Glycogen & glycolysis Flashcards
give examples of monosaccharides and disaccharide
Mono = glucose, galactose Di = lactose, sucrose
what does glucose & galactose make?
Lactose
what does glucose and fructose make?
Sucrose
how do we store carbohydrates?
Glycogen - a multi-branched polysaccharide of glucose
why do we need to store carbohydrates?
energy storage, structural components, enzyme components, DNA replication
what are the 2 major sites of glycogen storage?
liver & skeletal muscle (more is stored in muscle but its more concentrated in liver)
what happens if a problem enzyme is involved in glycogen breakdown? (disorder)
then will have low glucose levels in body - hypoglycaemia
Build up of glycogen in muscles and liver
what if a problem enzyme regulates glycogen synthesis?
reduced amounts of normal glycogen, abnormal glucose
symptoms of glycogen storage disorders?
type I - low blood sugar (Sweat, confusion, drowsiness) enlarged liver weaker muscles obesity kidney issues bleeding/clotting
what enzyme breaks down glycogen into glucose-1-phosphate?
Glycogen phosphorylase
what are the 3 types of bonds in glycogen?
Alpha-1,6 BRANCHES
alpha-1,4 links
as alpha-1,6 glycosidic bonds can’t be broken down by glycogen phosphorylase - what happens?
we need to use alpha-1,6-glucosidase which has transferase and debranching activity
what does alpha-1,6-glucosidase do?
enzyme that takes off the alpha-1,6 branches - then releases a glucose
How do we process glycogen breakdown products?
Glucose-1-phosphate (major) and glucose is converted to glucose-6-phosphate via phosphoglucomutase enzyme. This is then processed into glucose
how do skeletal muscle use glycogen breakdown products?
Glucose-6-phosphate into glycolysis pathway to generate ATP
How does liver use glycogen breakdown products?
Glucose-6-phosphate converted to glucose and sent to the brain for blood glucose
how is glycogen synthesised?
Glucose is converted to glucose-6-phosphate (hexokinase)
Glucose-6-phosphate converted to glucose-1-phosphae (phosphoglucomutase)
Glucose-1-phosphate converted to UDP-glucose (UDA-glycose phosphorylase)
UDP- glucose + glycogen via glycogen synthase = glycogen and UDP
what is UDP-glucose?
building block of glycogen - activated form of glucose
Enzymes involved in glycogen synthesis (4)
- hexokinase
- phosphoglucomutase
- UDP- glycose phosphorylase
- Glycogen synthase
MAIN enzymes in- glycogen breakdown & synthesis
Glycogen breakdown - glycogen phosphorylase
Synthesis - glycogen synthase
what does insulin do?
(insulin is released when we have high blood sugar levels promotes glycogen synthesis in liver and muscle
what does glucagon do?
released when we have low sugar levels = promotes glycogen breakdown in liver
HOW does glucagon stimulate glycogen breakdown?
increases cAMP and PKA+ which stimulates conversion of glycogen phosphorylase kinase to glycogen phosphorylase kinase (p)
- stimulates a cascade to break down
what are the key points of glucagon stimulated glycogen breakdown?
- amplification - single glucagon molecule activates many glycogen phosphorylase molecule
- Reverse covalent modifications - enzymes activated by phosphorylation amino acid residues.
- Receptor mediates- single molecule glucagon activates many cAMP molecules and so on
how does glucagon prevent glycogen synthesis?
Increases cAMP and PKA+ but coverts the active glycogen synthase into inactive form
how is glycogen breakdown stimulated in active muscle (exercise)
adrenaline, AMP, Ca2+ ions
AMP binds to inactive glycogen phosphorylase and promotes formation of the active
Ca2+ levels increase in exercise which promotes glycogen phosphorylase kinase activity
what is glycolysis?
regulated reaction that converts glucose into 2 pyruvate and 2 ATP
if there is high ATP - is enzyme inhibited or activated?
activated as we want to change it into ATP
what are the 3 key points of regulation in glycolysis?
- phosphofructokinase
- hexokinase
- pyruvate kinase
what is the most important enzyme in glycolysis?
phosphofructokinase - converts fructose-6-phosphate into fructose-1,6-bisphosphate
what is phosphofructokinase regulated by?
- ATP - activity is inhibited by ATP binding to an allosteric site as it lowers the affinity of it for fructose-6-phosphate
- Fructose-2,6-bisphosphate - it is an activator of phosphofructokinase - binds to allosteric site and enhances the affinity of it for fructose-6-phosphate
- Citrate - it enhances the inhibitory effect of ATP
what is hexokinase regulated by?
glucose-6-phosphate. FEEDBACK INHIBITION - If phosphofructokinase is inhibited, glucose-6-phosphate levels rise and this feeds back into the pathway to prevent the unnecessary conversion of glucose to glucose-6-phosphate
what is pyruvate kinase regulated by?
fructose-1,6-bisphosphate -
