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.

DNA – Deoxyribose Nucleic Acid

The basic structure of the DNAis that of two chains of nucleotidesattached to each other in form of a ladder. This ladder is then twisted into a spiral, forming a double helix.

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

DNA replication

DNA replication Depends on specific base pairing

The DNA untwists, and eachchain is replicated

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 continuousand segmented replication of the DNA

DNA Replication – Continuous vs. Segmented Replication

DNA Replication – Continuous vs. Segmented Replication

DNA Replication – Continuous vs. Segmented Replication

DNA Replication – Continuous vs. Segmented Replication

Errors in DNA replication?

Errors are usually very few – a type of DNA polymerase is involved in proof-readingand repair of mistakes. Final errors are usually about

one in a billion.

DNA polymerases and DNA ligases are also involved in repairing DNA damagefrom 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.

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.

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

Transcription

Transcription

Transcription

Translation

Once the genetic message has beentranscribed onto the mRNA, the tRNAhas the ability to use anticodons to translate the information into formof amino acid sequences.

Note that the transcription occurs in the nucleus, but the translation occursin the cytoplasm.

The proteins produced then go on tocarry out all the functions of the cell.

Translation

Translation

Translation

Translation

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.