7.2 Transcription & Gene Expression

By Darren AherneImage from https://worldwide.promega.com/resources/product-guides-and-selectors/protocols-and-applications-guide/epigenetics/

Essential Idea: Information stored as a code in DNA is copied onto mRNA.

7.2 Essential Idea: Information stored as a code in DNA is copied onto mRNA.

7.2 U1 Transcription occurs in a 5’ to 3’ direction.

7.2 U2 Nucleosomes help to regulate transcription in eukaryotes.

7.2 U3 Eukaryotic cells modify mRNA after transcription.

7.2 U4 Splicing of mRNA increases the number of different proteins an organism can produce.

7.2 U5 Gene expression is regulated by proteins that bind to specific base sequences in DNA.

7.2 U6 The environment of a cell and of an organism has an impact on gene expression.

7.2 S1 Skill: Analysis of changes in the DNA methylation patterns.

7.2 A1 Application: The promoter as an example of non-coding DNA with a function.

Application: The promoter as an example of non-coding DNA with a function.

• Only some DNA sequences code for polypeptides.

• Non-coding regions have other functions: tRNa production rRNA production (ribosomal

RNA) Control gene expression

Enhancers: regulatory sequences on DNA which increase the rate of transcription when proteins bind to them.Silencers: sequences on DNA which decrease the rate of transcription when proteins bind to them.

Application: The promoter as an example of non-coding DNA with a function.

• The Promoter is located near a gene’s location. It is the binding site of RNA polymerase- the enzyme that helps catalyze covalent bonds between mRNA nucleotides during transcription.

1: RNA Polymerase, 2: Repressor, 3: Promoter, 4: Operator, 5: Lactose

Promoter (3) in E. coli bacteria with and without lactose

http://en.wikipedia.org/wiki/Promoter_(genetics)

7.2 U5: Gene expression is regulated by proteins that bind to specific base sequences in DNA.

Gene expression in prokaryotes is a result of environmental factors• When lactose is not present, a repressor protein blocks

transcription. • When lactose is present, a repressor protein is deactivated.

Mr. Anderson on the Lac Operonhttps://www.youtube.com/watch?v=10YWgqmAEsQ

7.2 U6: The environment of a cell and of an organism has an impact on gene expression.

Epigenetics: the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself

Intro to Epigenetics

Exposure to sunlight has an effect on skin coloration in humans.

The Coppertone Girl

7.2 U2: Nucleosomes help to regulate transcription in eukaryotes.

Eukaryote DNA is associated with histone proteins.The histone protein tails can be modified: • Acetyl group: neutralizes the positive charge on histones,

making DNA less tightly coiled–> increases transcription • Methyl group: maintains positive charge on histones,

making DNA tightly coiled –> decreases transcription

http://learn.genetics.utah.edu/content/epigenetics/control/

7.2 S1: Skill: Analysis of changes in the DNA methylation patterns.

Direct methylation of DNA (not to histone tails) is thought to affect gene expression. • Increased methylation of DNA decreases gene expression

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 357

• DNA methylation is variable during our lifetime

• Amount of methylation depends on environmental factors

• Evidence for heritability

7.2 Nature of Science: Looking for patterns, trends and discrepancies—there is mounting evidence that the environment can trigger heritable changes in epigenetic factors.

• Environmental factors can increase or decrease epigenetic factors such as methylation or acetylation of DNA & histones.

• Different cells have different epigenetic patterns (methylation & acetylation).

• Growing evidence suggests that a cells epigenetic pattern may be passed on at a cellular level (cell division) and at an organism level (sex cells involved in reproduction)

Epigenetics and the influence of our genes: Courtney Griffins at TEDxOU

7.2 Nature of Science: Looking for patterns, trends and discrepancies—there is mounting evidence that the environment can trigger heritable changes in epigenetic factors.

From Biology Course Companion, Allott, A, Oxford University Press, 2014, p. 359

7.2 U1: Transcription occurs in a 5’ to 3’ direction.

From I-Biology.net

7.2 U1: Transcription occurs in a 5’ to 3’ direction.

From I-Biology.net

7.2 U1: Transcription occurs in a 5’ to 3’ direction.

From I-Biology.net

7.2 U1: Transcription occurs in a 5’ to 3’ direction.

From I-Biology.net

http://www.phschool.com/science/biology_place/biocoach/transcription/complete.html

7.2 U3: Eukaryotic cells modify mRNA after transcription.

http://bcs.whfreeman.com/thelifewire/content/chp14/1401s.swf

From I-Biology.net

7.2 U4: Splicing of mRNA increases the number of different proteins an organism can produce.

Proteins are often translated from mRNA with multiple exons.• The exons can be spliced together differently.• This can result in a different sequence of amino acids. • Consequently, a number of different protein structures and

functions are possible from the same mRNA• Depends on cell/tissue type.

TOK Link:The most recent analysis suggests there are about 20,500 genes in the human genome. Previous estimates were anywhere from 2,000 – 120,000 genes. This was a consequence of different criteria used to identify a gene.

Thanks to these fine folks, and any others that I may have forgotten!