Highlights Lecture #14 Spring 2017

1. Arachidonic acid is a 20 carbon fatty acid (eicosanoid) with 4 double bonds. It is a precursor of the prostaglandins. Prostaglandins are molecules that are involved in pain and swelling, among other phenomena in the body. The enzyme catalyzing their synthesis is called PGH Synthase, Prostaglandin Synthase, or Cyclooxygenase (COX). COX enzymes (there are several) are inhibited by aspirin and ibuprofen. These are known as NSAIDs (Non-steroidal anti-inflammatory drugs).

2. Compounds related to prostaglandins include leukotrienes, which are involved in allergic responses and may also be involved in asthma. The other class of compounds derived from prostaglandins include thromboxanes, which play roles in the stickiness of blood platelets.

Nucleic Acids

1. Nucleic acids are composed of building blocks called nucleotides. Nucleotides have three components – a sugar (ribose or deoxyribose), at least one phosphate, and a nitrogenous base (adenine, guanine, thymine, cytosine, or uracil).

2. DNA differs from RNA in that DNA contains the sugar deoxyribose instead of ribose and DNA contains the base thymine, whereas RNA substitutes the base, uracil.

3. The bases in nucleic acids are divided into two groups. Pyrimidines include cytosine, thymine, and uracil. Purines include adenine and guanine.

4. A nucleoside differs from a nucleotide in that a nucleoside only has a sugar and a base. It does NOT have phosphate.

5. Note the numbering of the sugar in a nucleotide. The phosphate goes on carbon number 5. The difference between ribose and dexoyribose is on carbon #2, where ribose contains a hydroxyl, but deoxyribose contains only a hydrogen.

6. The 5′ end of a nucleic acid is the end of the nucleic acid that has a free 5′ end (no bond). The 3′ end of a nucleic acid is the other end of the nucleic acid and it too is not tied up in a bond. All other 5′ and 3′ ends are joined together in phosphodiester bonds.

7. The “backbone” of a nucleic acid is composed of alternating phosphates and sugars and the bond linking them is called a phosphodiester bond. Phosphodiester bonds are to nucleic acids what peptide bonds are to proteins. The bases are NOT part of the backbone and in a DNA molecule are internal to the surrounding backbone.

8. The double helix of DNA was discovered by Watson, Crick, and Franklin in 1953. The most common form is called the B-form. It consists of two strands oriented in an anti-parallel fashion arranged in a right-handed fashion. Bases are located on the inside such that adenine forms 2 hydrogen bonds with thymine and cytosine forms 3 hydrogen bonds with guanine.

9. Other forms of DNA duplexes include the A form (right handed also and also the form of double stranded RNA) as well as the Z form of DNA (left handed).

10. Supercoiling is one aspect of the structure of DNA. Bacterial chromosomes are circular, so if twists are inserted (or removed) from standard B DNA, supercoiling arises.

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