Life’s Instruction Manual or What Genes are Made Of DNA Life’s Instruction Manual or What Genes are Made Of

Discovery of DNA 1952 Rosalind Franklin-studies DNA molecule using x-ray diffraction 1953 Watson and Crick- develop double helix model

The Shape of the DNA Molecule DNA is a complex organic molecule with a double helix shape. (a twisted ladder) It consists of 2 phosphate-sugar backbones connected by a series of nucleotide bases. (colored letters)

Labeling the Components

DNA Nucleotide Bases Adenine A Thymine T Guanine G Cytosine C These bases are joined together in a specific way… A with T G with C We call this base pairing.

How does this work? One purine always pairs with one pyrimidine. Bonding between A and T forms two hydrogen bonds Bonding between C and G forms three hydrogen bonds

DNA Structure

DNA Replication The bonds between the base pairs are weak hydrogen bonds and can be broken easily. This means that the molecule can unwind and unzip itself. Each side of the DNA molecule has all the information necessary to make a complementary (second) side. Each piece of “old” DNA will act as a template for a “new” piece of DNA.

DNA Copies Itself!! Because of base pairing, each strand of DNA can replicate itself making two new strands of DNA. It uses extra nucleotide bases (in cell) to create this copy. All of the work of DNA replication is done by enzymes!!

Enzymes! Enzymes are proteins that speed up (catalyze) chemical reactions. Some important enzymes in the process of DNA replication are Helicase: unwinds the DNA structure Polymerase: makes DNA for base pairing (new strand) Ligase: “glues” the new DNA strand together to fit to the old strand

Semi-Conservative Replication The result is that each new copy of DNA produced by this process is made up of ½ original DNA molecule and ½ new DNA molecule. This makes the process semi-conservative.

RNA RNA is a nucleic acid like DNA RNA is single stranded. RNA does not contain thymine but instead has the base called uricil which bonds with adenine. RNA has many functions in the cell, most importantly it is critical in the process of protein synthesis

Protein Synthesis The Central Dogma DNA holds the CODE to make Proteins RNA transfers the CODE to the Ribosome Proteins are strings of amino acids coded for by DNA Proteins are the “workhorses” of the cell Structure, enzymes, communication, etc.

Transcription The DNA message is transcribed into an mRNA message by complementary base pairing in the nucleus.

Transcription Steps DNA strands split mRNA creates a complementary strand to one of the DNA strands mRNA leaves the nucleus for translation

Translation The mRNA then goes into the cytoplasm to give the code for a protein to the ribosome. tRNA molecules will bring the correct amino acid to the ribosome.

Translation Steps mRNA goes to cytoplasm Ribosome attaches to start codon on mRNA tRNA (contains 3 letter code and amino acid) base pairs with mRNA Amino acids from base pairs are connected to form a chain Once stop codon is reached, chain of amino acids stops forming and leaves forming a protein

DNA

Mutations Sometimes mistakes can be made in the copying process of DNA. Any change in the original sequence of base pairs is called a mutation.

Mutations What happens when a mistake is made in replication of DNA? Most mutations are NOT helpful!! But every so often, a beneficial mutation occurs (black moths)

The Black Moth Peppered moths have a mutation making them appear mostly black In the 19th century, more black moths were found to exist then the original peppered type Having black wings found to be advantageous because of industry producing soot that was black during this time

Types of Mutations Point Mutations – the change in one single nucleotide base. substitution – one letter replaces another in the sequence. (ex. A->G) insertion – one letter is added to the sequence. (ex. a new T is added) deletion – one letter is removed from the sequence. (ex. a G is removed)

Make a substitution in the following DNA A T T G C G T G T G Make an insertion in the original sequence Make a deletion in the original sequence

Larger Mutations Inversions – when 2 or more bases (letters) are switched into reverse order. Duplications – when bases are repeated in the original order more than one time. Translocations – when bases are moved from one area of the sequence to another.

Make an 3 base inversion mutation in the following DNA sequence… A T T G C G T G T G Make a duplication of the inversion here Make a translocation of 3 bases