Chapter 11 Flashcards
what is plasma membrane and two functions
selective barrier separating cell contents from exterior
functions
-recognition
-import/export of small molecules
prokaryotes have ___ plasma membrane while eukaryotes have ___
one while euk have many
plasma membrane approx thickness
5-10 nm thick
what is special about nuclear and mitochondrial membranes
contain their own unique DNA
if you place pure phospholipids in water ______ are formed
liposomes
a bilayer of ____ forms the backbone of the plasma membrane and which types and most abundant
lipids
types:
- phospholipids (most abundant)
- cholesterol
- glycolipids
3 key components of cell membrane
-lipids
-proteins
-carbohydrates
fluid mosaic model
singer and nicolson (1972)
-proposed membranes were not rigid/composed of a lipid bilayer where proteins are embedded and float freely
what is the phospholipids structure
- a glycerol molecule
- two fatty acid tails (hydrocarbon chains) with COOH at end
- phosphate group
- polar group (choline polar group)
how long are fatty acid tails in human cells
typically 18-20 carbons
in the phospholipid structure describe the heads vs tails
heads - hydrophilic (polar)
tails - hydrophobic (non-polar)
what is amphipathic
has both hydrophilic and hydrophobic parts
what are the two categories of proteins found in membranes
integral and peripheral
(integral are integrated in membrane)
membranes are _____ and they do what ? what kind of diffusion?
fluid
they move, vibrate, spin, and exchange places within bilayer
lateral diffusion
how are membranes fluid
the phospholipids are NOT held together by covalent bonds, rather weaker HYDROPHOBIC INTERACTIONS stabilize them which allows movement
is it common for phospholipids to naturally flip from one side to the other?
no it’s very rare
proteins and phospholipids are constantly _____
moving
3 factors that affect membrane fluidity
- temperature
- fatty acid tail composition (saturation & length)
- cholesterol content
how does temperature affect membrane fluidity
↑ temperature = ↑ membrane fluidity (membrane becomes leaky)
↓temperature = ↓ fluidity (becomes gel like)
how does fatty acid tail saturation affect membrane fluidity
↑saturation = ↓ fluidity
unsaturated vs saturated
unsaturated = fluid
- double bonds cause tails to have kinks
saturated = not fluid (viscous)
- phospholipids packed tightly together
how does fatty acid tail length affect membrane fluidity
↑length = ↓fluidity
what enzyme can add double bonds to fatty acid tails (turn saturated into unsaturated)
desaturase
when temp is high you want to ____ saturation
increase
when temp is low you want to ____ saturation
decrease
which tail length is good for low vs high temps
low temps = want shorter chains (↑fluidity)
high temps = want longer chains (↓fluidity)
what does cholesterol do for the membrane
acts as a buffer & helps maintain constant fluidity (animal cells)
how does cholesterol affect membrane fluidity
- STIFFENS bilayer
present at high temps to avoid being too fluid as
-PREVENTS TIGHT PACKING of phospholipids
avoids crystallization at low temps
cell membrane is ___ symmetrical and this means what
NOT
- each monolayer has a distinct set of phospholipids and proteins (particularly important for proteins)
glycolipids only found on ____ side
ECF (extracellular fluid)
phosphatidylcholine mainly found on ___ side
ECF side
phosphatidylinositols are involved in ___ and pases signals on ___ side
cell signalling and passes signals on cytosolic side
cholesterol molecules distributed on ____ leaflets
both
scramblases
randomly moves phospholipids from one side to another
- work in the ER
how does asymmetry of the membrane result?
flippases = select specific phospholipids and move them to the appropriate bilayer
membranes are synthesized in the ____
E.R
lumen side will become the ____ monolayer while cytosolic side will ___
lumen - becomes exterior
cytosolic - remain facing cytosol
how are membranes a mosaic model ?
lipids - backbone
proteins - determine function
4 categories of membrane proteins
- transmembrane
- monolayer associated alpha helix
- lipid linked
- protein attached peripheral
what are transmembrane proteins (3)
- non polar/ hydrophobic
- in the membrane
- alpha helix shape to maximize number of hydrogen bonds
describe hydrophobic vs hydrophilic in transmembrane protein beta barrel porins
- hydrophilic AA line the inside of the barrel (allow water to pass thru)
-hydrophobic AA face the fatty acid tails
alpha helices are _____
amphipathic
describe monolayer associated alpha helix (2)
- almost entirely on cytosolic side
- anchored by an amphipathic alpha helix
describe lipid linked proteins (3)
- found outside of bilayer
- secured thru one or more covalent attachments to phospholipids
- on either side of the membrane
describe protein attached peripheral proteins (3)
- attached to other membrane proteins
- can be on either side
- DONT need a detergent to remove
describe cell membrane cortex
- meshwork of fibrous proteins attached to transmembrane proteins that adds strength and support to plasma membrane
in vivo cells ____ movement of proteins
restrict
describe glycocalyx (3)
-exterior sugar coating of plasma membrane
- on lumen side
- helps with cell recognition & protection from mechanical damage
glycolipid vs glycoprotein vs proteoglycans
(all included in glycocalyx)
lipid
- carbohydrate attached lipid
protein
- carbohydrate attached protein
proteoglycans
-sub category of glycoprotein (help protect)
what is glycosylation
attachment of carbohydrate to the backbone of a protein
