gene expression and cell differentiation

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


same in your rods (eye) and lung cells?



same in your liver and bone cells?


same in your blood cells and nerve cells?


Answer: 100%



same in your rods (eye) and lung cells?

Answer: 100%



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









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 Function…

How?

Use the link below to watch the NOVA video “Epigenetics”.

http://video.pbs.org/video/1525107473#

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.

Epigenome

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

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 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

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 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

http://www.newworldencyclopedia.org/entry/RNA

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.


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


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

http://www.genome.gov/glossary/

http://www.genome.gov/glossary/

http://www.genome.gov/glossary/?id=167




gene expression and cell differentiation

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