DNA Replication
What enzyme unwinds the DNA double helix at the replication fork?
Helicase
What enzyme performs transcription in bacteria?
RNA polymerase
What is the start codon for most proteins?
AUG
What is the definition of a plasmid?
A small, independently replicating DNA molecule.
What are chaperones, and what is their role?
Proteins that help other proteins fold correctly
Which enzyme adds nucleotides to the growing DNA strand during replication?
DNA polymerase III
What is the role of the sigma factor?
It directs RNA polymerase to promoter regions.
What are the three ribosomal sites involved in elongation?
A site, P site, and E site
What do R plasmids confer to bacteria?
Resistance to antibiotics and other inhibitors
What secondary structures are formed by hydrogen bonds in polypeptides?
α-helices and β-sheets
Why is the lagging strand synthesized in Okazaki fragments?
DNA can only be synthesized 5′→3′, requiring discontinuous synthesis
What is the Pribnow box and where is it located?
A –10 promoter sequence (TATAAT) recognized during initiation.
What enzyme attaches amino acids to their corresponding tRNAs?
Aminoacyl-tRNA synthetase
What are operons, and why are they important?
Clusters of genes transcribed together; allow coordinated gene expression
Which secretion system exports unfolded proteins across the cytoplasmic membrane?
The Sec system
Which enzyme removes RNA primers and replaces them with DNA?
DNA polymerase I
Name the two types of bacterial transcription termination
Rho-dependent and intrinsic (Rho-independent)
What happens during translocation in translation?
The ribosome shifts one codon, moving tRNA from the A site to the P site
What are transposable elements, and name one type
DNA segments that move within genomes (transposons or insertion sequences)
Which secretion system exports folded proteins containing twin-arginine signal sequences?
The Tat system
What is the function of proofreading activity in DNA polymerases?
To detect and correct mismatched base pairs, ensuring high fidelity.
In eukaryotes, what are the three major RNA processing steps?
5′ capping, intron splicing, and 3′ poly(A) tail addition
What is codon bias, and why is it significant?
Preference for certain codons in an organism; affects translation efficiency.
How do prokaryotic genomes differ from eukaryotic genomes in structure?
Prokaryotic genomes are typically circular, compact, and lack introns, while eukaryotic genomes are linear and contain introns
Proteins can fold into different levels of structure. Name the four levels of protein structure and briefly describe the type of interactions that stabilize each
Primary structure – linear sequence of amino acids (peptide bonds),
Secondary structure – local folding like α-helices and β-sheets (hydrogen bonds),
Tertiary structure – 3D shape of a polypeptide (hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges),
Quaternary structure – association of multiple polypeptides (same interactions as tertiary