MCB Lecture 13 Glycogenolysis and Glycogenesis, PDH, Citric acid cycle Flashcards
Describe the steps involved in glycogenolysis
- Glycogen phosphorylase enzyme breaks off glucose-1-phosphate molecules from the non-reducing end
NB phosphate attached, phosphate cleaved the a-1,4 bond
- Debranching enzyme has two functions:
a. transferring strings of glucose to the linear chain to isolate on glucose on the side branch
b. cleaving the a-1,6 bond of the glucose on the side chain
This creates a linear chain for further glycogen phosphorylase activity
- Phosphoglucomutase enzyme move the phosphate from 1C to 6C
The serine residue on the phosphoglucomutase enzyme is phosphorylated. This phosphate group move to the 6-carbon position, then the phosphate on the 1-carbon is cleaved and ends up on the serine residue.
Differentiate between Glycogenesis, glycogenolysis, gluconeogenesis and glycolysis.
Glycogenesis: making glycogen from glucose monomers
Glycogenolysis: breaking down glycogen into glucose monomers
Gluconeogenesis : converting pyruvate back to glucose
Glycolysis: breaking glucose down into pyruvate
Outline the steps in Glycogenesis
- UDP-glucose phosphorylase catalyses Glucose-1-phosphate molecules being added to UTP, making UDP-glucose, releasing pyrophosphate (PiPi)
- Glycogen synthase transfers the glucose from the UDP-glucose onto the end of a glycogen chain
- Glycogen branching enzyme transfers a group of glucose monomers in a linear chain onto the 6-carbon of another monomer, creating a branch.
- Glycogenin is the primer for a glycogen molecule.
Glycogen synthase isn’t able to start the molecule itself, a primer is required.
Glycogen in is both the primer and the enzyme making the primer
Describe the structure of glycogen
Branched chains of a-D-glucose monomers.
a-1,4 glycosidic bonds between the monomers in the linear chain
a-1,6 glycosidic bonds between the molecules at the branch points
It has a reducing and a non reducing end.
How is Citrate formed?
Anything else?
Acetyl-CoA + Oxaloacetate -> Citrate
Enzyme: citrate synthase
This is inhibited by ATP
Citrate -> ?
Enzymes?
Anything else?
Isocitrate
Aconitase
Isocitrate -> ?
Enzymes?
Anything else?
Alpha-ketogluterate
Isocitrate dehydrogenase
NADH produced
Alpha-ketogluterate -> ?
Enzymes?
Anything else?
Succinyl-CoA
Alpha-ketogluterate dehydrogenase complex
NADH produced
CO2 evolved
Succinyl CoA -> ?
Enzymes?
Anything else?
Succinate
Succinyl CoA synthetase
GTP evolved
Succinate -> ?
Enzymes?
Anything else?
Fumarate
Succinate dehydrogenase
FADH2 produced
Fumarate -> ?
Enzymes?
Anything else?
Malate
Fumarase
Malate -> ?
Enzymes?
Anything else?
Oxaloacetate
Malate dehydrogenase
NADH produced
At which points is GTP formed?
Succinyl-CoA -> Succinate
In which steps is NADH produced?
Isocitrate -> alpha-ketogluterate
Alpha-ketogluterate -> succinyl CoA
Malate -> Oxaloacetate
In which steps is FADH2 produced?
Succinate -> fumarate
Describe the function of the PDH complex
Converts pyruvate -> acetyl-CoA
3,4,5 reaction : 3 subunits of PDH
4-step reaction
5 cofactors
TPP, lipoate, NAD, FAD, CoA-SH
Which vitamins are especially important for metabolism?
Give some examples
These vitamins are cofactors for many important steps in cellular respiration
Niacin: NADH and NADPH Riboflavin: FAD and FMN Thiamin: TPP Pantothenic acid: coenzyme A Biotin: pyruvate carboxylase
Where is glycogen stored?
Mostly in muscle cells and liver cells as granules
What percentage of the total energy stored in a 70kg person is in the form of glycogen
Not much 1%
Which bonds are present in glycogen?
Alpha-1,4
Alpha-1,6
Where is the PDH complex?
In the mitochondria
What are the three irreversible steps of the citric acid cycle?
What is also important about these steps?
- Pyruvate -> acetyl CoA
- Isocitrate -> alpha ketogluterate
- Alpha ketogluterate -> succinyl co-A
They are the control steps of the citric acid cycle
How many vitamin Bs are there?
8
What is the first point of control of the citric acid cycle?
The PDH complex
Pyruvate -> acetyl CoA
Describe the first control point of the citric acid cycle
- The PDH complex
(+) ADP, pyruvate
(-) Acetyl-CoA, NADH, ATP
Describe the second control point of the citric acid cycle
- Isocitrate -> alpha ketogluterate
Isocitrate dehydrogenase
(+) ADP
(-) NADH, ARP
Describe the third control point of the citric acid cycle
- Alphaketogluterate dehydrogenase complex
(+) none
(-) NADH, ATP, succinyl-CoA
Which steps of glycolysis produce NADH?
i. Isocitrate -> alpha ketogluterate
ii. Alpha ketogluterate -> succinyl-CoA
iii. Malate -> oxaloacetate
Which steps of the citric acid cycle produce FADH2?
Succinate -> fumarate
Which steps of the citric acid cycle produce GTP?
Succinyl-CoA -> succinate
Which steps of the citric acid cycle evolve CO2?
Isocitrate -> alpha ketogluterate
Alpha ketogluterate -> succinyl-CoA
