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Science for Medicine > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

what are the three types of simple sugars found in nature?

A

glucose
galactose
fructose

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2
Q

what are simple sugars made up of?

A

six carbons (hexoses)

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3
Q

what are common types of disaccharides and what are they made up of?

A

sucrose - glucose + fructose
lactose - glucose + galactose
maltose - glucose + glucose

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4
Q

what are the different types of polysaccharides classified?

A

branched or unbranched

homeopolysaccharides or heteropolysaccharides

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5
Q

how can the branching of a polysaccharide be written as?

A

unbranched (linear) - alpha 1-4

branched - alpha 1-6

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6
Q

which disaccharides can or can’t be oxidised?

A

maltose and lactose can be oxidised

sucrose can’t be oxidised

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7
Q

what are the types of starch in plants and their prevalence in starch?

A

amylose (20%)

amylopectin (80%)

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8
Q

what is the animal variant of starch, and where is it found?

A

glycogen

found in liver and skeletal muscle

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9
Q

what is the difference between glycoproteins and proteoglycans?

A

proteoglycans - made up of GAG and protein. form part of ECM, are found in cell membranes
glycopeptides - can be involved in lots of functions, most proteins have carbohydrates attached

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10
Q

what are glycosaminoglycans?

A

cells secreting mucus, made up of hexuronic acid + amino-sugar

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11
Q

what are disorders caused by GAG imbalance, and what is an example?

A

mucopolysaccharidoses

eg Hurler’s syndrome

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12
Q

what enzymes break down carbohydrates and where?

A

mouth - salivary amylase
duodenum - pancreatic amylase
jejunum - lactase, sucrase, maltase, isomaltase, glucoamylase

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13
Q

how is glucose taken up by the blood?

A

from gut to endothelial cell (through ATPase pump)

from endothelial cell to blood (through GLUT 2 protein)

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14
Q

which protein transports which carbohydrate monomer to the blood?

A

glucose and galactose - GLUT2

fructose - GLUT5 (concentration gradient)

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15
Q

where is glucose stored?

A

in glycogen (liver and skeletal muscle)

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16
Q

what is the first thing that happens when glucose enters liver and other tissue cells?

A

liver: glucokinase adds phosphate and traps glucose in cell

other tissues: hexokinase adds phosphate to trap glucose in cell

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17
Q

what are the affinity and efficacy of glucokinase and hexokinase?

A

glucokinase - high Km and high Vmax

hexokinase - low Km and low Vmax

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18
Q

how is glycogen formed?

A

glycogenin binds glucose to itself
glycogen synthase continues the job
glycogen branching enzyme adds more glucose

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19
Q

how is glycogen broken down?

A

glycogen phosphorylase - removes glucose1phosphate

glucose 6 phosphatase - removes phosphate and allows glucose to leave cell

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20
Q

which glycogen breakdown enzyme is only present in liver cells?

A

glucose 6 phosphatase

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21
Q

what are two examples of disorders caused by lack of glucose 6 phosphatase or glycogen phosphorylase?

A

Von Gierke’s disease (no phosphatase in liver)

McArdle’s disease (phosphorylase in skel muscle)

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22
Q

how many steps are there in glycolysis?

A

10

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23
Q

which steps of glycolysis are spontaneous and therefore irreversible?

A

1, 3 and 10

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24
Q

what characterises glycolysis in terms of oxygen need?

A

it doesn’t require any oxygen

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25
Q

what is the net yield of glycolysis?

A

per cycle (G3P + DHAP):

  • 2ATP
  • 2NADH
26
Q

at which stages of glycolysis does ATP get used or produced?

A

stage 1 - ATP used (-1ATP)
stage 3 - ATP used (-1ATP)
stage 7 (+2ATP)
stage 10 (+2ATP)

27
Q

at which stage in glycolysis is NADH formed?

28
Q

what is the start and end result of glycolysis?

A

glucose –> pyruvate

29
Q

what are the three possible outcomes of pyruvate?

A

no oxygen: lactate
no or low oxygen: ethanol (fermentation)
oxygen: acetyl CoA (citric acid cycle)

30
Q

what catalyses the reaction from pyruvate to acetyl CoA?

A

pyruvate dehydrogenase

31
Q

what are the two main phases of glycolysis?

A

preparatory phase

pay-off phase

32
Q

what is redox balance, when and why does it occur?

A

what: it’s the recycling of NAD after glycolysis
when: when pyruvate becomes acetyl CoA
why: so it can be used for the next glycolysis, since NAD is limited

33
Q

what are the stages of gluconeogenesis, and why do they occur?

A

Step A and B: add 4C (oxaloacetate) to lactate/pyruvate = PEP
Step C: removes phosphate from fructose so it can’t split (hydrolysis)
Step D: remove phosphate from G6P (hydrolysis)
exist to bypass the irreversible reactions from glycolysis

34
Q

what is the functional difference between NADH and NADPH?

A

NADH - used in glycolysis for glucose metabolism

NADPH - used for anabolic reactions (making nucleotides) and as antioxidant

35
Q

why does drinking alcohol stop gluconeogenesis?

A

because gluconeogenesis needs NAD to start the process, but NAD is used up to metabolise ethanol into acetate

36
Q

what is the pentose phosphate pathway?

A

a process which produces NADPH and pentose sugars, which are used for nucleotides (riboses)

37
Q

what are the two stages of pentose phosphate pathway an what do they produce?

A

oxidative (irreversible anabolic) stage - produces lot of nucleotides
non-oxidative (reversible catabolic) stage - produces lots of NADPH

38
Q

what causes black water fever?

A

low NADPH levels, so oxygen free radicals don’t get cleared away by antioxidant properties of NADPH - RBC burst and turn urine black

39
Q

when does gluconeogenesis occur?

A

when there is not enough glucose available for use (eg fasting or low carb diet)

40
Q

what is the yield of the citric acid cycle?

A

3x NADH
1x FADH2
1x GTP
2x CO2

41
Q

what are the main 3 intermediary molecules in the citric acid cycle, and how many carbons do they each have?

A

Acetyl CoA - 2C
Oxaloacetate - 4C
Citrate 6C (oxaloacetate + acetyl CoA)

42
Q

where can Acetyl CoA be produced from?

A

glycolysis or fatty acid metabolism

43
Q

what are the main functions of the citric acid cycle?

A

harvest electrons for the electron transport chain

produce CO2

44
Q

does citric acid cycle use oxygen?

A

not directly, but electron transport chain does so indirectly so does CAC

45
Q

what are the three regulatory points of the citric acid cycle?

A

pyruvate dehydrogenase
isocitrate dehydrogenase
alpha-ketoglutarate dehydrogenase

46
Q

what is meant by the term amphibolic in the citric acid cycle?

A

it is used for catabolic processes (glucose breakdown) and anabolic processes (intermediate molecules used as building blocks for other structures)

47
Q

what is meant by anaplerotic reaction in the citric acid cycle?

A

it’s the process of replenishing intermediary molecules from the citric acid cycle when they have been used up to make other things (eg purines, pyrimidines, glutamate)

48
Q

what triggers the activation of pyruvate carboxylase in a citric acid anaplerotic reaction?

A

the build up of AcetylCoA at the start of the citric acid cycle

49
Q

what three processes are carried out by pyruvate dehydrogenase?

A

group transfer of COA-SH
decarboxylation (one CO2 taken off)
reduction of NAD to NADH

50
Q

how do the electrons from glycolysis-derived NADH get into mitochondrion from cytoplasm?

A

through glycerol phosphate shuttle, picked up by FAD to form FADH2

51
Q

what happens at the protein complex 1 in the electron transport chain?

A

electrons from NADH passed through Fe-S clusters to ubiquinone
ubiquinone + electrons = ubiquinol, shuttle to complex 2
4 protons are pumped into the intermembranous space

52
Q

what happens at the protein complex 2 in the electron transport chain?

A

electrons from FADH2 passed through Fe=S clusters to a second ubiquinone
ubiquinone + electrons = ubiquinol, shuttle to complex 3
no protons pumped out

53
Q

what happens at the protein complex 3 in the electron transport chain?

A

electrons from ubiquinol transferred onto cytochrome C
cytochrome C shuttles electrons to complex 4
4 protons pumped out

54
Q

what happens at the protein complex 4 in the electron transport chain?

A

electrons pass through Fe-Cu
electrons coupled with O2 to form H2O
2 protons pumped out

55
Q

what is the structure of ATP synthase?

A

F0 - sits in inner mitochondrial membrane, spins around

F1 - releases ATP

56
Q

what is the mechanism called by which ATP is formed and released, and how does it work?

A

binding-change mechanism

3 beta subunits: one for ATP, one for ADP+Pi and one that releases ATP

57
Q

what is meant by coupling and uncoupling of the electron transport chain with ATP synthesis?

A

coupling - electron transport chain and ATP synthesis are connected
uncoupling - protons are pumped out, water formed but no ATP made

58
Q

when can uncoupling of the electron transport chain and ATP synthesis happen in health and in disease, and what happens as a result?

A

heat production instead of ATP

  • malignant hyperthermia
  • brown fat in babies
59
Q

which protein complex of the electron transport chain also acts as an intermediate molecule in the citric acid cycle?

A

protein complex 2

60
Q

what is the total yield of ATP through glycolysis, citric acid cycle and electron transport chain?

A

30 to 32 ATP

61
Q

what is the mechanism that allows ATP synthase to rotate and ATP synthesis to occur?

A

proton motive force

62
Q

how are carbohydrates held together?

A

with covalent glycosidic bonds

Science for Medicine (6 decks)

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