PBC: Biochemistry

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Lipids

Structurally, 2 discrete sections

Polar, hydrophillic head

Nonpolar, hydrophobic tail

makes the molecule amphipathic: both polar and nonpolar qualities

Fatty Acids: make up the nonpolar, hydrophobic part of the phospholipid

hydrocarbon tail of usually even number of carbons

also has carboxyllic group (pKa ~4.5)

thus under physiological conditions, Acid is **deprotonated**

any double bonds in the acids usually are in cis

these increase unsaturation (monosaturated or polyunsaturated fats)

adding more bonds or increasing chain length: increase the melting point of the fatty acid

Biologically, triglycerides are stored in adipose tissues as fat

derived from the acylation of gycerol

used for E storage, insulation, and heat generation

only somewhat water solvable

Phospholipids

derived from phosphatidic acid

create a lot of variety from the oxygen attached to the PO4 head

these would give it different properties

Organization of Phospholipids

Mycele: hydrophobic tails point to the inside, to make nonpolar interior (outside is hydrophillic to mesh with the water)

Lipid Bilayer: makes for a hydrophobic border, but aqueous core and outside

both sets of hydrophobic tails are facing each other, which means that both phospholipid heads are facing away from each other, thus interacting with like groups

this creates a fluid mosaic layer around the cell, in which lipids and transmembrane proteins can float around in

Mechanism of transport through the bilayer

Passive Transport

based on the concentration gradient

flow is determined by inside concentration and outside concentration

if inside is bigger than outside, free energy is greater than zero --> no flow into the cell, flows out because that process is more spontaneous

Thus, solutes move from areas of high concentration to areas of low concentration

in this case, the transport does not need any help from proteins: it can diffuse through the membrane from HIGH to LOW concentration

Facilitated Diffusion

also goes from high to low (flows down the concentration gradient)

uses proteins to help move solutes through the membrane (probably molecule is not small or neutral enough to flow through the membrane into the cell)

Active Transport

uses energy to move solutes AGAINST concentration gradient (from LOW to HIGH)

uses energy to defy the free energy

ex) Na+/K+ ATPase pump

can allow Na and K to flow against their concentrationg radient

coupled movement allows them to flow against the ELECTROCHEMICAL gradient (not only the concentration gradient but also the gradient based on charge)

forces more Na out of the cell and more K into the cell

ATP movement can also be coupled with secondary molecules to move them into and out of the cell (ie. glucose)

Steroids:

in trans configuration with 6-6-6-5 rings: Flat structure

example: cholesterol:

helpful to maintain membrane stability and precursor to other steroids