Module 1 Flashcards
(44 cards)
Why can phospholipids be described as amphipathic molecules?
Because they have both hydrophobic and hydrophilic parts.
What does the fluid mosaic model mean?
That the membrane is fluid (i.e. moving and not sitting rigid) with a “mosaic” of proteins embedded in it.
How do amphipathic phospholipids form the cell membrane?
DRAW A DIAGRAM Phospholipids align to form a bilayer whereby the phophate (hydrophilic) heads line the outsides of the membrane, while the lipid (hydrophobic) tails form the inside of the membrane
What are the two types of lipid tails that can be formed and how do their shapes aid in their abilities to form an effective barrier?
- DRAW*
1) Unsaturated hydrocarbons: Has a double bond along the chain, leading to a bend in its configuration. This bending prevents tight packing.
2) Saturated hydrocarbons: Comprised entirely of single bonds, leading to straight (BUT FLEXIBLE) tails that move easily and can thus be packed closer together.
Describe phospholipid movement in the membrane
1) Movement of phospholipids
- Lateral movement (10 million times per second)
- Flip flop (once per month)
- Increasing temperature increases speed
How can membrane fluidity be changed?
- Lots of unsaturated hydrocarbon tails = fluid membrane DRAW
- Lots of saturated hydrocarbon tails = viscous membrane
- Increasing temperature increases fluidity.
**How does cholesterol within an animal cell membrane aid in fluidity?
*DRAW**
Cholesterol balances out cell fluidity and keeps it from extremes.
- It makes the membrane more fluid at low temperature and less fluid at high temperatures.
What is the difference between peripheral and integral proteins near a cell membrane?
Peripheral proteins line only one side of the membrane whilst integral proteins exist across the membrane and allow certain materials to pass through them.
Describe the structure of an integral protein and how this structure enables it to exist across the phospholipid bilayer
**DRAW
An integral protein is comprised of a continuous chain of amino acids.
- The N-terminus exists on the extracellular side, while the C-terminus exists on the cytoplasmic side of the membrane.
- The alpha helix proteins form the middle of the membrane and have hydrophobic side chains, causing this region to be hydrophobic (similar to the lipid tails surrounding it).
- Beta-pleated sheet proteins form the ends of the protein and have hydrophilic side chains, causing the region to be hydrophilic (similar to the phosphate heads around it).
How do we know it is a fluid (CONSTANTLY MOVING) mosaic?
DRAW
Mouse cell and human cells with differing membrane proteins were joined to form a hybrid cell. After an hour, the proteins had mixed.
What are the 6 major functions of membrane proteins?
- DRAW*
1. Transport
2. Enzymatic activity (catalyse important functions)
3. Signal transduction
4. Cell-to-cell recognition
5. Intercellular joining
6. Attachment to the cytoskeleton and the extracellular matrix (ECM)
What are lipid bilayers permeable to? What does this mean?
Few water molecules, and a few small, uncharged, molecules (e.g. oxygen and carbon dioxide).
This means that these particles can pass directly through the lipid bilayer without the need for other transport mechanisms.
What are lipid bilayers impermeable to?
HIM
- Small hydrophilic molecules (e.g. glucose)
- Ions (e.g. Na+, Ca2+,HCO3-, etc)
- Macromolecules (e.g. proteins and RNA)
Define passive transport and how it occurs
Passive transport = diffusion of a substance across a membrane with no energy investment.
Define diffusion and its relation to passive transport
Diffusion refers to the random motion by which molecules become equally distributed (thus eliminating a concentration gradient, provided the molecules can cross the membrane).
- No work is done in this process
Define osmosis and explain why it occurs.
The diffusion of water through a selectively permeable membrane into another aqueous compartment containing solute at a HIGHER concentration.
TL;DR: The movement of water across a selectively permeable membrane to equalize concentrations and establish equilibrium.
What are osmotica and what does this mean?
Osmotica refers to substances that cannot move across the membrane by passive diffusion and thus water moves instead to establish equilibrium.
Osmotica: SPIN- sugars, ions, proteins and nutrients.
Define tonicity and the three forms it can take
Tonicity- the ability of a solution to cause a cell to gain or lose water
1) Isotonic: Solute concentration =cell concentration; no net water movement across the plasma membrane.
2) Hypertonic: Solute conc > cellular conc; cell loses water
3) Hypotonic: Solute conc < cellular conc: cell gains water (hyPOHtonic)
Explain how osmosis can affect cell volume in hypertonic and hypotonic solutions
If water moves OUT of the cell, the cell volume DECREASES.
If water moves IN to the cell, the cell volume INCREASES.
Explain the effect of placing an animal or plant cell into hypertonic, isotonic or hypotonic solutions:
Hypotonic:
- Animal: cell volume increases to a point after which it may lyse (burst)
- Plant: Cell volume is normal as the rigid cell walls prevent lysis. (Plant cells are generally healthiest in this environment- uptake of water eventually balanced by the wall pushing back on the cell).
Isotonic:
- Animal: cell volume is normal
- Plant: Cell appears flaccid (limp)
Hypertonic:
- Animal: Cell volume decreases, cell undergoes crenation (appears shriveled)
- Plant: Cell volume decreases, cell is plasmolysed- protoplast (inner membrane of cell) contracts
What is the osmolarity of RBCs and how are they affected in different solutions?
Osmolarity= 300 osmol
Hypotonic: Cells lyse (hyPOHtonic), actual volume of cells decrease
Hypertonic: Cells crenate.
Define facilitated diffusion. Does it still use concentration gradients or require energy?
In facilitated diffusion, transport proteins speed up the passive movement of molecules across the plasma membrane.
- The aim is still to only EQUALIZE concentration gradients, and thus it occurs along the solute concentration gradient and does NOT require energy.
What are transport proteins and what types are there?
Transport proteins: Proteins that allow the passage of HYDROPHILIC substances across the membrane
Types DRAW:
a) Channel proteins, including aquaporins and ion channels: Open or close in response to a stimulus and are thus GATED CHANNELS
b) Carriers (or transporters) that bind to SPECIFIC molecules and change shape to shuttle them across the membranes, e.g. glucose transporters; amino acid transporters
What is the difference between passive and active transportation? What forms of transport proteins exist in each
PASSIVE = DOWN conc gradient (inc. diffusion and facilitated diffusion) ACTIVE = AGAINST conc gradient
Carrier proteins exist in both passive and active transportation, but ion channels ONLY exist in passive diffusion
