6.C: Students will explain the purpose and process of transcription and translation using models of DNA and RNA

Transcription

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2 6.C: Students will explain the purpose and process of transcription and translation using models of DNA and RNA

3 DNA mrna Protein

4 DNA is found in the nucleus, but making a protein occurs at the ribosome (either floating in the cytoplasm or attached to the rough ER) The DNA code must be copied and moved from the nucleus out to the cytoplasm (this is called transcription) Once in the cytoplasm, the code must be read so amino acids (building blocks of protein) can be assembled (this is called translation)

5 DNA cannot fit through the nuclear pores, and therefore cannot leave the nucleus to go to the ribosomes In order to get the DNA code out of the nucleus and into the cytoplasm, it must be turned into another nucleic acid called RNA RNA stands for ribonucleic acid

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7 RNA is different from DNA because it contains the sugar ribose (instead of deoxyribose) RNA does not contain the base thymine instead it has the base uracil A goes with U C goes with G The RNA molecule is single-stranded

8 Messenger RNA (mrna) copies the DNA code for a gene and carries that information to the ribosomes outside the nucleus Transfer RNA (trna) transfers (carries) amino acids to the ribosomes, where proteins are made

9 Long, straight chain of nucleotides Made in the nucleus copies the DNA code for a gene and then exits out the nuclear pores and goes to a ribosome Contains the nitrogen bases A, G, C, and U Carries information to build a specific protein A sequence of 3 bases is called a codon

10 Transfers (carries) amino acids to the ribosomes, where proteins are made Single-stranded molecule with an attachment site at one end for an amino acid The other end has three nucleotide bases called the anti-codon (complementary to the codon) Transfer = taxi

11 A codon designates a specific amino acid There are 20 amino acids created from the 64 possible codons One codon tells the ribosome to start translating (AUG), and three tell the ribosome to stop translating (UAA, UAG, or UGA)

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15 The production of a polypeptide chain Polypeptide chain = protein A string of amino acids held together with peptide bonds DNA mrna Protein The mrna is read in sets of 3 bases (codon) Two steps in protein synthesis transcription and translation

16 The process of copying the sequence of one strand of DNA (the template strand) and turning that information into mrna Requires the enzyme RNA polymerase

17 Practice: what would be the complementary RNA strand for the following DNA sequence? DNA 5 GCGTATG 3

18 Practice: what would be the complementary RNA strand for the following DNA sequence? DNA 5 GCGTATG 3 RNA 3 CGCAUAC 5

19 During transcription, RNA polymerase binds to DNA and separates the DNA strands RNA polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA Promoters are regions on DNA that show where RNA polymerase must bind to begin transcription Specific base sequences act as signals to stop transcription (termination signal)

20 Also known as RNA splicing After DNA is transcribed into RNA, it must be edited to make it functional Introns non-functional segments of RNA (they are taken out of the chain) Exons coding segments of RNA (they are left in) mrna leaves the nucleus through the nuclear pores and goes to the ribosome

21 The process of decoding the mrna and turning it into a polypeptide chain (protein) Ribosomes read mrna 3 bases (one codon) at a time

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24 Step 1 Initiation The mrna start codon (AUG) attaches to the ribosome The first trna molecule (with the first amino acid attached) moves into the P site A second trna molecule enters the A site

25 Step 2 Elongation Peptide bonds attach the amino acids together Once complete, the trna in the P site moves to the E site (exit site) and detaches The ribosome moves down the mrna, continuing to attach amino acids with peptide bonds

26 Step 3 Termination When the ribosome reaches one of the three stop codons, translation stops The ribosome releases the amino acid chain (polypeptide)

27 End Product The end product of protein synthesis is a protein (primary structure) A sequence of amino acids bonded together with peptide bonds (also called a polypeptide) aa2 aa3 aa4 aa5 aa199 aa1 aa200

28 Once it has been released, the polypeptide folds into its appropriate shape

29 There are 20 amino acids and 64 codons This means several different codons can specify the same amino acid There are several cases in which the third base of the codon can be changed, but the same amino acid will be coded for (silent mutation) Means the point mutation won t affect the final protein Ex: mrna GCU, GCA, GCG, GCC all code for the amino acid alanine

30 DNA mrna T A C C C G A G G T A G C C G C G T A T T start codon A U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

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