# Tutor profile: Megan V.

## Questions

### Subject: Biochemistry

Calculate the net charge of an Arginine side chain at pH 11.8?

STEP 1: Understand what we are trying to find here. Since the pKa of Arginine is 12.5 (which is within 1 unit of our 11.8 pH) we must calculate the exact charge as Arginine deprotonates from a charge of +1 to 0. (you will find this information in your notes or online) STEP 2: Calculate the ratio of deprotonated/protonated Arginine ( [d/p] ) with the following formula pH = pKa + log[d/p] d -> deprotonated arginine p -> protonated argine 11.8 = 12.5 + log[d/p] insert values given in question log[d/p] = 11.8 - 12.5 subtract to simplify log[d/p] = - 0.7 [d/p] = 10^(- 0.7) do the opposite of log (10^)to the other side to get [d/p] by itself [d/p] = 0.199 STEP 3: Calculate the degree of deprotonation ( α ). We must now find the fraction of Arginine that is deprotonated at pH 11.8 by using the following formula. [d/p] = α / (1 - α) α = degree of deprotonation 0.199 = α / (1 - α) input value from step 2 0.199(1 - α) = α cancel out the division by multiplying both sides by 1 - α 0.199 - 0.199α = α simplify 0.199 = α + 0.199α put the αs back on one side by adding 0.199α to each side 0.199 = 1.199α add αs α = 0.199 / 1.199 divide both sides by 1.199 α = 0.166 OR 16.6% STEP 4: Find the net charge when degree of deprotonation is 0.166 using the following formula. (degree of protonation x charge when protonated) + (degreee of deprotonation x charge when deprotonated) This looks complicated but its actually very simple, you already know must of it from the previous steps. The charge when protonated is +1 and when deprotonated its 0 (step 1), and the degree of deprotonation is 0.166 (step 3). Now all we need to do is find the degree of protonation which is simply: 1 - degree of deprotonation = degree of protonation 1 - 0.166 = degree of protonation 0.834 = degree of protonation Then put it all into the formula in the beginning of step 4 to find the net charge (0.834 x 1) + (0.166 x 0) = net charge 0.834 = net charge Therefore, the net charge of Arginine at pH 11.8 is +0.834 Good job, you have your answer!

### Subject: Biology

List some features and at least one important function of each of the following organs? -Brain -Liver -Small intestine -Stomach -Heart -Lungs

BRAIN Potential features you could say: located inside the skull (protective bone layer), made up of nervous tissue, weighs around 1.2–1.4 kg, is separated into 4 lobes (Frontal, Parietal, Occipital, Temporal), has grooves called sulci and ridges called gyri Function: controls the actions of the body including movement, organ function, conscious thought, and processing sensory information LIVER Features: located in the upper abdomen near the stomach, is divided into a left and right lobe and 4 lobes, each lobe is made up of many hepatic lobules which all have a portal triad (hepatic artery, portal vein, and bile duct) Functions: filtering blood from the digestive system and producing bile SMALL INTESTINE Features: is part of the gastrointestinal system, located in the lower abdomen between the stomach and the large intestine, made up of 3 parts (duodenum, jejunum, and ileum), usually between 3-5 meters, inside surface is made up of folds, villi and microvilli Function: site of chemical digestion and absorption in STOMACH Features: J-shaped muscular organ inside the abdomen, the walls are made of 4 layers (mucosa, submucosa, muscularis externa and the serosa), the inner mucosa has invaginations called gastric pit which have cells that produce the components of stomach acid (HCl) Function: site of chemical and mechanical digestion (via peristalsis) of food into chyme HEART Features: part of cardiovascular system, fist-sized muscular organ found in the chest, contains 4 chambers (Right atria, right ventricle, left atria and left ventricle), is connected to the lungs via the pulmonary artery and vein, blood enters through the superior vena cava and exits through the aorta Function: pump oxygenated blood to all areas of the body through blood vessels (arteries), and receive deoxygenated blood from veins LUNGS Features: part of the respiratory system, pair of organs found inside the chest cavity, each side contains a bronchus, bronchioles, alveoli, and many tiny blood vessels called capillaries, the right lung has 3 lobes and the left has only 2, are protected by the rib cage Function: gas exchange/respiration, taking oxygen from the environment and allowing it to diffuse into our blood to be used by our cells, and expelling the waste (carbon dioxide) into the environment

### Subject: Physics

Renee can swim at a speed of 2.5 m/s. She attempts to swim straight across a river (north) but is pushed eastward by the current at a speed of 4 m/s. What is the resulting velocity? (include units and direction in your answer)

STEP 1: Start by drawing your diagram. *Make sure your arrows/vectors have both a speed and direction.* Renee is swimming at 2.5 m/s north so draw your first arrow pointing upward and label it 2.5 m/s [N]. Then from the end of that arrow, draw another arrow pointing off to the right (aka EAST) to represent the current, label this 4 m/s [E]. Finally, connect the beginning of the first arrow with the end of the second with another arrow; this will be the hypotenuse (labelled h). Complete your drawing with a square to represent the right angle and a theta ( θ ) to represent the angle you want to find (angle between the north arrow and the hypotenuse). STEP 2: Calculate the length of the hypotenuse. Do this by using the Pythagorean theorem formula -> a^2 + b^2 = c^2 (the ^ means superscript, in this case ^2 means squared) lets say that: a= 2.5 m/s b= 4 m/s c= unknown hypotenuse 2.5^2 + 4^2 = c^2 input the numbers to the formula 6.25 + 16 = c^2 simplify by squaring the first 2 numbers 22.25 = c^2 add the 2 numbers together √(c^2) = √22.25 square root both sides to "get rid of" the ^2 (cancel by doing the opposite) c = 4.72 therefore, the hypotenuse length is 4.72 STEP 3: Calculate the unknown angle. Do this by using SOHCAHTOA, in this question I will be using sin (SOH) but you can use the cos or tan method if you like. θ = unknown angle o = 4 m/s h = 4.72 m/s sinθ = o / h sinθ = 4 /4.72 input numbers into formula sinθ = 0.848 divide to simplify θ = sin^(-1)(0.848) do the inverse sin to the other side to get θ by itself θ = 58.0 round to the closest 0.1, answer should be in degrees [N58°E] STEP 4: formulate an answer. When showing your work, it is important to have a clear final answer such as -> Therefore, Renee's resulting velocity was 4.72 m/s [N58°E]

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