Biochemistry

Question 1

what are the 3 main glycogen metabolic pathways

Answer 1

glycogenesis: synthesis of glycogen from glucose
glycogenolysis: breakdown from glycogen to from glucose
gluconeogenesis: de novo synthesis pf glucose from metabolic precursors (AAs, lactate)

Question 2

what is glycogen?

Answer 2

a polymer of glucose

Question 3

what 2 substances are needed for glycogenesis?

Answer 3

UDP & Glycogen synthase

Question 4

what is UDP?

Answer 4

activated form of glucose

Question 5

what is glycogen synthase?

Answer 5

key enzyme that synthesises glycogen from UDP-glucose.

Question 6

True/False…

glycogen synthase is rate limiting

Answer 6

True…

it can only add 1 glucose molecule to glycogen at a time

Question 7

what is the key enzyme for glycogenolysis?

Answer 7

glycogen phosphorylase

Question 8

what does glycogen phosphorylase do?

Answer 8

cleaves off 1 glucose from glycogen at a time.

Question 9

which organ can dephosphorylate glucose-6-phosphate to form glucose?

Answer 9

the liver, muscle can’t do this

Question 10

when does gluconeogenesis usually kick in?

Answer 10

during prolonged starvation

Question 11

what are the precursors, energy supply and location of gluconeogenesis?

Answer 11

precursors: AAs, lactate, glycerol
energy: oxidation of fatty acids from adipose tissue
location: liver

Question 12

what determines glycolysis or gluconeogenesis?

Answer 12

hormones, high AMP/ADP, high ATP, acetyl-coA etc

Question 13

what is the Cori Cycle?

Answer 13

lactate formation

Question 14

describe the Cori Cycle…

Answer 14

lactate formed in fast twitch muscles > lactate transported to liver by blood > liver converts lactate to glucose

Question 15

what are the 3 classes of lipids

Answer 15

simple (fatty acids, triglycerides)
compound (phosphorylase, glycol, lipo)
steroids (cholesterol, steroid hormones)

Question 16

True/False…

fatty acids are a straight chain

Answer 16

True

Question 17

True/False…

fatty acids have an odd number of C atoms

Answer 17

False…

even number

Question 18

what does saturated, unsaturated and polyunsaturated in terms of bonds mean?

Answer 18

saturated- single bond
unsaturated- double bond
polyunsaturated- several double bonds

Question 19

what are fats broken down to?

Answer 19

monoglycerides

Question 20

short and medium FAs absorbed by…

Answer 20

mucosal cells

Question 21

long FAs and monoglycerides are…

Answer 21

resynthesised into triglycerides

Question 22

what are chylomicrons?

Answer 22

triglycerides coated with protein, cholesterol, phospholipid

Question 23

what happens to chylomicrons

Answer 23

cleaved by lipases to form free fatty acids which can be resynthesised or oxidised

Question 24

triglycerides are composed of…

Answer 24

1 glycerol & 3 FAs, have a high energy yield

Question 25

what happens during lipolysis

Answer 25

1. initial cleavage of triglycerides by hormone sensitive lipases
2. FAs are then converted o acetyl-CoA (in cytoplasm- req 2 ATP)
3. FAs undergo oxidation to provide energy (matrix of mitochondria)

Question 26

what is the carnitine shuttle

Answer 26

allows acetyl CoA to travel to matrix for B-oxidation

Question 27

what does b-oxidation produce?

Answer 27

produces 1 acetyl-coA, 1 FADH, 1 NADH + H+, 1 fatty acyl-CoA

Question 28

how are ketone bodies formed?

Answer 28

formed in mitochondria of liver and eventually converted back to acetyl CoA

Question 29

what does fatty acid oxidation usually yield if carb and fat degradation is balanced?

Answer 29

acetyl co-A which enter Citric Acid Cycle

Question 30

what happens in fatty acid oxidation if in starvation or a diabetic?

Answer 30

oxaloacetate is used for gluconeogenesis, fatty acids are oxidised to provide energy so acetyl-CoA converted to ketone bodies

Question 31

what is dangerous about ketosis

Answer 31

ketoacidosis may occur

Question 32

where does de novo synthesis of fatty acids occur?

Answer 32

in the liver, kidney, mammary glands, adipose tissue and brain

Question 33

why does denovo synthesis of FAs occur?

Answer 33

during excess energy intake

Question 34

where does lipogenesis occur

Answer 34

cytoplasm

Question 35

what is citrate’s role in acetyl co A transport?

Answer 35

carries acetyl co-A from mitochondria to cytoplasm for lipogenesis

Question 36

once in cytoplasm, what happens to the acetyl co-A?

Answer 36

activated to malonyl-CoA which donates carbon atoms to new lipid

Question 37

what is the cycle of lipogenesis?

Answer 37

1. condensation
2. reduction
3. dehydration
4. reduction & release

Question 38

once what no of carbon atoms is reached, does the FA release itself?

Answer 38

C16

Question 39

what enzyme is needed for the synthesis of FAs from acetyl-coA

Answer 39

fatty acid synthase

Question 40

what enzyme controls lipogenesis?

Answer 40

acetyl-coA Carboxylase - activates acetyl-CoA to malonyl-CoA

Question 41

what is acetyl-coA Carboxylase activated and inhibited by?

Answer 41

activated: insulin, glucagon, epinephrine, citrate
inhibited: palmitoyl-CoA

Question 42

what does triglyceride synthesis require?

Answer 42

glucose-3-phosphate

Question 43

where does amino acid metabolism occur?

Answer 43

liver

Question 44

what happens if AAs can’t be degraded?

Answer 44

are absorbed into intestinal cells and released into blood

Question 45

what are AA produced ammonium ions excreted by and why?

Answer 45

they are toxic so excreted by urea, uric acid, creatinine

Question 46

how is urea synthesised?

Answer 46

AA > glutamic acid > NADH + NH4+ + aspartic acid > urea

Question 47

after removal of an amino group in transmission stage of urea synthesis, what are remaining carbon skeletons converted to?

Answer 47

either glucose or oxidised to join TCA cycle