Energy Production 1 Flashcards
What is the purpose of amylase
Breaks down carbs such as glycogen to dextrins in saliva and pancreatic amylase to monosaccharides in duodenum
Disaccharides attach to what in the GI tract
Brush border of of membrane of epithelial cells
What enzymes breakdown disaccharides
Lactase
Sucrose
Pancreatic amylase
Isomaltase
What are the three types of lactose intolerance
Primary- absence of lactase persistence allele occurring in adults with northwest Europe prevalence
Secondary- damage to small int. gastroenteritis, coeliac, chrohn’s, ulcerative colitis. Affects all ages and reversible
Congenital lactase deficiency- extremely rare autosomal recessive defect in lactase gene. Cannot digest breast milk
What are the symptoms of lactose intolerance
Bloating and cramps, flatulence, diarrhoea, vomiting, rumbling stomach
How are monosaccharides absorbed by the gut epithelia
Active transport by the sodium dependent glucose transporter 1 (SGLT1) then GLUT2 into blood
How is glucose uptaken by cells from the blood
GLUT1 (foetal, erythrocytes, blood brain)
GLUT2 (kidney, liver, beta cells, small int.)
GLUT3 (neurones, placenta)
GLUT4 (adipose, striated musc INSULIN REG)
GLUT5 (sperm intestine)
2 and 4 most important to know
What does the term absolute requirement mean and which cells have one for glucose
Only can metabolise glucose
RBC, Neutrophils, Innermost cells of kidney medulla, Lens of eye (no vessels so no oxygen)
What are the two phases of gylcolysis
Investment (uses 2 ATP) and payback (producing 4 ATP, 2 NADH per glucose). Net gain 2 ATP
What are the features of glycolysis
Central pathway for carb catabolism, occurs in all tissues cytoplasm, is exergonic and oxidative, 6C to 2 3C, pyruvate dehydrogenase produces lactase and regenerates NAD+
What are the main enzymes of glycolysis
Hexokinase (glucokinase in liver) which phosphorylase glucose to glucose-6-P
Phosphofructokinase- key control enzyme
Both irreversible
Pyruvate kinase
Why is glycolysis composed of so many steps
Chemistry easier, efficient energy conservation, versatility (pathways intermediates reverse), control
Why is glucose phosphorylated
Gives -ve charge to prevent backpassage across plasmalemma
Increases reactivity for subsequent steps
Why is step 3 (fructose 6P to fructose 1,6bisP) called the committing step
Like step one is irreversible due to large -ve delta G and commits to glycolysis pathway
Outline phase 2 of glycolysis
Cleavage of 6C to two 3C
Captures reducing power (NAD+ to NADH)
SUBSTRATE LEVEL PHOSPHORYLATION
How many irreversible steps are there in glycolysis
3 due to large -ve delta G. Converting pyruvate to glucose (gluconeogenesis) but bypass these
How many times higher is the rate of glycolysis in cancer and how is it measured
Up to 200 times. Use radiactive modified hexokinase substrate eg FDG) imaged with a PET scan
How is phospofructokinase PFK regulated
Allosterically (muscle)- inhibited by high ATP, stim by high AMP
Hormonal (liver)- inhibited by glucagon, stim by insulin
True or false, hexokinase exhibits product inhibition
True glucose6P inhibits hexokinase but not glucokinase
How else is glycolysis regulated in the body
Product inhibition
Metabolic regulation by NAD concentrations inhibiting step 6
Pyruvate Kinase by high insulin:glucagon ratio.
What are some important intermediates of glycolysis
Dihydroacetone-P which is converted to glycerol phosphate by GLYCEROL 3-PHOSPHATE DEHYDROGENASE for fat sythesis
1-3bisphosphoglycerate which is converted to 2,3-bisphosphoglycerate (2,3BPG) by BISPHOSPHOGLYCERATE MUTASE for regulation of haemoglobin O2 affinity promoting release
What is the purpose of lactate dehydrogenase
To convert pyruvate from glycolysis to lactate to resupply the cell with NAD+ from NADH produced prior
How is lactate metabolised
Sent through blood to the heart or liver where it is converted back to pyruvate for aerobic respiration by the same LDH enzmyme or for gluconeogenesis
Why might plasma lactate increase and outline hyperlactaemia and lactic acidosis
Depends on production rate, utilisation by liver heart muscles and disposal by kidneys
Normal conc in 1mM.
2-5mM is hyperlactaemia no change in blood pH due to buffering capacity
Lactic acidosis above 5 mM as above renal threshold so blood pH lowered
