chapter 5- plasma membrane Flashcards
list the roles of the cell membrane
- regulating materials in and out of cells
- surface antigens so the body’s immune system recognises the cell as self
- contains receptors for chemical signals
- may be the site of chemical reactions
what are intrinsic proteins?
- proteins imbedded in both sides of the bilayer (in the membrane) e.g. carrier proteins, channel proteins and glycoproteins
what are extrinsic proteins?
- proteins embedded in one side of the bilayer (not in the membrane) e.g. glycolipids and cholesterol
Describe the role of carrier and channel proteins
Carrier proteins= involved in active transport (often involves changing the shape of proteins) and passive transport into cells.
Channel proteins= facilitated diffusion of polar molecules and ions. Allows the passive movement of polar molecules through membranes
Describe glycoproteins
Glycoproteins are also intrinsic proteins:
They are embedded in the cell surface membrane with carbohydrate sugar chains of varying lengths and shapes attached. Involved in cell adhesion and acting as receptors for chemical signals.
When the chemical binds to the receptor, a response is given from the cell. This is either a direct response or sets off a list of events in the cell. This process is known as cell signaling.
Describe cholesterol (extrinisic protein)
Cholesterol:
Made of C, H, O.
It has no ester bonds, glycerol or fatty acids.
Cholesterol is an example of a sterol, not a fat or oil
Sterols are complex alcohol molecules based on the 4-carbon ring structure with a hydroxyl (OH) group at one end.
Hydrophobic/hydrophilic- cholesterol:
It has a hydroxyl group which makes the head polar and hydrophilic- attracted to the phosphate heads on the periphery of the membrane.
It also has a non-polar hydrophobic tail- attracted to the hydrophobic tails of the phospholipids in the center of the membrane.
The hydrophobic/hydrophilic nature of cholesterol adds stability to the membranes pulling phospholipids together.
They avoid phospholipids becoming too close by grouping close together= regulate the fluid of the membrane
Roles of cholesterol:
Role in cell membranes- stability
Used for hormones- progesterone and testosterone
Bile salts made from cholesterol
Describe glycolipid (extrinsic protein)
Glycolipids:
Lipids with a carbohydrate chain added. These molecules are called cell markers or antigens, can be recognized by the immune system as self or non-self (foreign).
The rate at which molecules diffuse across a membrane is affected by:
Surface area= the larger the surface area, the higher the rate of diffusion
Thickness of the membrane= the thinner the membrane, the higher the rate of diffusion
Describe the process of active transport of molecules via carrier proteins in the plasma membrane
Process of active transport:
The molecule or ion to be transported binds to receptors on the carrier proteins outside of the cell
On the inside of the cell, ATP binds to the carrier protein, then ATP hydrolyzes into ADP and phosphate
The binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up to the inside of the cell
The molecule or ion is released to the inside of the cell
The phosphate molecule is released from the carrier protein and forms ATP from ADP.
The carrier protein returns to its original shape.
The process is selective- specific substances are transported by specific carrier proteins
what is water potential
Water potential:
Water potential= the pressure exerted by water molecules as they collide with a membrane or container. It is measured in units of pressure pascals (Pa) or kilopascals (kPa). The symbol of water potential is the Greek letter Ψ
Pure water has a water potential of 0 kPa. This is the highest possible value for water potential, as the presence of a solute lowers the water potential below 0. All solutions have a negative water potential.
