Unit 1: KA3 - Membrane Proteins Flashcards
What is the accepted model of the plasma membrane called?
Fluid Mosaic model.
Describe the Fluid mosaic model.
- Phospholipid bilayer held together by hydrophobic reactions
- Integral membranes held by hydrophobic reactions
- membrane can move making it ‘fluid’
What are the two types of membrane protein?
- Integral: embedded within
- Peripheral: found on surface
Describe peripheral membrane proteins’ interactions with the membrane.
Bound to the surface of the phospholipid bilayer with ionic and hydrogen interactions, due to hydrophilic R group
Describe integral membrane proteins’ interactions with the membrane.
- Can be transmembrane (spanning entire membrane)
- Hydrophobic R groups allow strong interactions with hydrophobic tails of phospholipids.
How do differing membrane proteins react?
Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.
What does the phospholipid bilayer act as a barrier to?
Ions and most uncharged polar molecules.
What are examples of molecules that can diffuse straight through the phospholipid bilayer?
- Water
- CO₂
Define facilitated diffusion.
the passive transport of substances across the membrane through specific transmembrane proteins
What do different cell types need to perform specialised functions?
Different channel and transporter proteins
What is highly selective in plant and animal cells?
channel proteins
Describe gated channel proteins.
- Voltage gated: controlled by changes in ion concentration
.- Ligand gated: controlled by the binding of signal molecules.
Describe transporter proteins.
They bind to the specific substance to be transported and undergo a conformational change to transfer the substance across the membrane.
Describe active transport across the plasma membrane?
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
This requires a source of metabolic energy.
What is a common source of metabolic energy for active transport?
Hydrolysis of ATP
What enzyme hydrolyses ATP?
ATPase
What forms the electrochemical gradient?
The concentration gradient and the electrical potential difference.
Define the term membrane potential.
Difference in electrical charge on either side of a membrane, creating electrical potential difference
What maintains ion gradients?
ion pumps
How does the sodium potassium pump work?
- The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
- It actively transports sodium ions out of the cell and potassium ions into the cell.
- It has a high affinity for sodium ions within the cell; binding occurs; the pump is phosphorylated by ATP and changes conformation; sodium affinity lowers and are released; High affinity for potassium; binding occurs; dephosphorylation; conformation changes back; potassium released into cell
What are the concentrations of Potassium and sodium ions in the cell?
Potassium (K) - HIGH
Sodium (Na) - LOW
How many potassium and sodium ions are involved in one cycle of the sodium potassium pump?
- 3 Sodium ions are pumped out
- 2 potassium ions are pumped in
What is the importance of the sodium potassium pump in the small intestine?
the sodium gradient created by the sodium-potassium pump drives the active transport of glucose.
Describe Glucose symport and the direction of the gradients involved.
The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time, in the same direction.
Sodium Ions enter the cell down their concentration gradient, while glucose is pumped into the cell up its concentration gradient.
