Biochem carbs

• Carbohydrate metabolism


  The metabolic pathways and processes involved in the breakdown and utilization of carbohydrates in living organisms
• Stages of carbohydrate metabolism

  1. Digestion & absorption

  2. Acetyl-CoA generation

  3. Krebs cycle

  4. Oxidative phosphorylation
• ATP


  A form of circulating energy currency in cells, formed in catabolic pathways by phosphorylation of ADP
• Types of chemical bonds


  • Low-energy bonds (ester, glycosidic, peptide)
  • High-energy bonds (phosphate, sulfur)
• Redox reaction


  Oxidation accompanied by reduction
• Redox potential


  Affinity of a substance for electrons (electronegativity) compared to hydrogen
• Carbohydrate sources


  • polysaccharides: Starch, Glycogen, Cellulose
  • diaccharides: Sucrose, Lactose
  • monosaccharides: Glucose, Fructose
• Carbohydrate digestion


  1. Mouth (salivary α-amylase)

  2. Stomach (digestion stops temporarily)

  3. Small intestine (pancreatic α-amylase, intestinal disaccharidases)
• Disaccharidases


  Enzymes that break down disaccharides into monosaccharides (lactase, maltase, sucrase, α-dextrinase)
• The difference between a pathway and a cycle is that a pathway is a series of steps, while a cycle is a series of steps that repeats
• Glycogen, starch, cellulose, chitin, and amylopectin are examples of polysaccharides.
• The glycosidic bond is formed between the anomeric carbon atom of one monosaccharide molecule and the hydroxyl group on another.
• Polysaccharides can be classified as homopolymers or heteropolymers based on their composition.
• Monosaccharide → Disaccharide → Polysaccharide
• Polysaccharides can be broken down by enzymatic action or chemical reaction with acids.
• Starch is composed of two types of glucose units joined by alpha-1,4 linkages and some branching points where alpha-1,6 linkages occur.
• Cellulose consists of beta-glucose units linked together through beta-1,4 bonds to form long chains called microfibrils.
• Glycogen has a highly branched structure similar to amylopectin but with more branches per unit length.
• Starch is composed mainly of two types of glucose polymers: amylose (linear) and amylopectin (branched).
• Glycogen has a similar structure to amylopectin but contains more branches due to alpha-1,6 linkages.
• Cellulose consists of beta-glucose units linked together by beta-1,4 bonds.
• Amylase breaks down starch into maltose, which is then converted to glucose through the action of maltase.
• Cellulose is made up of beta-glucopyranose units linked together through 1→4 glycosidic bonds to form long chains called microfibrils.
• Amylose has a linear structure with alpha-1,4 linkages, while amylopectin has branching points due to alpha-1,6 linkages.
• Amylopectin has a branched structure with alpha glucopyranose units joined by both 1→4 and 1→6 glycosidic bonds.
• Starch consists mainly of two types of glucose polymers: amylose and amylopectin.
• The main difference between starch and glycogen is the degree of branching, which affects their solubility and digestibility.
• Glucoamylase converts glycogen to glucose.
• Cellulose


  Contains β-(1-4) bonds between glucose molecules
• In humans, there is no β-(1-4) glucosidase that can digest such bonds, so cellulose passes as such in stool
• Cellulose


  • Helps water retention during the passage of food along the intestine
  • Increases bulk of the stool
  • Distension of colon reflex contraction of colon preventing constipation
• Monosaccharides


  Glucose, fructose, galactose
• Absorption of carbohydrates


  1. Passive transport (facilitated diffusion)

  2. Active transport
• Passive transport


  • Sugars pass with concentration gradient (high to low)
  • Requires no energy
  • Used by fructose and pentoses primarly , but hexoses as glucose and galactose can passe through too.
  • glucose and galactose can also use this if concentration gradient is favorable
• Active transport


  • Uses sodium-dependent glucose transporter 1 (SGLT1)
  • Transports glucose against concentration gradient using energy
  • Sodium is transported down concentration gradient and drives glucose transport
• Glucose transporters


  • GLUT-1 (RBCs, brain)
  • GLUT-2 (liver, kidney, pancreas, basolateral membrane of small intestines)
  • GLUT-3 (neurons, placenta, testis)
  • GLUT-4 (heart, skeletal muscle, adipose tissue)
  • GLUT-5 (brush border of intestine, sperm)
• SGLT-1


  Intestinal glucose absorption transporter
• SGLT-2

  Renal glucose reabsorption transporter
• Glucose metabolism in feeding state

  1. Glycolysis

  2. Pyruvate to Acetyl CoA

  3. Krebs cycle

  4. Respiratory chain

  5. Minor pathways (PPP, UAP)

  6. Glycogenesis
• Glucose metabolism in fasting state

  1. Glycogenolysis

  2. Gluconeogenesis