Unit 1: Introduction and Biological Molecules – Study Guide

Unit 1: Introduction and Biological Molecules

This unit covers foundational concepts in general biology, focusing on the characteristics of life, scientific reasoning, and the structure and function of key biological molecules. Mastery of these topics is essential for understanding more advanced biological processes.

Chapter 1 – Introduction

This chapter introduces the organization of life, the scientific method, and the criteria that define living organisms.

• The Three Domains of Life: Life is classified into three domains: Bacteria, Archaea, and Eukarya. These domains are depicted on a phylogenetic tree, which shows evolutionary relationships.

• Distinguishing Features: Eukarya (the domain humans belong to) is characterized by cells with a nucleus and membrane-bound organelles, unlike Bacteria and Archaea.

• Defining Features of Living Organisms: Living things exhibit organization, metabolism, homeostasis, growth, reproduction, response to stimuli, and evolutionary adaptation.

• Scientific Laws, Theories, and Hypotheses:

  • Hypothesis: A testable, falsifiable statement or prediction.

  • Theory: A well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

  • Law: A statement describing consistent, universal relationships under certain conditions (e.g., Mendel's Laws).

• Elements of a Scientific Experiment: Key components include a testable hypothesis, controlled variables, independent and dependent variables, and reproducibility.

• Example: The classic experiment by Pasteur disproving spontaneous generation by using swan-necked flasks.

Chapter 2 – Water and Carbon Chemistry

This chapter explores the chemical basis of life, focusing on atomic structure, chemical bonds, and the unique properties of water and carbon.

• Atomic Number and Mass Number: The atomic number is the number of protons in an atom. The mass number is the sum of protons and neutrons. The average mass number (atomic mass) accounts for isotopes.

• Covalent vs. Ionic Bonds:

  • Covalent bonds involve the sharing of electron pairs between atoms.

  • Ionic bonds involve the transfer of electrons from one atom to another, resulting in oppositely charged ions.

• Polar vs. Nonpolar:

  • Polar molecules have unequal sharing of electrons, leading to partial charges (e.g., water).

  • Nonpolar molecules have equal sharing of electrons (e.g., O2).

• Types of Interactions Between Molecules:

  • Hydrogen bonds

  • Van der Waals interactions

  • Hydrophobic interactions

  • Ionic interactions

  • Covalent bonds

• Example: Water's high heat capacity and solvent properties are due to hydrogen bonding.

Chapter 3 – Proteins

This chapter examines the structure, function, and synthesis of proteins, which are essential macromolecules in all living organisms.

• Monomer of Proteins: Amino acids are the building blocks of proteins.

• Functional Groups in Amino Acids: Each amino acid contains an amino group (–NH2), a carboxyl group (–COOH), a hydrogen atom, and a variable R group (side chain).

• Individuality of Amino Acids: The R group determines the chemical properties and identity of each amino acid.

• Determining Amino Acid Chemistry (4 Steps):

  1. Identify the R group.

  2. Determine if the R group is polar, nonpolar, acidic, or basic.

  3. Assess the potential for hydrogen bonding or ionic interactions.

  4. Predict the behavior in aqueous environments.

• Bonds Between Amino Acids: Peptide bonds form between the carboxyl group of one amino acid and the amino group of another via a condensation reaction.

• Condensation vs. Hydrolysis Reactions:

  • Condensation (Dehydration) Reaction: Joins two molecules with the loss of water.

  • Hydrolysis Reaction: Breaks a bond by adding water.

• Forces in Protein Structure: Hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions contribute to primary, secondary, tertiary, and quaternary structure.

• Example: Hemoglobin's quaternary structure allows it to transport oxygen efficiently.

Chapter 4 – Nucleic Acids

This chapter discusses the structure and function of nucleic acids, the molecules responsible for genetic information storage and transfer.

• Types of Nucleic Acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• Monomer of Nucleic Acids: Nucleotides, each consisting of a phosphate group, a five-carbon sugar (deoxyribose or ribose), and a nitrogenous base.

• Functional Groups in Nucleotides: Phosphate group, hydroxyl groups, and amine groups in the nitrogenous bases.

• Bonds Between Nucleotides: Phosphodiester bonds link the 3' carbon of one sugar to the 5' phosphate of the next.

• Information Critical for Watson and Crick:

  • Chargaff's rules (A=T, G=C base pairing)

  • X-ray diffraction data (Rosalind Franklin)

  • Antiparallel strand orientation

• Differences Between RNA and DNA:

  • RNA contains ribose; DNA contains deoxyribose.

  • RNA uses uracil; DNA uses thymine.

  • RNA is usually single-stranded; DNA is double-stranded.

• First “Living” Molecule: RNA is hypothesized to be the first self-replicating molecule due to its ability to store information and catalyze reactions (the "RNA world" hypothesis).

• Example: mRNA carries genetic information from DNA to ribosomes for protein synthesis.

Chapter 5 – Carbohydrates

This chapter covers the structure, classification, and biological roles of carbohydrates, which are vital for energy storage and structural support.

• Naming Strategy for Carbohydrates: Carbohydrates are named based on the number of carbon atoms and the presence of aldehyde (aldose) or ketone (ketose) groups. Examples: glucose (hexose, aldose), fructose (hexose, ketose).

• Monosaccharides, Disaccharides, Polysaccharides:

  • Monosaccharide: Single sugar unit (e.g., glucose).

  • Disaccharide: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).

  • Polysaccharide: Long chains of monosaccharide units (e.g., starch, cellulose).

• Energy Storage: Carbohydrates are efficient energy sources due to their high proportion of C-H bonds, which release energy when oxidized.

• Common Polysaccharides and Their Functions:

  • Starch: Energy storage in plants.

  • Glycogen: Energy storage in animals.

  • Cellulose: Structural component in plant cell walls.

  • Chitin: Structural component in fungal cell walls and arthropod exoskeletons.

• Example: Glycogen is rapidly mobilized in muscle cells during exercise.

Table: Comparison of Biological Macromolecules

Macromolecule	Monomer	Bond Type	Main Functions
Proteins	Amino acids	Peptide bonds	Enzymes, structure, transport, signaling
Nucleic Acids	Nucleotides	Phosphodiester bonds	Genetic information storage and transfer
Carbohydrates	Monosaccharides	Glycosidic bonds	Energy storage, structure

Additional info: This guide expands on the brief points in the original notes to provide a self-contained overview suitable for exam preparation in a General Biology course.