BIO 181 Exam 1 Review: Biomolecules, Proteins, and Cell Structure

Exam 1 Review: Biomolecules, Proteins, and Cell Structure

Overview

This study guide summarizes key topics for Exam 1 in a General Biology course, focusing on biomolecules, protein structure, and cell structure. The content is based on lecture slides and assignment outlines, and is designed to help students prepare for the exam by reviewing major concepts and practicing with relevant questions.

Biomolecules

Major Classes of Biomolecules

• Carbohydrates: Organic molecules composed of carbon, hydrogen, and oxygen, typically with a 1:2:1 ratio. They serve as energy sources and structural components (e.g., glucose, starch, cellulose).

• Lipids: Hydrophobic molecules including fats, oils, phospholipids, and steroids. They function in energy storage, membrane structure, and signaling.

• Proteins: Polymers of amino acids that perform a wide range of functions, including catalysis (enzymes), structure, transport, and signaling.

• Nucleic Acids: DNA and RNA, which store and transmit genetic information.

Example: A substance composed almost entirely of carbon and hydrogen with few oxygen atoms is most likely a lipid (fatty acid).

Properties of Biomolecules

• Hydrophobic vs. Hydrophilic: Hydrophobic molecules (e.g., hydrocarbon chains in lipids) do not interact well with water, while hydrophilic molecules (e.g., sugars, amino acids with polar side chains) do.

• Functional Groups: Specific groups of atoms (e.g., hydroxyl, carboxyl, amino, phosphate) confer distinct chemical properties to biomolecules.

Proteins

Levels of Protein Structure

• Primary Structure: The linear sequence of amino acids in a polypeptide chain.

• Secondary Structure: Local folding patterns such as alpha helices and beta-pleated sheets, stabilized by hydrogen bonds.

• Tertiary Structure: The overall three-dimensional shape of a single polypeptide, stabilized by interactions among R-groups (side chains), including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

• Quaternary Structure: The arrangement of multiple polypeptide subunits in a protein complex.

Example: The alpha helix is a type of secondary structure stabilized by hydrogen bonds.

Bond Types in Proteins

• Peptide Bonds: Covalent bonds linking amino acids in the primary structure.

• Hydrogen Bonds: Stabilize secondary structures (alpha helices and beta sheets).

• Disulfide Bonds: Covalent bonds between cysteine residues, important in tertiary structure.

• Ionic Bonds and Hydrophobic Interactions: Contribute to tertiary and quaternary structure.

Protein Function and Structure

• Protein function is determined by its shape, which is a result of its structure at all four levels.

• Substitution of a hydrophilic amino acid for a hydrophobic one (or vice versa) in a crucial region can alter protein structure and function.

Cell Structure

Key Components

• Plasma Membrane: Composed of a phospholipid bilayer with embedded proteins; regulates the movement of substances in and out of the cell.

• Phospholipids: Consist of a polar head group (containing phosphate) and two hydrophobic fatty acid tails.

• Proteins in Membranes: Serve as channels, receptors, and enzymes.

Atomic Structure and Chemical Bonds

Atomic Structure

• Atomic Number: Number of protons in the nucleus.

• Atomic Mass: Sum of protons and neutrons.

• Electronegativity: The ability of an atom to attract electrons in a chemical bond. Fluorine (F) is the most electronegative element.

Chemical Bonds

• Covalent Bonds: Atoms share electron pairs; can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Transfer of electrons from one atom to another, resulting in charged ions.

• Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like O or N) and another electronegative atom.

Example: Water forms hydrogen bonds with other water molecules and with polar molecules.

Nucleic Acids

Structure of Nucleotides

• Nitrogenous Base: Adenine (A), Thymine (T), Cytosine (C), Guanine (G), or Uracil (U in RNA).

• Pentose Sugar: Ribose in RNA, deoxyribose in DNA.

• Phosphate Group: Links nucleotides together via phosphodiester bonds.

Base Pairing in DNA

• Adenine pairs with Thymine (A-T), and Cytosine pairs with Guanine (C-G).

• If a DNA sample contains 15% Adenine, it will also contain 15% Thymine, and 35% each of Cytosine and Guanine.

Practice and Exam Preparation

Study Strategies

• Complete practice exams and quizzes.

• Re-watch lecture recordings and review lecture notes.

• Use flashcards and study with peers.

• Consult OpenStax readings for additional context.

Exam Logistics

• Exam will be administered online using Lockdown Browser with Respondus monitor.

• 30 questions, 75 minutes.

• Questions will be drawn from Modules 1 and 2, Lectures 1-7.

Table: Comparison of Biomolecule Classes

Class	Monomer	Main Elements	Function
Carbohydrates	Monosaccharide	C, H, O	Energy, structure
Lipids	Fatty acid, glycerol	C, H, O (few O)	Energy storage, membranes
Proteins	Amino acid	C, H, O, N, (S)	Catalysis, structure, transport
Nucleic Acids	Nucleotide	C, H, O, N, P	Genetic information

Key Equations

• Atomic Mass: $\text{Atomic Mass} = \text{Number of Protons} + \text{Number of Neutrons}$

• Base Pair Percentage in DNA: $\%A = \%T$, $\%C = \%G$, $\%A + \%T + \%C + \%G = 100\%$

Summary

• Understand the structure and function of major biomolecules.

• Be able to identify types of chemical bonds and their roles in biological molecules.

• Review protein structure levels and the importance of amino acid properties.

• Prepare for the exam by practicing with quizzes, reviewing lectures, and studying key concepts.