Ribonucleic Acid (RNA) and Protein Synthesis Section 12-3 Summary The /RNA connection and RNA are partners in the business of making proteins. is a specialist. It provides stable, permanent storage of the code (or recipe) for making proteins RNA is a generalist (more versatile). It serves a variety of roles (including the chef ) to make (synthesize) proteins. Structure of RNA (ribonucleic acid) *Notice the differences (in red) from * A long chain of nucleotides SINGLE stranded Phosphate, sugar (ribose), nitrogenous base Adenine, guanine, cytosine, URACIL 3 Types of RNA messenger RNA () Instructions for assembling amino acids - copied from and taken to the rest of the cell. ribosomal RNA (rrna) The main pieces that make up ribosomes (along with some protein components). Ribosomes assemble proteins. transfer RNA (trna) Transfers (delivers) amino acids to ribosomes. 1
Checkpoint What are three differences between RNA and? What are the three types of RNA? RNA makes proteins from the information stored in the cell s nucleus (). This requires two different processes transcription and translation. process transcription types of RNA involved messenger RNA location nucleus function copy What does each kind of RNA do? translation messenger RNA transfer RNA trna cytoplasm make proteins ribosomal RNA rrna - the conversion of information from one form to another. In molecular genetics, transcription is when the code found in is transcribed into a complementary sequence of RNA. Similar, but not the same as replication. Some differences are RNA polymerase unzips the and assembles the strand. RNA polymerase binds to the at a site called the promoter. The copies one entire gene. In making the, Uracil replaces Thymine as the complement to Adenine. The other base complements are identical to those in cytosine (C) in RNA pairs with guanine (G) in guanine (G) in RNA pairs with cytosine (C) in adenine (A) in RNA pairs with thymine (T) in uracil (U) in RNA pairs with adenine (A) in 2
Checkpoint If the sequence is: nucleus ATT GTC CAC TGG AGC What will the be after transcription? RNA polymerase (messenger RNA) is DECODED by a RIBOSOME to make Proteins attaches to a ribosome As each codon (3 N- bases) moves through the ribosome like a ribbon The trnas with the correct anticodon bring the required amino acids. Anticodon - the 3-base sequence on each different trna that is complementary to a codon on. 3
Ribosome forms a peptide bond between this amino acid and the previous one This makes the polypeptide chain (what will be the protein) one a.a. longer. trna (minus its amino acid) released Ribosome moves to next codon Until a Stop Codon is reached New polypeptide is released Proteins Proteins The whole purpose of the genetic code is to assemble complicated proteins perfectly, over and over, millions of times. Proteins (polypeptides) are long chains of amino acids (20 different ones) that are connected in a specific order. How can just four letters (the four Nbases in RNA) code for the correct amino acid (if there are 20 different ones)? A, U, C, G vs. 20 different amino acids? RNA is read 3 letters at a time Like 3 letter words These 3 letter words are called codons. Examples AUG GGC UUA Cracking the Code UCGCACGGU UCGCACGGU Codons: UCG CAC GGU These codons are then translated into proteins by the interaction of ribosomes and trna s. trna s only deliver their specific amino acid to the ribosome when the has the appropriate complementary codon. We can use a chart to determine which amino acids are coded for by a given codon. 4
Codons: UCG CAC GGU Proteins Note the 20 amino acids plus the 3 stop codons Example: If a sequence is GGCTATCTA, The complementary sequence is CCG AUA GAU Using a genetic code chart (like on pg. 303), one can determine that these three codons correspond to the following amino acids: Proline Isoleucine Aspartic Acid Checkpoint If the sequence is: GTAGGCCTCTGGTGCACT What will the be after transcription? What will the amino sequence be? Summary Central Dogma of Molecular Biology Summary Checkpoint What does each type of RNA do? transcription translation Describe what happens in transcription. replication RNA Protein Describe the process of translation. Beginning with a sequence, you need to be able to figure out the amino acid sequence it codes for. If the sequence is TGAGGGAGA 5
Mutations Cells do rarely make mistakes copying their own resulting in a change in the. Mutation a change in genetic material. Types of mutations Gene mutations mutations that produce changes in a single gene. Chromosomal Mutations Changes in the number or structure of chromosomes. Results of mutations Can be very harmful Can be neutral (neither harmful nor good) Also result in genetic variability Good for changing environments Plant and Animal Breeders Polyploidy = extra sets of chromosomes (3N, 4N, 6n, 8n, 10n, etc.) Bananas, citrus fruits, seedless fruit Protein synthesis animations http://www.stolaf.edu/people/giannini/flas hanimat/molgenetics/transcription.swf http://www.stolaf.edu/people/giannini/flas hanimat/molgenetics/translation.swf http://student.ccbcmd.edu/~gkaiser/biotu torials/protsyn/translat.html Protein synthesis animations http://wwwclass.unl.edu/biochem/gp2/m_biology/ani mation/gene/gene_a1.html http://wwwclass.unl.edu/biochem/gp2/m_biology/ani mation/gene/gene_a2.html http://wwwclass.unl.edu/biochem/gp2/m_biology/ani mation/gene/gene_a3.html end 6