Chapter 3 – The Molecules of Cells

Organic Molecules

Organic molecules are fundamental to life, forming the basis of cellular structure and function.

• Definition: Organic molecules are compounds primarily composed of carbon atoms bonded to hydrogen, oxygen, nitrogen, and other elements.

• Key Features: Carbon's ability to form four covalent bonds allows for diverse structures such as chains, rings, and branching.

• Isomers: Molecules with the same chemical formula but different structural arrangements.

• Example: Glucose and fructose are structural isomers.

Functional Groups

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

• Hydroxyl (-OH): Found in alcohols; increases solubility in water.

• Carbonyl (C=O): Found in aldehydes and ketones; affects reactivity.

• Carboxyl (-COOH): Found in acids; acts as a proton donor.

• Amino (-NH2): Found in amines; acts as a base.

• Phosphate (-PO4): Found in nucleic acids; involved in energy transfer.

• Sulfhydryl (-SH): Found in thiols; forms disulfide bonds in proteins.

• Methyl (-CH3): Nonpolar; affects gene expression.

Functional groups add diversity and polarity, influencing molecular interactions and biological activity.

Building and Breaking Biological Molecules

Cells synthesize and degrade macromolecules through specific chemical reactions.

• Dehydration Reaction: Joins monomers by removing water to form polymers.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Monomer: Small, repeating unit of a polymer (e.g., amino acid).

• Polymer: Large molecule made of repeating monomers (e.g., protein).

Carbohydrates

Carbohydrates are energy sources and structural components in cells.

• Monosaccharide: Simple sugar (e.g., glucose, fructose).

• Disaccharide: Two monosaccharides joined (e.g., sucrose, lactose).

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

• Example: Cellulose provides structural support in plant cell walls.

Lipids

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

• Fat: Triglycerides; energy storage.

• Phospholipid: Major component of cell membranes; amphipathic.

• Steroid: Four fused rings; includes cholesterol and hormones.

• Anabolic Steroid: Synthetic variants of testosterone; used to promote muscle growth.

Trans fats are produced by hydrogenating unsaturated fats, leading to health risks such as heart disease.

• Saturated fats: No double bonds; solid at room temperature; less healthy.

• Unsaturated fats: One or more double bonds; liquid at room temperature; healthier.

• Trans fats: Unsaturated fats with trans double bonds; increase risk of cardiovascular disease.

Proteins

Proteins are polymers of amino acids, essential for structure, function, and regulation in cells.

• Composition: Made of amino acids linked by peptide bonds.

• Shape and Function: A protein's specific shape determines its function (e.g., enzymes, structural proteins).

• Structure Levels:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets formed by hydrogen bonding.

  • Tertiary: Three-dimensional folding due to interactions among side chains.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure due to heat, pH, or chemicals; most commonly caused by heat.

Nucleic Acids

Nucleic acids store and transmit genetic information.

• DNA: Double-stranded; stores genetic information.

• RNA: Single-stranded; involved in protein synthesis.

• Structure: Both are polymers of nucleotides (sugar, phosphate, nitrogenous base).

• Functions: DNA directs cell activities; RNA translates genetic code into proteins.

Major Atoms and Monomer Structures

Each class of biomolecule contains characteristic atoms and monomer structures.

Chapter 4 – A Tour of the Cell

Cell Structure and Components

Cells are the basic units of life, containing specialized structures for various functions.

• Plasma/Cell Membrane: Surrounds the cell; regulates entry and exit of substances.

• Cytoplasm: Gel-like substance inside the cell; contains organelles.

• Organelles: Specialized structures performing distinct functions (e.g., nucleus, mitochondria).

Microscopy

Microscopes are essential tools for studying cells.

• Light Microscope: Uses visible light; suitable for living cells.

• Electron Microscope: Uses electron beams; higher resolution.

  • Scanning Electron Microscope (SEM): Surface details.

  • Transmission Electron Microscope (TEM): Internal structures.

• Magnification: Enlargement of an image.

• Resolution: Ability to distinguish two points as separate.

Cell Theory

Cell theory is a foundational concept in biology.

• All living things are composed of cells.

• Cells are the basic unit of structure and function.

• All cells arise from pre-existing cells.

Cell Size and Surface Area

Cell size is limited by the ratio of surface area to volume, affecting transport and function.

• Smaller cells have a higher surface area-to-volume ratio, facilitating efficient exchange.

• Prokaryotic cells are generally smaller than eukaryotic cells.

Plasma Membrane Structure

The plasma membrane is a phospholipid bilayer with embedded proteins.

• Phospholipids form a double layer, with hydrophilic heads and hydrophobic tails.

• Proteins serve as channels, receptors, and enzymes.

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on structural features.

• Prokaryotic Cells: Lack a nucleus; DNA in nucleoid; simple structure; cell wall, plasma membrane, ribosomes.

• Eukaryotic Cells: Have a nucleus; complex organelles; larger size.

Nucleus and Nuclear Components

The nucleus is the control center of eukaryotic cells.

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Nucleolus: Site of ribosome synthesis.

Ribosomes and Endomembrane System

Ribosomes and the endomembrane system are involved in protein and lipid synthesis.

• Ribosomes: Sites of protein synthesis; found free in cytoplasm or attached to ER.

• Rough ER: Studded with ribosomes; synthesizes proteins.

• Smooth ER: Lacks ribosomes; synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes; break down waste.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Vacuoles: Storage and transport; large in plant cells.

Abnormal lysosomes can lead to accumulation of waste and cellular dysfunction.

Endomembrane System Function

The endomembrane system coordinates the production, modification, and transport of cell products.

• Proteins and lipids are synthesized in the ER, processed in the Golgi, and transported via vesicles.

• Products are exported or used within the cell.

Chloroplasts and Mitochondria

Chloroplasts and mitochondria are energy-converting organelles.

• Chloroplasts: Site of photosynthesis in plants; contain thylakoids and stroma.

• Mitochondria: Site of cellular respiration; produce ATP.

• Evolutionary Origin: Endosymbiotic hypothesis suggests these organelles originated from engulfed prokaryotes.

Cell's Internal Skeleton (Cytoskeleton)

The cytoskeleton provides structural support and enables movement.

• Microfilaments: Actin filaments; support cell shape and movement.

• Microtubules: Tubulin; maintain cell shape, guide organelle movement.

• Intermediate Filaments: Provide mechanical strength.

Cell Motility Structures

Cilia, flagella, basal bodies, and centrioles are involved in cell movement.

• Cilia: Short, numerous; move fluid over cell surface.

• Flagella: Long, few; propel cells.

• Basal Bodies: Anchor cilia and flagella.

• Centrioles: Organize microtubules during cell division.

Cell Surfaces: Plant vs. Animal

Plant and animal cells have distinct surface structures.

• Plant Cells: Cell wall, plasmodesmata.

• Animal Cells: Extracellular matrix, various junctions.

Cell Junctions

Cell junctions facilitate communication and adhesion between cells.

• Plasmodesmata: Channels between plant cells.

• Tight Junction: Prevents leakage between cells.

• Anchoring Junction: Provides mechanical stability.

• Gap Junction: Allows communication between animal cells.

Extracellular Matrix

The extracellular matrix supports and regulates animal cells.

• Composed of proteins (e.g., collagen) and polysaccharides.

• Provides structural support and mediates cell signaling.

Functional Categories of Cell Organelles

Cell organelles can be grouped by their primary functions.

Dynamic Nature of Cells

Cells are dynamic, with organelles constantly interacting and adapting to cellular needs.

• Organelle activities are coordinated for growth, division, and response to environmental changes.

• Membranes and cytoskeleton allow rapid reorganization.