8.1 DNA Structure & Function

Nucleic Acids

•DNA & RNA are nucleic acids•Monomer?

▫Nucleotides

5-C Sugar

P N- Base

DNA History•Watson & Crick

developed “double-helix” model of DNA structure in 1953

•Used work of Rosalind Franklin

http://www.nature.com/scitable/topicpage/rosalind-franklin-a-crucial-contribution-6538012

DNA Structure

•Double helix▫Two chains (strands) of nucleotides twisted

around each other•Within each strand:

▫Sugar-Phosphate Backbone formed by sugar & phosphates of nucleotides

▫Nucleotides of the backbone are connected by phosphate bonds

DNA Structure

http://click4biology.info/c4b/3/images/3.3/dinucleotide.gif

Phosphate bond

Making DNA

DNA Structure

•How are the two strands of nucleotides connected?

•Two strands arrange themselves so that the N-bases are in the center

•N-bases complementary bond with each other using hydrogen bonds▫Cytosine – Guanine (C-G)▫Adenine – Thymine (A-T)

DNA Function

•DNA acts as a blueprint for all life•DNA is arranged in genes

▫Gene: sequence of nucleotides in DNA▫Each chromosome contains hundreds of

genes!•One gene gives instructions for making

one specific protein▫Remember: protein function

Enzymes, transport, movement, immunity, etc

DNA Function

•Each protein is responsible for a trait▫Trait: physical manifestation of gene

•Each human has the same genes, but we are not all the same. Why?▫Different order of nucleotides in our genes!

RNA Structure

•Single-helix▫Only one strand of nucleotides

•The 5-C sugar in RNA is ribose•Does not have the base thymine, but has

the base uracil instead

http://www.tildee.com/Xbwj6f

RNA Function

•Enzymes make a RNA copy of one DNA gene▫RNA is much smaller than DNA

•The cell uses this RNA copy to make a protein

Central Dogma

DNA

RNA Protein