4: Biochemistry - Glycogen metabolism Flashcards
What is glycogenesis?
Synthesis of glycogen from glucose
What is glycogenolysis?
Breakdown of glycogen to form glucose
What is glycogen?
A storage unit of glucose
Where is glycogen found?
Liver cells
Muscle cells
The glycogen stored in the liver is stored and then released to maintain an appropriate [X]blood.
Name X.
Glucose
Muscle glycogen can:
a) only be consumed within a muscle cell
b) be consumed by the blood to maintain [glucose]
a - not available for maintenance of blood glucose
By which process do muscle cells use glycogen?
Glycolysis
When would muscle cells use glycogen?
During physical activity
Glycolysis allows muscle cells to generate ___.
ATP
Dietary carbohydrate contributes to blood sugar levels immediately following ___.
meals
Which process maintains blood sugar levels between meals?
Glycogenolysis
Which process maintains blood sugar levels when dietary carbohydrate isn’t available and liver glycogen stores have been depleted?
Gluconeogenesis
Glycogen is a polymer of which monosaccharide?
Glucose
Which bonds form long, straight chains of glucose molecules?
α 1-4 glycosidic bonds
Which carbons are bonded to form long, straight glycosidic bonds between glucose in a molecule of glycogen?
1 and 4
Which bonds form branches in a glycogen molecule?
α 1-6 glycosidic bonds
The more ___ a glycogen molecule has, the greater the rate at which glucose can be added or cleaved off it.
branches
Which protein, found on glucose chains, acts as a catalyst for glycogen synthesis by forming precursor glycogen molecules?
Glycogenin
Which protein is added to a glucose primer before glycogen synthesis?
Glycogenin
Before glucose can be used by a cell, it must be (phosphorylated / dephosphorylated) by an enzyme.
What is this enzyme called?
What is the end product of this reaction?
phosphorylated
Hexokinase
Glucose-6-phosphate
Which product is formed by the phosphorylation of glucose by hexokinase?
Glucose-6-phosphate
If immediate energy is required, glucose-6-phosphate can be used in which process?
Glycolysis
Name two possible fates of glucose-6-phosphate.
Used in glycolysis for immediate energy
or
Stored as glycogen
refer to glycogen synthesis diagram
For each glucose which is added to glycogen, 1 ATP is consumed.
Why?
ATP is used to regenerate UDP ⇒ UTP.
Which molecule activates glucose-1-phosphate before it is added to glycogen?
What is the name of the activated glucose molecule?
(Which enzyme carries out this process?)
UTP
UDP-glucose
(UDP-glucose pyrophosphorylase)
Which enzyme adds UDP-glucose to glycogen?
What is a byproduct of this reaction?
Glycogen synthase
UDP
Before precursor molecules can be used in biochemical processes, they need to be ___.
activated
Why can UTP be used to transfer glucose to a glycogen molecule?
The bond contains a lot of free energy (same concept with ATP)
How many glucose molecules are added by each reaction catalysed by glycogen synthase?
1
Can glycogen synthase introduce branches to a glucose chain?
No
What is the rate limiting enzyme of glycogenesis?
Why?
Glycogen synthase
It can only add on one glucose molecule at a time
Which enzyme introduces branches to a glycogen molecule?
Transglycosylase
Which type of bond introduces branches to a glycogen molecule?
Which enzyme is responsible?
α 1-6 glycosidic bonds
Transglycosylase
Which process involves the removal of glucose molecules from glycogen?
Glycogenolysis
Which enzyme removes a glucose molecule from glycogen by adding a phosphate molecule to it?
Glycogen phosphorylase
Write a word equation for glycogenolysis.
[glucose]n + Pi ⇒ [glucose]n-1 + glucose-1-phosphate
What is the rate limiting enzyme of glycogenolysis?
Why?
Glycogen phosphorylase
It can only remove one glucose molecule at a time
How is glucose-1-phosphate prepared for glycolysis following glycogenolysis?
It’s converted back into glucose-6-phosphate
Which enzyme is responsible for both:
glucose-6-phosphate ⇒ glucose-1-phosphate in glycogenesis
and
glucose-1-phosphate ⇒ glucose-6-phosphate following glycogenolysis?
Phosphoglucomutase
The liver can dephosphorylate glucose-6-phosphate and release it into the bloodstream as glucose.
Is this glycolysis?
No, different shortened process
Can skeletal muscle dephosphorylate glucose-6-phosphate as the liver does?
No - must go through glycolysis and Kreb’s instead
In the liver, which enzyme dephosphorylates glucose-6-phosphate into glucose for the bloodstream?
Glucose-6-phosphatase
Which transporter, found in liver cells, transports glucose into the blood?
GLUT2
If glycogenesis and ___ occured at the same rate, the whole process would be pointless.
glycogenolysis
Which hormone regulates the activity of:
glycogen synthase (glycogenesis)
and
glycogen phosphorylase (glycogenolysis)?
Insulin
The presence of insulin (stimulates / inhibits) glycogenesis and (stimulates / inhibits) glycogenolysis.
stimulates
inhibits
Which process and enzyme are stimulated by high insulin levels?
Glycogenesis, catalysed by glycogen synthase
Which process and enzyme are stimulated by low insulin levels?
Glycogenolysis, catalysed by glycogen phosphorylase
Which hormone, other than insulin, also affects the rates of glycogenesis and glycogenolysis?
Glucagon
match levels of insulin and glucagon to inhibition / stimulation of the two processes because they work as a pair
Which hormones, released in emergencies, stimulate glycogen phosphorylase and therefore glycogenolysis?
Adrenaline
Cortisol
Glycogen storage disease are associated with (hormone / enzyme) defects.
enzyme
