Ch. 8 Lipids and Membranes Flashcards
Criteria to classify a compound as a lipid
-Water-insoluble bio compounds in which some contain polar neutral or polar charged groups but the bulk of their structure is hydrocarbon like
Fatty acids
Properties: they are long-chain carboxylic acids and have up to 24 carbons
Classification based on absence or presence of double bonds: Fatty acids in the absence of double bonds are considered saturated with hydrogens and are straight linear shaped (examples palmitate & stearate). In the presence of double bonds fatty acids are considered to be monounsaturated or polyunsaturated ( examples oleate & linoleate) Double bonds are usually in the cis conformation and kink the acyl chain preventing the efficient packing with neighbors
Identify omega fatty acids:
- Is an essential fatty acid and has a double bond starting three carbons from its methyl end so the last carbon in the fatty acid chain is called the omega carbon. Fish oil is an example of a omega-fatty acid
Triacylglycerols
Other names: triglycerides
Components: triglycerides have glycerol backbones
Identify ester linkages: located linking each acyl group at the end of the triglycerol chain. There are 3 fatty acids esterified to the three hydroxyl groups of glycerol
Distinguish fats and oils and their origin and properties:
Fats (found in animals): solids @ room temp, 2/3 or 3/3 chains will be saturated, high m.p + b.p
Oils(found in plants): liquid @ room temp,2/3 or 3/3 chains unsaturated, low b.p
Glycerophospholipids
Identify them: Amphipathic with hydrophobic tails attached to polar or charged groups
Identify individual components
Identify linkages in them: Glycerol backbone with fatty acyl groups at positions 1 and 2 with a phosphate head group.
Specificity of phospholipases: help digest and cleave glycerophospholipids at specific sites, they are known as phospholipase A1, A2, C, D
Sphingolipids
Identify individual components: has sphingosine as the backbone. Sphingosine is made of serine and palmitate
Sphingophospholipids: have a polar head group(phosphocholine) and an acyl group
Identify linkages in them:
Distinguish cerebrosides and gangliosides
-Cerebrosides even though they do not have a charge it is polar neutral and still in the phosphate lipid bilayer. Cerebrosides have monosaccharides as head groups and they are amphipathic
-Ganglioside: Have oligosaccharides as head groups instead of phosphates.
Cholesterol
Structure and properties
- Cholesterol isn’t amphipathic and it is an important component of membrane lipids
- It is stored in the membrane and reduces its fluidity for the lipid bilayer because without it the bilayer would be flexible
- It is the most common steroid and is the precursor to all other steroids. It is also found in all animal cells
Waxes
Components and function
- Is a part of the lipid family. Esters made of a fatty acid and a very long alcohol
- Waxes function is to serve as water proofing agents. (i.e. beewax is an ester of palmitate and a 30-carbon chained alcohol.
Lipids bilayer
Structure and properties
-Lipid bilayers have two fatty acid tails. It is an array of amphipathic molecules whose tails associate with each other, out of contact with water, and whose head groups interact with water.
- Lipid bilayer is a fluid structure
Membrane proteins
Types: integral, peripheral, lipid-linked bilayer
Properties: Most proteins have a polar side and are globular shaped. No hydrophobic surfaces. Integral and lipid-linked proteins are more common. They are also mainly modified with carbohydrates attached to them.
Membrane proteins can span into the bilayer. They can also form a 7-helixes arrangement seen in bacteriorhodopsin and then form beta-barrel
The fluid mosaic model
Components: has extracellular space, protein, and carbohydrates
- Integral membrane proteins float in a sea of lipids and can move laterally but can’t undergo transverse movement. Carbohydrate chains of glycolipids and glycoproteins
