Introduction to Biology

(Apologies to the biologists in the room -- this is really not an adequate introduction to your field.)

More About Nucleotides

• Each strand of DNA has a backbone made of alternating sugar (deoxyribose) and phosphate groups.
• Attached to each sugar is one of the four bases--A, C, G, T.
• The two strands are held together by hydrogen bonds between the bases, with adenine forming a base pair with thymine, and cytosine forming a base pair with guanine.

• The two strands are reverse complements of each other -- if you know one strand, you also know what the other must be

The Genome

• the full set of hereditary information for an organism
• Humans have two copies of the genome -- in 46 chromosomes -- in every cell

• DNA is not your destiny. The way you live influences how your genome works.

Genes

• Genes: ~ 20,000
• Exons (code for protein) per gene: ~ 8 on average (max: 148)
• Nucleotides per exon: 170 on average (max: 12k)
• Nucleotides per intron: 5,500 on average (max: 500k)
• Nucleotides per gene: 45k on average (max: 2,2M)
• We share surprisingly large percentages of our genes with other creatures (14K shared genes with a worm!)

How a Gene is Expressed

This is a very simplified picture of what actually happens -- and is no longer thought to be as one-directional as it is portrayed in this illustration.

• DNA --> RNA --> protein
• Proteins have many diverse roles in cell

Errors

• Sometimes, the transcription / translation machinery makes mistakes
• The mistakes (mutations) sometimes occur in coding regions that are supposed to be making proteins
• Types of errors shown in the diagrams

Regulation of Gene Expression

• When should each gene be expressed?
• Every cell has same DNA but each cell expresses different proteins.
• Signal transduction: One signal converted to another
• Gene expression is controlled at many levels, including transcription and translation
• Gene regulation diversifies protein products within different cells