Chapter 14 - Gycolysis

Biochemistry - Exam 2

glucose

only fuel used by all cells in our body

glycolysis

metabolic pathway where glucose is oxidized to produce energy in the form of ATP

glycolysis importance

• universal pathway

• occurs in cytoplasm

• does NOT required oxygen

glycolysis in anaerobes

only significant source of ATP from CHOs

glycolysis in aerobes

significantly more ATP can be produced from subsequent steps such as Krebs cycle and oxidative phosphorylation

structures of NAD+/NADH and NADP+/NADPH

glycolysis - phase one

preparatory phase

preparatory phase

phase one reactions

glycolysis step one

glucose is phosphorylated at the hydroxyl group on C6 to d-glucose 6-phosphate

• enzyme: hexokinase

glycolysis step two

d-glucose 6-phosphate is converted to d-fructose 6-phosphate

• enzyme: phosphohexose isomerase

glycolysis step three

d-fructose 6-phosphate is phosphorylated at C1 to to yield d-fructose 1,6-bisphosphate

• enzyme: phosphofructose kinase

glycolysis step four

d-fructose 1,6-bisphosphate is split in half to yield two three carbon molecules: dihydroxyacetone phosphate and glyceraldehyde 3-phosphate

• enzyme: aldolase

glycolysis step five

dihydroxyacetone phosphate is isomerized into a second glyceraldehyde 3-phosphate

• enzyme: triose phosphate isomerase

glycolysis - phase two

payoff phase

glycolysis step six

glyceraldehyde 3-phosphate is oxidized and phosphorylated to form 1,3-bisphosphoglycerate

• enzyme: glyceraldehyde 3-phosphate dehydrogenase

glycolysis step seven

1,3-bisphosphoglycerate is converted to 3-phosphoglycerate and generates ATP

• enzyme: phosphoglycerate kinase

glycolysis step eight

3-phosphoglycerate is converted to 2-phosphoglycerate

• enzyme: phosphoglycerate mutase

glycolysis step nine

2-phosphoglycerate in converted into phosphoenolpyruvate and generates H2O

• enzyme: enolase

glycolysis step ten

phosphoenolpyruvate is converted into pyruvate and generates ATP

• enzyme: pyruvate kinase

payoff phase

phase two reactions

hypoxic conditions

pyruvate is fermented into ethanol and carbon dioxide in yeast

hypoxic condition products

ethanol, 2NAD+ and 2ATP

anaerobic conditions

pyruvate is fermented into lactate in vigorously contracting muscles

anaerobic condition products

lactate, 2NAD+ and 2ATP

aerobic conditions

pyruvate is converted into acetyl-CoA and then subsequently processed through the citric acid cycle to produce carbon dioxide and water

aerobic condition products

CO2/H2O, 10NAD+/2FAD+ and 28-30ATP

pyruvate metabolism summary

glycolysis energetics

fat and glucose metabolism in type 1 diabetes

feeder pathways for glycolysis

lactose feeder pathway products

glucose and galactose

• enzyme: B-galactosidase (lactase)

sucrose feeder pathway products

glucose and fructose

• enzyme: invertase (sucrase)

maltose feeder pathway products

two glucose

• enzyme: a-glucosidase (a-amylase)

acetyl-CoA production

gluconeogenesis

synthesis of glucose from non-carbohydrate substrates such as oxcaloacetate and pyruvate

gluconeogenesis

• pathway is identical in all organisms

• in humans, mainly occurs in liver and kidneys

gluconeogenesis pathway

gluconeogenesis: first bypass reaction

very expensive

gluconeogenesis: second bypass reaction

point of control

gluconeogenesis: third bypass reaction

pentose phosphate pathway

pentose phosphate pathway functions

• generate ribose-5-p

• (re) generate NADPH

pentose phosphate pathway defects