Highlights Lecture #24 Spring 2017

1. Gene therapy aims to replace defective genes with functional copies. Partially disabled retroviruses are sometimes employed to accomplish this.

2. Since retroviruses have a life cycle that includes a DNA stage and this DNA gets integrated into the genome of the host organism, they are potentially useful for carrying genes into the genome to correct genetic defects.They suffer from the disadvantage that it is difficult to target exactly where in the genome that their DNA integrates.

3. The immune system relies on proteinc called antibodies that recognize and bind to specific structures found in proteins, nucleic acids, or carbohydrates. An antibody has a Y shape containing four polypeptide chains – two longer ones called Heavy chains and two shorter ones called Light chains. Each of these chains has a constant region and a variable region. The variable region is the part that binds to the target. The target is called an antigen and the specific part of the antigen where the anibody binds is called the epitope.

4. Oncogenes are genes that cause cancer. They arise from normal cellular genes called proto-oncogenes by mutation. The proto-oncogenes generally have very important roles in helping to control cellular decisions regarding whether or not to divide.

5. For some oncogenes, mutation of a single base may disrupt cellular controls for division and convert a cell from normal, regulated division to uncontrolled division.

Highlights Carbohydrates

1. Glucose and fructose are common carbohydrates (sugars) and differ only that glucose is an aldehyde, whereas fructose is a ketone. Both have six carbons and you should know their structures (linear and circular forms – see below).

2. The letters ‘ose’ at the end of a name designate a sugar. An aldose is a sugar, like glucose, that is an aldehyde. A ketose is a sugar like fructose that is a ketone. A hexose has six carbons, a pentose has five carbons, a tetrose has four carbons, and a triose has three carbons.

3. The L form of a sugar (like L-glucose) differs from the D form of a sugar of the same name (like D-glucose) in that the two are mirror images of each other. Sugars that are mirror images of each other are called enantiomers. Sugar molecules that have the same number of carbons, and have different stereoisomeric configurations but that are NOT mirror images of each other are called diastereomers. Sugars that differ only in the configuration of one hydroxyl group on a single carbon are called epimers.

4. Sugars can form a ring structure due to the fact that carbons 1 and 5 (or 2 and 5) are located in close promity to each other and the alcohol on carbon 5 can react with the aldehyde on carbon one or the ketone on carbon two to form a hemiacetal or hemiketal respectively. The resulting ring structure is called a Haworth projection. The linear form, as written, is called a Fischer projection.

5. Sugars, like glucose, that form six membered rings are called pyranoses, whereas sugars, like fructose and ribose, that form five membered rings are called furanoses. You are responsible for knowing the pyranose form of glucose and the furanose forms of fructose and ribose. You are also responsible for the straight chain structures of each of these sugars.

6. Formation of a ring creates a new asymmtric carbon (called the anomeric carbon) on the carbon where the aldehyde or ketone originally was (carbon 1 or 2). The hydroxyl on this carbon can exist in a Haworth projection pointing upwards (beta) or downwards (alpha). Please note that linear forms of these sugars DO NOT have anomeric carbons, since the cyclization is what creates the asymmetry.

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