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All Biochemistry Resources Example Questions Example Question #1 : Amino Acids And Proteins Which of the following chemical elements are involved in a peptide bond? Carbon and nitrogen Nitrogen and hydrogen III. Carbon and oxygen I and II II and III II only I only I only A peptide bond is a covalent bond that connects adjacent amino acid molecules. The bond occurs between a carboxylic acid group on one amino acid and an amino group on the other. Specifically, the carbon atom from the carboxylic acid and the nitrogen atom from the amino group form a peptide bond; therefore, only carbon and nitrogen participate in a peptide bond. Nitrogen and hydrogen make up the amino group (), whereas carbon and oxygen make up the carboxylic acid group (). Remember that an amino acid has a central carbon. The central carbon always has an amino group, a carboxylic acid, and a hydrogen atom. The fourth group is different for each amino acid, which gives them unique properties. Example Question #1 : Amino Acids And Proteins Disrupting disulfide bonds of a polypeptide molecule alters its __________ structure, and disrupting hydrogen bonds alters its __________ structure. secondary . secondary tertiary . tertiary secondary . tertiary tertiary . secondary tertiary . secondary A protein molecule can have four different structural levels. Primary structure consists of the sequence of amino acids making up the polypeptide. Secondary structure consists of the sequence of amino acids and the intermolecular forces and covalent bonds that form between amino acid backbone components. Examples of intermolecular forces in secondary structures include hydrogen bonding, van der Waals forces, and dipole-dipole interactions. Tertiary structure involves covalent bonds, dipole-dipole interactions, and hydrophobic interactions between amino acid R-groups. Tertiary structure is responsible for the 3-dimensional shape of the polypeptide. An example of a covalent bond found in tertiary structure is the disulfide bond. This bond occurs between sulfur molecules in cysteine amino acids; therefore, disrupting the bonds stated in the question will alter the tertiary structure. Quaternary structure occurs when two or more polypeptide chains interact with each other and form bonds. Example Question #1 : Amino Acids And Proteins A researcher denatures a polypeptide. What can you conclude about this denatured polypeptide? It will have beta-pleated sheets, but will not have alpha helices It will have lost its intermolecular forces between nitrogen and hydrogen atoms It will have a reduced number of amino acid residues The hydrophobic side chains will be replaced with hydrophilic side chains It will have lost its intermolecular forces between nitrogen and hydrogen atoms Denaturing a polypeptide is the process of disrupting the secondary, tertiary, and quaternary structures. This means that denaturing a protein will lead to disruption in intermolecular forces such as hydrogen bonds. Recall that hydrogen bonds occur between a hydrogen atom and either a nitrogen, oxygen, or fluorine atom; therefore, denaturing a polypeptide will cause a disruption in the intermolecular forces between nitrogen and hydrogen (hydrogen bonds). Secondary structures can form unique structures called beta-pleated sheets or alpha helices. The beta-pleated sheets are formed when a polypeptide chain folds in such a way that it loops back to lie adjacent to an earlier segment. Alpha helices are formed when a polypeptide chain twists and forms a helical structure. Note that both of these structures involve intermolecular forces (hydrogen bonds, van der Waals, etc.) between amino acids. Denaturing a polypeptide will disrupt both of these structures. Recall that a denatured polypeptide will not lose its peptide bonds; therefore, the polypeptide will have its original number and sequence of amino acids (primary structure). The side chains of amino acids will not change during denaturation. The intermolecular forces and disulfide bonds between adjacent amino acids will change, but the composition of each amino acid won’t change. Example Question #4 : Macromolecule Fundamentals Which of the following polypeptide chains will have an overall negative charge at blood pH? III. II only III only II and III I and II III only To answer this question you need to know the single letter codes for the given amino acids. D-K-A-R-H-F is aspartic acid - lysine - alanine - arginine - histidine - phenylalanine. R-A-A-D-P-P is arginine - alanine - alanine - aspartic acid - phenylalanine - phenylalanine. E-P-H-D-V-W is glutamic acid - phenylalanine - histidine - aspartic acid - valine - tryptophan. To solve this question we need to figure out the overall charges of the three polypeptide chains. Recall that five amino acids are charged under physiological conditions (pH of 7.4). These five amino acids are glutamic acid (E), aspartic acid (D), arginine (R), lysine (K), and histidine (H). Glutamic acid and aspartic acid have an overall charge under physiologic pH. This occurs because their side chains are deprotonated. On the other hand, arginine, lysine, and histidine have a protonated side chain and have a charge. Knowing this information we can solve for the overall net charge on the three polypeptide chains. Polypeptide I: overall net charge of Polypeptide II: overall net charge of Polypeptide III: overall net charge of Example Question #1 : Amino Acids And Proteins Out of the 20 amino acids, how many of them are essential (meaning they cannot be manufactured by the body)? All amino acids are essential The amino acids histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine are considered essential amino acids as they cannot be made by the body. They need to obtained from outside sources/nutrients. Example Question #6 : Macromolecule Fundamentals You want to separate glutamic acid (pI=3.22), leucine, (pI=5.98) and lysine (pI=9.74), by ion exchange chromatography, using resin that contains groups. You deposit these amino acids on a balanced column at pH=2, and then elute the column, increasing the pH progressively up to pH=7. Indicate the elution order of these amino acids: Lys, leu, glu Glu, lys Glu, leu Leu, glu, lys Glu, leu, lys Glu, leu During ion-exchange chromatography, as you increase the pH of the mobile phase (the solution flowing through the column), you elute out proteins based on their isoelectric point (pI). So in this case, you first pass the pI of glutamic acid (Glu), and then that of leucine (Leu). You would never elute out the lysine, because the pI increase stops at 7 and never gets as high as lysine’s pI, 9.74. You have, however, successfully separated the three amino acids from each other, as the lysine remains in the column. Example Question #1 : Amino Acids And Proteins Sample A absorbs light at , and Sample B absorbs light at . Of the choices below, which macromolecules are likely to be present in each sample, respectively? Protein and nucleic acid Nucleic acid and protein Carbohydrate and nucleic acid Protein and protein Nucleic acid and carbohydrate Nucleic acid and protein Nucleic acids absorbs light at . The aromatic amino acids phenylalanine, tyrosine, and tryptophan absorb light at . Example Question #1 : Macromolecule Fundamentals Which of the following properties of amino acids are incorrect? All of these are true 18 of the 19 amino acids are in the R configuration, while cysteine is the only amino acid in the S configuration. Threonine and isoleucine are the only two amino acids with a 2nd chiral carbon The natural amino acids generally occur as L-enantiomers Arginine is the amino acid with the highest value 18 of the 19 amino acids are in the R configuration, while cysteine is the only amino acid in the S configuration. The opposite of the false statement is true: 18 of the 19 amino acids are in the S configuration, while cysteine is the only amino acid in the R configuration. Example Question #1 : Amino Acids And Proteins Protein I has a molecular weight of and a pI of 6.5, protein II has a molecular weight of and a pI of 8.0, and protein III has a molecular weight of and a pI of 10.5. If a sample containing proteins I, II, and III is run through a DEAE ion exchange column at pH 7.5, and the column is eluted with a gradient, what is the order of elution? I, III, II III, II, I I, II, III III, then II and I simultaneously I, then II and III simultaneously III, II, I Diethylaminoethyl (DEAE) cellulose is a positive weak ion exchanger. Any molecules with a positive charge will elute through the column first, whereas molecules with a negative charge will adhere to the DEAE column and elute after the salt wash. Since protein III has a pI greater than the pH of the column, it has a positive charge and elutes first. Protein II elutes second because its pI is less than the pH but close in value. Therefore protein II contains less of a negative charge than protein I. Example Question #1 : Amino Acids And Proteins Which of the following contributes most to a protein's secondary and tertiary structure, respectively? Hydrogen bonding, disulfide bonding Hydrogen bonding, hydrophobic interactions Covalent bonding, hydrogen bonding Disulfide bonding, hydrophobic interactions Peptide bonding, hydrogen bonding Hydrogen bonding, hydrophobic interactions Hydrogen bonding stabilizes secondary structure to form alpha helices and beta sheets. Hydrophobic interactions between nonpolar side groups dictate a protein's tertiary structure. Disulfide bonds are involved in the determination of a protein's tertiary and quaternary structures, but they are not the primary contributors. Certified Tutor Certified Tutor Certified Tutor
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Aminokiseline Aminokiseline su dio građe tijela koji pomaže proizvodnji određenih proteina za potrebe njegova održavanja i funkcioniranja. Zadužene su za proizvodnju energije, pomažu kod gubitka suvišnih kilograma, izgradnji mišićnog tkiva, raspoloženju i cjelokupnim funkcijama mozga. Razlikujemo esencijalne i neesencijalne aminokiseline. Esencijalne aminokiseline tijelo ne može samostalno proizvesti. Jedini način da se takve kiseline dobiju jest kroz prehranu (koja mora biti raznovrsna) ili pak korištenjem nadomjestaka prehrani. One pomažu oporavku vitalnih organa, mišićnog tkiva, žlijezdama, ligamentima, tetivama, koži, noktima i kosi. Također imaju važnu ulogu i kod stvaranja antitijela koja se bore protiv virusa i bakterija, dovode kisik u tijelo i pomažu kod mišićne aktivnosti. Devet esencijalnih aminokiselina su: arginin, histidin, leucin, izoleucin, lizin, metionin, fenilalanin, treonin, triptofan i valin. Valin, leucin i izoleucin su tri aminokiseline koje zajedno čine grupu zvanu BCAA tj. granu lančano povezanih aminokiselina. One se od drugih aminokiselina razlikuju prema svojem jedinstvenom kemijskom sastavu. Prema zadnjim istraživanjima pokazalo se da BCAA grupa aminokiselina ima antikatabolička svojstva (prevencija mišićnog sloma) te potpomažu razvoju mišićne mase. BCAA također poboljšavaju vezanje proteina, očuvanje dušika, oporavak mišića, smanjenje zamora mišića, pomažu kod rasta mišićne mase te kod prevencije očuvanja vezivnog tkiva. Neesencijalne aminokiseline tijelo može proizvesti. No, to ne znači da je to dostatna količina kako bi tijelo održavalo homeostazu, posebno za vrijeme bolesti ili stresa. Tijekom tog vremena potrebno je uzimati nadomjestke. Treba naglasiti da se neesencijalne aminokiseline stvaraju tijekom kemijske transformacije jedne ili više esencijalnih aminokiselina. Postoji 11 nesencijalnih aminokiselina a to su; prolin, serin, glicin, tirozin, glutaminska kiselina, asparginska kiselina, glutamin, alanin, arginin, asparagin i cistein. Osim ovih aminokiselina postoje neesencijalne koje tijelo može samostalno proizvesti ali one nisu dio proteina. Ovdje pripadaju citrulin, glutation, hidrokisprolin, ornitin i taurin i spadaju pod neproteinogenske aminokiseline. Kada uzimate aminokiseline trebate pripaziti da prije imena bude slovo “L” kao npr. L-glutamin, L-arginin… Aminokiseline iz organizma pripadaju skupini alfa, što bi značilo da imaju dušik na prvom ugljikovom atomu u molekuli. Dušikov atom ima na sebe prikvačen vodikov atom čime tvori amino skupinu. Od tuda dolazi naziv “amino”. Uz nju, aminokiseline sadrže i karboksilnu grupu, tu pripadaju masne kiseline. Karboksilna skupina je osnova karboksilne kiseline i iz toga je izveden naziv ‘kiseline’ . Karboksilna skupina je također vezana za alfa (prvi) ugljikov atom. Sastoji se od atoma ugljika, dva atoma kisika i atoma vodika. Amino i karboksilna grupa vezane su sa prvim ugljikovim atomom te daju molekuli asimetričnost koja zakreće polariziranu svjetlost. Naše tijelo može pravilno iskoristiti samo aminokiseline koje rotiraju svjetlost na lijevu stranu. Takve aminokiseline imaju slovo L ispred imena. Izuzetak su taurin, GABA i glicin te fenilalanin. Postoji preko 300 aminokiselina, neke su vrlo rijetke i proizvode se najčešće u laboratorijima. Nije potrebno istraživati sve aminokiseline. Dovoljno je znati nešto više o prethodno navedenima. Prije nego krenete s uzimanjem aminokiselina savjetujte se sa svojim liječnikom, pogotovo ako patite od kroničnih bolesti. Ema Barišić PREGLEDAJTE I PREUZMITE KATALOG S NAŠOM KOMPLETNOM PONUDOM! - Ljeto u Blue Gymu 2021.! - 28. svibnja 2021 - Otvaramo fitness centre Belveder i Kantrida od 3. svibnja 2021. - 2. svibnja 2021 - Privremeno zatvaranje fitnessa od 29.3. do 12.4.2021.