Forces Across Membranes 2 Flashcards
Why does a difference of charge occur across the membrane?
The ions creating the concentration gradient are charged particles, causing an electric gradient
What is an electrochemical gradient?
Net effect of the chemical and electrical gradients
What defines the movement of ions across the membrane?
The electrochemical gradient
What does movement against the electrochemical gradient require?
Energy (active transport)
What is the resting membrane potential?
-70mV inside compared to outside
What are the 5 mechanisms of movement across the membrane?
Endocytosis and exocytosis
Diffusion
Mediated transport
Osmosis
Filtration
What is endocytosis/exocytosis?
Mechanism for moving macro molecules across the membrane without disrupting them
What are the steps of endocytosis?
- Invigination of the membrane to form a vesicle
- Disintegration on the cytoplasmic surface of the membrane
- Releasing the contents
What is the process of exocytosis?
The reverse process of endocytosis (leaving the cell)
What is diffusion?
Process where gas or a substance in solution expands to fill all available space
What does diffusion means in terms of the movement of molecules?
Molecules spread from regions of high concentration to regions of low concentration
During diffusion what direction to molecules move?
From high concentration to low, although some do randomly go from low to high - but the net movement is from high concentration to low concentration
What must the barrier be to allow diffusion to occur?
Permeable to the substance
What expression describes the size of diffusion?
F = kpA(C2-C1)
kp is the permeability coefficient
A is the surface area
F is the magnitude of diffusion
What are the two ways diffusion through the membrane can occur?
Through the phospholipid bilayer or protein channels
What must molecules be to pass through the phospholipid bilayer?
Small
Lipophillic
Uncharged
Do any lipophobic molecules pass through the lipid bilayer by diffusion?
Yes, small uncharged ones such as CO2 and urea
What are the two ways that ions cross the membrane?
Through protein channels or mediated transport proteins
What are protein channels?
Transmembrane proteins that act as an aqueous route though the membrane
Why can molecules like glucose not use protein channels?
The molecules are too large
What forms of protein channels are there?
Open
Closed
What are closed protein channels controlled by?
Gates
What are the two types of closed protein channels?
Voltage gated protein channel
Ligand gated protein channel
What are voltage gated protein channels?
Open/close in response to alternations of the membrane electrical potential
What are ligand gated protein channels?
Open/close in response to a chemical such as a neurotransmitter or a hormone
What do ligand gated protein channels act as?
A receptor and a transporter
How do gated protein channels work?
Stimuli causes a conformational change of the protein which opens or closes the channel
When is electrochemical equilbrium reached?
When the electrical and chemical gradients are in balance
What is carrier mediated transport?
Proteins that are only open on one side of the membrane at any time that move molecules across
What are the two forms of carrier mediated transport?
Facilitated diffusion
Active transport
What is facilitated diffusion?
Movement of molecules through transport proteins down their electrochemical gradient
What is active transport?
Movement of molecules through transport proteins against their electrochemical gradients using energy (ATP)
How does carrier mediated transport switch the side of the membrane that it is open on?
A molecule binds to it and causes a conformational change which exposes the binding site on the other side
What do carrier mediated transport proteins act as (other than a transporter)
An enzyme as it hydrolysis ATP to release energy
What are active transporters otherwise known as?
Pumps
What do active transporters maintain?
The concentration gradient
What does each molecule of ATP allow to pass through a pump?
3 molecules of Na+ and 2 molecules of K+
How much of the bodies resting energy is used to pumps?
40%
