AP Biology Unit 1 Review: Chemistry of Life
AP Biology Unit 1 Review: Chemistry of Life
Unit 1 of AP Biology focuses on the Chemistry of Life, laying the foundation for understanding the essential molecules and interactions that form the basis of biological processes. This review guide provides an organized overview to help you master key concepts and prepare for your AP Biology exam.
Structure of Water and Hydrogen Bonding
Water is a unique molecule essential to life on Earth, largely due to its polarity and ability to form hydrogen bonds. The unequal distribution of charge makes water polar, allowing it to create hydrogen bonds with other water molecules. This property gives rise to essential behaviors such as:
Cohesion: Water molecules stick to each other, leading to surface tension that allows small insects to walk on water.
Adhesion: Water molecules are attracted to other substances, enabling processes like capillary action in plants.
Surface Tension: The cohesive forces between water molecules create a “film” on the surface, allowing it to resist external forces.
These properties are vital for many biological processes, from nutrient transport in plants to temperature regulation in organisms.
Elements of Life
The most common elements in biological molecules include carbon, hydrogen, nitrogen, oxygen, and phosphorus. These elements are the building blocks of life and play a role in forming a wide variety of molecules that carry out essential cellular functions.
Introduction to Biological Macromolecules
All living organisms are made up of four key macromolecules: proteins, lipids, carbohydrates, and nucleic acids. These macromolecules are formed by smaller units called monomers, which are bonded together through chemical processes like dehydration synthesis (building larger molecules by removing water) and broken down through hydrolysis (using water to break bonds).
Proteins: Made of amino acids, they perform numerous functions including catalyzing reactions and providing structural support.
Lipids: Composed of fatty acids and glycerol, they store energy and make up biological membranes.
Carbohydrates: Formed from sugar monomers, they provide energy and structural support.
Nucleic Acids: DNA and RNA store and transmit genetic information.
Properties of Biological Molecules
The structure of a biological molecule directly impacts its function. For example:
Nucleotides make up nucleic acids, with DNA carrying genetic information through its specific sequence of bases.
Amino Acids determine protein shape and function, with each amino acid having distinct chemical properties such as being polar, nonpolar, acidic, or basic.
Carbohydrates range in complexity, from simple sugars (monosaccharides) to complex polysaccharides. The complexity impacts how easily they are broken down to release energy.
Lipids can be saturated or unsaturated, affecting their physical state and role in cells. Saturated fats have no double bonds, making them solid at room temperature, whereas unsaturated fats contain double bonds, creating kinks that keep them liquid.
Structure and Function of Biological Molecules
The function of biological molecules is intricately tied to their structure:
Proteins: Amino acids form long chains, folded into specific shapes that determine their function in the body. These proteins can act as enzymes, hormones, or provide structural support.
Nucleic Acids: DNA forms a double helix with antiparallel strands and is responsible for storing genetic information. RNA plays a role in protein synthesis and has structural differences from DNA, such as being single-stranded and having uracil instead of thymine.
Lipids: Their hydrophobic nature allows them to form cell membranes, while the saturation level of fatty acids affects the fluidity of these membranes.
Carbohydrates: Broken down to release energy, the complexity of their structure (e.g., glucose vs. starch) affects how organisms use them.
Nucleic Acids
DNA and RNA are the two types of nucleic acids responsible for storing and transmitting genetic information. Key differences between them include:
DNA is double-stranded and contains the bases adenine (A), thymine (T), cytosine (C), and guanine (G).
RNA is single-stranded and uses uracil (U) instead of thymine.
DNA has a deoxyribose sugar, whereas RNA has a ribose sugar.
These structural differences give DNA its stability for long-term genetic storage, while RNA is more versatile for tasks like protein synthesis.
Key Vocabulary for Unit 1
Macromolecule: Large molecules made up of smaller subunits
Lipid: Nonpolar molecules used for long-term energy storage
Carbohydrate: Organic compounds that provide energy
Amino Acid: Building block of proteins
Nucleotide: Building block of nucleic acids
Hydrogen Bond: Weak bond between molecules important in the structure of DNA and properties of water
Cohesion & Adhesion: Properties of water that allow it to stick to itself and other substances
Hydrolysis & Dehydration Synthesis: Processes that break and form bonds between monomers
Study Resources
For more in-depth study, you can check out the live stream replays on the topics covered in Unit 1:
Water: The Molecule of Life
Water is a polar molecule with intramolecular covalent bonds between its partially positive hydrogen atoms and partially negative oxygen atom, creating an unequal distribution of electrons and a dipole moment. When water molecules bond with each other, they exhibit intermolecular hydrogen bonding. Although hydrogen bonds are weaker than covalent bonds, they are strong enough to play significant roles in many biological processes.
These interactions result in water’s unique properties, such as cohesion, adhesion, surface tension, high specific heat, and evaporative cooling. These properties make water essential to life on Earth by regulating temperature, supporting nutrient transport, and maintaining the stability of biological systems. 💧
Hydrophilic substances are attracted to water and have polar bonds that interact with water molecules.
Hydrophobic substances avoid water and lack polar bonds, making them unable to dissolve in water.
Macromolecules: Building Blocks of Life
Unit 1 also focuses on macromolecules—large, complex molecules essential for all biological functions. These include carbohydrates, lipids, proteins, and nucleic acids. Macromolecules are composed of smaller subunits called monomers, which link together through dehydration synthesis (removing water to form covalent bonds) and are broken apart by hydrolysis (adding water to break bonds). 🔗
The main elements in biological macromolecules are carbon, hydrogen, oxygen, nitrogen, and phosphorus. Carbon’s versatility allows it to form diverse and stable structures, essential for creating the variety of molecules needed for life. The functional groups—specific combinations of atoms—attached to carbon skeletons determine the chemical reactivity and properties of these molecules.
The six key functional groups you should know are:
Carboxyl
Carbonyl
Hydroxyl
Amino
Phosphate
Sulfhydryl
Functional groups give biological molecules their unique shapes and roles. Understanding these groups is essential for understanding how biological molecules interact and function. ⚙️
Carbohydrates 🧁
Carbohydrates are made of carbon, hydrogen, and oxygen. They serve as a primary energy source and contribute to the structural integrity of cells. For example:
Monosaccharides (simple sugars like glucose) provide immediate energy.
Polysaccharides (complex carbohydrates like starch and cellulose) provide energy storage and structural support.
In plants, cellulose makes up the cell wall, while chitin serves a similar function in the exoskeletons of insects and arthropods. Overall, carbohydrates provide short-term energy essential for cellular processes. ☀️
Lipids 🧈
Lipids are nonpolar macromolecules composed of carbon, hydrogen, and oxygen, and are known for their role in long-term energy storage. Lipids include fats, oils, and phospholipids, each with unique properties:
Saturated lipids 🍟 have no double bonds and tend to be solid at room temperature (e.g., butter).
Unsaturated lipids 🥑 have one or more double bonds, making them liquid at room temperature (e.g., olive oil).
Phospholipids are crucial for cell membrane structure. They have a polar, hydrophilic head and a nonpolar, hydrophobic tail, which allows them to form the phospholipid bilayer in cell membranes. This bilayer acts as a selective barrier, maintaining the cell’s internal environment.
Proteins 🥩
Proteins are the most diverse biological macromolecules, made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The building blocks of proteins are amino acids, which form polypeptide chains through peptide bonds.
Proteins perform a wide range of functions, including:
Catalyzing biochemical reactions as enzymes.
Transporting molecules within organisms.
Providing structural support (e.g., collagen in connective tissue).
Regulating immune responses and hormones.
Protein structure is organized into four levels:
Primary structure: The sequence of amino acids.
Secondary structure: Local folding patterns, such as alpha-helices or beta-sheets.
Tertiary structure: The overall 3D shape of the protein, determined by interactions between R-groups.
Quaternary structure: When multiple polypeptide chains bond together to form a functional protein.
Protein function is directly related to its structure, and even slight changes in the sequence or folding can significantly impact how a protein works.
Nucleic Acids 🧬
Nucleic acids—DNA and RNA—store and transmit genetic information. They are made of carbon, hydrogen, oxygen, nitrogen, and phosphorus. The monomers of nucleic acids are nucleotides, each consisting of a five-carbon sugar, a phosphate group, and a nitrogenous base.
DNA contains adenine (A), thymine (T), cytosine (C), and guanine (G).
RNA contains adenine (A), uracil (U), cytosine (C), and guanine (G).
DNA is a double-stranded helix with strands running in opposite (antiparallel) directions, which helps in storing genetic information stably. RNA, on the other hand, is typically single-stranded and plays a role in protein synthesis and other cellular functions.
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