Download Digestion of Sugars

Digestion of
Sugars
By: Jill Carreon, Paola Lara,
John Lear & Camila Soto
What are Sugars?
● Sugars are a simple Carbohydrates
● 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
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
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
How are Sugars Digested?
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
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
Absorption of Sugars
Two mechanisms:
● Active Transport
● Facilitated Diffusion
Transport Proteins:
● SGLT - Na+ Dependent
● GLUT - Na+ Independent
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+
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
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.
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
Glycogenesis
Enzymes
● Hexokinase
● Phosphoglucomutase
● UDP-glucose
pyrophosphorylase
Glycogenolysis
Enzymes
● Glycogen
debranching
enzyme
-transferase
-alpha 1-6
glycosidase
● Glycogen
phosphorylase
-alpha 1-4
glycosidase
● Phosphoglucomutase
Gluconeogenesis
● Very
similar to Glycolysis
Exceptions:
● Pyruvate to phosphoenolpyruvate
● Fructose 1,6 phosphate to Fructose-6phosphate
● glucose-6-phosphate to glucose
Fructolysis
*Metabolized exclusively in the liver
*Fructokinase
Fatty Acid Synthesis
● Acetyl
CoA cannot exit mitochondria
Amino Acid Synthesis
*Non-essential amino acids can be synthesized from intermediates of the Kreb’s Cycle.
Alpha-ketoglutarate
Pyruvate
Oxaloacetate
Glutamate Dehydrogenase
Alanine Aminotransferase
Aspartate Aminotransferase
Glutamate
Alanine
Aspartate
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
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.
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:
5’5” 125lb female:
1990 kcal/day
1380 kcal/day
BMR is 60% of the average human caloric expenditure
Physical activity is 30%, digestion/ heat production is 10%
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
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)
Digestion of
Sugars
THE END