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Ribonucleic Acid (RNA) and Protein Synthesis Section 12-3 Outline of today’s information RNA - basics 1 Summary Translation 2 Transcription 3 4 Replication 5 Outline of today’s information RNA - basics 1 2 3 4 5 The DNA/RNA connection DNA and RNA are partners in the business of making proteins. DNA 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 DNA* A long chain of nucleotides SINGLE stranded Phosphate, sugar (ribose), nitrogenous base Adenine, guanine, cytosine, URACIL 3 Types of RNA messenger RNA (mRNA) ribosomal RNA (rRNA) Instructions for assembling proteins out of amino acids – code is copied from DNA and taken to the rest of the cell. The main pieces that make up ribosomes (along with some protein components). Ribosomes assemble proteins. transfer RNA (tRNA) Transfers (delivers) amino acids to ribosomes. Checkpoint What are three differences between RNA and DNA? What are the three types of RNA? What does each kind of RNA do? RNA makes proteins from the information stored in the cell’s nucleus (DNA). This requires two different processes — transcription and translation. process types of RNA involved location function transcription messenger RNA mRNA nucleus copy DNA translation messenger RNA mRNA On a ribosome in the cytoplasm make proteins transfer RNA tRNA ribosomal RNA rRNA Outline of today’s information RNA - basics 1 2 Transcription 3 4 5 Transcription Transcription - the conversion of information from one form to another. In molecular genetics, transcription is when the “code” found in DNA is transcribed (or copied) into a complementary sequence of RNA. Cooking/Kitchen analogy of transcription of DNA into RNA If DNA is like a treasured cookbook in your grandmother’s house that is filled with dozens of family recipes, Then, the process of transcription is like copying down one recipe from Grandmother’s cookbook (let’s say, pecan pie) onto an index card that you can take home to use. The mRNA is the “index card with one copied recipe.” A brief description of transcription The enzyme RNA polymerase binds to a particular part of the DNA that says “the gene starts here.” 1. • This location is called the promoter site. RNA polymerase - the enzyme that makes an RNA copy of the DNA gene A brief description of transcription After the RNA polymerase binds to the promoter site, the 2 strands of the DNA begin to unzip to form a “bubble” of unpaired DNA strands. 2. • This allows space for the mRNA to be assembled. RNA polymerase - the enzyme that makes an RNA copy of the DNA gene A brief description of transcription The mRNA transcript is built nucleotide by nucleotide by the RNA polymerase as it moves over the DNA (gene). 3. • The assembled RNA nucleotides are complementary to the nucleotides on the DNA. RNA polymerase transcribing the gene RNA/DNA base-pairing rules (for making the mRNA) Complementary nucleotides In the new strand of RNA, ___________ pairs With __________ on the DNA template Guanine (G) Cytosine (C) Cytosine (C) Guanine (G) Adenine (A) Thymine (T) Uracil (U) Adenine (A) Example of base-pairing What would the mRNA sequence be if the DNA template strand were: ATTGGCGCTAAC ? A brief description of transcription 4. The end of transcription occurs when • the end of the gene is reached • the mRNA is cut loose • the mRNA is edited (in eukaryotes) to make it ready for use • the mRNA is exported out of the nucleus and into the cytoplasm. RNA polymerase transcribing the gene Checkpoint If the DNA sequence is: ATT GTC CAC TGG AGC What will the mRNA be after transcription? Can you now describe what is going on in this picture? nucleus mRNA RNA polymerase DNA Outline of today’s information RNA - basics 1 Translation 2 Transcription 3 4 5 Translation mRNA (messenger RNA) is DECODED by a RIBOSOME to make… Proteins mRNA attaches to a ribosome mRNA is read 3 bases at a time by the ribosome. This three-base unit is called a codon. Translation As each codon (3 N-bases) moves through the ribosome like a ribbon… The tRNAs with the correct anticodon bring the required amino acids. Translation (continued) Translation Anticodon - the 3-base sequence on each different tRNA that is complementary to a codon on mRNA. (codon) From Wikipedia commons The relationship between tRNAs and amino acids Each amino acid (a.a.) is carried by tRNAs that have anticodons complementary to the mRNA codons. We will look at how this genetic code works a little later. Translation The ribosome forms a peptide bond between this newly delivered amino acid and the previous a.a. in the chain. This makes the polypeptide chain (what will be the protein) one a.a. longer. ribosome Translation tRNA (minus its amino acid) is released The ribosome moves to next codon This continues until a Stop Codon is reached New polypeptide is released ribosome Can you now describe what is going on in this picture? 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? Proteins 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 mRNA UCGCACGGU UCGCACGGU Codons: UCG CAC GGU Translation These strings of 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 mRNA has the appropriate complementary codon. We can use a chart to determine which amino acids are coded for by a given codon. Codons: UCG CAC GGU Note the 20 amino acids plus the 3 stop codons Proteins Example: If a DNA sequence is GGCTATCTA, The complementary mRNA 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 DNA sequence is: GTAGGCCTCTGGTGCACT What will the mRNA be after transcription? What will the amino sequence be? Outline of today’s information RNA - basics 1 Translation 2 Transcription 3 4 Replication 5 DNA transcription and translation compared with DNA replication DNA transcription and translation One small gene at a time Nearly constant throughout cell’s life For assembling the proteins of which we, and all living things, are made. DNA replication Requires the copying of the cell’s entire collection of DNA. Is only performed once in the cell’s life. For reproduction where all the instructions for making an organism must be passed on. DNA replication Before a cell can divide, it needs to have two complete set of instructions, one for each of the two new daughter cells. The duplication of the cell’s DNA is called DNA replication. DNA replication This copying of DNA is very efficient and elegant because each strand has all the information needed to make the other strand (the base pairing rules allow you to reconstruct what the complementary sequence was). Base-pairing Rules • Adenine (A) always pairs with Thymine (T) • A •• T or T •• A • Connected by 2 Hydrogen bonds • Cytosine (C) always pairs with Guanine (G) • C ••• G or G ••• C • Connected by 3 Hydrogen bonds Steps in DNA Replication Step 1 The two strands of DNA are “unzipped” by the enzyme helicase. Steps in DNA Replication Step 2 Now, each separate strand of DNA can serve as a template to make a new complementary strand of DNA. The new strands are formed by the enzyme DNA polymerase which adds the correct nucleotides one at a time to make the new strands. Replication of DNA is semiconservative. That is, one side of each new DNA strand is "old" and the other side is "new". Outline of today’s information RNA - basics 1 Summary Translation 2 Transcription 3 4 Replication 5 Central Dogma of Molecular Biology transcription replication DNA translation RNA Protein Summary Checkpoint What does each type of RNA do? Describe what happens in transcription. Describe the process of translation. Beginning with a DNA sequence, you need to be able to figure out the amino acid sequence it codes for. If the DNA sequence is TGAGGGAGA… Mutations Cells do rarely make mistakes copying their own DNA resulting in a change in the DNA. 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 http://student.ccbcmd.edu/~gkaiser/biotu torials/protsyn/translat.html http://wwwclass.unl.edu/biochem/gp2/m_biology/ani mation/gene/gene_a3.html http://www.biostudio.com/demo_freeman _protein_synthesis.htm http://www.wisconline.com/objects/index_tj.asp?objID=AP 1302 http://www.abdn.ac.uk/~clt011/flash/sam ples/protein.swf