FUNBIO.2_carbohydrates_2023-24_WT.pptx

Royal College of Surgeons in Ireland - Medical University of Bahrain Biomolecules: Carbohydrates Class Course Code Title Lecturer Date Foundation Year Fundamentals of Human Biology FUNBIO. 2 Biomolecules: Carbohydrates Dr Ebrahim Rajab 26th September 2023 Biological Molecules FUNBIO. 2 Carbohyd...

Royal College of Surgeons in Ireland - Medical University of Bahrain Biomolecules: Carbohydrates Class Course Code Title Lecturer Date Foundation Year Fundamentals of Human Biology FUNBIO. 2 Biomolecules: Carbohydrates Dr Ebrahim Rajab 26th September 2023 Biological Molecules FUNBIO. 2 Carbohydrates FUNBIO. 3 Proteins FUNBIO. 4 Lipids and Nucleic Acids 22/12/2023 Biology RCSI-MUB Learning Outcomes • Introduce the four main elements of biological importance. • Describe the main classes of organic compounds. • Discuss the structure of monosaccharides and the glycosidic bond. • Explain polysaccharide structure and describe cellulose, starch and chitin. • Discuss the role of carbohydrates in glycosylated compounds 22/12/2023 Biology RCSI-MUB Organism Organ systems work together in a functional organism. Organisation of Living Matter Population Organism Organ system (e.g., skeletal system) Tissues and organs make up organ systems. Organ (e. g., bone) Tissues form organs. Tissue (e.g., bone tissue) Cells associate to form tissues. Cellular level Population Organ system Community The populations of different species that populate the same area make up a community. Organ Tissue A population consists of organisms of the same species. Community Bone cells Atoms and molecules Nucleus Cell make up the cytoplasm and form organelles, such as the nucleus and mitochondria (the Organelle Ecosyste site m of many energy transformations). Macromolecul Organelles perform Chemical level of e Biosphere various functions Atoms join to form the cell. Oxygen atom molecules. Molecule Hydrogen atoms Macromolecules are large molecules such as proteins Water and DNA. Ecosystem A community together with the nonliving environment forms an ecosystem. Biosphere Earth and all of its communities constitute the biosphere. Figure 1-6 p7 Biomolecules consist of compounds Carbohydrates [sugars] Proteins Lipids [Fats] Nucleic acids These are all Organic compounds: Compounds of C, H, O, N Organic compounds • The chemical components of the cell are known as organic compounds the study of which is Organic Chemistry • Organic compounds in cells Based mainly on Carbon compounds (C, H, O, N) The chemical reactions occur in an aqueous environment Within a relatively narrow range of temperatures Carbon atoms covalently bonded form the core of the molecule Many organic compounds found in organisms are extremely large macromolecules • Inorganic compounds: Very simple carbon compounds are considered inorganic if carbon is not bonded to another Carbon or Hydrogen. e.g. Carbon dioxide Inorganic acids, bases and salts • Why are these compounds so important? Constitute the structures of cells and tissues Participate & regulate metabolic reactions Transmit Information Provide energy for life Monomers and Polymers • Biological macromolecules are very large (1000’s atoms) –Most biological macromolecules are polymers produced by linking monomers (e.g. single sugar unit). Monomers Polymers • Combine to form functional units such as Polysaccharides (Carbohydrates), Proteins and nucleic acids • Produced by covalently linking monomers, which release water (condensation reactions). • Broken by Hydrolytic reactions (see glycosidic bonds) Carbohydrates • Carbohydrates are composed of Carbon, Hydrogen and Oxygen in a 1:2:1 ratio • Carbohydrate means hydrate (water of) carbon Reflects 2:1 ratio of hydrogen to oxygen (H2O) • Carbohydrates include Sugars, Starches and glycogen, Cellulose, Chitin Sugars and starches are energy sources for cells Cellulose and chitin are structural components • Carbohydrates are composed of sugar units – saccharides • Monosaccharides, Disaccharides and Polysaccharides Types of Carbohydrates sugars starches Energy source For cells cellulose/chitin Structural Carbohydrates – Sugars/Starches One sugar unit – Monosaccharides (are the simplest of the carbohydrates. They contain three to seven carbon atoms) eg: Glucose [a metabolic fuel] Two sugar units - Disaccharides eg: Sucrose (glucose + fructose) [table sugar] Many sugar units - Polysaccharides eg: Glycogen, Starch [fuel stores] Monosaccharide - Glucose Glucose most abundant monosaccharide A hexose sugar C6H12O6 White crystalline simple sugar An energy source in most organisms (oxidised cellular respiration) Used to synthesize other compounds e.g. Amino Acids and Fatty Acids Mechanisms have evolved to keep glucose at a relatively constant level in the blood. A failure of these mechanisms can lead to diabetes mellitus Open chain Ring Monosaccharide - Glucose • In solution as in the cell, Glucose exists as a ring of 5 Carbon and 1 Oxygen atom • Note that carbons are numbered right to left. • Carbon 1-5 in the ring • Carbon 6 is not in the ring • Carbon 1 and 5 join to the oxygen • To each of the carbons is attached a hydrogen (H) and a hydroxyl (OH) group 22/12/2023 Biology RCSI-MUB a b 𝛂-Glucose (ring form) 𝛂-Glucose Linear intermediate form β -Glucose (ring form) β -Glucose Glycosidic Bond • Monosaccharides can be joined together via glycosidic bonds (or o-glycosidic bonds) to create polymers (Disaccharides or polysaccharides) • Bond generally between carbon 1 of one molecule and carbon 4 of the other molecule (so called 1,4  -glycosidic bond) with a central oxygen atom. There are other bonds (e.g. 1,6-glycosidic bonds in polysaccharides which enable branching to occur – which allows for a more compact structure) 1 4 An o-glycosidic bond is where the ‘anomeric’ carbon (or stereocenter) is bound to an oxygen 22/12/2023 Common Disaccharides Commonly occurring disaccharides are • Maltose 2 -glucose molecules: Glucose-α(14)-glucose • Lactose 1 Glucose + 1 Galactose: Galactose-β(1-4)-glucose • Sucrose 1 Glucose + 1 Fructose: Glucoseα(1-2)-fructose 22/12/2023 Biology RCSI-MUB 22/12/2023 Biology RCSI-MUB Sucrose • Common table sugar • Extracted from cane or beet • Hydrolyzed by the enzyme invertase* to an equimolar mixture of glucose and fructose *In humans, invertase is found in the membrane of a cell lining the inner walls of the small intestine Maltose • A homodimer of glucose units occurs as a by-product of starch hydrolysis. • Degraded to glucose by Maltase starc h 22/12/2023 Biology RCSI-MUB Lactose: • Occurs in milk • Hydrolysed by Lactase (human) or β-Galactosidase (bacteria) • Some populations (Asian, South American, and African descent), have lactose intolerance characterized by nausea, pain, cramps diarrhoea. • Due to lactose accumulation in the ileum (as a result of lactase deficiency) • Osmotic effects 22/12/2023 Biology RCSI-MUB Polysaccharides • The most abundant carbohydrates in nature • Means many sugars • Thousands of monosaccharide rings joined by glycosidic linkages (usually glucose) • Enzymatic or acid hydrolysis of polysaccharides will release monosaccharides 22/12/2023 Biology RCSI-MUB Polysaccharides May be a long single chain or a branched chain. Includes starches, glycogen, cellulose and chitin May be a Homo- or Hetro- polysaccharide: • Homopolysaccharides are polymers composed of a single type of sugar monomer. • Glucans like starch, glycogen and cellulose are polysaccharides of D-glucose sugars. • Mannans include a plant polysaccharide that is a linear polymer of the sugar mannose • Heteropolysaccharides are polymers composed of more than one type of monosaccharide. e.g. Hyaluronic acid –maintains elastoviscosity of liquid connective tissues such as joint synovial fluid. 22/12/2023 Biology RCSI-MUB Storage Polysaccharides Starch is the carbohydrate used for energy storage in plants It is readily available as an energy source to most animals Glycogen is the human storage equivalent sometimes called animal starch It has more extensive branching than starch and is more water soluble The (Alpha) a 1-4glycosidic bond joining the glucose units can be broken by enzymes present in the gut It is mainly stored in the Liver and Muscle cells Both starch and glycogen are deposited as granules in the cytoplasm 22/12/2023 Biology RCSI-MUB Glycogen Glycogen is a branched biopolymer consisting of linear chains of glucose residues with further chains branching off every 8 to 12 glucoses or so. • Glucose units are linked together linearly by α(1→4) glycosidic bonds from one glucose to the next. • Branches are linked to the chains by α(1→6) glycosidic bonds between the first glucose of the new branch and a glucose on the stem chain Starch Starch Starch Starch is a mixture of two glucose homopolymers: (i) α-Amylose 20% (ii) Amylopectin 80% Parenchyma cells of the potato, showing the central cell with obvious nucleus and purple-stained starch. LM X83. Credit: © George Wilder/Visuals Unlimited a - Amylose α-Amylose A long unbranched chain of glucose units linked by α(1-4) bonds 200 to 1000 glucose units Not truly water-soluble but forms hydrated micelles (hollow spherical structure with hydrophobic groups on the inside and hydrophilic groups outside.) In the micelles, the polymer forms a helical coil (due to hydrogen bonding) Amylopectin Amylopectin A highly-branched polymer Branch every 24-30 glucose residues (depending on the species). 2000 to 200,000 glucose units Backbone linkages = α(1-4) Branch-points = α(1-6) Amyloplasts (a) Amyloplasts (or starch granules) are non-pigmented organelles found in some plant cells. They are responsible for the synthesis and storage of starch granules, through the polymerization of glucose. They also convert this starch back into sugar when the plant needs energy Hydrolysis of Starch (i) Hydrolysis of Starch Both  - and  -amylases degrade amylose to completion The α-Amylase enzyme: Found in saliva & pancreatic juices Important in digestion of starch Cleaves α(1-4) bonds randomly to produce a mixture of glucose and maltose The β-Amylase enzyme: Found in malt (germinated cereal grain), yeasts, moulds and bacteria Digestion of starch, glycogen and related polysaccharides Specific for α(1-4) bonds Cleaves single maltose units successively from the nonreducing end of the polymer Hydrolysis of Starch  - and  -amylases degrade amylopectin, but cannot break down  (1-6) bonds • Products include Dextrins (short chains carbohydrates) which are mixtures of polymers of D-glucose units linked by α-(1→4) or α-(1→6) glycosidic bonds. • Final product is a “Limit Dextrin” (i.e. a short chained branched amylopectin remnant, produced by hydrolysis of amylopectin with α-amylase) • Debranching enzyme, isomaltase (or α-dextrinase), is needed for complete degradation Cellulose • Cellulose is the most abundant carbohydrate on the planet • It makes up over 50% of carbon compounds in plants • It is a structural carbohydrate Wood is about 50% cellulose Cotton is about 90% cellulose The cell walls of plants are cellulose (almost completely extracellular) • Cellulose is a linear polymer of glucose units joined by (Beta) b 1,4 glycosidic linkages • Most animals do not have the enzymes necessary to break these 1-4  -glycosidic linkages • Cellulose only provides fibre in the diet (50% fecal material). in starch all the glucose repeating units are oriented in the same direction, but in cellulose each successive glucose unit is rotated 180 degrees relative to the last repeat unit. Polysaccharide – Chitin • Chitin is a structural carbohydrate found in animals • It is the main component in the cell wall of fungi • The monosaccharide units in chitin have an –OH (hydroxyl) group replaced by an –NH2 (amino) group • This is called a Glucosamine when the monosaccharide unit is glucose Also Forms the external skeleton of insects, crayfish and other arthropods Lobster shellcalcified chitin The subunits in Chitin are N-acetyl glucosamine N-acetyl glucosamine Chitin Glycoproteins e.g. Integral membrane proteins Glycosylation is the covalent addition of sugars to specific amino acids Glycoproteins Secreted proteins (e.g. antibodies) Contain oligosaccharides in glycosidic linkage to Serine, Threonine or Asparagine amino acids Phosphorylated Sugars Phosphorylated sugars occur as intermediates in energyyielding metabolism e.g. Glucose-6-phosphate (glycolysis) Phosphorylation also makes sugars anionic and allows some of them to participate in glycosidic bonding as reactive intermediates Recommended Reading Chapter 3 ‘The Chemistry of Life’ Organic Compounds Solomon 10th Ed. p44 -54 Solomon 11th Ed. p50 -55 Chapter 1 ‘A view of Life’ Solomon 11th Ed. p6 -7