Biological Membranes

Describe biological membranes

Cells / organelles have a phospholipid bilayer

Plasma membranes have a partially permeable membrane and are the site of chemical reactions , role in cell communication

What is the fluid mosaic model:

Plasma membrane described a fluid mosaic model due to movement of phospholipids, proteins, glycoproteins and glycolipids

Arrangement of proteins within the phospholipids

Describe the phospholipid and cholesterol features of fluid mosaic model

Phospholipid: acts as a bilayer due to hydrophilic heads attracted to water and hydrophobic tails repelled by water

Cholesterol is in some membranes, this restricts lateral movement of other molecules Useful = makes membrane less fluid at high temperatures and prevents water and ions leaking out of cell

Describe the protein features of the fluid mosaic model

Extrinsic (peripheral) proteins mechanical support, make glycoproteins and glycolipids. Function = cell recognition, act as receptors

Intrinsic (integral) proteins = protein carriers/ channels involved in transport of molecules across membranes

Protein channel form tubes filled water to enable water soluble ions to diffuse

Carrier proteins = bind to other ions and larger molecules, like glucose and amino acids, and change shape ro transport them to other side of membrane

Factors that affect membrane structure and personality

Temperature = increase kinetic energy of phospholipids, so they move more Increases fluidity of membrane and permeability and structure starts to break. Now particles can cross membrane easier

Too high = denatures carrier and channel proteins

Solvents = organic solvents (alcohol)dissolve phospholipid bilayer in membranes, damage causes fluidity of membrane to increase, and is more permeable

What are the six movements of transport across membranes

Simple diffusion

Facilitated diffusion

Osmosis

Active transport

Endocytosis

Exocytosis

Describe simple diffusion:

Net movement of molecules from area of high concentration to area of low concentration until equilibrium is reached

Doesn’t require energy (ATP)

Molecules must be lipid soluble and small to diffuses across membrane

Describe facilitated diffusion

Passive process, down concentration gradient through proteins

Movement of ions and polar molecules transported across membranes using protein channel / carrier proteins

Osmosis

Movement of water from area of high water potential to area of lower water potential across a partially permeable membrane

What are the different types of solutions?

Isotonic = water potential of solution is same in solution and the cell within the solution (normal)

Hypotonic = water potential of solution is more positive (closer to 0) than a (swelling)

Hypertonic = water potential of solution is more negative than the cell

Describe active transport

Movement of molecules and ions from area of low concentration to area go higher concentration (against concentration gradient) using ATP and carrier proteins

Talk about how active transport is selective

Only certain molecules can bind to receptors site on carrier proteins = selective

ATP binds to protein on inside of membrane and is hydrolysed to ADP and Pi

Then protein changes shape and open towards the inside of the membrane

Molecule released on other side of membrane

Pi molecule is released from protein, protein reverts to original shape

Describe process of endocytosis:

Type of active transport - bulk transport of molecules into a cell

Cell surface membrane bends inwards around molecule to form a vesicle Vesicle pinches off and moves within cytoplasm

Why can endocytosis be classed as phagocytosisi or pinocytosis?

Phagocytosis = when it is a solid particle being taken in Pinocytosis = when a liquid is being taken in

Requires energy from ATP for cell to engulf and change shape around material

Describe Exocytosis

Bulk transport of molecules out of a cell

Vesicles move toward cell surface membrane, fuse with membrane and the content of the vesicle is release out of cell

Required energy because ATP needed to move vesicle along cytoskeleton