IB Docs (2) Team MC test: Stereochemistry in biomolecules
Multiple choice test on B.10 Stereochemistry in biomolecules
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
How many chiral carbon atoms are present in one molecule of the straight-chain form of galactose?
All the carbon atoms with the exception of the first containing the aldehyde group and the sixth containing two hydrogen atoms and a hydroxyl group are chiral (i.e. contain four different groups attached to them).
Which is the correct structure for L-fructose?
Fructose is a ketone and the L-form has the -OH group on the the chiral carbon atom furthest from the ketone on the left.
Which is the correct structure for α-D-glucose?
Glucose has a six-membered ring and the -OH group on the first carbon atom lies below the plane of the ring.
Which row contains the correct information about the monomer from which cellulose is formed and the type of glycosidic bond(s) cellulose contains?
| Row | Monomer | Type of glycosidic bond(s) |
| 1 | α-D-glucose | 1,4 only |
| 2 | α-D-glucose | 1,4 and 1,6 |
| 3 | β-D-glucose | 1,4 only |
| 4 | β-D-glucose | 1,4 and 1,6 |
Cellulose is a linear polymer formed when β-D-glucose molecules condense together forming 1,4 glycosidic bonds.
Which are correct statements about amylose and amylopectin?
I. Both amylose and amylopectin are formed from the condensation of α-D-glucose molecules.
II. Both amylose and amylopectin contain 1,4 glycosidic bonds.
III. Both amylose and amylopectin are straight-chain polymers.
Although amylose and amylopectin both contain 1,4 glycosidic bonds, amylopectin also contain 1,6 glycosidic bonds which results in a branched structure.
Which structure shows the D enantiomer of alanine?
With the H atom pointing to the rear the other three groups must go clockwise in the order COOH, CH3 then NH2 for the D structure. Even if you do not know the CORN rule enantiomer 2 is the mirror image of the other three enantiomers which are all the L form.
Which process involving cis-fatty acids or their residues can lead to the formation of trans-fats?
During the hydrogenation process only partial hydrogenation may occur with some of the fatty acids undergoing cis/trans isomerization.
Rhodopsin is a biological pigment found in the rods of the retina at the back of the eye. Which best describes rhodopsin?
Retinal is formed from vitamin A in the retina. It acts as a co-factor with an opsin protein to form rhodopsin.
Which photochemical reaction occurs in rhodopsin that causes electrical signals to be sent to the brain?
Although the visual cycle involves 11-cis-retinal being converted into all-trans-retinal, then all-trans-retinol, then 11-cis-retinol before being oxidized back into 11-cis-retinal only the first conversion is brought about by light.
Which are correct statement concerning cis- and trans- oleic acid?
I. Molecules of trans-oleic acid have a more linear structure than molecules of cis-oleic acid.
II. Fats containing cis-oleic acid are thought to cause cholesterol to build up in the arteries, whereas fats containing trans-oleic acid help to remove cholesterol from the arteries.
III. The melting point of cis-oleic acid is lower than the melting point of trans-oleic acid.
Cis-oleic acid melts at 13 oC and trans-oleic acid melts at 45 oC. This is due to the fact that the more linear structure of trans-oleic acid enables the molecules to pack more closely together than cis-oleic acid molecules which have a branched structure. Trans-oleic acid, not cis-oleic acid, is thought to cause the build up of cholesterol in the arteries.
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