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My MCAT > Carbohydrate Structure > Flashcards

Carbohydrate Structure Flashcards

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MCAT flashcards
1
Q

What is the general formula for carbohydrates?

A

Cx(H2O)y

Carbs are comprised of a carbon backbone, carbononyl group (C=O) and at least one hydroxyl (-OH) group

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2
Q

a sugar that contains a terminal carbon group

A

aldose

because it contains an aldehyde

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3
Q

a sugar whose carbonyl group is not terminal

A

ketose

because it contains a ketone

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4
Q

Carbohydrates can be called trioses, tetroses, pentoses, hexoses, and even heptoses based on ….

A

The number of carbons it has

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5
Q

Identify this important triose

this is the simplest aldose
A

glyceraldehyde

Derivatives of glyceraldehyde are important intermediates in glycolysis

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6
Q

Name this important pentose

A

Ribose

Ribose 5-phosphate is also derived from glucase during the pentose phosphate pathway

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7
Q

Whenever you see a carbohydrate structural diagram, you can assume it’s a ____ isomer

A

D-isomer

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8
Q

Name the three most important hexoses to know for the MCAT

A

glucose
fructose
galactose

glucose is an aldohexose, fructose is a ketohexose, and galactose is an aldohexose.

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9
Q

Name the hexose that is found in dairy products and sugar beets. It is an aldose that can be rapidly converted to glucose.

A

galactose

it can be identified by having a C3 and C4 point in one direction, while C2 and C5 pointing in another
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10
Q

Name the hexose that is the main source of energy for the body under normal conditions. This is an aldose

A

Glucose

an aldohexose

can be identified by the hydroxyl group at C3 that points in the opposite direction of the other hydroxyl groups

Glucose + fructose = sucrose

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11
Q

Name the hexose that is present in many food sources and is metabolized by the liver. It is commonly produced by plants/fruits and is used as a sweetner. It is also a ketose

A

Fructose

a ketohexose

Glucose + fructose = sucrose

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12
Q

True or False

Pentoses and hexoses typically exist in cyclic forms under physiological conditions, not linear forms

A

True

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13
Q

When an alcohol adds to an aldehyde, the result is called a ____; when an alcohol adds to a ketone the resulting product is a ____

A

When an alcohol adds to an aldehyde, the result is called a hemiacetal; when an alcohol adds to a ketone the resulting product is a hemiketal

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14
Q

a hemiketal differs from a hemicetal in that instead of an -R, -OR, -OH, -H structure, it has a -R, -OR, -OH, ____ structure

A

a hemiketal differs from a hemicetal in that instead of an -R, -OR, -OH, -H structure, it has a -R, -OR, -OH, -R structure

the R group instead of the -H group is also the difference between a ketone vs an aldehyde
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15
Q

Name this functional group

A

ketone

a ketone is characterized by two -R groups being attached to a carbonyl group
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16
Q

Name the functional group

A

aldehyde

an aldehyde is characterized by an -R group and a H bound to a carbonyl group
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17
Q

____ are *cyclic * epimers; a pair of near-identical stereoisomers that differ at only the anomeric carbon, the carbon that bears the aldehyde or ketone functional group in the sugar’s open-chain form.

the OH and H groups are flipped at the anomeric carbon

A

anomers

α-D-Glucopyranose and β-D-glucopyranose are anomers.

The epimeric carbon in anomers are known as anomeric carbon or anomeric center.
Youtube link

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18
Q

What is the sterochemical relationship between these two molecules?

A

They are anomers

An anomer is a type of epimer; it is one of two stereoisomers of a cyclic sugar that differs only in its configuration at the hemiacetal or acetal carbon (the anomeric carbon)

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19
Q

A(n) ____ is one of two stereoisomers that differ in configuration at only one stereocenter.

A

epimer

Youtube link

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20
Q

A carbohydrate in which the group bonded to the anomeric carbon is trans (opposite) to the CH2O group on the other side of the pyranose or furanose ring ether oxygen atom

A

alpha anomers

alpha anomers are identified by a downwards OH group
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21
Q

A carbohydrate in which the group bonded to the anomeric carbon is cis (same side) to the CH2O group on the other side of the pyranose or furanose ring ether oxygen atom

A

beta anomers

beta anomers feature an upward OH group

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22
Q

the process of interconversion between alpha and beta anomers

involves the breaking and reforming of covalent bonds

A

mutarotation

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23
Q

the carbonyl carbon (of the aldehyde or ketone functional group) in the open-chain form of the sugar. It can also be identified as the carbon bonded to the ring oxygen and a hydroxyl group in the cyclic form.

A

anomeric carbon

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24
Q

The carbon in red is called the ____ carbon

A

carbonyl carbon

a carbon atom double-bonded to an oxygen atom

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25
Q

the simplest of sugars

A

monosaccharide

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26
Q

what bonds must form between monosaccharides to form more complex sugars?

A

Glycosidic bonds

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27
Q

Describe the process of glycosidic bond formation

A

An anomeric carbon of one sugar reacts with the hydroxyl group in another sugar in a dehydration (condensation) reaction; an H2O molecule is lost as the two monosaccharides condense to form a disaccharide

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28
Q

The formation of a glycosidic bond transforms a hemiacetal or hemiketal found at the anomeric carbon into an acetal or ketal because….

A

The -OH group characteristic of a hemiacetal/himiketal is transformed into a second -OR group, which defines an acetal/ketal

29
Q

The formation of a glycosidic bond transforms a hemiacetal or hemiketal found at the anomeric carbon into an acetal or ketal because….

A

The -OH group characteristic of a hemiacetal/himiketal is transformed into a second -OR group, which defines an acetal/ketal

30
Q

Name the three most common dissacharides that you should know for the MCAT

A
  • sucrose
  • lactose
  • maltose
31
Q

Name the sugar

This carbohydrate is “table sugar”, and is formed by combining glucose + fructose

A

sucrose

Glu(𝛼1--> β2)Fru describes the configuration of the glycosidic bond
32
Q

Name the sugar

This carbohydrate’s glycosidic bond formation can be abbreviated to Gal(β1–>4)Glu

A

lactose

lactose requires lactase to be hydrolyzed

33
Q

Name the carbohydrate

This carbohydrate’s bonds can be abbreviated by Glu(⍺1–>4)Glu. It is produced when amylase breaks down starch, and is present in a variety of food products i.e potatoes, pasta, and beer

A

maltose

34
Q

What is the most relevant function of polysaccharides for the MCAT?

A

Energy storage

starches are the most important ways we consume carbs. Think of potatoes, rice, and bread

35
Q

Humans store energy in the form of what polysaccharide carbohydrate?

A

Glycogen

glycogen is a polymer of glucose

36
Q

Where (in humans) is glycogen stored?

A

hepatocytes (liver cells) and muscle cells

glycogen stored in hepatocytes can be mobilized into the blood stream to regulate glucose levels and provide cells with energy, while glycogen in muscle cells is broken down to power glycolysis

37
Q

What is the glycogen stored in hepatocytes used for?

A

Glycogen stored in hepatocytes can be mobilized into the blood stream to regulate glucose levels and provide cells with energy, while glycogen in muscle cells is broken down to power glycolysis

38
Q

What is glycogen stored in muscle cells used for?

A

Glycogen in muscle cells is broken down to power glycolysis

39
Q

Name the polysaccharide comprised of a linear chain of glucose units linked by β(1–>4) bonds that is important for plant cells

A

cellulose

a polymer of glucose that maintains structure of cell walls

40
Q

Name the polysaccharide

Composted of linear chains of glucose linked by ɑ(1–>4) glycosidic bonds. It is a major component (20-30%) of starch, but is less easily digested than amylopectin

A

amylose

41
Q

Name the polysaccharide

Composed of linear chains of glucose linked by ɑ(1–>4) glycosidic bonds + branching due to ɑ(1–>6) glycosidic bonds every 24-30 units. Comprises about 70-80% of starch, and is broken down more easily than amylose

A

amylopectin

42
Q

Name the polysaccharide

20-30% amylose, 70-80% amylopectin. Major energy store produced by most green plants; most common form of carbohydrate in most diets

A

starch

43
Q

Name the polysaccharide

Major consituent of bacterial cell walls, and is a polymer composed of carbs that have been modified with amino acids

A

peptidoglycan

44
Q

Name the polysaccharide

Linear chains of glucose linked by ɑ(1–>4) glycosidic bonds + branching to ɑ(1–>6) glycosidic bonds every 8-12 units. Similar to amylopectin, but more branched. It’s synthesized in the liver and stored primarily in liver and muscle cells. It’s how the body stores glucose to be used

A

Glycogen

45
Q

Name the polysaccharide

A major component of cell walls in crustaceans, insects, and fungi

A

chitin

46
Q

The *d/l *(lowercase!)configuration of carbs is based on what quantity?

A

The optical rotation of light

this must be calculated empirically

there is no one-to-one relationshop between the direction fo which light is rotated and the structure of the compound. Note, enantiomers have the property of rotating plane-polarized light in opposite directions

47
Q

The D/L (uppercase!) system is used to categorize carbohydrates by what quantity?

A

A molecule’s spatial arrangement and configuration.

You can determine the arrangement based on Fischer projections

48
Q

The majority of carbohydrates found in nature are (D or L) isomers

A

D isomers

49
Q

How do we identify D-carbohydrates vs L-carbs using Fischer projections?

A

D carbohydrates are those with the bottom-most -OH group pointing to the right. L-sugars have the –OH on the left side

50
Q

isomers that have the same composition (that is, the same molecular forumula and connectivity) but that differ in the orientation of those parts in space. There are two kinds of ____: enantiomers and diastereomers.

A

steroisomer

51
Q

Stereoisomers that are not mirror images and are not superimposable

A

diastereomers

52
Q

Pairs of compounds with exactly the same connectivity but opposite three-dimensional shapes. They not the same as each other; one enantiomer cannot be superimposed on the other. They are mirror images of each other.

A

enantiomers

remember: all chiral centers must be FLIPPED

if two molecules have SWITCHED dashed/bold lines or COMPLETELY OPPOSITE ones then they are enantiomers
53
Q

Compare and contrast diasteromers and enantiomers

A

Enantiomers are a pair of molecules that exist in two forms that are mirror images of one another but cannot be superimposed one upon the other. Diastereomers are defined as compounds with the same molecular formula and sequence of bonded elements but are non-superimposable non-mirror images.

54
Q

Name the sterochemistry relationship

D vs L-Glucose are ____ of each other

A

Enantiomers

mirror images that are non-superimposable

for any monosaccharide, it's D and L form are enantiomers!
55
Q

True or False

For any carbohydrate, it’s D and L form are enantiomers

A

False. For any monosaccharide, it’s D and L form are enantiomers!

56
Q

Name the sterochemistry relationship between these two molecules

A

Epimers

These molecules are two isomers with different configurations of atoms around only one of several chiral centers
57
Q

True or False

Epimers are diasteriomers

A

True

Epimers are a type of diasteromer that differ at ONE chiral center

58
Q

a six-carbon carbohydrate ring

A

pyranose

59
Q

a five-carbon carbohydrate ring

A

furanose

60
Q

What process breaks down glycosidic bonds?

A

Hydrolysis

this process is necessaru for carb processing and metabolism

61
Q

True or False

Carbohydrates can particpitate in redox reactions

A

True !

For example, consider alsodes. Aldehydes can be oxidized to carboxylic acids. Oxidizing agents can be used to carry out these reactions.

62
Q

Also known as silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone

A

Tollens’ test

63
Q

identifies reducing sugars (monosaccharide’s and some disaccharides), which have free ketone or aldehyde functional groups.

A

Benedict’s test

64
Q

any sugar that is capable of acting as a reducing agent; any sugar that has a hemiacetal is a ____.

think: Benedict’s reagent

In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict’s reagent. In such a reaction, the sugar becomes a carboxylic acid.

A

reducing sugars

if a sugar can be converted into an* aldose*, it’s a reducing sugar

65
Q

Name the categories of sugars that are reducing sugars

A
  • monosaccharides
  • any sugar that has a hemiacetal
  • any sugar that can be converted into an aldose
  • any sugar with a free anomeric carbon

polysaccharides are considered generally non-reducing because it is rare for them to have a terminal reducing anomeric carbon

66
Q

True or False

The terminal C=O in aldoses can be easily oxidized to carboxylic acids

A

True

67
Q

True or False

Aldoses are reducing sugars

A

True

When an aldose gets oxidized, something else gets reduced, making the aldose a reducing agent, more specifically known as a reducing sugar

68
Q

Name the two most common methods for colorimetrically monitoring redox reactions involving sugars

A

Tollen’s test and Benedict’s reagent

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