lecture 4 - lipids and membranes

what are the roles of lipids?

• simple triacylglycerides are a major form of chemical energy storage

• phospholipids form membranes

• lipids can anchor to membranes

• lipids serve as signaling molecules

What are some features of the biological membrane?

• hydrophobic tail and hydrophilic head

• spontaneously form

• asymmetric

• contain cholesterol and protein

What is a saturated fatty acid?

fatty acid with NO double bonds

What is an unsaturated fatty acid?

fatty acid with at least ONE double bond

What is the typical structure of fats/oils?

a glycerol backbone, ester bonds, and fatty acid tails

What kinds of membrane lipids are there?

• phospholipids

• glycolipids

  • cholesterol

What is a phospholipid? What does its structure look like?

A phospholipid is one of the most abundant membrane lipids

What is a phosphoglyceride (type of phospholipid)?

Phosphoglycerides are composed of a glycerol backbone with two fatty acid tails, plus a phosphate and alcohol

What is a sphingomyelin (type of phospholipid)?

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A sphingomyelin is structurally the same as a phosphoglyceride, except the glycerol backbone is replaced as the amino alcohol sphingosine

What are glycolipids?

Glycolipids are a type of membrane lipid that are structurally similar to sphingomyelin, but the hydroxyl group is ether linked to one or more sugars instead of phosphocholine.

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The simplest glycolipid is a cerebroside.

What is a cerebroside (type of glycolipid)?

A cerebroside is the simplest glycolipid, only containing a monosaccharide ether-linked to the hydroxyl group

What is a ganglioside (type of glycolipid)?

A ganglioside is a more complex cerebroside, where they contain branched sugars instead of one monosaccharide

Where are the sugar residues from glycolipids located on the membranes?

Extracellular side

What is cholesterol?

Cholesterol is a membrane lipid that is amphipathic (water loving and hating). Cholesterol is able to prevent extreme membrane fluctuations in hot and cold temperatures due to the large size of the molecule.

What does amphipathic mean?

part hydrophilic and part hydrophobic

What are micelles?

Micelles are molecular aggregates with both hydrophilic and hydrophobic components. Typically shown in circular form. Micelles are useful for the transport of lipids and fat soluble vitamins

How does spontaneous membrane layer formations occur?

Hydrophobic interactions via van der waals attraction of the hydrophobic tails

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Hydrophilic interactions via electrostatic and hydrogen bonding of the hydrophilic heads

What is the difference between a micelle and a liposome?

A liposome has a double layer (bilayer) of lipids that forms an aqueous inner bubble

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A micelle has a monolayer of lipids, with outer hydrophilic heads and a hydrophobic inner bubble

What are some uses for liposomes?

They can be used for DNA and drug delivery

Are lipid bilayers permeable to ions?

no, ions and polar molecules cannot cross without the help of protein complexes

What is a peripheral protein?

Peripheral proteins are found in the periphery of the bilayer, or sometimes partially embedded into the bilayer

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Can be extracted through mild conditions.

What are integral proteins?

Integral proteins are found embedded into the lipid bilayer, they span the entire membrane.

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They can be extracted by detergents.

what is an alpha helical membrane spanning region?

It is a helix of hydrophobic amino acids that act as a transmembrane domain

How can transmembrane proteins be predicted within a hydropathy plot?

THe hydropathy plot contains a threshold that defines hydrophilic from hydrophobic. If a peak goes above the threshold, then that peak counts as one transmembrane domain.

What is a beta barrel?

A beta barrel is a bunch of beta sheets linked together to form ion channels

How can the membrane repair itself?

Using flippases, floppases, and scramblases

How does the membrane change in fluidity if the temperature increases?

The membrane will become more fluid

How does the membrane fluidity change if the temperature decreases?

The membrane becomes more packed and ordered

If a lipid has double bonds (unsaturated), what phase would the lipids be in?

liquid

If a lipid has no double bonds (saturated), what phase would the lipids be in?

solid