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What is the central dogma of molecular biology?
DNA is transcribed into RNA, which is then translated into protein.
What is a degenerate genetic code?
A degenerate code allows multiple codons to encode the same amino acid.
What is the initiation codon and what does it code for?
initiation codon is AUG, which codes for methionine.
What are the termination (stop) codons?
stop codons are UAA, UGA, and UAG.
What is the wobble hypothesis?
The third base in the codon can vary without affecting the amino acid it codes for, allowing mutations to occur without impacting protein function.
What are point mutations and their types?
Point mutations are changes in a single nucleotide. Types include:
Silent mutations (no effect on protein synthesis),
Nonsense mutations (produce a premature stop codon),
Missense mutations (result in a different amino acid),
Frameshift mutations (caused by nucleotide addition or deletion, changing the reading frame).
How does RNA differ from DNA?
ribose sugar instead of deoxyribose
uracil instead of thymine
single-stranded.
What are the three types of RNA and their roles?
mRNA: Carries the genetic message from DNA to the cytoplasm for translation.
tRNA: Brings amino acids and matches codons on mRNA with its anticodon.
rRNA: Makes up the ribosome and catalyzes protein synthesis.
What enzyme is responsible for transcription?
RNA polymerase II is responsible for synthesizing hnRNA from the DNA template strand.
What is the TATA box?
a promoter region where RNA polymerase II binds to initiate transcription
located about 25 base pairs upstream from the transcription start site.
What posttranscriptional modifications occur?
A 7-methylguanylate cap is added to the 5′ end.
A poly-A tail is added to the 3′ end.
Splicing occurs by snRNA and snRNPs in the spliceosome to remove introns and ligate exons.
How can eukaryotic cells increase gene product variability?
Eukaryotes can use alternative splicing, combining different exons to produce different gene products.
What is the role of tRNA in translation?
tRNA decodes the mRNA codons and brings the appropriate amino acid to the ribosome.
Where does translation occur?
Translation occurs in the ribosome.
How does translation initiation differ in prokaryotes and eukaryotes?
In prokaryotes, the 30S ribosome attaches to the Shine-Dalgarno sequence and lays down N-formylmethionine.
In eukaryotes, the 40S ribosome attaches to the 5′ cap and lays down methionine.
What happens during translation elongation?
a new aminoacyl-tRNA enters the A site
the growing polypeptide chain is transferred from the tRNA in the P site to the tRNA in the A site
the uncharged tRNA exits through the E site.
What occurs during translation termination?
When a stop codon enters the A site, a release factor adds a water molecule to the polypeptide chain, releasing the protein.
What are posttranslational modifications?
Protein folding by chaperones.
Formation of quaternary structure.
Cleavage of proteins or signal sequences.
Covalent additions like phosphorylation, carboxylation, glycosylation, and prenylation.
What is the Jacob–Monod model?
It explains how operons work by using repressors and activators to regulate gene expression.
What is an operon?
a cluster of genes transcribed as a single mRNA, regulated by an operator and promoter.
What is an inducible system in gene regulation?
is normally repressed but can be activated by an inducer that removes the repressor.
ex. lac operon
What is a repressible system in gene regulation?
is normally active but can be turned off by a corepressor binding with the repressor.
ex. trp operon
How do transcription factors regulate gene expression?
bind to promoter and enhancer regions to initiate or enhance transcription.
What are promoters and enhancers?
Promoters are within 25 base pairs of the transcription start site.
Enhancers are located more than 25 base pairs away and help boost transcription.
How does chromatin structure affect gene expression?
Histone acetylation increases chromatin accessibility and promotes transcription.
DNA methylation decreases chromatin accessibility and suppresses transcription.
