THE PROTOPLAST

The Cell   the basic unit of life

  came from the Latin word cella meaning storeroom or chamber

  term first used by Robert Hooke in 1665 while observing cork cells

The Cell   Composed of:

1.  Protoplast – the site of cellular metabolism

2.  Cell wall-outermost part of a plant cell

THE PROTOPLAST   Made up of:

  1. Nucleus

  2. Cytoplasm   consists of a liquid, colloidal phase of the

protoplast (cytosol/hyaloplasm/cytoplasmic ground substance)

  with membrane-bound organelles

THE PROTOPLAST   2. Cytoplasm

  with membrane-bound organelles  Bounded by double membranes  Bounded by single membrane

  ribosomes

  endomembrane systems

  cytoskeleton

PLASMA MEMBRANE (ectoplast/plasmalemma)   Controls passage of various substances into

and out of the protoplast   In transfer cells, are highly invaginated,

which facilitates transfer of materials

  It coordinates the synthesis and assembly of cell wall microfibrils (cellulose)

BIOLOGICAL MEMBRANES   Composition

1.  Phospholipids

2.  Proteins

3.  Carbohydrates

• Are amphipathic molecules with hydrophobic nonpolar hydrocarbon tails and hydrophilic heads

Membrane bilayer

Phospholipids

BIOLOGICAL MEMBRANES

Membrane Protein

2 types:   Integral proteins- integrated into the bilayer

•  May have access to only one side of the membrane

•  Span the entire bilayer and have access to both sides of the membrane (transmembrane protein)

  Peripheral proteins- bound to the hydrophilic surface of transmembrane protein

BIOLOGICAL MEMBRANES

BIOLOGICAL MEMBRANES

Membrane Protein F

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 Rosette of enzymes mediate the synthesis of cellulose microfibrils

BIOLOGICAL MEMBRANES

PROTOPLAST

Composed of:

Nucleus

Cytoplasm

NUCLEUS

• Information center of the cell

• Contains the bulk of the cell’s DNA

• Nucleolus- site of rRNA synthesis

NUCLEUS

Cytoplasm   Cytosol   Non-particulate portion; the liquid portion

  Contains proteins and other solutes

  Often assumes the physical properties of a gel

  Endomembrane system   These membranes are either in direct contact

or connected via transfer of vesicles, sacs of membrane.

  Endomembrane system   System includes the nuclear envelope,

endoplasmic reticulum, Golgi apparatus, vacuoles, and the plasma membrane.

  Cellular organelles   Membrane-limited compartments   Serve to compartmentalize the cells

  Cytoskeleton

Cytoplasm

ribosome

Sites of protein synthesis

• Small spherical bodies about 15-20 nm in diameter

• Consist of protein and RNA

• Found along ER, cytoplasm, within mitochondria and plastids

RIBOSOMES

ENDOMEMBRANE SYSTEM

Nuclear envelope   with 2 membranes; with pores through

which molecules of RNA may leave the nucleus and enter the cytoplasm

• Endoplasmic reticulum- continuous with nuclear envelope

• 2 types of ER

-smooth- tubular; site of lipid synthesis

-rough - lamellar; site of synthesis of membrane proteins and proteins to be secreted outside the cell and into the vacuole

• Golgi bodies (also called dyctyosomes, golgi stacks, golgi apparatus or simply golgi) -Consist of stacks of cisternae

-polarized structure

-receiving end from ER is cis face

-shipping side is the trans face

-finishes, sorts and ships cell products

Cell wall

chloroplast

cytosol

VACUOLE • Enveloped by tonoplast/vacuolar membrane

• Contains a variety of inorganic ions,organic acids, sugars, enzymes and secondary metabolic products including pigments

• plays a role in maintaining water balance of cells; active absorption of ions result in increase in turgor pressure in the cell and its expansion and growth

• Comparable to lysosomes of animal cells

Plasma Membrane

Cellular organelles and cytoskeleton

• Sites of respiration and synthesis of ATP

• Enveloped by 2 membranes

• Inner membrane is invaginated (cristae)

• Enzymes for ATP production found in inner membrane

 mitochondrial matrix,a fluid- filled space with DNA, ribosomes, and enzymes.

MITOCHONDRIA

PLASTIDS • Originate from proplastid pigments

Types:

Chloroplastids

• Contain photosynthetic pigments

• Site of photosynthesis

Chromoplastids

• Contain carotenoid pigments

• Often so concentrated that they form crystalline deposits

Leucoplastids

• Colorless plastids

• Types:

1. Amyloplastids

store starch

2. Elaioplastids store fats

3. proteinoplasts- store

proteins

PLASTIDS

PLASTID TYPES ARE INTERCONVERTIBLE

-etioplast is a plastid that develops in the absence of light; no chloroplast, no chlorophyll; characterized by prolamellar bodies composed of tubular membranes which comprise a paracrystalline lattice

MICROBODIES

• Bounded by a single membrane

• Peroxisomes-

-major site of O2 consumption; uses O2 in oxidation reactions that convert harmful m e t a b o l i c b y - p r o d u c t s i n t o n o n t o x i c substances such as water

-break down fats

-participate in photorespiration; enzymes in peroxisomes help minimize the loss of organic products due to photorespiration.

Peroxisome

Glyoxysomes- contain enzymes for the conversion of fats to carbohydrates during seed germination

Cytoskeleton  is a network of fibers extending throughout the cytoplasm.

 It provides mechanical support and maintains shape of the cell.  It provides anchorage for many organelles and cytosolic enzymes.

 plays a major role in cell motility.

-This involves limited movements of parts of the cell (streaming cytoplasm, vesicle and organelle movement).

-The cytoskeleton interacts with motor proteins.

-Three main types of fibers in the cytoskeleton:

• microtubules

• microfilaments

•  intermediate filaments.

CYTOSKELETON

 Approx 25 nm diameter

 Composed of 13 spherical protein subunits (dimers of α and ß tubulin)

 Comprise the spindle fibers in dividing cells that move chromosomes during cell division.

MICROTUBULES

 function as tracks that guide motor proteins carrying organelles to their destination.

 resists compression to the cell.

MICROTUBULES

CYTOSKELETON

  phragmoplast, a complex of microtubules that guides the orderly alignment of the vesicles in the midzone

MICROTUBULES

 exert some control over orientation of microfibrils because in regions of cell wall growth and cellulose microfibril synthesis , microtubules below the plasmalemma are routinely observed in an orientation parallel to that of the newly synthesized microfibrils

MICROTUBULES

 about 7 nm in diameter

 Composed of globular actin.

 An actin microfilament consists of a twisted double chain of actin subunits.

 help maintain cell shape.

ACTIN MICROFILAMENTS

  Involved in cleavage furrow formation

  On the cytoplasmic side of the cleavage furrow a contractile ring of actin microfilaments and the motor protein myosin form.

  Contraction of the ring pinches the cell in two

ACTIN MICROFILAMENTS

 involved in cytoplasmic streaming

-This speeds the distribution of materials within the cell.

ACTIN MICROFILAMENTS

intermediate in size at 8 - 12 nanometers   are specialized for bearing tension.  are more permanent fixtures of the cytoskeleton than are the other two classes.  they reinforce cell shape  nuclear side of the envelope is lined by the nuclear lamina, a network of intermediate filaments that maintain the shape of the nucleus.

Intermediate filaments

ERGASTIC SUBSTRANCES- products of cell metabolism

 Storage products

 starch in the form of starch grains

 proteins which form aleurone grains

 oils in elaioplasts or spherosomes (enveloped by single membrane or may be lacking)

 waxes- long-chain lipid compounds, that occur as part of the protective coating (cuticle) on the epidermis

LIPID BODIES OR OLEOSOMES • function: storage and transport of lipids

ERGASTIC SUBSTRANCES- products of cell metabolism

Waste products

Crystals -calcium oxalate crystals

-calcium carbonate crystals

Silica –common constituent of epidermal cell wall of grasses

-silica bodies – masses of silica which fill some epidermal cells

-provides protection from herbivory and mechanical strength

May be a form of stored calcium

CRYSTALS

ERGASTIC SUBSTRANCES   Tannins and tanniniferous substances are

phenolic by-products   primary function – protective,their

astringency serving as a repellent to predators   an impediment to the invasion of parasitic

organisms

The End