Lecture 3 - Basic Membrane Transport Concepts Flashcards
What are heart cells called?
Myocytes
Explain the fluid mosaic model
The model is fluid so the proteins can move, however they can’t move around the full structure, they are compartmentalised
Phospholipid bilayer - hydrophobic tails, hydrophilic heads
How are the molecules of the phospholipid bilayer held in place?
By their amino acid side chains
What is the glycocalyx shown to do?
Protect cells against calcium ions
The glycoproteins are -ve so they attracts +ve ions
Experiments have been shown that if the glycocalyx was removed, normal extracellular concentrations of calcium are toxic to the cell
What is the role of the plasma membrane?
Acts a selective barrier - regulate the passage of molecules coming in and out of the cell
Communication – environment and other cells
Cell growth/shape change/movement/cell division
What is meant by the term transporter proteins?
A generic term which includes both ion channels and ion pumps
What do ion channels do?
Allow the passage of ionic substances through the cell membrane
What do ion pumps do?
Move ions actively by a couple of different mechanisms, in the opposite directly to ion channels
Features of Sodium-Calcium Exchanger:
Doesn’t require ATP
It moves 3 Na into the cell as it moves one Ca ion out of the cell
The gradient of sodium moving into the cell which provides the driving force to move the calcium out of the cell, therefore its kinetic energy driving the movement of ions
What is the equation for Electrical current?
I = N x i P I = Electrical current N = The number of ion channels in the membrane i = The current that flows through one ion channel P = The probability of the ion channel being open at any one time
What is happening when the ion channel is at rest?
The activation gate is closed, so nothing can pass through the ion channel
What is happening when the ion channel is active?
The activation gate opens, so ions can pass through, The inactivation gate is also open
What is happening what the ion channel is inactive?
The inactivation gate is closed (activation gate still open), so ions cannot pass through
Features of Transverse Tubular system (T-tubules)
The sarcolemma in cardiac muscle forms T-tubules
The -tubules are like invagination’s, part of the cell membrane that dip in towards the cell
They are large in diameter compared to those in skeletal muscle
T-tubules of cardiac muscle are an elaborate network of sarcolemma tubules, the lumen of these are continuous with the extracellular space
Features of the Sarcoplasmic Reticulum:
Extensive network of tubules surrounding the contractile material in a tight net
Doesn’t connect directly to the outside of the cell, it is within the cell
Don’t come directly in contact with T-tubules, but when the T-tubules move into the centre of the cell, they come in close contact
SR is connected with the nuclear envelope – it is the equivalent of the endoplasmic reticulum in other cells
