Biochemistry Exam 5 (Chapter 23)

• Metabolism


  Sum total of all chemical reactions in a living organism
• Metabolism


  • Source of energy for the functioning of the human body
  • Needed for many of the cellular processes such as protein synthesis, DNA replication, RNA transcription, and membrane transport
• Subtypes of Metabolic Reactions

  • Catabolism
  • Anabolism
• Catabolism


  All metabolic reactions in which large biochemical molecules are broken down to smaller ones, usually energy is released in these reactions
• Anabolism


  All metabolic reactions in which small biochemical molecules are joined to form larger ones, usually require energy
• Catabolism


  • Oxidation of glucose
• Anabolism


  • Synthesis of proteins
• Metabolic Pathway


  Series of consecutive biochemical reactions used to convert a starting material into an end product
• Types of Metabolic Pathways

  • Linear
  • Cyclic
• Major pathways for all forms of life are similar
• Anabolism


  • Synthesis of a protein from amino acids
  • Formation of a triacylglycerol from glycerol and fatty acids
  • Formation of a nucleic acid from nucleotides
• Catabolism


  Hydrolysis of a polysaccharide to monosaccharides
• Types of Metabolic Reactions

  • Anabolism
  • Catabolism
• Knowledge of the cell structure is essential for understanding metabolism
• Prokaryotic cell


  • No nucleus and found only in bacteria
  • Presence of a single circular DNA molecule near the center of the cell called nucleoid
• Eukaryotic cell


  • Cell where the DNA is found in a membrane-enclosed nucleus
  • About 1000 times larger than bacterial cells
• Eukaryotic Cell Organelles and Their Function

  • Plasma membrane - Cellular boundary
  • Cytoplasm - Water-based material of a eukaryotic cell
  • Mitochondrion - Generates most of the energy needed for a cell
  • Lysosome - Contains hydrolytic enzymes needed for cell rebuilding, repair, and degradation
  • Ribosome - Site for protein synthesis
  • Nucleus - Site where DNA is found
• Mitochondrion


  • Responsible for the generation of most of the energy for a cell
  • Outer membrane - Permeable to small molecules, 50% lipid and 50% protein
  • Inner membrane - Highly impermeable to most substances, 20% lipid and 80% protein, Folded to increase surface area
  • Synthesis of ATP occurs here
• The cellular organelle responsible for the generation of most of the energy for the cell is the Mitochondrion
• Adenosine phosphates of interest


  • Adenosine monophosphate (AMP) - One phosphate group, Structural component of RNA
  • Adenosine diphosphate (ADP) - Two phosphate groups, Key component of metabolic pathways
  • Adenosine triphosphate (ATP) - Three phosphate groups, Key component of metabolic pathways
• Phosphoryl group


  Derived from a phosphate ion when it becomes part of another molecule
• The net energy produced in these reactions is used for cellular reactions
• In cellular reactions, ATP functions as both a source of a phosphate group and a source of energy
• Example of ATP function


  • Conversion of glucose to glucose-6-phosphate
• Role of Other Nucleotide Triphosphates in Metabolism

  • Uridine triphosphate (UTP) - Involved in carbohydrate metabolism
  • Guanosine triphosphate (GTP) - Involved in protein and carbohydrate metabolism
  • Cytidine triphosphate (CTP) - Involved in lipid metabolism
• Flavin Adenine Dinucleotide (FAD)


  • Coenzyme required in numerous metabolic redox reactions
  • Flavin subunit is the active form which gains H atoms when FAD is converted to FADH2
  • Ribitol is a reduced form of the sugar ribose
• Nicotinamide Adenine Dinucleotide (NAD)

  • Has coenzyme functions in metabolic redox pathways
  • NAD+ is the oxidized form, NADH is the reduced form
  • Typical cellular reaction in which NAD+ serves as the oxidizing agent is the oxidation of a secondary alcohol to give a ketone
• Coenzyme A


  • Derivative of vitamin B pantothenic acid
  • Active form of coenzyme A is the sulfhydryl group (–SH group) in the ethanethiol subunit of the coenzyme
  • Acetyl-CoA - Formed when acetyl group bonds to CoA–SH via a thioester bond
• Classification of Metabolic Intermediate Compounds

  • Based on their functions
• The intermediate molecule in metabolic reactions responsible for producing energy in the human body is ATP
• Why ATP is the best energy source for human beings

  It has an intermediate value in free energy, and it undergoes slow hydrolysis in an aqueous environment
• Carboxylate Ions (Metabolic Acids)

  • Fumarate
  • Oxaloacetate
  • Malate
  • α-ketoglutarate
  • Citrate
• None of the structural descriptions for metabolic carboxylate ions that are derivatives of succinic acid is incorrect
• High-energy compounds


  • Have greater free energy of hydrolysis than a typical compound
  • They contain at least one reactive bond called strained bond
  • Energy to break these bonds is less than a normal bond
  • More negative the free energy of hydrolysis, greater the bond strain
• Typically the free-energy release is greater than 6.0 kcal/mole (indicative of bond strain)
• There are two "strained" bonds present in an ATP molecule
• Energy needed to run the human body is obtained from food via a multistep process involving several different catabolic pathways
• There are four general stages in the biochemical energy production
• Strained bond


  Reactive bond with less energy to break than a normal bond
• More negative the free energy of hydrolysis


  Greater the bond strain