<span>A photon of UV light causes mutations in the double-stranded DNA via a photochemical reaction. The product of such photochemical reaction in DNA is a cyclobutane pyrimidine dimer. Dimers may be repaired by mechanisms of photoreactivation or nucleotide excision repair (NER), but if the repair doesn’t occur dimers are mutagenic.
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UV light is absorbed by a double bond in pyrimidine bases (thymine and cytosine in DNA). The bond is opened and UV-modified base can now react with neighbouring molecules. If neighbouring molecule is another pyrimidine base, the UV-modified base forms direct covalent bonds with it. A cyclic ring (cyclobutane), not normally found in DNA, is formed (links the two pyrimidines). Next step is forming a single bond between two carbon atoms on the rings.The product of this reaction is a 6-4 molecule pyrimidine-pyrimidone which is more mutagenic than cyclobutane pyrimidine dimers.</span>
Answer:
Messenger RNA on the ribosomes binds amino acids into a peptide chain called a preprohormone. the chain is directed into the ER lumen by a signal sequence of amino acids
-enzymes in the ER chop off the signal sequence, creating an inactive prohormone
-the prohormone passes from the ER through Golgi
-secretory vesicles containing enzymes and prohormone bud off the golgi. the enzymes chop the prohormone into one or more active peptides
-vesicle releases contents by exocytosis
-hormone moves into circulation for transport to its target
<h2>The answer is RNA</h2>
A. they both have prophase and metaphase. Mitosis and meiosis have the same steps, just a few of the steps are different, and in meiosis the steps are done twice.
Rough Endoplasmic Reticulum: series of connected flattened sacs, part of a continuous membrane organelle within the cytoplasm of eukaryotic cells, that plays a central role in the synthesis of proteins.
Smooth Endoplasmic Reticulum: comprises of a tube-like structure located near the cell periphery. These tubules or tubes sometimes branch forming a network that is reticular in appearance. The network of smooth endoplasmic reticulum allows for an increased surface area to be devoted to storage of key enzymes.
