1. Key Area 3- Membrane proteins Flashcards
Describe the fluid mosaic model
The phospholipid is the basis of the system. The phosphate group is hydrophilic which aligns towards the aqueous cytoplasm and external fluid whilst the fatty acids are non-polar and thus hydrophobic. This part sits inside the bilayer.
What do the regions of hydrophobic R groups do?
They allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer
What is the function of an integral membrane protein
They interact extensively with the hydrophobic region of the membrane phospholipids
What is an example of an integral membrane protein?
transmembrane protein
Which membrane protein has hydrophilic R groups on their surface?
Peripheral membrane proteins
How are peripheral membrane proteins bound to the surface of membranes?
Mainly by ionic and hydrogen bond interactions
What is the function of peripheral membrane proteins
They interact with the surfaces of membrane proteins
What is the phospholipid bilayer?
A barrier to ions and most uncharged polar molecules
How do small molecules such as oxygen and carbon dioxide pass through the bilayer
By simple diffusion
Define facilitated diffusion
Is the passive transport of substances across the membrane through specific transmembrane proteins
In order to perform specialised functions, different cell types have different…?
channel and transporter proteins
What are channel proteins?
Multi-subunit proteins with the subunits arranged to form water filled pores that extend across the membrane. In animal and plant cells, most channel proteins are highly selective
Why are some channel proteins gated and change conformation?
To allow or prevent diffusion
What are ligand gated channels controlled by?
The binding sequence of signalling molecules
What are voltage gated channels controlled by?
Changes in ion concentration
What is the role of transporter proteins?
They bind to a specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
What is active transport?
It uses pump proteins that transfer substances across the membrane against their concentration gradient
What is required for active transport to occur?
A source of metabolic energy
How do some active transport proteins provide the energy for conformational change required to move substances across the membrane?
hydrolyse ATP directly
How does ATP hydrolysis provide energy?
By the addition of water to breakdown ATP to ADP and Pi releasing energy
What components form the electrochemical gradient?
For a solute carrying a net charge, the concentration gradient and the electrical potential difference combines to form the electrochemical gradient
What determines the transport of a solute which carries a net charge?
The electrochemical gradient
How is an electrical potential difference (membrane potential) 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
What is an ion pump?
Uses energy from the hydrolysis of ATP to establish and maintain ion gradients
What is the function of 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.
Describe the sodium potassium pump process
The pump has a high affinity for sodium ions inside the cell, binding occurs, phosphorylation by ATP, conformation changes, the affinity for sodium ions to decrease thus releasing sodium ions out of the cell. Potassium ions bind outside the cell, dephosphorylation, conformation changes, potasium ions taken into cell, affinity returns to start
What happens for each ATP that is hydrolysed
3 sodium ions are transported out of the cell and 2 potassium ions are transported into the cell which establishes both concentration gradients and an electrical gradient
How does the sodium potassium pump account for a high proportion of the basal metabolic rate in many organisms?
As it is found in most animal cells
In the intestinal epithelial cells in the small intestine, what does the sodium potassium pump generate?
It generates a sodium ion gradient across the plasma membrane which drives the active transport of glucose
Describe the transport of glucose through intestinal cells
Sodium ions enter the intestinal cells, down the concentration gradient through a glucose symport channel. The energy from the flow allows the simultaneous transport of glucose into the cell against the concentration gradient. Glucose and sodium ions are thus transported simultaneously (at the same time and in the same direction) by a glucose symport channel.
