Study Notes: The Molecules of Cells & The Working Cell

Study Guide - Smart Notes

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Chapter 3: The Molecules of Cells

Overview of Organic Molecules

Organic molecules are the foundation of cellular structure and function. Understanding their classification and properties is essential for studying biological systems.

Four Main Classes: Carbohydrates, lipids, proteins, and nucleic acids are the major classes of organic molecules important to life.
Monomers and Polymers: Monomers are small, repeating units that join to form polymers through dehydration synthesis.
Dehydration Synthesis vs. Hydrolysis: Dehydration synthesis builds polymers by removing water; hydrolysis breaks them down by adding water.
Examples: Glucose (monomer) forms starch (polymer); amino acids (monomers) form proteins (polymers).

Properties and Functions of Lipids

Lipids are diverse hydrophobic molecules that play key roles in energy storage, membrane structure, and signaling.

Types: Fats, phospholipids, steroids, and waxes.
Structure: Most lipids are composed of fatty acids and glycerol.
Function: Energy storage, insulation, and forming biological membranes.
Example: Phospholipids form the bilayer of cell membranes.

Proteins: Structure and Function

Proteins are polymers of amino acids that perform a vast array of cellular functions.

Levels of Structure: Primary, secondary, tertiary, and quaternary structures determine protein shape and function.
Enzymes: Proteins that catalyze biochemical reactions by lowering activation energy.
Shape and Function: The specific shape of a protein is crucial for its function; denaturation disrupts this shape.
Example: Hemoglobin transports oxygen in blood.

Nucleic Acids: DNA and RNA

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides.

Structure: DNA is double-stranded; RNA is single-stranded.
Function: DNA stores genetic information; RNA is involved in protein synthesis.
Base Pairing: Adenine pairs with thymine (DNA) or uracil (RNA); cytosine pairs with guanine.
Example: The sequence of nucleotides in DNA determines the sequence of amino acids in proteins.

Key Terms Table

The following table summarizes important terms related to the molecules of cells:

Term	Definition
Amino acid	Building block of proteins
Carbohydrate	Organic molecule used for energy and structure
Phospholipid	Main component of cell membranes
Enzyme	Protein that speeds up chemical reactions
Nucleotide	Building block of nucleic acids
Polymer	Large molecule made of repeating monomers
Dehydration synthesis	Reaction that joins monomers by removing water
Hydrolysis	Reaction that breaks polymers by adding water
Fatty acid	Component of many lipids
Triglyceride	Lipid used for energy storage

Chapter 5: The Working Cell

Cell Membrane Structure and Function

The cell membrane is a dynamic structure that controls the movement of substances in and out of the cell.

Fluid Mosaic Model: Describes the membrane as a mosaic of proteins floating in a fluid lipid bilayer.
Phospholipids: Form the basic structure of the membrane, with hydrophilic heads and hydrophobic tails.
Selective Permeability: The membrane allows some substances to pass while blocking others.
Example: Oxygen and carbon dioxide diffuse freely; ions require transport proteins.

Transport Across Membranes

Cells use various mechanisms to move substances across membranes, maintaining homeostasis.

Passive Transport: Movement of substances down their concentration gradient without energy input (e.g., diffusion, osmosis).
Active Transport: Movement against the concentration gradient, requiring energy (ATP).
Facilitated Diffusion: Passive transport aided by membrane proteins.
Example: Sodium-potassium pump uses ATP to move ions across the membrane.

Enzymes and Cellular Reactions

Enzymes are biological catalysts that regulate the speed of chemical reactions in cells.

Activation Energy: The energy required to start a reaction; enzymes lower this barrier.
Active Site: The region of the enzyme where substrates bind and reactions occur.
Enzyme-Substrate Complex: Temporary association between enzyme and substrate during catalysis.
Induced Fit: The enzyme changes shape to better fit the substrate.
Example: Amylase catalyzes the breakdown of starch into sugars.

Enzyme Regulation

Cells regulate enzyme activity to control metabolic pathways and respond to changing conditions.

Competitive Inhibition: Inhibitor competes with substrate for the active site.
Noncompetitive Inhibition: Inhibitor binds elsewhere, changing enzyme shape and reducing activity.
Feedback Inhibition: End product of a pathway inhibits an earlier step, preventing overproduction.
Example: ATP inhibits enzymes in glycolysis when energy is abundant.

Key Terms Table

Term	Definition
Active site	Region of enzyme where substrate binds
Enzyme	Protein catalyst for biochemical reactions
Competitive inhibitor	Molecule that blocks substrate from active site
Noncompetitive inhibitor	Molecule that alters enzyme shape, reducing activity
Feedback inhibition	Regulation by end product of a pathway
Fluid mosaic model	Describes cell membrane structure
Selective permeability	Ability of membrane to control substance passage
Substrate	Molecule acted upon by an enzyme

Equations and Formulas

General Reaction Catalyzed by Enzymes:

Rate of Diffusion: