RNA and The Genetic Code Flashcards
Initiation Codon
AUG (methionine)
Stop Codons
UAG UAA UGA
Silent Mutations
no effect on protein synthesis, usually occurs in the wobble position
Nonsense (trunction) Mutations
produces a premature stop codon
Missence Mutations
produce a codon that codes for a different amino acid
Frameshift Mutations
results from nucleotide deletion or insertion and change the reading frame for subsequent codons
Structural Differences between DNA and RNA
Deoxyribose vs Ribose sugars
Substitution of Uracil for Thymine
Single stranded vs double stranded
mRNA
carries the message from DNA in the nucleus via transcription of the gene; travels to cytoplasm to be translated
tRNA
brings amino acids; recognizes the codon on the mRNA using its anticodon
rRNA
makes up much of the ribosome; enzymatically active
rRNA
makes up much of the ribosome; enzymatically active
Steps in Transcription in RNA
Helicase and topoisomerase unwind DNA
RNA polymerase II binds to TATA box within promotor region
hnRNA synthesized from DNA strand
Post-transcriptional modifications
Post Transcriptional Modifications to RNA
5’ Cap added
3’ Poly-A Tail added
Splicing by spliceosome to remove introns and splice together exons
Translation Stages in RNA
Initiation
Elongation
Termination
Posttranslational Modifications
Folding by chaperones
Formation of quaternary structure
Cleavage of proteins or signal sequences
Covalent addition of other biomolecules
Control of Gene Expression in Prokaryotes
Operons (Jacob Monod Model) are inducible or repressible clusters of genes transcribed as a single mRNA
Control of Gene Expression in Eukaryotes
Transcription factors search for promotor and enhancer regions in DNA
Promoters: within 25 base pairs of he transcription start site
Enhancers: more than 25 base pairs away from the transcription start site
Small and Large subunit of ribosome
40S and 60S
A-Site
holds the incoming aminoacyl-tRNA complex
P-Site
holds tRNA that carries the growing polypeptide chain
E-Site
where the inactivated tRNA pauses transiently before exiting the ribosome
Chaperone Proteins
assis in protein folding
Inducible Systems
repressor tightly bonded to operator system and acts as a roadblock, binding of a protein reduces transcriptional activity and to remove the block an inducer must bind the repressor protein
Repressible Systems
allow constant production of a product, the repressor is inactive until it binds to a corepressor and they tend to work in negative feedback loops with the product serving as the corepresser
Histone Acetylation
histone acetylases acetylate lysine residues and weakens the interactions of the histone with DNA, which opens the DNA chromatin formation therefore increasing gene expression levels
DNA Methylation
DNA methylases add methyl groups to cytosine and adenine which can silence genes
