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Questions and Answers
What is the fundamental unit of inheritance that affects a particular trait?
What is the fundamental unit of inheritance that affects a particular trait?
gene
What are the two primary components of a gene?
What are the two primary components of a gene?
coding sequence and regulatory sequence
What is the main product of genes?
What is the main product of genes?
Non-translated RNAs have no significant function in the cell.
Non-translated RNAs have no significant function in the cell.
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The genome size of higher organisms is significantly smaller compared to prokaryotes.
The genome size of higher organisms is significantly smaller compared to prokaryotes.
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What process allows eukaryotes to produce a greater diversity of proteins from a limited number of protein-coding genes?
What process allows eukaryotes to produce a greater diversity of proteins from a limited number of protein-coding genes?
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How do fully differentiated cells retain the potential to express all the genes required to build an organism?
How do fully differentiated cells retain the potential to express all the genes required to build an organism?
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What are the two main mechanisms that regulate gene expression in higher eukaryotes?
What are the two main mechanisms that regulate gene expression in higher eukaryotes?
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What is the primary function of RNA polymerase?
What is the primary function of RNA polymerase?
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What is the name of the region in bacterial promoters that is recognized by RNA polymerase to initiate transcription?
What is the name of the region in bacterial promoters that is recognized by RNA polymerase to initiate transcription?
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What are the two main mechanisms employed by transcriptional repressors in prokaryotes?
What are the two main mechanisms employed by transcriptional repressors in prokaryotes?
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The Lac operon is a classic example of a system where multiple genes involved in a specific metabolic pathway are regulated by a single promoter and repressor.
The Lac operon is a classic example of a system where multiple genes involved in a specific metabolic pathway are regulated by a single promoter and repressor.
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What is the key difference in the way prokaryotic and eukaryotic mRNAs are processed?
What is the key difference in the way prokaryotic and eukaryotic mRNAs are processed?
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Introns are non-coding sequences that are removed during mRNA processing.
Introns are non-coding sequences that are removed during mRNA processing.
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What is the name of the large molecular complex responsible for splicing introns from pre-mRNA?
What is the name of the large molecular complex responsible for splicing introns from pre-mRNA?
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Alternative splicing can lead to different protein isoforms from a single gene.
Alternative splicing can lead to different protein isoforms from a single gene.
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What is the function of ribosomes in protein synthesis?
What is the function of ribosomes in protein synthesis?
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What are the three binding sites on a ribosome?
What are the three binding sites on a ribosome?
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The process of translation is initiated when a ribosome recognizes the AUG codon on mRNA.
The process of translation is initiated when a ribosome recognizes the AUG codon on mRNA.
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What is the name of the enzyme that catalyses the formation of peptide bonds during translation?
What is the name of the enzyme that catalyses the formation of peptide bonds during translation?
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Translation ends with a stop codon that signals the termination of protein synthesis.
Translation ends with a stop codon that signals the termination of protein synthesis.
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What are the two subunits of prokaryotic ribosomes?
What are the two subunits of prokaryotic ribosomes?
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Eukaryotic ribosomes differ from prokaryotic ribosomes in size and composition.
Eukaryotic ribosomes differ from prokaryotic ribosomes in size and composition.
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Study Notes
Regulation of Gene Expression and Protein Translation
- Gene expression converts DNA information into RNA and protein products, influencing cellular phenotype.
- Cells use the same genome to produce diverse cell types by selectively expressing different genes at different times and locations.
- A gene is a genetic variant affecting a trait and can be described as a transcriptional unit encoding RNA or protein.
What Exactly is a Gene?
- Classical genetics define a gene as a genetic variant affecting a trait.
- A more precise molecular definition is a unit encoding RNA or protein with a biochemical/cellular function.
Gene Products
- Genes encode RNA molecules, some of which are translated into proteins (mRNA).
- Protein-coding genes are major contributors to cellular diversity.
- Non-translated RNAs like rRNA, tRNA, snRNA, miRNA, and lncRNA regulate gene expression and translation.
Gene Regulatory Sequences
- Gene regulatory sequences, like promoters, regulate gene expression by influencing when, where, and how much a gene is expressed.
- Variations in regulatory sequences can affect phenotypes due to changes in gene expression.
- Coding sequences can be affected, influencing protein or RNA products, and impacting cellular phenotypes.
Differential Gene Expression
- Fully differentiated cells still retain the ability to express all genes for whole organism production under appropriate circumstances.
- Cells differentiate from a fertilized embryo to specialized cell types exhibiting different gene expression patterns to perform specific functions.
- Environmental and developmental cues regulate gene expression.
Differential Gene Expression and Mechanisms
- Differential gene expression is regulated by diverse mechanisms, primarily transcriptional and post-transcriptional, for cell-type-specific expression.
- Transcription factors (TFs) are crucial in controlling gene expression through their specific DNA binding and activation/repression of target genes.
- External signals (environmental or cellular) activate TFs, which in turn, trigger downstream cascades of gene expression affecting cell function.
Prokaryotic vs. Eukaryotic Gene Expression
- Prokaryotes have a compact genome with closely positioned genes often organized into operons for coordinated expression, and gene expression is largely controlled at the transcriptional level.
- Eukaryotes have extensive non-coding DNA, and their gene expression exhibits more complex regulation at multiple levels: Transcriptional, post-transcriptional, translational, and post-translational.
- Eukaryotic cells have three main RNA polymerases (I, II, and III) that are specialized for different classes of RNA and use multiple transcription factors.
RNA Polymerases and Transcription Factors
- RNA Polymerase utilizes promoter sequences (like the TATA box or Pribnow box) within DNA to bind, initiating transcription.
- Eukaryotic RNA polymerase II requires general and gene-specific transcription factors for accurate binding and initiation of transcription.
- Histone modification (acetylation/deacetylation) is crucial for gene expression regulation. Histones can be modified by phosphorylation, impacting the accessibility/expression of DNA.
Chromatin Structure and Regulation
- DNA packaging and organization of DNA-histone complex (nucleosome) impact gene expression.
- Eukaryotic chromatin is tightly regulated by methylation of the DNA and histone modifications (like acetylation/deacetylation) leading to accessible or repressed states.
Splicing- Regulated Protein Diversity
- Eukaryotic gene expression exhibits more complexity due to pre-mRNA splicing where introns are removed, creating alternative forms of mRNA through different combinations of exons resulting in diverse protein variants.
- Alternative splicing increases the number of proteins an organism can produce from a relatively small set of genes.
Other Important Mechanisms
- Nucleosomes, SWI/SNF complexes and chromatin-binding proteins regulate access to promoters and the accessibility of gene regions.
- DNA methylation acts as a molecular "tag" regulating gene expression. It is implicated in in silencing gene expression by interfering with transcription factor binding or attracting repressor proteins, and influences development and tissue-specific gene regulation.
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