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MCAT: Biochemistry > Chapter 4: Carbohydrate Structure and Function > Flashcards

Chapter 4: Carbohydrate Structure and Function Flashcards

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MCAT flashcards
1
Q

What is the empirical formula to define monosaccharides?

A

Cn(H2O)n

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2
Q

What is the empirical formula to define complex sugars?

A

Cn(H2O)m

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3
Q

What are monosaccharides with three, four, five and six carbon atoms?

A

3: triose
4: tetrose
5: pentose
6: hexose

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4
Q

What are aldoses?

A

Carbohydrates that contain an aldehyde group as their most oxidized functional group

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5
Q

What are ketoses?

A

Carbohydrates that contain an ketone group as their most oxidized functional group

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6
Q

What would a six-carbon sugar with an aldehyde group be called?

A

Aldohexose

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7
Q

What is the simplest aldehyde and ketone sugars?

A

Aldehyde: glyceraldehyde
Ketone: dihydroxyacetone

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8
Q

What is the number of most carbonyl carbons in ketoses?

A

C-2

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9
Q

Carbonyl carbons in glyceraldehyde and dihydroxyacetone can participate in _____ linkages.

A

Glycosidic linkages

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10
Q

What are sugars acting as substituents via glycosidic linkages called?

A

Glycosyl residues

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11
Q

What are the common names of the four most important monosaccharides?

A
  • Fructose
  • Glucose
  • Galactose
  • Mannose
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12
Q

Learn the Fischer projections of the important monosaccharides.

A

Learn it

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13
Q

Differentiate D and L sugars.

A

D-sugars: highest-numbered chiral carbon with the OH group on the RIGHT
L-sugars: highest-numbered chiral carbon with the OH group on the LEFT

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14
Q

Define stereoisomers. What are they also called?

A
  • Compounds that have the same chemical formula
  • Differ form one another only in terms of the spatial arrangement of their component atoms
  • Optical isomers
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15
Q

Define enantiomers.

A

Stereoisomers that are nonidentical, nonsuperimposable mirror images of each other

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16
Q

Any molecule that contains _____ and no _______ has an enantiomer

A
  • chiral carbons

- internal planes of symmetry

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17
Q

What is absolute configuration?

A

The nomenclature system used for three-dimensional arrangement of atoms in isomers; the most common systems are D/L and (R)/(S)

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18
Q

What is the equation that allows us to calculate the number of stereoisomers with common backbone?

A

2^n

where n is the number of chiral carbons in the molecule

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19
Q

What is the optical rotation of D-glyceraldehyde? What is the optical rotation of L-glyceraldehyde? Do these optical rotations apply to all sugars?

A

D: +
L: -
No, it needs to be determined experimentally for every type of sugar

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20
Q

In the Fischer projection, what do the horizontal lines (wedges) designate? What about the vertical lines (dashes)?

A

Horizontal (wedges): out of the page

Vertical (dashes): into the page

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21
Q

How many chiral centers in D-glucose have the opposite configuration of L-glucose?

A

EVERY chiral center is opposite

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22
Q

The same sugars, in different optical families, are ________

A

enantiomers

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23
Q

Two sugars that are in the same family (both are either ketoses or aldoses, and have the same number of carbons) that are not identical and are not mirror images of each other are ______

A

diastereoisomers

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24
Q

Define epimers.

A

Diasteroisomers that differ in configuration at exactly one chiral center

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25
Q

What are the three main types of stereoisomers?

A
  • Enantiomers
  • Diastereoisomers
  • Epimers
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26
Q

Learn the steroisomers on page 109.

A

Learn it

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27
Q

How many enantiomers can a compound have? How many diastereoimers?

A

Enantiomers: ONE
Diastereoisomers: multiple

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28
Q

What is the nucleophile and electrophile found in monosaccharides?

A

Nucleophile: hydroxyl group
Electrophile: carbonyl group

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29
Q

Define cyclization.

A

Describes the ring formation of carbohydrates from their straight-chained forms

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30
Q

Monosaccharides can undergo intramolecular reactions to form cyclic _______ and ________

A
  • hemiacetals (aldoses)

- hemiketals (ketoses)

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31
Q

What are the two only cyclic molecules that are stable in solution? How many members do their rings contain?

A
  • Pyranose (6)

- Furanose (5)

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32
Q

Do sugars tend to exist predominantly in their cyclic or linear form?

A

Cyclic

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33
Q

How does a ring form in a monosaccharide?

A

Hydroxyl group acts as a nucleophile, so oxygen becomes a member of the ring structure

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34
Q

In a hemiacetal or hemiketal, the carbonyl carbon becomes chiral in the ring-formation process. What is it now referred to?

A

Anomeric carbon

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35
Q

Define anomeric carbon.

A

New chiral center formed in ring closure; it was the carbon containing the carbonyl in the straight-chain form

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36
Q

One of two rings can form during cyclization of a sugar molecule: a or B. What are they termed in reference to one another?

A

Anomers

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37
Q

What is an a-anomer?

A

-OH group of C-1 trans to the -CH2OH substituent (axial and down)

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38
Q

What is a B-anomer?

A

-OH group of C-1 cis to the -CH2OH substituent (equatorial and up)

39
Q

Are furanoses or pyranoses planar? Which adopts a chair-like configuration?

A

Furanose: planar
Pyranose: chair-like configuration

40
Q

When we convert the monosaccharide from its straight-chain Fischer projection to the Haworth projection, any group on the right in the Fischer projection will point _____

A

down

41
Q

What happens when you expose hemiacetal rings to water?

A

Cause them to spontaneously cycle between the open and closed form

42
Q

What is mutarotation?

A

Cyclic compounds shift from one anomeric form to another (a and B) with the straight-chain form as an intermediate

43
Q

When does mutarotation occur more rapidly?

A

When the reaction is catalyzed with an acid or a base

44
Q

Which configuration is less favorable in cyclic compounds: a or B? Why?

A
  • Alpha

- Hydroxyl group of the anomeric carbon is axial, adding to the steric strain of the molecule

45
Q

Mutarotation results in a mixture that contains both a- and B-anomers at ________ concentrations. Are they equal in terms of percentage?

A
  • equilibrium

- No

46
Q

What three reactions can monosaccharides undergo?

A
  • Oxidation-reduction
  • Esterification
  • Glycoside formation from nucleophilic attack
47
Q

Are monosaccharides oxidized or reduced to produce energy?

A

Oxidized

48
Q

When monosaccharides switch between anomeric configurations, the hemiacetal rings spend a short period of time in the open-chain aldehyde form. They can be oxidized to __________; these oxidized aldoses are called _______.

A
  • carboxylic acids

- aldonic acids

49
Q

Aldoses can be oxidized to _____ and reduced to ______

A

Oxidized: aldonic acids
Reduced: alditols

50
Q

Any monosaccharide with a hemiacetal ring is considered a ____________

A

reducing sugar

51
Q

When an aldose is in its ring form, oxidation yields what?

A

Lactone

52
Q

What type of compound is a lactone?

A

Cyclic ester with a carbonyl group persisting on the anomeric carbon

53
Q

What are the two standard reagents used to detect the presence of reducing sugars?

A
  • Tollen’s reagent

- Benedict’s reagent

54
Q

How does Tollen’s reagent test work? What happens in a positive test?

A
  • Utilizes Ag(NH3)2+ as an oxidizing agent

- Aldehydes reduce Ag+ to metallic silver

55
Q

How does Benedict’s reagent test work?

A
  • Aldehyde group of an aldose is readily oxidized, indicated by a red precipitate of Cu2O
56
Q

How can we detect the presence of reducing sugars in a glucose sample?

A

Utilize the enzyme glucose oxidase, which does not react with other reducing sugars

57
Q

Define tautomerization.

A

Refers to the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond

58
Q

Can ketones be oxidized to carboxylic acids?

A

No

59
Q

How do ketones form aldoses under basic conditions?

A

Tautomerize to form aldozes, via ketonol shifts

60
Q

Why do ketone sugars give positive Tollen’s and Benedict’s tests?

A

Since they can form aldoses under basic conditions

61
Q

What does the tautomerization of a ketone result in?

A

An enol

62
Q

What is an enol?

A

Compound with a double bond and an alcohol group

63
Q

What is an alditol?

A

When the aldehyde group of an aldose is reduced to an alcohol, the compound is considered an alditol

64
Q

What is a deoxy sugar?

A

Compound that contains a hydrogen that replaces a hydroxyl group on the sugar

65
Q

How can carbohydrates form esters?

A

Their hydroxyl groups are able to participate in reactions with carboxylic acids and carboxylic acid derivatives

66
Q

What is formed in the phosphorylation of glucose?

A

Phosphate ester

67
Q

What is a similar reaction to esterification?

A

Phosphorylation

68
Q

What do hemiacetals form when they react with alcohol? What do hemiketals form?

A
  • Acetals

- Ketals

69
Q

What is the basis for building complex carbohydrates? What does it require?

A
  • Glycoside formation

- Requires the anomeric carbon to link to another sugar

70
Q

What happens to do anomeric hydroxyl group when hemiacetals react with alcohols to form acetals?

A

Anomeric hydroxyl group is transformed into an alkoxy group, yielding a mixture of a- and B-acetals

71
Q

The resulting C-O bonds following hemiacetals reaction with alcohol are called glycosidic bonds, what are the acetals formed called?

A

Glycosides

72
Q

What are glycosides derived from furanose rings called? What are glycosides derived from pyranose rings called?

A
  • Furanoside

- Pyranoside

73
Q

Monosaccharides react with _______ to for acetals.

A

alcohols

74
Q

Name the three important disaccharides.

A
  • Sucrose
  • Lactose
  • Maltose
75
Q

What is the chemical name for sucrose?

A

glucose-a-1,2-fructose

76
Q

What is the chemical name for lactose?

A

galactose-B-1,4-glucose

77
Q

What is the chemical name for maltose?

A

glucose-a-1,4-glucose

78
Q

Differentiate homopolysaccharides and heteropolysaccharides.

A

Homopolysaccharide: polysaccharide composed entirely of a single monosaccharide
Heteropolysaccharide: polymer made up of more than one type of monosaccharide

79
Q

What are the three most important polysaccharides? What are they all composed of?

A
  • Cellulose
  • Starch
  • Glycogen
  • D-glucose
80
Q

When does branching in a polysaccharide happen?

A

When an internal monosaccharide in a polymer chain forms at least two glycosidic bonds, allowing for branch formation

81
Q

Which polysaccharide is the main structural component of plants?

A

Cellulose

82
Q

Is cellulose made of a-D-glucose or B-D-glucose? How are their glycosidic bonds linked?

A
  • B-D-glucose

- B-1,4 glycosidic bonds

83
Q

Which sugars can humans not digest?

A

B-linked sugars

84
Q

Are starches made up of a-D-glucose of B-D-glucose?

A

a-D-glucose; they are digestible

85
Q

What are the two types of starch?

A
  • Amylose: linear

- Amylopectin: branched

86
Q

What are the linkages for amylose and amylopectin?

A

a-1,4 glycosidic bonds

87
Q

Where are the branches linked in amylopectin?

A

a-1,6 glycosidic bonds

88
Q

What is amylose degraded by? (2) Where does it cleave? What does it yield?

A
  • B-amylase: cleaves amylose at the reducing end of the polymer (the one with the free anomeric carbon) to yield maltose
  • a-amylase: cleaves randomly along the chain to shorten it to maltose and glucose
89
Q

How is amylopectin degraded?

A

Debranching enzymes

90
Q

What is the carbohydrate storage unit in animals?

A

Glycogen

91
Q

How does glycogen differ from starch?

A

It has more a-1,6 glycosidic bonds, which makes it highly branched and optimizes the energy efficiency of glycogen and makes it more soluble in solution

92
Q

What degrades glycogen?

A
  • Glycogen phosphorylase
  • Cleaving GLUCOSE from the nonreducing end of a glycogen branch (no free anomeric carbon) and phosphorylating it, producing G-1-phosphate
93
Q

Which of the two forms of starch is more soluble in solution?

A

Amylopectin because of its branched structure

94
Q

Explain the difference between esterification and glycoside formation.

A
  • Esterification is the reaction by which a hydroxyl group reacts with either a carboxylic acid or a carboxylic acid derivative to form an ester
  • Glycoside formation refers to the reaction between an alcohol and a hemiacetal (or hemiketal) group on a sugar to yield an alkoxy group

MCAT: Biochemistry (12 decks)

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