NHM 361 Exam 2 Study Guide
NHM 361 Exam 2 Study Guide NHM 361
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This 7 page Study Guide was uploaded by Vanessa Notetaker on Monday October 3, 2016. The Study Guide belongs to NHM 361 at University of Alabama - Tuscaloosa taught by Amy Cameron Ellis in Fall 2016. Since its upload, it has received 40 views. For similar materials see Nutritional Biochemistry in Nutrition and Food Sciences at University of Alabama - Tuscaloosa.
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Date Created: 10/03/16
NHM 361 Fall 2016 Study Guide – Exam 2 Enzymes (ch. 10) 1. Why are enzymes important? Be familiar with the structure and function of enzymes. Enzymes are the biomolecules that catalyze reactions. Enzymes are proteins and are not destroyed after they catalyze a reaction but, because they are proteins they can easily be denatured by things like inadequate temperature or pH. Enzymes function by lowering the activation energy of a reaction, they do not make a reaction that wouldn’t normal happen, happen they simply speed up reactions. 2. Define the following classes of enzymes: a. Kinases- enzymes that catalyze the transfer of a phosphate group from a high energy donor (like ATP) to a substrate b. Phosphatases- enzymes that catalyze the removal of an inorganic phosphate group (dephosphorylate) 3. What is a “cofactor”? What is a cofactor called when it is an organic molecule? A cofactor is a specific molecule or metal ion that binds to an enzyme to render it functional. Without the cofactor the enzyme cannot catalyze the necessary reaction. When a cofactor is an organic substance it is called a coenzyme. 4. Define the following terms: a. Absolute specificity-when an enzyme only acts on ONE substrate to produce products b. Relative specificity- when an enzyme acts on multiple substrates that are structurally similar to produce products c. Apoenzyme- the protein part of the enzyme that is separable from its cofactor d. Holoenzyme- the complete enzyme-cofactor complex e. Active site- specific region on an enzyme where a substrate binds f. Competitive enzyme inhibition- an inhibitor that competes with substrate for binding at an active site. The substrate and competitive inhibitor are similar structurally g. Noncompetitive enzyme inhibition- an inhibitor binds to an enzyme somewhere that IS NOT the active site and this binding changes the active site so that the substrate can no longer bind to it. h. Feedback inhibition- according to how much product is made is whether or not production is tapered off. When you bring conditions back to homeostasis production is inhibited. i. Allosteric enzyme regulation (Note, allosteric regulation may upregulate or downregulate enzyme activity.)- when substances bind to enzymes at locations other than the active site to upregulate or downregulate activity 5. Contrast the “lock-and-key” theory of enzyme-substrate binding with the “induced-fit” theory. NHM 361 Fall 2016 Study Guide – Exam 2 The lock and key theory proposes that the active site of an enzyme is the rigid lock that can only work for a specifically shaped substrate or key. The new induced fit theory states that enzymes are not as rigid as the lock and key model suggests and that the active site of an enzyme can be partially flexible and that the conformation of the enzyme changes to accommodate substrate binding., 6. How would changing each of the following factors impact enzyme activity/reaction rates? a. Enzyme concentration- the higher the amount of enzyme the higher the reaction rate b. Substrate concentration- the higher amount of substrate the higher the reaction rate until the enzymes become so saturated with substrate that they cannot proceed any faster c. Temperature-enzymes have a temperature that they work best at called the optimal temperature and the further from the optimal temperature (higher or lower) the less the rate of reaction. d. pH- enzymes also have an optimal pH value where enzyme activity is the highest and the more you deviate from the optimum pH the less the rate of reaction 7. What is a zymogen? A zymogen is an inactive precursor of an enzyme. Also called a proenzyme. Nucleic acids (ch. 11) 1. Know the importance of protein synthesis and the “central dogma” of biology: DNA RNA Protein Protein synthesis is important because it allows the creation of amino acid chains from nucleic acids in the nucleus. After DNA replication, DNA is transformed into RNA through transcription and RNA makes a protein through translation. 2. What is a nucleotide? Know this structure well. A nucleotide is a monomer of nucleic acids. It is made of a heterocyclic base (nitrogenous base), a sugar (ribose or deoxyribose) and a phosphate 3. What are purines and pyrimidines? What is meant by “complementary base pairing”? Purines are nucleotide bases that are classified together because they have a double ring structure. They include adenine and guanine. Pyrimidines are nucleotide bases that only have a single ring structure and include uracil, thymine and cytosine. 4. Describe the similarities and differences between RNA and DNA molecules. RNA and DNA both have a nucleotide base, sugar and phosphate but, they differ in their sugars. RNA has ribose as its sugar and DNA has deoxyribose as its sugar. NHM 361 Fall 2016 Study Guide – Exam 2 5. Where does DNA exist in cells? DNA is in the nucleus of all human cells. 6. Define the following: a. Chromatin- DNA and histones. Form that DNA takes in the cell when division is not occurring b. Chromosomes- condensed chromatin that only exists during cell division. DNA is more tightly coiled around the histones than in chromatin c. Gene- sequence of nucleotides on a DNA molecule that determine the sequence of a polypeptide chain d. Genome- total collection of genes that specify an organism’s structure and function 7. Describe the major steps in DNA replication including the key enzymes discussed in class. In DNA replication the process begins when the enzyme helicase catalyzes the unwinding of the double helix. The process is semi conservative because the original strand of DNA is used as a template. To create the new strand of DNA and create a new double helix, DNA polymerase synthesizes the new DNA with the DNA template. The leading strand is synthesized continuously but, the lagging strand is synthesized in fragments because DNA can only be synthesized in the 5’ to 3’ direction. The lagging strand therefore has Okazaki fragments that are then covalently joined by an enzyme called DNA ligase. 8. Review the major steps in transcription. Know how the genetic message of DNA is copied to an mRNA molecule in the nucleus. Transcription is the creation of mRNA from DNA. RNA nucleotides pair with DNA nucleotides on the coding strand until a termination sequence is reached. The pre-mRNA molecule undergoes processing to remove non-coding intron sequences. The mRNA molecule then leaves the nucleus to bind to a ribosome in the cytoplasm. 9. Know the role of RNA polymerase enzymes in transcription. RNA polymerase assists in the rewinding of DNA after transcription 10.What is meant by the genetic code (i.e. codons)? The nucleotide triplets of DNA that carry genetic information in living human cells. 11.Contrast exons and introns. Exons are the coding sequences of DNA and introns are the noncoding portion of DNA that are spliced out in transcription 12.Review the major steps of translation at ribosomes in the cytoplasm. Know the basic structure of transfer RNA (tRNA), and how tRNA translates the code of mRNA nucleotides into the language of amino acids. 1. mRNA binds to ribosome by base pairing with rRNA 2. Anticodon of tRNA molecules bind with the codon on mRNA and deposit the corresponding amino acids NHM 361 Fall 2016 Study Guide – Exam 2 3. Peptide bonds form between amino acids of the new polypeptide chain 4. After synthesis, the new polypeptide chain may undergo post-translational modification tRNA contains a site for amino acid attachment and an anticodon site where mRNA attaches. tRNA translates the code of mRNA nucleotides into amino acids by translating one codon at a time and creating a chain of peptides with each anti-codon brought to the ribosome 13.Be aware that after proteins are synthesized, they may undergo “post- translational modification” in order to become functional proteins. Some may fold and coil in specific shapes. Others may be chemically modified by adding a phosphate group, sugar group, etc. to an amino acid. 14.What is a mutation, and how could a genetic mutation feasibly result in a dysfunctional protein? A mutation is a permanent change resulting from an incorrect sequence of bases on DNA. A mutation can lead to a dysfunctional protein because if one nucleotide is incorrect it can lead to the creation of a termination segment and cut the protein short, this is called a nonsense mutation. If one nucleotide is wrong it can also lead to the creation of an incorrect amino acid and a malfunctioning protein known as a missense mutation. Also the deletion of a single nucleotide may occur causing the whole nucleotide sequence to be shifted and have all the following codons code for entirely different proteins, this is called a deletion mutation. Digestion/Absorption (supplemental reading on Blackboard or ch. 1 of Krause) 1. Describe the mechanical and chemical digestion that takes place in the mouth. In the mouth, mechanical digestion occurs as a result of chewing the food and breaking it down. Chemical digestion occurs due to the enzymes ptyalin or salivary amylase that breaks down starch and lingual lipase that breaks down fat. 2. Name the enzyme that begins protein digestion in the stomach. Which cells secrete this enzyme? This enzyme is secreted as a zymogen; what is the zymogen, and how is it activated? Protein digestion in the stomach begins with pepsin. Pepsin is secreted as a zymogen by the chief cells of the stomach and is activated by HCl. A zymogen is an inactive form of an enzyme. 3. Identify the secretions of parietal cells in the stomach. What is the function of each of these secretions? Hydrochloric acid is secreted to denature proteins. Intrinsic factor is secreted and assists with vitamin B-12 absorption in small intestine. 4. What is chyme? NHM 361 Fall 2016 Study Guide – Exam 2 Chyme is the mixture of food, hydrochloric acid, gastrin, intrinsic factor, pepsin and gastric lipase. 5. What is the rhythmic muscle contraction that propels food through the GI tract? Peristalsis 6. What are the roles of the liver, gallbladder, and pancreas in digestion? The liver is where glycogen can be stored and is also the site of bile production. The gallbladder is where bile is stored for secretion into the small intestine. Bile is an emulsifier of fat that aids in fat digestion. The pancreas creates digestive enzymes such as amylase, lipase, protease, nucleases and insulin and glucagon. These enzymes break down fat, protein and nucleic acids. Insulin and glucagon regulate blood sugar. 7. Identify the source and function of each of the following hormones in digestion: a. Gastrin-Released from the stomach mucosa and stimulates parietal cells in the stomach to release hydrochloric acid that allows proteins to be denatured b. Secretin- an intestinal hormone secreted in response to acid in the duodenum that signals the pancreas to release bicarbonate rich fluid through pancreatic duct c. Cholecystokinin- an intestinal hormone that signals the gallbladder to release bile and also signals the pancreas to release a variety of hydrolytic digestive enzymes 8. Name the biomolecule that each of the following pancreatic enzymes acts on: a. Amylase- starch b. Lipase- fat c. Trypsin- protein d. Chymotrypsin- protein e. Carboxypeptidase- protein 9. Explain how pancreatic proteases are secreted as zymogens. How are these enzymes activated in the small intestine? Trypsin and chymotrypsin are secreted from the pancreas as inactive precursors/zymogens. Enterokinase activates the zymogen trypsinogen to trypsin and then, trypsin activates chymotrypsinogen to chymotrypsin 10.Compare and contrast carbohydrate, protein, and fat digestion in terms of where each occurs and the end products of digestion. Carbohydrate digestion begins in the mouth and usually ends in the small intestine unless it is insoluble and is broken down in the large intestine. The end products are monosaccharides. Protein digestion begins in the stomach and ends in the small intestine. The end products are amino acids, dipeptides and tripeptides. Lipid digestion begins in the mouth with lingual lipase and ends in the small intestine. The end products are monoglycerides, glycerol and free fatty acids. 11.Describe the absorption of each of these nutrients into lacteals or capillaries. NHM 361 Fall 2016 Study Guide – Exam 2 Lipids are absorbed in the brush border of the small intestine and enter epithelial cells. Once they enter they reform into triglycerides and are packaged in chylomicrons and are absorbed into lacteals to enter lymphatic circulation. The end products of carbohydrate digestion are maltase, sucrose and lactase and they are absorbed across the intestinal epithelium into capillaries which empty into the hepatic portal vein to the liver Peptidases in the brush border complete protein digestion so that amino acids, dipeptides and tripeptides are absorbed and then enter the hepatic portal vein to the liver. 12.What is the role of bile in fat digestion? Bile emulsifies fat. Emulsification is the breaking down of large fat globules into smaller fat molecules 13.Define the following: emulsification, micelle, chylomicron Emulsification is the breaking down of large fat globules into smaller fat molecules. Micelle is the formation that occurs from bile salts, monoglycerides and free fatty acids. The hydrophillic portions of the fatty acids form a circle and all point outward with their hydrophobic tails on the inside. The inner portion of the micelle is where the monoglyceride remains since it would not mix in water. Chylomicron is a particle that packages triglycerides, cholesterol, fat soluble viatmins and phospholipids for transport. 14.In what region of the small intestine does most absorption take place? Jejunum 15.Define the following: villus/villi, microvilli Villi are the fingerlike projections of the small intestinal mucosa, one villus is supplied by one capillary bed and one lacteal. Microvilli are tiny projections of the plasma membrane that form the brush border of the small intestine. 16.What are “brush border” enzymes? Brush border enzymes are enzymes in the brush border of the small intestine that finish the digestion of macromolecules like peptidases that finish protein digestion. 17.What are “normal flora”? Where are they found, and why are they beneficial? Normal flora are the hundreds of species of bacteria that colonize the colon. They are beneficial because they ferment fiber and resistant starch to form short chain fatty acids and gas and they also synthesize Vitamin K and some B vitamins. th th Metabolism and Energy (pages 345-356 in 7 ed. or pages 371-384 in 8 ed.) 1. What is a metabolic pathway? A metabolic pathway is a sequence of consecutive chemical reactions that convert a starting material into a product NHM 361 Fall 2016 Study Guide – Exam 2 2. Contrast anabolism and catabolism. Which is endergonic, and which is exergonic? Anabolism is the series of reactions involved in the synthesis of biomolecules and is endergonic or requires energy. Catabolism is the reactions involved in the breakdown of biomolecules and is exergonic, or releases energy. 3. Describe the “common catabolic pathway.” The common catabolic pathway is the point of intersection between the metabolic pathways of proteins, carbohydrates and lipids and begins with acetyl coA. 4. Contrast the energy yielded from the oxidation of glucose vs. fatty acids. Oxidation of 1 g of triglyceride to CO2 generates about six times as much ATP as does the oxidation of 1 g of hydrated glycogen, the polymeric storage form of glucose in animals. 5. Describe the structure and function of ATP. ATP is made of adenine, 3 phosphate groups and ribose. It functions as a high energy carrier. 6. Where is most ATP produced in the cell? Most ATP is produced in the matrix of the mitochondria. 7. Define each of the following, and identify the vitamin that serves as a precursor for each: a. Coenzyme A- Product of glucose, amino acids and fatty acids and is derived from pantothenic acid (Vitamin B5) b. Nicotinamide adenine dinucleotide- (NAD+) carrier of electrons and hydrogen ions that is an oxidizing agent in many metabolic pathways and is derived from niacin (Vitamin B3) c. Flavin adenine dinucleotide- (FAD) major electron carrier in the oxidation of fuel molecules that is derived from riboflavin (Vitamin B2) 8. Define the following: a. Energy balance- when a person’s intake of energy from food equals energy expenditure b. Positive energy balance- when intake is greater than expenditure c. Negative energy balance- when intake is less than expenditure 9. What is REE, and how is REE assessed clinically? REE is the resting energy expenditure and is assessed clinically by using indirect calorimetry and the Weir equation. The Weir equation uses carbon dioxide production and oxygen consumption. 10.What is RQ? RQ is the respiratory quotient. RQ is the ratio of carbon dioxide produced to oxygen consumed.
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