DNA to Protein – 12 Part one AP Biology

What is a Gene? A gene is a sequence of DNA that contains the information or the code for a protein or an RNA What is a code? A code is a molecular message in the language of DNA or RNA that instructs the cell how to make a protein or a RNA molecule

What is the code? The code is written with the DNA alphabet of A,T,C, and G’s The words of DNA are in groups of three bases called triplets

Genes It had been estimated that because there are 100,000 proteins that there must be 100,000 genes The Genome Project has revealed that there are actually less than 50,000 probably between 30,000 and 40,000

The Early Concept of a Gene In the 1940s, Beadle and Tatum showed that when an altered gene resulted in an altered phenotype, that altered phenotype always showed up as an altered enzyme.

Wild type vs. mutant The normal enzyme is referred to as the wild type An altered enzyme is referred to as a mutant and reflects a change in the genetic message to make the protein

The Experiment That Demonstrated the Relationship Between Gene and Protein

A Biochemical Pathway The pathway requires three enzymes to produce the product Each enzyme is a protein coded for by a gene

What is Gene Expression When the code of the gene is read and translated from the language of nucleic acids to the language of proteins( from bases to amino acids)

The structure of a gene GCGCGC CCAAT TATA BOX 3’ TAC EXON! AT INTRON CG EXON ATT5’ -100bp -40bp -30bp start GENE stop

Transcription The process of making a copy of messenger RNA complementary to the DNA strand The molecule that copies the DNA is a RNA Polymerase RNA polymerase reads 3’-5’ and makes the RNA 5’ ’

RNA Polymerase Looks for the signals of the CAT BOX Sees the TATA Binds to the promoter( conserved or similar in eukaryotes) Transcription begins with 3’TAC

Messenger RNA is made continuously Messenger RNA is made by the transcription of the bases in DNA into an RNA sequence This is called the primary sequence This sequence includes the introns and the exons As the m RNA( primary transcript) is made it is edited by a complex

Termination When the one of the three stop messages are reached the process of transcription ends The three stop messages are ATC 3’ ATT 3’ ACT 3’

The first two steps of processing pre-mRNA take place in the nucleus: The G cap, a modified GTP, is added to the 5¢ end. It facilitates the binding of mRNA to the ribosome and protects the mRNA from being digested by ribonucleases. A poly A tail is added to the 3¢ end. It is 100 to 300 residues of adenine (poly A) in length. RNA

RNA splicing removes the introns and splices the exons together: At the boundaries between introns and exons are consensus sequences. A small ribonucleoprotein particle (snRNP) binds to the consensus sequence at the 5¢ exon–intron boundary. Another snRNP binds near the 3¢ exon–intron boundary. Then other proteins bind, forming a large RNA–protein complex called a spliceosome. This complex cuts the RNA, releases the introns, and joins the ends of the exons. RNA Splicing

Spliceosome The spliceosome edits the messenger RNA transcript It works with small RNAs This removes the introns by recognizing the intron border The exons are connected and the code for the protein is now continuous

Figure The Spliceosome, an RNA Splicing Machine (Part 1) Spliceosome and snurps I

Spliceosome and snurps II