Amino Acids: Building Blocks of Proteins

Amino Acid

acid is any of a group of organic molecules that consist of a basic amino

group (―NH2), an acidic carboxyl group (―COOH), and an organic R group (or

side chain)

α-amino [alpha-amino] carboxylic acid

The term amino acid is short for

R-CH(NH2)-COOH

The general chemical formula for an amino acid is

peptides

proteins

Amino acids link together into short chains called _____________, which then fold into complex, functional three-dimensional structures known as ____________

16% to 20%

Protein makes up approximately _______________ of total human body weight, making it the

second most abundant compound in the body after water.

○ Amino group (-NH₂)

○ Carboxyl group (-COOH)

○ Hydrogen atom (-H)

○ R group or side chain (-R)

Most amino acids found in proteins are

α-amino acids.

● They contain a central alpha carbonThe alpha carbon is attached to:

Amino Group

Structure: -NH₂

● Contains one nitrogen atom and two hydrogen atoms.

● Acts as a base because it can accept a hydrogen ion (H⁺)

● In water, it commonly becomes: −NH₃

This group contributes to peptide-bond formation

Carboxyl Group

Structure: -COOH

● Contains a carbonyl group and a hydroxyl group.

● Acts as an acid because it can donate H⁺

● After losing H⁺ , it becomes: -COO⁻

−COOH → −COO⁻ + H⁺

This group also participates in peptide-bond formation

R Group

p is the variable part of an amino acid.

● It differs among the 20 protein-forming amino acids.

● It determines the chemical properties of the amino acid.

Physical Properties

the characteristics of amino acids that can be observe or measure without

changing its identity

Colorless, crystalline solids.

what is the state and appearance of amnio acids

200 C

what is the melting point of amino acid

soluble in water

Solubility of amino acids

Zwitterionic Nature

In neutral aqueous

solutions, amino acids exist primarily as dipolar

ions (zwitterions): the carboxyl group loses a

proton (-COO⁻) and the amino group gains one

(-NH₃⁺), yielding a net charge of zero.

Amphoteric Behavior

Because they contain

both basic (-NH₂) and acidic (-COOH) functional

groups, amino acids can act as both proton

acceptors and proton donors depending on the

solution pH.

Isoelectric Point (pI)

The specific pH level at which an amino acid's net

electrical charge is zero, preventing it from migrating toward an anode or

cathode in an electric field.

Peptide Bond Formation

The

α-carboxyl group of one amino acid

condenses with the α-amino group of

another via a dehydration synthesis

reaction, producing a covalent amide

linkage (-CO-NH-) to build peptides and

proteins.

Peptide Bond

as a covalent bond that connects two amino acids. Forms between carboxyl groups (-COOH) of one amino acid and the amino group (-NH2) of another amino acid. It allows amino acids to form peptides and proteins.

● Act as neurotransmitters

● Serve as precursors for neurotransmitters and other compounds

● Support antioxidant defense and cell signaling

● Contribute to energy metabolism and other physiological processes

Amino acids are best known as the building blocks of proteins, but they also

have important non-protein functions.

They can:

Glutamate

Major excitatory neurotransmitter in the CNS; important for learning,

memory, and synaptic plasticity

GABA

Major inhibitory neurotransmitter; helps prevent excessive neuronal

activity

Glycine

Inhibitory neurotransmitter, especially important in the spinal cord and

brainste

Tryptophan

Mood and sleep-wake regulation

Tyrosine

Movement, attention, motivation,

arousal, stress

Glutamate

Inhibition of neuronal activity

Histidine

Neural signaling and other

physiological functions

Glutamate + Cysteine + Glycine → Glutathione (GSH)

These three amino acids are used to make glutathione.

Glutathione

an important intracellular antioxidant. It helps protect cells from oxidative stress and reactive molecules.

Arginine → Nitric Oxide (NO)

is used to produce nitric oxide through nitric oxide synthase (NOS).

Nitric Oxide

acts as a signaling molecule. It promotes blood vessel relaxation and helps regulate blood flow.

Creatine

Made from arginine, glycine, and methionine

○ Supports cellular energy metabolism and rapid ATP regeneration.

Polyamines

Amino-acid-derived compounds involved in cell growth, proliferation, and regulation.

Nucleotides

Amino acids provide atoms needed to produce components of DNA and RNA

Melanin

contributes to skin, hair, and eye coloration and provides some UV

protection.

Neural communication

● Neurotransmitter production

● Antioxidant defense

● Cell signaling

• Energy metabolism

● DNA and RNA synthesis

● Melanin production

Amino acids also contribute to: