Unit 1 Cells and Proteins: Key Area 3 - Membrane Proteins Flashcards
What does the plasma membrane surround and what function does it serve?
The plasma membrane surrounds cells and controls entry and exit of materials.
What describes the structure of the plasma membrane?
The fluid mosaic model.
What is the plasma membrane composed of?
Phospholipids and Proteins.
What chemical property of the phospholipid head controls how the phospholipids are arranged in the plasma membrane?
The head is charged, therefore, hydrophilic (attracted to water). This is why the head sits on the outer surface of the plasma membrane.
What chemical property of the phospholipid tail controls how the phospholipids are arranged in the plasma membrane?
The tail is not charged, therefore, hydrophobic (repelled by water). This is why the tail sits on the inside of the plasma. membrane.
What gives the plasma membrane it’s fluid quality?
The phospholipids are constantly changing direction.
How are phospholipids arranged?
In a bilayer.
What way are the heads and tails of the phospholipid in the plasma membrane arranged?
The heads point out and the tails point in.
What molecule gives the plasma membrane it’s mosaic form?
Proteins
What are the 5 functions that proteins can carry out in the plasma membrane?
- Active transport
- Channel forming
- Enzymes
- Receptors
- Attachment proteins for the cell cytoskeleton
What are the 2 different types of protein in the plasma membrane?
- Integral
- Peripheral
Where are integral proteins found?
They are found within the membrane.
What are some integral proteins and what does this mean for for the membrane?
Some are transmembrane, this means they span the entire width of the membrane.
What do integral proteins interact with extensively?
The hydrophobic region of membrane proteins.
What are examples of integral proteins?
Channels, transporters and many receptors.
What part of integral proteins hold membrane proteins, within the phospholipid bilayer?
Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer.
Where are peripheral proteins found?
On the surface of the membrane.
What part of peripheral proteins means that they are bound to the surface of membranes?
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.
What do many peripheral proteins interact with?
Many peripheral membrane proteins interact with the surfaces of integral membrane proteins.
What do many molecules have to move through to pass across the membrane?
Many molecules have to move through proteins to cross the membrane.
What does the phospholipid bilayer do?
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules
What are examples of molecules that pass through the membrane without the need for proteins and how do they do this?
Small molecules such as oxygen or carbon dioxide pass through the layer by simple diffusion.
What is facilitated diffusion?
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins.
What proteins use the facilitated diffusion method?
Channel proteins and Transporter proteins.
To perform specialised functions, what do different cell types have in their membrane?
To perform specialised functions, different cell types have different channel and transporter proteins.
What are the 3 different types of transport using proteins?
- Channel proteins
- Transporter proteins
- Protein pumps
What are channel proteins?
Multi-subunit proteins with the subunits arranged to form water - filled pores that extend across the membrane.
What are most Chanel proteins in animal and plant cells?
Most channel proteins in animal and plant cells are highly selective.
What can some channel proteins be?
Some channel proteins are gated and change conformation to allow or prevent diffusion.
What do gated channel respond to?
Stimulus which causes them to open or close.
What are the 2 types of stimulus for gated channels?
- Chemical (ligand-gated)
- Electrical (voltage-gated)
What are Ligand-gated channels controlled by?
Ligand-gated channels are controlled by the binding of signal molecules.
What happens when the correct signal molecule binds to the gate on a ligand-gated channel?
The gate opens, allowing ions to flow through.
What are Voltage gated channels controlled by?
Voltage-gated channels are controlled by changes in ion concentration.
Are channel proteins passive or active transport?
Passive transport
Does passive transport require energy?
No
Does active transport require energy?
Yes
How do transporter proteins work?
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.
How do transporter Proteins differ from chemical proteins?
Transporter proteins involve a conformational change in the protein.
What do transporter proteins alternate between and what does this mean for the bilayer?
Transporter proteins alternate between two conformation so that the binding site for a solute is sequentially exposed on on side of the bilayer, than the other.
Are transporter proteins active or passive?
Passive
What does active transport use ?
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient.
What are pumps that carry out active transport?
Transporter proteins coupled to an energy source.
What is the energy source in the sodium-potassium pump?
Na/K-ATPases
What is required for active transport/a protein pump to transfer substances?
A source of metabolic energy.
What do some active transport proteins do and why is this?
Some active transport proteins hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane.
What are proteins which hydrolyse ATP directly called?
ATPases
For a solute carrying a net charge e.g. NA+, what happens to the concentration and electrical potential difference and why do they do this?
For a solute carrying a net charge, the concentration gradient and the electrical potential difference combine to form the electrochemical gradient that determines the transport of the solute. i.e. How and where the solute goes.
What is the concentration gradient?
The difference in concentration of a solute across the plasma membrane.
What is the electrical potential difference?
Also known as membrane potential. The electrical potential difference is a membrane potential is created when there is a difference in electrical charge on the two sides of the membrane.
What function do ion pumps carry out?
Ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients.
Are protein pumps active or passive?
Active
What is the function of the sodium-potassium pump?
The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis.
What does the sodium-potassium pump actively transport in and out of the cell?
It actively transports 3 sodium ions out of cells and 2 potassium ions in.
What does the maintenance of ion gradients by the sodium-potassium account for?
A significant part of the basal metabolic rate.
What are the steps involved in the sodium-potassium pumps?
- The pump has high affinity for sodium ions inside the cell
therefore binding occurs. - Pump hydrolyses ATP and phosphate attaches to it . Phosphorylation by ATP causes the conformation to change.
- Affinity for sodium ions decreases and sodium ions are released outside of the cell.
- Pump has high affinity for potassium ions outside the cell therefore binding occurs.
- Dephosphorylation occurs, causing conformation to change.
- Potassium ions taken into cell and affinity returns to start.
Where is the sodium-potassium pump found and what does this account for?
The sodium-potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms. (up to 25% in humans).
What is the function of the sodium potassium pump in the small intestine?
In intestinal cells the sodium potassium pump generates a sodium ion gradient across the plasma membrane, which drives the active transport of glucose.
What is the glucose transporter responsible for?
The active transport of the active transport of glucose - glucose symport - transports sodium ions and glucose at the same time.
What does a symporter do?
Transport molecules across the plasma membrane at the same time.
What happens in the glucose transporter?
Sodium ions enter the cell down their concentration gradient and the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.
