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BIOCHEM FINALS
Protein Metabolism
| Question | Answer |
|---|---|
| pH in small intestine is | 7.0 -8.0 |
| WHAT DOES THE pH DO IN THE SMALL INTESTINE? | helps neutralize the acidified gastric content |
| WHAT DOES Trypsin, chymotrypsin and carboxypeptidase DO? | in pancreatic juice released into the small intestine help hydrolyze proteins to smaller peptides |
| Aminopeptidase | secreted by intestinal mucosal membrane further hydrolyze the small peptides to amino acids |
| active transport process | Amino acids (aa) liberated are transported into blood stream via _______. |
| proteolytic enzymes | Pepsin, trypsin, chymotrypsin, carboxypeptidase, and aminopeptidase |
| net result of protein digestion | the release of the protein’s constituent amino acids |
| Amino acid pool | the total supply of free amino acids available for use in the human body |
| Dietary protein | one of three sources that contributes amino acids to the amino acid pool |
| Protein turnover | A repetitive process in which the body proteins are degraded and resynthesized |
| Biosynthesis of amino acids in the liver | only non-essential amino acids are synthesized |
| NITROGEN BALANCE | The state that results when the amount of nitrogen taken into the human body as protein equals the amount of nitrogen excreted from the body in waste materials. |
| Negative nitrogen imbalance | > Protein degradation exceeds protein synthesis > Amount of N in urine exceeds nitrogen consumed |
| tissue wasting | tissue proteins are being catabolized than are being replaced by protein synthesis. |
| Positive nitrogen imbalance | > Rate of protein synthesis (anabolism) is more than protein degradation (catabolism) > Results in large amounts of tissue synthesis |
| protein synthesis | anabolism |
| protein degradation | catabolism |
| Protein synthesis | > About 75% of amino acids go into ____ that is needed continuous replacement of old tissues (protein turnover) and to build new tissues (growth). |
| Synthesis of non-protein nitrogen-containing compounds | > Synthesis of purines and pyrimidines for nucleic acid syntheis > Synthesis of heme for hemoglobin, neutrotransmitters and hormones |
| Synthesis of non-protein nitrogen-containing compounds | > Amino acids are regularly withdrawn from the amino acid pool for the synthesis of nonprotein nitrogen-containing compounds |
| Synthesis of nonessential amino acids | can’t be synthesized because of the lack of appropriate carbon chain |
| Production of energy | > Amino acids are not stored in the body, so the excess is degraded > The degradation process is complex because each of the 20 standard amino acids has a different degradation pathway |
| DEGRADATION PATHWAYS | > The amino nitrogen atom is removed and converted to ammonium ion, which ultimately is excreted from the body as urea. |
| DEGRADATION PATHWAYS | > The remaining carbon skeleton is then converted to pyruvate, acetyl CoA, or a citric acid cycle intermediate, depending on its makeup, with the resulting energy production or energy storage. |
| Degradation of an amino acid takes place in two stages | > The removal of the -amino group and > The degradation of the remaining carbon skeleton |
| Transamination | > Involves transfer of the amino group of an -amino acid to an alpha keto acid > enzyme catalyzed reactions > Biochemical process in which the amino group of an alpha-amino acid is transferred to an alpha-keto acid |
| Initial effect of Transamination | > Collect the amino groups from a variety of amino acids into just two amino acids—glutamate (most cells) and alanine (muscle cells) >To regenerate pyruvate and oxaloacetate for use in further transamination reactions |
| amino acids—glutamate | most cells |
| alanine | muscle cells |
| Net effect of transamination | Collection of the amino groups from a variety of amino acids into a single compound—the amino acid glutamate |
| Oxidative deamination reaction | > Ammonium ion (NH4+) group is liberated from the glutamate amino acid formed from transamination > Occurs in liver and kidney |
| Oxidative deamination reaction | > is a biochemical reaction catalyzed by glutamate dehydrogenase in which glutamate is converted into alpha-keto glutarate with the release of an ammonium ion |
| UREA CYCLE | > is the series of biochemical reactions in which urea is produced from ammonium ions and carbon dioxide > transported via the blood from liver to the kidneys and eliminated from 98989the body via urine. |
| Urea | > white solid > melting point 133C > very soluble in water > odorless and colorless and has a salty taste |
| CARBAMOYL PHOSPHATE | > The fuel for the urea cycle > Two ATP molecules are expended in the formation of one carbamoyl phosphate molecule |
| CARBAMOYL PHOSPHATE | > A high energy phosphate bond is present in carbamoyl phosphate > It takes place in mitochondrial matrix |
| Stage 1 | Carbomyl group transfer |
| Carbomyl group transfer | transferred to ornithine to form citrulline in a reaction catalyzed by ornithine transcarbamoylase. |
| Carbomyl group transfer | The breaking of the high-energy phosphate bond in it drives the transfer process |
| Carbomyl group transfer | the first of the two nitrogen atoms and the carbon atom needed for the formation of urea have been introduced into the cycle |
| Stage 2 | Citrulline-aspartate condensation |
| Citrulline-aspartate condensation | transported into the cytosol, and reacts with aspartate to produce argininosuccinate utilizing ATP |
| Citrulline-aspartate condensation | In this reaction the second of two nitrogen atoms of urea is introduced into the cycle (One nitrogen comes from carbamoyl phosphate and the other from |
| Citrulline-aspartate condensation | This condensation, catalyzed by argininosuccinate synthase, is driven by the expenditure of ATP |
| Stage 3 | Argininosuccinate cleavage: |
| Argininosuccinate cleavage: | cleaved to arginine and fumarate by the enzyme argininosuccinate lyase |
| Argininosuccinate cleavage: | catalyzes the cleavage of argininosuccinate into arginine, a standard amino acid, and fumarate, a citric acid cycle intermediate. |
| Stage 4 | Hydrolysis of urea from arginine |
| Hydrolysis of urea from arginine | produces urea and regenerates ornithine - one of the cycle’s starting materials |
| Hydrolysis of urea from arginine | > The oxygen atom present in the urea comes from water > Orthinine is transported back to mitochondria to be used in the urea cycle |
| UREA CYCLE NET REACTION | > Total of four ATP molecules is expended in the production of one urea cycle molecule |
| UREA CYCLE NET REACTION | > Two molecules are consumed in the production of carbamoyl phosphate and the equivalent of two ATP molecule is consumed in step 2 of the urea cycle to give AMP (Adenosine Monophosphate) and two Pi (Inorganic Phosphate) |
| AMINO ACID CARBON SKELETONS | > The removal of the amino group of an amino acid by transamination/oxidative deamination produces an a-keto acid that contains the carbon skeleton from the amino acid |
| 7 degraded products | pyruvate, acetyl CoA, acetoacetyl CoA, alphaketoglutarate, succinyl CoA, fumarate, and oxaloacetate |
| Glucogenic amino acid | An amino acid that has a carbon- containing degradation product that can be used to produce glucose via gluconeogenesis. |
| Ketogenic amino acid | - An amino acid that has a carbon- containing degradation product that can be used to produce ketone bodies |
| AMINO ACID BIOSYNTHESIS | > Diet with lack of high quality proteins results in breakage of body proteins > Excess amino acids are converted to fat and stored |
| Non essential amino acids are synthesized in | 1-3 steps |
| Essential amino acids are synthesized in | 7-10 steps |
| HEMOGLOBIN CATABOLISM | > Red blood cells (RBCs) are highly specialized cells whose primary function is to deliver oxygen to cells and remove carbon dioxide from body tissues |
| The life span of a red blood cell is about | 4 months |
| Protein portion is | globin |
| Prosthetic group is | heme |
| Heme | contains four pyrrole groups joined together with an iron atom in the center |
| Degradation of hemoglobin | - Globin protein part is converted to amino acids and are put in amino acid pool - Fe atom becomes part of ferritin — an iron storage protein — saves the iron for use in biosynthesis of new hemoglobin molecules |
| BILE PIGMENTS | > The tetrapyrrole degradation products obtained from heme are known as bile pigments because they are secreted with the bile, and most of them are highly colored. |
| Biliverdin | green in color |
| Bilirubin | reddish orange in color |
| Stercobilin | brownish in color (gives feces their characteristic brown color) |
| Urobilin | yellow in color and present in urine (gives characteristic yellow color to urine). |
| Daily normal excretion of bile pigments | 1–2 mg in urine and 250–350 mg in feces. |
| Jaundice | Results from liver, spleen and gallbladder malfunction > gives the skin and white of the eye yellow tint. |
| INTERREALATIONSHIP AMONG METABOLIC PATHWAYS | > The metabolic pathways of carbohydrates, lipids, and proteins are integrally linked to one another. > A change in one pathway can affect many other pathways. |
| Feasting (over eating) | Causes the body to store a limited amount as glycogen and the rest as fat |
| Fasting (no food ingestion): | The body uses its stored glycogen and fat for energy. |
| Starvation (not eating for a prolonged period) | - Glycogen stores are depleted, - Body protein is broken down to amino acids to synthesize glucose. - Fats are converted to ketone bodies. |
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