Fundamental Concepts in General Biology: Cell Types, Chemical Bonds, Macromolecules, and Cytoskeleton

Eukaryotic vs Prokaryotic Cells

Cellular Organization

Cells are classified as either eukaryotic or prokaryotic based on their structural features and presence of membrane-bound organelles.

• Eukaryotic cells have membrane-enclosed organelles, including a nucleus.

• Prokaryotic cells are simpler, smaller, and lack a nucleus or other membrane-enclosed organelles.

• Most living organisms are composed of elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), with other elements present as trace elements.

Atomic Structure and Elements

Atomic Number and Mass

Atoms are the basic units of matter, defined by their atomic number and mass.

• Atomic number: Number of protons in the nucleus.

• Atomic mass: Sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

Chemical Bonds

Covalent Bonds

Covalent bonds involve the sharing of electron pairs between atoms, forming stable molecules.

• Covalent bond: Sharing of a pair of valence electrons by two atoms.

Ionic Bonds

Ionic bonds are formed by the transfer of electrons from one atom to another, resulting in charged ions.

• Cation: Positively charged ion (loses electron).

• Anion: Negatively charged ion (gains electron).

• Ionic bonds form between cations and anions, such as in sodium chloride (NaCl).

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

• Example: Hydrogen atom in water (H2O) bonding to oxygen or nitrogen in another molecule.

• Hydrogen bonds are important in stabilizing biological molecules like DNA and proteins.

Properties of Water and Functional Groups

Hydrophilic and Hydrophobic Substances

Substances interact with water differently based on their chemical properties.

• Hydrophilic: Affinity for water; dissolves or interacts well with water.

• Hydrophobic: Repels water; does not dissolve or interact well with water.

• Amphipathic: Contains both hydrophilic and hydrophobic regions (e.g., phospholipids).

Carbon and Functional Groups

Carbon is a versatile element, capable of forming four covalent bonds, allowing for a variety of molecular structures.

• Carbon can form tetravalence, creating complex molecules.

• Seven common functional groups in organic molecules:

  • Hydroxyl

  • Carbonyl

  • Carboxyl

  • Amino

  • Sulfhydryl

  • Phosphate

  • Methyl

Macromolecules: Formation and Types

Polymerization and Dehydration Reactions

Macromolecules are formed by joining monomers through dehydration reactions and broken down by hydrolysis.

• Dehydration reaction: Two monomers bond together by losing a water molecule.

• Hydrolysis: Polymers are disassembled by adding water, breaking the bond.

Polysaccharides

Polysaccharides serve as storage and structural molecules in cells.

• Starch and glycogen: Storage polysaccharides.

• Cellulose and chitin: Structural polysaccharides.

Lipids: Saturated and Unsaturated Fats

Lipids are hydrophobic molecules, including fats, which can be saturated or unsaturated.

• Saturated fats: Maximum number of hydrogen atoms, no double bonds, solid at room temperature, common in animals.

• Unsaturated fats: Have one or more double bonds, liquid at room temperature, common in plants.

Proteins: Structure and Denaturation

Proteins are polymers of amino acids, which have specific structural features and can undergo denaturation.

• All amino acids have an amino group, carboxyl group, and a unique side chain (R group).

• Amino acids are linked by peptide bonds.

• First amino acid: N-terminus (amino end); last amino acid: C-terminus (carboxyl end).

• Denaturation: Loss of protein structure due to changes in pH, salt concentration, temperature, or other factors.

Nucleic Acids

DNA and RNA

Nucleic acids store and transmit genetic information.

• DNA provides instructions for protein synthesis via messenger RNA (mRNA).

• Central Dogma: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

• Nucleotides consist of a nitrogenous base, a pentose sugar, and a phosphate group.

Cytoskeleton

Structure and Function

The cytoskeleton is a network of fibers that provides structural support, motility, and regulation within the cell.

• Three main types of cytoskeletal fibers:

  • Microtubules

  • Microfilaments

  • Intermediate filaments

• Roles include supporting cell shape, enabling movement, and regulating cellular activities.

Comparison Table: Eukaryotic vs Prokaryotic Cells

Feature	Eukaryotic Cells	Prokaryotic Cells
Nucleus	Present	Absent
Membrane-bound organelles	Present	Absent
Size	Larger	Smaller
Examples	Animals, plants, fungi, protists	Bacteria, archaea