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Peptide Glossary: Amino Acid, Peptide Bond, Half-Life, Reconstitution and More

A plain-English peptide glossary covering amino acids, peptide bonds, residues, molecular weight, half-life, reconstitution, BAC water, GLP-1 and research terms.

Published
May 18, 2026
Last reviewed
May 18, 2026
Reading time
4 min read
By
PeptideStat Editorial Team
This article separates published evidence from commercial claims. It is educational, not medical advice.

Peptide research gets confusing fast because chemistry terms, clinical terms, product labels and forum slang all get mixed together. This glossary keeps the definitions practical and links out to the relevant PeptideStat tools.

Start with what are peptides if you want the foundation first, or use the peptide chemistry calculator when you have a sequence to analyze. For practical handling terms, pair this with the peptide storage guide and peptide half-life guide.

Core Chemistry Terms

TermMeaningRelated tool or guide
Amino acidThe building block of peptides and proteins. Standard sequences use 20 common amino acids.Peptide chemistry calculator
PeptideA chain of amino acids linked by peptide bonds. Usually shorter than a protein, though cutoffs vary.What are peptides?
Peptide bondThe amide linkage connecting one amino acid residue to the next in a chain.Peptide basics
ResidueAn amino acid after it has been incorporated into a peptide or protein chain.Composition calculator
N-terminusThe amino end of a peptide sequence. Sequences are conventionally written from N-terminus to C-terminus.Sequence basics
C-terminusThe carboxyl end of a peptide sequence.Sequence basics
Molecular weightThe mass of the peptide molecule, usually shown in daltons or kilodaltons.Molecular weight calculator
Monoisotopic massThe mass calculated using the most abundant isotope of each element.Sequence calculator
Average massThe mass calculated from natural isotope abundance averages.Sequence calculator
GRAVYGrand average of hydropathy. A rough score for how hydrophobic or hydrophilic a sequence is.Hydropathy calculator
Extinction coefficientAn estimate of absorbance at 280 nm, mainly driven by tryptophan and tyrosine.Chemistry calculator

Handling and Calculator Terms

TermMeaningRelated tool or guide
ReconstitutionAdding a diluent to a dry or concentrated vial so a measured volume can be drawn.Reconstitution guide
BAC waterBacteriostatic water, a sterile water product containing preservative. Use depends on product instructions.Bacteriostatic water guide
ConcentrationAmount of peptide per volume, commonly mg/mL after reconstitution.Concentration calculator
UnitsSyringe scale markings. On a U-100 syringe, 100 units equals 1 mL.Unit converter
mcgMicrogram. 1 mg equals 1000 mcg.mg to mcg converter
Half-lifeThe time it takes for the amount of a compound in the body or model to fall by half.Half-life guide
Steady stateA repeated-dose pattern where peaks and troughs become more consistent over time.Half-life calculator
Beyond-use dateThe date after which a punctured, mixed or pharmacy-prepared product should not be used.Storage guide
Room-temperature excursionTime a product spends outside its labeled storage range.Storage and travel guide
SubcutaneousInjected under the skin into subcutaneous tissue.Injection safety guide

GLP-1 and Drug-Class Terms

TermMeaningRelated guide
GLP-1Glucagon-like peptide-1, an incretin hormone pathway involved in satiety and glucose regulation.What is GLP-1?
GLP-1 receptor agonistA drug that activates GLP-1 receptors, such as semaglutide or liraglutide.GLP-1 receptor agonists
Dual agonistA compound that activates two receptor pathways. Tirzepatide targets GIP and GLP-1 receptors.Tirzepatide database
Triple agonistA compound that activates three receptor pathways. Retatrutide targets GLP-1, GIP and glucagon receptors.Retatrutide guide
Amylin analogA compound designed around the amylin satiety pathway, such as cagrilintide.Cagrilintide database
InvestigationalStudied in clinical research but not approved for a specific consumer indication.Peptides for weight loss
Research-onlyNot approved as a medicine for the claimed consumer use.Peptide database

Quick Conversions

ConversionValueTool
1 mg to mcg1 mg = 1000 mcgUnit converter
U-100 syringe100 units = 1 mLReconstitution calculator
DaltonMass unit commonly used for molecules and peptidesMolecular weight calculator

References

  1. IUPAC Gold Book. Peptide definition.

  2. NCBI Bookshelf. Biochemistry, Peptide.

  3. ExPASy. ProtParam sequence parameter tool.

  4. Kyte J, Doolittle RF. A simple method for displaying the hydropathic character of a protein.

Filed under

peptide glossarypeptide terminologyamino acidsreconstitutionhalf-life

Continue in the database

Structured status, mechanism and evidence notes for compounds connected to this guide.

Dulaglutide

Trulicity

5/5
Weight lossApproved

Dulaglutide is a long-acting GLP-1 receptor agonist that stimulates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying and reduces appetite.

DetailsGuide

Exenatide

Byetta, Bydureon, exendin-4

5/5
Weight lossApproved

Exenatide activates the GLP-1 receptor to increase glucose-dependent insulin secretion, suppress inappropriate glucagon release, and slow gastric emptying.

DetailsGuide

Liraglutide

Victoza, Saxenda

5/5
Weight lossApproved

Daily GLP-1 analog. Reduces appetite and improves glycemic control via the same incretin pathway as semaglutide.

DetailsGuide

Semaglutide

Ozempic, Wegovy, Rybelsus

5/5
Weight lossApproved

Mimics the incretin GLP-1, slowing gastric emptying and reducing appetite while improving insulin secretion.

DetailsGuide

Tirzepatide

LY3298176, Mounjaro, Zepbound

5/5
Weight lossApproved

Activates GLP-1 and GIP receptors to improve glycemic control and reduce appetite + body weight.

DetailsGuide

Work with the numbers

Open reconstitution, unit-conversion and accumulation tools with editable examples.

Peptide reconstitution calculatorCalculate concentration, draw volume and syringe units from vial strength and BAC water.Open toolPeptide accumulation calculatorModel repeated dosing schedules with half-life, interval, peak and trough estimates.Open toolPeptide unit converterConvert mg, mcg, optional IU and syringe units from one reconstituted vial setup.Open toolPeptide chemistry calculatorAnalyze sequence length, molecular weight, composition, charge, hydropathy and notation.Open tool

Prefilled calculator shortcuts

Open calculators with editable examples for compounds mentioned around this guide.

Liraglutide accumulation calculatorPrefills 13 hour half-life and 24 hour interval examples.Open prefilled toolSemaglutide reconstitution calculatorPrefills a 5 mg vial, 2 mL BAC water and editable dose fields.Open prefilled toolSemaglutide accumulation calculatorPrefills 168 hour half-life and 168 hour interval examples.Open prefilled toolSemaglutide unit converterPrefills 250 mcg with a 5 mg vial example.Open prefilled toolTirzepatide reconstitution calculatorPrefills a 10 mg vial, 2 mL BAC water and editable dose fields.Open prefilled toolTirzepatide accumulation calculatorPrefills 120 hour half-life and 168 hour interval examples.Open prefilled tool

Explore the wider category

Compare the broader evidence landscape before focusing on one compound.

Weight Loss Peptides

Compare weight loss peptides including GLP-1, GIP, amylin and triple-agonist compounds by approval status, mechanism, half-life and evidence score.

Read next

FDA Peptide Compounding Rules: Category 2, Safety Risks and Research PeptidesFDA's Category 2 and withdrawn-nomination tables do not turn research peptides into approved drugs. They flag safety, quality and data gaps that buyers often miss.Peptide COA Guide: Purity, Mass Spec and Red FlagsA peptide COA can answer a narrow lab question. It cannot prove clinical evidence, safe human use, legal status, sterility or correct dosing by itself.Bacteriostatic Water Guide: What It Is, When to Use It and Safety RulesBacteriostatic water is sterile water with benzyl alcohol preservative. This guide explains what it is, when it is used, when not to use it, and how to handle it safely.