Biochemistry II F.RIsV Chapter 3: Gluconeogenesis

Biochemistry II
F.RIsV
Chapter 3: Gluconeogenesis
Why: Some organs need a continuous supply of glucose ( brain, erythrocytes, muscles )
Breakdown of liver glycogen can only supply glucose during short periods of fasting
Need a other biosynthesis of glucose
S.2 With glycerol:
by hydrolysis of Triacyglycerol (TG) in white adipose tissue (WAT)
→ delivered by the blood to the liver
→ in the liver converted to glycerol-3P by glycerol kinase (not in WAT)
→ formation of glyceraldehyde-3P ( creates NADH )
S.3 With amino acids (AA):
Hydrolysis of tissue proteins
→ Glucogenic AA = all except leucine and lysine
S.4 With lactate:
Blood lactate is taken up by the liver and converted back to glucose
→ needs ATP
S.5 Differences between glycolysis and neoglucogenesis
S.11 Glycogen:
– Polymer of glucose synthesized in liver and skeletal muscles if glucose excess
– Branched chain of a-D-glucose
S.12 Glycogenolysis
→ glucose-1P and free glucose
→ glucose-6P by phosphoglucomutase ( uses Ser to exchange P )
→ blood glucose controlled by the liver, G-6P to G
S.18 Regulation of carbohydrates in liver and muscles:
Chapter 4: The pentose phosphate (PP) pathway
Two phases, oxidative and nonoxidative
NADPH regulates the partitionning of G6-P between glycolysis and PP pathway
→ more NADPH = less PP but more glycolysis
S.2 The Oxydative Phase:
Products specialized molecules
→ No energy producted
→ But Ribose 5-phosphate and NADPH
Rate limiting step
irreversible
irreversible
S.6 The nonoxidative phase:
All reversable reactions permit to recycle the pentoseP in hexoseP
Allows the continued production of NADPH
Especially in cell with high needs for NADPH
tk
ta
tk transfers 2C
ta transfers 3C
donors = ketones
acceptors = aldoses
C5 + C5 with tk = C3 + C7
C7 + C3 with ta = C4 + C6
C5 + C4 with tk = C3 + C6
S.7 NADPH:
A high energy molecule using its electrons for reductive biosynthesis
High in liver, adrenal gland ans reproduction organs
Used for synthesis of FA, cholesterol and steroids
Protection against the oxidative stress
Important for cell in contact with O2 such as erythrocytes or cells of the lens and cornea
Reduces glutatione (GSH) which protects cell by destroying hydrogen peroxydes H2O2