Carbohydrate

Nutrient 1 - Sugar

  • Check-in code: PV-EV-CD

  • Instructor Email: charles.affourtit@plymouth.ac.uk

  • Course Code: BHCS1003 - CA03

Disturbed Energy Balance and Obesity

  • Obesity is a result of disturbed energy balance.

  • Associated Health Risks:

    • Type 2 Diabetes

    • Heart Disease

    • Morbid Obesity

    • Potentially leading to death.

  • Reference to the “Healthy Eating Mega Initiative” by Michelle Obama, emphasizing low-calorie diets, portion control, and healthier eating habits.

Obesity as a Global Phenomenon

  • Prevalence:

    • Obesity patterns in adults defined by BMI (> 25 kg/m²).

    • Data from the World Health Organization (WHO) 2022 indicates prevalence levels.

    • Percentage ranges of obesity:

    • > 40%

    • 35-39.9%

    • 30-34.9%

    • 25-29.9%

    • 20-24.9%

    • 15-19.9%

    • 10-14.9%

    • < 9.9%

Diabetes Statistics

  • International Diabetes Federation (2021):

    • Approximately 537 million adults (aged 20-79) living with diabetes.

    • Projections:

    • 643 million by 2030.

    • 783 million by 2045.

    • Demographics:

    • 3 in 4 adults with diabetes reside in low- and middle-income countries.

    • Diabetes Burden:

    • 1 in 10 people globally is living with diabetes.

    • 240 million individuals with undiagnosed diabetes.

Healthcare Costs Related to Diabetes

  • Direct NHS cost: £10 billion per year as of 2019.

  • Weekly expenditure: £192 million.

  • Daily expenditure: £27 million.

  • Hourly expenditure: £1 million.

  • Per minute: £19,000.

  • Per second: £315.

  • Health Complications:

    • Stroke

    • Diabetic retinopathy

    • Diabetic neuropathy

    • Diabetic cardiomyopathy

    • Reduced blood flow

    • Diabetic nephropathy

    • Diabetic foot syndrome

Complexity in Preventing Metabolic Disease

  • Common Advice:

    • Eat less

    • Exercise more

  • Obesity Realities:

    • Some individuals remain slim regardless of diet.

    • Some gain weight easily from food exposure.

    • Not all obese individuals develop metabolic diseases, and some thin individuals can suffer from metabolic syndrome.

Understanding Fuel Metabolism

  • Dynamic Research Area:

    • Focus on principles, thermodynamics, enzymology, pathways, regulation, control, and efficiency.

    • Structure aids in function understanding.

    • Areas of focus: Proteins (Jeremy) and Sugars, Fats, Lipoproteins (Affourtit).

Learning Objectives on Sugars

  • By the end of the lecture, you should be able to:

    • List the main physiological roles and pathological effects of sugars.

    • Explain the functional groups of sugar molecules: carbonyls (aldehydes or ketones) and hydroxyls.

    • Understand why carbohydrates are optically active and the significance of this in biology and medicine.

    • Discuss sugar cyclization, anomeric carbons, glycosidic bonds, reducing sugars, and sugar alcohols.

    • Describe how monosaccharides join via glycosidic bonds, including examples of disaccharides and polysaccharides.

    • Discuss the biochemical basis of lactose intolerance.

Physiological Roles of Carbohydrates

  • Carbohydrates: Abundant biological molecules.

  • Other Names: Saccharides, Saccharon (meaning sugar).

  • Roles:

    • Metabolic Fuels:

    • Glucose (dextrose), Fructose (laevulose)

    • Energy Stores:

    • Starch, Glycogen

    • Structural and Regulatory Functions:

    • Cell wall components, exoskeletons, receptor sites.

Chronic Hyperglycemia and Complications

  • Chronic Hyperglycemia leads to complications known as glucotoxicity, impacting numerous medical disorders:

    • Protein Glycation

    • Production of Reactive Oxygen Species (ROS)

Structure of Carbohydrates

  • Basic Composition:

    • Simple sugars are aldehyde or ketone derivatives of polyhydroxy alcohols.

    • Classification of Carbohydrates:

    • Aldose or Ketose?

    • Considering the number of carbon atoms:

      • aldotriose, ketotriose, ketohexose.

  • Example Structures:

    • D-Glucose, D-Glyceraldehyde, D-Fructose, aldohexose.

Nomenclature of Sugars

  • Names may differ based on context:

    • Layman: Grape sugar

    • Medic: Dextrose

    • Nutritionist: Glucose

    • Biochemist: Aldohexose

    • Chemist: (2R,3S,4R,5R)-2,3,4,5,6-Pentahydroxyhexanal

Molecular Chirality

  • Chiral Molecules:

    • Distinction between original and mirror images, which cannot be superimposed.

    • Asymmetric (chiral) centers in molecules lead to unique stereoisomers.

Optically Active Molecules

  • Optical Activity in Carbohydrates:

    • Carbohydrates exhibit optical activity due to asymmetric carbon atoms.

    • In the formation, anomeric carbon also possesses chirality.

Cyclization of Sugars

  • Molecular Cyclization:

    • Transformation from linear to cyclic structures, e.g., D-Glucose into alpha-D-Glucopyranose.

  • Examples of Sugar Structures:

    • Hemiactetal and Hemiketal formation explained in intra-molecular reactions.

Glycosidic Bond Formation

  • Glycosidic bonds form through acid-catalyzed condensation between an anomeric hydroxyl and an alcohol.

  • These stable bonds do not undergo mutarotation, thereby locking the ring structure.

Reducing Sugars

  • Some sugars possess reducing potential, allowing them to reduce mild oxidants if they have at least one free anomeric carbon.

  • Historically, early blood tests for diabetes utilized the reducing ability of glucose.

  • Discussion point: Explain why lactose can be a reducing sugar while sucrose cannot.

Aldehyde Reactions

  • Oxidation and Reduction:

    • Aldehydes can be oxidized to carboxylic acids or reduced to alcohols.

Biological Relevance of Sugar Alcohols

  • Examples: D-Glyceraldehyde yields Glycerol and D-Xylose yields Xylitol, the latter commonly utilized as a sweetener in sugar-free products.

Polymers of Sugars

  • Starch:

    • Glucose polymer formed by glucan chains linked by glycosidic bonds ( ext{α(1→4)} ).

    • Contains thousands of glucose units, forming regular helices as a plant energy store.

  • Cellulose:

    • Another glucose polymer but formed with ext{β(1→4)} bonds resulting in indigestible structure (plant cell wall).

  • Glycogen:

    • Animal starch with a branched structure formed by ext{α(1→6)} bonds, allowing for a complex storage mechanism.

  • Inulin:

    • A fructose polymer notable for testing kidney function, found in plant food reserves (e.g., onions, garlic, bananas), but poorly digested.

Key Takeaways

  • Sugars serve multiple roles including as cellular fuels, energy stores, building blocks, and their high levels can lead to pathological effects.

  • Sugars possess unique chemical activities due to their functional groups.

  • Ring structures of sugars exist in equilibrium between cyclical and linear forms.

  • Sugars are optically active, and their polymerization via glycosidic bonds can produce structural stability or locks in cyclic forms.

  • Available carbonyls in sugars determine their reducing capabilities.