Lecture 3 - Energy Storage Flashcards
Give two cells that have an absolute requirement for glucose
RBC’s/neutrophils/innermost cells of kidney medulla/lens of the eye
What is the ideal blood glucose concentration?
5mM
Give some symptoms of someone with low blood glucose (hypoglycaemia)
Confusion/weakness/nausea/muscle cramps/ brain damage and death at 0.6mM/L and below
Why does brain damage occur below 0.6mMol/L blood glucose?
Because although the brain can use ketone bodies for metabolism it still needs a sufficient level of glucose
Hyperglycaemia can be dangerous too, give two symptoms of hyperglycaemia?
Retinopathy/uropathy/nephropathy/poor wound healing
Why is a high level of glucose harmful in the body?
It can react with proteins and disruptive their function. This is called glycation of proteins (addition of glucose)
The two main stores of glycogen are the muscle and the liver, how do their functions differ?
Liver - used to replenish plasma glucose levels -> delivered to where it’s needed
Muscle - can only be used by the muscle for contraction, can’t exit the muscle
Glycogen is a polymer of glucose arranged in a tree like structure. What binds link the individual monomers of glucose and what bonds form the branch points every 8-10 residues?
Monomers - alpha 1-4 glycosidic bonds
Branch points - alpha 1-6 glycosidic bonds
Give a reason why glycogen a hugely branched structure is favourable
There are several points from which a glucose molecule can be cleaved, so more than one can be cleaved at once
Being stored as a large macromolecule it doesn’t bring water in
Starting from the first enzyme in glycogen SYNTHESIS name the enzymes involved
1) hexokinase/glucokinase in liver
2) phosphoglucomutase
3) G1P uridyltransferase
4) glycogen synthase/branching enzyme
Glycogenolysis can’t use all the same enzymes in reverse. What enzymes are different?
Debranching enzyme/glycogen phosphorylase depending on branch point or end point
Glucose-6P to change it back to glucose in the liver
What is missing in the muscle glycogen to mean that it can’t contribute to buffering blood glucose levels
The glucose-6-phosphatase enzyme
What is the rate limiting enzyme in
a) glycogenesis
b) glycogenolysis
a) Glycogen synthase
b) Glycogen phosphorylase
Glucagon phosphorylates and insulin dephosphorylates the rate limiting enzymes, would insulin increase or decrease the following enzyme activity
a) glycogen synthase
b) glycogen phosphorylase
A) increase
B) decrease
What hormone mirrors the actions of glucagon in regards to glucose mobilisation?
Adrenaline
Von Gierkes disease is a deficiency of glucose 6-phosphatase, what are the symptoms of this?
Hepatomegaly (enlarged liver)
Explanation - this enzyme mobilises glucose so it can be transported in the bloodstream. Without the glycogen builds up in the liver and enlarges it
McArdle’s disease results in the muscle not being able to mobilise glucose for muscle contraction. This results in the patient having severe tired ness on excercise, which enzyme is deficient in this?
Muscle glycogen phosphorylase
After how many hours post feeding is new glucose required via gluconeogenesis
8 hours
Explanation - because the lovers glycogen stores are by this point depleted
Where does gluconeogenesis occur?
Liver
A little bit in the kidney
Give the three main precursors which can feed into gluconeogenesis
Lactate
Glycerol
Amino acids (mainly alanine)
How is lactate produced in the muscle converted back into glucose for the muscle?
Via the cori cycle - lactate carries to the liver in blood -> converted back to glucose in liver -> back to muscle
Name the three main regulatory enzymes in gluconeogenesis, which two are the major two control points?
PEPCK
Fructose 1,6-bisphosphatase
Glucose-6-phosphatase
Top two are major control points
Glucagon and insulin again are the regulatory hormones of gluconeogenesis. Does glucagon increase or decrease activity of
a) PEPCK
b) fructose 1,6 bisphosphatase
a) increase
b) increase
Explanation - think in terms of increasing levels of circulating glucose
Triglycerides are a storied form of lipid made up of glycerol and fatty acids. What type of tissue are they stored in?
Adipose tissue
Explanation - TAGs are hydrophobic and need to be stored thus is this anhydrous form
What’s the key regulatory enzyme in fatty acid synthesis?
Acetyl-CoA carboxylase
Name two things that increase the activity of acetyl-CoA carboxylase and two things which decrease its activity
Increase - insulin/citrate
Decrease - glucagon/adrenaline/AMP
beta oxidation occurs in the mitochondria, where does fatty acid synthesis occur?
The cytoplasm
The mobilisation of fatty acids and glycerol from adipose tissue is controlled by what enzyme?
Hormone sensitive lipase
Does glucagon inhibit or stimulate hormone sensitive lipase?
Stimulates
Explanation - glucagon wants to increase blood glucose levels, HSL breaks TAGs down to glycerol and FA’s. The glycerol can go into gluconeogenesis
In what form is most energy stored in a human, the proportion of energy stored as this increases in obesity
TAG’s/adipose tissue
Name three differences between Beta oxidation (fatty acid oxidation) and fatty acid synthesis
B oxidation occurs in mitochondria, fatty acid synthesis in the cytoplasm
B oxidation is oxidative (produces reducing power), fatty acid synthesis is reductive (uses reducing power)
Insulin inhibits beta oxdation, insulin stimulates fatty acid synthesis
B oxidation requires little ATP, fatty acid synthesis needs a lot of ATP
Give the key regulatory enzymes in:
a) glycolysis
b) gluconeogenesis
c) lipogenesis
d) beta-oxidation
e) glycogenesis
f) glycogenolysis
glycolysis - pyruvate kinase, phosphofructokinase (main) , hexokinase
gluconeogenesis - PEPCK, Fructose-1,6 bisphosphatase
glycogenesis - glycogen synthase
glycogenolysis - glycogen phosphorylase
lipogenesis - acetyl-CoA carboxylase
beta oxidation - CAT1
