7.2 Transcription and gene expression
Information stored as a code in DNA is
copied onto mRNA.
Diana Carvajal
September 2014
HOMEWORK for next class: Define the following terms….
Gene expression is regulated by proteins that
bind to specific base sequences in DNA
- Prokaryotic cells: ex. lactose vs. repressor
protein.
- Eukaryotic cells: enhancers, silencers and
promoter-proximal elements (proteins).
Each cell of a multicellular eukaryotic organisms
expresses only a fraction of its genes. Gene
regulation is critical in the process of
development.
Promoter: example of non-coding DNA with a
function.
The environment of a cell and of an organism
has an impact on gene expression
Production of skin pigmentation in humans:
Exposure to sunlight affects it.
Gene “C” codifies for a precursor of the
pigment. A mutant, cs produces normal
pigmentation only in temperatures below body
temperature. At higher temperatures, less
pigment is produced.
Nucleosomes help to regulate
transcription in eukaryotes
http://cerch.org/wp-content/uploads/2011/02/DNA-methylation-image.jpg
Analysis of changes in the DNA methylation
patterns.
Expression of genes is regulated by:
• 1. Proteins that bind to DNA (enhancers, silencer,
promoter-proximal elements) and some non-coding
regions (promoters).
• 2. Environmental signals
• 3. Nucleosomes, together with methylation.
Looking for patterns, trends and
discrepancies—there is mounting evidence
that the environment can trigger heritable
changes in epigenetic factors
ANIMATION:
http://www.wiley.com/college/test/0471787
159/biology_basics/animations/fromGeneTo
Protein.swf
Transcription occurs in a 5’ to 3’ direction.
Eukaryotic cells modify mRNA after
transcription.
Different ways:
1. RNA splicing (noncoding regions will be taken out,
called introns-intervening sequences), only exons
codify for a protein.
2. Addition of poly-A tail (works as a message saying
it is mature mRNA).
mRNA splicing
Splicing of mRNA increases the number of
different proteins an organism can produce
Alternative splicing: process in gene expression where a sigle gene codifies for
multiple proteins (different structure and even different biological function).
TOK
• The nature versus nurture debate concerning
the relative importance of an individual’s
innate qualities versus those acquired through
experiences is still under discussion. Is it
important for science to attempt to answer
this question?