interfering substances in diet Poverty and

Why is sex-linked inheritance an example of nonmendelian inheritance? The Sex-linked inheritance is a kind of nonmendelian inheritance because it opposes Mendel's first law, wh

Q. How execute the two complementary nucleotide chains of the DNA facilitate the replication process of the molecule? The fact that DNA molecule is made of two polynucleotide c

NEURITE S - The processes of neurons are called neurites. These are of two types: dendrites or dendrons and an axon or axis cylinder or neuraxon. (a)      Dendrites (Den

Is there anything I can do to keep my brain healthy in older age? It is increasingly clear that how we live our lives on a daily basis strongly influences how well our brain ag

Explain the Female Reproductive System? The female reproductive system consists of the primary sex organs, the ovaries, and the accessory organs necessary to effect fertilizati

Why are glucorticoids used in transplant patients? Patients with transplanted organs are prone to host versus graft rejection as their own immune system tends to attack the gr

Define Larval Stage of Taenia Cystcercus? The pork tapeworn (T: solium) and beef tapeworn (T : saginata , which are endoparasites of humans who are the final hosts

is paper broken down by microorganisms