Lecture 2A: Nutrient Uptake: Nutrient transport through the Cell membrane: Simple Diffusion Flashcards
Why is nutrient transport important?
Because that is the way by which microorganisms or the cell is able to take in each nutritional requirements
If a cell is to grow and divide, it must take up its _________ and _________ from the environment.
Macronutrient and Micronutrient
serves as a challenge for nutrient transport
Impermeability of the cell membrane
Concentration of a given nutrient in the cytoplasm is often much ______ than its concentration in the environment for simple transport to occur
Lower
Facilitated diffusion
- Channel-mediated facilitated diffusion
- Carrier protein facilitated diffusion
Several possibilities have been suggested to account for the abnormally high membrane permeability of water
- Water is very small and so it just dissolves in bilayer better than larger solutes.
- Due to its size, water can enter very small statistical pores (w4.2 A in diameter)
- Passage down water chains.
- Water can be carried down kinks in acyl chains that result from acyl chain melting (“lipid melting”).
- Water may rapidly cross membranes through nonlamellar regions (e.g., micelles, cubic or H11 phase).
- High water permeability will occur ate regions of packing defect (e.g., surface of integral membrane proteins, boundary between membrane domains).
- Through pores or channels used to conduct ions.
- Through specific water channels known as aquaporins.
Potassium Channels in facilitated diffusion
- Calcium-activated potassium channel.
- Inwardly rectifying potassium channel
- Tandem pore domain potassium channel
- Voltage-gated potassium channel
Sodium channels
- Tetradotoxin (TTX)
- Saxitoxin (STX)
Water molecules pass through the aquaporin channel in _______ _____.
single file
Ionophores
- Valinomycin
- 18-Crown-6
- 2,4-Dinitrophenol
- Nystatin A
Two basic types of ionophores
Channel formers and mobile carriers
- 12-unit (dodeca) depsipeptide where amino acid peptide bonds are alternated with amino alcohol ester bonds.
- A macrocyclic molecule with the 12 carbonyl oxygens facing the inside of the ring where they chelate a single K+.
Valinomycin
a channel-forming ionophore that creates a hydrophobic pore across a membrane.
Nystatin
When present at sufficient levels, nystatin complexes with ________ and forms transmembrane channels that lead to K+ leakage and death of the fungus.
ergosterol
Nystatin allows for the ___ ___ ___ of various ions that dependon the dimensions of the pore
Rapid facilitated diffusion
Facilitated diffusion employs specific transporter and exhibit what
Michaelis Menten Saturation kinetics
a curve that shows how the rate of an enzyme-catalyzed reaction changes as the substrate concentration changes.
Michaelis-Menten saturation
