Tutor profile: Jordan S.
What is CRISPR and how does it play a role in gene editing?
CRISPR stands for "clustered regularly interspaced short palindromic repeats." These are short DNA sequences that play a key role in the fighting of infections in prokaryotic organisms. The sequences are derived from DNA fragments of invaders that have previously infected the prokaryote. The cell can then use this CRISPR to easily identify the genetic structure of similar invaders in subsequent infections. In recent years, we have taken this concept and applied it to gene editing. We can easily and cheaply develop these strands of CRISPR DNA to target known gene sequences in a variety of organisms. When you attach these short strands of DNA to a carrier enzyme, Caspase-9, this CRISPR-Cas9 complex can find complementary strands of DNA in the organism with high efficacy. This process has huge implications in gene editing as it allows scientists and researchers with a cost-effective way to target highly specific DNA sites and alter them in a variety of ways (cleaving the DNA completely, introducing new DNA segments, etc.)
Subject: Basic Chemistry
Why is it dangerous to improperly store bleach?
The answer to this question has to do with the contamination and/or decomposition of the bleach molecules under poor storage conditions. This decomposition can occur from a variety of factors including heating, exposure to sunlight, contact with certain metals, etc. The chemical formula for bleach, also known as sodium hypochlorite, is NaOCl. This molecule is comprised of a positively charged sodium cation (Na+) bonded with a hypochlorite anion (OCl-). Let's consider the decomposition of bleach with excess water: NaOCl + H2O --> NaOH + HOCl In this reaction, the bleach and water react to form sodium hydroxide and a species of hypochlorous acid. This hydrochlorous acid can easily degrade into hydrochloric acid and oxygen: 2HOCl --> 2HCl + O2 The truly dangerous part of this series of reactions is when this hydrochloric acid reacts with some of the sodium hypochlorite molecules in the original solution: NaOCl + 2HCl --> Cl2 + NaCl + H2O As in any typical acid/base reaction, the end products include water as well as a salt. But in this case, elemental chlorine is also created (in a gaseous state at room temperature). Chlorine gas is irritating to the throat and lungs, and in high enough concentrations/levels of exposure it can be acutely toxic.
Which of the following statements about enzymes is FALSE: A. Enzymes can acts as catalysts to initiate or accelerate biochemical reactions B. Enzymes are almost always categorized as proteins C. Enzymes operate the most efficiently at optimum pH levels D. Enzymes are destroyed during chemical reactions
Answer: D Let's break down each answer and see why D is the most correct answer. A: Generally speaking, the main function of an enzyme is to facilitate biochemical reactions, so this can easily be considered to be a true answer B: Proteins are large molecules that that are comprised of one or more chains of amino acid residues. Depending on the sequence of amino acids as well as the folding/3-D shape of the molecule, it can serve any number of functions. An enzyme is simply a specialized protein that can facilitate biochemical reactions, so this answer is true. C: Enzymes are sensitive to the pH in their surroundings. pH can be responsible for changing the 3-D structure of the enzyme, or even changing the charge on the amino acids that make up the protein. This could alter the shape/properties of the active site of the enzyme (aka where other molecules bind to the enzyme in order to undergo the chemical reaction), disallowing binding of certain substrates and affecting the overall efficiency of the enzyme. In some cases, pH can completely denature or destroy the enzyme rendering it completely unusable. Because of these facts, it's clear that pH has a direct correlation to enzyme efficiency. D: The most basic function of an enzyme is for a substrate to bind to its active site, the enzyme facilitating/accelerating a chemical reaction, and then releasing the substrate in order for more substrates to bind in the future. Under normal circumstances, an enzyme does not undergo permanent changes in it's composition or 3-D structure allowing it be used multiple times for many chemical reactions. Because enzymes are typically unaffected during this process, this is the correct answer.
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