Chapter 5- Plasma Membranes Flashcards
What are plasma membranes?
Membranes that cover the surface of every cell. They are PARTIALLY PERMEABLE.
What is the function of plasma membranes?
Describe the fluid mosaic model?
Explain why phospholipids form a bilayer in plasma membranes:
Describe what intrinsic and extrinsic proteins are:
What are Glycoproteins?
Glycoproteins are:
- intrinsic
- protein with carbohydrates attached- varying shape + size
What are the roles of Glycoproteins?
Describe cell-signalling. Include details on Hormone Receptors.
They are glycoproteins.
What are Neurotransmitters?
They are glycoproteins.
What are Glycolipids?
Glycolipids are lipids with attached carbohydrate (sugar) chains.
What are antigens?
Antigens are a type of glycolipid.
Why is membrane fluidity important for a cell’s normal function?
Fluid Membrane needed for many processes:
- diffusion of substances across membrane
- membranes to fuse during exocytosis
- cell move + change shape. E.g. macrophage during phagocytosis.
What property of a phospholipid makes the cell membrane fluid?
Lipids are short + unsaturated.
- Lipids with short + unsaturated tails have low melting point. - increases fluidity
- The double bonds in unsaturated fatty acids create kinks
- SO, lipid molecules are more loosely packed.
What effect does temperature increase have on the membrane permeability?
What effect does use of solvent have on membrane permeability?
What is an intrinsic protein?
Intrinsic proteins are transmembrane proteins.
They are embedded in both layers of membrane
Contain AAs with hydrophobic ‘R’ groups on external surfaces
That interact with hydrophobic core of membrane, keeping them in place.
What is an extrinsic protein?
Extrinsic proteins are peripheral proteins that are present in one side of the bilayer.
They have hydrophilic R groups on outer surfaces and interact with polar heads of phospholipid
Can be present in either layer
Can move between layers.
Describe the structure and function of Channel Proteins:
- Provide hydrophilic channel that allows passive movement of polar molecules and ions
- down a concentration gradient through membranes
- They are held in position by interactions between hydrophobic core of membrane and the hydrophobic R groups on outside of the channel proteins.
- allow polar and charged sub. to avoid hydrophobic interior
- fast transport
- some open all times, so open and close in response to specific signal
- e.g. aquaporins (conduct H2O through membrane v. quickly.)
Describe the structure and function of Carrier Proteins:
- passive (down concn gradient) and active (against concn gradient) transport.
- Shape of protein changes
- Uses Active Transport
- Active transport requires ATP to move sub. against concn. grad.
- usually transports macromolecules (lipids, polysacch.)
- create ion gradients
- e.g. sodium potassium pump
Define (simple) diffusion:
- Diffusion = net movement of particles from
- region of high concn to region of low concn
- down concn grad.
- Until equilibrium reached.
Simple diffusion:
- small, non-polar molecules ONLY
What kind of substances can and cannot diffuse through Phospholipid bilayer?
Can diffuse:
- non polar molecule
- fatty acids
- vitamins
- steroids
- O2, CO2, H2O(small amounts only)
Cannot diffuse:
- Na+ K+ Ca2+ H+
- Polar molecule
- Polysaccharide
- AAs Glucose
- Nucleic Acids
Describe how these factors affect rate of diffusion:
- temperature
- diffusion pathway
- surface area
- concentration difference
- size
What is Fick’s Law
What is facilitated diffusion?
Why does rate of uptake reach maximum in facilitated diffusion?
What has the highest value of water potential?
Distilled Water has highest value of water potential. = 0kPa
Solutions have lower water potential than pure water have - water potential
Define Osmosis:
Osmosis is the net movement of water molecules from region of high water potential to region of low water potential through PPM down water potential gradient.
What is solute potential?
What is pressure potential?
What is:
- Hypertonic
- Isotonic
- Hypotonic
Hypertonic = less water, low water potential
Isotonic = same net movement, no net gain or loss
Hypotonic = lots of water, high water potential
Describe different osmotic conditions in animal cells:
Describe different osmotic conditions on plant cells:
What do cells that do Active Transport need a lot of?
Mitochondria!! For ATP :))
Describe what happens in Active Tranport:
What is bulk transport?
When extremely large substances need to be moved across cell membrane. 2 types: endo + exo cytosis.
What occurs in endocytosis?
What occurs in exocytosis?
What are the stages of events in Na+ K+ Pump mechanism
- Cytoplasmic Na+ binds to Na/K pump
- Na+ binding stimulates phosphorylation by ATP
- Phosphorylation causes protein to change shape, expelling Na+ to outside
- Extracellular K+binds to protein triggering release of 1 phosphate group = ADP
- Loss of phosphate group restores proteins original formation
- K+ released and Na+ sites are receptive again
- Cycle repeats.
