Proteins and Amino Acids

• Proteins are made of amino acids and their polymers.

Amino Acids

• Consist of a carboxyl group (R-COOH), an amino group (H₂N-R), a hydrogen (H), and a side chain (R).
• Varying characteristics depend on the R group.
• Nonpolar R groups are hydrophobic.
• Polar R groups are hydrophilic.
• Acidic R groups are negatively charged.
• Basic R groups are positively charged and hydrophilic.

Bonding of Amino Acids

• The carboxyl end of one amino acid is placed next to the amino end of another.
• Enzymes cause dehydration, resulting in a peptide bond formation.
• Polypeptide chains are chains of amino acids bonded with peptide bonds.
• They have a specific sequence of amino acids.

Protein Shape and Function

• The shape of proteins is determined by genetic material and environmental factors, such as pH, temperature, and concentration.
• Alterations can make proteins inactive or denatured.
• Functions of proteins include acting as support (structural), storing amino acids (storage), transporting substances (transport), coordinating activities (hormonal), responding to stimuli (receptor), enabling movement (contractile), protecting against intruders (defensive), and speeding up chemical reactions (enzymatic).

Protein Structure

• There are four levels of protein structure: primary, secondary, tertiary, and quaternary.

Primary Structure

• Refers to the sequence of amino acids.
• It is determined from DNA.

Secondary Structure

• Coils and folds of the backbone formed through repeated hydrogen bonds.
• An α-helix is a coil formed from hydrogen bonds every four amino acids.
• A β-pleated sheet is made of parallel polypeptides from hydrogen bonds.

Tertiary Structure

• Involves interactions between side chains (R groups).
• Hydrophobic interactions occur with nonpolar side chains near the interior.
• Hydrogen bonds and ionic bonds are present.
• Disulfide bridges are bonds formed between sulfhydryl groups (-SH).
• The overall structure is stronger.

Quaternary Structure

• Multiple polypeptide chains are bonded together.

Carbohydrates

• Carbohydrates are simple sugars and their polymers.
• Monosaccharides are molecular formula multiples of CH₂O.
• They consist of a carbonyl group (C=O) and hydroxyl groups (-OH).
• Monosaccharides can be classified by the location of the carbonyl group (aldose, ketose), the number of carbon atoms (triose, pentose, hexose), and the placement of asymmetric carbons.
• Used to create energy (cellular respiration).
• It is required in the production of amino acids and fatty acids.
• Examples include glucose, galactose, and fructose.
• Disaccharides are the result of a dehydration reaction between two monosaccharides.
• Examples include sucrose, lactose, and maltose.
• Polysaccharides are hundreds to thousands of monosaccharides chained together.

Polysaccharides

• There are two main types: storage polysaccharides and structural polysaccharides.
• Storage polysaccharides have joined monomers to be broken down for energy later.
• They have 1-4 linkages.
• Helical in shape due to the bond angle.
• Examples include starch (in plants) and glycogen (in animals).
• Structural polysaccharides provide structure and protection.
• They are linear due to β glucose monomers.
• They have 1-4 linkages.
• Examples include cellulose (in plants) and chitin (in arthropods and fungi).

Glucose

• α Glucose and β Glucose are two forms.
• Placement of the hydroxyl group differs on carbon 1.