Unit 1 - Membrane Proteins Flashcards
What are integral proteins?
Proteins that have one or more segment embedded in the phospholipid bilayer
What are transmembrane proteins?
Proteins which span across the membrane and act as channels or transporters of ions
What are peripheral proteins?
Proteins which are temporarily bound to either surface of the membrane
What is facilitated diffusion?
The passive transport of substances across the membrane through specific proteins
What are transporter proteins?
Membrane proteins involved in the movement of ions, small molecules and macromolecules across a membrane
What are gated channel proteins?
Channel-forming proteins controlled by signalling molecules or ion concentration.
What are ligand-gated channels?
Transmembrane protein channels controlled by the binding of signal molecules
What are voltage-gated proteins?
Transmembrane proteins that form ion channels, activated by the changes in the electrical membrane potential
What is the electrochemical gradient?
A gradient of electrochemical potential, consisting of difference in solute concentration and difference in charge
What is the membrane potential?
An electrical gradient that forces ions to move passively in one direction
What is the sodium-potassium pump?
A protein that removes 3 sodium ions and takes 2 potassium ions into the cell during a cycle of action
What is a glucose-symport?
An integral membrane protein involved in transport of glucose and sodium ions across the membrane
What does the plasma membrane control?
Entry and exit of materials
What is the plasma membrane composed of?
-Phospholipids
-Proteins
What are the 2 regions of a phospholipid and what are their properties i.e. charge?
- Head region ( charged, hydrophilic, attracted to water )
- Tail region ( uncharged, hydrophobic, repelled by water )
What gives the membrane a fluid quality?
Phospholipids which are constantly changing position
Examples of proteins found in the membrane
- Active transport proteins
- Channel forming proteins
- Enzymes
- Receptors
Examples of integral proteins
- Channels
- Transporters
- Receptors
What do integral proteins interact with?
The hydrophobic region of membrane phospholipids
What holds integral proteins within the phospholipid bilayer?
Regions of hydrophobic R groups allow strong hydrophobic interaction, holding them in the membrane
How are peripheral proteins bound to the surface of the membrane?
They have hydrophilic R groups on their surface, so can be bound by ionic and hydrogen bonds interactions
What molecules does the phospholipid bilayer act as a barrier to?
Ion and most uncharged polar molecules
How do oxygen and carbon dioxide pass through the membrane?
Diffusion
What are the proteins involved in transporting substances?
- Channel proteins ( ligand-gated, voltage-gated)
- Transporter proteins
- Protein pumps
What proteins use the method of facilitated diffusion?
Transporter proteins and channel proteins
What are channels?
Multi-subunit proteins with the subunits arranged to form water-filled pores
What do gated proteins respond to?
Stimulus ( Chemical, Electrical )
How does the ligand-gated channel open?
When correct signal molecules bind, gate open allowing ions to flow through
How do transporter proteins work?
Transporter proteins bind to specific substances which are to be transported and undergo a conformational change to transfer the solute across the membrane
Why do transporter proteins alternate between 2 conformations?
So that the binding site is sequentially exposed on one side for the bilayer then the other
What are transporter proteins coupled to an energy source?
Pumps
What is required for protein pumps to transfer substances?
A source of metabolic energy
What do some active transport proteins do to provide energy?
Hydrolyse ATP directly
What are the proteins that hydrolyse ATP directly?
ATPases
How is the electrochemical gradient formed?
The concentration gradient and electrical potential difference are combined
What does the electrochemical gradient determine?
The transport of the solute carrying a net charge
What is the concentration gradient?
The difference in concentration of a solute across the plasma membrane
When is an electrical potential difference/membrane potential created?
When there is a difference in electrical charge on the two sides of the membrane
What does the sodium potassium pump use to establish and maintain ion gradients?
Energy from the hydrolysis of ATP
How does Na/K-ATPase transport ions?
Transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
The process of sodium potassium pump?
- Pump has high affinity for sodium inside the cell, binding occurs
- Pump hydrolyses ATP and phosphate attaches to pump
- Phosphorylation by ATP causes conformation of the protein to change
- Affinity for sodium ions decrease and 3 ions are released outside cell
- Pump now has high affinity for potassium outside the cell therefore 2 ions bind to pump
- Dephosphorylation occurs which causes conformation of protein to change
- Potassium ions taken into cell and affinity returns to start
What does the sodium-potassium pump account for a high proportion of?
High proportion of the basal metabolic rate (up to 25% in humans)
What does the sodium-potassium pump generate in the small intestine?
A sodium ion gradient across the plasma membrane which drives active transport of glucose
What is the glucose transporter called?
Glucose symport
What does the glucose symport do?
Transports sodium ions and glucose at the same time and in the same direction.
