Biochemistry of Metabolism

Question 1

what is glycogen?

Answer 1

major storage molecule for carbohydrates (glucose) in liver and muscle cells

Question 2

what is glycogenesis?

Answer 2

synthesis of glycogen from glucose

Question 3

what is glycogenolysis?

Answer 3

breakdown of glycogen to form glucose by cleaving glucose off the ends of the chains
Occurs in liver and muscle cells

Question 4

how if glycogen stored in the liver?

Answer 4

can be broken down between meals and released to maintain blood glucose levels for RBCs and brain without food

Question 5

how is glycogen stored in the muscle cells?

Answer 5

not available for maintenance of blood glucose

provides energy for the muscle cells via glycolysis and TCA during bursts of physical activity

Question 6

what is gluconeogenesis?

Answer 6

pathway which generates glucose from non-carbohydrate precursors

Question 7

how does dietary glucose affect blood glucose?

Answer 7

increases it quickly after meals, but it falls again quickly

Question 8

when is blood sugar lowest and why?

Answer 8

in the morning, before breakfast as long time between last meal and liver cant break down any more glycogen

Question 9

what is the primary source of glucose overnight?

Answer 9

gluconeogenesis

Question 10

what is the structure of glycogen? (what bonds)

Answer 10

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

Question 11

what is the function of glycogenin?

Answer 11

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

Question 12

how is glycogen synthesised?

Answer 12

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)

Question 13

what is UDP glucose?

Answer 13

uridine diphosphate + glucose molecule connected via phosphate ester bond
Activated form of glucose (glucose transfer molecule)

Question 14

what is the importance of the phosphate ester bond of UDP glucose?

Answer 14

contains high energy which can be released to transfer the glucose to the glycogen molecule (hydrolysis)

Question 15

what is the function of glycogen synthase?

Answer 15

Rate limiting enzyme of glycogenesis

Synthesises glycogen by adding glucose from UDP glucose to the ends of glycogen chains

Question 16

what is the branching enzyme?

Answer 16

transglycosylase that introduces 1-6 glycosidic branches to glycogen chains

Question 17

what enzyme catalyses glycogenolysis?

Answer 17

glycogen phosphorylase

takes glucose off the end of glycogen and adds a phosphate > glucose 1 phosphate > glucose 6 phosphate

Question 18

what are the steps of glycogenolysis?

Answer 18

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

Question 19

what 2 enzymes regulate glycogenesis and glycogenolysis overall, and via which hormones?

Answer 19

glycogenesis = glycogen synthase 
glycogenolysis = glycogen phosphorylase

Question 20

what effect does insulin have on glycogen synthase and glycogen phosphorylase?

Answer 20

hormone of the fed state

activates synthase, inhibits phosphorylase

Question 21

what effect does glucagon have on glycogen synthase and glycogen phosphorylase?

Answer 21

hormone of starved state
inhibits synthase
activates phosphorylase (as does adrenaline and cortisol)

Question 22

what are glycogen storage diseases?

Answer 22

diseases due to problems with enzymes of glycogenesis/glycogenolysis

Question 23

what are the 3 precursors used in gluconeogenesis?

Answer 23

lactate (lactic acid)
amino acids (from muscle)
glycerol (from fat)

Question 24

where does gluconeogenesis get energy?

Answer 24

from oxidation of fatty acids or muscle protein

Question 25

where does gluconeogenesis occur?

Answer 25

liver

small amounts in the kidneys

Question 26

how does the liver keep blood sugar levels constant?

Answer 26

glycogen synthesis/breakdown

gluconeogenesis

Question 27

gluconeogenesis is like glycolysis in reverse, true or false?

Answer 27

true (almost)

BUT - special reactions required to bypass the 3 irreversible reactions in glycolysis using 4 liver enzymes

Question 28

what is oxaloacetate?

Answer 28

4 carbon compound synthesised from pyruvate
allows gluconeogenesis to proceed
accepts acetyl groups in citric acid cycle during glycolysis

Question 29

is gluconeogenesis energy dependant?

Answer 29

yes

requires 6 for every glucose made

Question 30

what is the cori cycle?

Answer 30

lactic acid made from anaerobic glycolysis, taken to liver and glyconeogenesis occurs producing glucose

Question 31

what are the 2 classes of amino acids?

Answer 31

glucogenic = can be used to make glucose
ketogenic = cant be used to make glucose

Question 32

do amino acids enter gluconeogenesis via the citric acids cycle or via converting to pyruvate?

Answer 32

both

Question 33

what is the first step of gluconeogenesis?

Answer 33

conversion of pyruvate to oxaloacetate, stopping the citric acid cycle

Question 34

how are glycolysis and glyconeogenesis regulated?

Answer 34

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)