Question

1. When water and oil are added to a test tube, the two liquids form two separate layers (think of oil and vinegar in a bottle of salad dressing). If a solution of phospholipids was added to a mixture of water and oil, where would you find the phospholipids? Describe their orientation.

2.What is the name of the linkage that connects two nucleotides together in a strand of DNA or RNA?

3.In order to separate the two strands of DNA in a DNA double helix, what type of bond needs to be broken?

Thank you

Answer 1

(1)

Phospholipids are amphipathic structures. They have both hydrophilic and hydrophobic regions (hydrophilic head and hydrophobic tail). The structure of phospholipid from the cell membrane is given below:

The nonpolar regions of the phospholipid would dissolve in the oil and the polar regions would dissolve in the water if a solution of phospholipids was added to a mixture of water and oil.

Therefore, the layer of phospholipid will be found in the middle of the water and oil layers.

(2)

The DNA double helix structure is made of two polynucleotide chains having a sugar-phosphate backbone in which bases are projecting inside. The two chains of a double helix of DNA have an anti-parallel polarity and have right-handed coiling. If one chain has a polarity then, the other chain has a polarity and a purine always comes opposite to a pyrimidine.

The nitrogen bases are of two types: Purine and pyrimidine. The Adenine, Guanine are purines, and Cytosine, Thymine, and Uracil are the pyrimidines. The nitrogen bases in the two strands are joined through hydrogen bonds which form the base pairs. Adenine of one strand has two hydrogen bonding with Thymine from the opposite strand and vice-versa. Similarly, Guanine has three hydrogen bonding with Cytosine. The double helix of the DNA has a pitch size of 3.4 nm and each turn has 10 bp.

A nucleotide constitutes three components: a pentose sugar (deoxyribose in case of DNA and ribose for RNA), a nitrogenous base (purine: Adenine and guanine; pyrimidine: Cytosine, Thymine, and Uracil) and a phosphate group.

A nucleoside is formed when a nitrogenous base joins to the -OH of 1' C pentose sugar by a N-glycosidic linkage, like deoxyadenosine or adenosine, deoxyguanosine or guanosine, deoxycytidine or cytidine, and deoxythymidine or uridine. A nucleotide or deoxynucleotide is formed when the -OH group of 5' C of nucleoside links to the phosphate group by phosphoester bond. A dinucleotide is formed when two nucleotides are joined by 3'-5' phosphodiester linkage. A polynucleotide chain is formed when more nucleotides are linked by 3'-5' phosphodiester linkage.

Nucleotides are linked by phosphodiester bonds between 5' and 3' carbon atoms to form a polymer of nucleic acid. As an outcome, the sugar-phosphate backbone is formed and nitrogen bases are projected inside. On treatment with the enzyme, the phosphodiester bonds are hydrolyzed which link nucleotides together.

Therefore, the "phosphodiester linkage" is the correct answer.

(3)

Denaturation is a process in which the hydrogen bonds between the nitrogen bases are broken and the two strands in the double helix of the DNA separates when the DNA is heated at the higher temperature or when the pH is increased above 11.3.

Therefore, "hydrogen bonds" is the correct answer.