Carbohydrate Structure Flashcards
What is the general formula for carbohydrates?
Cx(H2O)y
Carbs are comprised of a carbon backbone, carbononyl group (C=O) and at least one hydroxyl (-OH) group
a sugar that contains a terminal carbon group
aldose
because it contains an aldehyde
a sugar whose carbonyl group is not terminal
ketose
because it contains a ketone
Carbohydrates can be called trioses, tetroses, pentoses, hexoses, and even heptoses based on ….
The number of carbons it has
Identify this important triose
glyceraldehyde
Derivatives of glyceraldehyde are important intermediates in glycolysis
Name this important pentose
Ribose
Ribose 5-phosphate is also derived from glucase during the pentose phosphate pathway
Whenever you see a carbohydrate structural diagram, you can assume it’s a ____ isomer
D-isomer
Name the three most important hexoses to know for the MCAT
glucose
fructose
galactose
glucose is an aldohexose, fructose is a ketohexose, and galactose is an aldohexose.
Name the hexose that is found in dairy products and sugar beets. It is an aldose that can be rapidly converted to glucose.
galactose
Name the hexose that is the main source of energy for the body under normal conditions. This is an aldose
Glucose
an aldohexose
Glucose + fructose = sucrose
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
Fructose
a ketohexose
Glucose + fructose = sucrose
True or False
Pentoses and hexoses typically exist in cyclic forms under physiological conditions, not linear forms
True
When an alcohol adds to an aldehyde, the result is called a ____; when an alcohol adds to a ketone the resulting product is 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
a hemiketal differs from a hemicetal in that instead of an -R, -OR, -OH, -H structure, it has a -R, -OR, -OH, ____ structure
a hemiketal differs from a hemicetal in that instead of an -R, -OR, -OH, -H structure, it has a -R, -OR, -OH, -R structure
Name this functional group
ketone
Name the functional group
aldehyde
____ 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
anomers
The epimeric carbon in anomers are known as anomeric carbon or anomeric center.
Youtube link
What is the sterochemical relationship between these two molecules?
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)
A(n) ____ is one of two stereoisomers that differ in configuration at only one stereocenter.
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
alpha anomers
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
beta anomers
beta anomers feature an upward OH group
the process of interconversion between alpha and beta anomers
involves the breaking and reforming of covalent bonds
mutarotation
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.
anomeric carbon
The carbon in red is called the ____ carbon
carbonyl carbon
a carbon atom double-bonded to an oxygen atom
the simplest of sugars
monosaccharide
what bonds must form between monosaccharides to form more complex sugars?
Glycosidic bonds
Describe the process of glycosidic bond formation
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
The formation of a glycosidic bond transforms a hemiacetal or hemiketal found at the anomeric carbon into an acetal or ketal because….
The -OH group characteristic of a hemiacetal/himiketal is transformed into a second -OR group, which defines an acetal/ketal
The formation of a glycosidic bond transforms a hemiacetal or hemiketal found at the anomeric carbon into an acetal or ketal because….
The -OH group characteristic of a hemiacetal/himiketal is transformed into a second -OR group, which defines an acetal/ketal
Name the three most common dissacharides that you should know for the MCAT
- sucrose
- lactose
- maltose
Name the sugar
This carbohydrate is “table sugar”, and is formed by combining glucose + fructose
sucrose
Name the sugar
This carbohydrate’s glycosidic bond formation can be abbreviated to Gal(β1–>4)Glu
lactose
lactose requires lactase to be hydrolyzed
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
maltose
What is the most relevant function of polysaccharides for the MCAT?
Energy storage
starches are the most important ways we consume carbs. Think of potatoes, rice, and bread
Humans store energy in the form of what polysaccharide carbohydrate?
Glycogen
glycogen is a polymer of glucose
Where (in humans) is glycogen stored?
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
What is the glycogen stored in hepatocytes used for?
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
What is glycogen stored in muscle cells used for?
Glycogen in muscle cells is broken down to power glycolysis
Name the polysaccharide comprised of a linear chain of glucose units linked by β(1–>4) bonds that is important for plant cells
cellulose
a polymer of glucose that maintains structure of cell walls
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
amylose
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
amylopectin
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
starch
Name the polysaccharide
Major consituent of bacterial cell walls, and is a polymer composed of carbs that have been modified with amino acids
peptidoglycan
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
Glycogen
Name the polysaccharide
A major component of cell walls in crustaceans, insects, and fungi
chitin
The *d/l *(lowercase!)configuration of carbs is based on what quantity?
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
The D/L (uppercase!) system is used to categorize carbohydrates by what quantity?
A molecule’s spatial arrangement and configuration.
You can determine the arrangement based on Fischer projections
The majority of carbohydrates found in nature are (D or L) isomers
D isomers
How do we identify D-carbohydrates vs L-carbs using Fischer projections?
D carbohydrates are those with the bottom-most -OH group pointing to the right. L-sugars have the –OH on the left side
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.
steroisomer
Stereoisomers that are not mirror images and are not superimposable
diastereomers
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.
enantiomers
remember: all chiral centers must be FLIPPED
Compare and contrast diasteromers and enantiomers
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.
Name the sterochemistry relationship
D vs L-Glucose are ____ of each other
Enantiomers
mirror images that are non-superimposable
True or False
For any carbohydrate, it’s D and L form are enantiomers
False. For any monosaccharide, it’s D and L form are enantiomers!
Name the sterochemistry relationship between these two molecules
Epimers
True or False
Epimers are diasteriomers
True
Epimers are a type of diasteromer that differ at ONE chiral center
a six-carbon carbohydrate ring
pyranose
a five-carbon carbohydrate ring
furanose
What process breaks down glycosidic bonds?
Hydrolysis
this process is necessaru for carb processing and metabolism
True or False
Carbohydrates can particpitate in redox reactions
True !
For example, consider alsodes. Aldehydes can be oxidized to carboxylic acids. Oxidizing agents can be used to carry out these reactions.
Also known as silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone
Tollens’ test
identifies reducing sugars (monosaccharide’s and some disaccharides), which have free ketone or aldehyde functional groups.
Benedict’s test
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.
reducing sugars
if a sugar can be converted into an* aldose*, it’s a reducing sugar
Name the categories of sugars that are reducing sugars
- 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
True or False
The terminal C=O in aldoses can be easily oxidized to carboxylic acids
True
True or False
Aldoses are reducing sugars
True
When an aldose gets oxidized, something else gets reduced, making the aldose a reducing agent, more specifically known as a reducing sugar
Name the two most common methods for colorimetrically monitoring redox reactions involving sugars
Tollen’s test and Benedict’s reagent
