1. By: Jill Carreon, Paola Lara, John Lear & Camila Soto
Digestion of Sugars
By: Jill Carreon, Paola Lara,
John Lear & Camila Soto

2. What are Sugars? ● Sugars are a simple Carbohydrates CnH2nOn
● Biological molecule composed of Carbons (grey), Hydrogens (white), Oxygens (red).
● Basic Chemical Structure:
CnH2nOn
● Sugars include:
● Monosaccharides (glucose, fructose, galactose)
● Disaccharides (sucrose, maltose, lactose)
● Polysaccharides (starch, glycogen)
● Oligosaccharides
● Provide us with energy for ATP production

3. Digestion of Sugars: Overview
● Sugars enter the body through the oral cavity and mix with salivary enzymes
● Sugars travel through the esophagus down to the stomach
● Sugars travel to the duodenum where the mix with pancreatic enzymes
● Sugars enter the small intestine, encounter brush border enzymes and are absorbed
● Sugars enter the bloodstream and travel to the liver for storage or to body cells for energy production

4. Overview of Enzymes Involved
Disaccharidase Example:
● Amylase - Convert polysaccharides to disaccharides
● Salivary Amylase
● Pancreatic Amylase
● Disaccharidase - Convert disaccharides to monosaccharides
● Maltase - breaks bond between two glucose molecules
● Sucrase - breaks bond between glucose and fructose molecules
● Lactase - breaks bond between galactose and glucose

5. How are Sugars Digested?

6. From the Mouth to the Stomach
● Sugars enter the oral cavity where mastication begins the process of mechanical digestion by breaking sugars in smaller and smaller pieces
● Salivary glands secrete saliva that contains the enzyme salivary amylase which begin the chemical digestion of sugars
Salivary Amylase (α-amylase):
● Begins the digestion of starch into maltose by cleaving alpha-1,4-glycosidic bonds
● It requires Cl- for activation
● Optimum pH 6.7 (range 6.6 to 6.8)
● The action of this enzyme stops in the stomach when the pH falls to 2
● Sugars travel to the esophagus which transports them to the stomach
● No enzymes in stomach to break glycosidic bonds
● Hydrochloric Acid (HCL) in the stomach sterilizes food to prevent harmful bacteria from entering the GI tract

7. From the Stomach to the Small Intestine
● Sugars leave the stomach through the pyloric sphincter and enter the duodenum.
● Pancreas secretes pancreatic juice which contains enzyme pancreatic amylase into the duodenum
Pancreatic Amylase
● Further hydrolyzes starch into maltose
● Requires Cl- for activation
● Optimum pH 7.1
● Sugars enter the small intestine where enterocytes (cells that line the lumen of the small intestine which contain microvilli) also known as the brush border secrete brush border enzymes collectively known as disaccharidases.
● Disaccharidases hydrolyze disaccharides such as maltose, sucrose, and lactose into the monosaccharides glucose, galactose, and fructose

8. Absorption of Sugars Two mechanisms: Transport Proteins:
● Active Transport
● Facilitated Diffusion
Transport Proteins:
● SGLT - Na+ Dependent
● GLUT - Na+ Independent

9. Active Transport ● Transports glucose and galactose
● Na+ dependent transporter (SGLT-1)
● Type of Co-Transport.
● Has two binding sites - one for Na+ and one for glucose/galactose
● Na+ binds, changes the transporting protein so that glucose/galactose can bind
● Na+ diffuses down its concentration gradient and pulls glucose/galactose along with it
Na+ K+ ATPase always working to create concentration gradient of Na+
SGLT-1 in intestinal cells
SGLT-2 in renal tubular cells. Used for reabsorption of glucose by kidneys. (wont discuss this)

10. Facilitated Diffusion
● Involved in transporting fructose into the cell and transporting glucose, fructose and galactose
out of the cell
● Na+ Independent Transporter (GLUT)
● No energy involved
● GLUT5 present in the luminal surface
● GLUT2 present in serosal surface of
intestinal epithelial cells
● GLUT5 transports fructose into the cell
● GLUT2 transports fructose, glucose, and
galactose out of the cell

11. Monosaccharides and the Blood
Consuming carbohydrates raises blood glucose levels, which triggers the pancreas to release insulin and glucagon into the blood. Insulin is the signal for the body to absorb glucose from the blood. Glucagon is the peptide hormone produced by 𝛂 cells in the pancreas. Insulin and glucagon are the hormones that help your body maintain your body’s ideal blood glucose levels.
The liver has a special job when it comes to glucose. When levels of glucose (and consequently insulin) are high in the blood, the liver responds to the insulin by absorbing glucose. It packages the sugar into bundles called glycogen. These glucose granules fill up liver cells, so the liver is like a warehouse for excess glucose.

12. Monosaccharides and the Liver
● After monosaccharides are absorbed into the blood, they go to the liver via the hepatic portal vein
● The liver performs different processes for each monosaccharide
● Fructolysis
● Glycogenesis
● Glycogenolysis
● Gluconeogenesis

13. Glycogenesis Enzymes ● Hexokinase ● Phosphoglucomutase
● UDP-glucose pyrophosphorylase
*slide looks simple, explanation takes longer. Same goes for the following two slides.

14. Glycogenolysis Enzymes -transferase -alpha 1-4 glycosidase
● Glycogen debranching enzyme
-transferase
-alpha 1-6 glycosidase
● Glycogen phosphorylase
-alpha 1-4 glycosidase
● Phosphoglucomutase
● Glucose-6-phosphate

15. Gluconeogenesis Exceptions: ● Very similar to Glycolysis
● Pyruvate to phosphoenolpyruvate
● Fructose 1,6 phosphate to Fructose-6-phosphate
● glucose-6-phosphate to glucose

16. Fructolysis
*Metabolized exclusively in the liver
*Fructokinase

17. Fatty Acid Synthesis
● Acetyl CoA cannot exit mitochondria

18. Amino Acid Synthesis
*Non-essential amino acids can be synthesized from intermediates of the Kreb’s Cycle.
Alpha-ketoglutarate
Glutamate Dehydrogenase
Glutamate
Alanine Aminotransferase
Pyruvate
Alanine
Aspartate Aminotransferase
Oxaloacetate
Aspartate

19. Vitamins What are Vitamins?
Micronutrients (not Macronutrients such as Sugars, Proteins, Lipids.)
Essential & organic compounds that act as coenzymes or have other specific functions
Two categories:
Fat-soluble: vitamins A, D, E, and K
Water-soluble: vitamins B1, B2, B3, B5, B6, B7, B6, B12, and C

21. Energy Consumption & Metabolism
calorie - unit of energy, the amount needed to raise 1g of H2O by 1॰C
Kilocalorie - (1000 calories) dietary “Calories”
1 gram of sugar is 4 kilocalories.

22. Body Metabolism: BMR
Basal Metabolic Rate - the amount of energy expended while the body is at normal rest (not digesting food or exercising).
Calculated using height, weight, gender, & age (decreases with age)
For example:
6’1” 190lb male: kcal/day
5’5” 125lb female: 1380 kcal/day
BMR is 60% of the average human caloric expenditure
Physical activity is 30%, digestion/ heat production is 10%
** Do we want to put briefly what BMI (VS BMR) is on this slide or keep the following slide?

23. Body Metabolism: BMI Body Mass Index (BMI)
May not be accurate for individuals who are disproportionately:
Shorter, taller, muscular
Obesity increases risk of:
diabetes mellitus

24. Diabetes Mellitus ↓ Insulin:
↓ Glycogenesis (conversion of blood glucose to liver glycogen)
↑ Glucagon:
↑ Glycogenolysis (conversion of liver glycogen to blood glucose)
↑ Gluconeogenesis (conversion of AA’s or lactic acid to glucose)

25. Digestion of Sugars THE END