Ch. 11.4 & 11.5: Transcription & Translation
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Transcript of Ch. 11.4 & 11.5: Transcription & Translation
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Ch. 11.4 & 11.5: Transcription & Translation
Objectives: • Explain one-gene-one polypeptide
hypothesis.
• Describe the process of transcription.
• Explain how RNA is edited.
• Describe how RNA is translated into a protein.
• Describe how amino acids are coded.
• Summarize protein synthesis.
Vocab.: Transcription, RNA (ribonucleic acid), mRNA, RNA polymerase, intron, extron,
RNA splicing
Translation, tRNA, codon, anticodon, Codon, rRNA
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One Gene, One Polypeptide
Genotype: sequence of nucleotides bases in DNA.
Phenotype: Organism traits; based on proteins & protein fxns
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Beadle & Tatum: Research leads to “One gene, one enzyme”
Beadle & Tatum Experiment: 9:57 min http://www.youtube.com/watch?v=vP_h08cT5jw
•Expose bread mold to X-rays (Mutation = Damaged DNA).
•Essential enzyme/amino acid cannot be made from damaged DNA.
•Mutated mold won’t grow on “minimal” medium that lacks enzyme/amino acid it can’t make.
“one enzyme” - not accurate. 1 gene = 1 poly-peptide (part of 1 enzyme/protein)
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RNA carries DNA instructions to Ribos.
Ribosomes make PROTEINS.RNA: Ribonucleic AcidSingle strand nucleotide1. 5-C Sugar: Ribose2. Phosphate3. Nitrogen base
(A, U, G, C)U = Uracil; Replaces TA binds to U; G binds to C
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Transcription: DNA --> mRNA • DNA cannot leave
nucleus.• DNA nucleotide sequence
is converted into mRNA (messenger RNA).
• mRNA leaves nucleus --> directs protein synthesis @ ribo. in cytoplasm.
http://www.youtube.com/watch?v=983lhh20rGY&feature=related
http://www.youtube.com/watch?v=41_Ne5mS2ls
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Transcription: RNA Polymerase• Enzyme that links
RNA nucleotides together (like DNA polymerase)
• Transcribes specific segments of DNA.
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RNA SPLICING: Editing mRNA
Splicing: In eukaryotes mRNA is modified before it leaves nucleus.
1. INTRONS removed/spliced
• non-coding sequences (junk)
• Do not code for amino acids
2. EXONS:
• Coding sequences
• Translate into amino acids (expressed)
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Modifying mRNA
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Translation: mRNA --> proteins• Based on CODON “language”
• 3-bases translate into a CODE for specific amino acids.
• Amino acids build polypeptides.
Nucleic acids --> Proteins
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TRANSLATIONEach codon codes for 1 amino acid.
Start codons:
AUG (start translating)
Stop codons:
UAA, UAG, UGA
Same codes for almost ALL organisms!
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Translation
Required• ATP• mRNA• Ribosomes• tRNA
tRNA: Transfer RNA• Translates codon of mRNA into amino acids.• “Fetches” correct amino acid• Attatches to correct codon.• Has “anti-codon” complement to attatch to codon.
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Translation: rRNA (Ribosome)
rRNA: ribosome (organelle)
• 2 subunits snap together.
• mRNA and tRNA join each other in RIBOSOME.
2 tRNA binding sites where translation happens:
P site: Growing polypeptide chain.
A site: new amino acid binds
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Translation: Elongation
Polypeptide chain grows.• Translation begins (AUG) codon• Amino acids are added by tRNA
(based on mRNA codons).• Translation ends (UAA, UAG, UGA);
stop codon.• Polypeptide released (Goes to E.R. and
Golgi for modification)
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Translation Summary