Enzymes, Signal transduction & receptors

Why is the tRNA charging reaction critical to translation?

It links the correct amino acid to its tRNA, ensuring accurate protein synthesis.

What are the tRNA-binding sites in the ribosome?

• A site: Aminoacyl-tRNA entry

• P site: Peptidyl-tRNA holds growing chain

• E site: Exit site for empty tRNA

What happens during translation initiation?

Small ribosomal subunit binds mRNA, initiator tRNA binds start codon, then large subunit joins.

How does translation differ on the RER vs. cytoplasm?
A:

• RER: Proteins made for secretion or membranes

• Cytoplasm: Proteins stay in cytosol or go to organelles

When is gene expression usually controlled?

: At transcription initiation — it’s energy efficient.

What is the usual action of regulatory proteins?

They bind DNA to either promote or block RNA polymerase.

: Key differences between gene regulation in prokaryotes and eukaryotes?

• Prokaryotes: Operons, fast, mostly transcriptional

• Eukaryotes: Complex, chromatin structure, more regulation levels

How do proteins interact with base-pairs without unwinding DNA?

They fit into the major groove and recognize base-specific patterns

: What are common features of DNA-binding motifs?

• Helix-turn-helix

• Zinc finger

• Leucine zipper

How is gene expression controlled in the lac operon? (lactose inducer adn glucose repressor)

The repressor blocks transcription unless lactose is present, which removes the repressor.

Role of general vs. specific transcription factors?

• General: Needed for all transcription

• Specific: Regulate certain genes

What is the Pol II initiation complex?

A group of proteins (including general TFs and Pol II) assembled at the promoter to start transcription.

: How can transcription factors act from far away?

through DNA looping, enhancers can affect distant promoters

: Name two kinds of epigenetic marks.

• DNA methylation: Silences genes

• Histone acetylation: Opens chromatin, promotes transcription

What do chromatin-remodeling complexes do?

they reposition or restructure nucleosomes to make DNA more or less accessible.