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principles of normal function > week 3 carbs revised > Flashcards

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
Q

what is the fate of absorbed glucose

A
  • diffuses through intestine wall into blood then onto liver
  • immediately phosphorylated to glucose 6-phosphate
26
Q

why is glucose phosphorylated into G-6-P

A

traps glucose inside cells because GLUT transporter doesn’t recognise it in this form

27
Q

what enzymes catalyses the reaction of glucose to G-6-P

A
  • glucokinase (in liver)

- hexokinase (in other tissues)

28
Q

how are glucokinase and hexokinase able to distribute glucose equally to liver and other tissues

A

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
Q

what are the steps in the synthesis of glucose

A
  • 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
Q

what is the degradation of glycogen

A
  • 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
Q

what is the fate of G-6-P

A
  • goes to liver, turns into glucose and then moves into blood
  • goes to skeletal muscle, goes through glycolysis and lactate and ATP produced
32
Q

what is the order of digestion organs in digestion of carbs

A

mouth > stomach > duodenum > jejunum

33
Q

what molecule does glycolysis start with

A

glucose

34
Q

what is the end result of glycolysis

A

pyruvate + 2ATP

35
Q

what are the first three steps of glycolysis

A
  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
Q

what is the result of the first three steps of glycolysis

A

F-1, 6 biP

37
Q

what are the 4th and 5th steps of glycoslysis

A
  1. F-1, 6-biP turns into G-3-P via aldolase
  2. 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
Q

what are the 6th, 7th, 8th and 9th steps of glycolysis

A
  1. oxidation of G-3-P > 1, 3 bisPG, via glyceraldehyde 3 phosphate dehydrogenase, 2x NADH produced
  2. 1, 3 bisPG + ADP > 3PG + ATP, 2x ATP produced, via phosphoglycerate kinase
  3. 3PG > 2PG, via phosphoglycerate mutase
  4. dehydration of 2PG > PEP, via enolase
39
Q

what is the 10th step of glycolysis

A
  1. transfer of P from PEP > ADP,
    2x ATP produced
    pyruvate produced, via pyruvate kinase
40
Q

what is the fate of pyruvate

A
  • 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
Q

what is the enzyme which catalyses the reaction of pyruvate to lactate

A

pyruvate dehydrogenase

- NAD+ regenerated which is need for glycolysis

42
Q

what is the cori cycle

A
  • (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
Q

what are the steps in glycolysis which are irreversible

A

1, 3, 10

  1. G-6-P cannot directly be converted back to glucose
  2. F-1, 6biP cannot be directly converted back into F-6-P
  3. pyruvate cannot be directly converted back into PEP
44
Q

what is gluconeogenesis

A
  • reverse of glycolysis (pyruvate back to glucose)
45
Q

what are the bypass reactions A and B which turn pyruvate back into PEP in gluconeogenesis

A
  • 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
Q

what is the bypass reaction C which converts F-1, 6biP back into F-6-P

A

F-1, 6-biP + water > F-6-P + Pi

- via fructose 1, 6-biphosphatase

47
Q

what is reaction D that converts G-6-P back into glucose

A

G-6-P + water > glucose

- dephosphorylation via glucose 6 phosphatase

48
Q

what is the enzyme which converts pyruvate into acetyl coA

A
  • pyruvate dehydrogenase complex (E1, E2, E3) (respiratory chain)
  • pyruvate oxidised in mitochondria
49
Q

at what points can galactose enter glycolysis

A
  • enter at G-6-P
50
Q

at what point can fructose enter glycolysis

A
  • at F-6-P (adipose tissue)
  • DHAP (liver)
  • G3P (liver)

principles of normal function (15 decks)

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