Nutrient Digestion Flashcards
What are monosaccharides? Name them.
Hexose sugars (6 carbons) which are broken down from complex carbs and absorbed by the small intestine
Glucose, fructose and galactose
What are disaccharides?
2 monosacs linked via a glycosidic bond
Where are disaccharides broken down?
Broken down into their constituent monosacs by the brush border enzymes in the small intestine
Name the disaccharides, their respective monomers and the enzymes which break them down
Lactose = glucose + galactose (lactase) Sucrose = glucose + fructose (sucrase) Maltose = glucose + glucose (maltase)
List the polysaccharides.
Starch
Cellulose
Glycogen
What is starch?
Plant storage form of glucose
What are the types of starch and what is the differences between them?
Alpha-amylose - glucose linked in straight chains
Amylopectin - glucose chains that are highly branched
What are glucose monomers linked by? What are branches linked by?
Linked by alpha-1,4 glycosidic bonds
Branches are alpha 1,6
What enzyme breaks down starch/polysaccharides into disaccharides?
Alpha-Amylase
2 types - one in saliva and one from the pancreas
What is cellulose?
A plant wall constituent its made of straight glucose chains linked by beta-1,4 glycosidic bonds
How is cellulose digested?
Need cellulase to digest but we do not have this, therefore it is digested by gut bacteria
Explain the structure and use of glycogen.
Glucose linked by alpha-1,4,-glycosidic bonds
Storage of glucose in the liver
What are intestinal villi?
Finger-like folds of columnar epithelium which increase the surface area in the gut
What do villi have on them that increase surface area even more?
Microvilli
How is glucose and galactose absorbed?
Absorbed via SGLT1 (a sodium glucose transport protein) along with Sodium from the lumen
Na+ leaves the cell as K+ enters
Glucose then leaves via GLUT-2 protein into the blood
How is fructose absorbed?
It doesn’t pain with Na+
Enters from lumen with GLUT-5 and leaves using GLUT-2
Explain the membranes of villi.
The epithelial cells that make up villi have two cell membranes:
- Apical at the top
- Basolateral on the sides/base
They are connected by a tight junction which also connects with adjacent villi to form a tight junctional complex
Explain molecule transport across intestinal villi.
Transcellular:
- in the top of the cell and out the bottom
- Since it goes through 2 different membranes it requires at least two transport proteins
Paracellular:
- Transport out the lumen between the villi
What are proteins and peptides?
Polymers of amino acids bound by peptide bonds
Small ones (i.e. 3-10 monomers) are called peptides rather than proteins
How are glycoproteins and lipoproteins etc produced?
Proteins undergo post-translational modification