Eukaryotic Vs. Prokaryotic Genes
suchdiverse creatures as mammals are remarkably similarNon-coding regions are much more divergent,including regulatory regionsSome speculate that much of the differences among usare due to differences in expression of genes, ratherthan differences in the proteins they code for.5
Post-transcriptional controlUnlike Prokaryotes, protein production in Eukaryotesis controlled at many points after transcription– Alternative splicing: Different exons are spliced together– mRNA degradation: Rates vary from mRNA to mRNA, andare under active control– Transport out of the nucleus: active transport through nuclearpores.– Subcellular localization: some mRNAs are constrained toparticular regions of the cell– mRNA binding proteins: control translation directly.Alternative splicingGenes can be alternatively spliced meaning thatdifferent sets of exons are assembled– Leads to proteins with shared and distinct subsequences.– Example: proteins responsible for frequency sensitivity inauditory hair cells.mRNA degradation3' UTR signals control degradation rates for particularproteins (e.g. cyclins)Iron transport is tightly regulated, including by activemRNA degradation control– Normally, the mRNA for transferrin receptor (an iron relatedenzyme) is rapidly degraded.– When iron concentration islow, another protein bindsto iron responsive elements(IREs) in the mRNA andreduces the degradation rate.6
Transport in and outof the nucleusActive transport of maturemRNAs out of the nucleusand of nuclear associatedproteins back in is mediatedby the nuclear pore.Subcellular localizationmRNAs and proteins can be targeted to specificregions of the cell. “Zip Coding”Controlled by 3' UTR sequencesFor example, mRNAs for proteins that will be excretedare directed to the rough endoplasmic reticulum (ER)for translation.Some transport is by microtubules.mRNA binding proteinsSome proteins need to be able to change synthesisrates very quickly.– mRNA synthesis and transport isn't fast.One mechanism is translational regulation– Example: Ferritin (opposite of transferrin). When ironconcentation is low, active IREs bind to 5' UTR and preventtranslation. Wheniron concentration is high,IREs inactivate, andtranslation begins immediately.7
Control of rRNA productionNucleolus is a specialized area of the nucleus formaking rRNA. Appears as dark spot.– Not bound by a membrane, but assembled by brining togethervarious pieces of DNA that code for rRNAs.– Manages rRNA recycling and assembly of rRNAs with proteinsto form ribosomalsubunits before transportto cytoplasm– Disappears during mitosis.Gene FamiliesIn metazoans, 50-75% of genes are found in groups ofsimilar but slightly different sequences called genefamilies.– Example: Human -globin, which transports oxygen in theblood, has 7 variants, 2 of which are expressed fetally.These arise from gene duplication events.– Similar to homologous recombination, but during sexualreproduction, makes an extra copy of the geneTandem repeats have identical members.– Example: histones, rRNAs, tRNAsPseudogenes are untranscribed duplicates.Repeated DNA elementsCertain genes that are transcribed at high levels musthave many tandem repeatsNumber of repeats is gene copy number.All Eukaryotes have copy number 100 for the 5SrRNA.– Embryonic human cells have 5-10 million ribosomes, andreproduce every 24 hours. That's a lot of rRNA synthesis!– Frogs have a 5S rRNA copy number of 20,000!Human DNA is also full of “junk” repeats of manyvarieties (ALUs, LINES, SINES, etc.)8
Gene Duplication and EvolutionGene duplication events are very important in theevolution of new functions for old genes.Genes that are similar to other genes in the samegenome are called paralogs.Duplications allow mutation without loss of oldfunction.Deactivated pseudogenes are even freer to mutate.Reactivation can restart transcription of changed gene.Coming attractionsWe've covered much of the molecular biology of theEukaryotic cell!Next we will start to look at some details ofmulticellular organisms:– Somatic vs. germ line cells & sexual reproduction– Specialized cell types and tissues– Development– Cell to cell signaling and control– The evolutionary origins of multicellular organisms9
Like in prokaryotes, Eukaryotic genes are regions of DNA that act as templates for the production of RNA by RNA polymerases Recall Prokaryotic transcription: – Transcription factors bind to specific DNA sequences upstream of the start of operons, or sets of related genes. – Transcribed mRNA is directly translated by ribosomes. In Eukaryotes,File Size: 737KBPage Count: 9
How are prokaryotic and eukaryotic cells the same? How are they different? How do eukaryotic and prokaryotic cells compare in scale? B.4A: Prokaryotic and Eukaryotic Cells Cell Structure and Function Background: Prokaryotic vs. Eukaryotic Cells A cell is the smal
6.12AB: Prokaryotic and Eukaryotic Cells Organisms and Environments Part II: A Closer Look at Eukaryotic Cells Fundamental Question: What are the similarities and differences between prokaryotic and eukaryotic cells? Study this cell type's characteristics to complete page 6 of your Student Journal. Characteristics of a Eukaryotic Cell:
CHAPTER 2: CELL STRUCTURE AND FUNCTIONS LEARNING OUTCOMES 2.1 Prokaryotic and eukaryotic cells a) State the three principles of cell theory b) Explain the structures of prokaryotic and eukaryotic cells c) Illustrate and compare the structures of prokaryotic and eukaryotic cells (plant &
18. Refer to Models 1 and 2 to complete the chart below. Write yes or no in the box for each cell. Bacterial Cell Animal Cell Plant Cell All Cells Cell Membrane Ribosome Cytoplasm Mitochondria Nucleolus Nucleus DNA Cell Wall Prokaryotic Eukaryotic 19. As a group, write a definition for a prokaryotic
Archaeal cell membrane structure Comparing Prokaryotic and Eukaryotic Cells Classification of prokaryotic cellular features: Invariant (or common to all) Ribosomes: Sites for protein synthesis - aka the grand translators. Cell Membranes: The barrier between order and chaos. Nucleoid Region: Curator of the Information. Appearance of DNA by EM
Jun 18, 2011 · Whichcell in the table is MOST LIKELY a eukaryotic plant cell? A. 1 B. 2 C. 3 D. 4 4. . One difference between plants and animals is that plants are A. prokaryotic and animals are eukaryotic. B. eukaryotic and animals are prokaryotic. C. autotrophs and animals are heterotrophs. D. heterotrophs and animals are autotrophs.
Eukaryotic organisms consist of 1 or more eukaryotic cells: Prokaryotic cell Nucleus Eukaryotic cell Organelles eukaryotic cells contain a “true nucleus” and other membrane-bound organelles Most eukaryotes are single-celled organisms, most
This, too, is still basic to conventional literary criticism and is also open to seriou objection. De Wette in 1805 assigned Deuteronomy to the time of Josiah, such that pentateuchal matter considered dependent on Deuteronomy would be still later than it; 160 years later this is still commonly held, despite opposition. In the first half of the 19th century rival theses arose alongside the .
