WEEK 8: 8.5 Flashcards
(25 cards)
digestion is accomplished by ?
hydrolysis
what is hydrolysis?
a chemical process where a molecule is cleaved by addition of water
lactase is converted into glucose and galactose via
hydrolysis
triglycerides are converted into monoglycerides and free fatty acids by?
hydrolysis
What carbohydrates are ingested?
starch, fibre/cellulose and disaccharides
what does salivary amylase do to ingested carbs?
create disacchridies (maltose) and ogliosacchirides
what occurs to these disacchrirides
brush border uses membrane bound enzymes sucrase, lactase and isomaltase and gluco-amylase to create glucose, glucose and galactose and glucose and fructose
How does absorption of monosaccharides occur?
SGLT1 (secondary active transport)
How are lipids digested?
- ingested trigly arrive in intestine as a large fat droplet
- bile salts and motility emulsify these fat droplets into smaller droplets, making them more accessible to enzymes
- pancreatic lipase, a digestive enzyme, converts trigly into monoglyceride and Free fatty acid
- co-lipase, a protein, anchors lipase to fat droplet surface so it can work effectively
- monogly and FFA combine with bile salt to form micelles
- micelles carry lipid to the surface of intestinal cells (enterocytes) for absorption
What is a micelle?
it’s water loving carrier vesicle that is formed by bile salts, lecithin and cholesterol
how are lipids absorbed?
It is a passive process, once the micelle releases contents at the cell membrane, these are resynthesised to triglycerides + coating apolipoproteins to form water soluble chylomicrons (type of lipoprotein)
these are then exocytosed and absorbed into the lymph
Describe the process of protein digestion
Pepsin breaks down a protein into a polypeptide
Pancreatic proteolytic enzymes break down polypeptide into peptides
Enzymes in the brush border, including aminopeptidases and intracellular peptidases create amino acids
How are these amino acids further digested?
they enter the cell by sodium and energy dependent symporters
Di and tripeptides enter by H+, Na+ and tertiary active transport
these di and tri peptides are broken down into amino acids within the cell
they exit the cell via facilitated diffusion and diffuse into the capillary
How is glucose and galactose transported into the cell?
Using an SGLT1 symport carrier that uses the sodium concentration gradient to move sodium/glucose/galactose into the cell
How does fructose enter the cell?
facilitated diffusion through GLUT5
What is the key enzyme that starts fructose metabolism?
ketohexokinase (Khk)
Once phosphorylated, what is fructose converted into?
glucose, glycerate and organic acids
What happens if fructose is oversaturated in the small intestine > 1g/kg of one’s body weight?
extra fructose escapes into the large intestine (bacteria ferments it into short-chain fatty acids) and liver (converted to fat), and can contribute to metabolic diseases if sustained long-term
what is the name for conversion of glucose into glycogen?
glycogenesis
Where is glucose stored?
In the liver
What is the process of glucose entering the cell?
- insulin binds to receptor
- signal transduction cascade
- exocytosis
- glucose enters the cell via GLUT 4
What happens to chylomicrons once they enter circulation?
lipoprotein lipase binds chylomicrons and cleaves trigly to fatty acids and glycerol
in adipose cells, they are recombined to trigly for storage
in muscle cells they are stored/oxidised to acetyl-CoA
remnants of chylomicrons are captured by liver, endocytosed and regraded
How are lipids transported in aqueous plasma?
nonpolar lipids like triglycerides/cholesteryl esters are associated with amphipathic lipids like phospholipids and proteins to water-liking lipoproteins
