1. DNA – Deoxyribose Nucleic Acid 1. DNA is composed of a chain of nucleotides, each made up of a sugar group, a phosphate group, and a nitrogenous base. 2. The phosphate groups of one nucleotide bind to the sugar group of the next nucleotide to build a sugar-phosphate backbone. 3. The nitrogenous bases of DNA include the pyrimidines Thymine and Cytosine, and the Purines Adenine and Guanine.

2. DNA – Deoxyribose Nucleic Acid The basic structure of the DNA is that of two chains of nucleotides attached to each other in form of a ladder. This ladder is then twisted into a spiral, forming a double helix.

3. DNA – Deoxyribose Nucleic Acid 1. Note that the sugar-phosphate are on the outside of the double helix 2. The nucleotides are very specific to each other, with Adenine and Thymine always binding to each other, and Guanine and Cytosine always binding to each other. 3. Also note that the sugar-phosphate chains run in opposite direction. This will later become important in DNA replication

4. DNA replication DNA replication Depends on specific base pairing The DNA untwists, and each chain is replicated

5. DNA replication DNA can only be replicated in only one direction, but remember that the chains of the DNA went in different directions DNA polymerase, the enzyme responsible for replicating DNA, can only add nucleotides to the 3’ (three prime) end of the strand This basic characteristic of DNA polymerase results in continuous and segmented replication of the DNA

6. DNA Replication – Continuous vs. Segmented Replication

10. Errors in DNA replication? Errors are usually very few – a type of DNA polymerase is involved in proof-reading and repair of mistakes. Final errors are usually about one in a billion. DNA polymerases and DNA ligases are also involved in repairing DNA damage from harmful radiation (e.g. UV) and/or toxic chemicals in the environment. Mutations can be in form of deletions, additions, and/or change of nucleotide types. Not all mutations that remain un-checked will have an effect on the protein product. Over evolutionary time, mutations are however a major source genetic variation. If it were not for mutations, none of the different life forms we see on earth today would exist.

11. RNA – Ribose Nucleic Acid Like DNA, RNA is also a made up of a chain of nucleotides. Unlike DNA however, the sugar group is a ribose instead of a deoxyribose. RNA forms single strands instead of the double strands formed by DNA In the RNA, the nitrogenous base Thymine normally found in the DNA is replaced by Uracil.

12. RNA – Ribose Nucleic Acid Cells have three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA The different forms of RNA are involved in the transcription and translation of genetic information

13. Transcription

16. Translation Once the genetic message has been transcribed onto the mRNA, the tRNA has the ability to use anticodons to translate the information into form of amino acid sequences. Note that the transcription occurs in the nucleus, but the translation occurs in the cytoplasm. The proteins produced then go on to carry out all the functions of the cell.

17. Translation

21. Regulation of Gene Expression 1. Cells regulate rate of transcription. 2. Cells regulate rate of translation. 3. Cells regulate protein activity by modifying the proteins. 4. Cells regulate protein activity through degradation.