Biochem 2: Lipids and Membranes Flashcards
lipids are a
heterogeneous class of naturally occurring organic compounds
- insoluble in water but soluble in operatic organic solvents
- some are amphipathic
forms of lipids include (2)
- open chain forms
- cyclic forms
open chain forms of lipids
- fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids
- lipid soluble vitamins
- prostaglandins, leukotrienes, and thromboxanes
cyclic forms of lipids
-cholesterol, steroid hormones, and bile acids
fatty acids are
an unbranched chain carboxylic acid, most commonly of 12-20 carbons
examples include oleic, palmitic, and linoleic
shorthand notation for fatty acids is
carbons : # double bonds
saturated vs. unsaturated
double bonds= saturated (kicks, more tightly packed together, higher melting points)
single bonds - unsaturated
the greater the degree of unsaturation, the _____ the melting points
lower
in most unsaturated fatty acids, the ____ isomer predominates, the ____ isomer is rare
cis isomer predominates
trans isomer rare
triacylglycerol (triglyceride) is an
ester of glycerol with three fatty acids
hydrolysis of triglycerides
can be hydrolyzed with base to yield glycerol and soaps
lipases are enzymes that:
hydrolyze esters in triglycerides
phosphoacylglycerols abundance and where they are found
second most abundant group of naturally occurring lipids, and they are found in plant and animal membranes
phospholipases are
enzymes that hydrolyze specific bonds in phospholipids
what are waxes made up of
a complex mixture of esters of long-chain carboxylic acids and alcohols
where are waxes found
as protective coatings for plants and animals
sphingolipids contain _____ and are found in
sphingosine- a long chain amino alcohol
-found in plants and animals, abundant in nervous system
(structural similarity to phospholipids)
glycolipids
a compound in which a carbohydrate is bound to an -OH group of the lipid
the sugars in glycolipids are mostly
glucose or galactose
-many glycolipids are derived from ceramics
glycolipids with complex carbohydrate that contains more than 3 sugars are known as
gangliosides
structure of steroids
a group of lipids that have fused-ring structure of 3 six-membered rings, and 1 five-membered ring
the molecular basis of membrane structure is in lipid components, describe them
- polar head groups are in contact with the aqueous environment
- nonpolar tails are buried within the bilayer
the major force driving the formation of lipid bilayers is
hydrophobic interaction
the arrangement of hydrocarbon tails in the interior can be either
rigid or fluid
- rigid if rich in saturated fatty acids
- fluid if rich in unsaturated fatty acids
plant membranes have a ____ percentage of unsaturated fatty acids than in animal membranes
higher
the presence of cholesterol is characteristic of ____ membrane
animal
_____ membranes are less fluid (more rigid) than ____ membranes
animal membrane are less fluid/more rigid
the membrane of _____ which contain no appreciable amounts of steroids, are most fluid
prokaryotes
functions of membrane proteins
- transport substances across membranes
- act as receptor sites
- and sites of enzyme catalysis
integral vs. peripheral proteins
- integral are embedded in the lipid bilayer
- peripheral are only loosely associated with the membrane
what is passive transport and what are the types
passive transport is driven by a concentration gradient
-simple diffusion and facilitated diffusion
simple vs. facilitated diffusion
both passive transport
- simple diffusion: a molecule or ion moves through an opening
- facilitated diffusion: a molecule or ion is carried across a membrane by a carrier/channel protein
active transport and types
active transport is a substance moved against a concentration gradient
-primary active transport and secondary active transport
primary active transport
transport is linked to the hydrolysis of ATP or other high energy molecule (for example Na+/K+ pump)
secondary active transport
driven by concentration gradient established by primary active transport
channel proteins vs. ion channels
- channel proteins: integral membrane proteins that form a channel
- ion channels: channel proteins with hydrophilic pores
most channel proteins are ___
gated
can be closed or open to ion passage
channel protein gate opens when:
ligand vs. voltage gated
protein is stimulated to change shape by a chemical signal (ligand) or an electrical charge difference (voltage-gated)
function of vitamin A
serves as the site of the primary photochemical reaction in vision
function of vitamin D
regulates calcium (and phosphorus) metabolism
function of vitamin E
serves as an antioxidant and is necessary for reproduction in rats and may be necessary for reproduction in humans
function of vitamin K
has regulatory function in blood clotting
what is the precursor for vitamin A (retinol)
beta-carotene
beta carotene -> vitamin A requires
enzyme-catalyzed cleavage of beta-carotene followed by reduction (gives 2 molecules of vitamin A)
what is rhodopsin and what is it required for
rhodopsin is a pigment required for vision that is made from vitamin A
what is the active molecule for rhodopsin formation and what does it react with?
the active molecule is retinal (vitamin A aldehyde) and it reacts with the protein opsin to form rhodopsin
the primary chemical event of vision in rod cells is
absorption of light by rhodopsin followed by isomerization of the 11-cis double bind to the 11-trans double bond
what is vitamin D and what is it used for
a group of structurally related compounds that are involved in the regulation of calcium and phosphorus metabolism
what is vitamin E used to trap and how were those formed ?
vitamin E is an antioxidant which traps HOO and ROO radicals formed as a result of oxidation by O2 of unsaturated hydrocarbon chains in membrane phospholipids
what is vitamin K made of and what is it used in
vitamin K has an important role in the blood-clotting process
-made of long unsaturated hydrocarbon side which consists of repeating isoprene units
