Macromolecules, Cell Structure, and Function: Study Guide (Chapters 5 & 6)

Macromolecules: Structure and Function

5.1 Macromolecules are Polymers, Built from Monomers

Macromolecules are large, complex molecules essential for life, constructed from smaller subunits called monomers. The process of assembling and disassembling these molecules is fundamental to cellular function.

• Polymers and Monomers: Polymers are long chains made by linking monomers through covalent bonds. Examples include polysaccharides (carbohydrates), proteins, and nucleic acids.

• Dehydration Synthesis: This is a chemical reaction where two monomers are joined by removing a water molecule. It is also called a condensation reaction.

• Hydrolysis: The reverse of dehydration synthesis, hydrolysis breaks polymers into monomers by adding water.

• Enzymes: Biological catalysts that speed up both dehydration and hydrolysis reactions, enabling efficient metabolism.

• Example: The formation of a disaccharide from two monosaccharides via dehydration synthesis.

5.2 Carbohydrates Serve as Fuel and Building Material

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They function as energy sources and structural components in cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose) classified by the number of carbon atoms and the position of the carbonyl group. Trioses: have three carbon atoms: glyceraldehyde, pentoses: have five carbon atoms: ribose and ribulose, hexoses: have six: glucose and fructose

• Polysaccharides: Polymers of monosaccharides linked by glycosidic bonds. Examples include starch, glycogen, and cellulose. These linkages are covalent bonds created by dehydration reactions where water molecules is removed to join 2 sugar units

• Structure and Function: The structure of polysaccharides (e.g., branching, type of linkage) determines their function (energy storage vs. structural support).

• Example: Starch: 2 forms amylose (unbranched) and amylopectin (branched). Starch is the energy storage in plants. vs. cellulose (structural support in plant cell walls).

5.3 Lipids are a Diverse Group of Hydrophobic Molecules

Lipids are nonpolar molecules that include fats, phospholipids, and steroids. They are important for energy storage, membrane structure, and signaling.

• Types of Lipids: Fats (triglycerides), phospholipids, and steroids (e.g., cholesterol).

• Fatty Acids: Can be saturated (no double bonds) or unsaturated (one or more double bonds). Saturated fats are typically solid at room temperature; unsaturated fats are liquid.

• Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails, crucial for forming biological membranes.

• Steroids: Lipids with a characteristic four-ring structure. Cholesterol is a key steroid in animal cell membranes.

• Example: The role of phospholipids in forming the lipid bilayer of cell membranes.

5.4 Proteins Include a Diversity of Structures, Resulting in a Wide Range of Functions

Proteins are polymers of amino acids, each with a unique sequence and structure that determines its function.

• Amino Acids: The building blocks of proteins, each with a central carbon, amino group, carboxyl group, and variable R group.

• Peptide Bonds: Covalent bonds linking amino acids in a polypeptide chain.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

  • Tertiary: Overall 3D shape due to interactions among R groups.

  • Quaternary: Association of multiple polypeptide chains.

• Function: Enzymes, structural proteins, transport, signaling, etc.

• Example: Hemoglobin's quaternary structure enables oxygen transport in blood.

5.5 Nucleic Acids Store, Transmit, and Help Express Hereditary Information

Nucleic acids (DNA and RNA) are polymers that store and transmit genetic information.

• Nucleotides: Monomers composed of a sugar, phosphate group, and nitrogenous base.

• Types of Bases: Purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).

• DNA vs. RNA: DNA contains deoxyribose sugar and uses thymine; RNA contains ribose and uses uracil.

• Base Pairing: In DNA, A pairs with T, and G pairs with C via hydrogen bonds.

• Function: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

• Example: The sequence of nucleotides in DNA determines the sequence of amino acids in proteins.

5.6 Genomics and Proteomics Have Transformed Biological Inquiry and Applications

Genomics and proteomics are fields that analyze the complete set of genes and proteins in organisms, revolutionizing our understanding of biology and disease.

• Genomics: The study of whole genomes, including gene sequencing, mapping, and analysis.

• Proteomics: The study of the entire set of proteins produced by an organism.

• Applications: Disease research, personalized medicine, evolutionary studies.

• Example: Using genomics to identify genetic mutations associated with cancer.

Cell Structure and Function

6.2 Eukaryotic Cells Have Internal Membranes That Compartmentalize Their Functions

Cells are classified as prokaryotic or eukaryotic based on their internal structure. Eukaryotic cells contain membrane-bound organelles, including a nucleus.

• Prokaryotic Cells: Lack a nucleus and most organelles; DNA is in the nucleoid region.

• Eukaryotic Cells: Have a nucleus and various organelles (e.g., mitochondria, endoplasmic reticulum).

• Similarities and Differences: Both types have plasma membranes, cytoplasm, and ribosomes, but differ in complexity and compartmentalization.

• Example: Plant and animal cells are eukaryotic, while bacteria are prokaryotic.

6.3 The Eukaryotic Cell's Genetic Instructions Are Housed in the Nucleus and Carried Out by the Ribosomes

The nucleus stores genetic material, while ribosomes are the sites of protein synthesis.

• Nucleus: Contains most of the cell's DNA; surrounded by a double membrane (nuclear envelope).

• Ribosomes: Complexes of RNA and protein that translate mRNA into polypeptides.

• Example: The nucleolus within the nucleus is the site of ribosomal RNA synthesis.

6.4 The Endomembrane System Regulates Protein Traffic and Performs Metabolic Functions

The endomembrane system includes organelles involved in synthesis, modification, and transport of cellular products.

• Components: Endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, and plasma membrane.

• Rough ER: Studded with ribosomes; synthesizes proteins for secretion or membrane insertion.

• Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification.

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

• Lysosomes: Contain digestive enzymes for breaking down macromolecules.

• Vesicles: Transport materials between organelles.

• Example: Secretory proteins are synthesized in the rough ER, processed in the Golgi, and exported via vesicles.

6.5 Mitochondria and Chloroplasts Change Energy from One Form to Another

Mitochondria and chloroplasts are organelles that convert energy into forms usable by the cell.

• Mitochondria: Sites of cellular respiration, generating ATP from glucose and oxygen.

• Chloroplasts: Found in plants and algae; sites of photosynthesis, converting solar energy to chemical energy.

• Endosymbiont Theory: Suggests mitochondria and chloroplasts originated from engulfed prokaryotes.

• Example: Muscle cells have many mitochondria due to high energy demands.

6.6 The Cytoskeleton is a Network of Fibers That Organize Structures and Activities in the Cell

The cytoskeleton provides structural support, enables movement, and organizes cellular components.

• Components: Microfilaments (actin), intermediate filaments, and microtubules.

• Functions: Maintains cell shape, enables cell movement (e.g., muscle contraction, amoeboid movement), and facilitates intracellular transport.

• Example: Microtubules form the mitotic spindle during cell division.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists