Biochem Chapter 8-Lipids
Which of the following compounds would have the highest rate of non facilitated transmembrane diffusion (passive diffusion)? What parameter explains the difference in diffusion rates? 1. glucose 2. 1-butanol 3. glycerol 4. Urea
1-butanol. All are small but 1-butanol is the least polar
A membrane consists of 50% proteins by weight and 50% phosphoglycerides by weight. Tha average molecular weight of lipids is 80 da, and of protein 50,000 da. Calculate the molar ratio
50 g lipid x 1 mol lipid/800g lipid = 0.0625 mol lipid 50 g protein x 1 mol protein/ 50,000 g protein = 0.001 mol protein Molar ratio of lipid protein 0.0625/0.001= 65:1
Define glycoprotein and glycolipid?
A glycoprotein is formed by covalent bonding between a carbohydrate and a protein, whereas a glycolipid is formed by covalent bonding between a carbohydrate and a lipid.
Phosphoacylglycerols
A phosphatidic acid with another alcohol esterified to the phosphoric acid moiety
Which statements are consistent with the known facts of membrane transport?
Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher. Transport proteins may be involved in bringing substances into cells.
Define Omega-3 Fatty Acid
An omega-3 fatty acid has a double bond at the third carbon from the methyl end.
Write the structural formula for a triacylglycerol and name the component parts
Any combination of fatty acids is acceptable
Suggest a reason why the cell membranes of bacteria grown at 20 celcius tend to have a higher priportion of unsaturated fatty acids than the membranes of bacteria of the sames species grown at 37C?
At the lower temperature, the membrane would tend to be less fluid. The presence of more unsaturated fatty acids would tend to compensate by increasing the fluidity of the membrane compared to one at the same temperature with a higher proportion of saturated fatty acids.
Suggest a reason why inorganic ions such as K+ Na+ and Ca2+ and Mg 2+ do not cross biological membranes by simple diffusion?
Biological membranes are highly nonpolar environments. Charged ions tend to be excluded from such environments rather than dissolving in them, as they would have to do to pass through the membrane by simple diffusion.
What structural features do a sphingomyelin and a phosphatidyl choline have in common? How do the structures of these two types of lipids differ?
Both sphingomyelins and phosphatidylcholines contain phosphoric acid esterified to an amino alcohol, which must be choline in the case of a phosphatidylcholine and may be choline in the case of a sphingomyelin. They differ in the second alcohol to which phosphoric acid is esterified. In phosphatidylcholines, the second alcohol is glycerol, which has also formed ester bonds to two carboxylic acids. In sphingomyelins, the second alcohol is another amino alcohol, sphingosine, which has formed an amide bond to a fatty acid
Egg yolks contain a high amount of cholesterol, but they also contain a high amount of lecithin. From a diet and health standpoint how do these molecules complement eachother?
Cholesterol is not very water-soluble, but lecithin is a good natural detergent, which is actually part of lipoproteins that transport the less soluble fats through the blood.
Peptide hormones, such as glucagon, must bind to receptors on the extracellular surface of their target cells before their effects are communicated to the cell interior. In contrast, receptors for steroid hormones, are intracellular proteins. Why?
Glucagon is large and polar and cannot cross the membrane. Steroids are small and nonpolar. They can passively diffuse through the membrane.
What is the energetic driving force for the formation of the phospholipid bilayer
Hydrophobic interactions among the hydrocarbon tails are the main energetic driving force in the formation of lipid bilayers.
Suppose that you are studying a protein involved in transporting ions in and out of the cells. Would you expect to find the nonpolar residues in the interior or exterior? why? would expect to find the polar residues in the interior or exterior? why?
In a protein that spans a membrane, the nonpolar residues are the exterior ones; they interact with the lipids of the cell membrane. The polar residues are in the interior, lining the channel through which the ions enter and leave the cell.
What structural features do a triaglycerol and a phosphotidyl ethanolamine?
In both types of lipids, glycerol is esterified to carboxylic acids, with three such ester linkages formed in triacylglycerols and two in phosphatidyl ethanolamines. The structural difference comes in the nature of the third ester linkage to glycerol. In phosphatidyl ethanolamines, the third hydroxyl group of glycerol is esterified not to a carboxylic acid but to phosphoric acid. The phosphoric acid moiety is esterified in turn to ethanolamine.
This component is the only component that might bind and transport sodium ions across the membrane
Integral
What are isoprene units and how do they relate to this chapter?
Isoprene units are five-carbon moieties that play a role in the structure of a number of natural products, including fat-soluble vitamins.
In fluorescence photobleaching studies, fluorescent groups are attached to membrane components in a cell. A very brief but intense laser beam pulse focused on a very small area destroys (bleaches) the fluorophores in that area. What happens to the fluorescence in that area over time?
It first fluoresces, then laser beam makes it so its not anymore, then it does again in one area
What is JAK2 and why is it important to the effect of hGH?
JAK2 stands for Janus Kinase 2. The hormone binding to the outside of the receptor causes an activation of the kinase on the inside of the cell. Activation of this and many kinases is the key signaling event in many pathways. Such kinases produce a second messenger that begins a cascade of molecular changes that effect the overall changes seen when hormones are released.
What happens when human growth receptor binds hGH?
KBinding of the hormone causes a movement of the transmembrane protein that is transmitted to the intracellular side. This causes a movement of the kinase and catalytic domains, activating the kinase activity of the receptor.
What are the main structural features of leukotrienes?
Leukotrienes are carboxylic acids with three conjugated double bonds.
Cytochrome c, a protein of the electron transport chain in the inner mitochondrial membrane, can be removed by relatively mild means, such as extraction with salt solution. In contrast, cytochrome oxidase from the same source can be removed only by extraction into detergent solutions or organic solvents. What kind of membrane proteins are cytochrome c and cytochrome oxidase? A) Cytochrome c is an integral membrane protein; cytochrome oxidase is a peripheral protein. B) Cytochrome c is a peripheral protein; cytochrome oxidase is a lipid-anchored protein. C) Cytochrome c and cytochrome oxidase are both integral membrane proteins. D) Cytochrome c is a peripheral protein; cytochrome oxidase is an integral membrane protein. E) Cytochrome c and cytochrome oxidase are both lipid-anchored proteins.
Likely a peripheral protein.
Give a reason for the toxicity that can be caused by lipid soluble vitamins
Lipid-soluble vitamins accumulate in fatty tissue, leading to toxic effects. Water-soluble vitamins are excreted, drastically reducing the chances of an overdose.
How can fluorescence techniques be used to monitor the motion of lipids and proteins in membranes?
Lipids can be "tagged" with a fluorescent moiety to observe their motion in membranes. Proteins have intrinsic fluorescence and can be monitored directly.
Crisco is made from vegetable oils which are usually liquid. Why is crisco a solid?
Many of the double bonds have been saturated. Crisco contains "partially hydrogenated vegetable oils."
Which of the following statements are consistent with what is known about membranes?
Membranes contain glycolipids and glycoproteins. Lipid bilayers are an important component of membranes.
Plants can synthesize trienoic acids (fatty acids with 3 double bonds) by introducing another double bond into a dienoic acid. Would you expect plants growing at higher temperatures to convert more or less of their dienoic acids into trienoic acids? A. they would convert more B. they would convert less C. there would be no difference
No. Trienoic acids would have lower melting points and at higher temps the plant would need fatty acids with higher melting points to maintain the proper fluidity
Suggest a reason why partially hydrogenated vegetable oils are used so extensively in packaged goods?
Partially hydrogenated vegetable oils have the desired consistency for many foods, such as oleomargarine and components of TV dinners.
This component may have been palmitoylated or myristoylated
Peripheral
This component can probably be separated from the others by simply washing the membrane with a neutral salt solution
Peripheral lipid
This component could be a glycoprotein
Peripheral or integral
This component could be a cerebroside or ganglioside
Phospholipid that helps to form bilayer
In order to separate this component from the others, harsh conditions such as strong detergents are needed
Phospholipid, integral lipids/proteins
This component might be able to flip-flop transversely with the assistance of a flippase
Phospholipids
Which is more hydrophillic, cholesterol or phospholipids?
Phospholipids are more hydrophilic than cholesterol. The phosphate group is charged, and the attached alcohol is charged or polar. These groups interact readily with water. Cholesterol has only a single polar group, an OH .
List two classes of compounds derived from arachidonic acid. Suggest some reasons for the amount of biomedical research devoted to these compounds.
Prostaglandins and leukotrienes are derived from arachidonic acid. They play a role in inflammation and in allergy and asthma attacks.
What are the main structural features of prostaglandins?
Prostaglandins are carboxylic acids that include a five-membered ring in their structure.
Proteins, nucleic acids, and carbohydrates are grouped by common structural features found within their group. What is the basis for grouping substances as lipids?
Solubility properties (insoluble in aqueous or polar solvents, soluble in nonpolar solvents). Some lipids are not at all structurally related.
Which statements are consistent with the fluid mosaic model
Some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane. (d)Carbohydrates are covalently bonded to the outside of the membrane.
How does the structure of steroids differ from that of the other lipids?
Steroids contain a characteristic fused-ring structure, which other lipids do not.
What is the role in vision of the cis-trans isomerization of retinal?
The cis-trans isomerization of retinal in rhodopsin triggers the transmission of an impulse to the optic nerve and is the primary photochemical event in vision.
Suggest a reason why the animals that live in cold climates have higher proportions of polyunsaturated fatty acids residues than animals that live in warm climates?
The higher percentage of unsaturated fatty acids in membranes in cold climates is an aid to membrane fluidity.
In the preparation of sauces that involve mixing water and melted butter, egg yolks are added to prevent separation. How?
The lecithin in the egg yolks serves as an emulsifying agent by forming closed vesicles. The lipids in the butter (frequently triacylglycerols) are retained in the vesicles and do not form a separate phase.
Succulent plants from arid regions generally have waxy surface coatings. Why is this beneficial
The waxy surface coating is a barrier that prevents loss of water.
Why can't triacylglycerols form a lipid bilayer?
They are too nonpolar. They dont have a polar or charged head group necessary to interact with the water on either side of membrane.
Which of the following lipids are not found in animal membranes?
Triacylglycerols
List the fat-soluble vitamins and give a physiological role of each
Vitamin A: Vitamin K Vitamin E Vitamin D
Why is it possible to argue that vitamin d is not a vitamin?
Vitamin D can be made in the body.
List an important chemical property of vitamin E
Vitamin E is an antioxidant.
Why can some vitamin K antagonists act as anticoagulants?
Vitamin K plays a role in the blood-clotting process. Blocking its mode of action can have an anticoagulant effect.