proteins

What are proteins made up of?

Proteins are made up of monomers called amino acids.

What are the five bases used to classify proteins?

• Structure • Biological function • Shape and solubility • Composition • Nutritional basis

What are the four levels of protein structure?

• Primary structure • Secondary structure • Tertiary structure • Quaternary structure

What is the primary structure of a protein?

The linear sequence and number of amino acids joined together by peptide bonds to form a polypeptide chain.

What bonds maintain the primary structure of proteins?

Peptide bonds and disulfide bonds are responsible for maintaining the primary structure.

What is the secondary structure of a protein?

The local spatial arrangement of a peptide segment, involving common shapes such as alpha helices and beta-pleated sheets.

What stabilizes the secondary structure of proteins?

Hydrogen bonds stabilize the secondary structure.

What is the backbone of a peptide chain composed of?

Repeating units of Ca-C(=O)-N(-H)-Ca form the backbone of the peptide chain. Six atoms constitute a planar peptide unit.

What is the tertiary structure of a protein?

The three-dimensional arrangement of all the atoms of a protein.

What is the quaternary structure of a protein?

The spatial arrangement of two or more folded polypeptide subunits combined together to form a functional protein.

What interactions hold the subunits of a quaternary protein structure together?

• Hydrogen bonds • Ionic interactions • Hydrophobic interactions

How are proteins classified according to biological function?

• Catalytic proteins (enzymes) • Transport proteins • Storage proteins • Contractile/motile proteins • Structural proteins • Defense proteins • Regulatory proteins • Other functional proteins

What are catalysts and what is their function?

Catalysts speed up chemical reactions by lowering the activation energy and are not used up during the reaction.

What are enzymes and what are their functions?

Enzymes are highly specialized proteins with catalytic activity that regulate almost all biological reactions occurring inside living cells.

How do catalytic enzymes work?

The substrate binds to a region of the enzyme called the active site. The active site is a specific pocket formed by the folding of the protein enzyme and is highly specific for its substrate.

What are transport proteins and what are their functions?

Transport proteins carry essential substances, including life-sustaining chemicals, gases and nutrients, throughout the body.

What are examples of transport proteins and what do they transport?

• Haemoglobin: Binds oxygen in the lungs and transports it to body cells for cellular respiration.

• Lipoproteins: Carry lipids from the liver to other organs through blood plasma.

What are storage proteins and what are their functions?

Storage proteins are stored in cells or tissues as reserved nutrients. They can be mobilized when needed to provide energy or meet nutrient requirements.

What are examples of storage proteins and what do they store?

• Casein: Stores protein in milk. • Ferritin: Stores iron in the spleen and liver.

What are contractile or motile proteins and what are their functions?

Contractile proteins enable movement by contracting, changing shape or allowing structures to move. They are involved in muscle contraction.

What are examples of contractile proteins and where are they found?

Actin and myosin are filamentous proteins found in muscle cells, where they function in the contractile system.

What are structural proteins and what are their functions?

Structural proteins provide support and form major components of body structures such as tendons, cartilage, bones, ligaments, hair, nails, feathers and silk fibres.

What are the examples of structural proteins and their locations or functions?

• Collagen: Major component of tendons, cartilage and bones.

• Elastin: Found in ligaments and allows stretching in two dimensions.

• Keratin: Found in hair, fingernails and bird feathers; tough and insoluble.

• Fibroin: Major structural protein in silk fibres and spider webs.

What are defense proteins and how do they protect the body?

Defense proteins protect organisms against foreign entities, harmful microbes and injury.

Immunoglobulins (antibodies) are produced by lymphocytes and neutralize foreign antigens produced by bacteria, viruses and other harmful microbes through precipitation or agglutination.

What are regulatory proteins and what are their functions?

Regulatory proteins control cellular and physiological activities. They include hormones and repressors that regulate physiological processes and enzyme biosynthesis.

What are examples of regulatory proteins and what do they regulate?

• Insulin: Produced in pancreatic tissue and regulates blood glucose levels.

• Growth hormone: Produced by the pituitary gland.

• Parathyroid hormone: Regulates calcium and phosphate transport in the body.

• Repressors: Regulate the biosynthesis of enzymes.

What are examples of other functional proteins and their functions?

• Monellin: A protein from an African plant with an intensely sweet taste, used as a non-toxic food sweetener.

• Antifreeze proteins: Found in the blood plasma of Antarctic fish and protect their blood from freezing in icy water.

• Resilin: An elastic protein found in the wing hinges of some insects.

How are proteins classified according to shape and solubility?

• Fibrous proteins • Globular proteins • Membrane proteins

What are the properties and examples of fibrous proteins?

• Rod-like structure. • Insoluble in water. • Polypeptide chains arranged parallel to the axis. • Chains held together by strong hydrogen and disulfide bonds. • Can be stretched and contracted like threads. Examples: Collagen, keratin, fibrinogen and muscle proteins.

What are the properties and examples of globular proteins?

• More or less spherical in shape. • Hydrophobic amino acids are distributed internally, while hydrophilic amino acids are on the outside. • Highly soluble in aqueous solutions. Examples: Myoglobin, albumin, globulin, casein, haemoglobin, enzymes and protein hormones.

What are membrane proteins and what are their properties?

Membrane proteins are associated with lipid membranes. Those embedded in the lipid bilayer contain extensive hydrophobic amino acids that interact with the non-polar interior of the bilayer. They are not soluble in aqueous solutions.

How are proteins classified according to composition?

• Simple proteins • Conjugated proteins

What are simple proteins and what are their characteristics?

Simple proteins yield only amino acids upon hydrolysis, with no other major organic or inorganic products. They generally contain approximately 50% carbon, 7% hydrogen, 23% oxygen, 16% nitrogen and 0–3% sulphur.

What are examples of simple proteins and their sources?

• Albumin: Egg. • Globulins: Serum. • Glutelin: Wheat. • Oryzenin: Rice.

What are conjugated proteins and what is a prosthetic group?

Conjugated proteins yield amino acids as well as additional organic or inorganic components upon hydrolysis. The non-amino acid component is called the prosthetic group.

How are conjugated proteins classified?

Conjugated proteins are classified according to the chemical nature of their prosthetic groups.

How are proteins classified according to their nutritional basis?

• Complete proteins • Incomplete proteins

What are complete proteins and what are their characteristics?

Complete proteins contain adequate amounts of all essential amino acids in the correct proportions required in the diet. They must not lack even one essential amino acid.

What are examples and sources of complete proteins?

• Meat • Fish • Poultry • Cheese • Eggs • Yogurt • Milk

What are incomplete proteins and what are their characteristics?

Incomplete proteins lack one or more essential amino acids in the correct proportions. Even if all essential amino acids are present, insufficient proportions of any one amino acid make the protein incomplete.

What are examples and sources of incomplete proteins?

• Grains • Nuts • Beans • Seeds • Peas • Corn

How can incomplete proteins be combined to create complete proteins?

Two or more incomplete protein sources can be combined so that the amino acids missing from one food are supplied by another. These are called complementary proteins because they compensate for each other's amino acid deficiencies.

What are the physical properties of proteins?

• Contain carbon, hydrogen, oxygen, nitrogen and small amounts of sulphur. • Composed of amino acids linked by peptide bonds. • Act as catalysts through enzymes that accelerate chemical reactions. • Provide structural support for cells. • Transport substances across cell membranes. • Provide defense against pathogens through antibodies. • Respond to chemical stimuli. • Secrete hormones.

What is protein denaturation?

Denaturation is the process by which proteins lose their native secondary, tertiary and quaternary structures due to external stress or chemical agents. The primary structure is generally retained.

What causes protein denaturation and what happens during the process?

Denaturation occurs when bonding interactions maintaining secondary and tertiary structures are disrupted. These include hydrogen bonds, salt bridges, disulfide bonds and non-polar hydrophobic interactions. A common observation is protein precipitation or coagulation.

How does heat cause protein denaturation?

Heat increases kinetic energy, causing molecules to vibrate rapidly and disrupt hydrogen bonds and non-polar hydrophobic interactions. Examples include egg proteins denaturing and coagulating during cooking and heat sterilization of medical instruments, which destroys bacteria by denaturing their proteins.

How does alcohol cause protein denaturation?

Alcohol disrupts hydrogen bonding within proteins by forming new hydrogen bonds with protein side chains. A 70% alcohol solution penetrates bacterial cell walls and denatures proteins and enzymes inside the cell. A 95% solution mainly coagulates proteins outside the cell wall, limiting penetration.

How do acids and bases cause protein denaturation?

Acids and bases disrupt salt bridges formed through ionic interactions between positively charged ammonium groups and negatively charged acid groups on amino acid side chains. Disruption of these interactions causes the protein chain to straighten.

How do heavy metal salts cause protein denaturation and what are their pharmaceutical applications?

Heavy metal salts disrupt ionic salt bridges in proteins and form insoluble metal-protein salts. Examples include salts containing mercury, lead, silver, thallium and cadmium. Their disinfectant applications include silver nitrate for preventing gonorrhea infections in newborn infants, treating nose and throat infections and cauterizing wounds, as well as mercury-containing preparations for preventing wound infections.

What are the examples of chemical and physical agents that cause protein denaturation?

• Acids: Acetic acid, trichloroacetic acid and sulfosalicylic acid. • Organic solvents: Ethanol and methanol. • Cross-linking agents: Formaldehyde and glutaraldehyde. • Chaotropic agents: Urea, guanidinium chloride and lithium perchlorate. • Disulfide bond reducers: 2-mercaptoethanol, dithiothreitol and TCEP. • Other agents: Picric acid, radiation and temperature.

What are examples of protein denaturation in everyday life?

• Cooking eggs: Proteins denature and coagulate, changing eggs from runny to solid. • Cooking food: Denaturation makes food proteins easier for enzymes to digest. • Milk curdling: Bacteria produce lactic acid, which protonates carboxylate groups, causes the milk proteins to become isoelectric and results in coagulation into a solid curd. • Human hair: Denaturation can occur in hair proteins.

What is the pharmaceutical importance of proteins?

Protein-based drugs are one of the fastest-growing classes of drugs. Insulin was the first pharmaceutical protein produced using genetic engineering and is now produced in large quantities using cloned Escherichia coli bacteria.

What are the pharmaceutical applications of proteins?

• Antibodies • Vaccines • Hormones • Enzymes • Human serum albumins

What are the health effects and nutritional significance of whey proteins?

Whey proteins may reduce the risk of diseases such as heart disease, cancer and diabetes. They are an abundant source of branched-chain amino acids and contain cysteine, which is used to produce glutathione. Large amounts of whey protein can increase cellular glutathione levels.

What is glutathione and what is its function?

Glutathione is an antioxidant that protects the body against free radical damage and certain toxins. Milk proteins have also been reported to reduce the risk of cancer in animals.

What are examples of proteins or protein-related substances mentioned in the lecture under pharmaceutical applications and clinical markers?

• Iron chelate protein. • Zinc chelate protein. • Alpha-fetoprotein (AFP). • Anaplastic lymphoma kinase (ALK). • Beta-2-microglobulin (B2M). • Epidermal growth factor receptor (EGFR). • NMP22.