Carbohydrates Overview Quiz

Carbohydrates

• Found in all living organisms
• Key roles include energy storage, transport, cell communication, structural components (plants, animals, bacteria, fungi), and DNA/RNA components.
• Composed of carbon, hydrogen, and oxygen; some also contain sulfur and nitrogen.
• Formula for most carbohydrates: (CH₂O)ₙ
• Consist of two or more hydroxyl groups and either an aldehyde or ketone group.
• Known as sugars, saccharides, or glycans.
• Simplest carbohydrates are glyceraldehyde and dihydroxyacetone (3 carbons).

Chirally Active Sugars

• Most sugars are optically active, meaning they can rotate plane-polarized light.
• Glyceraldehyde exhibits stereoisomerism.

Carbohydrate Classifications

• Based on the number of carbon atoms:
  • Triose (3 carbons)
  • Tetraose (4 carbons)
  • Pentose (5 carbons)
  • Hexose (6 carbons)
  • Examples of hexoses include glucose, mannose, and galactose.
  • Examples of pentoses include ribose, xylose, and arabinose.

Carbohydrate Rings

• Sugars with four or more carbons typically form ring structures.
• Most common for 5- or 6-carbon sugars.

Aldoses and Ketoses

• Aldoses contain an aldehyde group.
  • Examples include glucose (6 carbons), glyceraldehyde (3 carbons), and ribose (5 carbons).
• Ketoses contain a ketone group.
  • Examples include fructose (6 carbons) and ribulose (5 carbons).

Sugar Ring Conformations

• Rings exist in non-planar configurations (e.g., chair conformations).
• Axial positions are oriented up/down, perpendicular to the ring.
• Equatorial positions are in the same plane as the ring.
• Axial positions experience more steric hindrance.

Anomers

• Isomeric forms of cyclic sugars.
• Distinguished by the orientation of the hydroxyl group (-OH) on the anomeric carbon (C1 in aldoses, C2 in ketoses).
• Alpha- anomer: -OH group is axial.
• Beta- anomer: -OH group is equatorial.

D and L Sugars

• Most common sugars have 5-6 carbons and multiple asymmetric carbons (e.g., glucose has 4).
• Two stereoisomers of glucose.
• D and L forms are enantiomers (mirror images).
• Nearly all naturally occurring sugars are in the D-configuration.

Epimers

• Diastereoisomers (not mirror images) that differ at only one chiral carbon.
• D-glucose and D-galactose are epimers at carbon 4.
• D-glucose and D-mannose are epimers at carbon 2.

Carbohydrate Polymers

• Monosaccharides link to form more complex carbohydrates.
• Disaccharides (two monosaccharides), Oligosaccharides (2-10 monosaccharides), and Polysaccharides (more than 10 monosaccharides).
  • Glycosidic bonds hold the sugars together.

Glycosidic Bonds

• Covalent linkages formed between anomeric carbon of one monosaccharide and the oxygen atom of another alcohol molecule (O-glycosidic bond) or a nitrogen atom of an amine (N-glycosidic bond).
• Glycosidic bonds can form modified carbohydrates
• Can be alpha or beta.

Roles of Carbohydrates in Biology

• Major source of energy for metabolism.
• Important for energy storage (starch and glycogen).
• Structural components (cellulose, peptidoglycan).
• Involved in signaling (cell-cell communication, host-pathogen recognition).

Disaccharides

• Two monosaccharides joined by a glycosidic bond.
• Examples include maltose (two α-glucose), lactose (glucose and galactose), and sucrose (glucose and fructose).

Polysaccharides

• Energy storage polysaccharides like starch (plants) and glycogen (animals).
• Both primarily consist of glucose units linked by α-glycosidic bonds (branched and straight chains)

Starch and Glycogen

• Straight chains via α(1→4) linkages to form a helix
• Branched chains via α(1→6) linkages allowing for rapid enzyme access and quick release of glucose.

Cellulose

• Unbranched β-glucose polymer.
• Structural component of plant cell walls.
• β(1→4) linkages give rise to long, strong strainght chains that are difficult to digest.

Peptidoglycan

• Structural component of bacterial cell walls; consists of alternating NAG and NAM units linked by glycosidic bonds.
• Cross-linking peptides provide strength and rigidity; susceptible to penicillin.

Glycoconjugates

• Carbohydrates covalently attached to proteins or lipids.
  • Examples include glycolipids and glycoproteins.

Glycolipids

• Lipid + carbohydrate.
• Found in cell membranes; involved in cell recognition (e.g., blood groups).

Glycoproteins

• Protein + carbohydrate.
• Important for cell recognition and adhesion, protein folding and stability;
• Types:
  • N-linked: attached to asparagine side chains (often on secreted proteins).
  • O-linked: attached to serine or threonine side chains (often intracellular).

Proteoglycans

• Protein core with attached glycosaminoglycans (GAGs).
• Important components of the extracellular matrix.
• Provide lubrication and structural support.
• Bind water and form hydrated gels
• Important for cell adhesion.

Blood Groups

• Determined by specific glycosyltransferases that add sugars to core oligosaccharides.

Glycans (Complex Carbohydrates)

• Play a critical role in host-pathogen interactions.
• SARS-CoV-2's spike protein is heavily glycosylated, aiding its ability to bind to ACE2 receptors.

Phosphorus in Biology

• Essential component of many biological molecules.
• Found in bones (as hydroxyapatite).
• Constituent of cell membranes, energy molecules (ATP), and nucleic acids (DNA and RNA).

Phosphate Groups

• Phosphate (PO4⁻³) is tetrahedral
• Phosphate's importance for stability arising from electrons delocalising around phosphate.
• Importance in control of protein activity by adding/removing phosphate groups
• Important in high-energy molecules and nucleotides

Phosphodiester Bonds

• Found in nucleic acids; form the backbone.
• Formed through reaction of hydroxyl groups and phosphoric acid.

ATP and Hydrolysis

• Energy currency in cells;
• High-energy phosphate bonds (phosphoanhydride bonds), releasing energy through hydrolysis.
• Hydrolysis driven by electrostatic repulsion, resonance stabilization, and solvation of products.

Test your knowledge on carbohydrates and their classifications with this quiz. Explore key roles, structures, and optically active sugars. Dive into different types of carbohydrates based on the number of carbon atoms.