Lipids & Membranes intro Flashcards
What are lipids?
• Major class of biomolecules
What makes lipids different from other macromolecules?
- soluble in organic solvents, but barely in water if at all
- non-polymeric, don’t forms polymers
- instead they associate together by non covalent forces
What are some examples of lipids ?
(Not generally found in membranes:)
• Free fatty acids (intermediates in biosynthesis)
• Triglycerides (high energy storage)
(membrane lipids)
• Phospholipids (phosphoglycerides, sphingolipids)
• Steroids (ie cholesterol)
What are free fatty acids?
They are monocarboxylic acids ionised at neutral pH when free
(most are weak acids)
They are building blocks of lipids and a starting point for biosynthetic pathways
What is the chain length of fatty acids and what are they used for?
They have variable chain lengths of 2-24 C atoms:
• Most commonly 16-18C
• Short chain 2-6C (fermentation of fibre in the colon)
• Medium chain 6-12C (many plant oils)
in mammals chains are always linear.
saturated = single bonds
unsaturated = one or more double bonds
Give some examples of fatty acids
• Palmitic acid
• Stearic acid
• Oleic acid
• Linoleic acid
What is the importance of double bonds in fatty acids?
Saturated fatty acids (single bonds) are flexible and can ‘flap around all over the place’ gives narrow width, however unsaturated becomes bulky due to double bonds
In unsaturated fatty acids, are trans or cis forms more energetically stable?
Trans
In unsaturated fatty acids, is cis or trans forms found in naturally occurring fatty acids?
Cis
In unsaturated fatty acids, is cis or trans forms made by ruminant digestion?
Trans fatty acids
In unsaturated fatty acids, is cis or trans forms mostly made in industrial hydrogenation of vege fats?
most dietary Trans fats made there
What are the health implications of dietary trans fats?
• increase in cardiovascular diseases
What determines the mp of fatty acids?
• MP increases w chain length due to more overall attraction/bonds/vdws
• Decreases w number of double bonds due to vdw further so weaker/fewer bonds to line up
• cis lower than trans
What are examples of Arachidonic acid derived signalling molecules and what are they used for?
• Prostaglandin (uterine contractions
• Thromboxane (blood clotting)
• Leukotriene (blood clotting)
• Anandamide (Endocannabinoid)
• Tetrahydrocannabinol (Phytocannabinoid)
What is triglyceride composed of?
one glycerol and three fatty acid chains
What are triglycerides used for?
Bodys major energy store- fat more efficient at storing calories than glycogen.
Where does the body store triglycerides?
Adipose cells
Fats an oils are triglycerides. Differentiate the two:
• Fat are solid at room temp, oils liquid
• fat has high proportion of saturated fatty acids, oils unsaturated
• fat is linear (interactions w neighbouring chains), oils are kinked (fewer interactions w neighbouring chains)
• fats are often animal origin, oils are often plant origin
What is the general structure of phosphoglyceride?
Glycerol, 2 fatty acids, phosphate group + alcohol
(gives hydrophilic head and hydrophobic tail)
What are the alcohol substituents in phospholipids and their resulting name?
• Choline (phosphatidylcholine)
• Serine (phosphatidylserine)
• Ethanolamine (phosphatidylethanolamine)
• Inositol (phosphatidylinositol)
What are sphingolipids?
• Similar shape and properties but built around sphingosine (rather than glycerol like phosphoglycerides)
• simplest sphingolipids are ceramides (have polarity)
• often glycosylated to form complex glycolipids (ie gangliosides and cerebrosides)
- always found on outer leaflet of plasma membrane
- carb exposures sed externally and role in cell recognition
Membrane lipids self assemble to form bilayers. How does this help
The lipids in membranes determines its fluidity and symmetry to make the membrane intrinsically impermeable to hydrophilic solutes and ions
membrane lipids are very insoluble in water- instead it emulsifies
What happens to entropy during interaction of hydrophobic molecules and water?
Entropy decreases
What is the hydrophobic effect?
Entropy increases in water from:
• Dispersion of lipids (lowest entropy)
• clusters of lipids
• micelles (highest entropy)
Why do lipid bilayers spontaneously close to form sealed compartments?
More energetically favourable as sealed form
What makes membranes flexible?
Phospholipids can move within the plane
What affects membrane fluidity?
Fatty acid compositions: the length of chains and no. double bonds
(ie fats have less membrane fluidity whereas oils have more)
What decreases membrane fluidity?
Cholesterol
Why is membrane fluidity important?
• membrane proteins can move rapidly within the bilayer
• membrane lipids and proteins can diffuse from sites of insertion/synthesis
• membranes can fuse with one another
• membrane molecules can be shared during cell division
What allows transport between cellular organelles?
membrane vesicles
Phospholipid bilayers have low permeability to solutes and ions, give examples for different molecules and how they interact w membranes
The smaller the molecule and fewer favourable interactions with water the more rapidly it diffused across the lipid bilayers
• small non polar molecules diffuse easily (O2, CO2, N2, steroids & hormones)
• small uncharge molecules diffuse not quite as easily at slow rate(H2O, ethanol, glycerol)
• Larger uncharged polar molecules have very low permeability and require protein transport channels (amino acids, glucose, nucleosides)
• Ions have no permeability so require channels (H+, Na+, K+ etc)
