1.3 cell membrane and transport Flashcards
what does a phospholipids have?
Hydrophilic Heads - Point outwards, interact with tissue fluid/blood plasma as well as cytoplasm
Hydrophobic Tails - Point inside the membrane
Proteins
- Proteins in membranes are globular
- Found on surface (extrinsic) or extending across both phospholipid layers (intrinsic)
Carbohydrates
- Found pointing out of the cell attached as either glycoproteins or glycolipids. Collectively known as the glycocalyx. Glycocalyx act as cell to cell recognition.
Cholesterol
Present between phospholipids in animal cell membranes. Maintains the fluidity of the cell. Too much and the cell will be too rigid, too little and the cell membrane will break apart.
Fluid Mosaic Model
*Fluid as the proteins and lipids are able to move around within the membrane.
*Mosaic as its made up of lots of different components, in different shapes and sizes.
Lipid Soluble Substances
- Small uncharged molecules such as oxygen and carbon dioxide dissolve in the hydrophobic tails and diffuse across the cell membrane.
- Non polar substances such as Vitamin A also dissolve in phospholipids and diffuse across the membrane.
Water Soluble Substances
- Polar Molecules such as glucose and amino acids
- Charged ions such as Na+
Both cannot easily diffuse through the phospholipids. They pass through intrinsic proteins instead.
Temperature affecting permeability
Increase in temperature increases permeability.
Diffusion
Passive movement of molecules or ions down a concentration gradient from a region from high concentration to a lower concentration.
Factors Affecting Diffusion
Concentration Gradient: Greater the difference in concentration of molecules in two area, the more molecules that will diffuse in a certain time
Distance: Further the molecule has to travel, the longer the diffusion will take.
Surface area: The more area molecules have to diffuse the shorter time it will take.
Size of the diffusing molecule: Larger the molecules that have to fit through the phospholipid bilayer, the longer it takes
Nature of molecule: The more lipid soluble it is the faster it will diffuse.
Temperature: Molecules will speed up so they’ll collide more, increasing the rate of diffusion.
Facilitated Diffusion
- Passive transport of polar molecules or charged ions down a concentration gradient via channel or carrier proteins.
- Used to transport ions or molecules which are insoluble in phospholipids.
- Rate of facilitated diffusion is affected by no. of channel/carrier proteins and the steepness of the concentration gradient.
Channel Proteins
- Protein molecules with water-filled hydrophilic pores.
- Ions, being water soluble, can pass through because the pores are hydrophilic.
- Each channel is specific for one type of ion
- Channels open and close depending on the needs of the cell.
Carrier Proteins
- Allows diffusion of larger polar molecules such as glucose and amino acids.
- A polar molecule attaches to a binding site on the carrier protein. This causes the protein to change shape releasing the molecule through to the other side of the membrane.
Co-Transport
- Types of facilitated diffusion that brings molecules and ions into cells together on the same protein transport. e.g. sodium-glucose co-transport.
- Passive process
- The process can move glucose against its concentration gradient without the use of ATP - this is known as secondary active transport.
Active Transport
- Transport of ions and molecules against the concentration gradient.
- Requires an intrinsic carrier protein, as the carrier acts as a pump.
- Only charged particles or ions, that are insoluble in lipids can be actively transported.
