B4 Cell transport mechanisms Flashcards
What are membranes?
-keeping all cellular components inside the cell
Regulating exchange: allowing selected molecules to move
in and out of the cell
Structural support and allowing a cell to change shape.
Phospholipid
Phospholipids forms the structure of cell membranes, creating a barrier that separates the inside of the cell from outside. They also help control the movement of substances in and out of the cell.
Structure of a phospholipid
-Hydrophilic head- (consists of phosphate group)
The hydrophilic head of a phospholipid is attracted to water. It faces the outside of the cell. This helps phospholipids form a protective layer around the cell. (attracted to water)
-Hydrophobic tails point into the center of the cell membrane and are repelled by water. (don’t like water)
The functions:
-Allow lipid soluble substances to enter and leave the cell
-Prevent water soluble substances entering and leaving,
-To make the membrane flexible
Phospholipids in water
When exposed to water, phospholipids form one of two
structures:
-micelle - circle
-bilayer - square
In each structure, the hydrophilic heads face the water, and
the hydrophobic tails point inwards away from the water.
Cholesterol in cell membranes
-Molecular formula C(27)H(46)O
-Cholesterol is very important in controlling membrane fluid. The more cholesterol, the less fluid – and the less permeable – the membrane.
-Cholesterol is also important in keeping membranes stable at
normal body temperature – without it, cells would burst open.
-Intrinsic proteins
-Extrinsic proteins
- Goes all the way through the membrane (ion channels or transporters)
-bound to the inside or outside of the membrane
(receptors, enzymes or cell identifiers)
-Integral proteins (Intrinsic proteins)
Many integral proteins are carrier molecules or channels.
These help transport substances, such as ions, sugars and amino
acids, that cannot diffuse across the membrane.
Other integral proteins are receptors for hormones.
Peripheral proteins (Extrinsic proteins)
Peripheral proteins on the outside of the membrane help receive signals from hormones or neurotransmitters (Many are glycoproteins - have sugar attached to them)
Diffusion
Facilitated diffusion
-Net movements of molecules from an area of high concentration to area of low
- is a process where substances move across a cell membrane (Occurs down a concentration gradient)
Rate of diffusion
Temperature – higher temp = diffuse faster
Surface area – larger surface area = diffuse faster
Concentration – greater the difference = diffuse faster
Thickness of exchange surface - thinner surface =
diffuse faster
Size of particles – smaller particles = diffuse faster
Solid – slowest
Liquid – faster
Gas - fastest
two features of fluid mosaic model
-phospholipid bilayer
-with proteins embedded
