UNIT 1 - KA3 Flashcards
What is the function of the plasma membrane
The plasma membrane surrounds cells and controls entry and exit of materials
What is the fluid mosaic model
The fluid mosaic model describes the structure of the plasma membrane
What is the plasma membrane composed of
- phospholipids
- proteins
Phospholipid head
The head region of a phospholipid molecule is charged therefore hydrophilic (attracted to water)
Phospholipid tail
The tail region is uncharged and non polar therefore hydrophobic (repelled by water)
What gives the membrane its fluid quality
The phospholipids are constantly changing position this gives the membrane its fluid quality.
How are phospholipids arranged in the plasma membrane
The phospholipids are arranged into a bilayer in the plasma membrane
What does the hydrophobic centre of the phospholipid bilayer allow
The hydrophobic centre of the phospholipid bilayer allows oxygen and carbon dioxide to pass through directly by simple diffusion because they are small non polar molecules
How must many molecules pass through
Many molecules therefore must pass across the membrane with the help of proteins
What is the cell membrane embedded with
The cell membrane is embedded with protein which form a patchy mosaic
What are some functions of membrane proteins (5)
- active transport proteins
- Chanel forming proteins
- enzymes
- receptors
- proteins for the cell cytoskeleton
What are the two types of protein in the plasma membrane
1- integral protein
2- peripheral protein
Where are integral proteins found
These are proteins found within the membrane
What are transmembrane integral proteins
Some integral proteins are transmembrane, this means that they span the entire width of the membrane
What are examples of transmembranes
- channels
- transporters
- many receptors
What are phospholipid bilayer integral proteins held in place by
They are held in place by strong hydrophobic interactions with the lipid tails
What do regions of strong hydrophobic R groups allow
Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral proteins within the phospholipid bilayer
Where are peripheral proteins found
These proteins are found on the surface of the membrane
What kind of R groups predominate on the surface of peripheral membrane proteins
Hydrophilic R groups on their surface and are bound to the surface of membranes
What kind of interactions bind peripheral membrane proteins to the surface of the membrane / integral proteins
Mainly by weak ionic and hydrogen bond interactions
Summary of integral and peripheral
Integral - within membrane - hydrophobic - hydrophobic interactions
Peripheral - surface of membrane - hydrophilic - weak ionic and hydrogen bonds
What is the phospholipid bilayer a barrier to
The phospholipid bilayer is a barrier to ions and most uncharged polar molecules
What is facilitated diffusion
Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins
What do different cells have to perform specialised functions
To perform specialised functions, different cell types have different channel and transporter proteins
What are the types of proteins involved in transporting substances
1) Channel - a) ligand gated b) voltage gated
2) transporter proteins
3) protein pumps
What are most channel proteins in animal and plant cells
Most channel proteins in animal and plant cells are highly selective
What are channels
Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane.
Why are some channel proteins gated and change conformation
Some channel proteins are gated and change conformation to allow or prevent diffusion
What are ligand gated channels controlled by
Ligand-gated channels are controlled by the binding of signal molecules
What are voltage gated channels controlled by
voltage gated channels are controlled by changes in ion concentration
What is a key point about gated channel proteins
Whilst gated-channel proteins undergo conformational change to open or close the channel. movement of molecules across the channel is dependant on the concentration gradient and the molecule is not transported across the membrane by the action of proteins
Transporter proteins
Transporter proteins bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
What do transporters alternate between
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.
How does transporter protein differ from channel proteins
It differs from transport through channel proteins in that it involves a conformational change in the protein. The proteins actually pass the ions or molecules across the membrane rather than just providing a route through
What does active transport use
Active transport uses pump proteins that transfer substances across the membrane against their concentration gradient
What are pumps that mediate active transport
Pumps that mediate active transport are transporter proteins coupled to an energy source.
A source of what is required for active transport
A source of metabolic energy is required for active transport
What do some active transport proteins that hydrolyse atp do
Some active transport proteins hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane
What do ATPases hydrolyse
ATPases hydrolyse ATP
Describe what is meant by the term electrochemical gradient
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
What is a membrane potential (electrical potential difference)
A membrane potential (an electrical potential difference) is created when there is a difference in electrical charge on the two sides of the membrane.
How do ion pumps establish and maintain ion gradients
Ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients
What does the sodium-potassium pump transport
The sodium-potassium pump (also known as Na/K-ATPase) transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
Describe the action of the sodium - potassium pump include number of ions and directions
Three sodium ions are pumped out of the cell for every two potassium ions that are pumped into the cell
2-K-IN
Two potassium ions pumped into the cell three sodium pumped out
a
The pump has high affinity for sodium ions inside the cell therefore binding occurs
b
The pump hydrolyses ATP and phosphate attaches to it. Phosphorylation by ATP causes the conformation of the protein to change
c
The affinity for sodium ions decreases resulting in sodium being released outside the cell
d
The pump has high affinity for potassium ions outside the cell therefore binding occurs
f
Potassium ions are taken into the cell and the affinity returns to the start
Where is the sodium-potassium found
The sodium-potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms
What drives the active transport of glucose in the small intestine
In the small intestine, the sodium gradient created by the sodium-potassium pump drives the active transport of glucose
What does the sodium potassium pump generate in intestinal epithelial cells
In intestinal epithelial cells the sodium-potassium pump generates a sodium ion
gradient across the plasma membrane.
What is the glucose transporter responsible for the active transport of glucose in the small intestine
The glucose transporter responsible for the active transport of glucose in the small intestine is a glucose symport protein
What is a symporter protein
A symporter transports molecules across the plasma membrane at the same time and in the same direction
Describe the action of the glucose symport protein
Sodium ions enter the cell down their concentration gradient and the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient
