Module 2: Molecular Cell Biology

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Prokaryotic transcription

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-occurs in cytoplasm
-DNA is more accessible to RNA polymerase than eukaryotes
-RNA polymerase interacts directly with prokaryotic DNA
-mRNA produced as a result of transcription is not modified in prokaryotic cells
-Prokaryotes only contain three different promoter elements: -10, -35 promoters, and upstream elements
-no initiation complex
-Transcription and translation occurs simultaneously in prokaryotes

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Eukaryotic transcription

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-occurs in nucleus
-Eukaryotic DNA is wrapped around proteins called histones to form structures called nucleosomes. -Eukaryotic DNA is packed to form chromatin.
- other proteins mediate the interation between RNA polymerase and DNA in eukaryotes.
-Eukaryotic cells modify mRNA by RNA splicing, 5' end capping, and addition of a polyA tail.
-Eukaryotes contain many different promoter elements: TATA box, initiator elements, downstream core promoter element, CAAT box, and the GC box to name a few.
-Eukaryotes form an initiation complex with the various transcription factors that dissociate after initiation is completed.
-in eukaryotes the RNA is first transcribed in the nucleus and then translated in the cytoplasm.

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Transcription/Translation

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See word document/manual flashcards

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the processing of eukaryotic mRNA (splicing, capping, and poly A tails)

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o Eukaryotic genes often contain exons, nucleotide segments coding for protein, separated by introns, which are the non-coding segments. Therefore all eukaryotic pre-mRNA molecules go through capping at the 5’ end, removal of the introns via RNA splicing, and finally cleavage and polyadenylation at the 3’ end (see document for misc. details)

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miRNA

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o Micro RNA's are small non coding ribonucleotide-based (RNA) regulators of gene expression. These recently discovered small RNA molecules (18-24 nucleotides) negatively regulate target mRNA's and appear to have a role in many developmental processes as well as in the adult.

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Promoters

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o One promoter is found in all genes that produce proteins, the core or basal promoter. Apart from the basal promoter, there are ubiquitous upstream promoter sequences which attract other sequence-specific transcription factors (e.g. TFIIB and TFIIA) and help construct the transcription complex.

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Operators (Operons)

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series of genes that are arranged adjacent to each other so that they are transcribed from a single promoter and as a single mRNA molecule.

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Enhancers

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(DNA sequences) bind transcription factors called enhancer-binding proteins which increase the rate of transcription.

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Transcriptional gene regulation

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-transcription regulated by which transcription factors are present.
-most genes have more than one enhancer involved in its function. The amount of transcript produced by a gene is the end result of many small effects, each produced by an individual enhancer.
Second, many of the transcription factors work as dimers, and these pairs can sometimes be formed between different transcription factors, called heterodimers. By controlling which transcription factors are present and in what amounts, the cell can regulate the transcription of its genes, often in a very subtle, complex manner.

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Post-transcriptional gene regulation

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-RNA splicing to remove introns.
-control of the position and length of the poly A+ tail
-mRNA stability
-mRNA localization
-control of translation