Biochemistry Quiz: Enzymes and Metabolism
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Questions and Answers

What is the primary function of the enzyme rubisco in the Calvin cycle?

  • Converts acetyl-CoA in the Krebs cycle
  • Catalyzes the conversion of CO2 and RuBP (correct)
  • Reduces 3-PGA to G3P
  • Generates ATP during glycolysis

    • Glycolysis occurs in the mitochondria and requires oxygen.

    False

    What are the end products of glycolysis?

    Pyruvate and ATP

    What deficiency can lead to megaloblastic anemia and neurological damage?

    <p>Vitamin B12</p> Signup and view all the answers

    Vitamin C is stable and maintains its nutritional content when cooked.

    <p>False</p> Signup and view all the answers

    The conversion of glucose into pyruvate occurs during _____

    <p>glycolysis</p> Signup and view all the answers

    Match the metabolic pathways with their primary products:

    <p>Glycolysis = Pyruvate Calvin Cycle = G3P Krebs Cycle = ATP and CO2 Biosynthesis = Secondary metabolites</p> Signup and view all the answers

    Name two dietary sources of Vitamin C.

    <p>Citrus fruits and strawberries</p> Signup and view all the answers

    What is the primary outcome of the cyclization of farnesyl pyrophosphate?

    <p>Cholesterols</p> Signup and view all the answers

    Vitamin C plays a crucial role in the synthesis of ______.

    <p>collagen</p> Signup and view all the answers

    Which molecule is primarily recycled to regenerate RuBP in the Calvin cycle?

    <p>G3P</p> Signup and view all the answers

    Vitamins can be synthesized in the body.

    <p>False</p> Signup and view all the answers

    The Krebs cycle can occur under anaerobic conditions.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a function of Vitamin C?

    <p>Oxygen transport</p> Signup and view all the answers

    What is the significance of acetyl-CoA in the Krebs cycle?

    <p>It is the starting substrate for the Krebs cycle.</p> Signup and view all the answers

    The oxidized form of Vitamin C is known as dehydro-L-ascorbic acid.

    <p>True</p> Signup and view all the answers

    Name two fat-soluble vitamins.

    <p>A and D</p> Signup and view all the answers

    The overall reaction of glucose in the presence of ADP results in the production of _____ ATP molecules.

    <p>38</p> Signup and view all the answers

    What is the primary consequence of Vitamin B12 deficiency?

    <p>Neurological damage</p> Signup and view all the answers

    Vitamins A, D, E, and K are classified as __________ vitamins.

    <p>fat-soluble</p> Signup and view all the answers

    Match the following vitamins with their classification:

    <p>Vitamin C = Water-soluble Vitamin A = Fat-soluble Vitamin K = Fat-soluble Vitamin B12 = Water-soluble</p> Signup and view all the answers

    Match the functions of Vitamin C to their descriptions:

    <p>Antioxidant activity = Reduces oxidative stress Collagen synthesis = Supports skin and tissue health Defense against infections = Enhances immune function Iron absorption = Improves iron uptake in the body</p> Signup and view all the answers

    Which deficiency state is associated with a lack of vitamin C?

    <p>Scurvy</p> Signup and view all the answers

    Water-soluble vitamins can be stored significantly in the body.

    <p>False</p> Signup and view all the answers

    What term was derived from the initial isolation of a vital amine from rice bran?

    <p>Vitamin</p> Signup and view all the answers

    Which of the following statements about glycosides is true?

    <p>The aglycon part of glycosides is soluble in non-polar solvents.</p> Signup and view all the answers

    Glycosides are unstable towards alkalis.

    <p>False</p> Signup and view all the answers

    What color are most glycosides, except for flavonoids and anthraquinones?

    <p>Colorless</p> Signup and view all the answers

    Emulsin is an enzyme that hydrolyzes most ___________ linkages.

    <p>β-glycoside</p> Signup and view all the answers

    Match the glycoside with its corresponding effect or usage:

    <p>Digitalis = Cardiac glycoside Senna = Laxative agent Black mustard = Releases allyl isothiocyanate Saponin = Has antiseptic properties</p> Signup and view all the answers

    Which of the following functions do glycosides NOT serve?

    <p>Source of energy</p> Signup and view all the answers

    Name one therapeutic class that glycosides contribute to.

    <p>Cardiac medications</p> Signup and view all the answers

    Most glycosides have a sweet taste.

    <p>False</p> Signup and view all the answers

    What is the nomenclature for a cardioactive glycoside that has one double bond?

    <p>Cardenolide</p> Signup and view all the answers

    Cardanolides are glycosides that contain two double bonds.

    <p>False</p> Signup and view all the answers

    Which plant is the source of the drug Digitalis?

    <p>Digitalis purpurea</p> Signup and view all the answers

    Bufadienolides are derived from a condensation of a C21 steroid and a ______ unit.

    <p>C3</p> Signup and view all the answers

    Match the following glycosides with their corresponding aglycones:

    <p>Lanatoside A = Digitoxigenin Digoxin = Digoxigenin Gitaloxin = Gitoxigenin Digitoxin = Digitoxigenin</p> Signup and view all the answers

    What is the average concentration of glycosides in Digitalis purpurea?

    <p>0.16%</p> Signup and view all the answers

    Digoxin is derived from both Digitalis purpurea and Digitalis lanata.

    <p>False</p> Signup and view all the answers

    What are the names of the three important glycosides derived from Digitalis purpurea?

    <p>Digitoxin, gitoxin, gitaloxin</p> Signup and view all the answers

    Which of the following is an example of a primary metabolite?

    <p>Citric acid</p> Signup and view all the answers

    Secondary metabolites are typically produced during the early growth phase of an organism.

    <p>False</p> Signup and view all the answers

    What role do secondary metabolites play in ecological functions?

    <p>Defense mechanisms, such as serving as antibiotics and producing pigments.</p> Signup and view all the answers

    The primary metabolite commonly isolated from Corynebacteria glutamicum is __________.

    <p>L-glutamate</p> Signup and view all the answers

    Match the following metabolites with their respective categories:

    <p>Atropine = Secondary metabolite Ethanol = Primary metabolite Lactic acid = Primary metabolite Erythromycin = Secondary metabolite</p> Signup and view all the answers

    Which of the following is an application of citric acid in industries?

    <p>Used in pharmaceuticals</p> Signup and view all the answers

    What is the role of atropine in clinical treatments?

    <p>Atropine acts as a competitive antagonist for acetylcholine receptors.</p> Signup and view all the answers

    Primary metabolites are not essential for the growth of an organism.

    <p>False</p> Signup and view all the answers

    Which of the following is NOT a dietary source of Vitamin B7?

    <p>Sunflower seeds</p> Signup and view all the answers

    Vitamin B9 is essential for brain development and function.

    <p>True</p> Signup and view all the answers

    What role does Vitamin B7 play in metabolism?

    <p>It acts as a coenzyme that transfers carbon dioxide.</p> Signup and view all the answers

    A deficiency in Vitamin B7 can lead to symptoms such as __________ and depression.

    <p>fatigue</p> Signup and view all the answers

    Match the following vitamins with their primary uses:

    <p>Vitamin B7 = Fatty acid synthesis Vitamin B9 = Brain development Vitamin C = Antioxidant function Vitamin D = Calcium absorption</p> Signup and view all the answers

    What is one common symptom of Vitamin B7 deficiency?

    <p>Fatigue</p> Signup and view all the answers

    Vitamin B7 is particularly important for the metabolism of carbohydrates only.

    <p>False</p> Signup and view all the answers

    List two food sources that provide Vitamin B9.

    <p>Beans, fruits</p> Signup and view all the answers

    Which condition is associated with impaired fat absorption that could lead to a deficiency in Vitamin A?

    <p>Biliary cirrhosis</p> Signup and view all the answers

    Vitamin D3 can be derived from plant sources.

    <p>False</p> Signup and view all the answers

    What is the primary natural form of Vitamin A?

    <p>Retinol</p> Signup and view all the answers

    Vitamin A deficiency can lead to __________, which is characterized by night blindness.

    <p>nyctalopia</p> Signup and view all the answers

    What is one of the sources where Vitamin A can be found?

    <p>Fish liver oils</p> Signup and view all the answers

    Match each vitamin with its function:

    <p>Vitamin A = Vision Vitamin D = Calcium absorption Vitamin C = Immune function Vitamin K = Blood clotting</p> Signup and view all the answers

    Carotenoids are converted to Vitamin A if they possess at least one hydroxylated β-ionone ring.

    <p>False</p> Signup and view all the answers

    Name one of the roles of Vitamin A in the body.

    <p>Growth and development</p> Signup and view all the answers

    Which of the following is a consequence of Vitamin B12 deficiency?

    <p>Megaloblastic anemia</p> Signup and view all the answers

    Vitamin C is stable and maintains its nutritional content when cooked.

    <p>False</p> Signup and view all the answers

    What are two common dietary sources of Vitamin C?

    <p>Citrus fruits and strawberries</p> Signup and view all the answers

    Vitamin C plays a significant role in the synthesis of __________.

    <p>collagen</p> Signup and view all the answers

    Match the functions of Vitamin C with their descriptions:

    <ol> <li>Antioxidant activity = A. Reduces oxidative stress</li> <li>Collagen synthesis = B. Supports skin and tissue health</li> <li>Iron absorption = C. Enhances iron uptake</li> <li>Immune defense = D. Aids in fighting infections</li> </ol> Signup and view all the answers

    Which of the following symptoms is NOT typically associated with Vitamin B12 deficiency?

    <p>Enhanced mood</p> Signup and view all the answers

    Dehydro-L-ascorbic acid is the reduced form of Vitamin C.

    <p>False</p> Signup and view all the answers

    What is one important antioxidant property of Vitamin C?

    <p>It helps reduce oxidative stress.</p> Signup and view all the answers

    What is the mechanism of action for cardiac glycosides?

    <p>Inhibition of Na+/K+ ATPase enzyme</p> Signup and view all the answers

    Ouabagenin is less polar than K-strophanthidin.

    <p>False</p> Signup and view all the answers

    What are the main glycosides found in the seeds of Strophanthus kombe and Strophanthus hispidus?

    <p>K-strophanthoside and K-strophanthin-B</p> Signup and view all the answers

    The primary therapeutic use of oleander is for treating __________ insufficiency.

    <p>cardiac</p> Signup and view all the answers

    Match the following glycosides with their respective properties:

    <p>K-strophanthoside = Main glycoside in Strophanthus kombe Ouabagenin = Derived from S. grantus Oleanderin = Anticancer treatment potential Bufadienolide = Six-membered doubly unsaturated lactone ring</p> Signup and view all the answers

    Which of the following statements is true regarding the absorption of ouabagenin?

    <p>It is absorbed slowly and irregularly.</p> Signup and view all the answers

    K-strophanthin-B is a primary glycoside found in Strophanthus kombe.

    <p>True</p> Signup and view all the answers

    Identify one toxic effect associated with the plant Nerium oleander.

    <p>Cardiotoxicity</p> Signup and view all the answers

    Study Notes

    Photosynthesis: Carbon Fixation

    • Carbon dioxide (CO2) combines with the five-carbon molecule ribulose-1,5-bisphosphate (RuBP) through the enzyme RuBP carboxylase/oxygenase (rubisco)
    • This interaction produces a six-carbon intermediate, which splits into two molecules of the three-carbon compound 3-phosphoglyceric acid (3-PGA)

    Photosynthesis: Reduction

    • ATP and NADPH are used to convert 3-PGA molecules into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar
    • NADPH donates electrons to reduce a three-carbon intermediate in this process

    Photosynthesis: Regeneration

    • Some G3P molecules are used to synthesize glucose, while others are recycled to regenerate RuBP, the acceptor molecule for CO2
    • Regeneration requires ATP and a complex series of reactions

    Glycolysis

    • Glycolysis is a metabolic pathway that breaks down glucose into pyruvate
    • This process occurs in the cytosol of cells and does not require oxygen
    • The free energy released during glycolysis generates a net gain of two ATP molecules

    Citric Acid Cycle (Krebs Cycle)

    • The Krebs cycle, also known as the tricarboxylic acid cycle (TCA) or citric acid cycle, occurs in the mitochondrial matrix
    • Acetyl-CoA is oxidized to produce carbon dioxide and reduced coenzymes
    • These reduced coenzymes contribute to ATP production through the electron transport chain
    • The Krebs cycle is an eight-step process requiring oxygen
    • The overall reaction for glucose breakdown, in terms of ADP and ATP, is: C6H12O6 + 6CO2 + 38 ADP + 38P(inorganic) → 6H2O + 6CO2 + 38 ATP

    Biosynthesis of Secondary Metabolites

    • Biosynthesis is a multi-step, enzyme-catalyzed process involving the conversion of substrates into more complex products
    • Simple compounds are modified, transformed, or joined together to form macromolecules in this process
    • Biosynthetic pathways often involve multiple metabolic steps
    • Building blocks for secondary metabolites originate from primary metabolites, mainly from photosynthesis, glycolysis, or the Krebs cycle
    • Important intermediates in biosynthesis include acetyl CoA, shikimic acid, mevalonic acid, and malonic acid

    Vitamins

    • Vitamins are organic molecules essential for normal metabolic functions
    • They are not synthesized by the body and are required in small amounts
    • Vitamins do not provide energy and are not used as building blocks for cellular structures
    • Vitamin deficiencies can result in distinctive symptoms like beriberi, rickets, scurvy, and xerophthalmia
    • The term "vitamin" originated in 1911 when a vital amine thought to prevent beriberi was isolated from rice bran
    • Vitamins are diverse in their chemical structures, ranging from simple molecules like niacin to complex ones like cyanocobalamin
    • Vitamins are widely distributed in food sources, particularly fresh fruits, leafy vegetables, whole grains, eggs, and liver
    • Natural and synthetic vitamins are biochemically, nutritionally, and therapeutically indistinguishable
    • Vitamins can be used as dietary supplements or medicinal drugs
    • Vitamin supplements are considered to be foods for special dietary needs and are generally unnecessary with a balanced diet
    • When vitamins are used to treat a vitamin deficiency or prevent disease, they are considered drugs

    Vitamin Classification

    • Vitamins are classified into two groups:
      • Fat-soluble vitamins: (A, D, E, K) stored in the body, deficiencies are less common, but excess intake can be toxic
      • Water-soluble vitamins: (C, B complex) not stored significantly and excess is typically excreted in urine

    Glycosides

    • Glycosides are compounds formed by a sugar molecule and a non-sugar molecule (aglycone) linked by a glycosidic bond
    • They are widely distributed in plants and have various medicinal uses

    Glycosides: Physical Properties

    • Glycosides are typically solid, amorphous, and non-volatile
    • Most glycosides are colorless, but flavonoids are yellow, and anthraquinones are red or orange
    • Glycosides generally have a bitter taste
    • Most glycosides are odorless, with the exception of saponin (glycyrrhizin)

    Glycosides: Stability

    • Glycosides can be hydrolyzed by heating with dilute acids, cleaving the glycosidic linkages
    • Glycosides are relatively stable in alkaline conditions
    • Enzyme hydrolysis can occur with specific enzymes found in plants

    Glycosides: Importance

    • Glycosides play vital roles in plant life, serving as:
      • Sugar reserves
      • Waste products of plant metabolism
      • Detoxification agents
      • Osmotic regulators
      • Regulators of important metabolic substances
      • Defense mechanisms against microorganisms

    Glycosides: Medicinal Applications

    • Many therapeutic agents are derived from glycosides
    • Cardiac glycosides from plants like digitalis, strophanthus, and squill are important medical compounds
    • Laxative drugs, such as those containing senna, aloe, rhubarb, cascara sagrada, and frangula, contain anthraquinone glycosides
    • Sinigrin, a glycoside from black mustard, yields allyl isothiocyanate, which is a powerful irritant

    Cardioactive Glycosides: Nomenclature

    • The nomenclature of cardioactive glycosides follows a specific sequence:
      • Functional groups and their configurations are listed first
      • α or β configurations are denoted
      • The type of glycoside is indicated
      • The positions of double bonds are specified

    Cardioactive Glycosides: Biosynthesis

    • The aglycones of cardioactive glycosides are derived from mevalonic acid
    • The final molecules are formed through the condensation of a C21 steroid with a C2 unit (source of C-22 and C-23)
    • Bufadienolides are derived from the condensation of a C21 steroid with a C3 unit

    Drugs Containing Cardioactive Glycosides

    • Digitalis or Foxglove:

      • Dried leaf of Digitalis purpurea, belonging to the Scrophulariaceae family
      • "Digitalis" comes from the Latin "digitus" (finger) referring to the finger-shaped corolla
      • "Purpurea" is Latin and refers to the purple flower color
      • Contains many glycosides, key ones being digitoxin, gitoxin, and gitaloxin (average concentration of 0.16%)
      • Other glycosides identified include purpurea glycosides A, B, gluco-gitaloxin, and gluco-digitoxigenin
      • Primary glycosides have acetylated sugar moieties

    • Digitalis lanata:

      • Leaves contain nearly 70 different glycosides, all derivatives of five aglycones
      • Three of these aglycones (digitoxigenin, gitoxigenin, and gitaloxigenin) are also found in Digitalis purpurea
      • Digoxigenin and diginatigenin are unique to Digitalis lanata
      • Leaves are used as a source of digoxin and lanatoside C
      • Lanatoside A, B, and E are acetylated derivatives of purpurea A, B, and E, respectively

    Glycosides Derived from Digitoxigenin

    • Lanatoside A: Digitoxigenin---DX---DX----DX(AC)---G

    • Acetyl-digitoxin: Digitoxigenin---DX---DX----DX---(AC)

    • Digitoxin: Digitoxigenin------DX---DX----DX

    • Purpurea Gly A: Digitoxigenin---DX---DX----DX---G

    • Where:

      • DX = Digitoxose
      • DX (AC)=Acetyldigitoxose
      • G = Glucose

    Primary Metabolites

    • Involved in normal growth, development, and reproduction
    • Essential for proper growth
    • Formed during the growth phase
    • Examples include ethanol, lactic acid, and certain amino acids
    • Used industrially in the production of alcohol, amino acids like L-glutamate and L-lysine , and citric acid

    Secondary Metabolites

    • Organic compounds produced by modifying primary metabolite synthases
    • Formed during the stationary phase or near the end of growth
    • Play a role in ecological function, such as defense mechanisms.
    • Examples include atropine and antibiotics like erythromycin and bacitracin

    Vitamin A (Retinol)

    • Derivatives of β-ionone, excluding carotenoids
    • Retinol (alcohol), acetate, and palmitate esters are known forms
    • Easily absorbed (~80-90%) from the intestinal tract
    • Stored in body tissues, particularly the liver
    • Natural sources include fish liver oils
    • Dietary sources include animal organs (heart, kidney, liver)
    • Can be derived from plant carotenoids present in carrots and green leafy vegetables
    • Beta-carotene and related carotenoids are cleaved to yield retinal, which is reduced to retinol
    • Plays crucial roles in:
      • Vision
      • Growth and development
      • Immune function
      • Red blood cell formation
      • Skin and bone formation
      • Regulating gene transcription
    • Deficiency can lead to conditions such as:
      • Nyctalopia (night blindness)
      • Xerophthalmia
      • Hyperkeratosis of the skin
      • Growth retardation
      • Decreased resistance to infection

    Vitamin D

    • Includes several related steroids and their metabolites essential for calcium absorption and utilization
    • Two forms:
      • Vitamin D2 (ergocalciferol) - from plant sources and fortified foods
      • Vitamin D3 (cholecalciferol) - from animal-sourced foods

    Vitamin B7 (Biotin)

    • Coenzyme that transfers carbon dioxide
    • Important role in breaking down food (carbohydrates, fats, and proteins) into energy
    • Involved in various cellular processes, especially fat and protein metabolism in hair roots, fingernails, and skin
    • Used in fatty acid synthesis
    • Deficiency can cause fatigue, depression, and dermatitis

    Vitamin B9 (Folate)

    • Refers to materials with anemia properties
    • Essential for brain development and function
    • Helps in brain function and synthesis of red blood cells
    • Deficiency can lead to:
      • Megaloblastic anemia
      • Irreversible neurologic damage
      • Irritability, weakness, memory loss, mood swings, and tingling/numbness in arms and legs

    Vitamin C (L-ascorbic Acid)

    • Naturally occurring vitamin that prevents scurvy and has antioxidant properties
    • Found in equilibrium with dehydro-L-ascorbic acid (oxidized form), which also has antiscorbutic properties
    • Least stable of all vitamins
    • Good dietary sources: citrus fruits, tomatoes, strawberries, and fresh fruits/vegetables
    • Content is preserved by freezing but cooking can reduce it by up to 50%
    • Involved in:
      • Antioxidant activity
      • Enzyme activation and oxidative stress reduction
      • Collagen synthesis and iron absorption
      • Defense against infections and inflammation
    • Acts by inhibiting Na+/K+ ATPase enzyme which regulates ion transport across cell membranes

    Strophanthus

    • Dried ripe seeds of Strophanthus kombe or Strophanthus hispidus
    • Principal glycosides: K-strophanthoside, K-strophanthin-B, and cymarin, all based on strophanthidin
    • K-strophanthoside is the main glycoside in both species and is composed of strophanthidin and a trisaccharide
    • Strophanthin is used intravenously (I.V.) as a cardiotonic

    Ouabain (G-strophanthin)

    • Obtained from Strophanthus gratus
    • Most polar cardioactive glycosides
    • Acts as a cardiotonic, administered intravenously for prompt therapeutic effect
    • Oral administration not recommended due to slow and irregular absorption from the alimentary canal
    • Ouabagenin (the sugar is rhamnose) differs from K-strophanthidin by having two additional (OH) groups and a alcoholic group at specific carbon positions

    Oleander

    • Leaves of Nerium oleander are used to treat cardiac insufficiency
    • Main constituent is oleanderin, which is also being investigated for its anticancer potential
    • Considered poisonous due to the toxicity of some compounds, especially in large amounts
    • Contains the sugar oleanderin

    Bufadienolide

    • Found in the squill bulb of Urginea maritima (white squill) and Urginea indica (Indian squill)
    • Genins of squill glycosides differ from cardenolides in two ways:
      • They have a six-membered doubly unsaturated lactone ring
      • They have at least one double bond in the steroid nucleus

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