Key Terms
Central dogma
DNA -> RNA -> protein; genes specify mRNA; mRNA specifies protein. Codon: 3-nucleotide mRNA sequence specifying one amin
Flow
DNA -> (transcription) -> mRNA -> (translation) -> protein
Universality
Nearly all species use the same genetic code. A horse globin mRNA inserted into a tulip cell would produce horse globin.
Sigma (sigma) subunit
Initiation only. Recognizes the promoter.
Rho-dependent
Rho protein tracks along the growing mRNA behind the polymerase. Polymerase stalls at a run of G nucleotides on the DNA
Rho-independent
MRNA folds back on itself at a C-G rich region, forming a hairpin. Hairpin stalls the polymerase.
Enhancers and silencers
Bind regulatory transcription factors at variable distances from the gene; affect frequency of transcription but are not
Eukaryotic mRNA lifespan
Several hours. E.
Structure
7-methylguanosine attached via phosphate linkage. Functions: protects mRNA from degradation; recognized by ribosomes to
Introns marked by
GU at 5' end, AG at 3' end. Spliceosomes (protein + snRNA complexes) remove introns and rejoin exons with single-nucleot
Anticodon
3-nucleotide sequence on tRNA that base-pairs with mRNA codon.
Aminoacyl tRNA synthetases
Enzymes that charge tRNAs with correct amino acids Elongation factors: use GTP energy to move the ribosome
Note
Svedberg (S) units are NOT additive. 30S + 50S = 70S, not 80S.
Small subunit
Binds mRNA template. Large subunit: binds tRNAs sequentially; contains peptidyl transferase.
Each tRNA must interact with
Its aminoacyl synthetase, the ribosome, and the correct mRNA codon. Small molecule; enormous specificity.