Question

1. What are the three components of a nucleotide?

2. Name the nitrogenous bases for DNA/RNA

3. What is the complementary base pairing rule? Please, include the hydrogen bonds

4. Give two examples of
   1. Monosaccharide
   2. Disaccharide
   3. Polysaccharide

5. What is the difference between alpha 1, 4 glycosidic and beta 1, 4 glycosidic linkages? For each linkage, give 2 examples of organisms that use the linkage and what is the function of the linkage?

6. What is an isomer? Give two examples

7. What type of bond/linkage is found in
   1. Protein
   2. Nucleic acid
   3. Carbohydrate

Answer 1

• The three components of a nucleotide are a) ribose sugar b) a phosphate moiety and c) a nitrogenous base
• The nitrogenous bases for DNA are adenine, guanine, cytosine and thymine and for RNA they are adenine, guanine, cytosine and uracil.
• The complementary base pairing rule (also known as Chargaff's rule) states that in DNA, adenine always base pairs with thymine and cytosine base pairs with guanine. In RNA, uracil always base pairs with thymine. Adenine is bonded to thymine by 2 H-bonds and guanine is bonded to cytosine by three H-bonds.
• Two examples of a) monosaccharides are glucose (hexose) and ribose (pentose) b) disaccharides: sucrose and lactose c) polysaccharide: starch and cellulose.
• The -1,4 glycosidic linkage takes place between the -OH group of anomeric form of C-1 of one monosaccharide and that of C-4 of the next monosaccharide. In -1,4 glycosidic linkage takes place between the -OH group of anomeric form of C-1 of one monosaccharide and that of C-4 of the next monosaccharide. (The bonds has been shown in the image provided with the answer)

The -1,4 glycosidic linkage is present in both plants and animals.In plants, starch contains this linkage and in animal cells glycogen consists of glusose units linked by -1,4 glycosidic linkage. Both starch and glycogen are important storage polysaccharides in plants and animals which are basically glucose polymers.

The -1,4 glycosidic linkage is present in plants and fungi, arthropods. In plants, cellulose which is the primary component of plant cell wall contains repeating units of glucose linked by -1,4 glycosidic bonds. Chitin which is also the primary component of fungal cell wall and the exoskeleton component of arthropods consists of -1,4 glycosidic linkages.

• Isomers are molecules with same chemical formula but different arrangement of the atoms. Two examples of isomers are glucose and galactose where both contain the same no. of C atoms but differ in their stereochemistry at C-4.
• a) Proteins contain peptide bond formed by a condensation reaction between the carboxy terminal of one amino acid and the -amino group of the next amino acid.

b) Nucleic acid contains phosphodiester linkages between the 3'-OH group of one nucleotide and 5'- phosphate of the incoming nucleotide.

c) Carbohydrate contains glycosidic bond which may be a O-glycosidic bond or N-glycosidic bond.