Types of Membranes

• Types of Membrane

Cell Membrane (Plasma Membrane)

• Surrounds the cell and regulates the movement of materials in and out.

Nuclear Membrane

• Surrounds the nucleus and controls the movement of genetic material.

Mitochondrial Membrane

• Surrounds mitochondria and plays a crucial role in cellular respiration.

Semipermeable Membrane

• Allows certain molecules to pass through while restricting others.

Permeable Membrane

• Allows all molecules to pass through.

Impermeable Membrane

• Does not allow any molecules to pass through.

Selective Permeable Membrane

• Allows certain molecules to pass through while restricting others, based on size, charge, or other properties.

Dialysis Membrane

• Used for separating molecules based on size.

Biological Membrane

• Natural membranes found in living organisms.

Synthetic Membrane

• Man-made membranes used in narrow applications such as water filtration and medical devices.

Cell Membranes

• The cell membrane can be a compartment.

• Important in chemical reactions because of selective permeability.

• Controls which substances enter or leave the cell.

• Maintains a difference between internal and external environments.

• Supplies the cell with nutrients and removes waste.

• Controls volume and pH.

• Organization of Cell Membrane

Cell Membrane Structure

• The basic structure of all cell membranes is the lipid bilayer with many embedded proteins.
• A membrane is a continuous selectively permeable barrier.

Cell Membrane Organization

• Three layers can be seen in each membrane.
• Phospholipid molecules in the plasma membrane have hydrophilic heads that interact with water, and hydrophobic tails that interact with each other, forming a barrier to hydrophilic molecules.

Proteins

• Proteins exist in the phospholipid layer.

Endomembrane Concept

• All membranes (with very few exceptions) look the same and work the same.
• Membranes are recycled.

Cell Wall

• Microfibrils are bound together with hemicellulose and pectins, produced in dictyosomes or golgi bodies.
• Vesicles deposit membrane components in the wall, linked by hydrogen bonds, reinforcing wall structure.
• Differences in relative amounts of components lead to differences in wall properties e.g. flexibility, strength

Primary cell wall

• The middle lamella is an adhesive layer between cell walls in multicellular plants formed of pectins (pectic substances).
• Present in all plant cells, thin and pliable, allowing cells to enlarge.

Secondary Cell Wall

• Next to the plasma membrane.
• Necessary if cells must be unusually strong.
• Much thicker than the primary wall.
• Contains up to 25% lignin.
• Lignin waterproofs tissue, resists chemical, fungal, and bacterial attack.

Plastids and Mitochondria

• Cell walls are permanent and almost never depolymerized.
• Plastids and mitochondria:
  • Proplastids: Young, rapidly dividing cells with simple structures and few folds.
  • Chloroplasts: Contain green chlorophyll and undertake photosynthesis.

Chloroplast Structure

• Double outer membrane and controlling enzymes embedded in membranes such as Chlorophyll (hydrophobic tail)
• Inner membrane structures are extensively folded to increase surface area.

Plastids

• Includes membrane-bound structures:
• Thylakoids (sheet-like vesicles arranged in stacks called grana).
• Stroma/matrix fluid. Undertake photosynthesis
• Pigments capture sunlight energy
• Release energy by driving accumulation of H+ ions.

Plastids - Other

• Amyloplasts are non photosyntethic
• Few Inner Membranes
• Larg Starch grais
• Present in tissues such tubers -Chromoplasts
• Have a Lipid structure
• Bright red, yellow, orange
• Emdedded in Membranes
• Occur where there is Fruit Ripe Alter Oxikaloids
• Leukoplasts
  • Various Types of Synthesies

Mitochondria

• Own DNA

Central Vacuole

• Plant cells fuse vacuoles.
• Single membrane: tonoplasts.
• Occupies 50-90% of cell volume.
• Important for cellular processes such as growth (increase vacuolar water) and expansion (especially rapid at night).
• Storage for nutrients and ions and allows the cell to regulate ion levels.
• Stores calcium, waste product and are permanent.

Central Vacuole - Digestion

• For Aged/impaired organelles
• Fuses with Vacuole
• Allows Digestion to monomers

Water potential

• Chemical potential of water.
• Ability to do work.
• Pure water at 1 atm is equal to 0, 3 MPa.
• Pushing water is positive and pulling water is negative.
• Osmosis is a movement of a solvent through a selectively permeable membrane from an area of high concentration to low concentration until equilibrium is reached.

Osmosis vs Diffusion

• Different from diffusion because it involves a membrane.

Osmosis - definitions

• Solutes interacting with water decrease free energy.
• Number of particles dictate osmosis

Water Potential

• pressure potential (ψp).
• Compression (positive).
• Tension (negative).
• Hydrostatic pressure (exerted against surface).

Fluid Pressure

• Synt is created by vacuole on tonoplast membrane.
• Incorporates Matrix
• matric potential (ψm).
• Adhesion.
• Pulling Negative

Structures

• Non-dissolved structures such as cell walls
• are incorporated in endoplasmatic rybosomes

Important

• ER Golgi for all membranes
• Mitochondria and Nucleus
• ψ = ψs + ψp for living cells