Chapter 5: Structure and Function of Plasma Membranes Flashcards
How thick are plasma membranes?
5 to 10 nanometers
What are the principle components of the plasma membrane?
Lipids, proteins and carbohydrates attached to some lipids and proteins
What two lipids are in the plasma membrane?
Phospholipids and cholesterol
What is the protein, lipid and carbohydrate ratio in a typical human cell?
50:40:10
glycoprotein
proteins with carbohydrates attached to them
glycolipid
lipids with carbohydrates attached to them
Where are all carbohydrates in the plasma membrane?
Attached to lipids or proteins on the exterior surface
amphiphilic
describes a molecule with both a polar and nonpolar area
Which part of a phospholipid is charged?
The phosphate head
What charge does the phosphate head in a phospholipid have?
A negative charge
Which part of a phospholipid is nonpolar?
The fatty acids
micelle
spherical structure that phospholipids spontaneously form in water where all the phosphate head face outwards
liposome
spherical structure that phospholipids form in water where lipid bilayer forms
integral protein
proteins that are fully integrated into the plasma membrane
single-pass integral protein
proteins that only span the membrane once
multi-pass integral protein
proteins that span the membrane several times
How many protein segments can multi-pass integral proteins have?
Up to twelve segments
Which protein structure can span the membrane multiple times?
Proteins with alpha-helices
transmembrane integral protein
integral protein that reaches both sides of the plasma membrane
monotopic intergral protein
integral protein that are attached to only one side of the plasma membrane and do not reach both sides
peripheral protein
proteins loosely attached to integral proteins or phospholipids
How many monosaccharide units does a typical carbohydrate attached to the plasma membrane have?
2-60 monosaccharide units
What structures can carbohydrates attached to the plasma membrane be in?
Straight or branched
Which components of the plasma membrane help in cell identification?
Peripheral proteins and carbohydrates
Why is cell identification important?
It allows cell to differentiate from the body’s own cells and foreign cells
glycocalyx
the collective name for all carbohydrates attached to the plasma membrane
Is the glycocalyx hydrophilic or hydrophobic?
It is highly hydrophilic
How does the glycocalyx’s hydrophilic properties help the cell?
It attracts large amounts of water to the cell to aid in the cell’s interaction with the water
Which two factors affect the plasma membrane’s fluidity?
Unsaturated phospholipids and cholesterol
How do unsaturated phospholipids aid in the plasma membrane’s fluidity?
Due to the kink in unsaturated fatty acids, when it is cold and phospholipids pack together, space creaked by the kinks allows more fluidity
How does cholesterol aid in the plasma membrane’s fluidity?
It decreases the effects of temperature on the membrane
Where is cholesterol found in the plasma membrane?
Inside the phospholipid bilayer
selectively permeable
describes a membrane that allows only some substances to pass through it
Is the plasma membrane selectively permeable?
Yes
passive transport
naturally occurring movement of materials across membrane due to differences in concentration
concentration gradient
area of high concentration that is adjacent to an area of low concentration
Is the plasma membrane symmetric?
No, the interior and exterior sides are different
Which type of molecules can pass through the plasma membrane easily?
Nonpolar and lipid-soluble molecules
Which types of molecules cannot pass through the plasma membrane easily?
Polar molecules
diffusion
process of passive transport where substances in a high concentration move to a low concentration
facilitated transport
diffusion of materials with the help of membrane proteins
Why is facilitated transport necessary for ions?
Since ions are polar they will be repelled from the hydrophobic parts of the plasma membrane
transport protein
integral proteins involved in facilitated transportation of molecules across the plasma membrane
channel protein
protein that creates a channel for ions to pass through
What property do channel proteins have that allow for facilitated transport?
They are hydrophilic and this provides a hydrated opening for ions to pass through
aquaporin
channel protein that allows water through the plasma membrane at a high rate
What two forms can channel proteins be in?
They can be open at all times or they are gated
What does it mean for a channel protein to be ‘gated’?
It controls the opening and closing of its channel
carrier protein
transport protein that changes shape when it binds a substance to transport that substance
How selective are carrier proteins?
They are specific for only one substance
ligand
molecule that binds to another
Why can carrier proteins’ selectivity be a problem sometimes?
Since there are a limited number of carrier proteins for each substance, there is a limit to the rate of transportation regardless of the concentration gradient and not enough materials might be transported
Which membrane transport protein works faster?
Channel proteins work faster
osmosis
movement of water across a semipermeable membrane due to water’s concentration gradient
tonicity
describes how the concentration of solute in a solution can affect osmosis
osmolarity
describes a solution’s solute concentration
What does having a higher osmolarity mean?
The solution has fewer water molecules compared to solute
What does having a lower osmolarity mean?
The solution has more water molecules compared to solute
hypotonic
when the extracellular fluid has a lower osmolarity than the fluid inside the cell
hypertonic
when the extracellular fluid has a higher osmolarity than the fluid inside the cell
isotonic
when the extracellular fluid has the same osmolarity as the fluid inside the cell
What happens to red blood cells in a hypertonic solution?
Water leaves the cell and shrivels up
What happens to cells in a hypotonic solution?
Water enters the cell and may burst
lysis
destruction of a cell due to damage to the cell membrane by excessive water
crenation
destruction of a cell due to damage to the cell membrane when too much water leaves the cell
What happens to a red blood cell during lysis?
The spaces between the phospholipids and proteins becomes too large and the cell breaks apart
What happens to a red blood cell during crenation?
The solutes in water is left behind in the cell which makes the cytosol denser and prevents diffusion, causing the cell to lose function
osmoregulation
mechanisms that cells use to prevent the effects to osmosis
turgor pressure
force inside a cell that pushes the cell membrane against the cell wall
How do plant cells combat osmotic efffects?
The cell wall prevents the cell membrane from expanding too much
Do plant cells have a higher or lower osmolarity than its cellular environment?
Plant cells’ cytoplasm is always slightly hypertonic
plasmolysis
when the cell membrane detaches from the cell wall due to osmotic effects when water leaves the cell
What happens when plants are not watered?
They lose turgor pressure and start to wilt
contractile vacuole
vesicle that collects and pumps out excessive water to prevent lysis in a hypotonic environment
active transport
transport of materials across the membrane that requires the cell’s energy
Where does the cell get its energy in active transport?
Usually from ATP
electrical gradient
a difference in charge across the plasma membrane
Is the inside of a cell positively or negatively charged?
Negatively
Do cells have a higher or lower concentration of K+ compared to its environment?
Cells have a higher concentration of K+
Do cells have a higher or lower concentration of Na+ compared to its environment?
Cells have a lower concentration of Na+
electrochemical gradient
the combined concentration and electrical gradients affecting an ion
What is the electrochemical gradient for K+ in cells?
The concentration gradient drives K+ out of the cell but the electrical gradient drives K+ into the cell
What is the electrochemical gradient for Na+ in cells?
The concentration gradient drives Na+ into the cell and the electrical gradient also drives Na+ into the cell
active transport pump
mechanism that actively transports substances against its electrochemical gradient
What are the three types of transport proteins?
Uniporters, symporters and antiporters
uniporter
transport protein that carries only one specific molecule
symporter
transport protein that carries two different molecules in the same direction
antiporter
transport protein that carries two different molecules but in opposite directions
primary active transport
moves ions across the plasma membrane by using ATP directly
secondary active transport
moves ions across the plasma membrane as a result of the electrochemical gradient caused by primary active transport
Na+-K+ ATPase
sodium-potassium pump
sodium-potassium pump
maintains the electrochemical gradient and the correct concentrations of K+ and Na+ in cells
In which direction does the sodium-potassium pump move K+ and Na+?
K+ is moved into the cell and Na+ is moved out of the cell
How many Na+ are moved for every K+?
For every three Na+ moved out of the cell, two K+ are moved into the cell
What are the two forms a sodium-potassium pump can be in?
It can be oriented to the cell’s interior or exterior
What happens when the sodium-potassium pump is oriented towards the cell’s interior?
The carrier has a high affinity for Na+ and these ions bind to the protein
How is Na+ pumped out of the cell?
When Na+ attaches to the pump, the pump hydrolyses ATP and a phosphate group attaches to it, changing the pumps shape and reorienting outwards and releasing the Na+
What happens when the sodium-potassium pump is oriented towards the cell’s exterior?
The carrier has a high affinity for K+ and these ions bind to the protein
How is K+ pumped into the cell?
When K+ attaches to the pump, the phosphate group from the previously hydrolysed ATP detaches and the pump orients itself to the interior, releasing the K+
electrogenic pump
pump that creates a difference in charge across the membrane
What happens as a result of primary active transport?
Since more Na+ is being pumped out of the cell than K+ into the cell, the cell’s interior becomes negatively charged
How does secondary active transport work?
Due to excessive Na+ outside the cell from primary active transport, an electrochemical gradient is created and Na+ are driven inside the cell through channel proteins
What does secondary active transport move across the membrane?
Na+ is moved into the cell, along with other substances like glucose and some amino acids
bulk transport
transport of large macromolecules through the cell membrane
endocytosis
type of active transport where the cell membrane invaginates
and forms a pocket around its target, pinching the pocket off into a vesicle inside the cell
phagocytosis
when a cell takes in a large particle by surrounding the target and engulfing it
clathrin
protein that helps form coated vesicles in endocytosis
How does clathrin help in endocytosis?
It coats a portion of the inner cell membrane in preparation to stabilise the vesicle formed by endocytosis and disengages before the vesicle merges with a lysosome
endosome
organelle of a fused vesicle and lysosome
pinocytosis
when a cell takes in molecules along with the water that surrounds it by surrounding and engulfing it
What are the differences between phagocytosis and pinocytosis?
- Phagocytosis engulfs a large molecule as if eating it and pinocytosis drinks the water and the particles inside of the water
- Vesicles in phagocytosis are a lot larger
- Vesicles in pinocytosis do not need to fuse with a lysosome
potocytosis
a variation of pinocytosis
caveolin
coating protein that plays a role, similar to clathrin, in potocytosis
lipid raft
special part of lipid bilayer that contains more glycosphingolipids and receptor proteins
caveola
specialised vesicle made up of lipid rafts and coated with caveolin that is the main transport vesicle in potocytosis
receptor-mediated endocytosis
when a cell takes in specific materials with the help of receptor proteins
What is the difference between phagocytosis and receptor-mediated endocytosis?
Normal phagocytosis involves eating any macromolecules, but receptor-mediated endocytosis uses receptor proteins to bind to certain substances
Does receptor-mediated endocytosis only allow certain substances to enter?
No, sometimes other substances may gain entry at the same site
exocytosis
process of removing materials from the cell
How does exocytosis work?
Vesicles containing waste materials in the cell fuse with the plasma membrane and open up to release the waste
