Lecture 3 - Carbon and the Molecules of Life

Lecture 3 - Carbon and the Molecules of Life

Introduction

• Focus on the significance of carbon in biological molecules.

Carbon's Versatility

• Carbon is the basis of most biological molecules.

• It demonstrates versatility in covalent bonding, allowing it to connect effectively with other abundant elements (e.g., hydrogen, oxygen, nitrogen).

• Serves as a backbone for various large and intricate biological molecules including:

  • Metabolic intermediates

  • Proteins

  • Nucleic acids

  • Carbohydrates

  • Fats

  • Sterols

• Forms structural isomers, cis-trans isomers, and enantiomers, each with distinct biological roles.

Simple Carbon Organic Compounds

• Types of carbon compounds based on bonding:

  • Methane:

  • Molecular Formula: CH₄

  • Structural Formula:

    • Ball-and-Stick Model

    • Space-Filling Model

  • Ethane:

  • Molecular Formula: C₂H₆

  • Ethene (ethylene):

  • Molecular Formula: C₂H₄

Isomers and Structural Variations

Cis-Trans Isomers

• Cis Isomer:

  • The two Xs (substituents) are located on the same side of the double bond.

• Trans Isomer:

  • The two Xs are situated on opposite sides of the double bond.

Enantiomers

• Defined as mirror image isomers of the same molecule.

• Example structures:

  • L isomer:

  • Configuration:

    • CH₃ H

    • NH₂

  • D isomer:

  • Configuration:

    • CH₃ H

    • NH₂

Importance of Enantiomers

• Dopamine:

  • L-dopa: Biologically active form.

  • D-dopa: Inactive form.

Chemical Groups and Their Properties

• Hydroxyl group (—OH):

  • Properties: Alcohol

  • Example: Ethanol

• Carbonyl group (C ═ O):

  • Types: Ketone, Aldehyde

  • Examples: Acetone (Ketone), Propanal (Aldehyde)

• Carboxyl group (—COOH):

  • Type: Carboxylic acid or organic acid

  • Example: Acetic acid

• Amino group (—NH₂):

  • Type: Amine

  • Example: Glycine

• Sulfhydryl group (—SH):

  • Type: Thiol

  • Example: Cysteine

• Phosphate group (—OPO₃²⁻):

  • Type: Organic phosphate

  • Example: Glycerol phosphate

• Methyl group (—CH₃):

  • Type: Methylated compound

  • Example: 5-Methylcytosine

Covalent Modifications of Common Structures

• Alterations in steroid structures lead to different biological functions:

  • Example molecules:

  • Estradiol

  • Testosterone

  • Structural variations have significant functional impacts.

Sugars and Their Types

• Monosaccharides:

  • Serve as an energy source and provide carbon units for amino acid and lipid production.

• Disaccharides and Polysaccharides:

  • Act as storage reservoirs of sugar units.

• Oligosaccharides:

  • Covalently bonded to lipids (e.g., blood group antigens) and proteins (e.g., antibody molecules).

• Polysaccharides:

  • Function structurally in plant and microbial cell walls and as a storage form of glucose.

Monosaccharides in Equilibrium

• Monosaccharides exist in equilibrium between linear and ring forms.

• Example representation of glucose's structure:

  • Rings of different conformations (e.g., alpha and beta forms).

Isomers of Glucose

• Alpha Glucose:

  • Structure featuring specific hydroxyl group positioning.

• Beta Glucose:

  • Different hydroxyl positioning leading to distinct properties.

• Both forms are prevalent in biological systems as energy sources.

Dehydration Reactions and Hydrolysis

Polymer Synthesis

• Dehydration Reaction:

  • Involves the removal of a water molecule to form new bonds.

• Diagrammatic representations of the process to synthesize longer polymers from monomers.

Polymer Breakdown

• Hydrolysis:

  • The addition of a water molecule that breaks a bond between monomers, facilitating polymer breakdown.

Sugars Joining through Condensation

Specific Reactions

• Dehydration reactions for synthesizing maltose and sucrose:

  • Maltose: Formation through a 1–4 glycosidic linkage between glucose molecules.

  • Sucrose: Formation through a 1–2 glycosidic linkage between glucose and fructose.

Polysaccharides for Storage & Structure

• Starch:

  • Composed of α glucose monomers linked by 1–4 linkages.

• Cellulose:

  • Composed of β glucose monomers linked by 1–4 linkages.

Lipids: Membranes and Signaling Molecules

• Function:

  • Serve as structural building blocks of membranes and function as signaling molecules.

• Composition:

  • Mainly formed from long chain hydrophobic fatty acids linked to a glycerol backbone:

  • Saturated fatty acids (no double bonds) pack tightly; solid state at room temperature.

  • Unsaturated fatty acids (double bonds present) pack less tightly; liquid state at room temperature.

• Phospholipids:

  • Form bilayers in cellular membranes.

• Sterols:

  • Stiffen membranes and serve as hormone signals.

Fatty Acid Attachment and Ester Formation

• Detail the chemical process of attaching fatty acids to glycerol to create an ester bond, which involves one of three dehydration reactions in fat synthesis.

Adipose Tissue Structure

• Representation of human adipose cell structure showing:

  • Fat droplets containing triglycerides, formed from three fatty acids attached to a glycerol backbone.

Phospholipid Structure and Function

• Biological membranes consist of phospholipids, which include:

  • Diacylglycerol: with a phosphorylated head group attached to the third carbon, featuring hydrophobic tails and a hydrophilic head.

  • Structural formula representations including hydrophobic and hydrophilic regions indicating their functional roles in membranes.

Cholesterol and Lipid Regulation

• Cholesterol:

  • Important molecule involved in cellular membrane fluidity and hormone signaling.

• Structural forms including unesterified cholesterol and cholesteryl ester indicating its role in lipid function.

Atherosclerosis

• Description of atherosclerotic plaque formation within blood vessels, including:

  • Endothelium

  • Lumen

  • Composition of thrombus and plaque.