Tutor profile: Arlena C.
Identify what glycolysis is and describe the steps involved.
Glycolysis is the process of converting glucose, a basic six carbon sugar, to two molecules of pyruvate which can be used in anaerobic respiration to generate ethanol, carbon dioxide or lactic acid, or can enter the Krebs cycle of aerobic respiration. The first step of glycolysis is the phosphorylation of glucose at the 6th carbon by the enzyme hexokinase and a molecule of ATP to generate glucose-6-phosphate. Glucose-6-phosphate is then acted on by phosphoglucose isomerase to produce fructose-6-phosphate. Fructose-6-phosphate is acted upon by phosphofructokinase and a molecule of ATP to produce fructose-1,6-biphosphate. This is then converted to a molecule of glyceraldehyde-3-phophate and a molecule of dihydroxyacetone phosphate by an aldolase. The molecule of dihydroxyacetone is converted to glyceraldehyde-3-phosphate, so there are two molecules in total, both of which undergo the same steps. Glucose-3-phosphate dehydrogenase is converted to 1,3-bisphosphoglycerate by glucose-3-phosphate dehydrogenase and a molecule of NADH and inorganic phosphate. Phosphoglycerate kinase is used to convert 1,3-bisphosphoglycerate to 3-phosphoglycerate, generating a molecule of ATP in the process. 3-phosphoglycerate is converted to 2-phosphoglycerate by phosphoglycerate mutase, and is then converted to phosphoenolpyruvate by enolase. Finally, phosphoenolpyruvate is converted to pyruvate by pyruvate kinase, generating an ATP molecule in the process. This pyruvate can then proceed into the Krebs cycle or undergo anaerobic respiration.
Subject: Basic Chemistry
Explain the concept of electronegativity and how it pertains to the formation of hydrogen bonds.
Electronegativity refers to how likely an atom is to take the shared pair of electrons formed in a covalent bond for itself. Certain atoms, for example those with more protons, have a stronger pull and thus the shared pair of electrons will spend more time with them. In the case of hydrogen bonds: hydrogen has a weak electronegativity in comparison to some atoms like oxygen fluorine or nitrogen. The difference is so great that it generates a highly polar covalent bond where the electrons are mainly away from the hydrogen. Because of the electronegativity difference, hydrogen has a fractional positive charge, and the other atom will have a fractional negative charge. Hydrogen can then use its partial positive charge to interact with the negative charges on other molecules.
Describe the components of the DNA damage response.
Cellular DNA is subject to many exogenous and endogenous sources of damage. In order to respond to these, the cell employs the various methods of the DNA damage response. These methods include nucleotide excision repair, base excision repair, mismatch repair, and repair of double strand breaks. Base excision repair is used to fix smaller base lesions such as single strand breaks or oxidation. It involves the excision of the damaged base from the DNA, followed by the replacement of the correct base by the DNA replication machinery. Larger adducts which are capable of helical distortion such as photoproducts generated by UV damage, are fixed through nucleotide excision repair. This is divided into transcription coupled repair, or global genome repair. The DNA surrounding the lesion is excised to generate an oligonucleotide fragment. The gap where the lesion was is then filled by cellular replication machinery. Mismatch repair primarily recognises base/base mismatches and insertion/deletion mispairs. Double strand breaks can be repaired either through non-homologous end joining or by homologous repair. In non-homologous end joining the blunt ends of the DNA are stitched together at random, hence why this method can often result in deletion of nucleotides. Homologous repair uses the matching sister chromatid as a template to repair the double strand break.
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