[2] Class 7: Glycolysis And Gluconeogenesis Flashcards
3 components to monosaccharide:
- Carbon number
- Functional group
- Stereoisomer form
Only 5 carbon sugar to know:
D-ribose
3 carbon sugars to know:
Dihydroxyacetone
D-glyceraldehyde
6 carbon ketose sugar?
D-fructose
Major component of DNA
Deoxyaldose
Theyre components of glycoproteins and glycolipids: cell signaling and adhesion
Acetylated amino sugars
Glycosaminoglycans and proteoglycans. Present in cell membrane and ECM
Acidic sugars
Constituted the gangliosides in oligodendrocyte of the NS
Sugar esters
Food additives, gains importance in uncontrolled diabetes leading to cataracts and peripheral neuropathy, used in synthesis of lipids
Sorbitol, mannitol
Sugar alcohols
Ex of sugar alcohols:
Sorbitol, mannitol, and xylitol
Sugar alcohols that can be converted to fructose and metabolized normally, their slow metabolism is what helps reduce calories and weight gain.
Sorbitol, mannitol, and xylitol
Non-sugar based artificial sweeteners trick the receptors on tongue and aren’t metabolized like sugar. How does this effect endocrine?
Disrupts insulin signaling
Giving a phosphate generally…
Activates
Disaccharide
2 monosaccharides glycosidic linkage
Starch amylose
Polysaccharide of glu residues w/ alpha-1,4 glycosidic bonds
Amylopectin
Amylose w/ addition of alpha-1,6 glycosidic branch points
A major plant polysaccharide
Unbranded polymer of glucose residues joined by beta-1,4 linkages, allowing to form very long and straight chains
Dietary fiber
Cellulose
Metabolizes one molecule of glucose to 2 molecules of pyruvate w/ 2 net ATP
Glycolysis
Glycolysis and oxygen
Anaerobic
Glucose is the only fuel that: 2 things…
The brain uses under nonstarvation conditions and the only fuel that red blood cells can use at all.
How can pyruvate and lactate be salvaged?
By being resynthesized to glucose in gluconeogenesis
Sources of glucose in diet:
Starch, glycogen, disaccharides (esp. sucrose and lactose)
Complete oxidation efficiency > …
Anaerobic glycolysis
The only insulin dependent glucose uptake GLUT4
In skeletal, muscle, heart, adipose
Why would GLUT 2 [main transporter for liver] have a low affinity for glucose uptake:
The liver doesnt want to store glu. It wants to maintain it throughout body.
Ubiquitous but high in RBC’s and brain
High affinity for glucose
GLUT1
The main glucose transporter in neurons
GLUT3
How many stages to glycolysis?
3;
1st is 6 carbons-investment
2nd: is converting into 3 carbons and conversion of DHAP to G3P
3rd: converting to pyruvate- gaining ATP
Traps glucose in the cell
Hexokinase
Which stage in glycolysis, the conversion of glucose to fructose 1,6-bisphosphate
Stage 1
Strategy to stage 1 glycolysis:
Traps the glucose in cell, for a A compound that can be readily cleaved into 2 phosphorylated 3- carbon units
What enzyme does liver use to convert glucose into glu-6-P?
Glucokinase
What are the 2 steps involving energy investment in stage 1 glycolysis?
Glucose->G6P by hexokinase/glucokinase
F6P-> F1,6BP by phosphofructokinase
What regulates hexokinase?
Negative feedback inhibition by product- G6P
Regulation of glucokinase:
Stimulated by glucose, F-1P, and insulin
Inhibited by glucagon and F6P
Regulation of phosphofructokinase
Stimulated by AMP and F2,6-BP
Inhibited by ATP and Citrate
Which stage of glycolysis?
Fructose 1,6-BP into 2 3-C fragments by Aldolase reaction
And isomerase
Products are readily interconvertible
Stage 2
What conditions represent high energy? (3)
High ATP
High NAD+
Low NADH
When there’s high energy which of the products of stage 2, DHAP and GAP (G3P) is favored?
DHAP is favored under high energy conditions b/c it is converted to glycerol 3 phosphate- that way it can form triacylglycerols -FAT
What percentage of f1,6BP becomes GAP, usually?
Usually, 99% becomes GAP to continue glycolysis….in the event of high energy conditions the reaction will regress to DHAP for fat storage
Glyceraldehyde 3-P creates:
NADH (x2) that will be used in oxidative phosphorylation
1,3-BPG is converted to 3-PG by
Phosphoglycertae kinase and this forms the first ATP (x2) of glycolysis
2-PG is converted to_______ by:
Phosphoenolpyruvate by dehydration rxn by enolase
Phosphate is removed from phosphoenolpyruvate by:_________ creating:
Pyruvate kinase;
Pyruvate (x2)
Pyruvate is what type of molecular structure?
Stable ketone
3 irreversible steps of glycolysis:
1- glu-G6P
3-F6P-F1,6BP
10-PEP- Pyruvate
Regulation of pyruvate kinase:
Stimulated by insulin and Fructose 1,6-BP
Inhibited by Alanine, ATP, and glucagon
After glycolysis, aerobic:
Anaerobic?
Pyruvate to TCA;
Pyruvate to lactate–then, hopefully cori cycle…
Disaccharide of glucose and fructose makes=
Sucrose
Disaccharide composed of glucose and galactose =
Lactose
Fructose and galactose are converted to:
Glycolysis intermediates
In times of high energy, fructose quickly turns to:
FAT
Why would fructose quickly turn to fat in times of high energy?
Remember that GAP is readily interconvertible w/ DHAP, and although GAP is formed 99% of the time…this isn’t the truth when there is high energy conditions b/c the GAP is converted to DHAP which becomes triacylglycerols- it is the backbone of fat.
3 regulated steps in glycolysis for ATP need
Hexokinase
PFK
Pyruvate kinase
Main organ in glucose regulation
Liver
NO hexokinase in liver: it is glucokinase….how is this regulated?
Glucose is permanently trapped in liver cell.
It is not inhibited by G3P (product of glucokinase)
What type of regulation is used for pyruvate kinase:
Allosteric effectors and covalent modification
Pyruvate kinase is more ________ when phosphoirylated
Inactive- under conditions of low BG
Pyruvate kinase is more ________ when dephosphorylated
ACTIVE - under conditions of high BG
Glucokinase has a ____ Km
High
= low affinity
Hexokinase Km is significantly ________ than glucokinase
Lower
Fates of pyruvate
Lactate
TCA
-other micoorganisms can convert pyruvate to ethanol
What must occur before pyruvate can enter TCA cycle?
Pyruvate must undergo oxidative carboxylation to form acetyl CoA
Pyruvate can be reduced to lactate w/ the regeneration of:
NAD+
Precursor for pentose phosphate pathway
glucose-6-phosphate
Which organ(s)depends on glucose as primary fuel or only fuel
Brain and
RBCs- only use glucose
Brains daily glucose req’ment amt.:
Whole body req’ment:
120 g
160g
Glucose always has ____ g in body fluids, but there’s about _____g available from glycogen
20 g;
190 g
How long would glucose reserves last a person?
About a day or so.
What bodily process is important during a long period of fasting or starvation?
Gluconeogenesis
Synthesis of glucose from noncarbohydrate precursors
Major precursors are lactate, AA’s, and glycerol (but not FA’s)
Pathways convert pyruvate to glucose
Pathway is not a reversal of glycolysis
Gluconeogenesis
Enzymes of irreversible reactions in the liver:
Glucokinase
Phosphofructokinase
Pyruvate kinase
What are the 4 enzymes used in gluconeogenesis to ‘bypass’ irreversible steps of glycolysis:
Pyruvate carboxylase (pyruvate->OAA)
Phosphoenolpyruvate carboxykinase (OAA->PEP)
Fructose-1,6-BPtase (F-1,6-BP->F-6-P)
Glucose-6-phosphatase (G-6-P->glu)
Regulation of pyruvate kinase:
Stimulated by insulin and F-1,6-BP
Inhibited by alanine, ATP, and glucagon
Stimulation of glucose-6-phosphatase
Stimulated by cortisol
Regulation of fructose-1,6-BPtase:
Stimulated by citrate and cortisol
Inhibited by AMP and F-2,6-BP
Regulation of PEP carboxylase
Stimulated by cortisol, glucagon, thyroxine
Regulation of pyruvate carboxylase
Stimulated by acetyl CoA and cortisol
Inhibited by ADP
First step of gluconeogenesis:
Pyruvate is converted to OAA
Source of OAA in gluconeogenesis:
How about pyruvate:
Some AA’s source of OAA and pyruvate
Lactate also is a source of pyruvate
Generation of free glucose
For glucose to leave the liver the phosphate must be removed from glucose-6-phosphate
Which reaction? Enzyme?
G-3-P to glucose
Glucose 6-phosphatase
Where is glucose-6-phosphatase located?
In the lumen of the endoplasmic reticulum
G3P is transported to the ER by
A specific protein (T1) and another protein (T2) then transports glucose back to the cytoplasm
Glycolysis __________ ATP;
Gluconeogenesis __________ ATP
Generates;
Consumes
What is the best way to determine which pathway will be most active btw glycolysis and gluconeogenesis:
Energy charge (ATP/ADP ratio)
Gluconeogenesis and glycolysis are _____________ regulated
Reciprocally
Lactate produced in skeletal muscle and RBC’s can be converted back to pyruvate in the liver
Cori cycle
What is the benefit of the cori cycle?
Since lactate is able to be converted back to pyruvate, the pyruvate can be used in gluconeogenesis to form glucose in times of low energy.
