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Cellular Biology

Cellular Biology - Nucleus contain protect DNA...

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Nucleus – contain & protect DNA, transcription, partial assembly of ribosomes - Nuclear envelope - In prokaryotes, there is no nuclear envelope that forms a separate compartment, so the genome can remain accessible to the cytoplasm. Replication, transcription and translation happens in the same compartment in prokaryotes. - Genes can be mapped genetically and physically to the chromosome they reside on and to a specific location on the chromosome, called the locus . - Heterochromatin – densely packed chromatin where genes tend to be inaccessible and are turned off. - Euchromatin – loosely packed and allow genes to be activated. If a retrovirus inserts its genome into regions of heterochromatin and nowhere else, the retroviral genes will not be expressed very frequently, and the virus will tend to remain as a provirus unless a change in the surrounding heterochromatin allows viral genes to be expressed. Nucleolus – “ribosome factory” - Contains loops of DNA, RNA polymerases, and rRNA - It’s larger in cells that are actively synthesizing protein. The DNA serves as a template for rRNA production. - Is the site of transcription of rRNA by RNA pol I . (mRNA is transcribed by RNA pol II, and tRNA is transcribed by RNA pol III). Bacteria only have a single kind of RNA polymerase which is responsible for all transcription, but multiple DNA polymerases Nuclear envelope – consists of 2 lipid bilayers - At points, the outer nuclear membrane is continuous with the membrane of the rough ER. The space between the nuclear membranes is contiguous with the ER lumen, which is isolated from the cytoplasm. - Contains nuclear pores that allows the passage of material into and out of the nucleus . (Usually small molecules < 60 kilodaltons) - Larger proteins can be marked with signal-specific sequences called nuclear localization sequences . These proteins are translated in cytoplasmic ribosomes and are then imported into the nucleus by specific transport mechanisms. Mitochondria – produce ATP via Kresb cycle and oxidative phosphorylation - Possess their own genome - Endosymbiotic theory – the mitochondria use a different system of transcription and translation than nuclear genes do, so investigators postulated that mitochondria originated as independent unicellular organisms living within larger cells. - If a women has a disease caused by an abnormality in her mitochondrial genome, all of her children will have the disease since they will inherit mitochondria exclusively from her. Ribosomes – synthesize proteins
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Rough ER – location of synthesis/modification of secretory, membrane-bound, and organelle proteins. - Plays an integral role in directing protein traffic to different parts of the cell. - Proteins synthesized on the rough ER will end up either secreted into the extracellular environment, as integral plasma membrane proteins, in the membrane or interior of the ER, Golgi or lysosomes .
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