Membranes Flashcards
what do phospholipids do in the membrane
Phospholipids arrange themselves into a bilayer which creates the wall of the membrane. Meanwhile there are glycolipids (sugars attached to the top of a lipid in the bilayer) are steroids like cholesterol throughout the membrane.
what kinds of proteins are in cell membranes
Proteins, including glycoproteins (sugars attached to a protein), are associated with one or both sides of the membrane. Integral proteins go through the membrane, while peripheral proteins are just on one side of it.
describe the fluid mosaic membrane
The membranes of cells exhibit a behaviour described by the fluid mosaic model. Where the membrane is liquid like and all parts can move around at up to 2 um per second. Though they rarely swap which layer they are on.
what does the membrane being Amphipathic mean
The membrane is Amphipathic: meaning it has both hydrophilic and a hydrophobic regions.
what side of a membrane has carbs
The non-cytosolic side of the membrane can have carbohydrates, Glycolipids, and Glycoproteins. While the cytosolic side does not.
what are lipid rafts
Lipid rafts are regions of high cholesterol where other components of the membrane accumulate. It moves around as a unit, before later dissolving.
Reduced cholesterol in lipid rafts is associated with autism and intellectual disabilities.
what is membrane fluidity
Saturated hydrocarbon tails (which have no kinks) lead to tight packing, making the membrane more viscous, which is not ideal in many cases.
Unsaturated hydrocarbon tails (have kinks) prevent tight packing, making it more fluid at lower temperatures.
Certain plants, animals, or other organisms adjust their membranes to be more unsaturated to deal with colder temperatures. Only for exothermic organisms.
what can move within a membrane
- Lipids move laterally
- Proteins move laterally if not anchored to other proteins
Proof: If you take two cells with different proteins and fuse them into a hybrid cell. After a certain amount of time, the proteins will be all spread out and mixed.
describe membrane proteins
Can be integral or Peripheral
Hydrophobic and hydrophilic regions.
Non-polar amino acids vs polar or charged amino acids
Extracellular side = the N terminus
Cytoplasmic side = the C terminus
what are the 6 functions of membrane proteins
- Transport (passive or active)
- Enzymes (kept organized in membrane)
- Signal transduction (signal molecules to bind to receptors outside)
- Cell to Cell recognition (glycoproteins, used in embryo development immune response)
- Intercellular joining (holds cells together for long term)
- Attachment to the cytoskeleton and extracellular matrix (ECM)
how do protein-protein interactions affect HIV virus
Example of protein-protein interaction of HIV virus and human receptor proteins:
If the human cell has the receptor CD4 and co-receptor CCR5, the HIV virus will be let into the cell (this is the case for most people)
If the cell doesn’t have the co-receptor CCR5, the HIV virus can’t get into the cell (certain people who are resistant to HIV)
what does selective permeability mean
Exchange of molecules across membranes: Sugars, Amino acids, metabolic waste products, O2, CO2, and ions (Na+, K+, Ca2+, Cl-)
Some molecules are allowed to cross, some are excluded.
How permeable are small hydrophobic membranes, small polar molecules, charged molecules, and macromolecules in cell membranes.
- Small Hydrophobic molecules can pass through the bilayer
- Small polar molecules can pass through, but not very well
- Charge molecules can pass through the hydrophobic region
- Macromolecules can’t pass through normally, but can be brought in through phagocytosis
Other molecules can make their way into the cell through other means.
what are different transport helpers
Membrane proteins can help other molecules pass through the membrane
Channel proteins are passive transporters, ex aquaporins
Carrier transporters are passive and active transporters.
describe diffusion
Diffusion: passive transport → no energy is needed
Molecules move passively from high concentration to low concentration. Substance will diffuse down its own concentration gradient (from high to low []) Spontaneously.
describe osmosis
Semipermeable membranes can let some things like water through, while blocking others like sugars.
Osmosis is the diffusion of water from a region of high free water to regions of lower free water concentration.
what is tonicity and how do animal cells react to different tonicity solutions
Tonicity is the capability of a solution to modify the volume of a cell by changing the water content.
If an animal cell is in a hypertonic (high) concentration of non-permeable solutes it can become shrivelled from water loss.
If it is in an isotonic solution is is as normal
If it is in a hypotonic (lower) concentration solution of non-permeable solutes it can lyse from too much water.
Some organisms like paramecium have contractile vacuoles that are used for osmoregulation.
what happens to a plant cell in solutions of different tonicity
If a plant cell is in a hypotonic solution of non-permeable solutes it can become turgid (swollen within its cell wall)
In an isotonic solution is is flaccid.
In a hypertonic solution it become Plasmolyzed and pulls off the cell wall.
what allows facilitated diffusion
Facilitated diffusion
Channel proteins:
- Aquaporins
- Ion channels: gater
Carrier/transporter proteins:
- glucose transporter
describe active transport
Use energy to transport solutes against gradient.
Allows cells to maintain solute concentrations that differ from the concentrations of the environment.
Ex: Na-K pump in animals (electrogenic pump)
Low Na+ concentration in cytosol so Na+ is pumped outside.
High K+ in cytosol so K+ is pumped inside.
what are the steps in an Na/K pump
steps:
- Binding Na+
- phosphorylation by ATP
- Conformational change: released Na+
- Binding K+ → dephosphorylation
- conformational change: restoring original shape
- K+ is released and Na+ can bind again
2K+ and 3Na+ pumped
what are proton pumps and co-transporters
Proton pump: in plants, fungi, bacteria, transport protons (H+) out
Co-transporters: use diffusion of H+ to transport sucrose
what is exocytosis
Exocytosis: secretion of large molecules like insulin neurotransmitters
what is endocytosis and the types
Endocytosis: uptake of large molecules, larger particles
Phagocytosis = cell eating (large molecules)
Pinocytosis = cell drinking (small molecules)
Receptor mediated endocytosis = Vesicles coated with specific receptors that specific solutes bind to
Hypercholesterolemia: high cholesterol level in blood → receptor are defective or missing.
