week 3 carbs revised Flashcards

1
Q

what are the major carbs in our diet

A
  • starch (rice)
  • glycogen (meat)
  • cellulose and hemicellulose (plant cell wall, can’t digest)
  • oligosaccharides containing (a1-6) linked galactose (peas, beans)
  • lactose, sucrose, maltose
  • glucose, fructose
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2
Q

what are the monosaccharides which are major carbs in our diet

A
  • glucose
  • fructose
  • galactose = (oligosaccharide containing (a1-6) linked galactose)
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3
Q

what kind of sugars are monosaccharides

A
  • hexoses (6 carbons sugars)
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4
Q

what are the disaccharides which are major carbs in our diet

A
  • maltose
  • lactose
  • sucrose
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5
Q

what are the bonds linking monosaccharides called

A
  • glycosidic bonds
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6
Q

what are the characteristics of maltose

A
  • major carb in diet
  • disaccharide
  • anomeric, C-1 is available for oxidation therefore it is a reducing sugar
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7
Q

what are the characteristics of lactose

A
  • major carb in diet
  • disaccharide
  • formed from glycosidic bond between galactose and glucose
  • it is a reducing sugar
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8
Q

what are the characteristics of sucrose

A
  • major carb in diet
  • disaccharide
  • non-reducing sugar
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9
Q

what is the starch formed from

A

amylose and amylopectin linked by glycosidic bond (two types of glucose polymer), form alpha helices with few reducing ends and many non-reducing ends
- amylopectin contains (a1-6) branches

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10
Q

where is glycogen stored

A

90% in liver and skeletal muscle

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11
Q

what is the function of glycogen in the liver

A
  • replenish blood glucose when fasting
  • if blood glucose falls then glycogen > G-6-P > glucose into blood
  • G6P > glucose via glucose 6 phosphatase
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12
Q

what is the function of glycogen in the skeletal muscle

A
  • catabolism produces ATP for contraction
  • no G-6-P
  • glycogen > lactate via glycolysis
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13
Q

what is the structure of glycogen

A
  • polymer of glucose (a1-4) and (a1-6) branch every 8-12 residues
  • stores glucose
  • major carb in diet
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14
Q

what is a proteoglycan

A
  • carb > protein

- in connective tissues

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15
Q

what is a glycoprotein

A
  • protein > carb

- in membrane, ECM, blood, Golgi complex

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16
Q

what is a glycosaminoglycan (GAG)

A
  • un branched polymers
  • repeating units of hexuronic acid and an amino sugar
  • in mucous and synovial fluid
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17
Q

what is the digestion of carbs in the mouth

A
  • salivary amylase hydrolyses (a1-4) bonds of starch
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18
Q

what is the digestion of carbs in the stomach

A

no digestion of carbs in the stomach

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19
Q

what is the digestion of carbs in the duodenum

A
  • same as mouth

- pancreatic amylase hydrolyses (a1-4) bonds of starch

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20
Q

what is the digestion of carbs in the jejunum

A

final digestion by mucosal cell surface enzymes

  1. isomaltase hydrolyses (a1-6) bonds
  2. glucoamylase removes glucose from non-reducing ends
  3. sucrase hydrolyses sucrose
  4. lactase hydrolyses lactose
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21
Q

what are the main products of digestion

A
  • glucose
  • galactose
  • fructose
22
Q

how is glucose absorbed

A
  • via Na+ - glucose symport

- ATP driven and maintains low cellular sodium concentration

23
Q

how is galactose absorbed

A

utilises gradients to facilitate its transport

24
Q

how is fructose absorbed

A
  • binds to GLUT 5 and moves down conc. gradient into blood
25
what is the fate of absorbed glucose
- diffuses through intestine wall into blood then onto liver - immediately phosphorylated to glucose 6-phosphate
26
why is glucose phosphorylated into G-6-P
traps glucose inside cells because GLUT transporter doesn't recognise it in this form
27
what enzymes catalyses the reaction of glucose to G-6-P
- glucokinase (in liver) | - hexokinase (in other tissues)
28
how are glucokinase and hexokinase able to distribute glucose equally to liver and other tissues
hexokinase (other tissues) - low Km = high affinity, so even at low conc. able to get glucose - low Vmax so tissues are easily satisfied and don't need much glucose glucokinase (liver) - high Km = low affinity - but high Vmax so able to grab glucose quickly, so most glc in liver
29
what are the steps in the synthesis of glucose
- glycogenin covalently binds to glucose (from UDP-glucose) - glycogen synthase extends glucose chains - chains formed by glycogen synthase broken by glycogen branching enzyme and re-attached via (a1-6) bonds to give branch points
30
what is the degradation of glycogen
- glucose monomers removed one at a time from reducing ends as G-1-P via glycogen phosphatase - de-branching enzyme removes set of 3 glucose residues and attaches them to nearest non-reducing end via (a1-4) bonds - final glucose then removed by breaking (a1-6) linkage to release free glucose this leaves unbranched chain
31
what is the fate of G-6-P
- goes to liver, turns into glucose and then moves into blood - goes to skeletal muscle, goes through glycolysis and lactate and ATP produced
32
what is the order of digestion organs in digestion of carbs
mouth > stomach > duodenum > jejunum
33
what molecule does glycolysis start with
glucose
34
what is the end result of glycolysis
pyruvate + 2ATP
35
what are the first three steps of glycolysis
1. phosphorylation of glucose to glucose 6-phostphate (IRREVERSIBLE), via hexokinase, uses 1ATP 2. G-6-P > F-6-P, via phospho-hexo-isomerase 3. phosphorylation of F-6-P > F1, 6-biP (IRREVERSIBLE), Bia phospho-fructo-kinase-1, 1ATP used
36
what is the result of the first three steps of glycolysis
F-1, 6 biP
37
what are the 4th and 5th steps of glycoslysis
4. F-1, 6-biP turns into G-3-P via aldolase 5. F-1, 6-biP may turns into DHAP but that then turns into G-3-P, via triose iso-phosphate isomerase so we know have 2x G3P to start second half of glycolysis
38
what are the 6th, 7th, 8th and 9th steps of glycolysis
6. oxidation of G-3-P > 1, 3 bisPG, via glyceraldehyde 3 phosphate dehydrogenase, 2x NADH produced 7. 1, 3 bisPG + ADP > 3PG + ATP, 2x ATP produced, via phosphoglycerate kinase 8. 3PG > 2PG, via phosphoglycerate mutase 9. dehydration of 2PG > PEP, via enolase
39
what is the 10th step of glycolysis
10. transfer of P from PEP > ADP, 2x ATP produced pyruvate produced, via pyruvate kinase
40
what is the fate of pyruvate
- fermentation to ethanol and CO2 in yeast - in aerobic conditions citric acid cycle then terminal respiration - in anaerobic conditions we get lactate in muscle (NAD+ also produced which is needed for glycolysis)
41
what is the enzyme which catalyses the reaction of pyruvate to lactate
pyruvate dehydrogenase | - NAD+ regenerated which is need for glycolysis
42
what is the cori cycle
- (in liver) lactate>pyruvate>glucose (then move to blood) (then move to muscle) glucose>pyruvate>lactate (then move to blood then back to liver) - so gluconeogenesis in liver, glucose moves through blood to muscle, then glycolysis and fermentation in muscle - this repays oxygen debt run up by muscles in low O2
43
what are the steps in glycolysis which are irreversible
1, 3, 10 1. G-6-P cannot directly be converted back to glucose 3. F-1, 6biP cannot be directly converted back into F-6-P 10. pyruvate cannot be directly converted back into PEP
44
what is gluconeogenesis
- reverse of glycolysis (pyruvate back to glucose)
45
what are the bypass reactions A and B which turn pyruvate back into PEP in gluconeogenesis
- pyruvate moves into mitochondria - pyruvate converts into oxaloacetate - oxaloacetate converts into malate - malate moves out of mitochondria - malate turns back into oxaloacetate - oxaloacetate turns into PEP
46
what is the bypass reaction C which converts F-1, 6biP back into F-6-P
F-1, 6-biP + water > F-6-P + Pi | - via fructose 1, 6-biphosphatase
47
what is reaction D that converts G-6-P back into glucose
G-6-P + water > glucose | - dephosphorylation via glucose 6 phosphatase
48
what is the enzyme which converts pyruvate into acetyl coA
- pyruvate dehydrogenase complex (E1, E2, E3) (respiratory chain) - pyruvate oxidised in mitochondria
49
at what points can galactose enter glycolysis
- enter at G-6-P
50
at what point can fructose enter glycolysis
- at F-6-P (adipose tissue) - DHAP (liver) - G3P (liver)