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Lecture 15

Lecture 15.docx

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Biology 1202B
Brenda Murphy

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1 MiRNA (Chapter 14) Human Development  Human egg when released from the ovary is almost completely metabolically active  Within seconds of the egg & sperm meeting, there is rapid cell division o Mitosis (growth) produce cells of the body  Cells differentiate into specialized cells with different functions through translation and transcription  Every nucleated cell of the body contains the same DNA template and genes o Ie. Liver cells do not contain different DNA than skin cells  Structural and functional differences in cell types result from the presence or absence of the products resulting from expressed (transcribed, or transcribed & translated) genes rather than the actual presence of genes themselves on DNA  It is not enough just to have a gene present in DNA through a very complex system o Genes must be expressed (or not expressed) o In the correct tissue (special) o At the correct time (temporal) Gene Expression (Transcription &/or Translation) is like Music Played by an Orchestra  Gene is present in DNA but it is ―on‖ or ―off – but there is a lot of variability in this o Gene is expressed/not expressed o This may change at different tissues or at different times  Development vs. puberty time vs. 20’s are different – some diseases are age specific due to being turned on/off at different times  Gene is individually fine tuned o May be loud (forte) or quiet (piano) o Staccato (short ½ life) vs. legato (long ½ life)  Gene’s tuning is dynamic & aware of its surrounding  Adjust your volume relative to the volume around you o If done properly you get music (normal development) o If not, you get noise (abnormal/lethal development) Regulation of Gene Expression in Prokaryotes  Simple, single celled organisms with generation times in minutes  Rapid & reversible alterations so they can adapt quickly to changes in their environment o Genes are organized into a functional unit called an operon  I.e. coordinated synthesis of proteins with related functions o Example: Lac operon is an example of transcriptional regulation demonstrating how genes are turned on and off Regulation of Gene Expression in Eukaryotes 2  Multicellular cells  More complicated since nuclear DNA is bound to histones o Thus they need chromatin remodeling to loosen histone DNA interaction  Acetylases add acetyl groups to histones  Acetyl Groups = CH 3O  DNA is wrapped on the outside of the proteins—not easily accessible to transcription factors  Therefore, need to do something to the DNA to allow it to bind to the enzymes o Or, Slide nucleosomes (just a little bit) away from the gene’s promoter region o DNA is wrapped around a core of two molecules of each histones H2A, H2B, H3 and H4  Higher level of compaction when H1 is linked to adjacent nucleosomes - Promoter DNA is not accessible to proteins (RNA polymerase, Transcription Factors) that bind to initiate transcription - Using ATP energy, chromatin remodeling complex binds and slices nucleosomes along DNA - Promoter DNA is accessible and the gene may be active - May be active – need RNA polymerase and transcription factors to turn it on – if they are not present, even though the promoter may be accessible, there are other things that affect if it is turned on or off Regulation of Gene Expression in Eukaryotes  More complicated since nuclear DNA is bound to histones o Thus, need chromatin remodeling to loosen/slide nucleosomes from the promoter  This produces a large number of cells, and produces a large number of different types of cells o Transcriptional Regulation – Which genes are transcribed? Most VIP o Post-Transcriptional Regulation – Types & availability of mRNAs to ribosomes o Translational Regulation – Rate at which proteins are made o Post-Translational Regulation – Availability of the finished protein Central Dogma  DNA ---- (transcription) ---> mRNA --- (translation) -
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