12-3 RNA and Protein Synthesis

Page 300

A. Introduction

• 1. Genes are coded DNA instructions that control the production of proteins within the cell.

B. The Structure of RNA

• 1. RNA (Ribonucleic Acid) is similar to DNA because they are BOTH long chains of nucleotides.

• REVIEW: What are the 3 parts of a nucleotide?

B. The Structure of RNA• 2. There are 3 major differences between DNA

and RNA:

DNA RNASugar# of StrandsNitrogen Bases

C. 3 Types of RNA

• 1. Messenger RNA (mRNA) carries the coded information from genes on DNA to the rest of the cell.

C. 3 Types of RNA

• 2. Ribosomal RNA (rRNA) are part of the structure of a ribosome where proteins are made.

C. 3 Types of RNA• 3. Transfer RNA (tRNA) transfers each amino

acid to the ribosome as it is specified by coded messages in the in mRNA.

D. Transcription

• 1. Process of copying part of the nucleotide sequence of DNA into a complementary sequence in RNA.

D. Transcription

• 2. Requires an enzyme called RNA Polymerase which binds to DNA and separates DNA strands.

D. Transcription

• 3. RNA Polymerase uses 1 strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

D. Transcription

• 4. Promoters are specific base sequences that signal to RNA Polymerase where to begin transcription.

E. RNA Editing

• 1. After RNA is transcribed, it needs to be edited so that only the sections that code for proteins are used.

E. RNA Editing• 2. Introns are not involved in coding for

proteins and are removed from RNA chains.

E. RNA Editing

• 3. Exons code for proteins and are kept in RNA chains because they are “expressed” in protein synthesis.

F. The Genetic Code

• 1. Proteins are made by joining amino acids into long chains called polypeptides.

F. The Genetic Code

• 2. The genetic code of mRNA is read in groups of 3 letters called codons.

F. The Genetic Code

• 3. Each codon codes for a specific amino acid (there are 20 total).

G. Translation

• 1. Decoding mRNA into a polypeptide (protein).

• LETS PRACTICE!• AUG-GGG-CCC-UAA• AUG-UGU-CAG-UAG

G. Translation

• 2. Before translation can occur, mRNA is transcribed and edited in the nucleus before being released into the cytoplasm.

G. Translation

• 3. mRNA attaches to a ribosome and moves through one codon at a time.

G. Translation

• 4. As the codons move through the ribosome, tRNA molecules deliver the matching amino acid to build the polypeptide chain.

G. Translation

• 5. tRNA carry an anticodon that is complementary to the codon of the mRNA.

G. Translation

• 6. The polypeptide chain continues to grow until it reaches a STOP codon.