Unit 1 Chapter 6: Lipids and Membranes Flashcards
What are the 7 main functions of lipids
- energy storage
- cell membranes
- capture of light energy
- hormones and vitamins
- insulation
- electrical insulation of nerves
- water repellency
Are lipids soluble or insoluble in H2O, why?
insoluble, because they are hydrocarbons, and therefore are non-polar
What is the structure of a fatty acid
a hydrocarbon chain bonded to a hydroxyl
What are the 3 types of lipids found in cells
fats, steroids, phospholipids
What are fats
composed of 3 fatty acids, bonded to glycerol(3C)/ therefore, also called triglycerides
How do fats form
via dehydration between hydroxyl of the glycerol and the caroxyl of a fatty acid
What bond joins glycerol and fatty acids
ester linkage
True/False: fats are polymers and fatty acids are monomers
false
What are steroids
a family of lipids distinguished by their bulky 4 ring structure (differ based on side chain)
What are phospholipids
a glycerol, linked to a phosphate and either 2 chains of isoprene(archaea) or 2 fatty acids(bacteria/eukarya)/phosphate is also bonded to a small charged/polar group
-hydrophilic head/hydrophobic tail
Why are vitamins A and D added to milk
they are lipid soluble
What does amphipathic mean and which lipids have this quality
- to have both hydrophilic and hydrophobic elements
- phospholipids (steroids can also be)
What is the main role of fats
store energy
Which lipids are key components of plasma membranes
phospholipids and steroids
Why do bilayers seal/form an enclosed space
it is energetically favourable
What is a micelle
tiny droplets that form when phospholipid tails are forced together (in a circle)
What is a lipid bilayer
forms when 2 sheets of phospholipids align
Do micelles and lipid bilayers require energy to form
no they form spontaneously
Describe the permeability of the lipid bilayer and what does it mean
highly selectively permeable/ some substances cross the membrane much easier than others
Rank the permeability of substances across the lipid bilayer
small NP molecs> large NP molecs>small polar molecs>large polar molecs>ions
How to phospholipids behave in the bilayer (movement)
in constant lateral motion, very rarely flip to other side of bilayer
What is the difference between sat. and unsat. fats
sat fats are straight chains that stack nicely (max H-atoms), unsat fats have a double bond which creates a kink and prevents them from stacking nicely
How does saturation vs unsaturation affect the lipid bilayr
unsat fats create gaps which increase permeability, sat fats stack and therefore reduce permeability
How are hydrophobic interactions between phospholips tails affected by saturation and length of hydrocarbon chain
interactions weaken in unsat fats (due to gaps)
interactions strengthen in sat fats as length increases
What does adding cholesterol do to membrane permeability
reduces it by increasing density of the hydrophobic section due to its bulky ring structure
How does temperature affect membrane permeability
permeability decreases as temp decreases, as temps drop molecs in the bilayer move more slowly as a result the phospholipid tails pack together more tightly and eventually begin to solidify
Can proteins be amphipathic
yes due to the versatility of their side chains (polar and non-polar)
What is diffusion
the passive mixing of substances ALONG a concentration gradient(high to low), driven by an increase in entropy
Why does diffusion happen
Brownian motion (random walk) due to thermal motions and collisions
What determines rate of diffusion
distance, temp,size of molecule, steepness of conc.gradient
What is osmosis
diffusion of H2O across a semi permeable membrane driven by an increase in entropy
What is a hypertonic solution
higher concentration of solute outside of cell, water flows out, results in cell shrivelling/shrinking
What is a hypotonic solution
higher concentration of solute inside cell, water flows in, results in cell swelling/maybe bursting
What is an isotonic solution
equal concentration of solute inside and outside of cell
What is the hypothesis of the Fluid Mosaic Model
integral proteins are in the actual membrane and peripheral are on the outside
What are artificial membrane experiments used for
determining how fast different solutes can cross the membrane (if at all) when different types of phospholipids are used
What are channel proteins/ion channels
selective specialized membrane proteins that form pores or holes in the membrane that allow ions to move from high to low concentrations and from like charge to unlike charge via diffusion
-pore is hydrophilic, exterior is hydrophobic (at least for water ones anyways)
What is facilitated diffusion
diffusion involving channel proteins and carrier proteins
What are gated channels
channels that open or close in response to the binding of a particular molecule or to a change in the electrical charge on the outside of the membrane
What is passive transport
transport that is powered by diffusion along an electrochemical gradient and does NOT require energy
What are carrier proteins
proteins are involved in facilitated diffusion and that bind to the transported substance and change shape in the process
What happens when all carrier protein binding sites are full
the carrier channel is SATURATED and the rate of diffusion levels off
What is active transport
transport that requires energy and works AGAINST an electrochemical gradient
How does active transport get its energy
from a phosphate group and ATP (phosphate binds to protein, makes ADP, then phosphate unbinds and rejoins ADP to make ATP)
How does the Na/K pump work (primary active transport)
- 3 sodium ions bind
- phosphate from ATP binds which makes the pump change shape
- sodium ions out, 2 potassium ions bind
- phosphate group unbinds which makes pump change shape
- potassium in, cycle repeats
- sets up a concentration gradient that allows other processes to occur
What is secondary active transport (cotransport)
uses established gradients to move substances, ie. our bodies use the energy from the sodium gradient provided from the Na/K pump to move glucose in against its conc.gradient
What is the general function of membrane proteins
to allow ions and molecs that normally do not cross lipid bilayers to enter or exit cells
What are cotransporters
proteins used in secondary active transport
