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# Tutor profile: Andrés L.

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Andrés L.
Medical Student and Online tutor for 2 years
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## Questions

### Subject:Chemistry

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Question:

I have a chemistry lab question and do not know where to start? I am confused on what to do. This is the question(s): Calculate the expected pH values of the buffer systems from the experiments (a,b,c,d), using the Henderson-Hasselbalch equation shown in the Background section. Use for pKa values: carbonic acid = 6.37 and acetic acid = 4.75. Experiment A 5 mL .1 M acetic acid + 5 mL .1 M sodium acetate Experiment B 1 mL .1 M acetic acid + 10 mL .1 M sodium acetate Experiment C 5 mL .1 M carbonic acid + 5 mL .1 M sodium bicarbonate Experiment D 1 mL .1 M carbonic acid + 5 mL .1 M sodium bicarbonate pH = pKa + log [A-/HA]

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Andrés L.

Okay so for this problems we need to use the Henderson-Hasselbalch equation, the equation states that the pH of a system is determined by the pKa plus the logarithm of the molar concentration of the acid divided by the molar concentration of the base. Experiment A We need to convert the 1M concentration of both reactants and take them to moles. 5 ml x 1 mole of acetic acid/1000ml of solution = 0.005 moles of acetic acid 5 ml x 1 mole of sodium acetate/1000ml of solution = 0.005 of sodium acetate pH = 4.75 + log[0.005/0.005] pH = 4.75 + log[1] pH = 4.75 + 0 pH = 4.75 Experiment B Same goes with this experiment 1ml x 1 mole of acetic acid/1000 ml of solution = 0.001 moles of acetic acid 10 ml x 1 mole of sodium acetate/1000 ml of solution = 0.01 moles of sodium acetate pH = 4.75 + log[0.001/0.01] pH = 4.75 + (-1) pH = 4.75 - 1 pH = 3.75 Experiment C and D Same as before just change the pKa.

### Subject:Biochemistry

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Question:

What's the organophosphate's mechanism of action? And what's the normal function of the acethylcolinesterase and colinergic receptors?

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Andrés L.

Okay so first of all let's start by explaining the normal function of acetylcholinesterase: it's an enzyme that can be found in the synaptic space (the space between a pre-synaptic membrane and a post-synaptic membrane). The mechanism of action of this enzyme it's that it catalyzes the breakdown a neurotransmitter called acetylcholine (this neurotransmitter has many functions but the most important are muscle contraction, heart rate regulation and glandular secretion) that binds to the cholinergic receptors (muscarinic and nicotinic) in the post-synaptic membrane. Our body needs to breakdown this neurotransmitter in the synaptic space because if the acetylcholine concentration it's too high it will produce a constant stimulus in the post-synaptic cell, it then can produce pathologic reactions in the body such as muscle spasms, bronchial secretion and bradycardia. Now, the cholinergic receptors are a type of receptors that only binds acetylcholine (that's why they are called cholinergic). When the acetylcholine binds to these receptors on, let's say, a muscle fiber, they open ionic channels that depolarize the cell and activate the action potential of the cell that produces the muscle contraction. Depending on the receptor it can stimulate or inhibit a function. I'll attach a picture of the different receptors and their function when acetylcholine binds to it. Okay so now that we've defined the functions of a cholinergic receptor and acetylcholinesterase we can talk about the mechanism of action of organophosphates: The organophosphate binds to the acetylcholinesterase esteric site. By binding to this site it blocks the enzyme so when it tries to breakdown the acetylcholine it can't because there's already a molecule occupying the acetylcholine space. This action inhibits the acetylcholinesterase function. Since it can't breakdown the acetylcholine, as I said, the neurotransmitter accumulates in the synaptic space and it produces the symptoms that I already mentioned.

### Subject:Biology

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Question:

What does transformation mean? - Plasmid and the use in biotechnology. What is GFP, describe it. How is GFP used in nature? How is GFP used in biotechnology? (Please complete sentences if possible)

Inactive
Andrés L.

-What is a Plasmid and it's uses in biotechnology? A plasmid is a strand or loop of DNA that is typically found in bacteria as well as archae (single-cell organisms) and eukarya (organisms of complex cell structure). Plasmids carry only a few genes and exist independently of chromosomes, the primary structures that contain DNA in cells. Able to self-replicate, plasmids can be picked up from the environment and transferred between bacteria. Plasmids are used by their host organism to cope with stress-related conditions. Many plasmids, for example, carry genes that code for the production of enzymes to inactivate antibiotics or poisons. Others contain genes that help a host organism digest unusual substances or kill other types of bacteria. Several characteristics of plasmids make them easy to modify genetically. Firstly, they have relatively small DNA sequences, between 1,000 and 20,000 DNA base pairs. Secondly, they are easy to cut open, without falling apart, and snap back into shape. This makes it easy to insert new DNA into plasmids. Once a new DNA is inserted, the modified plasmid can be grown in bacteria for self-replication to make endless copies. -The GFP GFP stands for green fluorescent proteins, it is composed of 238 amino acid residues that exhibits bright green fluorescence when exposed to light in the blue to ultraviolet range. It was first found in a species of jellyfish called Aequorea victoria. GFP is used in nature by the jellyfish to create bioluminescence and by many other animals, it is quite unknown why the jellyfish uses this kind of light. The green fluorescent protein is used in biotechnology for many things, such as fluorescent microscopy. Another application is in is to express the protein in small sets of specific cells. This allows researchers to optically detect specific types of cells in vitro (in a dish), or even in vivo (in the living organism). Genetically combining several spectral variants of GFP is a useful trick for the analysis of brain circuitry Other interesting uses of fluorescent proteins in the literature include using FPs as sensors of neuron membrane potential, tracking of AMPA receptors on cell membranes, viral entry and the infection of individual influenza viruses and lentiviral viruses. And another grea application is for transgenic petslike green fluorescent zebrafish (GloFish) that were initially developed to detect pollution in waterways but now they sell them as glowing zebrafish pets.

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