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7.2: Transcription and Gene Expression

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Define "gene expression."



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
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Define "gene expression."



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Gene expression is the processes by which information of a gene (DNA) is converted into the resulting phenotype. Gene expression consists of DNA transcription, RNA processing, and translation.
Image: Define "gene expression." Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Outline why gene expression must be regulated.



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Gene regulation is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein). Different cells in a multicellular organism may express very different sets of genes, even though they contain the same DNA.

Gene expression is regulated to ensure that the correct proteins are made when and where they are needed. Regulation may occur at any point in the expression of a gene, from the start of the transcription phase of protein synthesis to the processing of a protein after synthesis occurs.
Image: Outline why gene expression must be regulated. Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Outline the role of enhancers in the regulation of gene expression.



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Many eukaryotic genes possess enhancer sequences, which can be found at considerable distances from the genes they affect. Enhancer sequences are DNA sequences that, when bound by proteins called transcription factors, "enhance" (meaning activate or "turn on") the transcription of an associated gene.
Image: Outline the role of enhancers in the regulation of gene expression. Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Outline the role of silencers in the regulation of gene expression.



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Silencer sequences are DNA sequences that, when bound by proteins called repressors, "silence" (meaning disactivate or "turn off") the transcription of an associated gene.
Image: Outline the role of silencers in the regulation of gene expression. Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Explain the control of gene expression in eukaryotes.



Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.
Gene expression can be controlled by turning on/off genes at different times so only specific mRNA is produced through transcription. In eukaryotic cells, most genes are turned off (not being transcribed) at any one time. Gene expression is primary controlled by proteins called transcription factors, which bind to DNA to either increase or decrease transcription by enhancing or inhibiting the ability of RNA polymerase to bind to the promoter.

When DNA is coiled around histone proteins in a methylated nucleosome, the transcription factors can not bind to DNA. This will "silence" a gene so it will not be transcribed.

When acetylated, nucleosome will uncoil. This will expose the DNA, allowing transcription factors to bind. As a result, a genes will be accessible for transcription.

Hormones and environmental chemicals can interact with transcription factors to indirectly affect gene expression. For example, the plant hormone auxin interacts with transcription factors to regulate gene expression in plant meristems.
Image: Explain the control of gene expression in eukaryotes. Understanding: Gene expression is regulated by proteins that bind to specific base sequences in DNA.