MCAT Lipids

Question 1

Lipids are amphipathic ( ampihlilic) what does this mean?

Answer 1

They have a hydrophobic and hydrophilic properties (hydrophobic tails and hydrophilic heads).

Question 2

What happens when liposomes are put into aqueous solution?

Answer 2

Lipids form lipid droplets in cells where free fatty acids form micelles.

Question 3

How is fats used for energy by the cell?

Answer 3

Via beta- oxidation in either the mitochondria or peroxisomes. Involves creating acetyl- coa from carbons 1 and 2 and the beta carbon is oxidized.

Question 4

Describe the shape of fatty acids?

Answer 4

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.

Question 5

Does unsaturated or saturated fatty acids have a higher melting point?

Answer 5

Saturated fatty acids have a higher melting point than unsaturated fatty acids because saturated fatty acids can extend and minimize steric hinderance.

Question 6

What is the main role of triaclyglycerides in the cell?

Answer 6

They’re structures of three fatty acid chains linked via an ester linkage to glycerol. Primarily serve as energy storage in animals.

Question 7

How are triaclyglycerides stored in animal cells?

Answer 7

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.

Question 8

Describe the structure and use of waxes?

Answer 8

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.

Question 9

What are peripheral proteins?

Answer 9

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

Question 10

Integral proteins

Answer 10

Proteins embedded in the membrane (transmembrane proteins). Will not come out of the membrane unless you use a detergent.

Question 11

Amphoteric proteins

Answer 11

Proteins that can be associated with the membrane and sometimes not.

Question 12

Describe the structure of phosphoglycerides ( glycerophospholipids)

Answer 12

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.

Question 13

Sphingolipids

Answer 13

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

Question 14

Describe the structure of steroids.

Answer 14

They have 2 cyclohexane rings with a pentane ring attached.

Steroid hormones are hydrophobic and serve as hormones.

Question 15

Cholesterol

Answer 15

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.

Question 16

Role of terpenes and terpenoids

Answer 16

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.

Question 17

Prostaglandins. Role of prostaglandins.

Answer 17

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.

Question 18

What is the fat- soluble vitamins?

Answer 18

A,D,E,K

Question 19

Vitamin A ( carotene)

Answer 19

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.

Question 20

Vitamin D

Answer 20

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.

Question 21

Vitamin E

Answer 21

Contains tocopherols which has an aromatic ring which destroys free radicals. This helps with aging and to deter cancer.

Question 22

Role of Vitamin K

Answer 22

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.

Question 23

Sphingomyelins

Answer 23

Sphingolipids that are involved in myelin.

Question 24

Describe the plasma membrane?

Answer 24

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.

Question 25

Describe the fluid mosaic model

Answer 25

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.

Question 26

Lipid rafts

Answer 26

Their a mass of similar lipids and associated proteins. That play an important role in cell signaling.

Question 27

Flippases

Answer 27

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).

Question 28

Membrane receptors

Answer 28

When a ligand binds it participates in facilitated diffusion or active transport.

Question 29

Cell- cell junctions

Answer 29

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.

Question 30

What role does carbohydrates have on the cell membrane?

Answer 30

Cell signaling and cell recognition

Question 31

Gap junctions

Answer 31

Allows for direct cell communication.

Question 32

Connexons

Answer 32

Allow for the transport of water and small molecules. Composed of 6 molecules of connexin.

Question 33

Tight junctions

Answer 33

Prevent leakage in-between cells. Found in epithelial cells.

Question 34

Desmosomes

Answer 34

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.

Question 35

Hemidesmosomes

Answer 35

Anchors epithelial cells to the underlying basement membrane.

Question 36

Role of the cell membrane

Answer 36

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.