Optional Science

Today is an optional day.

Nucleic Acids and DNA

In the last lesson you learned about four kinds of organic molecules -- carbohydrates, lipids, proteins, and nucleic acids.    This lesson tells more about nucleic acids and specifically about DNA, which stores genetic information.    Remember that this is just an introduction. 

Nucleic acids are polymers composed of monomer units known as nucleotides. There are a very few different types of nucleotides. The main functions of nucleotides are information storage (DNA), protein synthesis (RNA), and energy transfers (ATP and NAD).

Deoxyribonucleic acid (better known as DNA) is the physical carrier of inheritance for 99% of living organisms. The bases in DNA are C, G, A and T.  

DNA functions in information storage. The English alphabet has 26 letters that can be variously combined to form over 50,000 words. DNA has four letters (C, G, A, and T, the nitrogenous bases) that code for twenty words (the twenty amino acids found in all living things) that can make an infinite variety of sentences (polypeptides). Changes in the sequences of these bases information can alter the meaning of a sentence.

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Resources

Tutorial on Macromolecules
Importance of Carbon (Hippocampus)
Interactive Worksheet:  Tree of Life
(main page with concept map)

Organic Compounds quizlet

DNA discovery

Watch
A 3-part introduction to the discovery and idea of DNA.   Each part is about 3 minutes long.   It is meant to give you a general overview.   Go on to next section

Part I


Part II



Part III

Macromolecules

This is just an introduction to a huge subject.  The basic points to remember are listed below.  You remember the last lesson, telling how the element of carbon is unique because of its ability to form many different kinds of bonds.    This makes organic life possible.  

You might notice that carbohydrates, lipids (fats and oils) and proteins are all basic parts of our diet. 

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Carbon Compounds

• Four groups of carbon compounds found in living things are carbohydrates, lipids, nucleic acids, and protein.
• Living things use carbohydrates as their main source of energy. Plants and some animals also use carbohydrates for structural purposes.
• Lipids can be used to store energy. Some lipids are important parts of biological membranes and waterproof coverings.
• Nucleic acids store and transmit hereditary, or genetic, information.
• Proteins:  Some proteins control the rate of reactions and regulate cell processes. Some proteins build tissues such as bone and muscle. Others transport materials or help to fight disease.

Review of Properties of Water

A slideshow on water polarity.

Water's Polarity

DO:

Flashcards on Properties of Water
A quiz on water -- its importance and properties

Solubility

Main Ideas:

• Acidic solutions contain higher concentrations of H+ ions than pure water and have pH values below 7.
• Basic, or alkaline, solutions contain lower concentrations of H+ ions than pure water and have pH values above 7.

Read, then go to next section

The solubility of many molecules is determined by their molecular structure. You are familiar with the phrase "mixing like oil and water." The biochemical basis for this phrase is that the organic macromolecules known as lipids (of which fats are an important, although often troublesome, group) have areas that lack polar covalent bonds. The polar covalently bonded water molecules act to exclude nonpolar molecules, causing the fats to clump together. The structure of many molecules can greatly influence their solubility. Sugars, such as glucose, have many hydroxyl (OH) groups, which tend to increase the solubility of the molecule.

Water tends to disassociate into H+ and OH- ions. In this disassociation, the oxygen retains the electrons and only one of the hydrogens, becoming a negatively charged ion known as hydroxide. Pure water has the same number (or concentration) of H+ as OH- ions. Acidic solutions have more H+ ions than OH- ions. Basic solutions have the opposite.

An acid causes an increase in the numbers of H+ ions and a base causes an increase in the numbers of OH- ions.

The pH scale is a logarithmic scale representing the concentration of H+ ions in a solution. Remember that as the H+ concentration increases the OH- concentration decreases and vice versa . If we have a solution with one in every ten molecules being H+, we refer to the concentration of H+ ions as 1/10.

Remember from algebra that we can write a fraction as a negative exponent, thus 1/10 becomes 10-1. Conversely 1/100 becomes 10-2 , 1/1000 becomes 10-3, etc. Logarithms are exponents to which a number (usually 10) has been raised. For example log 10 (pronounced "the log of 10") = 1 (since 10 may be written as 101). The log 1/10 (or 10-1) = -1. pH, a measure of the concentration of H+ ions, is the negative log of the H+ ion concentration. If the pH of water is 7, then the concentration of H+ ions is 10-7, or 1/10,000,000. In the case of strong acids, such as hydrochloric acid (HCl), an acid secreted by the lining of your stomach, [H+] (the concentration of H+ ions, written in a chemical shorthand) is 10-1; therefore the pH is 1.