Gene Expression and Cell Differentiation CSCOPE Unit: 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.

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 Images Courtesy of Wikimedia Commons

What percentage of the DNA is the same in your rods (eye) and lung cells?

What percentage of the DNA is the same in your liver and bone cells? Images Courtesy of Wikimedia Commons

How can these cells, that have very different functions, have the exact same DNA in the nucleus?

How does the body use the exact same set of instructions to make such different structures?

 HOW does DNA specify for traits in an organism?  HOW does DNA instruct cells?

 Insert appropriate animations here (see Advance Preparation).

 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.

What Does Gene Expression Mean? Let’s look at different ways it is regulated. (Graphic courtesy of Marianne Dobrovolny)

 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.

 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.

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.

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

Eukaryote: Transcriptional Regulation  Much more complicated and involves:  Many regulatory proteins (transcription factors)  Enhancers and TATA Box

Eukaryote: Transcriptional Regulation

Gene Regulation

 One gene can result in several different proteins through a process called: Alternate mRNA Splicing

 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

 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

 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

This technology helps scientists understand the differences in different types of cells, despite the fact that they have the exact same DNA.

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 NOVA scienceNOW. “Epigenetics.” Retrieved September 16, 2012 from