Chapter 6: Carbohydrates Flashcards
Recent studies on cell surface carbohydrates has demonstrated an unusually high concentration of __ (IUPAC name __) on the surface of some cancer cells. It is a complex monosaccharide that is found on all our normal cells, as well. It is a signal that a cell is “__,” thereby protecting it from attack by our immune system. If certain cancer cells have an abundance of sialic acid on the surface, those cancer cells are essentially __ to the cells of our immune system that should attack and destroy them.
- sialic acid
- N-acetylneuraminic acid
- self
- invisible
How do medical researchers aim to make cancer cells more visible to the immune system?
- Researchers attach the enzyme sialidase to an antibody that binds to cancer cells, facilitating the removal of sialic acid from the cell surface.
- The enzyme sialidase, when attached to the antibody, clips away the sialic acid from the cancer cell surface, making them identifiable as foreign by the immune system.
__ are the most abundant class of bioorganic molecules on planet Earth. Although their abundance in the human body is relatively low, they constitute about __ by mass of dry plant materials.
- Carbohydrates
- 75%
Two major types of biochemical substances
- bioinorganic substances (no carbon)
- bioorganic substances (contains carbon)
Subtypes of bioinorganic substances and their abundance in the human body
- water (70%)
- inorganic salts (about 5%)
Subtypes of bioorganic substances and their abundance in the human body
- Proteins (about 15%)
- Lipids (about 8%)
- Carbohydrates (about 2%)
- Nucleic acids (about 2%)
Green (chlorophyll-containing) plants produce __ via photosynthesis.
carbohydrates
Formula of photosynthesis
CO2 + H20 + Solar energy –(chlorophyll/plant enzymes)–> carbohydrates +O2
Two main uses for the carbohydrates in plants:
- In the form of cellulose, carbohydrates serve as structural elements
- In the form of starch, they provide energy reserves for the plants
__ is a polymer of glucose, a sugar produced by the plant during photosynthesis, and used as a source of energy. It is stored as __ in structures called __.
- Starch
- grains/granules
- amyloplasts
__ is the major carbohydrate source for humans and animals. The average human diet should ideally be about __ carbohydrate by mass.
- Dietary intake of plant materials
- two-thirds
Carbohydrates have the following functions in humans:
- Carbohydrate oxidation provides energy.
- short-term energy reserve
- supply carbon atoms for the synthesis of other biochemical substances
- genetic control of growth and development
- structural components of cell membranes.
- cell–cell and cell–molecule recognition processes.
carbohydrates that contribute to short-term energy reserve in the human body
carbohydrates stored in the form of glycogen
What is the primary function of carbohydrate oxidation in humans?
Carbohydrate oxidation provides energy, releasing approximately 4 kilocalories (kcal) of energy per gram when cells “burn” carbohydrates for fuel.
Besides energy, what do carbohydrates supply for the synthesis of other biochemical substances?
Carbohydrates supply carbon atoms necessary for the synthesis of proteins, lipids, and nucleic acids.
carbohydrates that are involved in the genetic control of growth and development of living cells
ribose and deoxyribose
carbohydrates involved in the structure of cell membranes
Carbohydrates linked to lipids
carbohydrates involved in various cell–cell and cell–molecule recognition processes.
Carbohydrates linked to proteins
the basis for the term carbohydrate (“hydrate of carbon”)
Cn(H2O)n
Most simple carbohydrates have empirical formulas that fit the general formula __ which can be written as __
- CnH2nOn
- Cn(H2O)n
A carbohydrate is a __, a __, or a compound that yields __ or __ upon hydrolysis.
- polyhydroxy aldehyde
- polyhydroxy ketone
- polyhydroxy aldehydes
- polyhydroxy ketones
Carbohydrates are classified on the basis of __
molecular size
Types of carbohydrates
- Monosaccharide
- Disaccharide
- Oligosaccharide
- Polysaccharide
- type of carbohydrate that contains a single polyhydroxy aldehyde or polyhydroxy ketone unit.
- cannot be broken down into simpler units by __.
- water-soluble, white, crystalline solids
- Monosaccharides
- hydrolysis reactions
- type of carbohydrate that contains two monosaccharide units covalently bonded to each other
- crystalline, water-soluble substances.
Disaccharides
Hydrolysis of a disaccharide produces __.
two monosaccharide units
Give 2 examples of disaccharides
- Sucrose (table sugar)
- lactose (milk sugar)
type of carbohydrate that contains 3-10 monosaccharide units covalently bonded to each other.
oligosaccharide
- seldom encountered in biochemical systems.
- usually found associated with proteins and lipids in complex molecules that have both structural and regulatory functions.
“Free” oligosaccharides
Complete hydrolysis of an oligosaccharide produces several __
monosaccharide molecules
- a __ produces 3 monosaccharide units
- a __ produces 6 monosaccharide units
- trisaccharide
- hexasaccharide
a polymeric carbohydrate that contains many monosaccharide units covalently bonded to each other. The number of monosaccharide units present in a polysaccharide varies from a few hundred units to over 50,000 units.
polysaccharide
carbohydrates that undergo hydrolysis under appropriate conditions to produce monosaccharides
- disaccharides
- oligosaccharides
- polysaccharides
The prefixes __ and __ found in the complete name of a monosaccharide are used to identify one of two possible isomeric forms called __.
- D- ; L-
- stereoisomers
By definition, each member of a pair of stereoisomers must have the same molecular formula and the same bonding pattern; D- and L- differ in the __ in the molecule.
spatial arrangements of atoms
A carbon atom that has four different groups bonded to it
chiral carbon
Any molecule containing a chiral carbon is a __ and will exist as a pair of __.
- chiral molecule
- enantiomers
images that coincide at all points when the images are laid upon each other.
Superimposable mirror images
images where not all points coincide when the images are laid upon each other.
Nonsuperimposable mirror images
Different responses are usually observed for right-handed and left-handed forms of a molecule, and our bodies typically use only _____ of the two forms of a chiral compound.
one
What are the three possible scenarios regarding the biological activity of the two forms of a chiral compound?
- Sometimes both forms are biologically active, each form giving a different response;
- Sometimes both elicit the same response, but one form’s response is many times greater than that of the other; and
- Sometimes only one of the two forms is biochemically active.
How many stereoisomeric forms can a compound with n chiral centers have, according to the general rule?
a maximum of 2^n stereoisomeric forms
When three chiral centers are present, how many stereoisomers are possible?
At most, eight stereoisomers are possible (2^3 = 8), forming four pairs of enantiomers.
isomers in which atoms have different connectivity
constitutional isomers
three types of constitutional isomers
- skeletal
- positional
- functional group isomers
isomers with different carbon atom arrangements and different hydrogen arrangements
skeletal isomer
isomers that differ in the location of the functional group
positional isomer
isomers that contain different functional groups
functional group isomers
isomers with atoms of the same connectivity that differ only in the orientation of the atoms in space
stereoisomers
types and subtypes of stereoisomers
- enantiomers
- diastereoisomers
–> cis-trans isomers
–> Most other diastereoisomers (two or more chiral centers)
- stereoisomers that are non-superimposable mirror images of each other
- Handedness (D and L forms) is determined by the configuration at the highest-numbered chiral center.
enantiomers
stereoisomerism that results from restricted rotation of chemical bonds
- sometimes possible when a ring is present
- sometimes possible when a double bond is present
cis-trans isomers
What is the characteristic feature of an optically active compound?
rotates the plane of polarized light
How does the plane-polarized light setup work?
- Begin with a sodium lamp emitting unpolarized light.
- Use a polaroid filter to create plane-polarized light.
- Shine the light through a tube with an enantiomer solution.
- Place a second polaroid filter (analyzer) after the tube.
- Rotate the second filter to observe changes in light intensity, demonstrating how enantiomers interact with plane-polarized light.
a chiral compound that rotates the plane of polarized light in a clockwise direction.
dextrorotatory compound
a chiral compound that rotates the plane of polarized light in a counterclockwise direction
levorotatory compound
Why do enantiomers share the same boiling points, melting points, and densities?
These physical properties are not influenced by chirality, as they depend on intermolecular forces, which remain identical for enantiomers.
How do enantiomers’ solubilities in achiral and chiral solvents differ?
- same solubility = achiral solvents (e.g. ethanol)
- different solubilities = chiral solvents (e.g. d-2-butanol)
What influences the rate and extent of reaction for enantiomers with another reactant?
achiral reactant = same rate and extent of reaction
chiral reactant = different rate and extent of reaction
Why do enantiomers generate different responses in the human body?
Receptor sites in the body have associated chirality. Enantiomers consistently produce varied responses when interacting with these sites, ranging from slight to very different responses.
The response of the body to the D isomer of the hormone is __ than its response to the L isomer of the hormone.
20 times greater
Classification of monosaccharides based on the type of carbonyl group
- aldose
- ketose
a monosaccharide that contains an aldehyde functional group.
aldose
aldoses are
polyhydroxy aldehydes.
a monosaccharide that contains a ketone functional group.
ketose
ketoses are
polyhydroxy ketones
How are monosaccharides typically classified?
according to:
- number of carbon atoms
- their functional group
classification for an aldose with 3 carbons
aldotriose
classification for a ketose with 6 carbons
ketohexose
Which two trioses are essential intermediates in glycolysis?
The simplest trioses:
- D-Glyceraldehyde (chiral molecule)
- dihydroxyacetone (achiral molecule)
Biochemically Important Monosaccharides
- D-Glyceraldehyde and Dihydroxyacetone (glycolysis)
- D-Glucose and D-Galactose
- D-Fructose
- D-Ribose
Biochemically Important Monosaccharide
* Found in high amounts in ripe fruits
* Blood sugar
* Also called dextrose
D-Glucose
D-Glucose is also called
dextrose
Biochemically Important Monosaccharide
* seldom encountered as a free monosaccharide
D-Galactose
Biochemically Important Monosaccharide
* Synthesized from glucose in the body for the production of lactose (a disaccharide of glucose and galactose)
D-Galactose
Biochemically Important Monosaccharide
* called brain sugar because it is a component of glycoproteins found in brain and nerve tissue
D-Galactose
Biochemically Important Monosaccharide
* also present in the chemical markers that distinguish various types of blood—A, B, AB, and O
D-Galactose
Biochemically Important Monosaccharide
* biochemically the most important
ketohexose.
D-Fructose
Biochemically Important Monosaccharide
- also known as levulose and fruit sugar
D-Fructose
D-Fructose is also known as
- levulose
- fruit sugar
Biochemically Important Monosaccharides
* sweetest-tasting of all sugars
* found in many fruits and is present in honey in equal amounts with glucose
* used as a dietary sugar because less is needed for the same amount of sweetness
D-Fructose
Biochemically Important Monosaccharide
* 5-carbon sugar (pentose)
* Component of ribonucleic acids (RNAs) and energy-rich compounds such as adenosine triphosphate (ATP).
D-Ribose
What distinguishes the structures of D-Glucose and D-Ribose?
number of carbon atoms
How do the structures of D-Fructose and D-Glucose differ?
- D-Glucose has an aldehyde functional group
- D-Fructose has a ketone functional group.
What is the structural consequence for monosaccharides with five or more carbon atoms?
they exist in equilibrium between open-chain and cyclic structures
Why are cyclic structures dominant in the equilibrium of monosaccharides?
intramolecular reaction between the carbonyl group (C=O) and a hydroxyl group (-OH), forming cyclic hemiacetals
The cyclic hemiacetal forms of D-Glucose result from the intermolecular reaction between the carbonyl group and the hydroxyl group on Carbon 5. How many enantiomers are made and what is the basis in naming them?
- 2 enantiomers
- depends on how ring closure occurs
In the cyclic hemiacetal forms of monosaccharides, what name is given when the -OH group in Carbon 5 is above? Below?
-b (beta)-
- a (alpha)-