Please enable JavaScript.
Coggle requires JavaScript to display documents.
Glycoloysis - Coggle Diagram
Glycoloysis
Glycolysis Pathway
Glycolytic Inputs:
Sucrolysis
pathways include:
invertase pathway
sucrose hydrolyzed to glucose and fructose by invertases
irreversible
sucrose synthase
sucrose hydrolyzed to fructose and UDP-glucose
catalyzed by sucrose synthase
occurs in cytoplasm
sources include sucrose imported from source tissues or stored in vacuoles
hydrolysis of sucrose to hexoses or hexose phosphates that then enter glycolysis
Starch Degradation
sites include amyloplasts and chloroplasts
Glc-6-P primarily exits amyloplasts
DHAP primarily exits chloroplasts
pathways include:
starch phosphorylase
no energy input required
active during stress to provide glucose for glycolysis and OPPP
amylase
requires ATP
active during nocturnal degradation of starch
Glycolytic Outputs
Pyruvate
TCA cycle (increased O2)
Fermentation (decreased O2)
TCA Cycle
Irreversible Reactions:
Hexokinases (glucokinases, fructokinases)
ATP-Phosphofructokinase
Pyruvate Kinase
FAMILIARIZE WITH P21
Metabolic Regulation
Pyruvate Kinase controlled through allosteric inhibition by citrate, a-Ketoglutarate, and Malate and by-passed by Malate shuttle
ATP-phosphofructokinase inhibited allosterically by PEP, which is mitigated by Pi
ratio of PEP/Pi in cytoplasm important determinant of ATP-phosphofructokinase activity
Fructose-2,6-bisphosphate acts as allosteric inhibitor of Fru-1,6-P2 phosphatase and as an allosteric activator of PPi-phosphofructokinase
controls which pathway metabolizes hexoses (gluconeogenesis vs glycolysis)
Genetic Regulation
hexokinase sensing of carbohydrate metabolism
ATP Balance per Hexose:
ATP generated per hexose: 4, via phosphoglycerate kinase and pyruvate kinase
ATP consumed per Hexose: 2, via hexokinases and ATP-phosphofructokinase
Net ATP synthesis: 2
Substrate-Level phosphorylation
direct transfer of Pi from substrate to ADP
substrate must have sufficient free energy of hydrolysis
NADH Balance:
NADH Generated per Hexose: 2, via glyceraldehyde-3-P DH
Reduction of NAD+ to NADH
2e- and 2H+ transferred from organic compound to NAD+ to form NADH
electrons transferred to other organic compounds
Electrons transferred to MET
NADH consumed per hexose: 2, via malate dehydrogenase
Unique Plant Features
PPi-phosphofructokinase
reversible rxn
allosteric inhibition via ATP in animals and PEP in plants
control point - glycolysis v OPPP
Fru-1,6-P2 phosphatase
controls glycolysis v gluconeogenesis, the latter of which is not common in plants and occurs in oil seeds during germination
Conversion of PEP to malate
oxidizes NADH to NAD+ (analogous to fermentation)
mechanism to reduce organic acids
malate used to shuttle reducing equivalents into mitochondria
Anapleurotic Reactions:
Glc-6-P made into OPPP via nucleotide biosynthesis, nucleic acid biosynthesis, ADP, ATP, NAD, NADP, FMN, CoA, and cytokinins
Glyceraldehyde-3-P made into OPPP
DHAP made into fatty acids via lipid synthesis and membrane synthesis
PEP to the Shikimic Acid Pathway via aromatic amino acids, protein biosynthesis, alkaloids, flavonoids, and lignins
Pyruvate to alanine via protein biosynthesis
Low O2 in Plants
conditions that limit O2 availability:
high metabolic activity in meristems
seed germination prior to rupture of seed coat
flooding (primary condition limiting O2)
Reduction in pO2 in soil
air in soil pores completely displaced by water
diffusion 10,000x greater in air than in water
solubility of O2 lower in water than in air
no diffusion when air space less than 10%
Root response to soil pO2
respiration impaired below 5% O2
Km of COX for O2 is less than 1 micromolar, so diffusion limits respiration
shift from aerobic respiration to fermentation
degrees of O2 stress:
Aerobic
Hypoxic
Anoxic
Anaerobic
plants respond to low O2 conditions:
activation of fermentation pathways
re-direction of protein synthesis
morphological adaptations
Anaerobic Stress Protein (ANP) Synthesis
Starch and Sucrolytic enzymes:
amylase
sucrose synthase
glycolytic enzymes:
hexokinase
glucose-6-phosphate isomerase
phosphoglucomutase
aldolase
enolase
glyceraldehyde-3-P dehydrogenase
Fermentation enzymes:
pyruvate decarboxylase
alcohol dehydrogenase
lactate dehydrogenase
ANPs induced when O2 is limiting
general protein synthesis is inhibited
selective expression of ANPs via transcription and translation
Anaerobic Gene Expression:
regulation of anaerobic gene expression
ADH transcription linked to anaerobic TFs
TFs bind AREs
Not all ANPs have AREs
Primary Metabolism
Pathways common to all
nucleic acid synthesis
amino acid biosynthesis
protein biosynthesis
lipid metabolism
energy generation
Anapleurotic Reactions
Glycolysis
TCA Cycle
Basic Energy Metabolism
free energy transferred between reactions by ATP or NAD(P)H
includes:
Aerobic respiration
complete oxidation of substrate to CO2
electron transport system generates H+ gradient
O2 is terminal electron acceptor and reduced to H2O
ATP synthesized via chemiosmosis
default energy-generating pathway in most organisms
Anaerobic Respiration
Oxidation of substrate to CO2 and organics
electron transport system generates H+ gradient
alternate electron acceptors in place of O2
ATP synthesized via chemiosmosis
operates when O2 is limiting
used in bacteria
Fermentation
Glycolytic Fermentation
glycolysis coupled with fermentation
oxidation of substrate to CO2 and organic compounds
no electron transport system involved
ATP synthesized by substrate level phosphorylation
primitive pathway found in all organisms--operates when O2 is limiting and oxidizes NADH
Mechanism for oxidation of NADH
NADH/NAD pool relatively constant
permits continued glycolysis without respiration
Fermentative pathways:
ethanolic fermentation (plants and yeast)
Ethanol is primary end-product in plants
ADH genetically linked to flood tolerance
detoxifies acetaldehyde
Accumulation of acetaldehyde is toxic
3 more items...
does not contribute to cytoplasmic acidosis
oxidizes NADH
lactic fermentation (plants and animals)
activated first by low O2
oxidizes NADH to NAD+
accumulation of lactic acid causes cytoplasmic acidosis, which can quickly lead to death
Regulation of fermentation:
LDH/PDC stat:
based on pH optimum of enzymes
LDH: pH 9
PDC: pH 6
initially, cytosol at pH 7.4
LDH activated; lactate synthesized
PDC inactivated; ethanol not synthesized
lactate acidifies cytoplasm to pH 6.7
PDC activated; ethanol synthesized
LDH inactivated; lactate not synthesized
Based on Km of enzymes for pyruvate
PDH: Km = 50-75 microM
PDC: Km = 250 - 1000 microM
PDH outcompetes PDC for pyruvate
increased pyruvate allows PDC to bind to it
NADH is an allosteric activator of PDC
Secondary Metabolism
utilizes unique biochemistry, is highly variable, and results in phytochemicals and pharmaceuticals