Review 8 Flashcards
Metabolism Rate-Limiting Enzymes
- Glycolysis - Phosphofructokinase-1
- Fermentation - Lactate dehydrogenase
- Glycogenesis - Glycogen Synthase
- Glycogenolysis - Glycogen phosphorylase
- Gluconeogenesis - Fructose-1,6-bisphosphatase
- Pentose Phosphate Pathway - Glucose-6-phosphate dehydrogenase
Functions of Hexokinase
- Phosphorylates glucose preventing it from leaving the cell via transporters.
- Glucose 6 phosphate can be stored as glycogen.
Regulation inhibitor of Hexokinase
Glucose-6-phosphate
Regulation Inhibitor of Glucokinase
Insulin
Phosphofructokinase-1 Functions
- Phosphorylates Fructose 6 phosphate
2. Main control point for glycolysis, catalysis the rate-limiting irreversible step.
Phosphofructokinase-1 Inhibitor
- ATP
2. Citrate
Phosphofructokinase-1 Activator
- AMP
- Insulin
- Phosphofructokinase-2 activation even in the presence of sufficient ATP
Glyceraldehyde 3-phosphate dehydrogenase Function
Oxidation and addition of inorganic phosphate to glyceraldehyde-3-phosphate
Glyceraldehyde 3-phosphate dehydrogenase Important stuff
Substrate - Glyceraldehyde-3-phosphate
Products - NADH, 1,3-bisphosphoglycerate
3-Phosphoglycerate kinase
- Transfers phosphate from 1,3 bisphosphoglycerate to ADP producing ATP and 3-phosphoglycerate.
- Not dependent on oxygen
- Reversible
3-Phosphoglycerate kinase Important Stuff
Substrate Phosphorylation: ADP is directly phosphorylated to ATP using high energy intermediate.
Pyruvate Kinase function
- Substrate-level phosphorylation of ADP using the high-energy substrate phosphoenolpyruvate (PEP)
- Irreversible
Pyruvate Kinase Positive Regulator
Fructose 1,6 phosphate product of PFK-1
Dihydroxyacetone Phosphate function (DHAP)
It is used in hepatic and adipose tissue for glycerols.
1,3-Bisphosphoglycerate and PEP
Produce only ATP gained in
anaerobic respiration by substrate level phosphorylation
Glycogen storage
- Liver to maintain glucose levels in the blood
2. Skeletal muscle to provide energy for vigorous exercise
LEARN THE GRAPH FOR GLYCOGENESIS
Look at Al’s handout
Steps in Glycogenesis
- Glycogenin - Core protein
- Glucose: Glucose-6-phosphate is converted to glucose-1-phosphate
- Glycogen synthase integrates Glucose-1-phosphate into glycogen
- Branching adds the alpha 1,6 linked branch
Glycogen synthase function, inhibitor, and activator
- Integrates glucose-1-phosphate into glycogen
- Rate limiting enzyme for glycogen synthesis
- Stimulated by Glucose-6-phosphate and insulin
- Inhibited by Glucagon and epinephrine
Glycogenolysis DIAGRAM/GRAPH
Learn this STUFF
Glycogen Phosphorylase
- Rate limiting enzyme breaks down glycogen with inorganic phosphate not water.
- Breaks 1,4 glycosidic linkage NOT 1,6
Glycogen Phosphorylase Inhibitor and Activator
- Activator - Glucagon, AMP, and Epinephrine
2. Inhibitor - ATP
Debranching Enzyme
- Breaks 1, 6 linkage
2. Glucose-1-phosphate is then converted to glucose-6-phosphate to enter glycolysis.
LOOK AT GLUCONEOGENESIS GRAPH
Look online or somewhere
Gluconeogenesis Facts
- Activator - Glucagon, epinephrine, growth hormone
- Inhibitor - Insulin
- Glycogen stores last 12-24 hours.
Gluconeogenesis Substrates and NOT USED
- Glycerol from fat
- Lactate from Anaerobic glycolysis
- Certain amino acids except for Leucine and Lysine
- DO NOT USE Fatty acids and acetyl-coA
Ketogenic Amino acids
- Leucine
2. Lysine
Gluconeogenic Amino acids
All except lysine and leucine
Pyruvate Carboxylase
- Shifts pyruvate to gluconeogenesis
- Produces oxaloacetate(OAA) from pyruvate which can enter the citric acid cycle or produce glucose.
- Oxaloacetate is reduced to malate which can leave the mitochondria.
- fatty acids produce Acetyl-CoA which power the cell and INHIBIT PDH and ACTIVATES pyruvate carboxylase.
PEP carboxykinase (PEPCK)
- Converts OAA to PEP and requires GTP.
2. Activators - glucagon and cortisol
Fructo 1,6-biphosphotase
- The reverse of PFK1 by hydrolyzing phosphate to produce fructose 6-phosphate.
- Activators - ATP and glucagon
- Inhibitors - AMP, fructose2,6-bisphosphate, and Insulin
- Rate limiting enzyme in gluconeogenesis
Gluco-6-phosphatase
- converts Glu-6-P to Glucose allowing Glucose to be transported out of the cell
- Located in the lumen of ER.
- Circumvent - hexokinase and glucokinase
- NOT present in skeletal muscles; skeletal muscles cannot release glucose into blood.
Other important gluconeogenesis notes
- Dependent on fatty acid oxidation for energy which requires the breakdown of triglycerides by the liver.
- Lactic acid produced by aerobic respiration must be converted back to pyruvate by the liver and pyruvate can be converted back to glucose.
- Acetyl-CoA can be converted into ketones which can be used for energy and transported in the blood.
LEARN THE PENTOSE PHOSPHATE PATHWAY
Look it up
Pentose Phosphate Regulation
- Activator - NADP+ and Insulin
2. Inhibitor - NADPH
Pentose Phosphate Pathway notes
- Occurs in the cytoplasm.
- Produced NADPH and creates ribose 5-phosphate
- Oxidation of Glucose 6-phosphate to 6-phosphogluconate is irreversible and rate-limiting.
- Intermediates can be exchanged between glycolysis and PPP.
NADPH functions
- NADPH acts as electron donor in biochemical reactions (fatty acids, cholesterol).
- Production of bleach for immune functions.
- Protects against free radicals by producing glutathione.
- NADH feeds the electron transport chain.
How do products of glycolysis pass to the mitochondria?
- Facilitated diffusion.
- NADH requires 1 ATP to be transported into the matrix.
- CoA-SH has a cysteine (thiol group) which forms a covalent bond with acetyl-group forming a thioester.
- Thioester contains an S instead of an O in the OR group of a typical ester.
Kreb’s Cycle Caveat
- Oxygen is not directly required, the pathway will not occur anaerobically because of the accumulation of NADH and FADH2 which will inhibit the cycle.
- Each turn produces 1ATP, 3NADH and 1 FADH2
Kreb’s Cycle Acronym
Please, Can I Keep Selling Seashells For Money, Officer
Kreb’s Cycle
Pyruvate (Acetyl-coA) -> Citrate -> Isocitrate -> Alpha-ketoglutarate -> Succinyl-CoA -> Succinate -> Fumarate -> Malate -> Oxaloacetate
Citrate formation
- Acetyl-CoA transfers two carbons from pyruvate to a 4-carbon.
- Citrate synthase catalyzed.
Citrate isomerization to Isocitrate
- DEHYDRATION resulting in ELIMINATION followed by HYDROLYSIS causing ADDITION of water.
- Aconitase catalyzed
Alpha Ketoglutarate formation
- Oxidation by Isocitrate Dehydrogenase followed by decarboxylation
- Rate limiting step of citric acid cycle
- First DECARBOXYLATION and then production of CO2.
Succinyl-CoA Formation
- Catalyzed by Alpha-ketoglutarate dehydrogenase complex.
2. Decarboxylation resulting in the formation of CO2 and NADH.
Succinate formation
1 . HYDROLYSIS of the thioester bond on succinyl-CoA yields succinate and CoA–SH.
- GTP is produced.
- Succinyl-CoA synthetase catalyzed.
Fumarate Formation
- Doesn’t take place in Matrix, takes place on the inner membrane.
- Succinate is oxidized to yield fumarate by Succinate Dehydrogenase.
- FAD is reduced to FADH2
Malate Formation
Fumarase causes HYDROLYSIS of alkene in fumarate.
Oxaloacetate formation ANEW
- Malate dehydrogenase causes OXIDATION of malate to oxaloacetate.
- NAD+ is reduced to NADH.
LOOK AT KREB’s CYCLE DIAGRAM
CONFIRM ALL OF THIS
Electron Transport Chain Notes
- Electrons are passed from Complex 1 to Q to complex 2 to complex 3 to cytochrome C to Complex 4.
- Ultimately O2 accepts becoming substrate level and forms H2O.
- Complex 1 oxidizes NADH and becomes reduced. Complex 1 becomes oxidized by Q and passes 2 hydrogens into the IMS while Q becomes reduced.
