Glucose is generated by Dietary Carbohydrates
Starch + glycogen: main source of glucose Mainly brocken down by α-amylase (cleaves α 1->4)
2
Glycolysis is an Energy-Conversion Pathway in Many Organisms
3
4
Summary of glycolysis
-> 10 reaction steps -> 1 x C-6 (glucose) converted into 2x C-3 (pyruvate) -> oxidation of glucose -> 2 NADH generated -> 2 ATPs used + 4 ATPs generated -> pay off: 2 ATPs
5
6
Glucose Metabolism Under Aerobic and Anaerobic Conditions
Final Electron-acceptor: Aerobic -> O2
Anaerobic -> Pyruvate
Cytosol
7
Why do we need to produce lactate or ethanol (yeast) anaerobic and not stop at pyruvate?
Gycolysis: Oxidation reaction generates NADH from NAD+
Under anaerobic conditions: reaction from Pyruvate to Lactate or Ethanol -> regenerate NAD+
Under aerobic conditions: regeneration of NAD+ happens in respiratory chain (mitochondria) -> via 2 different shuttles
-> Regeneration of NAD+
Uridine diphosphate galactose Galactose toxic if transferase is missing
8
Regulation of glycolysis in the muscle
ATP inhibits all 3 enzymes Need for ATP (high AMP) activates PFK
-> ATP based regulation
9
Regulation of glycolysis in the liver
Regulation by: -> ATP -> glucose level in blood -> need for building bocks for biosynthesis
10
Regulation of glycolysis in the liver
Proteins responsible for uptake of glucose into the cell -> regulate blood glucose level Uptake of glucose (tranporters) -> metabolism of glucose
11
• Brain and blood cells depend on glucose -> 160g/day (mainly for the brain)
• Glucose in the blood: 20g, as glycogen: 190g
• Starvation > 1day other metabolites for energy!
-> Gluconeogenesis pathway: • Takes place in liver (and kidneys) • Important to maintain blood glucose level
• Major precursors: glycerol, amino acids,
lactic acid
• Specific enzymes in addition to glycolysis (for the irreversible steps in glycosis)
12
Synthesis of glucose from non-carbohydrate precursors: -> gluconeogenesis
Triacylglycerols (Lipids) taken up by diet -> brocken down to fatty acids and glycerol
cannot by converted to glucose
glucose
13
Glycolysis <-> gluconeogenesis
Glycolysis: in the cytosol Gluconeogenesis: major part in cytosol -> 1st step in mitochondria -> shuttle
Reverse reaction of glycolysis thermodynamically not favorable !!!
Biotin: prosthetic group -> carrier for CO2
14
Synthesis of glucose from non-carbohydrate precursors: -> gluconeogenesis
Pyruvate (end product of glycolysis) -> under aerobic conditions -> shuttle into Mitochondria -> converted into acetyl-CoA -> citric acid cycle
Gluconeogenesis -> start with pyruvate in mitochondria 1st Step: convertion to oxaloacetate -> malate/oxaloacetate shuttle glycolysis
15
Synthesis of glucose from non-carbohydrate precursors: -> gluconeogenesis
Free glucose is important control point -> pathway ends mostly with glucose-6-P -> finished just if glucose is needed (in blood) -> advantage of stopping at glucose-6-P -> trapped in the cell (cannot shuttle outside)
Last step of gluconeogenesis: in ER lumen -> glucose shuttled back to cytosol -> leaves cell
16
Synthesis of other saccharides through gluconeogenesis
17
18
Reciprocal regulation of glycolysis & gluconeogenesis
• Pathways not active at same time
• Regulated by products of reaction and precursors (allostery)
• Regulated by hormones: glucagon & insulin, through F-2,6-BP
• Regulated at the transcriptional level of genes
In the liver: aim is to maintain blood glucose level
glucagon insulin
transcription
19
Pathway Integration during a sprint
20
Top Related