Cell membranes and Transport
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what is the width of the cell membrane
7-8 nm
what is the cell membrane made up of
phospholipids proteins carbohydrates cholesterol
phospholipid heads are
hydrophilic (polar)
what are collectively know as glycocalyx and are formed through glycosylation
glycoproteins and glycolipids
where is cholesterol present in cell membrane and what does it control
present between phospholipids and helps control membrane fluidity
name the two proteins in cell membranes
extrinsic and intrinsic
name the functions of cell membranes
structural support control of substances cell-cell recognition isolate organelles from cyctoplasm bio chemical reactions
phospholipids function in cell membranes
form a selective bilayer that allows non polar molecules through but prevents passage of charged molecules (polar)
extrinsic protein function
associated with one layer only may act as receptors for hormones
intrinsic proteins function
act as channels to allow passage of polar molecules like glucose
carbohydrate side chain function
cell to cell recognition cell adhesion cell to pathogen interactions
cholesterol function
controls membrane fluidity
why is it called the fluid mosaic model
fluid - proteins and lipids are able to move around within the membrane mosaic - made up of lots of component with different size and shape all arranged in a random pattern
which substance moves through cell membranes easier
lipid soluble uncharged, non polar substances
how do lipid soluble small uncharged molecules and non polar substances move across a membrane
dissolve in hydrophobic phospholipid tails and diffuse across the membrane eg- oxygen, CO2, vitamin A
how do water soluble polar molecules and charged ions move across a membrane
cannot easily diffuse through phospholipids so pass through intrinsic proteins eg- glucose, amino acids, Na+
what factors affect membrane permeability
temperature organic solvent eg- ethanol/ acetone
which two methods of transport are an active process requiring ATP
active transport bulk transport
rate of diffusion equation
surface area x difference in concentration / length of diffusion path
why does temperature increase permeability
molecules have more kinetic energy so diffuse more quickly
how do organic solvents affect permeability
emulsifies the phospholipids and denature protein making gaps in the membrane meaning it is more porous
diffusion
the passive movement of a molecule or ion down a concentration gradient from a region of high concentration to a region of low concetration. The random net movement due to particles kinetic energy
rate of diffusion equation
surface area x difference in concentration / length of diffusion path
what are the 6 factors affecting diffusion rate
Concentration gradient thickness of surface surface area size of molecule nature of molcule temperature