12 3 Notes RNA and Protein Synthesis Information

12 -3 Notes RNA and Protein Synthesis

Information, Please Section 12 -3 • DNA contains the information that a cell needs to carry out all of its functions. In a way, DNA is like the cell’s encyclopedia. Suppose that you go to the library to do research for a science project. You find the information in an encyclopedia. You go to the desk to sign out the book, but the librarian informs you that this book is for reference only and may not be taken out. 1. Why do you think the library holds some books for reference only? 2. If you can’t borrow a book, how can you take home the information in it? 3. All of the parts of a cell are controlled by the information in DNA, yet DNA does not leave the nucleus. How do you think the information in DNA might get from the nucleus to the rest of the cell? Go to Section:

12 -3 Vocabulary • Messenger RNA- (m. RNA) – RNA molecule that carries copies of instruction for the assembly of amino acids into proteins from DNA to the rest of the cell. • Ribosomal RNA- (r. RNA) – Type of RNA that makes up the major part of the ribosomes.

12 -3 Vocabulary • Transfer RNA (t. RNA) – Type of RNA molecule that transfer amino acids to ribosomes during protein synthesis. • Transcription– Process in which part of the nuclotide sequence of DNA is copied into complemetary sequence in RNA. Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase DNA RNA

12 -3 Vocabulary • RNA polymerase– Enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription. • Promoter – Region of DNA that indicates to an enzyme where to bind to make RNA.

12 -3 Vocabulary • Intron– Intervening sequence of DNA; does not code for a protein. • Exon– Expressed sequence of DNA; codes for a protein.

1. The Structure of RNA a. It consists of long chains of nucleotides, like DNA b. There are three main differences from DNA RNA DNA 1) Sugar is ribose Sugar is deoxyribose 2) Single stranded Double stranded Contains uracil Contains thymine

2. Types of RNA a. Main function is protein synthesis b. There are three main types of RNA 1) Messenger RNA (m. RNA): carry copies of instructions for assembling amino acids 2) Ribosomal RNA (r. RNA): located on ribosomes, where proteins are assembled 3) Transfer RNA (t. RNA): transfers each amino acid to the ribosome as specified by m. RNA

3. Transcription a. Transcription: the DNA nucleotide sequence is copied into a complementary RNA sequence b. The DNA strands unzips, and assembles nucleotides to form an RNA strand from the DNA template c. m. RNA is edited before leaving the nucleus d. Introns (intervening sequences not needed in the code) are cut out leaving exons (expressed sequences needed in the code) e. m. RNA is sent to the ribosome

• Codon- 12 -3 Vocabulary – Three-nucleotide sequence on messenger RNA that codes for a single amino acid. • Translation– Decoding of m. RNA message into a polypeptide chain. • Anticodon – Group of three bases on a t. RNA molecule that are complementary to an m. RNA codon.

12 -3 Part 2 1. Translation is the decoding of an m. RNA message into a polypeptide chain (protein)

2. There are four main steps to translation a. m. RNA must be transcribed from DNA in the nucleus and released into the cytoplasm b. m. RNA attaches to the ribosome at a start codon 1) As each m. RNA codon goes through the ribosome, the proper amino acid is attached using the genetic code 2) The Genetic Code is a universal “language” for reading m. RNA 3) t. RNA molecules have amino acids attached to one end and three unpaired bases at the other 4) The three bases, called the anticodon, are complementary of the m. RNA codon 5) The codons fit in place

Nucleus Messenger RNA is transcribed in the nucleus. Phenylalanine t. RNA m. RNA Transfer RNA Methionine The m. RNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the m. RNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the t. RNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome m. RNA Lysine Start codon

The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its t. RNA. The t. RNA floats away, allowing the ribosome to bind to another t. RNA. The ribosome moves along the m. RNA, binding new t. RNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome t. RNA m. RNA Completing the Polypeptide m. RNA Translation direction The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

c. Polypeptide chain grows until ribosome reaches a stop codon on the m. RNA 1) It releases the m. RNA, completing translation 2) This protein molecule can range from 50 to 3, 000 amino acids

Concept Map Section 12 -3 RNA can be Messenger RNA also called which functions to m. RNA Go to Section: Ribosomal RNA Carry instructions also called which functions to r. RNA Combine with proteins from to to make up DNA Ribosomes Transfer RNA also called which functions to t. RNA Bring amino acids to ribosome