Cell Biology Exam 1 Study Guide: Chemistry of the Cell, Macromolecules, and Cell Structure

Chapter 2: The Chemistry of the Cell

Cell Theory

The cell theory is a foundational concept in biology, describing the properties and significance of cells in living organisms.

• All organisms consist of one or more cells: Every living thing is composed of cells, whether unicellular or multicellular.

• The cell is the basic unit of structure for all organisms: Cells are the smallest units that carry out all life processes.

• All cells arise ONLY from pre-existing cells: New cells are produced by the division of existing cells.

The Importance of Carbon

Carbon is a central element in biological molecules due to its unique chemical properties.

• Atomic Number: Carbon has an atomic number of 6, meaning it has 6 protons.

• Bonding: Carbon typically forms four covalent bonds, allowing for complex molecules.

• Covalent Bonds: These are strong chemical bonds where atoms share electron pairs. Types include single, double, and triple bonds.

• Other Atoms in Biological Compounds: Commonly bonds with hydrogen, oxygen, nitrogen, phosphorus, and sulfur.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen. Found in cell membranes and energy storage molecules.

• Chemical Characteristics: Carbon's ability to form stable chains and rings is essential for the diversity of organic molecules.

Common Side Groups

Functional groups are specific groups of atoms within molecules that confer particular chemical properties.

Group	Structure	Properties
Carboxyl	-COOH	Negatively charged, acidic
Amino	-NH2	Positively charged, basic
Hydroxyl	-OH	Polar, forms hydrogen bonds
Sulfhydryl	-SH	Forms disulfide bonds
Phosphate	-PO4	Negatively charged, involved in energy transfer

Polarity

Polarity refers to the distribution of electrical charge over the atoms in a molecule.

• Polar molecules: Have regions of partial positive and negative charge, allowing them to interact with water.

• Nonpolar molecules: Lack charged regions and do not mix well with water.

Properties of Water

Water is essential for life due to its unique chemical and physical properties.

• Cohesion and Adhesion: Water molecules stick to each other and to other surfaces.

• High Specific Heat: Water can absorb a lot of heat before changing temperature.

• Solvent Properties: Water dissolves many substances, facilitating chemical reactions.

• Density of Ice: Ice is less dense than liquid water, allowing it to float.

• Biological Relevance: These properties support cellular processes and temperature regulation.

Membranes

Cell membranes are critical for compartmentalization and regulation of substances.

• Basic Structure: Composed of a phospholipid bilayer with embedded proteins.

• Hydrophobic/Hydrophilic Regions: Phospholipid tails are hydrophobic; heads are hydrophilic.

• Amphipathic: Molecules with both hydrophobic and hydrophilic regions.

• Facilitated Diffusion: Movement of substances across membranes via proteins (e.g., aquaporins for water).

Organic Compounds in Cells

Cells contain four major classes of organic compounds: carbohydrates, lipids, proteins, and nucleic acids.

• Polymerization: Monomers join to form polymers via dehydration synthesis (condensation reaction).

• Breaking Bonds: Polymers are broken down by hydrolysis reactions.

Chapter 3: The Macromolecules of the Cell

Proteins

Proteins are complex macromolecules that perform a wide variety of functions in cells.

• Functions: Enzymes, structural support, transport, signaling, and more.

• Basic Structure: Composed of amino acids linked by peptide bonds.

• Side Groups (R Groups): Determine the properties and classification of amino acids.

• Assembly: Proteins are assembled by ribosomes through translation, forming peptide bonds via condensation reactions.

Categories of Amino Acids

• Nonpolar (hydrophobic)

• Polar (hydrophilic)

• Charged (acidic or basic)

Traits of All Proteins

• Stable shapes/conformations

• At least one molecular target

• At least one cellular function

Levels of Protein Organization

• Primary: Sequence of amino acids

• Secondary: Repetitive regions (alpha helix, beta-pleated sheet, random coil)

• Tertiary: Overall 3D structure; stabilized by interactions between side chains

• Quaternary: Multiple polypeptides assemble to form a functional protein

Protein Folding and Chaperones

• Chaperones assist in proper folding and prevent misfolding.

• Misfolded proteins can be nonfunctional or harmful.

Classes of Chemical Bonds Stabilizing Proteins

Bond Type	Description
Hydrogen Bonds	Weak bonds between polar groups
Van der Waals Forces	Weak, non-specific interactions
Hydrophobic Interactions	Nonpolar side chains cluster away from water
Ionic Bonds	Attraction between charged side chains
Disulfide Bonds	Covalent bonds between cysteine residues

Covalent Modifications

• Disulfide bonds: Permanent stabilization, often in extracellular proteins.

• Lipid addition: Anchors proteins to membranes.

• Phosphorylation: Addition of phosphate groups, regulates activity.

• Sugar addition (glycosylation): Important for cell recognition.

• Methylation/Acetylation: Regulates protein function and gene expression.

Non-covalent Modifications

• Allosteric regulation, typically short-term and reversible.

Interactions in Protein Structure

• Interactions between amino acids help form the 3D structure.

• Alpha helices and beta-pleated sheets are common secondary structures.

• Motif vs. Domain: Motifs are short, recurring structural elements; domains are larger, functionally distinct regions.

• Fibrous vs. Globular vs. Transmembrane Proteins: Fibrous proteins provide structural support; globular proteins are functional and soluble; transmembrane proteins span cell membranes.

Nucleic Acids

Nucleic acids store and transmit genetic information.

• DNA vs. RNA: DNA is double-stranded, contains deoxyribose; RNA is single-stranded, contains ribose.

• Nucleotides: Monomers of nucleic acids; consist of a sugar, phosphate, and nitrogenous base.

• Purines: Adenine (A), Guanine (G); Pyrimidines: Cytosine (C), Thymine (T), Uracil (U in RNA).

• Phosphodiester Bond: Links nucleotides together in a chain.

• Hydrogen Bonds: Form between complementary bases (A-T, G-C) in DNA.

• Base Pairing: Ensures accurate replication and transcription. $A$ pairs with $T$ via 2 hydrogen bonds; $G$ pairs with $C$ via 3 hydrogen bonds.

• Antiparallel and Semiconservative: DNA strands run in opposite directions; replication conserves one original strand.

Carbohydrates

Carbohydrates are energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen).

• Assembly: Monomers joined by glycosidic bonds via condensation reactions.

• Glucose Formula: $C_6H_{12}O_6$

• Glycogen: Storage form of glucose in animals.

Lipids

Lipids are hydrophobic molecules important for energy storage and membrane structure.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Saturated vs. Unsaturated: Saturated have no double bonds; unsaturated have one or more double bonds.

• Trans Fats: Unsaturated fats with trans double bonds; associated with health risks.

• Triglycerides: Three fatty acids linked to glycerol.

• Phospholipids: Major component of cell membranes; amphipathic.

• Sphingolipids: Important in membrane structure and signaling.

• Steroids: Lipids with a four-ring structure; include cholesterol and hormones.

Chapter 4: Cells and Organelles

Theory of the Origin of Cells

Cells are thought to have originated from pre-existing cells through evolutionary processes.

• Endosymbiotic Theory: Eukaryotic cells evolved from symbiotic relationships between primitive cells.

Cell Structure and Function

• Prokaryotes vs. Eukaryotes vs. Archaea: Prokaryotes lack a nucleus; eukaryotes have a nucleus and organelles; archaea are distinct from both.

• Surface to Volume Ratio: Influences cell size and efficiency of transport.

• Cellular Structures: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, etc.

• Vesicles: Membrane-bound compartments for transport.

• Endocytosis/Exocytosis: Processes for importing/exporting materials.

DNA Organization

• Deoxyribonucleotide: Composed of deoxyribose sugar, phosphate, and base.

• Major Differences between RNA and DNA: DNA has deoxyribose and thymine; RNA has ribose and uracil; DNA is double-stranded, RNA is single-stranded.

• DNA Structure: Double helix with minor and major grooves; nucleosomes formed by DNA wrapping around histones.

• Chromatin: DNA-protein complex; can be euchromatin (active) or heterochromatin (inactive).

• Chromosomes: Highly condensed chromatin, visible during mitosis.

Levels of DNA Organization

• Double-stranded helix

• Nucleosome formation

• 30-nm fiber formation

• Protein-RNA scaffold

• Chromosome formation during mitosis

Heterochromatin vs. Euchromatin

• Heterochromatin: Densely packed, transcriptionally inactive.

• Euchromatin: Loosely packed, transcriptionally active.

Viruses, Viroids, and Prions

• Viruses: Infectious agents composed of nucleic acid and protein coat.

• Viroids: Infectious RNA molecules without a protein coat.

• Prions: Infectious proteins causing neurodegenerative diseases.

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard cell biology curriculum.