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.

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 same in your blood cells and nerve cells?

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

What percentage of the DNA is the Images Courtesy of Wikimedia Commons 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 same in your blood cells and nerve cells? Answer: 100%

same in your rods (eye) and lung cells? What percentage of the DNA is the Images Courtesy of Wikimedia Commons same in your rods (eye) and lung cells? Answer: 100%

What percentage of the DNA is the Images Courtesy of Wikimedia Commons same in your liver and bone cells? Answer: 100%

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 tell cells what to do?

Animations http://www.dnatube.com/video/2933/The-Human- Genome-Project-Video--3D-Animation-Introduction http://www.dnalc.org/resources/3d/10-triplet-code.html http://www.dnalc.org/resources/3d/09-how-much-dna- codes-for-protein.html Use these animations as a review to remind students how information is carried in DNA. Remind students of the universality of DNA and how the structure of DNA is the same for almost all organisms. Explain to students that this also applies to the DNA triplets and they code for the same amino acids in most organisms.

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. Use the information on the handout to guide a discussion, emphasizing these three core concepts. Students may use additional resources, as well as discussion time, to add information to their handouts.

Now, we are going to do some activities that will help you better understand: 1. Gene expression 2. How gene expression is regulated 3. How regulation of gene expression causes cells to become different 4. 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 Function… How? Use the link below to watch the NOVA video “Epigenetics”. http://video.pbs.org/video/1525107473#

Epigenetics NOVA Video 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. SE B.5C requires students to describe the role of DNA in cell differentiation. It is important that they understand that DNA is chemically and structurally modified, as described above and in the activity Epigenetic Control of Gene Expression. Make sure they are clear that this chemical and structural modification plays an important role in the differentiation process.

Epigenome http://commonfund.nih.gov/epigenomics/figure.aspx

Cell Differentiation 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 mechanisms 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

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

Posttranscriptional Control: Non-Coding RNA IMPORTANT: Not all of our DNA codes for mRNA that then translate 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 See a more complete list here: http://www.newworldencyclopedia.org/entry/RNA#List_of_RNA_types SE B.5C requires students to describe the role of RNA in cell differentiation. It is important that they understand that some of the genome is non-coding, which means it transcribes into ncRNA. This ncRNA plays an important role in how genes are expressed in different types of cells.

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 The big idea here is that gene expression is a regulated process. This regulation process is very complex and interrelated.

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

DNA Microarrays Activity

In Your Science Notebooks, Complete the Following Sentence: DNA microarrays help scientists study the human genome by…

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 Images Courtesy of Wikimedia Commons NOVA scienceNOW. “Epigenetics.” Retrieved September 16, 2012 from http://video.pbs.org/video/1525107473#