Foundations of Modern Biology II & Cellular & Molecular Biology: Key Concepts Summary

A series of vocabulary flashcards covering key concepts from the Foundations of Modern Biology II & Cellular & Molecular Biology lecture notes.

Operon

A cluster of genes transcribed as a single mRNA, enabling coordinated regulation.

lacZ

Gene that encodes
β-galactosidase, which hydrolyzes lactose into glucose and galactose.

lacY

Gene that encodes lactose permease, a membrane protein transporting lactose into the cell.

lacA

Gene that encodes transacetylase, possibly involved in detoxifying sugars entering via permease.

Negative Control

Mechanism where the Lac I repressor binds to the operator to block RNA polymerase when lactose is absent.

Inducer (Allolactose)

Molecule that binds to Lac I, inactivating the repressor, allowing transcription of lac genes.

CAP-cAMP Complex

A positive regulator that enhances lac operon transcription when glucose levels are low.

Transcription Factors

Proteins that bind to specific DNA sequences, modulating transcription by promoting or blocking RNA polymerase action.

Core Promoter

The site where the basal transcription apparatus assembles, including the TATA box.

Enhancers

Distal regulatory DNA sequences that increase transcription through transcription factor binding.

Post-Transcriptional Regulation

Gene expression regulation occurring after transcription, often through RNA interference mechanisms.

miRNA (microRNA)

Small non-coding RNAs that bind target mRNAs to block translation or accelerate degradation.

Eukaryotic Gene Regulation

Mechanisms that adjust gene expression in eukaryotic cells through various regulatory elements.

RNA Polymerase (Prokaryotic)

The enzyme in prokaryotes responsible for synthesizing RNA from a DNA template.

Sigma Factor

A subunit of prokaryotic RNA polymerase that recognizes and binds to promoter sequences, initiating transcription.

Coupled Transcription-Translation

A characteristic of prokaryotic gene expression where translation begins before transcription is complete.

RNA Polymerase II

The eukaryotic enzyme responsible for transcribing protein-coding genes (pre-mRNA) and some snRNAs.

Eukaryotic General Transcription Factors (GTFs)

Proteins that bind to the core promoter in eukaryotes, assisting RNA Polymerase II in forming the preinitiation complex.

Mediator Complex

A large protein complex in eukaryotes that transduces regulatory signals from transcriptional activators and repressors to RNA polymerase II.

Chromatin Remodeling

Mechanisms in eukaryotes that alter chromatin structure, making DNA more or less accessible for transcription.

Shine-Dalgarno Sequence

A ribosome binding site in prokaryotic mRNA, located upstream of the start codon, ensuring proper initiation of translation.

fMet-tRNA (N-formylmethionine tRNA)

The initiator tRNA in prokaryotes, carrying N-formylmethionine to the start codon for protein synthesis.

70S Ribosome

The complete functional ribosome in prokaryotes, composed of 30S and 50S subunits.

80S Ribosome

The complete functional ribosome in eukaryotes, composed of 40S and 60S subunits.

Kozak Sequence

A consensus sequence in eukaryotic mRNA surrounding the start codon, important for the accurate and efficient initiation of translation.

Eukaryotic Initiation Factors (eIFs)

Proteins involved in assembling the 80S ribosome at the start codon in eukaryotic translation.

Poly(A) Tail

A long chain of adenine nucleotides at the 3' end of eukaryotic mRNA, contributing to mRNA stability and promoting translation initiation.

Key difference in RNA Polymerase types between prokaryotes and eukaryotes?

Prokaryotes typically have one RNA Polymerase for all RNA types, while eukaryotes have three (RNA Pol I, II, III) for different classes of RNA.

How does transcription initiation differ between prokaryotes and eukaryotes concerning promoter recognition?

In prokaryotes, the Sigma Factor directly recognizes and binds to promoter sequences; in eukaryotes, General Transcription Factors (GTFs) bind to the core promoter, forming a preinitiation complex, to recruit RNA Polymerase II.

What is a fundamental structural difference affecting gene expression in prokaryotes versus eukaryotes?

Prokaryotic DNA is not organized into chromatin, allowing direct access for transcription; eukaryotic DNA is packaged into chromatin, requiring remodeling for gene access.

What is the significance of 'coupled transcription-translation' in prokaryotes?

In prokaryotes, translation of mRNA can begin before its transcription is complete because both processes occur in the cytoplasm and there's no nuclear envelope separation.

Why is coupled transcription-translation not possible in eukaryotes?

Eukaryotic transcription occurs in the nucleus, and the mRNA must be processed and exported to the cytoplasm for translation, physically separating the two processes.

How do ribosomes differ in prokaryotic vs. eukaryotic translation initiation?

Prokaryotes use a 70S ribosome with fMet-tRNA and the Shine-Dalgarno sequence for initiation; eukaryotes use an 80S ribosome with Met-tRNA and the Kozak sequence for initiation.

What is a major regulatory difference concerning mRNA transcript structure and processing between prokaryotes and eukaryotes?

Prokaryotic mRNA is often polycistronic (codes for multiple proteins) and lacks extensive processing; eukaryotic mRNA is monocistronic, requires 5' capping, 3' polyadenylation, and splicing before translation.

What happens to the lac operon when lactose is present and glucose is absent?

Allolactose inactivates the Lac I repressor, and the CAP-cAMP complex binds to DNA, strongly activating transcription of lac genes to utilize lactose.

What happens to the lac operon when lactose is present and glucose is also present?

Allolactose inactivates the Lac I repressor. However, cAMP levels are low due to glucose, so the CAP-cAMP complex does not form effectively, resulting in low-level transcription of lac genes.

What happens to the lac operon when lactose is absent (regardless of glucose)?

The Lac I repressor remains active and binds to the operator, blocking RNA polymerase and preventing transcription of lac genes.

Beyond the TATA box, what are regulatory DNA sequences that influence eukaryotic gene expression from a distance?

Enhancers and Silencers are distal DNA sequences that bind specific transcription factors to either increase or decrease the rate of transcription.

Describe the role of chromatin remodeling in eukaryotic gene regulation.

Chromatin remodeling complexes use energy to reposition, remove, or alter nucleosomes, making DNA either more accessible (euchromatin) or less accessible (heterochromatin) for transcription.

How does the Poly(A) tail contribute to eukaryotic mRNA function?

The Poly(A) tail contributes to mRNA stability, protects it from degradation, and plays a role in the efficient initiation of translation.

Explain the concept of gene expression checkpoints in eukaryotes.

Eukaryotic multicellular organisms regulate gene expression at multiple points including chromatin structure, transcription initiation, RNA processing, mRNA transport, mRNA stability, translation, and post-translational modification.