Pathways linking Glycogen, Glucose & Pyruvate Flashcards
Glycogen to glucose
Glycogenolysis
Glucose to glycogen
Glycogenesis
Pyruvate to glucose
Gluconeogenesis
Glucose to pyruvate
Glycolysis
When does glycogenesis take place?
When blood glucose levels are sufficiently high to allow excess glucose to be stored in liver + muscle cells.
What is glycogenesis inhibited by?
Presence of G-6-P
What is glycogenesis stimulated by?
Insulin
What does insulin do for glycogenesis?
Facilitates the uptake of glucose into muscle cells but not req for liver cells.
But, in liver cells insulin does stimulate glycogenesis.
Why does the overall pathway of glycogenesis consume energy?
Due to 1 ATP + 1 UTP being consumed for each mol of glucose used.
Where is hexokinase found and where is glucokinase found?
Hexokinase = Muscle, brain + adipose tissue
Glucokinase = Liver + pancreas
Relationship of G-6-P with hexokinase + glucokinase
Hexokinase = Allosterically inhibited by G-6-P
Glucokinase = NOT inhibited by G-6-P
Which is induced by insulin in NORMAL individuals? - glucokinase or hexokinase?
Glucokinase
Glycogenesis
Overview of the change in glucose showing only the substrates
Glucose
G-6-P
G-1-P
Uracil-diphosphate glucose (UDP)
Glycogen
GLYCOGENESIS
Enzyme for
Glucose –> G-6-P
Glucokinase or hexokinase
GLYCOGENESIS
Enzyme for G-6-P to G-1-P
Phosphoglucomutase
GLYCOGENESIS
Enzyme for G-1-P to Uracil-diphosphate glucose (UDP)
UDP-glucose pyrophosphorylase
GLYCOGENESIS
Enzyme for
UDP glucose to Glycogen
Glycogenin
Glycogen synthase +/or glycogen branching enzyme
What does UDP-glucose consist of?
2 P groups + uracil (nucleic acid)
What -ively regulates glycogenesis by disrupting the proteins needed for the process?
Epinephrine/Adrenaline
What does epinephrine do to glycogenesis?
Stops it + starts glycogenolysis to convert glucose into energy,
Cells need much ATP to overcome the threat.
Where is potential energy found in glycogens?
W/in the glucose residues that make up its structure.
In response to the bodys demands, these reduces can be cleaves from the non-reducing ends of the glycogen branches + put through energy releasing pathways.
Where does glycogenolysis take place?
Muscle + liver cells
When does glycogenolysis take place?
When more energy is needed.
When ATP levels are low
How many units of glucose can 1 mol of glycogen contain?
30,000 units of glucose linked together with its centre structure as the protein glycogenin.
How is each glucose mol removed from the glycogen mol?
Phosphorolysis
= Breaking down of a molecular bond by adding phosphoric acid
Step 1 in glycogenolysis
Glycogen phosphorylase breaks the bond linking glucose to glycogen by substituting a phosphoric group PO32-
Glucose that’s been detached is known as G-1-P.
GLYCOGENOLYSIS
What happens once a glucose has been detached from glycogen + now known as G-1-P?
Phosphoglucomutase converts G-1-P to G-6-P so the cells can make ATP.
What is glycogenolysis stimulated by?
Epinephrine/adrenaline
Equation for glycolysis
1 glucose –> 2 pyruvate + 2H20 + 2ATP + 2NADH + 2H+
Where does glycolysis occur?
Cytosol
What does glycolysis require?
2 NAD+
2 Pi
2 ADP
Oxidised vs reduced NAD
Oxidised = NAD+
Reduced = NADH
Which steps of glycolysis are the energy requiring ones?
1–>5
Which steps of glycolysis are the energy releasing ones?
6–> 10
GLYCOLYSIS
Step 1
Phosphorylation: P group is transferred from ATP to glucose = G-6-P
Glucose + ATP –> ADP + G-6-P
By HEXOKINASE
GLYCOLYSIS
STEP 2
What happens with the G-6-P?
G-6-P –> Fructose-6-phosphate (isomer of G-6-P)
By Phosphoglucomutase
GLYCOLYSIS
STEP 3
What happens with fructose-6-phosphate
Fructose-6-phosphate –> Fructose-1,6-biphosphate
Through phosphorylation of a 2nd ATP mol.
Catalysed by phosphofructokinase
GLYCOLYSIS
STEP 4
What happens with Fructose-1,6-biphosphate
Split by aldolase –> Dihydroxyacetone phosphate + Gylceraldehyde-3-phosphate
(isomers of each other)
GLYCOLYSIS
STEP 5
What happens to dihydroxyactetone-P
Converted into glyceraldehyde-3-phosphate by triose-phosphate isomerase
GLYCOLYSIS
STEP 6
What happens to Glyceraldehyde-3-phosphate
Oxidised by G-3-P dehydrogenase
Enzyme also catalyses NAD+ –> NADH + H+
== Overall reaction releases energy used to phosphorylate G-3-P to create 2 x 1,3-bisphosphoglycerate mol.
GLYCOLYSIS
STEP 7
What happens to each 1,3-biphosphoglycerate mol?
Donates a P group to an ADP mol –> 2x ATP + 2x 3-phosphoglcyerate.
By phosphoglycerate kinase
GLYCOLYSIS
STEP 8
What happens to each 3-phosphoglycerate mol?
Phosphoglyceromutase converts them into 1 x 2-phosphoglycerate mol.
GLYCOLYSIS
STEP 9
What happens to the 2-phosphoglycerate mol?
Enolase removes 1 H20 mol from it to create 2 mol of phosphoenolpyruvate
Net prod of glycolysis
2 mol of ATP
2 mol of pyruvate
2 mol of NADH
GLYCOLYSIS
STEP 10
What happens to the mol of phosphoenolpyruvate?
Phosphoenolpyruvate + ADP –> 2 ATP + 2 Pyruvate
Catalysed by pyruvate kinase.
What can happen after glycolysis if O2 is NOT present?
Pyruvate is used in anaerobic respiration
What can happen after glycolysis if O2 is present?
Pyruvate prod can be used in aerobic respiration
In gluconeogenesis, Pyruvate can be converted into glucose.
What other substrates can be converted into glucose through this pathway?
aa
Lactate
Glycerol
Where does gluconeogenesis take place?
Mostly in liver
Can happen in small amounts in kidney + small intestine
Where does the TCA cycle take place?
Mitochondrial matrix
When does gluconeogenesis occur?
When blood sugar levels become low
Steps to gluconeogenesis when using pyruvate as the substrate
2 pyruvate mol + ATP –> oxaloacetate (by carboxylation)
Oxaloacetate –> Malate = Red by NADH (can now leave mit)
Once out of mit = Malate –> oxaloacetate (by oxidation)
Oxaloacetate –> phosphoenolpyruvate by PEPCK
Phosphoenolpyruvate –> Fructose-1,6-biphosphate –> Fructose-6-P (Req. ATP)
Fructose-6-P –> G-6-P by phosphoglucoisomerase
G-6-P + ADP–> glucose + ATP by G-6-phosphatase
Where does gluconeogenesis begin?
Mitochondria or cytoplasm
What is the only waste product produced by the TCA cycle?
CO2
Must be removed from the cell.
What happens after glycolysis breaks glucose into 2 small 3C mol (pyruvate)?
TCA cycle transfers their energy to e- carriers for use in the ETC to prod ATP
For every 1 pyruvate mol added to the TCA cycle, what is produced?
2 mol of CO2
3 mol of NADH
1 mol of FADH2
1 mol of GTP
(X2 due to EVERY glucose mol prod 2 pyruvate mol when broken down).
Transformation of pyruvate –> Acetyl-CoA (ready to enter TCA cycle)
Pyruvate diff. from cytoplasm into mitochondrial matrix.
Pyruvate is dehydrogenated + decarboxylated to form an (2C) acetyl group each.
Both are picked up by CoA to then become AcCoA (2C)
What equation can be used to summarise the link reaction? (Transformation of pyruvate into Acetyl-CoA)
Pyruvate + NAD + CoA —- AcCoA + red. NAD + CO2.
List the 8 intermediates of the TCA Cycle
Oxaloacetate
Citrate
Isocitrate
a-ketoglutarate
Succinyl-CoA
Succinate
Fumarate
Malate
How many protein complexes does the ETC have/.
4
What happens at the start of the ETC?
NADH is oxidised at 1st P pump: NADH –> NAD+ + 2H+
High energy e- fuel the 1st P pump to pump these 2H+ from MATRIX –> IM space.
2 e- then passed to mobile e- carrier in membrane to take e-‘s to 2nd pump.
Energy is used to pump 2P across membrane into IM space.
– Repeats at 3rd pump.
2e-‘s passed to 1/2 of an O2 mol (final e- acceptor) to combine w/ 2H+ –> H20.
== P pumps create a P gradient between IM space + matrix == P diff ⬇️ conc grad through ATPsynthase. Energy released is used for ADP + Pi –> ATP.
