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Definition
-1908 - Proposed relationship between genes and the production of enzymes. - Studied patients with metabolic defects.
- Hypothesized disease due to missing enzyme. - Knew it had a recessive pattern of inheritance (need defect from both parents) -Patients missing gene that encodes for Phenylalaine Hydroxylase - “inborn error of metabolism” - Structure and function of genetic material was unknown at the time of his work. |
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Patient’s body accumulates abnormal levels of homogentisic acid (alkapton).
-Causes damage to cartilage
-Damage to heart valves |
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-became aware of Garrod’s work in early 1940s
-Studied Neurospora crassa (common bread mold)
-Only carbon source (sugar), inorganic salts and biotin needed for growth.
-Enzyme synthesizes molecules it needs
-Mutant strains unable to grow unless supplemented
-Their hypothesis - A single mutation would result in the requirement for a single type of vitamin or supplement.
-Stimulated research into other substances including arginine
-Isolated several mutants requiring arginine for growth
-Wild-type can grow without the added supplements
-Types 1,2,3 require addition of a supplement
-Beadle and Tatum concluded that single gene controls the synthesis of a single enzyme. |
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| One gene = one enzyme hypothesis |
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Definition
-Beadle and Tatum concluded that single gene controls the synthesis of a single enzyme.
-Hypothesis has been modified
-Enzymes are only a single category of cellular proteins, genes also code for other proteins.
-Some proteins composed of one or more polypeptides
-More accurate to say one gene encodes one polypeptide
-Hemoglobin composed of 4 polypeptides, each required for proper function
-NEW - One gene = one polypeptide |
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-Proposed by Francis Crick in 1958
Transcription > Translation
(DNA > RNA > Protein) |
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| Transcription (part of central dogma) |
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Definition
-Produces an RNA copy or transcript of a gene
-Structural genes produce messenger RNA (mRNA) that specifies the amino acid sequence of a polypeptide. |
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| Translation (part of central dogma) |
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Definition
| Process of synthesizing a specific polypeptide on (at) a ribosome. |
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Term
| 1st stage of transcription |
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Definition
Initiation - recognition step
-In Bacteria (only), sigma factor causes RNA polymerase to recognize prometer region
-Stage is complete when DNA strands separate near promoter to form an open complex. |
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| 2nd stage of transcription |
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Definition
Elongation - RNA polymerase synthesizes RNA
-Template or coding strand used for RNA synthesis (opposing strand not used)
-Synthesized 5’ to 3’ (template read 3’ to 5’)
-Uracil substituted for Thymine |
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| 3rd stage of transcription |
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Definition
Termination - RNA polymerase reaches termination sequence
- Causes RNA polymerase and RNA to disassociate from DNA |
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| RNA processing (Bacteria vs. Eukaryotic) |
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Definition
-Bacterial mRNA proceeds directly to translation
-Eukaryotic pre-mRNA must be processed into mature mRNA |
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| RNA procession - eukaryotes (only) |
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Definition
-Introns - transcribed but not translated (found in many eukaryotic genes)
-Discovered in the 1970s
-Considered ‘junk’ DNA
-Exons - coding sequence bound into mature mRNA |
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| RNA transcription - Splicing - eukaryotes (only) |
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Definition
| removes introns and connects exons. |
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Definition
-Removes introns precisely
-Complex molecule
-Composed of snRNPs (small nuclear RNA) |
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if a strand is spliced in a different way may produce a different product
-rRNA and tRNA are self-splicing (includes ribosome molecules) |
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-3' end
-Consists of 100-200 nucleotides
-Increases stability and lifespan in cytosol
-Not encoded in genome |
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Definition
| -5' -Modified guanosine -Needed for proper exit from nucleus and binding to ribosome |
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Definition
-Coded mRNA is used to create polypeptide by ribosomes
-Cells use a lot of energy for this (E.Coli =90%)
-Requires mRNA, tRNA and ribosomes |
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Definition
groups of three base pairs in mRNA
-Most codons specify a specific amino acid (also start and stop codon s)
-Degenerate - more than one code can specify the same amino acid |
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-codon: AUG
-5' - binds with ribosomal binding site. |
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-Different tRNA molecules encoded by different -Common features of all tRNA
-Cloverleaf shape
-Anticodon
-Acceptor system for binding to specific amino acid |
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Definition
-Has Anticodon - 3 RNA nucleotide that recognizes mRNA specifically
-Proper Amino acid attaches to opposing binding site |
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Term
| Aminoacyl-tRNA synthetase |
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Definition
Catalyzes attachment of amino acids to tRNA
-One for each of the 20 amino acids
-Ability to recognize and attach has been called ‘second genetic code’ |
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| tRNA with amino acid attached |
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Definition
-Prokaryotes have one kind of ribosome
-Eukaryotes have distinct ribosomes in different cellular compartments
-Found most abundantly in cytosol
-Also in mitochondria and chloroplasts (similar to bacterial ribosomes) |
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| -Specifically target and shut down ribosomes in bacteria only |
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Definition
| Determines ribosome shape |
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| Ribosomal Structure - A site |
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Definition
| aminoacyl site (1st site/where tRNA enters) |
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Term
| Ribosomal Structure - P site |
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Definition
| peptidyl site (where amino acids are joined together) |
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Term
| Ribosomal Structure - E site |
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Definition
| exit site (tRNA is released) |
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Term
| Stages of Translation - 1. Initiation |
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Definition
-mRNA, tRNA and ribosomal units form a complex
I. Requires ribosomal initiation factors
II. Requires energy input from GTP via hydrolysis |
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Term
| Stages of Translation - 2. Elongation (1st of 3) |
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Definition
| I. Aminoacly tRNA brings a new amino acid to the a Site. i. Binding occurs due to codon/anticodon reaction. ii. Elongation factors hydrolyze GTP to provide energy to bind tRNA to A site. iii. Peptidyl tRNA is in the P site. iv. Aminoacyl tRNA is in the A site. |
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Term
| Stages of Translation - 2. Elongation (2nd of 3) |
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Definition
II. A peptide bond is formed between the amino acid at the A site and the growing peptide chain.
i. The polypeptide is removed from the tRNA in the P site and transferred to the amino acid at the A site - peptidyl transfer reaction.
ii. rRNA catalyzes peptide bond formation - ribosome is a ribozyme. |
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Term
| Stages of Translation - 2. Elongation (3rd of 3) |
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Definition
| III. Movement of the ribosome toward the 3’ end of the mRNA by (length of one codon). i. Shifts tRNA to E and P sites. ii. Next codon in now at the A site. iii. Used (uncharged tRNA) exits from E site. |
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| Stages of Translation - 3. Termination |
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Definition
-Ribosome reaches a stop codon. Polypeptide is released and units disassemble.
I. Stop codon arrives at A site.
II. Release factor binds to stop codon at the A site.
III. Bond between polypeptide and tRNA hydrolyze to release polypeptide.
IV. Ribosomal subunits and release factors disassociate. |
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