Week 1.3 - Carbohydrate digestion and absorption Flashcards
Why do we store nutrients as macromolecules?
breakdown of nutrients causes osmotic pressure, and if osmotic pressure is too high, we will lose a lot of water quickly
What form do monosaccharide hexoses come in?
aldoses or ketoses depending on whether they have an aldehyde group or a ketone group
What does the suffix -oses mean?
has many hydroxyl (-OH) groups
What is the most common form glucose is found in?
beta D glucose
What is beta vs alpha glucose?
beta has -OH on top of carbon 1 and alpha has it on bottom
What is D vs L glucose?
D has most -OH groups on right white L has most on left
What are the ketoses and aldoses hexoses?
glucose and galactose are aldoses.
fructose is ketoses.
What are the disaccharides and their constituents?
glu+glu=maltose
glu+fru=sucrose
glu+galac=lactose
How does lactose intolerance cause its symptoms?
no lactase means lactose cant be digested. bacteria begin to work on it, producing gas and irritation. osmotic pressure from lactose causes water to enter lumen from blood.
What is glycogen and where is it found?
main storage of glucose in humans and animals, found in liver and muscle
What is starch and its forms?
storage of glucose in plants.
has alpha glycosidic bonds
can be unbranched or branched - amylose and amylopectin
What is amylase?
enzyme used to breakdown starch and glycogen to glucose. found in saliva. cant break down cellulose.
What can and cant break down cellulose and why?
amylase cant as cellulose has beta glycosidic bonds. amylase only breaks alpha glycosidic bonds. bacteria can break down cellulose for energy, using enzyme called cellulase
What is cellulose?
beta 1-4 glycosidic bonds - unbranched. found in plant cell wall and undigestable by humans.
What is cellulose used for in humans?
dietary fibre to help prevent constipation.
What is the structure of the enterocytes?
- apical membrane with microvilli
- epithelial cells
- baso-lateral membrane
- tight junctions between epithelial cells
What are the mechanisms of transport through the duodenal epithelium?
- trans-cellular through epithelial cell
- paracellular through tight junctions
- Vectoral transport - uses specific carriers
How are specific carriers produced?
- nucleus transcribes DNA to RNA,
- goes to endoplasmic reticulum where mRNA
- produces amino acids, become protein
- golgi apparatus
- vesicle to apical membrane
How does glucose transport through the epithelium of small intestine?
- NaK pump creates gradient
- SGLT1 on apical membrane brings glucose in with 2 Na+ down gradient
- Once in, GLUT2 allows glucose out via secondary active transport
What is the brush-border membrane?
the apical membrane of epithelium with microvilli - resembles brush brittles
Where can GLUT1 be found?
mostly in kidney tubules
Why does Na+ movement direct water movement?
It is one of the most osmotically active molecules, so drags water out with it - lumen to blood.
How do fructose and galactose transport out of the small intestine lumen?
galactose can go through same mechanism as glucose
fructose has different transporters at proximal duodenum - in through GLUT5 and out through GLUT2 (same) passively down conc. gradient
What is different about the fructose enter mechanism?
it is not Na+ dependent. water doesn’t move out with fructose. GLUT5 uses passive absorption
