Chrras Posted December 12, 2019 Posted December 12, 2019 Hi, my professor just uploaded the correct answers to our exam, and he is known to make a lot of mistakes in exam sets. We've been given the past four exam sets, and I have been able to find several mistakes, all of which he recognized when I contacted him - and I am no great mastermind of biology, so that says something about the amount of mistakes. Based on that, I suspect there might be mistakes in the exam set from last week. I am quite biased myself, so I would like someone (who also knows a lot more about biology and biochemistry than me) to look through the answers, and tell me if they are indeed all correct, or if some of them are ambiguous. There are 52 questions, but all are multiple choice. Thanks in advance!
CharonY Posted December 12, 2019 Posted December 12, 2019 ! Moderator Note I have deleted the pdf for now, since we generally do not encourage to download files, especially from first-time posters for safety reasons. Feel free to post the questions which you are doubtful about, though.
Chrras Posted December 12, 2019 Author Posted December 12, 2019 (edited) Sure, I get your point. There are several questions that I doubtful about, however. But I'll post them here: Which molecule in the cell membrane makes the cell membrane more permeable? Triglycerides Saturated phospholipids Unsaturated phospholipids Cholesterol Vitamin A A cell is dehydrated and starts shrinking. Which aqueous solution will make the cell grow to its normal size as fast as possible? An isotonic solution A hypotonic solution A hypertonic solution The concentration of soluble components in the solution has no impact on cell size Cells can't change their water uptake through osmosis The majority of a given integral membrane protein is placed in the cell membrane, while only the N- and C-terminal amino acids are poking out of the membrane. Which type of amino acids is this membrane protein made up of? Hydrophilic amino acids Hydrophobic amino acids Polar amino acids Positively charged amino acids All types of amino acids er equally abundant in integral membrane proteins If Km is low it means that an enzyme: Have a high catalytic activity Increase the activation energy Increase the DeltaG (Gibbs energy) of the reaction Have a low catalytic activity All of the mentioned options The following sentences describe enzymes, but which is true? There is a linear relationship between S and turn-over-velocity at low S Reactions catalysed by enzymes follow saturation kinetics Enzyme activity can not be inhibited by molecules that are similar to the substrate. Allosteric inhibition describe a substrate competitive inhibition All the sentences are correct What is the net outcome of ATP by full oxidation of 1 mole of sucrose in a eukaryotic cell? 60 mol 62 mol 108 mol 18 mol 30 mol During photosynthesis photons are excited to a higher energy level. Which enzyme (among others) are part of this? Photosystem 1 Cytochrome B Rubisco Ferrodoxine Hexokinase To make 1 molecule of Glucose in the calvin cylce 18 ATP is consumed. How many protons is needed in the photosynthetic ATPase to make these 18 ATP? 54 41 88 18 103 In a newly synthesized eukaryotic DNA molecule you observe mutations for every 150 nucleotides throughout the DNA strand, but only on the new DNA strand. Where do these mutations come from? They arise spontaneously in the DNA They come from synthesis of the leading strand They come from synthesis of the lagging strand You cannot know from where the mutations arise This replication mistake is due to an error in the telomerase enzyme Which process cause the genetic diversity as the result of cell division by meiosis? The random separation of chromosomes during meiosis I The formation of recombinant chromatids during meiosis I The random separation of chromatids during meiosis II The formation of recombinant chromatids and the random separation of the chromosomes Meiosis do not result in genetically different cells but in genetic identical cells A female mouse carries a recessive X-linked mutation causing disease. The female mouse mates with a healthy male mouse (P) and they produce an offspring of 10 female and 10 male mice (F1). How many of the mice in the F1 generation do you expect to be sick? 1 1 male mouse 5 male mice 5 female mice 10 male mice 10 female mice Which of the following statements is incorrect? Eukaryotic cells can generate mRNA that encodes several polypeptides Prokaryotic cells can generate mRNA that encodes several polypeptides The expression of genes in eukaryotic cells can be regulated by transcription factors Eukaryotic cells can perform alternative splicing Prokaryotic cells can have operons Which of the following statements about prophages is correct? Prophages are composed of DNA Prophages are released from bacterial cells Prophages can infect bacterial cells Prophages are composed of both protein and DNA Prophages attach themselves to the cell wall of bacteria using special binding proteins Which of the following statements is incorrect? (not answered) Antisense RNA can be used to regulate gene expression Antisense RNA has a complementary DNA sequence Expression vectors have an origin of replication DNA can be generated/amplified using synthetic chemistry, enzymes, or cells Reporter genes are seldom used for expression plasmids Epigenetics does NOT involve Methylation of ribosomes Methylation of DNA Acetylation of histones Regulation of gene expression RNA polymerases Which of the following statements is incorrect? Recombinant IgG antibodies can be used as biotherapeutic Most antibody formats can be chemically synthesized scFv antibodies are NOT found naturally in the body Hybridoma technology exploits that antibodies can be affinity matured in vivo Antibodies er particularly relevant for the neutralization of extracellular targets Which of the following methods has the highest chance of success for discovering an antibody that binds to the protein albumin from mice Antibody phage display technology using albumin from mice as the antigen Hybridoma technology using albumin from mice as antigen Chemical synthesis of an antibody library designed to bind albumin from mice Screening of healthy human volunteers that have an antibody repertoire of antibodies that bind to albumin from mice Screening of healthy mouse volunteers that have an antibody repertoire of antibodies that bind to albumin from mice The (supposed) correct answer is in green, my answer is in purple. Some of them are qualified guesses, others I am genuinely confused about. Thanks in advance Edited December 12, 2019 by Chrras formatting went wrong
CharonY Posted December 12, 2019 Posted December 12, 2019 From a quick look I did not see obvious errors in the correct answers, however from your responses I do see that you may have some fundamental misunderstandings on several topics. I think it would be worthwhile for you to discuss the things you are confused about with your fellow students. 1
Dagl1 Posted December 12, 2019 Posted December 12, 2019 Regarding the questions (after Charon's comment I hope i'm not too wrong): 1. More permeable = cis-unsaturated phospholipids (http://bio1510.biology.gatech.edu/module-3-molecules-membranes-and-metabolism/02-membranes/ I presume this is right, didn't look into it mucm) 2. Hypotonic 3. Can't immediately find a source. 4. Don't think either of those answers has something to do with Km but I hope someone can correct me if I am wrong, but Km is just a substrate concentration needed for 1/2 Vmax (catalytic activity), but the Km concentration does not tell us anything about what value Vmax has right? 5. not sure what the first answer here says. but I think the second answer (saturation kinetics) is right? "enzyme-catalysed reactions display saturation kinetics." https://en.wikipedia.org/wiki/Enzyme_kinetics 6. I think 60 but no clue really 7.That question is strange, I suppose it is Photosystem 1 Cytochrome B, but I think the question is bad, as none of those enzymes (as far as I know) have anything to do with the "higher energy levels of photons". ehh I skip the rest. @CharonY Do you not think the question/answers of 4 and 7 are strange? And is the wiki quote I posted at question 5 incorrect or? Maybe I have to brush up my enzyme kinetics;p 1
Chrras Posted December 12, 2019 Author Posted December 12, 2019 (edited) Thanks to both of you. There's no doubt that I must have mixed up some concepts in the heat of the moment, which must be why some of my answers are directly opposite of the correct one. 1: I see that now, doing the course they always described it as "fluidity" not "permeability" so I did not know what that term meant. I can see that I was wrong i 2-3, dunno what I thought about. I am as confused about 4 as you are. 5: I thought that it was saturation kinetics, which wikipedia also says, but apparently not. Can anyone confirm if wikipedia is wrong? 6: I have no clue either, but I guessed 30. According to this reply on Quora, it is 30: https://www.quora.com/How-many-moles-of-ATP-are-produced-from-one-mole-of-glucose, not 60 as the answer says. Oh it's sucrose, I read it as glucose both during the exam and after. No problem then 7: I couldn't find anything about photosystem 1 having to do with "exciting photons to a higher energy level" either. Edited December 12, 2019 by Chrras
CharonY Posted December 12, 2019 Posted December 12, 2019 1 hour ago, Dagl1 said: Do you not think the question/answers of 4 and 7 are strange? And is the wiki quote I posted at question 5 incorrect or? Maybe I have to brush up my enzyme kinetics;p Quote 4. Don't think either of those answers has something to do with Km but I hope someone can correct me if I am wrong, but Km is just a substrate concentration needed for 1/2 Vmax (catalytic activity), but the Km concentration does not tell us anything about what value Vmax has right? This is technically correct. Or conversely one could say that in class the term catalytic activity was used in a very colloquial sense. A better way to phrase it would be using affinity. I.e. low Km indicates high substrate affinity. That being said, looking at the answers one can eliminate every other answer even if it may not be quite accurate (as the rest makes no sense). 5 probably refers to reaction rate at very low substrate concentration. As enzyme is provided in surplus under these conditions, the relationship is roughly linear. 7 is probably phrased badly. Obviously photons are exciting electrons in pigments and not vice versa. But even then, just by elimination one can infer that either PS1 or PS2 are meant (the light harvesting elements of photosynthesis).
Dagl1 Posted December 12, 2019 Posted December 12, 2019 I personally don't feel like a question is valid if you have to find the most right answer among those that are all wrong. 24 minutes ago, CharonY said: 5 probably refers to reaction rate at very low substrate concentration. As enzyme is provided in surplus under these conditions, the relationship is roughly linear. Regarding 5, while that might be the case, the question is: which of these statements is true, and the answer, that catalytic reactions mediated by enzymes follow saturation kinetics, or am I misunderstanding your comment. I think as a student you have a lot of ground to complain and demand proper questions on tests.
CharonY Posted December 12, 2019 Posted December 12, 2019 It depends a bit on how topics are covered in class. Perhaps unfortunately sometimes inaccurate phrasing is used, but on the other hand, if you get the principle it should be possible to deduce the correct answer. I will say that the phrasing in the questions maybe too much on the questionable side for 7 but I am generally also not a big fan only using the exact terms all the time- I found that if students do not get the principles I only need to use an alternative (but valid) phrasing to trip them up too much. Students tend then to memorize mostly which ultimately is to their detriment. Of course a balance has to be found but that is often down to the class itself. Also often definitions are not as clear as one might think. Enzyme activity is sometimes used colloquially to refer to different things but ultimately it is defined in terms of enzyme units (technically, katals) which is a bit out of the scope of pure kinetics. With regard to 5, saturation kinetics generally refers to situation of high levels of substrate (i.e. when the enzyme is saturated). I.e. if you look at the curve it would be the part where the you see the reaction plateauing. So stating that enzyme kinetics generally follows that relationship is obviously wrong (i.e. it only follows once actual saturation is reached). Answer 1 describes a specific regime of the reaction and for that, it is correct (at Km <<S V0=(Vmax/Km).
Chrras Posted December 13, 2019 Author Posted December 13, 2019 Thanks to both of you! 4, 5 and 7 are definitely a bit ambiguous, and I'll try to contact my professor so he can respond to my concerns. Regarding the other questions (8-17) I can definitely see some which I guessed wrongly, but also some that I am still in doubt about, and even some of which where subjects which the class never touched.
BabcockHall Posted December 13, 2019 Posted December 13, 2019 (edited) "Reactions catalysed by enzymes follow saturation kinetics." The way I read this, it means that the Michaelis-Menten/Briggs-Haldane equation is followed. This is often true, but it is clearly false for many regulated enzymes (phosphofructokinase-1, for example), which follow sigmoidal kinetics. With respect to 4 if KM becomes smaller, then V/K becomes larger (keeping Vmax constant). V/K is the apparent second order rate constant for the rate when S << KM. It is also proportional to kcat/KM, one measure of catalytic efficiency. I agree with the answer in the key. Edited December 13, 2019 by BabcockHall
BabcockHall Posted December 14, 2019 Posted December 14, 2019 With respect to Q7, both RUBISCO and hexokinase can be eliminated from consideration because there is no net oxidation or reduction of carbon atoms and no photochemistry. They are clearly not part of photosynthesis. RUBISCO is obviously a key player in the Calvin-Benson cycle.
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now