Information stored in DNA is copied onto mRNA through transcription. Transcription occurs from 5' to 3' in eukaryotes. Eukaryotic cells further modify mRNA after transcription through splicing and other processes. This increases the number of proteins that can be produced from a single gene. Gene expression is regulated by proteins binding to specific DNA sequences and the cell's environment.

1. 7.2 Transcription & Gene
Expression
Essential Idea: Information stored as
a code in DNA is copied onto mRNA.
Image from https://worldwide.promega.com/resources/product-guides-
By Darren Aherne and-selectors/protocols-and-applications-guide/epigenetics/

2. 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.

3. 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.

4. 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.
Promoter (3) in E. coli bacteria with and
without lactose
1: RNA Polymerase, 2: Repressor,
3: Promoter, 4: Operator, 5:
Lactose
http://en.wikipedia.org/wiki/Promoter_(geneti
cs)

5. 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 Operon
https://www.youtube.com/watch?v=10YWgqmAEsQ

6. 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. 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/co
ntent/epigenetics/control/

8. 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
• DNA methylation is variable
during our lifetime
• Amount of methylation
depends on environmental
factors
• Evidence for heritability
From Biology Course Companion, Allott, A, Oxford University
Press, 2014, p. 357

9. 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

10. 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

11. 7.2 U1: Transcription occurs in a 5’ to 3’ direction.
From I-Biology.net

12. 7.2 U1: Transcription occurs in a 5’ to 3’ direction.
From I-Biology.net

13. 7.2 U1: Transcription occurs in a 5’ to 3’ direction.
From I-Biology.net

14. 7.2 U1: Transcription occurs in a 5’ to 3’ direction.
From I-Biology.net
http://www.phschool.com/science/biology_place/bioc
oach/transcription/complete.html

15. 7.2 U3: Eukaryotic cells modify mRNA after transcription.
http://bcs.whfreeman.com/thelifewire/co
ntent/chp14/1401s.swf
From I-Biology.net

16. 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.

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