2.5 Biological membranes Flashcards
What is a phospholipid bilayer made up of?
- Hydrophilic Phosphate head
- Hydrophobic Fatty acids
What does hydrophilic mean?
Likes water
What does hydrophobic mean?
Doesn’t like water
What does partially permeable mean?
Allows some things to pass in and out however not others
What is simple diffusion?
The movement of molecules through a semi-permeable membrane where molecules move along a concentration gradient.
What molecules can simply diffuse?
- Lipid soluble molecules
- Non-polar molecules
- Small molecules
What can’t simply diffuse through the membrane?
- Charged molecules
- Large molecules
How do charged molecules move in and out of a cell?
Travel through carrier proteins
Why can small molecules pass through the membrane?
Can fit between phosphate lipid heads
Why can lipid soluble molecules pass through the membrane?
Dissolve into lipids and pass through
What is the role of membranes?
- Separates cell components from external environments
- Regulates transport of materials in/out of the cell
- Might contain enzymes with specific metabolic pathways
- Contains antigens so the immune system can recognise that the cell is it’s own
- Releases chemical signals and contains receptors for cell communication
- Site of Chemical reactions
Examples of membranes within the cell
- mitochondria have folded inner membranes called Cristae so there is a larger surface area for aerobic respiration and localise enzymes that are needed for it
- Inner membranes in chloroplast called thykaloid where photosynthesis reactions take place
- Small intestine lining where digestive enzymes are on plasma membrane of epithelial cells which catalyse the break down of sugars
How is a concentration gradient maintained?
Molecules entering the cells pass to organelles for metabolic reactions (oxygen passes to the mitochondria)
Factors affecting diffusion
- Temperature (more kinetic energy)
- Diffusion distance (how thick the membrane is)
- Surface Area (more space to diffuse through)
- Size of molecules (smaller is faster)
- Concentration gradient (steeper is faster)
What does polar mean?
Charged and can interact with water
