Protein Synthesis Notes

Main Idea DNA codes for RNA, which guides protein synthesis. Protein Synthesis is the making of proteins.

Protein Synthesis Overview In protein synthesis RNA uses a code from the DNA strand in the nucleus to make proteins for the cell. There are two main stages of protein synthesis: Transcription and Translation.

The Importance of Proteins Recall that proteins are the building structures of cells and are important in catalyzing events in cells. The shape of a protein determines how the protein functions in the organism. How the protein is built is very important.

Central Dogma DNA codes for RNA and RNA codes for proteins. RNA is a nucleic acid that is similar to DNA, however RNA: Contains the sugar ribose and the base uracil instead of thymine. Usually is single stranded

Types of RNA - There are 3 different types of RNA used in Protein Synthesis. Messenger RNA (mRNA) – takes the DNA message to the ribosome ▫Long strands of RNA nucleotides that are formed complementary to one strand of DNA Ribosomal RNA (rRNA) - helps in protein production ▫Associates with proteins to form ribosomes in the cytoplasm Transfer RNA (tRNA) – transfers or brings amino acids to the protein factories (ribosomes) ▫Small segments of RNA nucleotides that transport amino acids to the ribosome

Comparison of Three Types of RNA Each type of RNA has a different shape and a different job (function.) Describe each type of RNA.

The Process of Protein Synthesis Protein synthesis takes place in two main stages. Transcription – DNA’s message is transcribed by mRNA in the nucleus and taken to the ribosomes. Translation – rRNA and mRNA work together with tRNA to translate DNA’s message into a strand of amino acids or a protein.

Transcription Through transcription, the DNA code is transferred to mRNA in the nucleus. DNA cannot leave the nucleus! mRNA takes the DNA message out to the ribosomes. DNA is unzipped in the nucleus and RNA polymerase binds to a specific section where an mRNA will be synthesized. The mRNA strand is complimentary to the DNA strand. However, instead of A pairing with T (thymine), in mRNA T is replaced with U or uracil.

RNA Processing The code on the DNA is interrupted periodically by sequences that are not in the final mRNA. Intervening sequences are called introns. Remaining pieces of DNA that serve as the coding sequences are called exons.

The Code Experiments during the 1960s demonstrated that the DNA code was a three base code. The three-base code in DNA or mRNA is called a codon. The three base code, or codon, in mRNA determines the amino acid that is produced. A Rosetta stone or coding chart is used to decode the message. Which amino acid does CAG code for? ___

Translation In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. At the middle of the folded strand, there is a three- base coding sequence called the anticodon. Each anticodon is complementary to a codon on the mRNA. As tRNA brings amino acids to the ribosome, a chain of amino acids (polypeptide) is built until a STOP message is received. When the STOP message is received, the new protein is released to be used by the cell. Which codon is a STOP codon? _______

Visualizing Transcription and Translation Transcription takes place in the nucleus. Translation occurs in the cytoplasm and results in the formation of polypeptides.

Using your own words, write the story of protein synthesis. Start in the nucleus.

One Gene – One Enzyme The Beadle and Tatum experiment showed that one gene codes for one enzyme. We now know that one gene codes for one polypeptide (protein.)