glycolysis Flashcards
catabolic pathway
-exergonic rxns, that breakdown complex molecules into simple ones (ATP generation)
-convergent process
anabolic pathway
-endergonic rxns, synthesis of complex molecules from simple precursors (requires ATP)
-divergent process
metabolism
sum of all chemical changes (rxns) occurring within a cell, tissue or body
what helps glucose enter cells?
GLUT transport proteins, through facilitated diffusion
GLUT isoforms that are always present in plasma membrane, and their location?
GLUT 1 in RBC’s
GLUT 2 in hepatocytes, pancreatic B cells, and kidneys
brain neurons: GLUT 3
GLUT isoforms that are insulin dependent and their location?
GLUT 4 in striated muscle (skeletal/cardiac) and adipose tissue
what are SGLT1 and SGLT2 and where are they found?
they are sodium-dependent glucose cotransporters, found in intestinal epithelial cells, and renal tubules
-secondary active transport
general info of glycolysis
-occurs in the cytoplasm
-breakdown of glucose in a series of enzyme-catalyzed rxns to yield 2 pyruvate
-anaerobic pathway
What form are all sugar derivatives?
D-isomers
2 main purposes of glycolysis
- to oxidate glucose to provide ATP for all tissues
- provide intermediates for other metabolic pathways
2 stages of glycolysis
- energy investment phase: first 5 steps, phosphorylates intermediates using ATP
- energy generation phase: last 5 steps, net formation of 2 ATP per glucose by substrate-level phosphorylation
kinase
adds phosphate group
isomerase
converts a molecule from one chemical structure to another
mutase
moves functional group from one position to another on same molecule
dehydrogenase
oxidizes the substrate by removing one or more H+ atoms
cleaving enzyme
catalyzes the splitting of a molecule into two smaller molecules
enolase
removes a molecule of H20
energy investment phase
consumes 2 ATP
glucose –>2 Glyceraldehyde-3-phosphate
energy generation phase
produce 4 ATP and 2 NADH
2 glyceraldehyde-3-phosphate –>
2 pyruvate
rxn 1 of glycolysis
phosphorylation of glucose, uses either hexokinase or glucokinase (pancreas/liver)
glucokinase in the liver
initiates metabolism of glucose and helps regulate blood glucose levels
hyperglycemic periods
hepatocyte glucose uptake is increased due to increased activity of GLUT 2 and glucokinase
hypoglycemic periods
hepatocyte glucose levels are reduced and liver becomes a provider of glucose (breaks down glycogen)
glucokinase in the pancreas
functions to modulate insulin secretion to control glucose uptake by muscle/fat cells
glucose-6-phosphate
prevents exit from cell due to phosphorylation
rxn 3 of glycolysis
uses 1 ATP to change Fructose-6-phosphate to yield fructose-1,6-phosphate, uses enzyme phosphofructokinase-1
what step is the rate limiting “committed step” of glycolysis?
rxn 3, enzyme phosphofructokinase
rxn 10 of glycolysis
PEP cleaved to form 2 pyruvate, generating ATP, uses enzyme pyruvate kinase
3 regulated/irreversible steps of glycolysis
rxn 1, 3, and 10
insulin vs glucagon
insulin: promotes glycolysis
glucagon: DOESNT promote glycolysis
ATP:AMP ratio
low ATP means high AMP –> activates AMPK stimulating glycolysis
what happens to pyruvate in aerobic and anaerobic conditions?
aerobic: pyruvate enters the mitochondria and becomes acetyl-coA
anaerobic: pyruvate becomes lactate
lactate dehydrogenase isozymes isozymes
heart (H): supports aerobic metabolism
mucles (M): supports anaerobic metabolism
karkinoma (K): found in cells w/ high metabolic rates (present in retina)
corneal epithelium in low oxygen conditions
lactate production via HM3 LDH, often due from lid closure and CL wear
ocular lens (LDH)
no mitochondria, so favor lactate, LDH types HM3 and M4 are found in the lens
Retina (LDH)
LDH K4 opens the pathway to lactate when the aerobic pathway can’t be used anymore
Pentose phosphate pathway
branches from G6P, 3 functions
1. generation of ribose 5-phosphate, needed for nucleotide biosynthesis
2. generation of NADPH for production of FA’s
3. cell detoxification by removal of destructive forms of O2
where does the pentose phosphate pathway occur at?
tissues heavily involved in lipid biosynthesis and nucleotide synthesis
- liver, adipose tissue, adrenal cortex (lipids), bone marrow, skin, gastric mucosa (nucleotides)
Red blood cell glucose metabolism
insulin independent, metabolized mainly by glycolysis, end product is lactate
Brain glucose metabolism
insulin independent, glycolysis to pyruvate
muscle and heart glucose metabolism
insulin stimulated, glycolysis to pyruvate, and synthesize a lot of glycogen
adipose tissue glucose metabolism
insulin stimulated, either glycolysis, or acetyl-coA for FA synthesis, uses pentose phosphate shunt
Liver glucose metabolism
high blood glucose: liver removes glucose from blood and either undergoes glycogenesis or glycolysis
low blood glucose: liver supplies the blood with glucose by glycogenolysis or gluconeogenesis
Does glycolysis happen in high or low ATP levels
low ATP
