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Biological Chemistry > Carbohydrates 2 > Flashcards

Carbohydrates 2 Flashcards

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1
Q

Two monosaccharides can be joined via ?

A

A glycosidic bond between two anomeric carbons

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2
Q

The product has ?

A

Two acetal groups and one hemiacetal

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3
Q

Some disaccharides retain?

A

A reducing end (e.g. lactose); others do not (e.g. sucrose)

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4
Q

A bond formed between the anomeric C atom and an O atom of an alcohol is called ?

A

An O-glycosidic bond, and the product is called a glycoside

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5
Q

Sucrose is obtained from?

A

Sugar cane/beets and is composed of a glucose linked to a fructose. The linkage is α for glucose and β for fructose, and is cleaved by sucrase

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6
Q

Lactose is the disaccharide of ?

A

Milk that consists of a galactose linked to a glucose by a β-1,4 linkage. Lactase cleaves lactose

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7
Q

Maltose, a degradation product of ?

A

Large oligosaccharides, is composed of two glucose molecules linked by an α-1,4 linkage. Maltose is hydrolysed by maltase

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8
Q

Oligosaccharides are ?

A

Short chains of sugars

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9
Q

More than 150 different oligosaccharides have been identified in ?

A

Human milk, with the composition and amount varying among women

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10
Q

These carbohydrates are not digested by the infant, but ?

A

Play an important protective role against bacterial infection

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11
Q

How do they function ?

A

Function pro-biotically and as “decoys” for pathogenic bacteria

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12
Q

Polysaccharides can be:

A
  • Homopolysaccharides (one type of monomer unit)
  • Heteropolysaccharides (multiple types of monomer units)
  • Linear (one type of glycosidic bond)
  • Branched (multiple types of glycosidic bonds)
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13
Q

Glycogen and starch are insoluble due to ?

A

To their high molecular weight and often form granules in cells

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14
Q

Granules contain ?

A

Enzymes that synthesise and degrade these polymers

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15
Q

Glycogen and amylopectin (starch) have?

A

One reducing end but many nonreducing ends: Enzymatic processing occurs simultaneously in many nonreducing ends

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16
Q

What kind of polymers are both of these ?

A

Both are homopolymers of glucose

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17
Q

Glycogen functions as ?

A

The main storage polysaccharide in animals, in skeletal muscle and liver

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18
Q

What is Starch a mixture of ?

A

Two homopolysaccharides of glucose (Amylose and Amylopectin)

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19
Q

Explain Amylose and Amylopectin ?

A
  • Amylose is an unbranched polymer of ( α-1,4) linked residues.
  • Amylopectin is branched like glycogen, but the branch points with (α-1,6) linkers occur every 24–30 residues.
  • Molecular weight of amylopectin is up to 200 million
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20
Q

Explain in depth Cellulose?

A
  • Cellulose is a linear homopolysaccharide of glucose. Glucose monomers form (β-1,4) linked chains
  • Hydrogen bonds form between adjacent monomers (blue dashed lines)
  • There are additional H-bonds between chains.
  • Structure is now tough and water insoluble.
  • It is the most abundant polysaccharide in nature: cotton is nearly pure fibrous cellulose
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21
Q

What does the glycosidic bond determine ?

A

Polysaccharide structure

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22
Q

Explain how bonds can determine this ?

A
  • Cellulose: bond points up, in starch: bond points down
  • α-amylase (in saliva) breaks down the α-1,4-glycosidic bonds found in glycogen and starch but humans can’t digest cellulose (β-1,4 linkages)
  • The β-1,4 linkages favor straight chains, which are optimal for structural purposes
  • The α-1,4 linkages favor bent structures, which are more suitable for storage
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23
Q

Agar is a ?

A

Branched heteropolysaccharide composed of agarose and agaropectin

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24
Q

What does Agar serve as?

A

A component of cell wall in some seaweeds

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25
Q

Agar solutions form ?

A
  • Agar solutions form gels that are commonly used in the laboratory as a surface for growing bacteria
  • Agarose solutions form gels that are commonly used in the laboratory for separation DNA by electrophoresis
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26
Q

Explain Glycoproteins ?

A

The protein is the largest component by weight. Glycoproteins play a variety of roles, including as membrane proteins

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27
Q

Explain Proteoglycans ?

A

The protein is attached to a particular type of polysaccharide called a glycosaminoglycan. By weight, proteoglycans are mainly carbohydrate. Proteoglycans play structural roles or act as lubricants

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28
Q

Explain Mucins or mucoproteins ?

A

Like proteoglycans, mucins are predominantly carbohydrate. The protein is characteristically attached to the carbohydrate by N-acetylgalactosamine. Mucins are often lubricants.

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29
Q

Explain Glycolipids ?

A

Lipids modified by the attachment of carbohydrates

30
Q

In all classes of glycoproteins, carbohydrates are attached to the ?

A

The nitrogen atom in the side chain of asparagine (N-linkage) or to the oxygen atom of the side chain of serine or threonine (O-linkage).

31
Q

The N-linked glycan groups are attached to asparagine residues in the protein using a ?

A

GlcNAc monosaccharide

32
Q

O-linked glycan groups are attached to serine or threonine residues using a ?

A

GalNAc monosaccharide.O-linked glycan groups are GalNAc often followed by Gal or GlcNAc

33
Q

What is common to all N-linked oligosaccharides and serves as the foundation for a wide variety of these compounds ?

A

A pentasaccharide core (shaded gray) of mannose (green circles) and N-acetylglucosamine (blue square) residues

34
Q

The glycoprotein erythropoietin EPO is secreted by ?

A

The kidneys and stimulates the production of red blood cells

35
Q

EPO is composed of ?

A

165 amino acids and isN-glycosylated at three asparagine residues andO-glycosylated on a serine residue

36
Q

How much of carbphydrate by weight is the mature EPO ?

A

The mature EPO is 40% carbohydrate by weight, and glycosylation enhances the stability of the protein in the blood

37
Q

The availability of recombinant human EPO has ?

A

Greatly aided the treatment of anaemias

38
Q

However, some endurance athletes have used recombinant human EPO to increase ?

A

The red-blood-cell count and hence their oxygen-carrying capacity

39
Q

Glycoproteins have an important role in ?

A

Cell recognition & signalling. Immune cells communicate with each other by cell–cell interactions between glycoproteins and glycan-binding proteins (e.g. lectin) on the cell surface: intrinsic recognition

40
Q

Extrinsic reactions occur between ?

A

Host cells and pathogens

41
Q

Many pathogens gain entry into cells by first binding to ?

A

Carbohydrates on the cell surface

42
Q

Infection spreads when?

A

A viral protein, neuraminidase (sialidase), cleaves the glycosidic bonds between the sialic acid residues and the rest of the cellular glycoprotein, freeing the virus to infect new cells.

43
Q

N-linked glycosylation begins and continues in the ?

A

N-linked glycosylation begins in the endoplasmic reticulum and continues in the Golgi complex

44
Q

O-linked glycosylation occurs only in ?

A

The Golgi complex

45
Q

Glycoproteins are sorted according to ?

A

Signals encoded in the amino acid sequence and structure

46
Q

Proteoglycans are key components of ?

A

The ECM and serve as lubricants

47
Q

What are Proteoglycans either ?

A

They are either membrane-bound through a GPI anchor or a transmembrane α helix on the protein or are secreted into the ECM

48
Q

Mucopolysaccharidoses, such as Hurler disease, are ?

A

Pathological conditions that result from the inability to degrade proteoglycans

49
Q

What are Glycosaminoglycans composed of ?

A

Glycosaminoglycans are composed of repeating units of a disaccharide, one of which is a derivative of an amino sugar and one of which carries a negative charge, either as a carboxylate or sulfate

50
Q

Cartilage is composed, in part, of ?

A

The proteoglycans aggrecan, chondroitin sulphate and keratan sulphate, with the protein collagen

51
Q

The glycosaminoglycan component of aggrecan cushions ?

A

Joints by releasing water on impact, and then rebinding water

52
Q

What is the second most abundant biomolecule in nature ?

A

Chitin

53
Q

Chitin is ?

A

A glycosaminoglycan: linear homopolysaccharide of N-acetylglucosamine

54
Q

N-acetylglucosamine monomers form ?

A

β-1,4-linked chains

55
Q

What do β-1,4-linked chains form ?

A

Extended fibres that are similar to those of cellulose: they are tough and flexible, insoluble and cannot be digested by vertebrates

56
Q

Where is Chitin found ?

A

In cell walls in mushrooms and in exoskeletons of insects, spiders, crabs, and other arthropods

57
Q

In mucins, the protein component is ?

A

Extensively glycosylated to serine and threonine residues, with the first carbohydrate being N-acetylgalactosamine

58
Q

A region of the protein backbone rich in serine and threonine, called ?

A

Variable number of tandem repeats (VNTR), is the site of glycosylation

59
Q

Mucins serve as ?

A

Lubricants and adhere to epithelial cells, acting as a protective barrier

60
Q

In gram-negative bacteria, lipopolysaccharides (LPS) cover ?

A

The peptidoglycan layer

61
Q

Different bacterial species have ? But have in common ?

A

Subtly different LPS structures, but they have in common a lipid region (lipid A), a core oligosaccharide also

62
Q

The O-specific chain is ?

A

The principal determinant of the serotype (immunological reactivity) of the bacterium.

63
Q

The outer membranes of the gram-negative bacteria S. typhimurium and E. coli contain ?

A

So many LPS molecules that the cell surface is virtually covered with O-specific chains

64
Q

The human ABO blood antigens contain ?

A

75% glycoproteins and 25% glycolipids

65
Q

The blood groups are determined in part by ?

A

The type of sugars located on the head groups in glycosphingolipids

66
Q

The structure of sugar is determined by ?

A

An expression of specific glycosyltransferases

67
Q

Who will have the O antigen ?

A

Individuals with no active glycosyltransferase will have the O antigen

68
Q

Who will have the A blood group ?

A

Individuals with a glycosyltransferase that transfers an N-acetylgalactosamine group

69
Q

Who will have the B blood group ?

A

Individuals with a glycosyltransferase that transfers a galactose group

70
Q

Blood types must be carefully ?

A

Matched for donation to avoid an immune response

71
Q

What are both Blood Groups O and Group AB?

A

Blood group O are “Universal donors” whereas group AB are “Universal receivers”

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