allow mutations to occur without affecting the protein
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Point mutations
silent, missense, nonsense
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Silent mutations
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
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Nonsense mutations
mutations which produce a premature stop codon
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Missense mutations
produce a codon that codes for a different amino acid
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Frameshift mutations
nucleotide addition or deletion and change the reading frame of subsequent codons
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RNA vs DNA
ribose vs. deoxyribose, single stranded vs. double stranded, uracil vs. thymine
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Three major types of RNA
mRNA, tRNA, rRNA
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messenger RNA (mRNA)
Carries the message from DNA in the nucleus via transcription of the gene; it travels into the cytoplasm to be translated.
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transfer RNA (tRNA)
brings in amino acids; recognizes the codon on the mRNA using its anticodon
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Ribosomal RNA (rRNA)
makes up much of the ribosome; enzymatically active
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Transcription steps
-helicase and topsisomerase unwind DNA double helix
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-RNA polymerase II binds to TATA box within promoter region of gene
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-hnRNA synthesized from DNA template strand
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hnRNA
Heterogeneous nuclear RNA; the primary transcript made in eukaryotes before splicing.
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posttranslational modification
-7-methylguanylate triphosphate cap added to 5' end
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-poly-A tail added to the 3' end
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-splicing
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Splicing
the process of removing introns and reconnecting exons in a pre-mRNA
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Alternative splicing
Splicing of introns in a pre-mRNA that occurs in different ways, leading to different mRNAs that code for different proteins or protein isoforms. Increases the diversity of proteins.
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Where does translation occur?
at the ribosome
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Three stages of translation
initiation, elongation, termination
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Posttranslational modifications
-folding by chaperones
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-formation of quaternary structure
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-cleavage of proteins or signal sequences
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-covalent addition of other biomolecules (phosphorylation, carboxylation, glycosylation, prenylation)
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Operons
inducible or repressible clusters of genes transcribed as a single mRNA
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transcription factors
search for promoter and enhancer regions in the DNA
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Promoters
within 25 base pairs of the transcription start site
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Enhancers
more than 25 base pairs away from the transcription start site
Studied by 1 person
