About Proteins

• Proteins contain the elements carbon, hydrogen, oxygen, and nitrogen; sulfur is present in two amino acids.

Protein Structure

• Amino acids are the monomers of proteins.
• Dimers, known as peptides, consist of two amino acids linked by a peptide bond.
• Polypeptides are polymers, chains of amino acids.

Protein - Rich Foods

• Animal sources rich in protein include beef, pork, poultry, eggs, and dairy products, which are complete protein sources.
• Plant sources of protein include grains, beans, nuts, tofu, and soy milk; processed soybeans are complete proteins.

Protein Function

• Enzymes catalyze (speed up) chemical reactions involved in metabolism, such as digestive enzymes.
• Structural proteins like keratin (found in hair and nails) and collagen (in ligaments, tendons, and skin) provide support.
• Hemoglobin transports oxygen, and membrane channels regulate the movement of substances.
• Antibodies provide defense by fighting infections.
• Hormones like insulin regulate metabolism, while growth hormones influence height.
• Actin and myosin facilitate motion in muscles for movement and contraction.

Levels of Protein Structure

• The primary structure is the linear sequence of amino acids.
• Secondary structures include α (alpha) helices and ß (beta) pleated sheets formed by hydrogen bonding.
• Tertiary structure is the final three-dimensional folding of a polypeptide (examples: enzymes, antibodies, hormones).
• Quaternary structure arises when two or more polypeptides interact (examples: hemoglobin, insulin).

Amino Acids

• Amino acids share a central carbon atom, an amino group (−NH2), an acidic group (−COOH), and a hydrogen atom.
• Amino acids differ in their variable "R" group, which can range from a simple hydrogen atom to complex rings, and can be polar or nonpolar; some contain sulfide (−SH) groups.

Genes and Proteins

• Genes in DNA code for amino acid sequences, determining protein shape and function.
• Approximately 20,000 proteins have been identified in humans.

Essential Amino Acids

• Essential amino acids cannot be synthesized by humans and must be obtained through diet.

Protein Synthesis

• Proteins are synthesized in the ribosome

Central Dogma of Biology

• DNA is transcribed into RNA, which is then translated into protein.
• DNA sequences dictates RNA sequences, that dictate protein amino acid sequences and structure.

Forming Peptide Bonds

• Glycine molecules link through a dehydration reaction, forming a peptide bond and releasing a water molecule.

R Groups

• An R group is a variable side chain attached to the central carbon atom in an amino acid that defines its properties, such as whether it is hydrophobic, hydrophilic, simple, or complex.

Enzymes

• Enzymes accelerate chemical reactions by bringing reactants together.
• Enzymes lower the activation energy required for reactions.
• Factors such as optimal temperature and pH affect enzyme reaction rates; extreme conditions can denature enzymes, reducing their functionality.

Factors affecting enzyme reaction rates

• Increased enzyme concentration (with limited substrate): Increases the rate to a saturation point with substrate exhaustion.
• Increased substrate concentration (enzyme limited): Increases rate until enzymes are saturated; then plateaus.
• Temperature: Increasing temperature raises the rate until the optimum is exceeded, denaturing the enzyme.
• pH: Deviations from the optimum pH decrease enzyme activity due to denaturation.

Key Vocabulary

• Active site: The area on an enzyme where a substrate binds.
• Conformation: A protein's specific 3D shape.
• Ribosome: The organelle where proteins are synthesized.
• Amino group: (−NH₂), a basic group in amino acids.
• Carboxyl group: (−COOH) an acidic group in amino acids.
• Denature: The loss of protein structure and function due to external conditions like temperature or pH.
• Substrate: A molecule acted upon by an enzyme.
• Alpha helix/Beta sheets: Secondary protein structures resulting from hydrogen bonding.
• Peptide bond: The bond linking amino acids.
• Dipeptide: Two amino acids linked by a peptide bond.
• Optimum temperature/pH: The conditions at which enzyme activity is highest.

Secondary Structure

• Hydrogen bonding between the −CO group of one amino acid and the −NH group of another along polypeptide chains causes the formation of an alpha helix or a beta sheet

Tertiary Structure

• Hydrophobic interactions, hydrogen bonds, ionic bonds, covalent bonds, and disulfide linkages (−S−S−) between R groups lead to the development of a protein’s tertiary structure.

Primary Structure

• Covalent peptide bonds between amino acids are the type of bond found in a protein’s primary structure.

Protein Diversity

• Different sequences and lengths of the 20 amino acids produce a variety of proteins.

Dipeptide Formation

• Two amino acids combine, releasing a water molecule (H from the amino group and OH from the acid group) to form a dipeptide in a dehydration reaction, also known as a condensation reaction.