Unit 1: Membrane Proteins Flashcards
(22 cards)
What type of molecules interact with integral membrane proteins?
Integral membrane proteins interact extensively with the hydrophobic region of membrane phospholipids.
What type of R groups do peripheral membrane proteins have and where are they located?
Peripheral membrane proteins have hydrophilic R groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions. Many peripheral membrane proteins interact with the surfaces of integral membrane proteins
What is facilitated diffusion?
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins
What does the phospholipid bilayer act as a barrier towards?
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules
What molecules can pass through the phospholipid bilayer?
Some small molecules, such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion
What is the function of transporter proteins?
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
How is the binding site made available on each side of the bilayer by transporter proteins?
Transporters alternate between two conformations so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other.
what type of proteins does active transport use?
Active transport uses PUMP PROTEINS that transfer substances across the membrane against their concentration gradient
Pumps that mediate active transport are transporter proteins coupled to an energy source.
What type of proteins use facilitated diffusion?
Channel proteins and transporter proteins.
What are channel proteins?
Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane.
How selective are channel proteins?
Most channels are highly selective
What types of gated channels are there?
Voltage gated
Ligand gated
Transporter proteins (passive)
Protein Pumps (active process)
How do ligand gated channels work?
Ligand-gated channels are controlled by the binding of signal molecules. When the correct signal molecule binds, the gate opens and allows ions to flow through
How do voltage gated channels work?
Voltage-gated channels are controlled by changes in ion concentration
Describe a membrane potential
A membrane potential (an electrical potential difference) is created when there is a difference in electrical charge on the two sides of the membrane.
What is an example of an ion pump?
Sodium-potassium pump
Describe the direction of sodium ions and potassium ions in the pump?
The pump actively transports sodium ions out of the cell and potassium ions into the cell
How does the sodium potassium pump source its energy?
The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
Describe the process of the sodium potassium pump?
- Pump has a high affinity for sodium ions within the cell, therefore binding of sodium ions to the pump occurs within the cell.
- Phosphorylation by ATP occurs, causing a conformational change of the protein
- Pump loses affinity for sodium ions, causing sodium ions to be released outside of the cell.
- pump has high affinity for potassium ions outside of the cell, causing binding of potassium ions outside of the cell occurs
- Dephoshorylation occurs, causing conformational change of the protein
- Pump loses affinity for potassium ions, causing potassium ions to be released into the cell. Affinity returns to the start
Describe the movement of sodium ions and potassium ions in the pump for one ATP that is hydrolysed?
For each ATP hydrolysed, three sodium ions are transported out of the cell and two potassium ions are transported into the cell. This establishes both concentration gradients and an electrical gradient.
What is the name of the protein that is directly responsible for hydrolysing ATP?
ATPases
Describe the function of the sodium potassium pump in the small intestine?
In the small intestine, the sodium gradient created by the sodium-potassium pump drives the active transport of glucose
The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time and in the same direction
Sodium ions enter the cell down their concentration gradient; the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.
