Lecture 7: Glycolysis: Regulation Flashcards
Glucokinase overview
glucose sensor
affects insulin secretion from pancreatic beta cells
phosphofructokinase 1 (PFK-1)
one of 3 metabolic valves in glycolytic pathway
allosterically regulated
disarcharide sugars
maltose, sucrose, lactose
give rise to monosacchardes sugars to enter glycoltic pathway
Regulated valves
rate-limiting enzymes in metabolic pathways
open and close in response to cell conditions
Regulation of glycolytic pathway (glycolysis and gluconeogenesis)
reversible steps in both regulate in both pathways (shown wide in pictures)
irreversible steps have actual changes in free energies (delta G) that are very negatie and require PATHWAY SPECIFIC ENZYMES (shown as skinny)
glucokinase and hexokinase
catalyze same reaction
differ in properties
Hexokinase I
high affinity for substrate (at low concs, enzyme has half activity)
phosphorylates a variety of hexose sugars
in ALL tissues
INHIBITED by product of reaction (glucose-6-P)
Glucokinase
low affinity for substrate (it takes a lot more substrate to reach half max enzyme activity)
Spefic for GLUCOSE
only in liver and pancreatic cells
NOT inhibited by glucose-6-P
Role of glucokinase in liver cells
high blood glucose levels-> hexokinase and glucokinase active in liver cells
hexokinase will become inhibited
traps glucose in liver cells more than in other tissues because glucokinase doesn’t become inhibited, which allows more glucose to be trapped as gluco-6-P
liver is where we store most glycogen
role of glucokinase in pancreatic beta cells
glucokinase sequesters glucose inside cells
initiate signaling pathway leading to release of INSULIN into blood
this makes glucokinase a glucose sensor
Km values
tells what substrate concentration is needed to reach half maximum activity
Glucose transporters are called
GLUC transporters
review slide 7
review slide 7
what happens to flux through glycolytic pathways when glucokinase is activated by glucose?
flux will increase because glucokinase is activated at high glucose levels (while hexokinase is inactivated)
what turns off glucokinase?
a lack of glucose
what effect would a mutation in glucokinase have on insulin secretion
insulin secretion will decrease, but won’t go away because hexokinase can still get some to be secreted
How would you treat diabetes that is cauased by glucokinse mutation
give insulin
diabetes not actually caused by this!
See slide 9 for questions
see slide 9 for questions
is PFK1 stimulated or inhibited by a high energy charge (keep in mind that this is in the ATP using stage)
INHIBITED
if we have a lot of ATP around, we don’t need to make more ATP.
we do need enough ATP around to make the reaction happen, but we need to have a need to make ATP
T state
INACTIVE conformation
R state
ACTIVE conformation
Allosteric regulator of PFK-1
a tetramer
F-2,6-BP–> super activator of PFK-1 activity
AMP——–>activator
ADP——–> activaor
Citrate—-> inhibitor
ATP——–> inhibitor
citrate and PFK-1 activity
inhibits
because citrate is a metabolite of the citrate cycle, it builds up when energy levels are high
F-2,6,BP and PFK-1 activity
super-duper activator (activating PFK-1 is its only job)
NOT a metabolite of glycolysis, just a regulatory molecule
see slide 11 for questions
see slide 11 for questions
review slide 12
review slide 12
disaccharide sugars
maltose
sucrose
lactose
all of them can make glucose!!!!!
maltose
from starch
enzyme is maltase to give 2glucose
sucrose
table sugar
enzyme is sucrase to give glucose and fructose
lactose
from milk
enzyme is lactase to give glucose and galactose
glycerol
glycolytic intermediate derived from degradation of triglycerides (fats)
glycerol backbone is left once cleaved. it can enter glycolytic pathway
why does decreased lactase enzyme cause stomach problems when eating dairy?
when lactase in small intestine can’t digest it, bacteria in the colon CAN digest it
by product of bacteria digestion is methane for ex
cleaving maltose
makes to molecs of glucose
lactose
cleaves into glucose and galactose
galactose undergoes a pathway using galactokinase and ATP and generating Glucose-1P
Sucrose
splits into glucose and fructose
ATP used before each kinase
Fructose in liver:
fuctokinase phosphorylayes to make eventually 2 3-carbon molecs. ATP used on one to make GAP
Fructose in muscle:
hexokinase phosphorylates it to make fructose-6-P which continues into glycolysis
review slide 15
review slide 15
Fructose intolerance
due to deficiency in emzyme fructose-1-P aldolase (which splits in into 2 3-carbon molecs)
too much dietary fructose causes build up in fructose1-P, this depletes Pi in liver and inhibits ATP synthesis
review slide 16
review slide 16
what is the treatment for people with fructose intolerance?
limit fructose intake!
why aren’t there people with a complete loss of PFK-1
they would die
glycolytic metabolites of glycolysis can provide carbon skeletons for…
amino acid synthesis
pentose phosphate pathway
triacylglyceride synthesis
aerobic conditions in mitochondria
Pyruvate converted to….
acetyl CoA
wich goes into citrate cylce or is converted to fatty acids
ANaerobic conditions in cytoplasm
Pyruvate converted to….
Lactate
regenerates NAD+
Anaerobic conditions in yeast
Pyruvate converted to….
ethanol
NAD+ regenerated
Which glycolytic enzyme requires NAD+ as a substrate?
Glyceraaldehyde-3-P dehydrogenase
NAD+ used to…
make NADH
What would happen to metabolic flux through glycolysis if NAD+ not regenerated
it would stop!!!!
Which glycolytic enzyme is responsible for decreased flux through the glycolytic pathway when NAD+ is not regenerated by LDH
Glyceraaldehyde-3-P dehydrogenase
Lactase dehydrogenase (LDHA) defeciency
they can’t do much exercise because they can’t use glycolysis to make ATP needed
when we talk about electron transport, where are they transported?
into the mitochondria (via shuttle systems)
the molecules itself is NOT transported into mitochondira
Shuttle systems…
regenerate NAD+ when pyruvate is oxidized in mitochondria
responsible for oxitizing CYTOSOLic NADH (so the enzymes an continue to act)
Review slide 22 for example questions
Review slide 22 for example questions
lactose
sugar (carb)
lactase
enzyme (protein)
lactate
small metabolite
