Comprehensive Biochemistry Midterm Review Guide

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Biochemistry and the Language of Chemistry

Types of Chemical Bonds

Chemical bonds are fundamental to molecular structure and function in biochemistry. They determine how atoms interact and form molecules.

Covalent Bonds: Strong bonds formed by the sharing of electron pairs between atoms. Essential for the stability of organic molecules.
Noncovalent Bonds: Weaker interactions that play critical roles in molecular recognition and structure. Types include charge-charge (ionic), dipole interactions, van der Waals forces, and hydrogen bonds.

Types of Covalent Bonds

Charge-Charge (Ionic) Interactions: Attraction between oppositely charged ions.
Dipole Interactions: Occur between molecules with permanent dipoles.
Van der Waals Forces: Weak, transient interactions due to temporary dipoles.
Hydrogen Bonds: Special dipole-dipole interaction involving hydrogen bonded to electronegative atoms (e.g., O, N).

Role and Properties of Water

Water is the universal solvent in biochemistry, influencing molecular interactions and biological processes.

Polarity: Water's polar nature enables hydrogen bonding and solvation of ions.
High Heat Capacity: Stabilizes temperature in biological systems.
Solvent Properties: Facilitates biochemical reactions and transport.

Acids and Bases

Acids and bases regulate pH, which is crucial for enzyme activity and molecular stability.

Acid: Donates protons (H+).
Base: Accepts protons.
pH: Measure of hydrogen ion concentration;

The Energetics of Life

Free Energy and Thermodynamics

Biochemical reactions are governed by the laws of thermodynamics, which dictate energy changes and spontaneity.

Free Energy (G): Determines whether a reaction is spontaneous.
First Law of Thermodynamics: Energy cannot be created or destroyed.
Second Law of Thermodynamics: Entropy (disorder) of the universe increases.
Enthalpy (H): Heat content of a system.
Entropy (S): Measure of disorder.
Exergonic Reactions: ; spontaneous.
Endergonic Reactions: ; non-spontaneous.

Nucleic Acids

Structure and Function

Nucleic acids store and transmit genetic information. DNA and RNA are the primary types.

Monomers: Nucleotides (composed of a sugar, phosphate, and nucleobase).
Phosphodiester Bonds: Link nucleotides in a chain.
Nucleobases: Purines (A, G) and pyrimidines (C, T, U).
Nucleosides: Sugar + base (no phosphate).
Nucleotides: Sugar + base + phosphate.

DNA vs. RNA

DNA: Double-stranded, deoxyribose sugar, bases A, T, G, C.
RNA: Single-stranded, ribose sugar, bases A, U, G, C.

Levels of Structure

Primary: Sequence of nucleotides.
Secondary: Double helix (DNA), stem-loop (RNA).
Tertiary: Higher-order folding (e.g., chromatin, ribosome structure).

Central Dogma

Replication: DNA synthesis.
Transcription: RNA synthesis from DNA template.
Translation: Protein synthesis from mRNA.

Introduction to Proteins

Monomeric Components: Amino Acids

Proteins are polymers of amino acids, which have diverse chemical properties.

Amino Acid Structure: Central carbon, amino group, carboxyl group, side chain (R group).
Peptide Bonds: Link amino acids; formed via condensation reaction.
Stereochemistry: Most amino acids are L-isomers.
Essential vs. Nonessential Amino Acids: Essential must be obtained from diet; nonessential can be synthesized.

Properties of Amino Acid Side Chains

Polar, Nonpolar, Acidic, Basic: Side chains determine protein folding and function.

Protein Structure

Primary: Sequence of amino acids; written N-terminus to C-terminus.
Secondary: Local folding: α-helix and β-sheets.
Tertiary: Overall 3D structure.
Quaternary: Assembly of multiple polypeptide chains.

Structure Defines Function

Protein function is determined by its structure, which is dictated by amino acid sequence.

Protein Function and Evolution

Groups of Proteins and Their Functions

Proteins serve diverse roles, including catalysis, transport, structural support, and immune defense.

Antibodies: Immune proteins; composed of heavy and light chains; recognize antigens via shape and charge complementarity.
Globins: Oxygen transport proteins (e.g., hemoglobin); exhibit cooperative binding and allosteric effects; mutations can cause diseases like sickle cell.
Actin/Myosin: Structural and motor proteins involved in muscle contraction.
Enzymes: Biological catalysts; require cofactors; lower activation energy; form enzyme-substrate (ES) complexes; exhibit T (tense) and R (relaxed) states; follow lock and key or induced fit models; regulated by allosteric effectors and inhibitors.

Enzyme Kinetics

Michaelis-Menten Equation: Describes rate of enzyme-catalyzed reactions.
Enzyme Inhibitors: Competitive, noncompetitive, uncompetitive types.

Lipids, Membranes, and Cellular Transport

Classes of Lipids

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

Fatty Acids: Long hydrocarbon chains with carboxyl group.
Triacylglycerols: Storage form; three fatty acids esterified to glycerol.
Phospholipids: Major membrane component; amphipathic.
Glycolipids: Lipids with carbohydrate groups; important in cell recognition.
Steroids: Four-ring structure; includes cholesterol and hormones.

Cell Membranes

Fluid Mosaic Model: Membranes are dynamic, with proteins and lipids moving laterally.
Asymmetry: Different lipid and protein composition on inner and outer leaflets.
Transport: Includes diffusion, facilitated transport, passive and active transport, ion channels, pumps, and cotransport mechanisms.

Signal Transduction

First Messengers: Extracellular signals (e.g., hormones).
Second Messengers: Intracellular signaling molecules (e.g., cAMP).
Lipid Hormones: Steroid hormones act as signaling molecules.

Carbohydrates

Structure and Classification

Carbohydrates are energy sources and structural components. They exist as monomers (simple sugars) and polymers (complex carbohydrates).

Monomers: Simple sugars (monosaccharides).
Polymers: Oligosaccharides (short chains), polysaccharides (long chains).

Isomerism in Carbohydrates

Tautomers: Isomers differing by the position of a hydrogen and double bond.
Enantiomers: Mirror-image isomers.
Diastereomers: Non-mirror-image stereoisomers.
Anomers: Isomers differing at the anomeric carbon.
Epimers: Isomers differing at one chiral center.

Cyclic Forms

Monosaccharides can cyclize to form ring structures (e.g., glucose forms pyranose).

Carbohydrate Modifications

Sugar Phosphate Esters: Addition of phosphate groups.
Lactones and Acids: Oxidation products.
Alditols: Reduction products.
Amino Sugars: Contain amino groups.
Glycosides: Sugars linked to other molecules via glycosidic bonds.

Oligosaccharides and Polysaccharides

Disaccharides: Two monosaccharides linked (e.g., sucrose).
Polysaccharides: Long chains (e.g., starch, cellulose).

Functions

Storage: Glycogen, starch.
Structure: Cellulose, chitin.
Glycoproteins: Proteins with carbohydrate groups; important in cell signaling and recognition.

Summary Table: Major Biomolecule Classes

Class	Monomer	Bond Type	Main Functions
Nucleic Acids	Nucleotide	Phosphodiester	Genetic information storage, transmission
Proteins	Amino Acid	Peptide	Catalysis, structure, transport, signaling
Lipids	Fatty Acid (varies)	Ester, glycosidic, etc.	Energy storage, membranes, signaling
Carbohydrates	Monosaccharide	Glycosidic	Energy, structure, cell recognition

Example: Hemoglobin is a globin protein that transports oxygen in blood. Its function depends on cooperative binding and allosteric regulation, and mutations can lead to sickle cell disease.

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