· initiation at different AUG positions out of frame with another lead to distinct polypeptides
nucleosomes
· spherical particles that resemble beads on a string
· DNA wraps around them, associate with H1 histone, and condenses several times to form intact chromatids
triplet binding assay
· Nirenberg and Leder developed this to determine some specific codon assignments
· ribosomes bind to single codon of three nucleotides so the complementary amino acid-charged tRNA can bind
positive vs. negative control
· negative: genetic expression occurs unless shut off by regulator molecule
· positive: transcription occurs only when regulator molecule directly stimulates RNA production
RNA polymerase II (eukaryotic)
· transcribes wide range of genes
· activity dependent on cis-acting elements and trans-acting transcription factors
· core promotor determines where it binds to DNA
chromatin remodelling
· chromatin structure must change to accommodate DNA-protein interactions and allow for replication and gene expression
· chromatin must relax, expose regions of DNA to regulatory proteins, and have a reversal mechanism for inactivity
classifications of mutations
· point mutation/base subsitution
· missense: different amino acid - gain/loss of function or neutral
· nonsense: early stop codon prematurely terminates translation
· silent mutation: new triplet code but same amino acid (degeneracy)
alkylating agents
· donate alkyl group (CH3 or CH3CH3) to amino or keto groups in nucleotides
· alter base-pairing affinity and result in transition mutations
· ex. mustard gas (lethal to mammals)
reading frame
· contiguous sequence of nucleotides
· insertions and deletions cause a frameshift mutation -> triplet code revealed
nonsense mutations
· produce a stop codon early
· translate is terminated and partial polypeptide is produced
