Protein Synthesis-How do we go from genotype to phenotype

RNA There are three differences between RNA and DNA: –RNA is single stranded, DNA is double stranded –RNA contains uracil and not thymine, DNA contains thymine not uracil –RNA has ribose as its sugar, DNA has deoxyribose

There are three types of RNA: –Messenger RNA (mRNA)-is made by copying the DNA DNA can’t leave the nucleus Takes strand message to ribosomes –Transfer RNA (tRNA)-carries the correct amino acid to the ribosome from the cytoplasm –Ribosomal RNA (rRNA)-makes up the ribosome

Protein syntheis The DNA of a person contains about 50,000 genes each of which codes for the making of a protein. Hair and hemoglobin are proteins that your body makes. Enzymes are also proteins. Everything in your body is based on the making of proteins!

Transcription The first phase of protein synthesis is transcription which takes place in the nucleus. This is the process of copying DNA into mRNA. It allows the code that is on DNA to be copied and taken to the ribosome via mRNA.

Steps of Transcription RNA polymerase will initiate the making of mRNA in the same way that DNA polymerase replicates DNA. We call this the start codon. A codon is a set of three bases and all RNA is divided up in sets of three. The transcription continues until the stop codon is reached. Then, the polymerase releases the DNA and the newly synthesized RNA strand.

TRANSCRIBE THESE ON YOUR NOTEGUIDE. A T C A T T C G G G A T C C A T T A C G G G A UAGUAAGCCCUA GGUAAUGCCCU

SPLICING Before the mRNA can go to the ribosome, it needs to be spliced. –The junk (parts of the DNA that are noncoding regions) called introns need to be cut out. –Exons (coding regions) are then stuck together. This is the correct concise message.

Translation The second part of protein synthesis takes place at the ribosome. The mRNA that was made in transcription travels out of the nucleus and to a ribosome on the ER or in the cytoplasm.

Amino acids that are freely floating in the cytoplasm are transported to the ribosome by the tRNAs. Part of the tRNA contains a region of three bases called the anticodon. –The anticodon will match with the mRNA complementary codon. –THE ANTICODON DOES NOT TELL WHAT AMINO ACID IS ATTACHED TO IT.

Making a protein The mRNA attaches to one of three binding sites on the ribosome. As the ribosome moves along the mRNA, each mRNA codon is paired with the correct tRNA anticodon. The pairing of the next amino acid creates a bond between the two amino acids called a peptide bond. In this way, the entire mRNA molecule is read, making an increasingly long chain of amino acids all bonded to one another, until a stop codon is reached.

Watch the animation. online.com/objects/index.asp?objID=AP1302

Finishing protein synthesis Protein synthesis stops when it hits the stop codon The chain of amino acids will be released and fold into its unique shape. This usually happens at the ER or the GA. The order of amino acids dictates the shape of the protein. The shape determines the function of the protein. port.com/ /lib/ /Animations/Protein%20Synthesis%20%20long. swf

Write the anticodons for the codons A U G C A U U A G G C C A U C G A A U A C A G G A U UACGUAAUCCGGUA GCUUAUGUCCUA

Write the amino acid sequence from the mRNA sequence. A U G C A G C A U U A U A C C C G A A U A C A G G A U Methionine glutamine histidine tyrosine threonine Arginine isoleucine glutamine aspartic acid