Plant cell structure

Plant cell organelles

• Cell Membrane

• Nucleus

• Cytoplasm

• Mitochondria

• Golgi Complex

• Ribosomes

• Smooth Endoplasmic Reticulum

• Rough Endoplasmic Reticulum

• Cell Wall

• Chloroplast

• Central Vacuole

• Lysosomes

Plant and animal cells: both have many common components such as :

Nucleus, Mitochondria, ER, Golgi, Ribosomes, Plasma membrane, Cytosol, & Microtubules and microfilaments (cytoskeleton)

• But Plant Cell has these unique components:• Cell wall• Chloroplast• Central VacuoleBy contrast, Animal Cell has:• Centrioles • Lysosomes

MitochondriaProduces energy and involved in

cellular respiration

Golgi apparatusPackaging and transport center of

the cell

Ribosomes for protein synthesis

RE for protein synthesisSE for lipid synthesis

VACUOLE (Plant cell only) Filled with fluidHelps maintains pressure and shape of cell

•Contains Chlorophyll

• Transforms solar energy into ATP and sugar in a process called photosynthesis

The cell wall

Cell wall consists of:

(1) Middle lamella –mostly pectin, cements adjacent cells together(2) Primary cell wall• Found in all plant cells• Cellulose matrix with hemicellulose, proteins, pectin, lignin, cutin, and wax• Characteristic of undifferentiated cells or ones that still are growing(3) Secondary cell wall• Just inside primary cell wall• Characteristic of mature cells• Comprised of hemicellulose and lignin

•10-25 nm in diameter• Consists of long-chain polysaccharides • The composition varies between different species•The polysaccharide chain folded into fibers and micro-fibrils

Primary & Secondary wall

• Growing cells have primary cell walls that are usually thin and extensible, although tough.

• Mature cells no longer needs to be extensible: a rigid, secondary cell wall is produced by either:

• hardening of primary cell wall , or

• adding secondary cell wall between plasma membranes and primary wall

Primary Cell Wall

• The cell wall is a network of

1.Microfibril threads (chains of cellulose)

2.Cross-linking polysaccharides (hemicellulose)

3.Matrix of mainly acidic polysaccharides (pectins)

4.Calcium bridges pectin chains

• Cellulose and cross-linking glycans

(hemicellulose) provides tensile strength,

• Pectin is the sticky polysaccharide.

• The middle lamella is rich in pectin and cement adjacents cells together.

• Proteins Constitutes about 5%.

Connections between Cells: Plasmodesmata•Are microscopic channels through the cell walls and middle lamella. • Link adjacent plasma membranes and cytoplasm•They enable intercellular transport and communication between cells.

Cellulose

• Linear polymer of glucose,

with (β1-4)linkages to form long straight chains (2-250K residues).

• About 36 cellulose chains are associated by hydrogen bonds to a crystalline structure known as a microfibril.

• These structures are impermeable to water, of high tensile strength, very resistant to chemical and biological degradations

Structure of cellulose

Hemicellulose

• Hemicellulose is a heterogeneous group of branched polysaccharides polymers that cross-link cellulose fibrils forming a network.

• They all have a long linear backbone composed of one type of sugar (glucose, xylose, or mannose) with several branches

Structure of hemicellulose

Pectin

• Pectins are a heterogeneous group of branched polysaccharides that contain many negatively charged Galacturonic acid.

• They form negatively charged, hydrophilic network that gives compressive strength to primary walls and contributes to cell-cell adhesion.

•Pectin is a soluble compound in the absence of Ca2+/Mg2+, but forms amorphous deformable gel in their presence. • Food industries use of this property when preparing jellies and jams.

Structure of pectin

Lignin

• The most common additional polymer in secondary walls is lignin

• Found mostly in the walls of the xylem vessels and fiber cells of woody tissues.

• Lignin causes the walls to become thick, stiff, and incompressible. Lignin provides the structural strength needed by large trees to reach heights in excess of 100 m. Without lignin these trees would collapse on themselves

Structure of lignin

Cell wall and Turgor

• Cell walls is made of neutral and charged polysaccharides absorbs H2O because it has a hypotonic environment.

• Increased H2O in the cell Turgor Pressure• If a plant cell is turgid, It is very firm, a healthy

state in most plants• If a plant cell is flaccid, It is in an isotonic or

hypertonic environment

PLANT CELL

• Hypertonic solution→ Plasmolysed cell

• Isotonic solution→ Non-turgid or wilted cell

• Hypotonic solution→ Turgid cell (Usual environment

ANIMAL CELL

• Hypertonic solution→Cell shrinks

• Isotonic solution→Normal (Usual environment)

• Hypotonic solution→Cell swells