MCAT Lipids Flashcards
Lipids are amphipathic ( ampihlilic) what does this mean?
They have a hydrophobic and hydrophilic properties (hydrophobic tails and hydrophilic heads).
What happens when liposomes are put into aqueous solution?
Lipids form lipid droplets in cells where free fatty acids form micelles.
How is fats used for energy by the cell?
Via beta- oxidation in either the mitochondria or peroxisomes. Involves creating acetyl- coa from carbons 1 and 2 and the beta carbon is oxidized.
Describe the shape of fatty acids?
They have a carboxylic acid head group (carboxylate ion at physiological pH) and a long chain of carbons that can be saturated ( with hydrogens ) or unsaturated ( contains double bonds).
For unsaturated fatty acids the double bonds almost always form cis bonds.
Does unsaturated or saturated fatty acids have a higher melting point?
Saturated fatty acids have a higher melting point than unsaturated fatty acids because saturated fatty acids can extend and minimize steric hinderance.
What is the main role of triaclyglycerides in the cell?
They’re structures of three fatty acid chains linked via an ester linkage to glycerol. Primarily serve as energy storage in animals.
How are triaclyglycerides stored in animal cells?
In oily droplets called adipocytes, energy release from them is slower and so this energy is used for longer- lasting energy over a long time.
Describe the structure and use of waxes?
They’re structures of long chain saturated or unsaturated fatty acids joined with a long chain alcohol.
They’re used in many organisms as a water- repellant.
What are peripheral proteins?
Structures that stick to the membrane and so their interactions with it isn’t very strong. Can be removed by chelating agents, urea, changing to pH, or carbonate.
Electrostatic interactions with the plasma membrane
Integral proteins
Proteins embedded in the membrane (transmembrane proteins). Will not come out of the membrane unless you use a detergent.
Amphoteric proteins
Proteins that can be associated with the membrane and sometimes not.
Describe the structure of phosphoglycerides ( glycerophospholipids)
They are structures with a glycerol backbone with 2 fatty acid chains linked to the glycerol via an ester linkage and a phosphate group linked via phosphodiester linkage.
They play an important role in cell signaling, recognition, and binding.
Sphingolipids
Lipids that has -OH, -NH2, -OH groups followed by a long change unsaturated fatty acid chain.
Various groups attaches to those groups.
Serve sites of biological recognition
Describe the structure of steroids.
They have 2 cyclohexane rings with a pentane ring attached.
Steroid hormones are hydrophobic and serve as hormones.
Cholesterol
A steroid that plays an important role in plasma membrane fluidity.
- At low temperature is keeps membrane from solidifying.
- At high temperatures it keeps membrane from become too fluid.
Role of terpenes and terpenoids
Precursors to steroids and other signaling molecules. They’re built from isoprene.
Terpenoids are derivatives of terpenes that has gone oxygenation or rearrangement of the carbon skeleton.
Prostaglandins. Role of prostaglandins.
20 carbon unsaturated carboxylic acid that contains a 5-carbon ring, they’re derived from arachidonic acid.
- Serves a role in paracrine and autocrine signaling.
- Regulates synthesis of CAMP.
What is the fat- soluble vitamins?
A,D,E,K
Vitamin A ( carotene)
Important in vision, growth and development, and immune function.
Retinal is important for vision.
Retinol when oxidized to retinoic acid is important in epithelial gene expression during development.
Vitamin D
Either obtained by diet or UV reactions in the skin. In the liver and kidneys vitamin D is converted to calcitriol which increases calcium and phosphate uptake in the gut increasing production of bone.
Vitamin E
Contains tocopherols which has an aromatic ring which destroys free radicals. This helps with aging and to deter cancer.
Role of Vitamin K
Important in posttranslational modification of prothrombin which is involved in the blood clotting cascade.
Also responsible for presenting calcium binding sites on calcium- dependent proteins.
Sphingomyelins
Sphingolipids that are involved in myelin.
Describe the plasma membrane?
It’s a semipermeable membrane in that it chooses what enters and exits the cell. It’s a phospholipid bilayer. Described by the fluid mosaic model.
Describe the fluid mosaic model
Term used to describe the plasma membrane. It’s fluid in that the lipids can move very fast via simple diffusion and the membrane is composed of various proteins, carbohydrate, and lipid projections.
Lipid rafts
Their a mass of similar lipids and associated proteins. That play an important role in cell signaling.
Flippases
Enzymes that exist in the flipping of a lipid from one layer to the next through the hydrophobic interior ( enzyme must help because of the polar head group going through the hydrophobic interior).
Membrane receptors
When a ligand binds it participates in facilitated diffusion or active transport.
Cell- cell junctions
connections between adjacent cells that allows for direct cell communication and forms a cohesive layer.
Generally composed of cell adhesion molecules (CAMs) which allows the cells the recognize each other.
What role does carbohydrates have on the cell membrane?
Cell signaling and cell recognition
Gap junctions
Allows for direct cell communication.
Connexons
Allow for the transport of water and small molecules. Composed of 6 molecules of connexin.
Tight junctions
Prevent leakage in-between cells. Found in epithelial cells.
Desmosomes
Attaches cells together by anchoring to their cytoskeletons. Transmembrane protein attached to intermediate filament of another cell.
Usually found at the interface of two epithelial layers.
Hemidesmosomes
Anchors epithelial cells to the underlying basement membrane.
Role of the cell membrane
Controls what enters and exists the cell. Small, nonpolar compounds rapidly diffused through while large, polar compounds must be transported across.
Movement is controlled by intracellular energy stores and concentration gradients.
