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Gene Expression and
Cell Differentiation
CSCOPEUnit: 08 Lesson: 01
There are hundreds of different types of cells in your body, and
each type has a unique function. We’re going to compare some different types of cells to see
how much they have in common.
Your Best Guess
For each pair of cells in your body, you are going to predict what
percentage of DNA is the same in the two types of cells. Record your
prediction in your science notebooks.
same in your blood cells and nerve cells?
What percentage of the DNA is the
Images Courtesy of Wikimedia Commons
What percentage of the DNA is the
same in your rods (eye) and lung cells?
Images Courtesy of Wikimedia Commons
What percentage of the DNA is the
same in your liver and bone cells?
same in your blood cells and nerve cells?
What percentage of the DNA is the
Answer: 100%
Images Courtesy of Wikimedia Commons
What percentage of the DNA is the
same in your rods (eye) and lung cells?
Answer: 100%
What percentage of the DNA is the
same in your liver and bone cells?
Answer: 100%
Images Courtesy of Wikimedia Commons
Hmmm…
How can these cells, that have very different
functions, have the exact same DNA in the nucleus?
Hmmm…
How does the body use the exact same set of
instructions to make such different structures?
Taking a step back…
HOW does DNA specify for traits in an organism?
HOW does DNA instruct cells?
Animations
Insert appropriate animations here (see Advance Preparation).
Carrying Information in DNA
Core Concepts
DNA triplets code for one amino acid.
Amino acids link together to form polypeptides.
Genes code for polypeptides that control things such as: The expression traits (how we look) The function of the cell Other genes
A very small percentage of the human genome actually codes for proteins.
Now, we are going to do some activities that will help you better understand:
1. Gene expression2. How gene expression is regulated3. How regulation of gene expression causes cells to become different4. How environmental factors play a roll in cell differentiation
What Does Gene Expression Mean?
Let’s look at different ways it is regulated.(Graphic courtesy of Marianne Dobrovolny)
Different Cells Have Different Functions…
How?
Embed a video clip on epigenetics here.
Epigenetics
What causes cells with the same DNA to differentiate?
What is one way to turn genes on and off?
What causes changes in epigenetics? For example, why do identical twins continue to become more different in terms of their epigenetics as they get older?
Gene Regulation
Gene Regulation: Modification of Genome
(DNA)
Sections of DNA called transposons can be moved to different chromosomes.
Chemical factors can structurally change the DNA, turning it on or off. Chemical processes: DNA methylation & histone
modification Epigenome
Gene regulation at the DNA level happens in eukaryotes and rarely, if ever, in prokaryotes.
Epigenome
The term epigenome is derived from the Greek word epi, which literally means "above" the genome.
The epigenome consists of chemical compounds that modify, or mark, the genome in a way that tells it what to do, where to do it, and when to do it (i.e., turn genes on and off)
Different cells have different epigenetic marks.
The environment causes changes in our epigenetics.
Epigenome
In a fetus, cells with the exact same DNA
are directed to differentiate by
chemical signals that cause certain genes to be switched on or
off in.
Cell Differentiation
Gene Regulation
Gene Regulation: Transcriptional Regulation
Transcriptional factors (regulatory proteins) turn transcription on and off or increase and decrease.
This mechanism happens in eukaryotes and prokaryotes.
Prokaryotes: Transcriptional
Regulation
Operon – functioning unit of DNA containing the following: A set of genes (DNA the codes for mRNA) Regulatory sections (DNA that controls the
expression of the gene)
Prokaryotes:Transcriptional Regulation
This gene is
“turned on.”
Prokaryotes:Transcriptional Regulation
This gene is
“turned off.”
Eukaryote:Transcriptional
Regulation
Much more complicated and involves: Many regulatory proteins (transcription
factors) Enhancers and TATA Box
Eukaryote:Transcriptional Regulation
This gene is
“turned on.”
Gene Regulation
One gene can result in several different proteins through a process called:
Alternate mRNA Splicing
Posttranscriptional Control:
mRNA Processing
Posttranscriptional Control:
Non-Coding RNA IMPORTANT: Not all DNA codes for mRNA that then
translates into proteins!!!
Some DNA codes for non-coding RNA (ncRNA). This ncRNA plays a very important role in gene expression.
Some examples of ncRNA you are familiar with and others you are not: tRNA – helps in translation rRNA – helps in translation miroRNA – prevents translation from happening siRNA – destroys mRNA molecules snRNA – helps splice exons together during mRNA
processing
Gene Regulation
Translational Regulation:
These mechanisms prevent the synthesis of proteins.
Example: Regulatory proteins bind to specific
sequences in the mRNA and prevent ribosomes from attaching.
Happens in eukaryotes and prokaryotes
Gene Regulation
Protein Modification:
Proteins are chemically modified (ex. folded ) after they are made.
These chemical mechanisms can cause the folding process of proteins to change therefore altering how that protein will be expressed.
Gene Regulation
DNA Microarrays
This technology helps scientists understand the differences in different types of cells, despite the fact that they have the exact same DNA.
In your science notebooks, complete the following
sentence:
DNA microarrays help scientists study the human genome by…
Information Sources
National Institutes of Health. National Human Genome Research Institute. “Talking Glossary of Genetic Terms.” Retrieved October 16, 2011, from http://www.genome.gov/glossary/ http://www.genome.gov/glossary/?id=167
NOVA scienceNOW. “Epigenetics.” Retrieved September 16, 2012 from http://video.pbs.org/video/1525107473#