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Biomolecules and Carbohydrates

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What is the primary function of carbohydrates in cell walls and exoskeletons?

Structural component

What is the chemical formula of carbohydrates?

(CH2O)n

What is the molecular weight range of carbohydrates?

90-200,000,000 Da

What is the name of the process by which plants produce carbohydrates?

Photosynthesis

What is the term for a group of atoms within a molecule with distinctive chemical properties?

Functional group

What is the term for the process of covalently linking carbohydrates with proteins?

Glycosylation

What is the term for the role of carbohydrates in cell-cell signaling?

Informational molecules

What is the name of the carbohydrate molecule with a molecular weight of 90 Da?

Glyceraldehyde

What is the simplest carbohydrate that exists in two isomeric forms that are mirror images of each other?

Glyceraldehyde

What is the term for a compound that contains an asymmetric center and thus can occur in two non-superposable mirror-image forms?

Chiral compound

What is the purpose of a polarising filter in the context of optically active compounds?

To pass only waves with vibration aligned in the same direction

In a Fischer projection formula, where is the carbonyl group situated?

At the top

What is the term for a carbon atom that has four different substituents attached?

Chiral atom

What is the term for a molecule that can be superimposed on its mirror image?

Achiral molecule

What is the term for the rotation of the plane of vibration of light caused by a chiral compound?

Optical activity

In a sugar molecule, which carbon atom is designated as D or L?

The carbon atom farthest from the carbonyl carbon

What is the primary characteristic that distinguishes aldoses from ketoses?

The presence of an aldehyde group or a ketone group

What is the term for a simple sugar that consists of a single sugar unit?

Monosaccharide

How are the carbon atoms in a monosaccharide numbered?

Based on the location of the carbonyl carbon atom

What is the general formula for a hexose sugar?

C6H12O6

What is the suffix of glucose and fructose?

-ose

Why do carbohydrates have many isomers?

Because of the arrangement of the -OH groups in their structures

What is the characteristic of an aldose sugar?

The carbonyl carbon atom is at the end of the carbon chain

What is the primary reason why obtaining enantiomerically pure compounds is important in medicine?

To reduce toxicity and improve selectivity

Which of the following sugars is a ketose?

Fructose

What is the main difference between enantiomers and epimers?

Enantiomers are non-superposable mirror images, while epimers differ in configuration at one asymmetric center

What is the characteristic that distinguishes L and D enantiomers of a chiral molecule?

Different directions of rotation of plane-polarized light

What is the term for a sugar molecule that contains an aldehyde or ketone group and two or more hydroxyl groups?

Saccharide

Why do some simple sugars occur in the L-form?

Because they have different biological properties

What is the term for a chiral center in a molecule?

Asymmetric center

What is the primary role of chirality in biology?

To influence the biological properties of molecules

What is an example of a pair of epimers?

D-glucose and 2-deoxy-D-glucose

What determines the classification of monosaccharides?

The number of carbon atoms and the functional 'carbonyl' group

What is a characteristic of sugars that differ in configuration at only one carbon atom?

They are epimers

What type of representation is used to show the configuration of groups around chiral centers?

Fischer projection formulas

What is the term for a simple sugar in which the carbonyl carbon atom is a ketone?

Ketose

What is the bond between a sugar and another molecule through an intervening oxygen?

Glycosidic bond

What is the term for a carbohydrate consisting of several monosaccharide groups joined by glycosidic bonds?

Oligosaccharide

What is the term for a carbohydrate consisting of a single sugar unit?

Monosaccharide

What is the term for a linear or branched polymer of monosaccharide units linked by glycosidic bonds?

Polysaccharide

What type of stereoisomers are glucose, galactose, and fructose?

Isomers

What is the term for the carbon atom in a sugar molecule that has four different substituents attached?

Chiral center

What type of bond is formed when an aldehyde is attacked by an alcohol?

Hemiacetal

What is the term for a sugar molecule with a carbonyl group that is a ketone?

Ketose

Why do some simple sugars occur in the L-form?

Because they are the mirror image of the D-form

What is the term for the process of a sugar molecule forming a ring structure?

Cyclisation

What is the characteristic that distinguishes aldoses from ketoses?

The presence of an aldehyde or ketone group

What is the term for a carbon atom with four different substituents attached?

Chiral center

What is the result of the condensation reaction between two monosaccharides?

Formation of a glycosidic bond

What is the role of the anomeric carbon in glycosidic bond formation?

It participates in the condensation reaction

What is the difference between a hemiacetal and an acetal?

A hemiacetal is formed from a monosaccharide, while an acetal is formed from two monosaccharides

What is the term for a disaccharide with no reducing ends?

Nonreducing disaccharide

What is the purpose of the Haworth perspective formula?

To represent the chemical structure of a monosaccharide

What is the term for the process by which a hydroxyl group from one monosaccharide adds to the anomeric carbon of another monosaccharide?

Condensation

What is the characteristic of a nonreducing disaccharide?

It has no reducing ends

What is the term for a molecule formed by the condensation of two alcohol molecules with an aldehyde molecule?

Acetal

What type of bond is formed between two monosaccharide units in a disaccharide?

Glycosidic bond

What is the term for a sugar that cannot donate electrons to other molecules and therefore cannot act as a reducing agent or be oxidized in aqueous solution?

Non-reducing sugar

What is the term for the carbon atom in a sugar at the new stereocenter formed when a sugar cyclizes to form a hemiacetal?

Anomeric carbon

What type of reaction is involved in the formation of a hemiacetal?

Nucleophilic addition

What is the term for a method for representing cyclic chemical structures so as to define the configuration of each substituent group?

Haworth perspective formulas

What type of reaction is involved in the condensation of two monosaccharides to form a disaccharide?

Condensation reaction

What is the term for two stereoisomers of a given sugar that differ only in the configuration about the carbonyl (anomeric) carbon atom?

Anomers

What is the term for a carbohydrate consisting of two covalently joined monosaccharide units?

Disaccharide

What is the difference between α-Glucose and β-Glucose?

The placement of the hydroxyl group on Carbon 1

What is the result of nucleophilic attack on the anomeric carbon in aldopyranose?

The formation of a hemiacetal linkage

What is the term for the carbon atom that becomes a new chiral center during cyclisation of monosaccharides?

Anomeric carbon

What is the type of ring formed when the hydroxyl group at C-5 (or C-6) reacts with the keto group at C-2?

Furanose

What is the most common anomer of D-Fructose?

β-D-Fructofuranose

What is the term for the process of intramolecular cyclisation of monosaccharides?

Cyclisation

What is the effect of mutarotation on the anomeric carbon?

It changes the configuration of the hydroxyl group

What is the difference between aldofuranose and aldopyranose?

The stability of the ring

What is the configuration of the hydroxyl group if it is on the opposite side of the ring as the CH2OH moiety?

b

What type of reaction is a dehydration reaction?

Condensation

What is the bond between two monosaccharides called?

Glycosidic bond

What is the term for a monosaccharide that has a free hemiacetal?

Reducing sugar

What is the glycosidic bond between monomers?

An acetal

What is the term for the carbon atom involved in the glycosidic linkage?

Anomeric carbon

What is the disaccharide formed by the condensation of two glucose molecules via a carbon 1-4 bond?

Maltose

What is the significance of the hemiacetal at the second monomer?

It makes the sugar reducing

Agarose is a component of which substance commonly used in laboratories?

Agar

What is the primary function of the extracellular matrix (ECM)?

To provide structural support to cells

What type of polymers are glycosaminoglycans?

Linear heteropolysaccharides

What is the characteristic that distinguishes polysaccharides from other carbohydrates?

They serve as stored fuel and structural components

What is the primary function of peptidoglycan in bacterial cell walls?

To provide structural support

What is the role of hyaluronan in the extracellular matrix (ECM)?

To aid diffusion and provide support

What is the characteristic of agarose and agar solutions?

They form gels at low temperatures

What is the primary function of cellulose in plant cell walls?

To provide structural support

What is the role of glycosaminoglycans in the extracellular matrix (ECM)?

To support and aid diffusion

What is the characteristic of glycans?

They serve as stored fuel and structural components

Study Notes

Carbohydrates

  • Carbohydrates are the most abundant biomolecule on Earth, with approximately 100 billion metric tons produced annually through photosynthesis.
  • They are a vital dietary staple in many parts of the world, and their functions include energy source, energy storage, structural component, and informational molecules.
  • Carbohydrates can be covalently linked with proteins to form glycoproteins, glycolipids, and proteoglycans.

Classification of Carbohydrates

  • Carbohydrates are classified based on the number of carbon atoms they have, with the formula (CH2O)n, where 'n' is the number of carbon atoms ≥ 3.
  • They can range in size from small (e.g., glyceraldehyde, Mw = 90 Da) to huge (e.g., amylopectin, Mw = 200,000,000 Da).

Functional Groups of Biomolecules

  • A functional group is a group of atoms within a molecule with distinctive chemical properties.
  • When two or more substituents are shown in a molecule, they are designated as R1, R2, and so forth.

Monosaccharides

  • Monosaccharides are classified into two classes: aldoses and ketoses, based on the type of carbonyl group they possess.
  • Aldoses have an aldehyde group, while ketoses have a ketone group.
  • Monosaccharides can also be classified based on the number of carbon atoms they have, such as trioses, tetroses, pentoses, and hexoses.

Fischer Projection Formulas

  • Fischer projection formulas are a 2D method for representing 3D molecules to show the configuration of groups around chiral centers.
  • The carbonyl group is situated at the top, and the last achiral CH2OH is at the bottom.

Chiral Centers and Enantiomers

  • Chiral centers are atoms with substituents arranged so that the molecule is non-superposable on its mirror image.
  • Enantiomers are stereoisomers that are non-superposable mirror images of each other.
  • Chiral compounds can interact with polarized light, causing the plane of vibration to rotate.

Importance of Enantiomers

  • Obtaining enantiomerically pure compounds is crucial in medicine, as the two enantiomers of a chiral molecule can have very different biological properties.
  • Enantiomers can differ in bioavailability, rate of metabolism, metabolites, excretion, potency, selectivity, and toxicity.

Epimers

  • Epimers are two sugars that differ only in the configuration around one carbon atom.
  • D-glucose and D-mannose are examples of epimers.

Definitions

  • Aldose: A simple sugar in which the carbonyl carbon atom is an aldehyde.
  • Carbohydrate: A sugar (monosaccharide) or one of its dimers (disaccharide) or polymers (polysaccharide).
  • Chiral center: An atom with substituents arranged so that the molecule is non-superposable on its mirror image.
  • Chiral compound: A compound that contains an asymmetric center (chiral atom or chiral center) and thus can occur in two non-superposable mirror-image forms.
  • Disaccharide: A carbohydrate consisting of two covalently joined monosaccharide units.
  • Enantiomers: Stereoisomers that are non-superposable mirror images of each other (L - laevorotatory and D - dextrorotatory).
  • Fischer projection formulas: A 2D method for representing 3D molecules to show the configuration of groups around chiral centers.
  • Glycosidic bond: Bonds between a sugar and another molecule (typically an alcohol, purine, pyrimidine, or sugar) through an intervening oxygen.
  • Isomers: Any two molecules with the same molecular formula but a different arrangement of molecular groups.
  • Ketose: A simple monosaccharide in which the carbonyl group is a ketone.
  • Monosaccharide: A carbohydrate consisting of a single sugar unit.
  • Oligosaccharide: Several monosaccharide groups joined by glycosidic bonds.
  • Polysaccharide: A linear or branched polymer of monosaccharide units linked by glycosidic bonds.

Monosaccharides

  • Monosaccharides can exist in a straight or cyclic structure.
  • In aqueous solutions, aldotetroses and monosaccharides with 5 or more carbon atoms occur predominantly as cyclic structures.
  • Glucose, Galactose, and Fructose are all isomers of one another (same chemical formula, different structural formula).

Cyclic Structure: Hemiacetals and Hemiketals

  • Aldehyde and ketone carbons are electrophilic, while alcohol oxygen atoms are nucleophilic.
  • When aldehydes are attacked by alcohols, hemiacetals form, and when ketones are attacked by alcohols, hemiketals form.
  • Formation of an additional asymmetric carbon atom (anomeric carbon) can exist in two stereoisomeric forms.

Cyclisation of Monosaccharides

  • There can be multiple configurations of a ring structure.
  • Two possible ring structures for Glucose exist: α-Glucose and β-Glucose.
  • The difference between α-Glucose and β-Glucose is the placement of the hydroxyl group on Carbon 1.
  • Aldopyranose is more stable than aldo furanose.
  • Mutarotation occurs when the anomeric carbon is attacked by a nucleophile.

Anomers

  • Anomers are two stereoisomers of a given sugar that differ only in the configuration about the carbonyl (anomeric) carbon atom.
  • The anomeric carbon is the carbon atom in a sugar at the new stereocenter formed when a sugar cyclizes to form a hemiacetal.

Disaccharides

  • Two monosaccharides bond together (dehydration reaction) to form a carbohydrate called a disaccharide.
  • A dehydration reaction is a condensation reaction, where two molecules combine to form one single molecule, losing a small molecule in the process.
  • The bond between two monosaccharides is known as a glycosidic bond.

The Glycosidic Bond

  • Two sugar molecules can be joined via a glycosidic bond between an anomeric carbon and a hydroxyl carbon.
  • The glycosidic bond (an acetal) between monomers is less reactive than the hemiacetal at the second monomer.
  • A second monomer with a hemiacetal is reducing, while the anomeric carbon involved in the glycosidic linkage is non-reducing.

Non-Reducing Disaccharides

  • Two sugar molecules can also be joined via a glycosidic bond between two anomeric carbons.
  • No remaining hemiacetals are present, and the product has two acetal groups and no hemiacetals.
  • There are no reducing ends, and this is a non-reducing sugar.

Key Concepts

  • Haworth perspective formulas are a method for representing cyclic chemical structures to define the configuration of each substituent group.
  • Hemiacetal/Hemiketal is formed when an alcohol oxygen atom adds to the carbonyl carbon of an aldehyde or a ketone following nucleophilic attack.
  • Nucleophilic addition is the initial attack of a nucleophile (hydroxyl group) on the slightly positive carbon center of the carbonyl group.
  • Reducing sugar is a sugar in which the carbonyl (anomeric) carbon is not involved in a glycosidic bond and can therefore undergo oxidation.
  • Non-reducing sugar is a carbohydrate that cannot donate electrons to other molecules and therefore cannot act as a reducing agent or be oxidized in aqueous solution.

Polysaccharide Structure

  • Polysaccharides can be composed of 1, 2, or several different monosaccharides in straight or branched chains of varying length.

Homopolysaccharides

  • A homopolysaccharide is a polysaccharide made up of one type of monosaccharide unit.
  • Examples: starch, glycogen, chitin, cellulose.

Heteropolysaccharides

  • A heteropolysaccharide is a polysaccharide containing more than one type of sugar.
  • Examples: agarose, peptidoglycans, glycosaminoglycans.

Starch

  • Starch is a mixture of two homopolysaccharides of D-glucose: amylose and amylopectin.
  • Amylose is an unbranched polymer of (α1 → 4) linked residues with a molecular weight that varies from a few thousand to over 1 million.
  • Amylopectin is branched like glycogen, but the branch-points with (α1 → 6) linkers occur every 24–30 residues, with a molecular weight of up to 200 million.
  • Starch is the main storage polysaccharide in plants and is heavily hydrated due to the number of exposed -OH groups.

Glycogen

  • Glycogen is a branched homopolysaccharide of glucose.
  • Glucose monomers form (α1 → 4) linked chains.
  • Branch-points with (α1 → 6) linkers occur every 8–12 residues, making it more compact than starch.
  • Molecular weight reaches several millions, and it functions as the main storage polysaccharide in animals, abundant in the liver and skeletal muscle.

Other Polysaccharides

  • Dextrans: bacterial and yeast polysaccharides, with poly-D-glucose forming (α1 → 6) linked chains.
  • Cellulose: an unbranched homopolysaccharide of glucose, with D-glucose monomers forming (β1 → 4) linked chains.
  • Chitin: a linear homopolysaccharide of N-acetylglucosamine (NAG), found in cell walls of mushrooms and exoskeletons of insects, spiders, and other arthropods.
  • Agar and Agarose: complex mixtures of heteropolysaccharides containing modified galactose units, used in laboratory settings.
  • Glycosaminoglycans: linear polymers with repeating disaccharide units, found in animals and bacteria, containing sulfate groups.

Polysaccharide Functions

  • Serve as stored fuel and structural components of cell walls and extracellular matrix.
  • Some homopolysaccharides fold in 3D, forming helical structures with interchain hydrogen bonding.
  • Heteropolysaccharides, such as peptidoglycan and agar, strengthen bacterial and algal cell walls.
  • Glycosaminoglycans provide support and aid diffusion in the extracellular matrix.

This quiz covers the importance of carbohydrates, types of biomolecules, and their functions in cells and organisms. It also touches on their role in cell recognition and adhesion.

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