Carbon-Based Molecules Part 3: Hydrogen Bonds and Nucleic Acids

Objectives SWBAT describe and compare and contrast the functions and structures of the carbon- based molecules: carbohydrates, lipids, proteins, and nucleic acids.

Starter Water has a very special property that we here in Iowa are able to appreciate on a yearly basis. With your tablemate, or if you do not have a tablemate, then the person in front or behind you, try to figure out what water’s special property is. I will give you a couple of minutes. Hang on to your answers – we will use them shortly.

Hydrogen Bonds Life depends on hydrogen bonds (Examples: in water and between nitrogen bases in DNA). – Hydrogen bonds are weak compared to covalent bonds. Water is a polar molecule. – Polar molecules have slightly charged regions. O HH _ ++

Hydrogen Bonds –Nonpolar molecules, like lipids (this is review) do not have charged regions. –Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms. –file:///C:/Program%20Files/McDougal%20Littell/Power%2 0Presentations- Biology/START%20Power%20Presentations.htmlfile:///C:/Program%20Files/McDougal%20Littell/Power%2 0Presentations- Biology/START%20Power%20Presentations.html

Hydrogen Bonds Hydrogen bonds are responsible for three important properties of water. Cohesion – cohesion from the hydrogen bonds makes water molecules stick to each other (water forming beads and surface tension). Cohesion is attraction among molecules of only 1 substance. Adhesion – attraction among molecules of different substances (water molecules stick to other things). This is very important because it is what helps plants transport water from their roots to their leaves.

Hydrogen Bonds The red liquid is water, it is curved down because of greater adhesion than cohesion. The mercury on the left shows greater cohesion – evidenced by the upward curve of the mercury in the test tube.

Hydrogen Bonds High specific heat – Hydrogen bonds give water an abnormally high specific heat. Thus, water resists changes in temperature. Compared to many other compounds, water must absorb more heat energy to increase in temperature. This property is very important in cells! The chemical energy released by cell processes releases a great deal of heat and water helps to absorb that heat – protecting the cell.

Hydrogen Bonds Alone, oxygen and hydrogen have very low specific heats (as does methane and many other compounds we have studied) but put them together and we have chemical (and thus biological) majesty.

Return to Starter Water’s special property: it expands, becomes less dense in its solid phase. – Thus it floats and does not sink as we might suppose.

Water in it 3 States

Nucleic Acids Nucleic acids are polymers of monomers called nucleotides. Nucleotide – is composed of a sugar, a phosphate group, and a nitrogen containing molecule called a base (we will talk a lot more 2 nd semester about these). DNA and RNA are the two types of nucleic acids.

Example: Nucleotide Monomer A phosphate group nitrogen-containing molecule, called a base deoxyribose (sugar)

Nucleic Acids - Polymers This shows the two strands of DNA that connect, via hydrogen bonds, and twist to form a double helix. RNA is single stranded.

Nucleic Acids DNA stores genetic information. RNA builds proteins. DNA RNA

Entrance Ticket for Next Time What causes hydrogen bonds to form between polar molecules? In what kind of molecule are the instructions for building proteins stored?