Biochemistry Chapter on Sugars and Amino Acids
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Questions and Answers

Which of the following describes deoxysugars?

  • They are always monosaccharides.
  • They are sugars with additional hydroxyl groups.
  • They have one or more hydroxyl groups replaced by hydrogen atoms. (correct)
  • They are exclusively found in plant polysaccharides.

    • 2-Deoxyribose is a deoxysugar component of RNA.

    False (B)

    What is the glycosidic bond formed from glucose and fructose called?

    Sucrose

    N-Linked oligosaccharides are attached to the nitrogen atom of the amino acid __________.

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

    Match the following disaccharides with their components:

    <p>Sucrose = Glucose + Fructose Lactose = Glucose + Galactose Maltose = Glucose + Glucose Fructose = Fructose + Glucose</p> Signup and view all the answers

    Which deoxysugar is known for giving DNA greater stability compared to RNA?

    <p>2-Deoxyribose (D)</p> Signup and view all the answers

    Polysaccharides are formed from short chains of monosaccharides.

    <p>False (B)</p> Signup and view all the answers

    Define oligosaccharides and their primary function.

    <p>Short chains of monosaccharides attached to proteins or lipids, functioning in cell recognition and signaling.</p> Signup and view all the answers

    What role do metal ions play in metal ion catalysis?

    <p>They activate water molecules. (D)</p> Signup and view all the answers

    Nonessential amino acids can be synthesized by the body.

    <p>True (A)</p> Signup and view all the answers

    Name one example of a metal ion that stabilizes negative charges in catalytic processes.

    <p>Zn²⁺ or Mg²⁺</p> Signup and view all the answers

    Glutathione (GSH) is composed of _____, cysteine, and glycine.

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

    Match the following amino acids to their source:

    <p>Serine = Phosphoglycerate Cysteine = Phosphoglycerate Glycine = Phosphoglycerate Glutamate = Synthesis in the body</p> Signup and view all the answers

    What is formed in the first step of glutathione synthesis?

    <p>Gamma-glutamylcysteine (B)</p> Signup and view all the answers

    A positive nitrogen balance occurs when the intake of nitrogen exceeds its loss.

    <p>True (A)</p> Signup and view all the answers

    What are two functions of glutathione?

    <p>Involvement in DNA/RNA synthesis and protection from radiation.</p> Signup and view all the answers

    Which glucose transporter is primarily involved in glucose uptake by liver cells?

    <p>GLUT2 (C)</p> Signup and view all the answers

    Muscle cells use GLUT2 for glucose uptake.

    <p>False (B)</p> Signup and view all the answers

    What is the first step in glycogenesis after glucose enters the cell?

    <p>Glucose-6-Phosphate Formation</p> Signup and view all the answers

    Glycogen synthesis is primarily carried out by the enzyme __________.

    <p>glycogen synthase</p> Signup and view all the answers

    What is the role of the branching enzyme in glycogen synthesis?

    <p>Adds branches to the glycogen molecule (B)</p> Signup and view all the answers

    Name one hormone that stimulates glycogenolysis in the liver.

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

    Match the steps of glycogenesis with their descriptions:

    <p>Glucose-6-Phosphate Formation = Traps glucose inside the cell Isomerization to Glucose-1-Phosphate = Conversion of G6P to G1P Activation by UDP-Glucose = Forms UDP-glucose from G1P Glycogen Synthase Activity = Adds glucose units to glycogen chain</p> Signup and view all the answers

    High concentrations of free glucose in the __________ influence glycogen synthesis.

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

    What happens as a result of a deficiency in vitamin B12?

    <p>Accumulation of methylmalonyl-CoA (C)</p> Signup and view all the answers

    The liver can utilize ketone bodies for energy.

    <p>False (B)</p> Signup and view all the answers

    What is the primary source of NADPH for fatty acid synthesis?

    <p>Pentose phosphate pathway</p> Signup and view all the answers

    During prolonged fasting, excess acetyl-CoA is converted into __________.

    <p>ketone bodies</p> Signup and view all the answers

    Which molecule is produced at the end of the degradation of odd chain fatty acids?

    <p>Propionyl-CoA (B)</p> Signup and view all the answers

    Match the following components with their roles in fatty acid synthesis:

    <p>Acetyl-CoA = Required for fatty acid synthesis NADPH = Provides reducing power Malonyl-CoA = Source of two carbon units Pentose phosphate pathway = Main source of NADPH</p> Signup and view all the answers

    What transformation is required for Acetyl-CoA to enter the cytoplasm?

    <p>Transformed into a transportable substance</p> Signup and view all the answers

    Unsaturated fatty acids require the same enzymatic steps for degradation as saturated fatty acids.

    <p>False (B)</p> Signup and view all the answers

    What substance is formed when glycine is added to gamma-glutamylcysteine?

    <p>Glutathione (GSH) (B)</p> Signup and view all the answers

    Gamma-glutamyl transpeptidase is involved in the recycling of amino acids.

    <p>True (A)</p> Signup and view all the answers

    What does the enzyme gamma-glutamyl cyclotransferase release from the gamma-glutamyl-amino acid complex?

    <p>Free amino acid</p> Signup and view all the answers

    The process of converting ammonia into glutamine involves the reaction of glutamate and __________.

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

    Match the following pairs of compounds with their respective enzymes:

    <p>Alfa-ketoglutarate = ALT Oxaloacetate = AST Pyruvate = GPT Cysteinylglycine = Dipeptidase</p> Signup and view all the answers

    Which of the following is NOT involved in the synthesis of glutathione?

    <p>Ammonia (D)</p> Signup and view all the answers

    Oxidative deamination results in the release of ammonia, which is non-toxic to the brain.

    <p>False (B)</p> Signup and view all the answers

    Name one role of free amino acids after being transported into the cell.

    <p>Protein synthesis</p> Signup and view all the answers

    What type of bond links the glucose units in amylose?

    <p>α(1,4) glycosidic bond (C)</p> Signup and view all the answers

    Glycogen is more highly branched than starch.

    <p>True (A)</p> Signup and view all the answers

    Name one function of polysaccharides.

    <p>Energy reserve or structural material.</p> Signup and view all the answers

    Lipids are hydrophobic or _______ organic compounds.

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

    Which of the following is a structural polysaccharide found in plant cell walls?

    <p>Cellulose (C)</p> Signup and view all the answers

    Match the following polysaccharides with their characteristics:

    <p>Amylose = Unbranched chains of D-glucose Glycogen = Highly branched storage in animals Cellulose = Linear chains of glucose with β(1,4) bonds Chitin = Modified glucose in exoskeletons</p> Signup and view all the answers

    Triglycerides store more energy per gram than carbohydrates.

    <p>True (A)</p> Signup and view all the answers

    What role do lipids play in cellular membranes?

    <p>They form the lipid bilayer.</p> Signup and view all the answers

    Study Notes

    Metabolic Pathways

    • Pathways are sequential, leading from a starting molecule to a final product.
    • They can be reversible or irreversible.
    • Cells often require energy (ATP) to store substances within a metabolic pathway.

    Energy Storage and Utilization

    • ATP is the primary energy currency of the cell.
    • Cells store energy in glycogen or triacylglycerols
    • During fasting, glucose is rapidly used and gluconeogenesis produces glucose from non-carbohydrate sources
    • Glucose uptake occurs through insulin-dependent or insulin-independent transporters.

    Glycolysis

    • Converts glucose to lactate under anaerobic conditions, producing 2 ATP molecules.
    • Converts glucose to pyruvate under aerobic conditions, which can enter the Krebs cycle via acetyl-CoA.
    • Mature red blood cells rely solely on glycolysis.

    Glycogen Breakdown

    • This process occurs in the liver and skeletal muscles and is different in each tissue because of the presence/absence of glucose-6-phosphatase.

    Glycogen Synthesis

    • Glucose is initially phosphorylated to glucose-6-phosphate (G6P) trapping it inside the cell.
    • G6P is then converted into glucose-1-phosphate (G1P) by phosphoglucomutase.
    • G1P is activated by binding with uridine diphosphate (UDP), forming UDP-glucose.
    • UDP-glucose is added to the growing glycogen chain by glycogen synthase.
    • Branching enzyme introduces branches to increase solubility and mobility of the glucose.

    Pentose Phosphate Pathway

    • The objective is to produce NADPH.
    • NADPH is crucial for reducing agents in biosynthetic reactions.

    Gluconeogenesis

    • Synthesizes glucose from non-carbohydrate precursors (lactate, amino acids, glycerol) when carbohydrate sources are insufficient.
    • The pathway utilizes some but not all of the steps of glycolysis, bypassing the irreversible steps with unique gluconeogenic enzymes.
    • Key enzymes include Pyruvate Carboxylase and PEPCK.
    • Influenced by hormones like glucagon (stimulates gluconeogenesis) and insulin (inhibits gluconeogenesis).

    Cori Cycle

    • Involves the conversion of lactate produced in muscles during anaerobic conditions to glucose in the liver and back to lactate in the muscle.

    Glucose-Alanine Cycle

    • A pathway that transfers nitrogen (amino groups) from the muscles to the liver.

    Lipid Metabolism

    • Fatty acids are broken down into acetyl-CoA.
    • This acetyl-CoA enters the Krebs cycle to produce energy.
    • Synthesis involves combining acetyl-CoA and malonyl-CoA to build fatty acids.
    • Transport into the mitochondria is essential, using carriers and the carnitine shuttle.
    • Cholesterol and bile acid synthesis, use intermediates, and are critically important for cell membranes and other functions.

    Beta-Oxidation

    • Fatty acids are broken down into acetyl-CoA.
    • NADH and FADH2 are produced, which enter the electron transport chain.
    • ATP is produced during oxidative phosphorylation.

    Oxidative Phosphorylation

    • Electrons from NADH and FADH2 are passed along the electron transport chain.
    • This generates a proton gradient, which powers ATP synthesis
    • This reaction requires oxygen (O2).

    Amino Acid Metabolism

    • Initial step involved removal of the amino group.
    • Byproducts are used to synthesize fatty acids, glucose, and to generate energy.

    Urea Cycle

    • Converts ammonia into urea for excretion.
    • Important for nitrogen homeostasis.
    • Involves several enzymes and intermediates.

    Cholesterol Synthesis

    • Acetyl-CoA is the starting material.
    • The mevalonate pathway is a key step in the synthesis.
    • Cholesterol is essential for membrane structure and steroid hormone synthesis.

    Regulation of Cellular Processes

    • Citrate and malonyl-CoA are allosteric effectors.
    • Glucagon and insulin affect a number of processes, including synthesis and breakdown of fatty acids, carbohydrates, and protein
    • Von Gierke's Disease (G6Pase deficiency)
    • Pompe's Disease (a-1,4-glucosidase deficiency)
    • Cori's Disease (debranching enzyme deficiency)
    • McArdle's Disease (muscle glycogen phosphorylase deficiency)
    • Lactic Acidosis (impaired metabolism due to low oxygen)
    • Pyruvate Kinase Deficiency (impaired ATP production)
    • Glucose 6-Phosphate Dehydrogenase deficiency

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    Sebenta de Bioquímica 2024/25 MIM UFP PDF

    Description

    Test your knowledge on deoxysugars, polysaccharides, and the roles of amino acids in biochemistry. This quiz covers key concepts such as glycosidic bonds, oligosaccharides, and the impact of metal ions on catalysis. Dive into the world of biochemistry and see how well you understand these essential topics!

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