3.2.3 Transport across cell membranes Flashcards
What is meant by the ‘fluid mosaic’ model of the cell membrane?
Fluid - molecules can move
Mosaic - lots of different molecules like proteins and phospholipids
What type of molecules are transported by active transport?
- Large
- Polar
- Water soluble
What are the functions of phospholipids in the cell membrane?
- Let lipid soluble molecules enter and leave the cell
- Stop water soluble molecules from entering or leaving the cell
- Make the membrane flexible (self healing)
What type of molecules are transported by simple diffusion?
- Small
- Non-polar (not water soluble)
- Lipid soluble
Why does active transport require energy?
- Movement of particles against the concentration gradient
- Energy from the hydrolysis of ATP to change the shape of the carrier protein
What are 6 functions of proteins in the cell membrane?
- Provide structural support
- Act as protein carriers to transport water soluble molecules
- Act as protein ion channels to transport water soluble molecules
- Form recognition sites to identify cells
- Help cells adhere together (eg to form tissue)
- Act as receptors (eg for hormones)
What are the functions of glycoproteins in the membrane?
- Act as recognition sites (eg hormones)
- Help cells recognise each other
- Help cells attach to each other to form tissues
What is water potential? What is the water potential of pure water? How does it change as more solutes are dissolved in?
- Pressure created by water molecules
- 0 (highest possible value)
- Becomes more negative
How are some transport processes passive?
They rely on natural kinetic energy
What is the function of cholesterol in the membrane?
- Add strength to membrane (hydrophobic so bind to phospholipid tails)
- Makes membrane less fluid at higher temperatures
- Reduce lateral movement of other molecules eg phospholipids
- Stop leakage of water and dissolved ions from cell
What is osmosis?
- Movement of water from an area of higher water potential
- To an area of lower water potential
- Through a partially permeable membrane
- DOWN the concentration gradient
What happens when lots of water moves into an animal cell vs a plant cell?
Animal: cell bursts - osmoticlysis
Plant: cell becomes turgid (can’t burst - cell wall)
What are the functions of membranes within cells?
- Control entry and exit of materials in organelles
- Separate organelles from cytoplasm so specific metabolic reactions can occur inside them
- Provide and internal transport system (eg endoplasmic reticulum and vesicles)
- Isolate enzymes that may damage the cell (eg lysosomes)
- Provide a surface area for reactions to occur on
What is the function of glycolipds in the membrane?
- Help maintain stability of the membrane
- Act as recognition sites
- Help cells attach to each other to form tissues
What type of molecules are transported by facilitated diffusion?
- Large
- Polar
- Water soluble
What proteins in the membrane are required for active transport?
Carrier proteins
What form of transport is not specific?
Simple diffusion
What is diffusion?
- Net movement of particles
- From an area of higher concentration
- To an area of lower concentration
- Down a diffusion gradient
Occurs until concentration of particles on each side is equal and a dynamic equilibrium is reached
What are intrinsic and extrinsic proteins?
Extrinsic proteins: on surface or party embedded in membrane.
* Give mechanical support
* Act as cell receptors for molecules like hormones
Intrinsic proteins: span across phospholipid bilayer.
* Enzymes
* Carriers to transport water soluble molecules across membrane (protein channel or protein carrier)
What happens when lots of water moves out of an animal cell vs a plant cell?
Animal: cell shrivels
Plant: plasmolysis occurs (cell membrane still tethered at points to cell wall)
What proteins in the membrane are required for facilitated diffusion?
- Protein ion channels (usually for ions- small)
- Carrier proteins (larger molecules like glucose or amino acids)
What features would you expect to find in a cell specialised for absorption?
- Folded microvilli so large surface
area - Large number of carrier /channel proteins so fast rate of absorption/ active transport/facilitated diffusion
- Large number of mitochondria to make more ATP/release energy for active transport
