Metabolism 2 Flashcards
How do you get from starch, or glycogen, to glucose that can be absorbed in the intestine?
Starch or glyc. is digested by salivary amylase into dextrins, and then the dextrins are digested by pancreatic amylase into disaccharides (maltose and isomaltose) and then THOSE are broken down by dissacharidases in the brush border (maltase, etc). You can skip steps if you start out as a mono or disaccharide.
What type of enzyme is salivary alpha amylase and why does that matter?
salivary Alpha-amylase is an endoglycosidase, and that means itmakes cuts in the centre (not the ends) of longer molecules, so it cant produce dissacharides. pancreatic can.
What type of bond does salivary alpha amylase break?
alpha 1-4 bonds.
where are the dissacharides?
in the brush border!
maltase vs isomaltase- what type of bonds are cleaved?
maltase cleaves 1-4, isomaltase cleaves 1-6.
what happens if you lose your brush border?
cant absorb, wasting syndrome
Why do we get gas when eating legumes?
alpha galactosidase (we dont have it) is what cleaves the gal-glu bond (alpha 1-6 linkage) that legumes have/
What happens if a lactose intollerant person eats milk? (metabolically)
Lactase isnt present to break apart glucose and galactose, and so the undigested lactose can cause diarrhea or gas due to water retention(osmotic) and bacteria breaking it down(fermentation).
How are glucose and galactose transported into intestinal cells? How does fructose enter? How are they transported OUT of the cells?Where do they go after leaving the cell?
SGLT1 for gluc and gal, and GLUT5 for fructose (think Five for Fructose). All are transported out by Glut2.After leaving the cell they enter the portal circulation and go to the liver
What are the sugars even used for???? (broadly speaking)
Glucose is stored as glycogen or used freely, and the other sugars can feed into glucose pathways mainly.
How does glucose get into cells? (other than the intestinal wall cells)
The intestine uses SGLT, (requires ATP) but GLUT is used in other cells and works vis facilitated diffusion!!)There are 14 isoforms of GLUT
List what you know about the GLUT isoforms.
GLUT isoforms have differing affinities for glucose, and they are also tissue specific
Where does glycolysis occur? Does it require oxygen? In what situations is it extra important?
Occurs in the cytoplasm, does not require O2, and is extra important for producing O2 without the krebs cycle( when working out (low O2) or in red blood cells (no mitochondria) )
What happens if red blood cells dont have parts of the glycolysis cycle?
Hemolytic anemia!!
What are the two main stages of glycolysis?
First, glucose is is converted into two trioses. two atps are used up. in the second step, the two trioses are converted to pyruvate and 4 atps are produced, as well as two nadh.
Glycolysis is regulated through 3 main steps- what are they?
- Glucose to glucose 6 phosphate, catalyzed by hexokinase or glucokinase.
- fructose 6 phosphate to fructose 1,6bis phosphate (catalyzed by PFK)
- conversion to pyruvate (catalyzed by pyruvate kinase)
important differences between glucokinase and hexokinase:
Km affinity for glucose allosteric control hormonal control substrates purpose
glucokinase is only present in liver and pancreatic beta cells. It has a high km, and a low affinity for glucose. It is not inhibited by glu.6P, and its synthesis is stimulated by insulin to increase phosphorylation.
Hexokinase has a low km, and a high affinity for glucoce but it IS inhibited by gluc6P, and so it can only phosphorylate so much.
What is the first commited step to glycolysis?
the PFK catalyzed step, fructose 6 phosphate to fructose 1,6 bisphosphate. (irreversible phosphorylation)
what is the key enzyme in control of glycolysis?
PFK1
Three things that regulate PFK1.
- ATP, AMP, and citrate.
- Inhibited by hydrogen ions (lactate produciton is involved).
- fructose 2-6 bisphosphate
Three things that regulate PFK1.
- ATP, AMP, and citrate.
- Inhibited by hydrogen ions (lactate produciton is involved).
- fructose 2-6 bisphosphate(important in the liver)
Whats the most important stimulator of PFK1? How does it work? What can it overcome?
fructose 26 bisphosphate. This is produced when insulin levels are high, and PFK2 is upregulated. the fructose 26 bisphosphateis an allosteric activator of PFK. This can overcome the ATP inhibition put on PFK
How is pyruvate kinase regulated? 3 ways
PK is stimulated by fructose 16 bis, and is inhibited by ATP. It is also inhbited by glucagon, which causes the enzyme to be phosphorylated and deactivated.
usually NADH is rapidly removed from the cytoplasm, but what happens when O2 is low?
It accumulates, and youre not getting that NAD+ being produced. but you can have LACTATE made to fix it all.
Lactate production and why the heck it matters
Fortunately, when oxygen is missing, lactate can be made from pyruvate using lactate dehydrogenase. You get NADH + Pyruvate ———> NAD+ + lactate.
Whats the difference in the end products when you go through anaerobic glycolysis?
You dont get that net production of NADH, because it gets cycled back to make ATP. Youre only netting 2 ATP here.
Three things pyruvate can do
- go into the TCA cycle
- get converted to lactate
- get converted to ethanol by bacteria. `
What happens to lactate produced?
Can be used by muscles, or taken up by the liver that converts it back to pyruvate. BUT going from lactate to glucose requires 6 ATPs.
Where does insulin control glycolysis?
insulin can upregulate glucokinase, and also PFK2.
Where does glucagon come in
glucagon inhibits PK, and it also inhibits PFK2.
what enzyme converts pyruvate to lactate
lactate dehydrogenase
when does citrate regulate things
PFK 1 is inhibited by it.
