1. DNA LS 5.3

2. What is DNA? ■Deoxyribonucleic Acid –The hereditary material ■This is what you get from your parents, and what is passed to offspring during reproduction ■A type of nucleic acid (recall 4 main biological molecules) ■A characteristic of all living things –The smallest bacteria has DNA ■DNA is very similar between organisms –Evidence for common ancestry ■Contains the instructions for the organism –Called genes

3. DNA, Chromosomes and Genes ■DNA is the hereditary material –Usually long and stringy (chromatin) ■Wraps around proteins during cell division (chromosomes) ■A segment of DNA that contains instructions is called a gene

4. Discovery of DNA ■People knew something existed that passed traits on, but didn’t know what it was. –Mendel called them factors –Darwin said something would be found that explains how traits are passed ■In the early 1900’s, DNA was suspected to be the hereditary material ■Rosalind Franklin and Maurice Wilkins –Took X-ray photographs of DNA ■James Watson and Francis Crick –Took Franklin and Wilkins’ work and discovered the structure of DNA

5. Structure of DNA ■DNA is a chain of smaller units –Like links on a chain –Looks like a twisted ladder ■Called a double helix ■The smaller units are called nucleotides ■A nucleotide is made up of 3 parts –The backbone is made of: ■A sugar, called deoxyribose ■A phosphate group –The interior (rungs of the ladder) have: ■Nitrogen bases

6. Nitrogen Bases ■4 of them –Adenine (A), Thymine (T), Guanine (G), Cytosine (C) –Their sequence determines the gene ■Bases come in pairs –They are held together by bonds ■They give the DNA molecule its shape –A-T (apple tree) –C-G (car garage)

7. DNA Replication ■Occurs whenever the cell splits (mitosis: recall S-phase) ■DNA unzips (just like a zipper) and splits apart –Each ½ provides a template to form another identical molecule ■Example: Find the complementary strand –A G T C G A –T C A G C T

8. RNA ■Another nucleic acid ■Ribonucleic Acid ■Similar to DNA, but key differences –Where DNA has 2 sides, RNA is single-sided –Where DNA has deoxyribose as its sugar, RNA has ribose –Where DNA has Thymine (T), RNA replaces it with Uracil (U) ■T DOES NOT EXIST IN RNA!

9. Types of RNA ■mRNA (messenger RNA)-carries message from nucleus to ribosomes ■rRNA (ribosomal RNA)-RNA in a ribosome that reads the code ■tRNA (transfer RNA)-carries amino acid to ribosome

10. Making a protein ■Proteins are chains made of units called amino acids –The sequence of amino acids determines the protein’s shape ■The shape determines the job ■The sequence of amino acids is determined by the gene –Better definition for gene: a segment of DNA that codes for a specific protein ■mRNA is made from a strand of DNA (Called transcription) –Practice: What RNA strand would form from this DNA strand? ■A T G C G T A ■U A C G C A U – Because it is small, mRNA can leave the nucleus ■It travels to a ribosome, where rRNA bonds to it ■tRNA carries amino acids to the ribosome, and place them in the correct spot (translation) –The amino acids bond together, forming the protein

11. Central Dogma of Biology ■Dogma-an idea known to be true that is central to the field ■DNA  RNA  Proteins  Traits

12. Mutations ■Change in nucleotide sequence on DNA ■Different types –Nucleotides can be deleted –A wrong nucleotide can be added –The wrong nucleotide can replace the correct one –Chromosome parts can be broken ■Can be natural, or can be the result of a mutagen (something in the environment that causes a mutation) –Smoking, alcohol, disease, excess sunlight, asbestos, etc.

13. Results of Mutations ■Most mutations are neutral –You’d never even know it happened ■The cell repairs it, or it occurs in noncoding (junk) DNA ■Other mutations are bad –Can lead to disease, such as cancer ■Occasionally, mutations are beneficial –Give something to the offspring that they did not previously have ■Example: Making an animal’s coat look a little more similar to its surroundings –This is what natural selection acts on (more to come next chapter)