Questions and Answers
A always pairs with __
T
G always pairs with __
C
What are the three steps in the central dogma of molecular biology?
What is the role of RNA in gene expression?
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What is the protein synthesis factory called?
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In prokaryotes, control of gene expression occurs at the level of translation.
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What enzyme is produced by E. coli when lactose is present?
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In eukaryotes, where is pre-mRNA formed?
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What is splicing in the context of gene expression?
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What are transcription factors?
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Study Notes
DNA and RNA Fundamentals
- DNA stands for Deoxyribonucleic acid; RNA stands for Ribonucleic acid.
- DNA is composed of four bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
- Purines: A and G; Pyrimidines: C and T.
- A always pairs with T, and G always pairs with C in the DNA structure.
Gene Expression Overview
- DNA contains cellular instructions; proteins execute these functions.
- The central dogma of molecular biology: DNA → RNA → Protein.
- Gene expression involves transcription of DNA into messenger RNA (mRNA) and subsequent translation into proteins.
Translation Process
- mRNA is a template for protein synthesis, utilizing a triplet code (3 nucleotides correspond to one amino acid).
- Transfer RNA (tRNA) serves as a go-between, having a specific tRNA for each amino acid.
- tRNA has an amino acid at one end and a triplet code at the other, pairing with mRNA during translation.
Ribosomes and Protein Synthesis
- Ribosomes are the factories for protein synthesis.
- tRNAs carrying amino acids align at the ribosome to match the sequence specified by mRNA.
Control of Gene Expression
- In prokaryotes, gene expression is primarily controlled at the transcription level.
- In E. coli, the presence of glucose influences whether lactose is metabolized; β-galactosidase is produced only when lactose is available.
Eukaryotic Gene Expression Control
- Eukaryotic gene expression control occurs at various levels, including during processing, transport, and degradation of mRNA.
- Pre-mRNA is formed in the nucleus and modified before entering the cytoplasm for translation.
- Transcription factors mediate transcription initiation in eukaryotic cells.
Alternative Splicing
- Exons can be spliced differently to produce various proteins from the same gene.
- Muscle α-tropomyosin uses 12 exons, generating distinct mRNA variants in different tissues.
Post-Translational Modifications
- Proteins undergo modifications post-translation, affecting their function and lifespan.
- Protein degradation is also a component of gene expression regulation in eukaryotes.
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