lecture 1 (week 8)

Question 1

what is a major feature of lipids?

Answer 1

they have low solubility in water: they are hydrophobic

Question 2

what are some biologically important lipids?

Answer 2

phospholipids, fats, sterols and (some) vitamins

Question 3

what is the structure of a fatty acid?

Answer 3

composed of a carboxyl group with a long hydrocarbon chain

Question 4

what type of fatty acids have an even number of carbons?

Answer 4

naturally occurring fatty acids.

Question 5

Fatty acids are rarely found free in the body. What/where are they usually found? (2)

Answer 5

part of a lipid molecule

or complexed to a carrier protein (eg albumin)

Question 6

what types of fatty acids can be absorbed directly into the bloodstream?

Answer 6

short and medium chain fatty acids

Question 7

what happens to the long chain fatty acids which cannot be absorbed directly into the bloodstream?

Answer 7

they are synthesised

Question 8

what is a cis unsaturated fatty acid?

Answer 8

a fatty acid in which the hydrogen atoms are on the same side of the carbon to carbon double bond

Question 9

what is a trans fatty acid?

Answer 9

an unsaturated fatty acid in which the two hydrogen atoms are on different sides of the carbon to carbon double bond

Question 10

what type of fatty acids gives the ratio for carbon atoms to double bonds of 16:1?

Answer 10

saturated

Question 11

what type of fatty acids gives the ratio for carbon atoms to double bonds of 18:1?

Answer 11

unsaturated

Question 12

what type of fatty acids gives the ratio for carbon atoms to double bonds of 20:4?

Answer 12

polyunsaturated

Question 13

for fatty acids named in the ‘delta’ method, which end is the first carbon called delta?

Answer 13

the carboxyl group end. (the carbon atoms are labelled from there) and the double bonds labelled as delta 1,3,5 etc

Question 14

How do you name omega fatty acids?

Answer 14

by labelling the end with the methyl group as carbon number one and the first carbon to carbon bond from there.

Question 15

what are some important structural features of sterols?

Answer 15

OH group on the end of the 4 ring structure provides a degree of polarity to the molecule; The four ring structure is very rigid and strong but also is flat which allows the molecule to fit into small places (e.g. in the cell membrane)

Question 16

what are some examples of where you would find sterols in the body?

Answer 16

bile acids, steroid hormones, vitamins and in the cell membrane (cholesterol)

Question 17

what is the basic disease mechanism for inherited disorders involving lipid pathways?

Answer 17

there is usually an enzyme missing which causes an accumulation of lipids at one stage in the pathway (e.g. Gaucher’s, Riemann pick, Tay-Sachs, Fabry disease)
Largely affect neurological system, liver, spleen and bone marrow.

Question 18

what are the three different types of lipids found in membranes?

Answer 18

phospholipids/glycolipids: Glycerophospholipids, sphingolipids; sterols: cholesterol

Question 19

what is the structure of a glycerophospholipid (from bottom to top)?

Answer 19

two fatty acids attached to one glycerol attached to a phosphate, attached to an alcohol.

Question 20

what is the structure of sphingomyelin? (the first type of sphingolipid)

Answer 20

one fatty acid and one sphingosine molecule attached to a phosphate group attached to an alcohol.

Question 21

what is the structure of GSL (GalCer) (the second type of sphingolipid)?

Answer 21

one fatty acid and one sphingosine molecule attached to a sugar

Question 22

what is the most common alcohol which forms part of the polar head of phospholipids?

Answer 22

choline (the polar head group is composed of the alcohol and the phosphate

Question 23

what are some other molecules which can form the polar head along with the phosphate group in phospholipids?

Answer 23

ethanol amine, serine and inositol

Question 24

what is the fluid mosaic model of the phospholipid bilayer?

Answer 24

fluid matrix - the phospholipid is constantly moving and can also change by lateral and rotational movements. The phospholipid bilayer is a two dimensional solvent (water-soluble and lipid-soluble)

Question 25

what are the two different classes of proteins in the plasma membrane?

Answer 25

peripheral proteins (extrinsic proteins) bonded to the surface of the membrane or partially embedded in the membrane. Integral proteins (intrinsic proteins) which usually span the entire lipid bilayer

Question 26

what can staining the membrane with fluorescence then bleaching be used to show?

Answer 26

the fluidity of the membrane (the more fluid the quicker the recovery)

Question 27

how are phospholipid bilayers asymmetrical?

Answer 27

new phospholipids are generated by enzymes in the ER facing cytosol. They use fatty acids available in the cytosolic half of the bilayer. They release the new phospholipid into the same side of the bilayer. Lipids can be transferred to the other side of the bilayer by flippases which can be specific to certain phosholipds, which results in asymmetry in the bilayer.

Question 28

where does membrane synthesis occur?

Answer 28

in the ER

Question 29

what are lipid rafts?

Answer 29

organising centres in the membrane. involved in vesicle trafficking and cell signalling. Often contain higher quantities of cholesterol which makes them more rigid

Question 30

what are lipid linked membrane proteins?

Answer 30

proteins on the plasma membrane which are covalently bonded to a protein either outside or inside the cell.

Question 31

what is the structural composition of a transmembrane alpha helix protein like?

Answer 31

the hydrophobic amino acid side chains are often arranged to the outside of the protein which increases the bonds and therefore stability of the transmembrane proteins.

Question 32

how to transmembrane proteins create pores in the membrane?

Answer 32

the inside fifth transmembrane proteins are hydrophilic whereas the outside (the part embedded in the cell membrane) is hydrophobic

Question 33

what is an example of membrane associated proteins?

Answer 33

pleckstrin. (membrane associated proteins usually contain domains which selectively bind to phospholipids and have about 100 amino acids which bind to certain types of phospholipids

Question 34

what type of membrane proteins are especially important in signal transduction?

Answer 34

protein-attached proteins