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The Role and Structure of RNA Daily Challenge: I CAN analyze and explain the role that RNA plays in the production of proteins through transcription and translation. Nucleic Acids • There are 2 types of nucleic acids. – DNA or deoxyribonucleic acid – RNA or ribonucleic acid • All living things have both DNA and RNA. • Nucleic acids are made of nucleotides and carry genetic information. DNA vs. RNA • DNA – Deoxyribonucleic acid – Double-stranded – Sugar = deoxyribose – Nucleotide Bases: • Adenine • Thymine • Guanine • Cytosine • RNA – Ribonucleic acid – Single-stranded – Sugar = ribose – Nucleotide Bases: • Adenine • Uracil • Guanine • Cytosine Purpose of DNA • DNA can be copied, but that does NOT explain how a gene works. • DNA contains coded instructions for making proteins. • The first step of making proteins is decoding the genetic messages by copying the nucleotide sequence from DNA into RNA. Functions of RNA • In most cells RNA molecules have just one job — protein synthesis. • Protein synthesis is the process by which amino acids are joined together to make proteins. • Amino acids are the building blocks of proteins. • There are a total of 20 amino acids. • The assembly of amino acids is controlled by RNA. Types of RNA • There are three types of RNA that each play an important role in protein synthesis. • The three types are: mRNA — Messenger RNA tRNA — Transfer RNA rRNA — Ribosomal RNA Messenger RNA (mRNA) Messenger RNA serve as messengers from DNA to the rest of the cell. They carry copies of the instructions found on genes. Transfer RNA (tRNA) tRNA takes the messages from mRNA and decodes them for the ribosome. During the construction of a protein, transfer RNA transfers each amino acid to the ribosome. Ribosomal RNA (rRNA) Proteins are assembled on ribosomes made of ribosomal RNA. Ribosomal RNA helps build the actual protein. rRNA puts together the amino acid messages carried by mRNA and decoded by tRNA. Protein Synthesis: An Overview Daily Challenge: I CAN explain the processes of transcription and translation as it relates to the process of protein synthesis. Protein Synthesis • Protein synthesis uses the information in genes to make proteins. • There are 2 Steps: –Transcription –Translation Transcription • DNA is copied into a complementary sequence of mRNA by the enzyme RNA Polymerase. • mRNA leaves the nucleus and goes to the cytoplasm. • The mRNA sequence is read in triplets (group of 3 bases) called “codons.” • Each codon codes for a specific amino acid. (Each codon is like a word in a sentence) Amino Acid Codon Chart Transcription • Transcription requires RNA polymerase, an enzyme a lot like DNA polymerase • RNA polymerase binds to DNA, separates the strands, and uses one strand as a template for making mRNA. • RNA polymerase “polymerizes” (links together) the nucleotides that make up mRNA Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase DNA RNA Where to Start? • RNA polymerase doesn’t randomly bind to DNA. • It will only bind to sites known as promoters—regions of DNA that have specific sequences. • Promoters are signals that say “START RNA HERE!” • Similar signals also tells transcription to stop. Start/Stop Codons • There are 64 different codons. • Most code for amino acids. • There will always be a “Start” codon (AUG) at the beginning. It is like capitalizing the 1st letter of a sentence. • There will always be a “Stop” codon (UGA, UAA, UAG) at the end. It is like a period at the end of a sentence. Translation • tRNA translates the mRNA using “anticodons.” • Each tRNA molecule has an anticodon on one end and an amino acid on the other. • tRNA transfers the amino acids to the ribosome in the correct sequence. • The ribosome made of rRNA links the amino acids together to build the polypeptide chain or protein. Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. Phenylalanine tRNA mRNA Lysine Transfer RNA The mRNA 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 mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Methionine anticodon Ribosome mRNA Start codon The Polypeptide “Assembly Line” The ribosome joins the two amino acids— methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Lysine Growing polypeptide chain Ribosome tRNA tRNA mRNA Completing the Polypeptide mRNA Translation direction Ribosome The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. Protein Synthesis Review • DNA carries the information in the form of genes to build proteins. • RNA polymerase copies the DNA strand into messenger RNA (mRNA) which carries the DNA message. • Transfer RNA (tRNA) reads the message of mRNA, gathers the correct amino acids, and delivers them to the ribosome for assembly. • Ribosomal RNA (rRNA) then takes the amino acids from transfer RNA and links them together to make the protein. Remember This! • DNA is like the master blueprint. • RNA is like the blueprint copy the workers use. • The workers are ribosomes. • Proteins are the finished product. • Proteins are the keys to almost EVERYTHING that living cells do! Protein Synthesis Activity • Step 1: Transcription – Copy the “gene” into the complementary sequence of mRNA. – This must be done in the “Nucleus.” • Step 2: Translation – Translate the mRNA using the “tRNA cards” posted around the room. The codon should match up with a word. – If you have done this correctly, your sentence should make sense!!! – Don’t forget the punctuation (Start/Stop codons)!!