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carbohydrates Flashcards

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1
Q

What are the 3 important monosaccharides?

A

Glucose
galactose
fructose

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2
Q

what are the 3 important disaccharides?

A

maltose
lactose
sucrose

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3
Q

why is maltose known as a reducing sugar?

A

because the anomeric C1 can be oxidised.

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4
Q

sucrose is a reducing sugar; true or false?

A

False

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5
Q

what is the difference between a homopolysaccharide and a heteropolysaccaride?

A

homopolysaccharide - one monomeric species

heteropolysaccharide - two or more monomer species

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6
Q

what two polymers make up starch?

A

amylose and amylopectin.

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7
Q

what is the main difference between amylose and amylopectin?

A

amylopectin has alpha 1>6 bonds which cause it to be branched.

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8
Q

what is the purpose of glycogen?

A

storage carbohydrate (used to store glucose)

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9
Q

why is it beneficial to store glucose in a polymeric form?

A

compactness - saves space
easy for the polymers to be synthesised or degraded to monomers
polymers are osmotically inactive (as opposed to glucose) - saves energy..

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10
Q

what is a glycoprotein?

A

protein with a carbohydrate covalently attached

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11
Q

What are glycosaminoglycans formed from?

A

Repeating units of hexuronic acid and an amino sugar (unbranched)

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12
Q

how are proteoglycans formed?

A

from Glycosaminoglycans covalently attaching to proteins

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13
Q

what are mucopolysaccharidoses?

A

group of genetic disorders caused by the absence or malfunction of enzymes that are required for the breakdown of glycosaminoglycans. e.g hurler syndrome.

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14
Q

what facilitates diffusion of glucose into the epithelial cells of the intestine?

A

Na+-glucose symporter, which is driven by high extracellular Na+

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15
Q

what are disaccharide deficiencies characterised by?

A

abdominal distension and cramps

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16
Q

what is the most common disaccharide deficiency?

A

lactose intolerance

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17
Q

why does lactase deficiency cause disaccharide deficiency symptoms?

A

undigested lactose is broken down by gut bacteria which causes gas build up and irritant acids
lactose is osmotically active, so it draws water from the gut into the lumen, which causes diahorrea

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18
Q

how is glucose “trapped” in the cell?

A

it is phosphorylated to glucose-6-phosphate.

19
Q

what catalyses conversion of glucose to glucose-6-phosphate?

A

hexokinase and glucokinase

20
Q

when would glucokinase and hexokinase be used?

A

glucokinase - when there is a high concentration of glucose

hexokinase - when there is a low concentration of glucose

21
Q

what are 3 fates of G-6-P?

A

glycolysis
conversion to glycogen for storage
pentose phosphate pathway

22
Q

where is the majority of glycogen in the body stored?

A

the liver and skeletal muscle.

23
Q

why is G-6-P converted to lactate in skeletal muscle but not in the liver?

A

skeletal muscle does not have glucose-6-P phosphatase enzyme.

24
Q

how is glycogen synthesised?

A

glycogenin covalently binds Glc from UDP, forming chains of approx. 8 Glc residues
then glycogen synthase takes over and extends the Glc chains
chains formed by glycogen synthase are then broken by glycogen branching enzyme and are re-attached (alpha 1,6,) bonds to give branching points.

25
Q

how is glycogen degraded (mobilised)?

A

glucose monomers are removed one at a time from the non reducing ends as glucose-1-phosphate
Glc near the branch is removed in a 2-step process by a de-branching enzyme
transferase activity of de-branching enzyme removes a set of 3 Glc residues from the branch and attaches them to the nearest non-reducing end via an (alpha 1,4,) bond
glucosidase removes. final branched glucose by breaking (alpha 1,6) linkage.

26
Q

How many new molecules of ATP are formed during glycolysis per mol of glucose?

A

2 ( 4 overall but 2 are used to start the process of glycolysis)

27
Q

what catalyses the conversion of glucose to G-6-P and is this reaction reversible or irreversible?

A

hexokinase/glucokinase

irreversible

28
Q

what catalyses conversion of G-6-P to F-6-P and is this reaction reversible or irreversible?

A

Phosphohexose isomerase

reversible

29
Q

what catalyses phosphorylation of F-6-P to F-1,6-bisP and is this reaction reversible or irreversible?

A 
PFK-1 (this reaction uses 1 ATP)
essentially irreversible (this reaction is the first committed step of glycolysis)
30
Q

what catalyses cleavage of F-1,6-bisP and is this reaction reversible or irreversible?

A

aldolase

readily reversible

31
Q

what catalyses interconversion of triose sugars and is this reaction reversible or irreversible?

A

triose phosphate isomerase

readily reversible

32
Q

what triose sugar can participate in glycolysis?

A

glyceraldehyde-3-phosphate (other triose sugar is converted to G-3-P)

33
Q

what catalyses phosphate transfer from 1,3-bisPG to ADP and is this reaction reversible or irreversible?

A

phosphoglycerate kinase

reversible (due to being coupled to step 6, the oxidation of G-3-P)

34
Q

what catalyses phosphate transfer from PEP to ADP and is this reaction reversible or irreversible?

A 
pyruvate kinase
essentially irreversible (this reaction also produces pyruvate)
35
Q

what steps in glycolysis are irreversible?

A

1,3,10

36
Q

Why does NAD need to be regenerated?

A

NAD is required for the reduction of various intermediate metabolites.

37
Q

what are the 3 fates of pyruvate?

A

conversion to either lactate, acetyl coA or ethanol

38
Q

what is the interaction between breakdown of glucose in skeletal muscle and formation of glucose in the liver?

A

Cori cycle

39
Q

what catalyses conversion of pyruvate to lactate?

A

lactate dehydrogenase

40
Q

what catalyses conversion of pyruvate to acetyl coA?

A

pyruvate dehydrogenase

41
Q

how many “bypass reactions” are there in gluconeogenesis?

A

4

42
Q

what are the steps for direct conversion of pyruvate to oxaloacetate?

A

pyruvate>oxaloacetate (within mitochondrion)>malate>oxaloacetate (outside mitochondrion)

43
Q

what enzyme catalyses conversion of pyruvate to oxaloacetate?

A

pyruvate carboxylase

44
Q

what enzyme catalyses conversion of oxaloacetate to PEP?

A

PEP carboxykinase

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