Lectures 9-10 - Glucose metabolism Flashcards
How are carbs digested in humans? 4 steps (hint: where, what into what? by what?)
- Mouth: dietary carbs to polysacs, sucrose, lactose, maltose by salivary amylases
- Stomach: no digestion of carbs because low pH inactivates low pH
- Pancreas: polysacs, sucrose, lactose, maltose into monosacs (glucose, galactose, fructose) by pancreatic amylase
- Small intestin: absorption of monosacs into bloodstream through active transport
why is glucose an excellent fuel? (3)
- yields good amount of energy
- can be efficiently stored
- many tissues can meet energy needs on glucose only
glucose is a precursor to 4 things?
- all the amino acids
- membrane lipids/Fatty acids
- nucleotides in DNA and RNA
- cofactors in metabolism
Glucose can have 4 purposes/fates
- storage by converting to glycogen, starch, sucrose
- oxidation via glycolysis by converting to pyruvate –> energy
- oxidation via pentose phosphate pathway by converting to ribose 5-phosphate –> nucleic acid synthesis
- synthesis of structural polymers by converting to extracellular matrix and cell wall polysaccharides
What is glycolysis? in terms of glucose transformation
glucose is degraded to 2 pyruvates
What is gluconeogenesis? in terms of glucose transformation
glucose is formed from non-carbohydrate sources
What is glycogenesis? in terms of glycogen transformation
glycogen polymerized from glucose units
What is glycogenolysis? in terms of glycogen transformation
glycogen is degraded to glucose units
what is fermentation?
anaerobic degradation of glucose to obtain energy conserved as ATP
kinases are enzymes that?
transfer phosphate groups btw ATP and various substrates
mutases catalyze what?
migration of functional groups
which mammalian tissues/cell types has glycolysis as sole source of metabolic energy? (4)
- erythrocytes
- brain
- sperm
- renal medulla
free energy released in glycolysis is conserved as (2)
ATP and NADH
glycolysis is evolutionarily conserved. what does it mean?
almost same in all species
- differs among species in details of regulation of glycolysis and fate of pyruvate formed
how many ATP consumed/produced in prep phase/payoff phase of glycolysis? net?
- prep phase: use 2 ATPs
- pay-off: produce 4 ATPs
- Net: gain 2 ATP
Step 1 of glycolysis
- what to what?
- type of reaction?
- enzyme? types?
- goal (2)
- reversible?
- uses ATP?
- glucose –> glucose 6-phosphate
- phosphorylation
- hexokinase –> 4 isoforms
- traps glucose inside cell –> lowers intracellular unphosphorylated glucose to allow further uptake
- irreversible
- yes! and Mg2+
Step 2 of glycolysis
- what to what?
- type of reaction?
- enzyme?
- goal (2)
- reversible?
- uses ATP?
- glucose 6 phosphate to fructose 6 phosphate
- isomerization
- phosphohexose isomerase
- Makes next steps easier: C1 of fructose easier to phosphorylate by PFK + allows for symmetrical cleavage by aldolase
- reversible
- no!
Step 3 of glycolysis
- what to what?
- what type of reaction?
- enzyme?
- goal
- reversible?
- uses ATP?
- fructose 6-phosphate to fructose 1,6-bisphosphate
- 2nd priming phosphorylation
- phosphofructokinase-1 (PFK-1)
- generates a symmetric 6 carbon molecule
- irreversible
- yes!
What is the first committed step of glycolysis
step 3: 2nd priming phosphorylation –> formation of fructose 1,6-bisphosphate
Step 4 of glycolysis
- what to what?
- what type of reaction?
- enzyme?
- goal
- reversible?
- uses ATP?
- fructose 1,6-bisphosphate to dihydroxyacetone phosphate (DHAP) AND glyceraldehyde 3-phosphate (GAP)
- aldol cleavage/lysis
- aldolase
- 6C sugar cleaved into two 3-C high energy phosphate sugars
- reversible
- no!
Step 5 of glycolysis
- what to what?
- what type of reaction?
- enzyme?
- goal
- reversible?
- uses ATP?
- dihydroxyacetone phosphate to glyceraldehyde 3-phosphate
- triose phosphate interconversion
- triose phosphate isomerase
- conver DHAP to GAP because only GAP is substrate for next enzyme
- reversible
- no
Step 6 of glycolysis
- what to what?
- what type of reaction?
- enzyme?
- goal
- reversible?
- uses smtg?
- GAP and Pi to 1,3-bisphosphoglycerate
- oxidation of GAP
- glyceraldehyde 3-phosphate dehydrogenase (GAPDH)
- produces first energy-rich molecule –> oxidation of GAP with NAD+ gives NADH
- reversible
- inorganic phosphate and NAD+
Step 7 of glycolysis
- what to what?
- what type of reaction?
- enzyme?
- process
- reversible?
- uses smtg?
- 1,3-bisphosphoglycerate + ADP –> 3 phosphoglycerate + ATP
- substrate level phosphorylation (no oxidation required)
- phosphoglycerate kinase
- 1,3-bisphosphoglycerate donates phosphate group to ADP to make ATP
- reversible
- uses ADP and Mg2+