Lesson Overview 13.1 RNA

The Role of RNA sugar in RNA is ribose instead of deoxyribose How does RNA differ from DNA? sugar in RNA is ribose instead of deoxyribose (2) RNA is generally single-stranded and not double- stranded (3) RNA contains uracil (U) in place of thymine (T)

Comparing RNA and DNA RNA copies info from DNA and can take that info OUTSIDE of the nucleus safely Job of RNA is to assemble amino acids into proteins

Functions of RNA The three main types of RNA are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA)

Messenger RNA The RNA molecules that carry copies of DNA instructions are known as messenger RNA (mRNA)

Ribosomal RNA ribosomal RNA (rRNA) - makes up the ribosome (where mRNA gets “read”)

Transfer RNA transfer RNA (tRNA) – carries (transfers) each amino acid to the ribosome

Transcription Using template from DNA to make RNA Takes place in nucleus Makes single strand of RNA Uracil (U) is paired up with adenine (A)

Transcription THREE MAJOR STEPS: 1. INITIATION – RNA polymerase attaches to promoter region and unwinds DNA 2. ELONGATION – RNA polymerase adds bases (A, U, C, G) to make transcript 3. TERMINATION – transcript reaches termination site and is released

Transcription Transcription requires an enzyme, known as RNA polymerase, that is similar to DNA polymerase/helicase - unwinds DNA strands and pairs up bases http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/animations.asp

RNA Editing Sometimes RNA needs to be modified (edited) INTRONS – portions of RNA that are cut out and discarded EXONS - The remaining pieces thjat are put back together

13.2 Ribosomes and Protein Synthesis Lesson Overview 13.2 Ribosomes and Protein Synthesis

The Genetic Code The transcript contains a code for making proteins The first step in decoding genetic messages is to transcribe a nucleotide base sequence from DNA to RNA The transcript contains a code for making proteins

The Genetic Code Proteins are made by joining amino acids together into long chains, called polypeptides. As many as 20 different amino acids are commonly found in polypeptides.

The Genetic Code Each three-letter “word” in mRNA = codon A codon consists of three consecutive bases that specify a single amino acid to be added to the polypeptide chain

How to Read Codons Because there are four different bases in RNA, there are 64 possible three-base codons (4 × 4 × 4 = 64) in the genetic code

Start and Stop Codons The codon AUG serves as the START codon for protein synthesis. After AUG, mRNA is read until it reaches one of three different “stop” codons

Translation The decoding of an mRNA message into a protein is a process known as translation Happens at the ribosome (in cytosol/cytoplasm) http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/animations.asp http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter12/animation_quiz_2.html

Steps in Translation 1. ribosome attaches to an mRNA molecule in the cytoplasm

Steps in Translation 2. ribosome reads each codon of mRNA, and directs tRNA to bring the specified amino acid into the ribosome

Steps in Translation 3. the ribosome then attaches each amino acid to the growing chain (attaching them together by PEPTIDE bonds

Steps in Translation 4. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule

Steps in Translation Each tRNA molecule carries just one kind of amino acid In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon

The Molecular Basis of Heredity The central dogma of molecular biology is that information is transferred from DNA to RNA to protein