Chapter 14 Flashcards
(15 cards)
Breakdown of carbohydrates
- salivary amylase breaks carbs into polysaccharides, dextrins, sucrose, lactose, and maltose
- in the small intestine, pancreatic amylase breaks those down into monosaccharides: glucose, galactose, and fructose
- active transport
- in the intestinal lining, monosaccharides are absorbed in the bloodstream
Small intestine enzymes involved
Alpha-glucosidase: digests maltotriose and any bigger oligosaccharides
Alpha-dextrinase: digests limit dextrin
Sucrase: digests sucrose to glucose and fructose
Lactase: digests lactose to glucose and galactose
Maltase: cleaves maltose into two glucose molecules
GLUT1 and GLUT3
All mammalian cells
Basal glucose uptake
KM lower than normal serum glucose concentration
Constant rate of transport
GLUT2
Liver and pancreatic b cells
Very high KM for glucose
Glucose enters only when lots of glucose is present (after meals)
Signals pancreas to produce insulin
GLUT4
Muscle and fat cells
Number of GLUT molecules increases when insulin is present
Increases uptake in these cells
Glycolytic pathway
Common in all cells, prokaryotic and eukaryotic Three stages (10 reactions)
Stage 1: glucose converted to fructose 1,6-bisphosphate
Stage 2: cleavage of fructose 1,6-bisphosphate to two three-carbon fragments
Stage 3: three-carbon fragments oxidized to pyruvate, ATP harvested
Fates of Pyruvate
can be used in fermentation to ethanol in yeast
can be converted to 2 Acetyl Co-A in the citric acid cycle
can be used in fermentation to lactate in contracting muscles
Under anaerobic conditions, animals reduce pyruvate to lactate
During strenuous exercise, lactate builds up in the muscle
The acidification of muscle prevents its continuous strenuous work
The lactate can be transported to liver and converted to glucose there
Under anaerobic conditions, yeast ferments glucose to ethanol
Both steps require cofactors:
Mg++ and thiamine pyrophosphate in pyruvate decarboxylase
Zn++ and NAD+ in alcohol dehydrogenase
Free energy changes and the glycolytic pathway
- the control steps are not in equil and involve ATP
- they have a high and negative free energy so they are essentially irreversible under standard conditions
The glycolytic pathway and cancer
- glycolysis is upregulated in cancer cells and they are able to proliferate using glycolysis
- excess glycogen appears pink in scans so tumors can be viewed that way
The glycolytic pathway and diabetes
-glucose can’t be used so fatty acids are used as an alternative fuel source
Gluconeogenesis precursors
Major precursors are lactate, amino acids, glycerol:
Lactate formed by muscles during strenuous exercise
Amino acids come from dietary protein (common) or skeletal muscle (starvation)
Glycerol comes from triacylglycerols in fat cells
(converted to DHAP)
Gluconeogenesis is not just the reverse of glycolysis
Some of the glycolytic reactions are irreversible using a common enzyme
Gluconeogenesis bypasses these reactions:
Pyruvate kinase
PFK
Hexokinase
Pentose Phosphate Pathway (PPP)
The main goal is to produce NADPH for anabolic reactions and ribose 5-phosphate for nucleotides
Reduced glutathione is a powerful antioxidant
