Carbohydrates 4 Flashcards
What are some tissues that completely rely on glycolysis for their energy?
Brain
Nervous system
RBCs
Testes
Embryonic tissue
What happens if we have no more carboyhydrates but need more glucose?
It can be generated from non-carbohydrate molecules in the liver
Why is gluconeogensis not the direct reverse of glycolysis?
Due to the 3 irreversible steps (steps 1, 3 and 10)
What is gluconeogensis?
The generation of glucose from non-carbohydrate substances
How many reactions are used to bypass the irreversible steps of glycolysis?
4
What does the bypassing of the irreversible steps of glycolysis allow?
Gluconeogenesis and glycolysis to be regulated seperately
What irreversible reaction does A and B of gluconeogenesis deal with?
PEP to glycolysis
What is step A?
The conversion of pyruvate to oxaloacetate
What is step B?
The conversion of oxaloacetate to PEP
What do reactions A and B look like?
What step of glycolysis does reaction C bypass?
F-6-P to F-1,6-bisP
What does reaction C look like?
Why is reaction C not the direct reverse of F-6-P to F-1,6-bisP?
It would require the transfer of a phosphyl group which is energetically unfavourable
What step of glycolysis does reaction D bypass?
Glucose to G-6-P
What does reaction D look like?
Where is G-6-P converted to glucose?
In the lumen of the endoplasmic reticulum
What does the conversion of G-6-P to glucose in the ER require?
G-6-P to be shuttled into the ER and glucose to be shuttled out, an inorganic phosphate is also shuttled out
What does this pump controlling the conversion of G-6-P to glucose look like?
How many points can galactose and fructose enter glycolysis?
Several
What is fructose converted into to enter glycolysis?
Glucose-6-phosphate
What is fructose converted into in adipose tissue to enter glycolysis?
Fructose-6-phosphate
What is fructose in the liver converted into to enter glycolysis?
Glyceraldehyde-3-P (GAP) or dihudroxyacetone-P (DHAP)
Where is most fructose metabolised?
Liver
What pathway does fuctose use to become DHAP or GAP in the liver?
Fructose-1-phosphate
How much ATP does the conversion of fructose to DHAP or GAP use?
1 or 2
What does the conversion of fructose to DHAP or GAP look like?
What is galactose converted to G-1-P through?
UDP-galactose
What are the steps of galactose becoming glucose-6-phosphate to enter glycolysis?
- Galactose comes in and is phosphorylated
- UDP glucose transfers UDP molecule to galactose
- Captures electrons by producing NADH
What does the pentose phosphate pathway produce?
NADPH and pentoses (5C) sugars
Where and what is NADPH used for?
Liver (fatty acid synthesis)
Mammary gland (fatty acid synthesis)
Adrenal cortex (steroid synthesis)
RBC (antioxidant)
What are pentoses precursers for?
ATP
RNA
DNA
What are the two stages of the pentose phosphate pathway?
Oxidation (irreversible)
Non oxidation (reversible)
Is the oxidation stage of the pentose phosphate pathway reversible?
No
Is the non oxidation stage of the pentose phospate pathway reversible?
Yes
What happens during the oxidative stage of the pentose phosphate pathway?
Generates NADPH
Converts G-6-P to a pentose phosphate
What happens during the non oxidative stage of the pentose phosphate pathway?
Forms lots of different 3, 4, 5, 6 and 7 carbon sugars
What does the pentose phosphate pathway look like?
What does NADPH link?
Anabolic and catabolic pathways
Are NAD+ and NADP+ the same?
They are both electron carriers but they are not the same
What are NAD+ and NADP+?
Electron carriers
What is NAD+ used for?
Metabolism of sugars in glycolysis and the citric acid cycle
What is NADP+ used for?
Anabolism to make things like fatty acid
What does breaking down ethanol require?
NAD+
What does the breakdown of ethanol look like?
Why does breaking down lots of ethanol inhibit gluconeogenesis?
Low NAD+ to facilitate the reaction as most has bean used to breakdown ethanol
What does a low level of NAD+ lead to?
Lacticacidaemia (increase[blood lactate])
Hypoglycaemia (decreased [blood glucose])
What is black water fever?
A difficiency of G-6-P dehydrogenase
What does black water fever cause?
Low RBC NADPH levels
Build up of free radicals and H2O2 which damages cells
