Membrane Transport Flashcards
How do cells within an organism exchange compounds with their environment?
- by passing them across their biological membranes
Transport can also occur across membrane-bound organelles - what are these?
- nucleus
- endoplasmic reticulum
- mitochondria
What compounds are commonly exchanged across membranes?
- glucose
- ions
- amino acids
What molecules is the lipid bilayer fairly permeable to?
- fairly permeable to a few uncharged molecules such as oxygen and carbon dioxide
- these can flow through the hydrophobic barrier relatively easily
The lipid bilayer is very hydrophobic and therefore retards diffusion of what molecules across the membrane?
- retards diffusion of hydrophilic, polar, or ionic compounds across the membrane
By preventing the crossing of certain molecules this makes the lipid bilayer able to do what?
- specialise what they do
The lipid bilayer has developed means to move what compounds across their membranes?
- to move hydrophilic compounds across their membranes
The membrane of a living cell is much more complex than a simple phospholipid bilayer - they incorporate what within them?
- lipids (cholesterol, steroid)
- peripheral and integral proteins
- glycoproteins
How do membrane proteins transport ions and small molecules that do not pass readily through due to the hydrophobic tails?
What is this process referred to as?
- by passive diffusions
- referred to as facilitated transport
What are the reasons that ions are not capable of passing through the membrane?
- due to their hydrophilic nature
- or because of moving against a concentration gradient
What are the two types of facilitated membrane transport?
- passive
- active
What is the major difference between active and passive transport?
- the major difference is that active transport requires an input of free energy to function
- passive doesn’t require energy
What is passive transport also referred to as?
- accelerated diffusion
Passive transport can move molecules at a faster rate than normal diffusion - therefore can bring what about more rapidly?
- can bring equilibrium about more rapidly
What does passive transport not generate for a compound?
- does not generate a concentration gradient for a compound across a membrane
- but can only dissipate the gradient
In passive transport no energy is required - why is this?
- because the process of reaching equilibrium is energetically favoured
What does active transport involve?
- involves moving a solute across a membrane against its concentration gradient
What is required for active transport?
- requires the input of free energy
What does active transport utilise for energy?
- source of energy within the cell us adenosine triphosphate, and many transport proteins utilise the hydrolysis of ATP
Passive transport can be facilitated by types of transporters called pores or channels - what do these provide?
- these provide passageways across the membrane of the right size and environment for a particular compound to cross
What do porins do?
- porins from aqueous channels and accelerate passive diffusion of small hydrophilic molecules across the membrane
- such as aquaporins to allow water to pass through in the kidneys
Solute selectivity of porin is determined by what?
- the characteristics of the amino acid side chains at the entrance and inferior lining of the pore as well as the size of the opening
What makes a pore specific for small anions?
- the positively charged regions at the mouth of the pore and the constriction site
Ion channels are more complex than porins, generally requiring what to form a membrane passageway?
- requiring more than one subunit to from a membrane passageway
