Carb metab Flashcards
What are aldoses
Monosaccharide with aldehyde group at C-1
What are ketoses
Monosaccharide with ketone group at C-2
What is a monosaccharide
Basic sugar unit, e.g. glucose, galactose, fructose
What is a disaccharide
2 mono units linked via glycosidic bond (lactose and sucrose)
What is an oligosaccharide?
3-10 mono units
What is a polysaccharide?
Multiple mono units (starch)
What is alpha-amylase and where is it found
Random hydrolyses alpha-1,4 glycosidic bonds, except those that act as branch points (near alpha-1,6 linkage)
Found in saliva and pancreatic juice
What is sucrase-isomaltase complex?
- Sucrase hydrolyses sucrose to form glucose and fructose
- Maltase hydrolyses maltotriose and maltose
- Isomaltase hydrolyses alpha-1,6 linkages
What is glucoamylase complex
Hydrolyses alpha-1,4 glycosyl units, starting from the non-reducing end of chains
How is sucrose digested
Hydrolysis of sucrose into glucose and fructose by sucrase
How is lactose digested
Hydrolysis by lactase.
What are the effects of lactase deficiency
No lactose absorption in lower intestine, bacterial fermentation of lactose producing lactic acid and gases, lactose and lactic acid is osmotically active, draws water into the lumen resulting in diarrhoea
Describe the absorption of glucose and fructose in intestines.
SGLT1 (active transport):
- Na+ dependent cotransporter, works with Na+/K+ ATPase pump
- energy from Na+ ionic conc gradient, secondary active transport
- actively transports glucose and galactose into epithelial cells
GLUT 5:
Tansports fructose via facilitated diffusion- passive transport
Monosaccharides exit epithelial cells into bloodstream via GLUT2 (facilitated diffusion, passive)
Describe the transport of glucose in the liver and pancreatic beta cells
GLUT 2, low affinity transporter
in pancreas: regulate the secretion of insulin
in liver, remove excess glucose in the blood
Describe the transport of glucose in the brain and nerve tissues
GLUT3: high affinity transporter
Allows for basal glucose uptake
Describe the transport of glucose in the heart and skeletal muscles
GLUT 4, regulated by insulin, high affinity transporter-> in the presence of insulin, increase in translocation of GLUT4 to the cell surface
What is the glycaemic index
Describes blood glucose response after consumption of a carbs containing test food relative to a carbs containing reference food
High GI food-> blood glucose level increases rapidly after consumption
How does oral rehydration therapy function
ORS solution contains glucose, sodium chloride, potassium chloride and trisodium citrate
Solution retains fluid and salts within body via osmotic pressure, prevent excretion, replace lost fluid and salts
SGLT 1 cotransports glucose and sodium into epithelial cells, so when glucose is absorbed in the intestines, water and sodium is absorbed as well
What is the purpose of glycolysis in catabolism
Occurs when ATP is required, even in the absence of O2
Only source of ATP for cells without mitochondria (e.g. RBC)
Describe the action and regulation of hexokinase
Forms G6P from glucose using 1 ATP and giving 1 ADP
Inhibited by product, G6P
What is the difference between hexokinase and glucokinase
Glucokinase is a type of hexokinase only found in liver cells and beta pancreatic cells, has a higher Km value and thus lower affinity to glucose.
Glucokinase only functional at high glucose levels, to slow down glycolysis in the liver, as glucose is used for glycogenesis to generate glycogen
Describe the action and regulation of phosphofructokinase-1
Reacts with F-6-P to form F-1,6-biphosphate
Uses 1 ATP and gives 1 ADP
Positive regulation
- AMP
- F26BP
Negative regulation
- ATP
- Citrate
Describe the action and regulation of glyceraldehyde 3-P dehydrogenase
Glyceraldehyde 3-phosphate—-> 1,3-Bisphosphoglycerate
Using 1 NAD-> NADH+H+ and 1 Pi
Describe the action and regulation of phosphoglycerate kinase
SUBSTRATE LEVEL PHOSPHORYLATION
Using 1 ADP to give 1 ATP
1,3-bisphosphglycerate-> 3-phosphoglycerate