Carbohydrates | Biology | Quiz | Visionlearning
Start studying Chapter 7 quizzes. Learn vocabulary, terms, and more The relationship between D-glucose and D-fructose is: Question options: A) anomers. B). Quiz 1. This activity contains 12 questions. Ribose is the sugar used in RNA. What is the stereochemical relationship between D-erythrose and D-threose?. Quiz on Lecture Carbohydrates 1 Monosaccharides, such as ribose, fructose, glucose, and mannose differ significantly d) their number of carbon atoms.
See how L-Erythrose and L-Threose build on the stereocenter established in L-glyceraldehyde highlightedand D-Erythrose and D-Threose build on the stereocenter established in D-glyceraldehyde highlighted.
The configuration of L-erythrose and L-threose only differs at one stereocenter. This relationship has a name that you might see sometimes: The most familiar name on that list should be ribose, which is the sugar backbone of ribonucleic acid RNA.
On the left hand side in the diagram below, we have the L-aldopentoses, which all share the same configuration of the bottom stereocenter when the aldehyde is placed at the top. Their enantiomers, the D-aldopentoses, are on the right hand side, which all share the same configuration of the bottom stereocenter highlighted. Why and how all organisms on earth ended up with D-sugars is a mystery, as one presumes that L-sugars would have worked just as well. Clarkeas well as a somewhat poorly received Star Trek novel.
D and L Sugars — Master Organic Chemistry
Some are rarely, if ever, found in nature idoseanyone? Here are the D-aldohexoses. Note how they all have the same configuration of the bottom chiral centre — the same one we saw in D-glyceraldehyde. Interestingly, L-glucose has been explored as a sugar substitute. Its taste is indistinguishable from naturally occurring D-glucose, but provides no nourishment since it cannot be broken down by our chiral enzymes.
Amino Acids If you draw amino acids in the Fischer projection with the most oxidized group at the top the carboxylic acid then you can also assign L- and D. Some D- amino acids are naturally occurring, but they are rare mostly found in bacteria, with the notable exception of platypus venom and are not coded by mRNA.
- D and L Sugars
- Reducing Sugars
This is good organic chemistry bar trivia. Cysteine is the weirdo. Of course, sugars are not always so helpfully drawn in Fischer projections — they form rings. Thanks to Thomas Struble for assistance with this post. The same is true for — -erythrose, which returns a completely identical compound.
From this it can be deduced that the structure of the new compound must be such that the molecule has an internal mirror plane i. A compound with equal and opposite optical rotation is formed by performing the same operation on — -threose.
These two compounds are enantiomers. Hold on for a second. So why does fructose give a positive test? Although fructose is a keto sugar, and ketones generally give a negative test with the Benedict, there is an exception.
They are also reducing sugars that give a positive Fehlings, Benedict, or Tollens test picture of lactose positive test is further below. The poster child for a non-reducing sugar is sucrosea. Sucrose is a disaccharide of glucose and fructose. See if you can find a hemiacetal in its structure, below: This is obtained by heating glucose in acidic methanol.
Sugars are able to form long chains with each other in arrangements known as polysaccharides.
What is the relationship between D-glucose and D-fructose?
Common examples of polysaccharides are starch, cellulose, and glycogen. Hemiacetals are present, but only at the termini of the polymer. Starch, for example, generally has about individual units of glucose, but only one unit the terminus has a hemiacetal. Therefore these polysaccharides are not considered reducing sugars.
For example, starch gives a negative test see below.
Note that starch and sucrose are blue, classifying them as non-reducing sugars. Test Yourself Make sense? Quiz yourself on whether the following sugars are reducing sugars or non-reducing sugars. One thing about all three tests is that the active reagent is not particularly bench stable and has to be freshly prepared.
The purpose behind using the tartrate is that it coordinates to the copper II and helps prevent it from crashing out of solution. Once prepared, the substance to be analyzed is added, and the mixture is heated for a brief period. This results in a carboxylic acid and red Cu I which precipitates out as copper I oxide.
Biochemistry Multiple Choice Quiz: 24
The ingredients are copper II sulphate, sodium carbonate, and sodium citrate. The test is performed by adding the substance to be analyzed and heating briefly.
The first three lines below describe the procedure. Silver nitrate is converted to silver hydroxide, which forms silver I oxide, Ag2O. Then, addition of aqueous ammonia NH3 results in formation of the silver-ammonia complex which is the active oxidant. The sample to be tested is then added to the freshly prepared active oxidant in a basic solution.
A positive test results in a beautiful mirror of silver metal being precipitated out on the reaction vessel. A variant of this procedure is used for the preparation of mirrors. How Does It Work?