A gene is a segment of DNA that holds the ‘directions’ for a certain physical trait such as eye color The ‘directions’ contained on a gene or genes tells a cell how to make a certain protein The way that the protein is made determines the way the trait is expressed

Only a fraction of genes in a cell are expressed (made into RNA) at any given time. How does the cell decide which will be turned on and which will stay “silent”? Promoter regions that show RNA polymerase where to start. There are other Regulatory sites that control whether a gene is ON or OFF.

Group of genes that operate together are called an Operon When an Operon is turned OFF a repressor molecule binds to the operon, blocking RNA polymerase When and Operon is turned ON the repressor molecule is released and RNA Polymerase is allowed to copy the genes

GENE is turned “ON”

RNA Structure Also made of nucleotides RNA is single stranded - allows it to leave the nucleus while DNA cannot Contains Uracil instead of thymine A-U G-C There are three kinds of RNA: rRNA, tRNA, mRNA

Reading the codes DNA is copied by mRNA mRNA’s code is then translated into amino acids Remember A-T (U) G-C Translate this DNA code into mRNA code: GAGTTCACGTTG mRNA code:

Now translate the mRNA code into amino acids using the chart CUCAAGUGCUUC Leu Lys Cys Phe

DNA Structure in Prokaryotes Approximately 5 million base pairs (3,000 genes) DNA molecule in bacteria is circular & found in the cytoplasm Prokaryotes have NO nucleus!

The Human Genome The complete genetic code for humans is now known The Human Genome project has deciphered the order of the 3.2 billion base pairs in the 23 human chromosomes Now scientists are working on learning about how and where all the different proteins coded for on our DNA is being used

The Human Genome This information is important in research for the cause, treatment & prevention of disease

The End Hooray! We are done!