Nutrient Digestion 1 Flashcards
What are the principle dietary constituents?
Carbohydrates
Protein
Fat
Vitamins
Minerals
Water
What are different classes of carbohydrates?
Monosaccharides
Disaccharides
Polysaccharides
What are monosaccharides?
Hexose sugars (6C)
What are examples of monosaccharides?
Glucose
Galactose
Fructose
Where are monosaccharides absorbed?
Small intestine
What bond connects disaccharides?
Glycosidic bond
What and where are disaccharides broken down into monosaccharides?
By brush border enzymes in the small intestine
Why are all complex carbohydrates broken down into monosaccharides?
Only monosaccharides can be absorbed
What is lactose formed from?
Glucose and galactose
What enzyme breaks lactose down into glucose and galactose?
Lactase
What is sucrose formed from?
Glucose and fructose
What breaks sucrose down into glucose and fructose?
Sucrase
What is maltose formed from?
Glucose and glucose
What breaks maltose down into 2 glucose monomers?
Maltase
What are some examples of polysaccharides?
Starch
Cellulose
Glycogen
What is starch?
Plant storage form of glucose
What are some examples of starch?
a-amylose (glucose linked in straight chains)
Amylopectin (glucose chains highly branched)
What are glucose monomers linked by in starch?
a-1, 4 glycosidic bonds
What are a-1, 4 glycosidic bonds broken down by?
Amylases
What is cellulose?
Constituent of the plant cell wall
Unbranched linear chains of glucose monomers linked by B-1, 4 glycosidic bonds
cannot be broken down naturally and needs bacteria to be broken down (bacteria in large intestine)
What are B-1, 4 glycosidic bonds broken down by?
Cellulase
What is cellulose also known as?
Dietary fibre
Why is cellulose only broken down by bacteria and not enzyme?
Animals do not synthesis cellulase which is required to break down B-1, 4 glycosidic bonds
What is glycogen?
Animal storage form of glucose
How are glucose monomers linked in glycogen?
a-1, 4 glycosidic bonds
Where are maltase, sucrase and lactase found?
Brush border of the small intestine
What increases the surface area of epithelial cells?
Villi for absorption
What are the 2 membranes of epithelial cells?
Apical membrane facing the lumen of the gut
Basal and lateral membranes facing the blood circulation
What is transepithelial transport?
Travelling through both the apical and basal membranes of epithelial cells
What is transport from the lumen to the blood circulation around the cells called?
Paracellular transport
What is transport from the lumen to the blood circulation through the cells called?
Transcellular
Which 2 of the 3 monosaccharides are absorbed by the same mechanism?
Glucose and galactose
What is the process of glucose/galactose absorption?
1) Na/K ATPase found on basolateral membrane which hydrolyses ATP to pump Na out of the cell and Na into the cell created Na concentration gradient allowing SGLT1 to work
2) 1 Na and 1 glucose travel from gut lumen into cell through SGLT1 transporter protein
3) Glucose concentration develops inside cell to leaves down gradient into the circulation through GLUT-2 transport protein
4) Concentration gradient of Na causes water to travel from lumen of gut to blood through leaky membrane between cells
What transport protein does 1 Na and 1 glucose use to travel from gut lumen into cell?
SGLT1 transporter protein
Why does SGLT1 transporter protein need both Na and glucose to bind to transport molecules into the cell?
Both binding causes conformational change that flips the protein, having an extremely high affinity when facing gut lumen and extremely low affinity when facing inside the cell to release the molecules
What allows SGLT1 to work?
The concentration gradient of Na created by Na/K ATPase pumping Na out of the cell and K into the cell
What protein does glucose use to leave the cell to the blood cirulation?
GLUT-2 transport protein
Why does water travel from the gut lumen into the blood circulation during glucose/galactose absorption?
Concentration gradient of Na affects the osmolarity
What is the process of fructose absorption?
1) Fructose travels into the cell from the lumen through the GLUT-5 transport protein
2) Enters the circulation from the cell through the GLUT-2 transport protein
What transport protein does fructose use to enter the cell from the gut lumen?
GLUT-5 transport protein
What transport protein does fructose use to enter the blood circulation from the cell?
GLUT-2 transport protein
Does water travel from the gut lumen to the blood circulation during fructose absorption?
No because fructose transporters do not rely on Na gradient created by Na/K ATPase so osmolarity remains unchanged
What are proteins?
Polymers of amino acids linked together by peptide bonds (between amino and carboxy ends)
What bonds connects the polymers of amino acids to form proteins?
Peptide bond
What do proteins often undergo after being synthesised?
Post-translational modifications
What are examples of post translational modifications?
Addition of CHO making glycoproteins
Addition of lipid making lipoproteins
What are small proteins (3-10 amino acids in length) known as?
Peptides
What enzymes hydrolyse peptide bonds to reduce proteins to amino acids?
Proteases or peptidases (known as peptidases when break down peptides which are small proteins)
What are examples of proteases?
Trypsin and chymotrypsin
What are the different categories of peptidases?
Endopeptidases
Exopeptidases (aminopeptidase and carboxypeptidase)
What do endopeptidases do?
Break bond in the middle of a protein
What do exopeptidases do?
Break bond at the end of a protein
What do aminopeptidases do?
Break bond at the amino terminal of a protein
What do carboxypeptidases do?
Breaks bond at the carboxy terminal of a protein
How many naturally occuring amino acids are they?
20
What can be said about the transporting mechanisms of amino acids?
They all have their unique transporting mechanisms
What is the process of a typical absorption mechanism of a protein?
1) Na/K ATPase pumps Na from cell to circulation and takes in K
2) Due to Na concentration gradient Na and amino acid are transported into th cell by SAAT1 transporter protein
3) Amino acid enters the circulation through a transporter protein down its concentration gradient
4) Water travels from gut lumen into circulation due to Na concentration gradient created by Na/K ATPase
What transporter protein takes in Na and amino acid from the gut lumen into the cell?
SAAT1
Does water travel from the gut lumen to the circulation during protein absorption?
Yes due to Na concentration gradient created by Na/K ATPase
What can be absorbed instead of individual amino acids?
Di and tri-peptides
What is the process of di/tri peptides being absorbed?
1) Di/tripeptide enters the cell from lumen with H ion through PepT1 transporter protein
2) H ion leaves cell back into lumen through NHE3 so Na can enter the cell
3) This H ion entering the lumen acidifies it and creases an acidic layer
4) Na leaves the cell into circulation due to ATPase, whilst K enters the cell from the circulation
5) Di/tripeptide leaves the cell into the circulation through transporter protein
6) Water travels from lumen into circulation due to Na concentration gradient created by Na/K ATPase
What transporter protein does di/tripeptide and H use to enter the cell from the gut lumen?
PepT1
What transporter protein does H use to leave the cell and return to the gut lumen with Na coming in from the lumen?
NHE3 transporter protein
