Introduction to Membranes Flashcards
How can phospholipids spontaneously form membranes?
Through their amphipathic nature
How is a micelle formed with phospholipids?
Forms because single-tailed phospholipids are conical and their amphipathic nature
Describe phospholipid movement within a bilayer.
Can move freely laterally and quickly
Flip/Flop movement is rare because the polar head is unstable in a hydrophobic environment
What are some effects of high temperatures on the phospholipid bilayer?
Kinetic energy is increased to cause increased flexibility and permeability and creates gaps between phospholipids
What are some adaptations to high heat on phospholipid bilayers?
i) increase in hydrocarbon tail length
ii) decrease in C=C to increase saturation
iii) increase in cholesterol to increase hydrophobicity and create a pylon to slow down phospholipids
What are some effects of low temperatures on the phospholipid bilayer?
Space between phospholipids decreases to cause decreased flexibility and permeability
What are some adaptations to low heat on phospholipid bilayers?
i) increase C=C to decrease saturation to make molecules larger
ii) decrease hydrocarbon tail length to decrease hydrophobicity
iii) add cholesterol to act as a spacer between phospholipids
What are two types of proteins embedded into the membrane bilayer?
Integral membrane protein and peripheral membrane protein
What defines a substance that can freely diffuse across a phospholipid bilayer?
Permeable
What is impermeable?
A substance that cannot cross the hydrophobic core because it’s either too large or charged
What are the rankings of CO2, glucose and ions from most permeable to least permeable?
CO2
Glucose
Ions
Why can ions not cross the plasma membrane?
They cannot cross because of a hydration shell of H2O that surrounds the ion due to polarity
What is the movement of molecules from a high concentration to a low concentration?
Diffusion (Passive Transport)
What type of solution is a cell in when the solute concentration is higher within the cell than in the solution?
Hypotonic solution
What are the risks of a cell being in a hypotonic solution?
Can cause osmotic lysis
Describe an isotonic solution.
In an isotonic solution, the concentration of solute is equal inside and outside of the cell
What type of solution is when the concentration of solute is higher outside of a cell?
Hypertonic solution
What are the risks to a cell in a hypertonic solution?
Plasmolysis may occur
What is plasmolysis?
The cell shrinks as water goes to the outside of the cell
What form of transport describes molecules moving down their concentration gradient using channel proteins or carrier proteins?
Facilitated diffusion
What is a channel protein?
Protein that allows transport of specific solutes without changing shape
What is a carrier protein?
Protein that allows transport of specific solutes by changing shape
What type of transport requires energy?
Active transport
What is the transportation of molecules up their concentration gradient using energy?
Active transport
What are the three functions of active transport?
i) to concentrate nutrients in the cell
ii) to expel wastes
iii) to maintain a voltage/chemical gradient
Describe the process of a Sodium/Potassium pump.
i) 3 Na+ bind to a pump from within the cell
ii) ATP provides energy for the protein to change shape
iii) 3 Na+ are released extracellularly
iv) 2 K+ bind to the pump from outside the cell
v) ATP provides energy for the protein to change shape
vi) 2 K+ are released intracellularly
What is the role of an electrogenic pump?
It generates a voltage difference across the membrane
What is the electric function of the Na/K pump?
To maintain a charge difference across the membrane called membrane potential which gives an electrochemical gradient
What is membrane potential?
A charge difference across the membrane
What is an electrochemical gradient?
There is a difference in concentration of a charged molecule across the membrane
What is cotransport?
The transport of 2 molecules simultaneously
How is Na/K pump an example of cotransport?
2K+ come into the cell down both electro and chemical gradients and 3Na+ go out of the cell down concentration gradient but against a charge
What is an antiporter?
The transport of 2 molecules in different directions
What is a symport?
The transport of 2 molecules in the same direction
Describe the Na/Glucose cotransporter.
Na+ flows down its gradient into the cell but takes glucose with it into the cell (glucose against concentration gradient)
What is coupled transport?
The use of one gradient to establish another
What are the two types of bulk transport?
Endo and exocytosis
What describes bulk transport going out of the cell?
Exocytosis
Describe the process of exocytosis.
i) sorted material from Golgi
ii) vesicle forms around material to be exocytosed
iii) vesicle fuses with membrane
iv) secretion of material
What is a small membrane-bound compartment that contains cargo in a cell?
Vesicle
What is endocytosis?
Bulk transport going into the cell
What is phagocytosis?
Bulk transport of non-specific material into the cell
Describe the process of endocytosis.
i) material comes to the plasma membrane
ii) vesicle forms around the material at membrane
iii) vesicle is transported to the lysosome
iv) lysosome digests the material
What is Receptor-Mediated Endocytosis?
Endocytosis of a specific ligand
What is a ligand?
Anything that binds to a receptor
What is a receptor?
An integral membrane protein that recognizes and binds a specific ligand
Describe Receptor-Mediated Endocytosis.
i) ligand approaches receptor in a clathrin-coated pit
ii) ligand binds to its specific receptor
iii) a receptor circled vesicle forms carrying ligand
iv) lysosome digests ligand
v) receptors are recycled
