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Biochem block3 Lecture 26 Chapter 8
How many stages does glycolysis have?
How many total reactions occur during glycolysis?
What does glycolysis generally being with and end with?
Starts with glucose and ends with 2 molecules of pyruvate
What occurs during stage one of glycolysis?
Glucose is phosphorylated and cleaved to form two G-3-P
What occurs during stage two of gycolysis?
From this point on, there are two of each molecule
What is pyruvate converted to in anaerobic organisms?
Anaerobic organisms convert pyruvate to waste product (lactate).
What is pyruvate converted to in aerobic organisms?
Aerobic organisms use
as an electron accepter and convert pyruvate
into CO2 and H2O
cycle/electron transport chain)?
When is glycolysis activated and what is its general function?
Activated when energy is needed
Glucose is uses 2 ATP molecules to produce 2 pyruvates, 4 ATP (net gain of 2), and 2 NADH
How is NAD+ used?
NAD+ is used as an
These electrons are used in the electron transport chain to make more ATP
D-Glucose + 2 ADP + 2 Pi + 2 NAD+ -->
Glucose is____ using ____ and requires ___to form___
Hexokinase, Mg2 or Glucokinase (GK)
__ converts glucose-6-phosphate to__
Phosphoglucose isomerase (PGI)
__catalyzes the __ of fructose-6-phosphate to__
__ cleaves the fructose-1,6-bisphosphate to form __
Both dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
Products used quickly
End of 1st stage
__ catalyzes the__ of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP)
Triose phosphate isomerase
__ removes a__and adds __ to glyceraldehyde-3-phosphate to form__
Hydride ion (H:-)
Converts NAD+ to NADH and requires a molecule of inorganic phosphate
___ catalyzes the production of __ from __and one of the phosphoryl groups on glycerate-1,3-bisphosphate leaving __
Glycerate-3-phosphate or 3-phosphoglycerate
__ interconverts 3-phosphoglycerate and __
__removes a molecule of __from glycerate-2-phosphate to form__
__catalyzes the formation of __ using the__ from
What is step 1 of glycolysis?
Phosphorylation of Glucose
What is step 2 of glycolysis?
G6P to F6P
What is step 3 of glycolysis?
Phosphorylation of F6P
What is step 4 of glycolysis?
Cleavage of F1,6P
What is step 5 of glycolysis?
Isomerization of DHAP to GAP
What is step 6 of glycolysis?
Oxidation of GAP
What is step 7 of glycolysis?
Phosphoryl group transfer
What is step 8 of glycolysis?
Interconversion of 3PG to 2PG
What is step 9 of glycolysis?
Dehydration of 2PG to form PEP
What is step 10 of glycolysis?
Production of Pyruvate from PEP
What happens when glucose and other 6 carbon sugars enter the cell?
It is phosphorylated in the cytoplasm by enzymes called hexokinases
Prevents the sugar from leaving the cell
What are Hexokinases I, II, and III inhibited by and how are they saturated?
What is Hexokinase IV and mention other important fact?
Also known as Glucokinase
Only found in the liver, some cells of the intestines, pancreas, and brain;
[glucose] and is not inhibited by G6P
What inhibits and what stimulates PFK-1?
AMP and F-2,6-bisphosphate
What is Phosphofructokinase-2 (PFK-2)?
A bifunctional enzyme
Acts like a phosphatase (low blood sugar) or kinase (high blood).
In response to glucagon (_), acts like a __to __and makes__which decreases__ and stimulates__
Low blood sugar
In response to insulin (_), acts like a __to __and makes__ by stimulating__activity and also stimulates __
High blood sugar levels
Where is the first place energy is generated during glycolysis?
During step 7 (Phosphoryl group transfer)-
Phosphoglycerate kinase catalyzes the formation of ATP using one phosphate from glycerate-1,3-bisphosphate leaving glycerate-3-phosphate
Where is the second place energy is generated during glycolysis?
Step 10 (Production of Pyruvate from PEP)
Pyruvate kinase catalyzes the formation of ATP using the phosphate from phosphoenolpyruvate leaving pyruvate
Which steps are irreversible?
Steps 1,3, and 10
What happens to pyruvate in anaerobic conditions?
Anaerobic organisms convert pyruvate to waste product(s)
Lactate formation (muscle cells)
Ethanol formation (yeast)
What happens to pyruvate in aerobic conditions?
Aerobic organisms use oxygen as an electron accepter and convert pyruvate into CO2 and H2O (citric acid cycle/electron transport chain)
How is lactate formed?
Under anaerobic conditions (like during strenuous exercise), pyruvate is converted to lactate in muscle cells
What is one of the main events during lactate formation?
This reaction converts some of the NADH back to NAD+ allowing the cell to continue to make ATP via glycolysis
Normally, the NAD+ would be regenerated during oxidative phosphorylation, but this is impeded by the lack of oxygen
How is ethanol produced?
Yeast and some bacteria can convert pyruvate to acetaldehyde and then to ethanol
This involves the decarboxylation of pyruvate and the reduction of acetaldehyde
How is the rate of glycolysis controlled?
Allosteric regulation of: hexokinase (1), PFK-1 (3), and pyruvate kinase (10)
What is the inhibitor of hexokinase?
ATP (distant product)
What is the activator of PFK-1?
Fructose-2,6-bisphosphate (signaling response to high glucose levels)
AMP (ATP level sensor)
What is the inhibitor of PFK-1?
Citrate (citric acid cycle)
ATP (distant product)
What is the product of PFK-1?
What is the activator of Pyruvate kinase?
Fructose-1,6-bisphosphate (upstream precursor)
AMP (ATP level sensor)
What is the inhibitor of pyruvate kinase?
Acetyl-CoA (citric acid cycle)
What is the product of pyruvate kinase?
What is glucagon and how is it released?
peptide hormone (29 amino acids) released by a-cells (pancreas) when blood glucose is low
Activates the phosphatase of PFK-2 and thereby decreases the activity of PFK-1, slowing down glycolysis
What is insulin and how is it released?
Peptide hormone (51 amino acids) released by b-cells (pancreas) when blood glucose is high
Activates the kinase of PFK-2 which increases the activity of PFK-1, increasing the rate of glycolysis
What is released in response to high blood sugar?
What is released in response to low blood sugar?
Where does gluconeogenesis primarily occur?
Generally explain the steps of gluconeogenesis?
The reverse of glycolysis with the exception of three key steps:
Hexokinase, PFK-1, and pyruvate kinase
Name the steps of gluconeogenesis:
Synthesis of PEP
Conversion of fructose-1,6-bisphosphate to fructose-6-phosphate
Formation of glucose from glucose-6-phosphate