Anabolic reactions build larger molecules from smaller units; dehydration synthesis is the process of linking monomers by removing a water molecule, forming a covalent bond.
Dehydration synthesis results in a dehydrated product; hydrolysis is the reverse, where water is added to break bonds.
Characteristic memory aid:
Dehydration → product is "dehydrated" (loses water).
Hydrolysis → product is hydrated (gains water).
Role of enzymes:
Dehydration synthesis is catalyzed by a polymerase enzyme (e.g., DNA polymerase is a common example in biochemistry contexts).
Hydrolysis is catalyzed by a hydrolase enzyme.
Macromolecules, Monomers, and Polymers
Most biological molecules are large and built from small units called monomers to form long chains called polymers or macromolecules.
A process of linking monomers is dehydration synthesis (loss of water); the reverse process is hydrolysis (addition of water).
Visual cue: generic monomers with OH groups can link to form polymers via dehydration synthesis; water is released in the process.
Important distinction for biochemistry vs general biology: some naming conventions and enzyme specifics can be nuanced; enzymes may be more specific in vivo.
Carbohydrates: Monosaccharides, Polysaccharides, and Bonds
Monosaccharides: simple sugars, typically with a general formula of ext(CH<em>2extO)</em>n; many variations exist (e.g., glucose is a key sugar).
Glucose is particularly important as an energy source for brains, organs, tissues, and cells.
When monosaccharides join, they form disaccharides (two units) or polysaccharides (many units).
Linkages between monosaccharides are called glycosidic linkages (a type of covalent bond).
The dehydration reaction forms these bonds and releases water:
Example general representation: extMonomer<em>1−extOH+extMonomer</em>2−extH<br/>ightarrowextBond+extH2extO
Do not memorize every end-group detail for this course; focus on the concept that sugars form larger carbohydrates via dehydration and are broken down by hydrolysis.
Amino Acids, Peptides, and Proteins
Amino acid structure:
Each amino acid has a central (alpha) carbon with four groups:
An amino group (–NH₂)
A carboxyl group (–COOH)
A hydrogen atom (–H)
An R group (side chain) that determines the amino acid’s properties (polarity, charge, size).
R group diversity:
Polar (hydrophilic) side chains
Electrically charged side chains: acidic (negative) or basic (positive)
Some are acidic or basic, affecting interactions and folding in water.
Sequence and structure:
The sequence of amino acids determines how a polypeptide folds into a functional protein.
When amino acids join, they form peptide bonds (a covalent bond) between the carboxyl of one amino acid and the amino group of the next.
A chain of amino acids is a polypeptide; when it folds and achieves function, it is a protein.
Amino acid supplements:
Some people take free amino acids as supplements instead of whole protein for faster absorption.
Whole protein must be digested first; amino acids can be absorbed more quickly, bypassing digestion.
Practical context: athletes sometimes consider amino acid supplements to support rapid availability, especially around workouts.
Nucleotides, Nucleosides, and Nucleic Acids
Nucleotide structure: three parts
Phosphate group
Sugar (ribose in RNA, deoxyribose in DNA)
Nitrogenous base (purine or pyrimidine)
Nucleoside vs nucleotide:
A nucleoside is a sugar attached to a nitrogenous base.
A nucleotide is a nucleoside with one or more phosphate groups.
Polynucleotides:
Bases along a sugar-phosphate backbone give rise to nucleic acids like DNA and RNA.
DNA vs RNA sugars:
DNA contains deoxyribose
RNA contains ribose
Base types:
Purines: Adenine (A) and Guanine (G)
Pyrimidines: Cytosine (C) and either Thymine (T) in DNA or Uracil (U) in RNA
Backbones and linkages:
Nucleotides are linked by phosphodiester bonds, forming a sugar-phosphate backbone.
The backbone is negatively charged due to phosphate groups.
Antiparallel strands:
DNA consists of two polynucleotide strands running in opposite directions (5'→3' on one strand and 3'→5' on the other).
Base pairing rules (Chargaff):
Cytosine pairs with Guanine (C≡G) via three hydrogen bonds.
Adenine pairs with Thymine (A=T) in DNA via two hydrogen bonds; in RNA, Adenine pairs with Uracil (A=U).
Base pairing visual (conceptual):
The bases form rungs of a ladder between the two antiparallel strands.
Key memory aid (Chargaff’s rule):
A and T pair, G and C pair; in any double-stranded DNA, %A ≈ %T and %G ≈ %C.
DNA Structure and Function Basics
Overall DNA form: double helix with two antiparallel polymer strands; bases stack inside the helix like steps on a ladder.
Bases and information storage: the sequence of bases encodes genetic information.
Evidence of the backbone’s charge: the phosphate groups confer a negative charge to the backbone, influencing electrophoresis and molecular biology techniques.