the process by which DNA directs the synthesis of proteins, or RNAs in some cases
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In eukaryotic cells, transcription cannot begin until...
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several transcription factors have bound to the promoter
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The anticodon of a particular tRNA molecule is
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complementary to the corresponding mRNA codon.
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5′-CTTCGGGAA-3′
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Using Figure 17.5, identify a 5′ → 3′ sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys.
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B
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Which of these is a tRNA?
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What enzyme catalyzes the attachment of an amino acid to tRNA?
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aminoacyl-tRNA synthetase
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The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.
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CUG
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The initiator tRNA attaches at the ribosome's _____ site.
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P
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Who formulated the one gene-one enzyme hypothesis?
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Beadle and Tatum
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Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of _____.
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RNA
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5' cap
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A modified form of guanine nucleotide added onto the nucleotide at the 5' end of a pre-mRNA molecule
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Archibald Garrod
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the first to suggest that genes dictate phenotypes through enzymes that catalyze specific chemical reactions in the cell
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"inborn errors of metabolism"
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a term coined by Archibald Garrod, refferring to an inheirted disease reflecting a person's inability to make a particular enzyme
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Tatum and Beadle
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American genetists that coined the "one gene-one enzyme" hypothesis from their various experiments
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Tatum/Beadle experiment
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...
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one gene-one enzyme hypothesis
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the function of a gene is to dictate the production of a specific enzyme
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one gene-one polypeptide
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...
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inaccuracy of "one gene-one polypeptide"
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1) many eukaryotic genes can code for a set of closely related polypeptides in a process called alternative splicing
2) quite a few genes code for RNA moleucles that have important functions in cells even though they are never translated into protein
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RNA vs DNA
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1) ribose instead of deoxyribose as a sugar
2) uracil not thymine
3) ACCU
4) usually single stranded
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transcription
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the synthesis of RNA using DNA as a template
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messenger RNA (mRNA)
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the carrier of information from DNA to the cell's protein-synthesizing machinery
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translation
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the synthesis of a polypeptide under the directions of mRNA
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ribosomes
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the site of translation
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difference of genetic information flow between bacteria and eukaryotes?
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1) DNA is not segregated from ribosomes and the other protein synthesizing equipment, since there is no nucleus in bacteria
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The lack of segregation of DNA in bacteria results in...
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simultaneous translation and transcription
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primary transcript
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...
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central dogma of Francis Crick
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...
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bacterial transcription/translation
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In a bacterial cell, which lacks a nucleus, mRNA produced by transcription is immeadiately translated without additional processing.
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eukaryotic translation/transcription
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The nucleus of a eukaryotic cell provides a seperate compartment for transcription. The original transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.
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triplet code
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A set of three-nucleotide-long words that specify the amino acids for polypeptide chains
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template strand
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the DNA strand that provides the pattern for ordering the sequence of nucleotides in an RNA transcript
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For each gene, one DNA strand functions as a template for transcription. The base-pairing rules for DNA synthesis also guide transcription, but uracil (U) takes the place of thymine (T) in RNA. During translation, the mRNA is read as a sequence of base triplets, called codons. Each codon specifies an amino acid to be added to the growing polypeptide chain. The mRNA is read in the 5'-3' direction.
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triplet code
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Marshall Nirenberg
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deciphered the first codon by translating poly-U into a peptide for phenylalanine
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redundancy of the genetic code
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Codons that are synonyms for a particular amino acid differ onlt in the third base of the triplet.
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reading frame
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on an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis
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universiality of genetic code
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DNA is a language shared by all living things that must have been operating very early in the history of life.
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exceptions to the universiality of the genetic code
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1) translation systhems in which a few codons differ
2) slight variations in genetic coder and in organelles
3) stop codons can be translated into one of two amino acids not found in most organisms
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RNA polymerase
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the enzyme that pries apart the 2 DNA strands and joins the RNA nucleotides as they base-pair along the DNA template
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promoter
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a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place
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terminator
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in bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA moleucle and detach from the DNA
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transcription unit
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a region of DNA that is transcribed into an RNA molecule
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stages of transcription
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1) initiation
2) elongation
3) termination
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initiation
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After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
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elongation
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The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5'-3'. In the wake of transcription, the DNA strands reform a double helix.
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termination
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Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.
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transcription factor
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a regulatory protein that binds to DNA and affects transcription of specific genes
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transcription initiation complex
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the completes assembly of transcription factors and RNA polymerase bound to a promoter
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RNA processing
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modification of RNA transcripts including splicing out introns, joining together of exons, and alteration of the 5' and 3' ends
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