hello everybody my name is Iman welcome back to my YouTube channel today we're gonna do practice problems associated with our last and final chapter for MCAT biochemistry this chapter is all about non-enzymatic protein functions and protein analysis let's go ahead and get started problem one says at what PH can protein a best be obtained through electrophoresis all right so we're given some information about protein a b and c we really want to get that protein a it has a pi of 4.5 um protein B has a pi of 6 and protein C has a pi of 9.5 so if um if you remember um PR is the isoelectric point all right proteins can be separated based on the separated on the basis of their isoelectric point the pi is the pH at which the protein or amino acid is electrically neutral so it has an equal number of positive and negative charges all right now in most electrophoresis experiments we attempt to separate out one component from the other now we're attempting here to isolate protein a only so a pH that causes protein a to be negative while proteins B and C are neutral are or positive is going to be the best all right because that pi all right now looking at these PHS pH 5.5 is going to accomplish this goal proteins b and c will be positively charged here a pro a pH of 4.5 which is what the pi of protein a is would make protein a neutral and it would thus not migrate across the gel all right any neutral impurities would also remain in the well with protein a and that makes this pH not the best choice but a pH of 5.5 will accomplish the goal all right it will accomplish the goal and so the answer to question one is D two says what is a function of sodium dodecal sulfate SDS and SDS page all right sodium dodecal sulfate is a detergent it's going to digest proteins to form to form my cells with uniform negative charges now because the protein is sequestered within the mic cell other factors like the charge of the protein and the shape have very minimal role during separation and so in essence the protein micelles can be modeled as being spheres that are only dependent on size all right if you remember when we covered SDS we said it's a it's an electrophoresis method that is going to let us really just compare size all right SDS page is going to denature the protein it's going to mask the native charge so that comparison of size is more accurate all right but you should also know that the functional protein can't be recaptured from the cell because it was denatured using the SDS detergent all right now let's read these answer choices a says SDS stabilizes the gel Matrix improving resolution during electrophoresis this is not correct proteins to give them uniformly negative charges so that separation is based purely on size this is a true statement C says SDS raises the pH of the gel all right this is not correct um separating multi-unit proteins into individual subunits no that's just not correct SDS cellular solubilizes proteins to give them uniformly positive charges so separation is based on Purely pH also not correct not based on of pH remember it's based purely on size so the correct answer for two here is going to be B three says which of the following is not involved in cell migration all right looking at the choices dynein flagella actin centrioles from all the given choices all of them are involved in cell movement except the last answer Choice centrioles centrioles are composed of microtubules but they're but are involved in mitosis not in cell migration and so three is d fantastic forces which of the following protein is most likely to be found extracellularly all right the most our answer choices are two billion myosin collagen and actin the most prevalent extracellular proteins are keratin elastin and collagen tubulin and actin are primary cytoskeletal proteins while mycin is a motor protein all right so just some quick information on that we want what is most likely to be found extracellularly we said that's keratin elastin and collagen and only one of these is in the answer choices so the answer choice to four is C it's collagen fantastic five says hormones are found in the body in a very low concentration but they tend to have strong effect what types of receptors are hormones most likely to act on all right we have ligand-gated ion channels enzyme linked receptors and G protein coupled receptors for a ligand present and low quantities to have a strong action we expect it to initiate a second messenger Cascade system why because second messenger systems amplify signals because enzymes can catalyze a reaction more than once while they are active and then often activate other enzymes now what falls under this kind of of second messenger system both enzyme-link receptors and g-protein-coupled receptors use second messenger systems and so that means that means two and three are correct and the only answer choice that encompasses that is C so the answer just for five is C 6 says which of the following is most likely to be found bound to a protein in the body all right we have sodium potassium chloride and calcium ions that are not readily accessible in the cytoplasm or the extracellular space are likely to be bound to a binding protein classically calcium and magnesium are protein bound without this background knowledge though this question can still be answered how well sodium and potassium must exist in their free state to participate in action potentials right that's something we do know so that means we can cancel them out all right chloride is readily excreted by the kidney which would not be true if it were protein bound so it pretty much cancels out this answer choice too calcium has to must be sequestered into in both the bloodstream and intracellularly because calcium is used for muscle contraction and it's used for exocytosis and many other cellular processes that must be tightly regulated all right and so which is likely to be found bound to a protein in the body calcium but also as a side note make sure you remember that both calcium and magnesium are protein bound fantastic seven says which of the following characteristics is not attributed to antibodies Ace says antibodies bind to more than one distinct antigen B says antibodies label antigens for targeting by other immune cells C antibodies can cause agglutination by interaction with an antigen and D antibodies have two heavy chains and two light chains we're trying to find which one of these statements is not true all right antibodies are specific to a single antigen all right each B cell produces a single type of antibody with a constant region that is specific to the host and a variable region that is specific to the antigen all right now if we look keep that in mind looking at these answer choices antigens label antibodies label antigens for targeting by other immune cells this is true antibodies can cause agglutination by interaction with it with an antigen this is true antibodies have two heavy chains and two light chains this is true antibodies bind to more than one distinct antigen that is not true antibodies are specific to a single antigen so which of the following characters is not true the correct answer to 7 is a fantastic eight says Which ion channels are responsible for maintaining the resting membrane potential all right ungated voltage-gated ligand-gated or no ion channels okay the resting membrane potential is displayed by cells that are not actively involved in Signal transduction ungated or or I guess quote-unquote leak channels they permit limited free flow of ions while the sodium potassium pump is also active and correct for this leakage like in gated and voltage-gated channels are involved in cell signaling and in the pacemaker potentials of certain cells but cause deviation from the resting membrane potential all right now we're trying to find which one is responsible for maintaining the resting potential not the voltage-gated not the ligand-gated but the ungated channels so 8 is a nine says which of the following is not a component of all trimeric G proteins all trimeric G proteins have an alpha beta and gamma subunit all right so that's going to cancel out a b and c all right and that means which of the following is not a component of all primary G proteins this last one g of I all right now remember also gsgi and GQ those are subtypes they are subtypes specifically of the ga subunit of the primary G proton all right subunits GS GI and GQ like we talked about in the review these are subtypes of the G Alpha subunit of the trimeric G protein which will also have a beta and gamma subunit all right and Fanta fantastic which of the following methods would be best to separate large quantities of the following proteins all right we have their pis they have very close pis they have different masses all right the proteins here they differ primarily in their masses in their molecular weights all right their pis are very close so what we don't want to do is use ion exchange chromatography it's all right also we don't want to use the isoelectric focusing idea here because they all have the same very similar Pi values all right what is better here all right a native page while it can be used we're dealing with with with quite heavy um proteins and we have large quantities native page is not very good for large quantities all right we have we're separating large quantities of proteins with different sizes the best answer Choice here is going to be size exclusion chromatography fantastic eleven says which amino acids contribute most significantly to the pi of a protein we have lysine Glycine and Arginine the overall Pi of a protein is determined by the relative number of acetic and acidic and basic amino acids the basic amino acids that you should know and memorize are arginine lysine and histidine and the acetic amino acids are aspartic in glutamateic acid all right those are all going to contribute significantly most significantly to the pi of the protein all right so from that list what do we see here we see lysine and Arginine glycine has only a hydrogen as its side chain it's neither acidic nor basic all right and so the only correct the answers here would be lysine and Arginine and that is encompassed in answer Choice C so 11 is C fantastic oh it seems that that is the last problem so we have reached the end of our review I hope this was helpful let me know if you have any comments questions or concerns down below other than that good luck happy studying and have a beautiful beautiful day future doctors