1.3 MEMBRANE PROTEINS Flashcards
What is the cell membrane made up of?
A bilayer of phospholipids and proteins
Why is the membrane described as semi-permeable?
It only allows certain molecules to enter/exit the cell
What does the phospholipid bilayer act as a barrier to?
Ions and most uncharged polar molecules
Give two examples of small molecules that can pass through the phospholipid bilayer?
Oxygen and Carbon Dioxide
What types of proteins control ion concentration and concentration gradients?
Transmembrane proteins such as channels and transporters
Why do different cell types/compartments have different channel and transporter proteins?
To allow them to perform specialised functions
What type of transport are channel proteins involved in?
Passive transport
Give an example of a channel protein.
Aquaporin
What is the benefit of having gated channel proteins?
Allows for control over the rate of diffusion
What are ligand-gated channels?
Channels controlled by signal molecules
What are voltage-gated channels?
Channels controlled by changes in ion concentrations
What is the purpose of transporter proteins?
To change conformation in order to transport molecules across a membrane
Give an example of a facilitated transporter protein.
Glucose symport
Do facilitated transporter proteins require energy?
No because they are a passive form of transport
Give an example of an active transporter protein.
Na/KATPase
What provides the energy for the conformational change in active transporter proteins?
Energy from hydrolysis of ATP
What is hydrolysis?
Energy stored in high-energy bond is released
What is the purpose of signal transduction?
To convert an extracellular chemical signal to a specific intracellular response
Give four possible intracellular responses brought about by signal transduction.
Activation of a G protein, change in uptake/secretion of molecules, rearrangement of cytoskeleton, activation of proteins which regulate gene transcription
What is a G protein?
A molecular switch involved in transmitting extracellular signals within the cell
What does the sodium potassium pump do?
Transports ions against a steep concentration gradient
What is the sodium potassium pump’s energy source?
ATP
What does the pump have an affinity for inside the cell?
Sodium ions
What happens after ions bind to the pump?
Phosphorylation by ATP causes a conformational change
