Carbohydrates Overview Quiz

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Questions and Answers

What is the primary form in which phosphorus is stored in the human body?

As hydroxyapatite (correct)

As nucleotides

As phosphoric acid

As proteins

Which statement best describes the function of phosphates in protein activity?

Phosphates enhance the stability of proteins.

Phosphates bind irreversibly to proteins.

Phosphates degrade proteins.

Phosphates can switch proteins on or off by altering their shape. (correct)

What is the significance of the pKa value in relation to phosphoric acid?

It indicates the concentration of water in the solution.

It represents the point where acid and conjugate base concentrations are equal. (correct)

It shows the strength of phosphoric acid compared to other acids.

It is used to determine the solubility of phosphates.

Which bond is formed as a result of the reaction between two hydroxyl groups in phosphoric acid?

Phosphodiester bond Signup and view all the answers

Which factor does not contribute to the high free energy of ATP hydrolysis?

Low concentration of ATP in muscle cells Signup and view all the answers

What is the empirical formula for most carbohydrates?

(CH2O)n Signup and view all the answers

Which type of carbon linkage is found in starch and glycogen?

Alpha 1,4 and 1,6 glycosidic bonds Signup and view all the answers

In which case is the anomeric carbon located specifically at C1?

In all aldoses Signup and view all the answers

What distinguishes D and L sugars?

The arrangement of atoms around the first asymmetric carbon Signup and view all the answers

Which of the following is a characteristic of epimers?

They differ at only one chiral carbon. Signup and view all the answers

Which of the following carbohydrates is a disaccharide?

Both B and C Signup and view all the answers

What configuration do sugar rings typically adopt?

Non-planar chair configuration Signup and view all the answers

What is the primary function of cellulose in plant cells?

Providing tensile strength Signup and view all the answers

How does penicillin affect bacterial cells?

Inhibits peptidoglycan synthesis Signup and view all the answers

Which type of linkage is found in alpha-glucans?

Alpha 1,4 glycosidic bond Signup and view all the answers

What is the primary role of glycosyltransferase enzymes?

Transfer sugars to other molecules Signup and view all the answers

What structure do glycoproteins typically contain?

Carbohydrates linked to amino acids Signup and view all the answers

Which of the following correctly describes the structure of peptidoglycan?

Alternating residues of NAG and NAM Signup and view all the answers

What component primarily determines the function of proteoglycans?

Carbohydrate portion Signup and view all the answers

Which blood group produces no functional glycosyltransferases?

Blood group O Signup and view all the answers

In the context of SARS-CoV-2, what is the role of glycans on the spike protein?

Act as a shield against antibodies Signup and view all the answers

What accounts for the compact and easily accessible structure of alpha-glucans?

Kinked alpha 1-4 linkages Signup and view all the answers

Study Notes

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.

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Description

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.