Ch 10 Membranes Flashcards
Who has cholesterol?
Eukaryotes only, not prokaryotes! (Ex: bacteria)
Define amphipathic/amphiphilic?
Having one polar end and one nonpolar end (ex: membrane lipids )
What are membranes composed of?
50% lipids, 50% proteins 
Where are membranes found? 
Separating the cell from the outside, and separating the internal parts of the cell. For example, the nucleus, lysosomes, the Golgi apparatus, the mitochondria, and the endoplasmic reticulum 
What makes a cell a cell? 
The membrane! Its what separates the cell from the water in the outside, and from the being flooded 
What are omega’s? What do the three and six mean? 
Omega’s are unsaturated fatty acids! The three or the six depends on where the double bond is counting from the methyl end towards the carboxyl end of the fatty acid 
Cis versus trans fatty acid?
CIS fatty acid creates a kink, which means they don’t fit as tightly together so stays liquid at room temp. Trans. Fatty acid is not naturally occurring causes no kink, and it only resulted from hydrogenation 
What are fatty acids?
 Long chain hydrocarbons. Either unsaturated or saturated. 
Aspartic acid?
Abbreviation: ASP
Letter: D
Side chain : negative 
Glutamic acid?
abbreviation: GLU
Letter : E
Side chain : negative
Arginine?
Abbreviation: ARG
Letter : R
Side chain : positive
Lysine?
Abbreviation: LYS
Letter : K
Side chain : positive
Histidine?
Abbreviation: his
Letter : H
Side chain : positive
asparagine ?
Abbreviation: ASN
Letter: N
Side chain: uncharged polar
Glutamine?
Abbreviation: GLN
letter: Q
Side chain: uncharged polar
Serine?
abbreviation: SER
Letter: s
Side chain : uncharged polar
Threonine?
abbreviation: THR
Letter : T
Side chain : uncharged polar
Tyrosine?
Abbreviation: TYR
Letter : Y
Side chain : uncharged polar
Alanine?
Abbreviation: ala
Letter: A
Side chain : nonpolar
Glycine?
Abbreviation: GLY
Letter : G
Side chain : non-polar
Valine?
Abbreviation: VAL
Letter : V
Side chain: nonpolar
Leucine?
Abbreviation: Leu
Letter : L
Side chain : nonpolar
Isoleucine?
Abbreviation: ILE
Letter : I
Side chain : nonpolar
Proline?
Abbreviation: PRO
Letter: P
Side chain : nonpolar
Phenylalanine?
abbreviation: PHE
Letter: F
Side chain : non-polar
Methionine?
Abbreviation: MET
Letter:M
Side chain: non-polar
Tryptophan?
Abbreviation: TRP
Letter : W
Side chain : nonpolar
Cysteine?
Abbreviation: CYS
Letter: C
Side chain : non-polar
What does a condensation reaction require?
A ribosome to catalyze, and ATP 
Liposome vs micelle?
Liposome: has aqueous center and a double layer of phospholipids (a sealed, ball shaped, bi-layer)
Micelle: hydrophobic center, one layer ball shaped, made up of single tail with single polar head (ex:soap)
How do detergents disrupt membranes?
They kill bacteria’s cell membranes bc they are amphipathic, so disrupts membrane integrity
Is the lipid bilayer fluid? How was this proven?
Yes, mostly. Proven by membrane proteins shown to move around via cell fusion and (FRAP) photobleaching then watching. Also by laser tweezers pulling it.
What 4 types of motion are always occurring in the lipid bilayer ?
- Lateral diffusion (lipids swing back and fourth on one plane.
2.) Flexion (wiggling tails)
3.) Rotation (spinning around axis)
4.) Flip flop (rare,flips lipid on top/bottom. Energy expensive, needs enzyme)
What is three factors affect fluidity?
1.) Saturation (biggest effect)
increasing saturated leads to lipids being packed more tightly, decreasing movement (the more unsaturated the more kinks so can move around more)
2.) Temperature
Increase temperature increases movement
(Even sat fats can be melted)
3.)Hydrocarbon chain length (bigger tails=less movement)
How does winter wheat survive?
It increases proportion of unsaturated fatty acids, which allows it to stay colder and liquid and yet not freeze so can still function .
What does Cholesterol do in eukaryotic cells?
(20% of animal membrane lipids, but not a phospholipid )
-packs between phospholipids
-at high temps: raises the melting point (keeps membrane solid, stabilizes)
-at low temps: prevents freezing (keeps liquid to keep fluidity, stabilizes)
What is the structure of cholesterol?
An OH polar head, 4 steroid rings in middle, non-polar tail. (Amphipathic like phospholipids) smaller than normal phospholipids bc is a sterol, has little polar head and shorter non polar tail.
What are lipid rafts?
Distinct domains that form when cholesterol is present, and have decreased fluidity compared to the rest of the membrane.
-“local regions on membrane where fluidity is decreased”
-an Amazon warehouse that stores the proteins and things needed nearby so it’s ready quick when a specific function is needed.
What does it mean that the Lipid bilayer is Asymmetrical ?
The inside layer is not the same as the outside layer! Certain things are distributed on certain sides of the membrane, to perform certain functions.
What are the four components to a phospholipid structure?
1: amino acid head (ex:serine)
2: phosphate group (held by ester bonds)
3: glycerol backbone
4: two hydrocarbon tails
What components make up a glycolipid?
sugar attached to O attached to glycerol backbone, which is attached to both OH polar head and two non polar hydrocarbon tails
What are two types of phospholipids?
N
What charge is present on the inside of the membrane?
A negative charge! This makes it easier to dissolve via empathic substances, like detergents, because attracts the charge
Scramblease versus flippase?
Scramblease: scrambles, so Serine is on the outside, signaling for cell destruction (apoptosis)
Flippase: flips serine from outside to inside to protect the cell from apoptosis!
How does membrane asymmetry distinguish between live cells and dead cells? 
Because the type of lipids on the outside versus the inside signal, life or death (ex:serine)
What is a glycolipid? 
Sugar groups, covalently attached to membrane phospholipids. Create sugar border on the outside of cells with the function to facilitate cell to sell recognition.
(Anything with glycol/sugar will always point outwards of the membrane)
What do membrane proteins do?
Control, cellular access and activity. Proteins are 50% of the plasma membrane.
What are the four types of membrane proteins?
1: transporters: move things across the membrane
2: anchors: keep specific parts of the membrane, where it needs to be for a specific function
3; receptors: takes external signal and transforms it to an internal meaningful signal
4: enzymes: do tasks inside the cell
(Tare)
What are peripheral membrane proteins?
Loosely associated with the membrane not actually embedded. Usually interact via protein to protein interactions (bonding) with an integral membrane protein.
What are integral membrane proteins?
Embedded in membrane in some form
What are the three types of integral membrane proteins?
1: transmembrane: goes through membrane, nonpolar, because needs to be able to pass through the membrane seven times from one side all the way to the other.
2: mono layer associated: embedded on one side of the membrane, but not all the way through, somewhat nonpolar
3: lipid linked: attached to a lipid, that is already in the membrane.
What shape are trans membrane proteins?
(integral membrane proteins)
Alpha, helix, consisting in its majority of non-polar proteins, no center of the helix, but rather nonpolar on every side. How together by hydrogen bonds
What shape are transmembrane porins? Aka “beta barrels”
The form a barrel, which is like a tunnel, made up of beta sheet proteins. This barrel is polar on the inside, in order to allow the aqueous liquids on either side of the membrane to pass through. However, the external outside of the barrel is nonpolar in order to allow it to pass through the hydrophobic membrane. 
What is the hydropathy index?
The measure of how much energy it takes to force an amino acid into water.(if negative the amino acid is polar, if it is above zero, the amino acid is non-polar)
How to read hydropathy index on a chart?
Dark green regions indicate nonpolar regions with a value above the zero line. Light green regions indicate polar molecules with a value below zero line. The number of peaks are the number of past trans membrane proteins that are present. For example, if there are seven peaks then there are seven transmembrane segments on that protein 
How are computational programs able to predict membrane protein topology?
Because amino acid sidechain chemistry can be used to predict hydrophobicity, and the likelihood of membrane localization
What are four reasons some membrane proteins have limited movement?
1: self assembled aggregates: for example, lipid raft. Chemically attracted to each other, and therefore self aggregate.
2: tethered to intracellular molecules: something inside the cell can hold these proteins in place
3: tether to extracellular matrix: something outside the cell can hold these proteins in place
4: attachment to proteins on other cells
What are membrane domains?
Specialized areas of cell membranes in which membrane proteins are restricted in movement
Polarized cell versus non-polarized cell?
polarized cell; has different “poles” (like north/south) that has specific domains/sides for different jobs.
Non-polarized cell : Random, even, distribution of proteins throughout the cell
What is an example of a polarized cell that has membrane domains?
An epithelial cell!
-Has three different membrane domains with different jobs and different proteins
1: apical plasma membrane: on top with protein A (with a job that is likely to grab glucose)
2: lateral plasma membrane: the horizontal membrane that separates the apical and the basal with protein B present (who’s job is likely to expel glucose)
3: basal plasma membrane: the bottom membrane with protein B
What does it mean if the bilayer has “two dimensional fluid”
The lipids travel across one one the sides of the membrane, they do not cross over to the other (no flip flop)
Plasma membrane versus internal membrane?
Plasma membrane: encases the cell
Internal membrane : encloses and intracellular compartment (for example: the Golgi complex the mitochondria the nucleus)
Where are the internal membranes? (7)
The endoplasmic reticulum, the nucleus, peroxisomes, lysosomes, the Golgi apparatus, mitochondria, transport vesicles
How are the different components of a phospholipid held together?
Esther bonds
Explain the structure of a glycolipid?
A glycerol backbone, with an OH, polar head attached to the leftmost carbon, and a sugar attached to an oxygen that is attached to the right most carbon
The two left carbons on the glycerol then attached to two hydrocarbon tails with an NH and a double bond O on one attachment.
What are the two main categories of phospholipids?
1: Phosphoglycerides ( most common in animal cells)
2: sphingolipids (doesn’t have the -O ester bonds separating glycerol and the fatty acid chain
Why can’t phospholipids form mycelles?
Because they have two hydrophobic tails, not one
How many hydrophobic tails does cholesterol have?
One
What is a membrane domain?
Distinct domains with decreased fluidity, compared to the rest of the membrane. Forms when cholesterol is present.
How does cholera sneak into our cells?
It will bind to a specific sugar on the membrane of the cell
What form do transmembrane proteins usually take?
Alpha helixes! (more common than transmembrane porins/beta barrels)
What do beta barrels allow in and out of the cell?
Small molecules and water
What do you call sections on a hydropathy index that have a positive value and are dark green?
Transmembrane segments (a.k.a. Non-polar)
What can amino acid sidechain chemistry be used to predict?
Hydrophobicity and the likelihood of membrane localization
What is the structure of glycerol?
Ch2-Ch2-Ch2. When linked to fatty acid tails via ester bonds it becomes Ch2-Ch2-Ch2
O O
(Third C has O above it linked to phosphate group)
What is the main phospholipid in most animal cells?
Phosphoglyceride with 1 saturated and 1 unsaturated fatty acid tail
(3:phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine) different based on head groups
Sphingolipid vs glycolipid?
Glycolipid =glycerol backbone
Sphingolipid= spingosphibe backbone
What are the two types of phospholipids?
Phosphoglycerides and sphingolipids
What are the three types of membrane lipids?
Phospholipids, sterols, and glycolipids
