MSK - Biochemistry - Glycolysis; Gluconeogenesis; Glycogen Metabolism Flashcards
How many reactions occur in glycolysis?
What phase are the first 5 known as?
What phase are the second 5 known as?
10;
the investment/preparatory phase;
the payoff phase
What are the two goals of the investing/preparatory phase of glycolysis?
How many ATP are invested at this point?
- To make the process irreversible
- To split the 6-carbon sugar into two 3-carbon sugars
2
By the end of the glycolytic investing/preparatory phase, glucose has been split into two molecules known as:
Glyceraldehyde-3-phosphate
In the second five glycolytic reactions, the payoff phase, what high energy molecules are produced?
What is the net gain of glycolysis?
4 ATP, 2 NADH;
2 ATP, 2 NADH
Of the ten glycolytic reactions, which are the most important for a healthcare provider to know?
1, 3, 6, 7, (9), 10
The GLUT transporters work via what type of transport?
Facilitated diffusion
What GLUT transporters are found in virtually all mammalian tissues and maintain basal glucose levels?
GLUT1, GLUT3
What GLUT transporter is found in liver and pancreatic cells (as well as the basolateral portion of epithelium in the small intestine) and removes excess glucose from the blood / controls insulin secretion?
GLUT2
What GLUT transporter is found in muscle and fat cells and is insulin sensitive?
GLUT4
What GLUT transporter is found in mucosal membranes and spermatozoa for fructose transport?
GLUT5
GLUT1 and GLUT3 are found in what tissues?
What is their purpose?
Virtually all mammalian tissues - maintain cellular basal glucose needs
GLUT2 is found in what tissues?
What is its purpose?
Pancreatic tissues - control insulin secretion;
Liver and small intestinal tissues - removes excess glucose from blood
GLUT4 is found in what tissue(s)?
It is ________-sensitive.
Muscle and adipose;
insulin
GLUT5 transporters move what substance?
Fructose
For GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5, state the relative Km for each.
(place them in order of increasing Km)
GLUT3 - 1 mM
GLUT1 - 1 - 2 mM
GLUT4 - 5 mM
GLUT5 - 10 mM
GLUT2 - 15 - 20 mM
Normal physiological glucose levels are around: ____mM.
5.5
(100 mg/dl)
Which GLUT transporters are transporting glucose almost all the time?
Which GLUT transporters are transporting glucose in the well-fed state only?
GLUT1, GLUT3, GLUT4;
GLUT2
(note: GLUT5 transports fructose)
Describe the basic steps of insulin secretion.
1. Glucose levels rise (GLUT2 Km = 15 - 20 mM)
2. GLUT2 transporters allow glucose into pancreatic β cells
3. ATP is formed via glycolysis
4. ATP turns off K+ leak channels
5. The cell depolarizes
6. Calcium floods the cell and insulin is released
What is the 3-carbon end product of glycolysis?
Pyruvate
How do anti-hyperglycemic drugs such as sulfonylureas or meglitinides work?
What drug does the opposite?
They close ATP-sensitive K+ channels in pancreatic β cells
(note: these are channels that were pumping K+ into the cell);
diazoxide (treats insulinoma-induced hypoglycemia)
Should type I diabetics be given sulfonylureas and/or meglitinides?
Should type II diabetics be given sulfonylureas and/or meglitinides?
They shouldn’t. They don’t have β cells;
Yes
Where are GLUT4 transporters when glucose levels are low?
Where are GLUT4 transporters when glucose levels are high?
Endocytosed;
on the plasma membrane (exocytosed)
What is the first step of glycolysis?
Why is this step important (3 reasons)?
Hexokinase adds a phosphate to glucose (making G6P).
- Energy investment
- Traps glucose in cell
- Ionic charges increase favorability of subsequent interactions
What are substrates and product of the first step of glycolysis/
Glucose (+ hexokinase + ATP + Mg2+) –> Glucose-6-phosphate
Why is the first step of glycolysis (shown below) a favorable reaction (- ΔG)?
ATP coupling
Why is the hexokinase found in the liver (hexokinase IV) called glucokinase?
Does it have any inhibitors?
It only acts on glucose;
yes, F6P
What is the [glucose] Km for hexokinase I (or II and III)?
What is the [glucose] Km for hexokinase IV (glucokinase)?
0.05 mM;
5 mM
Which is allosterically inhibited by G6P, hexokinase I or glucokinase?
Hexokinase I
When GLUT2 transports glucose into liver cells, what effect does this have on glucokinase?
It draws it out of the nucleus
Which of the following would inactive liver glucokinase by shuttling it into the nucleus, incoming glucose or liver gluconeogenesis?
Liver gluconeogenesis
What happens in step two of glycolysis?
What enzyme is responsible?
G6P is turned into F6P;
phosphohexose isomerase
What is the commitment step of glycolysis?
Via what enzyme?
Step 3;
phosphfructokinase-1 (PFK-1)
What are the two investment steps of the preparatory phase (1st five steps) of glycolysis?
Steps 1 and 3
What are the substrates and main product of the 3rd step of glycolysis?
F6P (+ PFK-1 + ATP + Mg2+) –> F1,6BP
What are some allosteric activators of the third step of glycolysis (shown below)?
AMP, ADP, F2,6BP
What are some allosteric inhibitors of the third step of glycolysis (shown below)?
ATP, citrate
What effect does F2,6BP have on the third step of glycolysis (shown below)?
What effect does citrate have on the third step of glycolysis (shown below)?
Allosteric activation;
allosteric inhibition
What enzyme catalyzes the formation of F2,6BP?
What enzyme catalyzes the breakdown of F2,6BP?
PFK-2;
F2,6BPase -2
True/False.
PFK-2 and F2,6BPase-2 are two separate domains of the same enzyme and both can be active at the same time.
False.
They are two separate domains of the same enzyme, but only one is active at any one point in time
What effect does glucagon have on FBPase-2 activity?
How?
Increased;
phosphorylation of the enzyme via PKA
What effect does insulin have on PFK-2 activity?
How?
Increased;
dephosphorylation of the enzyme via phosphoprotein phosphatase
Does glucagon activate the F2,6BPase-2 or PFK-2 domain?
How?
Does insulin activate the F2,6BPase-2 or PFK-2 domain?
How?
F2,6BPase-2, phosphorylation via PKA;
PFK-2, dephosphorylation via PPP
What effect does glucagon have on F2,6BP levels? How?
What effect does insulin have on F2,6BP levels? How?
Decreased, via PKA –> F2,6BPase-2 activity;
increased, via PPP –> PFK-2 activity
Does F2,6BP allosterically activate or inhibit glycolysis?
Activate
Describe glucagon’s overall effects on the following:
PKA or PPP
F2,6BPase-2 or PFK-2
F2,6BP
Glycolysis
Gluconeogenesis
PKA activity increased
F2,6BPase-2 activity increased
F2,6BP decreased
Glycolysis inhibited
Gluconeogenesis stimulated
Describe insulin’s overall effects on the following:
PKA or PPP
F2,6BPase-2 or PFK-2
F2,6BP
Glycolysis
Gluconeogenesis
PPP activity increased
PFK-2 activity increased
F2,6BP increased
Glycolysis stimulated
Gluconeogenesis inhibited
What happens in step 4 of glycolysis (starting with F1,6BP)?
What happens in step 5 of glycolysis?
The F1,6BP is chopped into DHAP and glyceraldehyde-3-phosphate;
the DHAP is isomerized into glyceraldehyde-3-phosphate
Name an allosteric inhibitor of hexokinase I.
G6P
What occurs in step 6 of glycolysis?
Why is this important?
Inorganic phosphate is added to glyceraldehyde-3-phosphate to form 1,3-bisphosphoglycerate;
there are now two phosphates on each molecule, yielding four ATP total in the payoff phase (2 ATP net)
In step 6 of glycolysis, inorganic phosphate is added to glyceraldehyde-3-phosphate to form 1,3-bisphosphoglycerate.
What enzyme accomplishes this and what electron acceptor is needed?
Glyceraldehyde-3-phosphate dehydrogenase;
NAD+
What steps of glycolysis involve ATP hydrolysis?
What steps of glycolysis involve NADH production?
What steps of glycolysis involve ATP production?
Steps 1 and 3;
step 6;
steps 7 and 10
Why is it important that F1,6BP (from an original glucose molecule) is cleaved into two separate halves during glycolysis?
The energy generated in the payoff phase is doubled
What is the term that describes the fact that reactions with fairly neutral ΔGs with occur rapidly if very thermodynamically stable reactions occur later in the flow?
(E.g. the less favorable steps 2 and 5 of glycolysis happen readily because steps 1, 3, and 10 occur?)
Substrate flux
What happens in step 7 of glycolysis?
Via what enzyme?
1,3-Bisphosphoglycerate is turned into 3-phosphoglycerate and ATP is formed;
phosphoglycerate kinase
The ATP production in glycolysis is termed ___________-_____ phosphorylation.
This in contrast with __________ phosphorylation.
Substrate, level;
oxidative
Which must have a higher energy state, 1,3-bisphosphoglycerate or ATP?
(reaction 7 of glycolysis shown below)
1,3-Bisphosphoglycerate
(used for substrate-level phosphorylation)
What happens in step 8 of glycolysis (starting with 3-phosphoglycerate)?
What happens in step 9 of glycolysis?
3-PG is isomerized to 2-PG by PG mutase;
2-PG is dehydrated to phosphoenolpyruvatase by enolase
What happens in step 10 of glycolysis?
Via what enzyme?
Phosphoenolpyruvate is turned into pyruvate and ATP;
(substrate-level phosphorylation)
pyruvate kinase
What glycolytic intermediate is one of the highest energy compounds that we know of?
Phosphoenolpyruvate
(much higher than ATP or 1,3-BPG)
Which must have a higher energy state, phosphoenolpyruvate or ATP?
(reaction 10 of glycolysis shown below)
Phosphoenolpyruvate
(used for substrate-level phosphorylation)