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BIOCHEMISTRY > ME03 - Carbohydrates of Physiologic Significance > Flashcards

ME03 - Carbohydrates of Physiologic Significance Flashcards

1
Q

Biomedical Importance of Carbohydrates

A

(In plants) synthesized from carbon dioxide and
water by photosynthesis and stored as starch.
o (In animals), synthesize carbohydrates from amino acids
_ Most are derived ultimately from plants
_ Acts as a storage form of energy in the body
_ Serves as cell membrane components that mediate some forms of intercellular communication
_ Serves as a structural component of many organisms, including the cell walls of bacteria, the exoskeleton of many insects, and the fibrous cellulose of plants.

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2
Q

Most important carbohydrate

A

Glucose

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3
Q

How is Glucose formed

A

Hydrolysis of Dietary Starch and Disaccharides; Converted to glucose through GLYCOLYSIS

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4
Q

Precursor for synthesis of all the other carbohydrates in the body

A

Glycogen _ for storage
_ Ribose and Deoxyribose _ in nucleic acids, building blocks
_ Galactose _ synthesis of lactose in milk, glycolipids, in combination with protein in glycoproteins & proteoglycans

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5
Q

Disease associated with CARBOHYDRATE METABOLISM

A

Diabetes Mellitus (most predominant disease in our country)
Galactosemia
Glycogen Storage Diseases o Lactose Intolerance

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6
Q

study of the roles of sugars in health and disease

A

Glycobiology

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7
Q

entire complement of sugars of an organism, whether free or present in more complex molecules

A

Glycome

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8
Q

analogous term to genomics and proteomics; the comprehensive study of glycomes

A

Glycomics

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9
Q

Carbohydrate Digestion

A

( High Carb Meal) Starch, Sucrose, Lactose - {Salivary amylase, Pancreatic amylase} – Maltose, Isomaltose, Sucrose, Lactose – (Brush border dissacharides) – Glc, Gal, Fru – (Na+/Glc symporter, active transport) – Intestine then bloodstream

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10
Q

Explain Hyperglycemia in well-fed state

A

Hyperglycemia _ inc blood glucose; transient hyperglycemia is good. We all become hyperglycemic first 2 hrs after a meal. Persistent hyperglycemia in diabetes is bad because it goes into the blood but it cannot go inside the cell

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11
Q

Classification of Carbohydrates

A

Monosaccharides | Dissacharides | Oligosaccharides | Polysaccharides

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12
Q

Simple sugars; sugars that cannot be hydrolyzed into simpler carbohydrates

A

Monosaccharides Example: Aldoses (with aldehyde group) or Ketoses (with Ketone group)

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13
Q

_ - OH group attached to glucose molecule
_ Aldehyde or ketone group has been reduced to
an alcohol group

A

Polyhydric alcohols (sugar alcohols or polyols)
_ Poorly absorbed in the body, Occurs naturally in foods

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14
Q

How is monosaccharides formed to create larger structures

A

Linked by glycosidic bonds

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15
Q

Condensation products of two monosaccharide units

A

Dissacharides Example; lactose (Glu + Gal), maltose (Glu + Glu) , isomaltose, sucrose (Glu + Fru),
trehalose

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16
Q

Condensation products of three to ten Monosaccharides

A

Oligosaccharides

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17
Q

More than ten monosaccharide units

A

Polysaccharides | Sometimes classified as Hexosans or Pentosans
May be linear or branched polymers

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18
Q

polysaccharides in food that are not digested by human enzymes and are the major component of dietary fiber

A

Nonstarch Polysaccharides

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19
Q

Examples of Non-starch Polysaccharides

A

Cellulose - from plant cell walls (glucose polymer) Inulin - the storage carbohydrates in some plants (fructose polymer)

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20
Q

What are the types of Isomerism`

A

Straight Chain, Cyclic Structure, Chair

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21
Q

structural formula (aldohexose)

A

Straight - Chain

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22
Q

a hemiacetal formed by reaction between the aldehyde group and a hydroxyl group

A

Cyclic Structure

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23
Q

molecule is viewed from the side and above the plane of the ring; the bonds nearest to the viewer are bold and thickened, and the hydroxyl groups are above or below the plane of the ring

A

Haworth projection

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24
Q

Difference between Chair vs Cyclic Formula

A

Chair confirmation _ explains formula but not different
reactions
Cyclic formula_ better idea, idea how it interacts with heme, water etc., gives 3D idea

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25
Q

compounds that have the same chemical formula but have different structures

A

Isomers

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26
Q

Most of the naturally occurring monosaccharides

A

D sugars

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27
Q

Determines whether the sugar belongs to the D or L series.

A

The orientation of - H and _OH groups around the carbon atom adjacent to the terminal primary alcohol carbon o -OHontherightside:Disomer o -OHontheleftside:Lisomer

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28
Q

A beam of plane-polarized light is passed through a solution of an optical isomer.

A

Optical Activity
oright, dextrorotatory (+)
oleft, levorotatory (_)

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29
Q

The direction of rotation of polarized light is independent of the stereochemistry of the sugar, True or False

A

True, so it may be designated D (-), D (+), L (-), or L(+)

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30
Q

Naturally occurring form of fructose

A

D (-) isomer

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31
Q

_ a six-membered ring
_ For glucose in solution, more than 99% is in
the pyranose form

A

Pyran

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32
Q

a five membered ring

A

Furan

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33
Q

What is the ring structure of an aldose

A

hemiacetal (combination of aldehyde and an alcohol group)

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34
Q

What is the ring structure of ketose

A

Hemiketal

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35
Q

How is Crystalline Glucose converted to a-d-glucopyranose and B-glucopyranose

A

Crystalline glucose is _-d-glucopyranose. The cyclic structure is retained in the solution, but isomerism occurs about position 1, the carbonyl or anomeric carbon atom, to give a mixture of _-d- glucopyranose (38%) and _-glucopyranose (62%)

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36
Q

Isomers differing as a result of variations in configuration of the _OH and _H on carbon atoms 2, 3, and 4 of glucose

A

Epimers Most important epimers of glucose:
o Mannose - Epimerized at carbon 2 Most important epimers of glucose:
o Mannose - Epimerized at carbon 2 o Galactose - Epimerized at carbon 4o Galactose - Epimerized at carbon 4

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37
Q

How is Fructose has the same molecular formula as glucose but differs in its structure

A

Aldose-ketose Isomerism since there is a potential keto group in position 2, whereas in glucose there is a potential aldehyde group in position 1

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38
Q

formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide, and a second compound that may or may not (in the case of an aglycone) be another monosaccharide

A

Glycosides

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39
Q

Why is it that If the second group is a hydroxyl, the O-glycosidic bond is an acetal

A

because it results from a reaction between a hemiacetal group (formed from an aldehyde and an _OH group) and another _ OH group

40
Q

If the hemiacetal portion is glucose, the resulting compound is a ____________

A

Glucoside

41
Q

If the hemiacetal portion is galactose, the resulting compound is a ____________

A

Galactoside

42
Q

Importance of glycosides in medicine

A

because of their action on the heart (cardiac glycosides) all contain steroids as the aglycone.

43
Q

A molecule in which a sugar is bound to another functional group via a glycosidic bond

A

Glycosides

44
Q

Types of glycosidic bond

A

O-Glycosidic bond; N-glycosidic bond

45
Q

Glycoside that is an inhibitor of the Na+-K+ ATPase of cell membranes.

A

Ouabain

46
Q

Example of glycoside that acts an an antibiotic

A

Streptomycin

47
Q

Sugars in which one hydroxyl group has been replaced by hydrogen
_ Lack an Oxygen Atom

A

Deoxy sugars

48
Q

Examples of deoxy sugars

A

_ Deoxyribose - derived from the sugar ribose by loss of an oxygen atom
_ l-fucose - Cosmetics, pharmaceuticals, dietary supplements
_ 2-deoxyglucose - Competitively inhibits G6 PO4

49
Q

Components of Glycoproteins, Gangliosides, & Glycosaminoglycans

A

Amino Sugars (Hexosamines)

50
Q

Examples of Amino Sugars (Hexosamines)

A

_ d-glucosamine - Constituent of hyaluronic
acid (water holding/filler)
_ d-galactosamine - Chondrosamine
(cartilage) a constituent of chondroitin
_ d-mannosamine

51
Q

Clinical Importance of hexosamines

A

antibiotics (eg, erythromycin) contain amino sugars, which are important for their antibiotic activity

52
Q

How are glycosidic bonds named?

A

Glycosidic bonds between sugars are named according to the numbers of the connected carbons and with regard to the position of the anomeric hydroxyl group of the sugar involved in the bond
_ If the anomeric hydroxyl is in the _ configuration, the linkage is an _-bond
_ .If it is in the _ configuration, the linkage is a _-bond.

53
Q

How is LACTOSE synthesized

A

Lactose is synthesized by forming a glycosidic bond between carbon 1 of _-galactose and carbon 4 of glucose. The linkage is, therefore, a _(1_4) glycosidic bond

54
Q

sugars composed of two monosaccharide residues linked by a glycoside bond

A

Dissaccharides

55
Q

What is an invert sugar

A

Hydrolysis of sucrose yields a mixture of glucose and fructose called “invert sugar” because fructose is strongly levorotatory and changes (inverts) the weaker dextrorotatory action of sucrose

56
Q

What are the Structures of important disaccharides:

A

The _ and _ refer to the configuration at the anomeric carbon atom

57
Q

What happens when the anomeric carbon of the second residue takes part in the formation of the glycosidic bond, as in sucrose,

A

the residue becomes a glycoside known as a furanoside or a pyranoside

58
Q

What happens as the disaccharide no longer has an anomeric carbon with a free potential aldehyde or ketone group

A

it no longer exhibits reducing properties

59
Q

How is B-fructofuranose residue made up

A

results from turning the _-fructofuranose molecule through 180 degrees and inverting it.

60
Q

What are the important disaccharides

A

Maltose | Sucrose | Lactose

61
Q

The most important dietary carbohydrate in cereals, potatoes, legumes, and other vegetables

A

Starch

62
Q

A-glucosidic chain of Starch

A

glucosan or glucan

63
Q

2 main constituents of Starch

A

Amylose, Amylopectin

64
Q

Composition of Amylopectin

A

o 24 to 30 glucose residues
o _1 _ 4 linkages in the chains
o _1 _ 6 linkages at the branch points

65
Q

_ measure of its digestibility
_ based on the extent to which it raises the blood
concentration of glucose

A

Glycemic Index ranges from 1 (or 100) to 0 for those that are not hydrolysed at all
_ 55 or less = Low (good)
_ 56- 69 = Medium
_ 70 or higher = High (bad)

66
Q

_ Animal starch
_ Storage polysaccharide
_ More highly branched structure than amylopectin _ Muscle glycogen
_ Contain up to 60,000 glucose residues

A

Glycogen

67
Q

_ polysaccharide of fructose found in tubers and roots of dahlias, artichokes, and dandelions
_ readily soluble in water
_ used to determine the glomerular filtration rate _ no nutritional value

A

Inulin

68
Q

Intermediates in the hydrolysis of starch

A

Dextrins

69
Q

Chief constituent of plant cell walls
_ Insoluble
_ Consists of _-d-glucopyranose units linked by _1 _ 4 bonds

A

Cellulose

70
Q

_ an important source of bulk in the diet
_ major component of dietary fiber

A

Cellulose

71
Q

structural polysaccharide in the exoskeleton of crustaceans and insects

A

Chitin

72
Q

How many glycosidic bonds Chitin have?

A

4, N-acetyl-d-glucosamine units joined by _1 _ 4 glycosidic bonds

73
Q

_ occurs in fruits
_ a polymer of galacturonic acid linked -1 4

A

Pectin

74
Q

_ Aka mucopolysaccharides
_ Contains amino sugars and uronic acids

A

Glycosaminoglycans

75
Q

_ attached to a protein molecule
_ substance of connective tissue
_ Hold water occupy space

A

Proteoglycan

76
Q

Why is Proteoglycan holding water and occupy space

A

hold large quantities of water and occupy space, thus cushioning or lubricating other structures, because of the large number of _OH groups and negative charges on the molecule which, by repulsion, keep the carbohydrate chains apart

77
Q

Example of Proteoglycan

A

hyaluronic acid, chondroitin sulfate, and heparin

78
Q

_ Proteins containing branched or unbranched
oligosaccharide chains
_ occur in cell membranes
_ Glycosylation
_ 5% of the weight of cell membranes

A

Glycoproteins
_ aka Mucoproteins

79
Q

Serum albumin is a glycoprotein. True or False

A

TRUE

80
Q

are N- or O- acyl derivatives of
neuraminic acid

A

Sialic acids

81
Q

A nine-carbon sugar derived from mannosamine (an epimer of glucosamine) and pyruvate

A

Neuraminic acid

82
Q

Sialic acids are constituents of both _________ and ________

A

Glycoproteins and Gangliosides

83
Q

has 130 amino acid residues and spans the lipid membrane, with polypeptide regions outside both the external and internal (cytoplasmic) surfaces

A

Glycophorin

84
Q

attached to the amino terminal portion of glycoprotein outside the external surface

A

Carbohydrates

85
Q

Carbohydrates are also present in apo-protein B of plasma lipoproteins. True or False

A

TRUE

86
Q

Importance of Salivary a-amylase in the digestion of carbohydrates

A

During mastication, it acts briefly on dietary starch and glycogen, hydrolyzing random _(1_4) bonds
Because branched amylopectin and glycogen also contain _(1_6) bonds, which _-amylase cannot hydrolyze, the digest resulting from its action contains a mixture of short,branched and unbranched oligosaccharides known as dextrins
Carbohydrate digestion halts temporarily in the stomach, because the high acidity inactivates salivary _-amylase.

87
Q

Importance of Salivary pancreatic a-amylase in the digestion of carbohydrates

A

When the acidic stomach contents reach the small intestine, they are neutralized by bicarbonate secreted by the pancreas, and pancreatic _-amylase continues the process of starch digestion.

88
Q

Importance of Salivary intestinal disaccharides in the digestion of carbohydrates

A

The final digestive processes occur primarily at the mucosal lining of the upper jejunum and include the action of several disaccharidases

89
Q

Intestinal absorption of monosaccharides in the Digestion of Carbohydrates

A

o The duodenum and upper jejunum absorb the bulk of the monosaccharide products of Digestion
o However, different sugars have different mechanisms of absorption
o galactose and glucose are transported into the mucosal cells by an active, energy- dependent process that requires a concurrent uptake of sodium ions, and the transport protein is the sodium-dependent glucose cotransporter 1 (SGLT-1)
o Fructose utilizes an energy- and sodium- independent monosaccharide transporter (GLUT-5) for its absorption.
o All three monosaccharides are transported from the intestinal mucosal cell into the portal circulation by yet another transporter, GLUT-2

90
Q

Abnormal degradation of disaccharides

A

o Because only monosaccharides are absorbed, any deficiency (genetic or acquired) in a specific disaccharidase activity of the intestinal mucosa causes the passage of undigested carbohydrate into the large intestine
o As a consequence of the presence of this osmotically active material, water is drawn from the mucosa into the large intestine, causing osmotic diarrhea
o This is reinforced by the bacterial fermentation of the remaining carbohydrate to two- and three-carbon compounds (which are also osmotically active) plus large volumes of CO2 and H2 gas, causing abdominal cramps, diarrhea, and flatulence.

91
Q

brush border
enzymes are rapidly lost in normal individuals with severe diarrhea

A

Digestive enzyme deficiency

92
Q

represents a reduction in the amount of enzyme produced
It is thought to be caused by small variations in the DNA sequence of a region on chromosome 2 that controls expression of the gene for lactase, also on chromosome 2.

A

Lactose intolerance

93
Q

This autosomal recessive disorder results in an intolerance of ingested sucrose

A

Congenital sucrase-isomaltase deficiency

94
Q

Identification of a specific enzyme deficiency can be obtained by : ________

A

performing oral tolerance tests with the individual disaccharides.

95
Q

reliable test for determining the amount of ingested
carbohydrate not absorbed by the body, but which is metabolized instead by the intestinal flora

A

Measurement ofhydrogen gas in the breath

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