Biochemistry of Metabolism Flashcards
what is glycogen?
major storage molecule for carbohydrates (glucose) in liver and muscle cells
what is glycogenesis?
synthesis of glycogen from glucose
what is glycogenolysis?
breakdown of glycogen to form glucose by cleaving glucose off the ends of the chains
Occurs in liver and muscle cells
how if glycogen stored in the liver?
can be broken down between meals and released to maintain blood glucose levels for RBCs and brain without food
how is glycogen stored in the muscle cells?
not available for maintenance of blood glucose
provides energy for the muscle cells via glycolysis and TCA during bursts of physical activity
what is gluconeogenesis?
pathway which generates glucose from non-carbohydrate precursors
how does dietary glucose affect blood glucose?
increases it quickly after meals, but it falls again quickly
when is blood sugar lowest and why?
in the morning, before breakfast as long time between last meal and liver cant break down any more glycogen
what is the primary source of glucose overnight?
gluconeogenesis
what is the structure of glycogen? (what bonds)
branched chain made of many glucose molecules joined together in chains via alpha 1-4, glycosidic bonds.
Branches are introduced by alpha 1-6, glycosidic bonds
what is the function of glycogenin?
has catalytic activity, acts as a primer
can add up to 4 glucose molecules to itself which allows glycogen synthase to create glycogen as it can only add on glucose, it cant start it
how is glycogen synthesised?
glucose phosphorylated to glucose 6 phosphate > glycolysis if needed or converted to glucose 1 phosphate > activated to UDP glucose > glycogen synthase bonds together glucose parts of UDP glucose (UDP recycled to make more UDP glucose using 1 ATP)
what is UDP glucose?
uridine diphosphate + glucose molecule connected via phosphate ester bond
Activated form of glucose (glucose transfer molecule)
what is the importance of the phosphate ester bond of UDP glucose?
contains high energy which can be released to transfer the glucose to the glycogen molecule (hydrolysis)
what is the function of glycogen synthase?
Rate limiting enzyme of glycogenesis
Synthesises glycogen by adding glucose from UDP glucose to the ends of glycogen chains
what is the branching enzyme?
transglycosylase that introduces 1-6 glycosidic branches to glycogen chains
what enzyme catalyses glycogenolysis?
glycogen phosphorylase
takes glucose off the end of glycogen and adds a phosphate > glucose 1 phosphate > glucose 6 phosphate
what are the steps of glycogenolysis?
glucose cleaved off end of glycogen and converted to glucose 1 phosphate by adding a phosphate (via glycogen phosphorylase) > glucose 1 phosphate > glucose 6 phosphate > dephosphorylated in liver and resulting glucose released into blood stream (via GLUT 2 transporter) OR undergoes glycolysis in skeletal muscle
what 2 enzymes regulate glycogenesis and glycogenolysis overall, and via which hormones?
glycogenesis = glycogen synthase glycogenolysis = glycogen phosphorylase
what effect does insulin have on glycogen synthase and glycogen phosphorylase?
hormone of the fed state
activates synthase, inhibits phosphorylase
what effect does glucagon have on glycogen synthase and glycogen phosphorylase?
hormone of starved state
inhibits synthase
activates phosphorylase (as does adrenaline and cortisol)
what are glycogen storage diseases?
diseases due to problems with enzymes of glycogenesis/glycogenolysis
what are the 3 precursors used in gluconeogenesis?
lactate (lactic acid)
amino acids (from muscle)
glycerol (from fat)
where does gluconeogenesis get energy?
from oxidation of fatty acids or muscle protein
where does gluconeogenesis occur?
liver
small amounts in the kidneys
how does the liver keep blood sugar levels constant?
glycogen synthesis/breakdown
gluconeogenesis
gluconeogenesis is like glycolysis in reverse, true or false?
true (almost)
BUT - special reactions required to bypass the 3 irreversible reactions in glycolysis using 4 liver enzymes
what is oxaloacetate?
4 carbon compound synthesised from pyruvate
allows gluconeogenesis to proceed
accepts acetyl groups in citric acid cycle during glycolysis
is gluconeogenesis energy dependant?
yes
requires 6 for every glucose made
what is the cori cycle?
lactic acid made from anaerobic glycolysis, taken to liver and glyconeogenesis occurs producing glucose
what are the 2 classes of amino acids?
glucogenic = can be used to make glucose ketogenic = cant be used to make glucose
do amino acids enter gluconeogenesis via the citric acids cycle or via converting to pyruvate?
both
what is the first step of gluconeogenesis?
conversion of pyruvate to oxaloacetate, stopping the citric acid cycle
how are glycolysis and glyconeogenesis regulated?
1) hormonally (glucagon - stimulates neogenesis, inhibits glycolysis, Insulin = opposite)
2) allosteric effectors in cells (ADP/AMP, ATP, fructose 2,6 biphosphate, citrate/alanine/acetyl CoA)
