Chapter 5.1 cell membranes Flashcards
What is the purpose of a membrane?
They separate cells from their external environment. allow cell to carry out its diverse functions
What are cell membranes made up of?
- Lipids
- protiens (imbedded or associated, preform functions such as transporting molecules)
- carbohydrates (usually attached to lipids (glycolipids) and proteins (glycoproteins)
What is the most common typeof lipid found in a cell membrane? and what is it made up of?
Phospholipid
- a glycerol backbone
- phosphate group (hydrophilic, polar, forms hydrogen bonds)
- 2 fatty acids (hydrophobic, non-polar no H bonds)
What is the scientific word(s) for a molecule that is
- water loving
- water fearing
- both water loving and water fearing
- hydrophilic
- hydrophobic
- amphipathic
in an aqueous solution, how do amphipathic molecules behave?
- they spontaneously arrange themselves into various structures.
- The polar head is located on outside to interact with water
- The non-polar fatty tails are faced in away from water.
What are the possible structure shapes a amphipathic molecule can form?
- micelle (bulky head and single fatty acid tail) aka soap
- bilayer (less bulky head and two hydrophobic tails)
- liposome (environments with a neutral pH)
What is the cell theory
- All organisms are made up of cells
-the cell is the fundamental unit of life
-cells come from preexisting cells
cells are defined by membranes
Why is pH important for a phospholipid bilayer?
insures that the head groups are in their ionized (charged) form and hydrophilic.
why do liposomes form?
if phospholipids are added to a test tube of water at neutral pH and the spontaneously form spherical bilayer structures.
why are liposomes most likely involved in early evolution?
- can form, break, re-form in environments
- can grow by incorporating more lipids
why are lipids able to move in the plane of the membrane?
- Freely associated with each other (van Der Waals forces) between fatty acid tails
- these weak interactions can easily break and reform
what determines membrane fluidity?
depends on which type of lipid makes up the membrane
- long fatty acid tails, saturated, are interactions, tighter packing = reduced lipid mobility
- short fatty acid tails, unsaturated, double bonds, reducing tightness of packing = enhancing lipid mobility.
What is another type of lipid that influences membrane fluidity?
Cholesterol
- major component of of animal cell membrane
- represent about 30% by mass of membrane
What are the similarities and differences between cholesterol and phospholipids
-both amphipathic
cholesterol
-hydrophilic region contains OH group
-hydrophobic region consists of four interconnected carbon rings with an attached hydrocarbon chain
How is cholesterol inserted into the lipid bilayer?
The cholesterols head interacts with the hydrophilic head group of phospholipids, while the ring structure participates in VdW interactions with the fatty acid chains.
How does cholesterol increase or decrease membrane fluidity?
depends on temperature
- high temp= ridged (interaction of ridge ring structure with fatty acid tails reduces mobility)
- low temp= fluid (prevents phospholipids from packing tightly with other phospholipid.
What is the purpose of cholesterol in the membrane?
-helps maintain a constant state of membrane fluidity by preventing dramatic transitions from a fluid to a solid state.
how do rings work in cholesterol
- can’t rotate
- makes sure there isn’t too much plasma membrane movement at high temperature
- rings= big= can’t pack together as much
What is a lipid raft?
specific types of lipids that cluster in patches on the plasma membrane.
What are the functions of the different membrane proteins
- transporters
- receptor
- enzyme
- anchor
what is the function of the transport protein?
Moves ions or other molecules across the membrane
what is the function of the receptor protein?
allows cells to receive signals from the environment?
what is the function of the protein enzyme?
catalyze chemical reactions
what is the function of the protein anchors?
attach to other proteins and help to maintain cell structure and shape
what are the two groups membrane proteins can be classified into and why?
Integral membrane proteins
-permanently associated with cell membrane and can’t be separated from the membrane experimentally without destroyed the membrane itself
Peripheral membrane proteins
-temporarily associated with the lipid bilayer or with integral membrane proteins through weak non covalent interactions. They are easily separated from the membrane by simple experimental procedures that leave membrane in tact.
What do integral membrane proteins consist of?
- include Transmembrane proteins that span the entire lipid bilayer.
- composed of 3 regions
- 2 hydrophilic (one from each membrane face)
- 1 connecting hydrophobic region
How does the the peripheral membrane protein interactions work.
associated with ether internal or external side of membrane.
- play the role of transmitting information received by external signals.
- interact with polar heads of lipids or integral membrane proteins by non covalent interactions.
Where are integral proteins located?
in the membrane
Where are peripheral proteins located?
attached to the outside or inside of membrane
why is the membrane fluid?
molecules move laterally in the membrane so the membrane is fluid
