Question

Protein functions: identify and briefly explain the function of 5 proteins found in the section on Structure & Motion; briefly explain the function of albumin and hemoglobin in the section Fluid & Acid-base Balance.

Answer 1

Function of 5 proteins found in the section on Structure & Motion

Proteins are very important molecules in our cells and are essential for all living organisms. Each protein within the body has a specific function, from cellular support to cell signaling and cellular locomotion. In total, there are seven types of proteins, including antibodies, enzymes, and some types of hormones, such as insulin.

Antibodies
Antibodies are specialized proteins involved in defending the body from antigens (foreign invaders). They can travel through the bloodstream and are utilized by the immune system to identify and defend against bacteria, viruses, and other foreign intruders. One way antibodies counteract antigens is by immobilizing them so they can be destroyed by white blood cells.

Contractile Proteins
Contractile proteins are responsible for muscle contraction and movement. Examples of these proteins include actin and myosin.

Enzymes
Enzymes are proteins that facilitate biochemical reactions. They are often referred to as catalysts because they speed up chemical reactions. Enzymes include lactase and pepsin, which you might hear of often when learning about specialty diets or digestive medical conditions. Lactase breaks down the sugar lactose found in milk. Pepsin is a digestive enzyme that works in the stomach to break down proteins in food.

Hormonal Proteins
Hormonal proteins are messenger proteins which help to coordinate certain bodily activities. Examples include insulin, oxytocin, and somatotropin. Insulin regulates glucose metabolism by controlling the blood-sugar concentration. Oxytocin stimulates contractions during childbirth. Somatotropin is a growth hormone that stimulates protein production in muscle cells.

Structural Proteins
Structural proteins are fibrous and stringy and because of this formation, they provide support for various body parts. Examples include keratin, collagen, and elastin. Keratins strengthen protective coverings such as skin, hair, quills, feathers, horns, and beaks. Collagens and elastin provide support for connective tissues such as tendons and ligaments.

Storage Proteins
Storage proteins store amino acids for the body to use later. Examples include ovalbumin, which is found in egg whites, and casein, a milk-based protein. Ferritin is another protein that stores iron in the transport protein, hemoglobin.

Transport Proteins
Transport proteins are carrier proteins which move molecules from one place to another around the body. Hemoglobin is one of these and is responsible for transporting oxygen through the blood via red blood cells. Cytochromes are another that operate in the electron transport chain as electron carrier proteins.

Protein Structure
We can divide the structure of protein molecules into two general classes: globular proteins and fibrous proteins. Globular proteins are generally compact, soluble, and spherical in shape. Fibrous proteins are typically elongated and insoluble. Globular and fibrous proteins may exhibit one or more types of protein structure.

Function of albumin and hemoglobin in the section Fluid & Acid-base Balance

Protein especially albumin accounts for greater proportion (95%) of non bicarbonate buffer in plasma. The most important buffer groups of proteins are imidazole groups of histidine (pK about 7.3) and each albumin contains 16 histidines.

The reaction to the right is the main mechanism of non bicarbonate buffer system and the component Pr‑/HPr represents all non bicarbonate buffer system. The main purpose of non bicarbonate buffer system is to maintain constant H+.

The buffer value of non bicarbonate buffers of erythrocyte fluid is about 63 mmol/L. Hemoglobin accounts for major part (53 mmol/L), with remainder being mainly caused by 2,3-DPG. The imidazole group of hemoglobin is the most important buffering groups. When oxygenated, H+ ions are liberated from Hb a phenomenon called the Haldane effect. Similarly release of oxygen by binding to hydrogen is called Bohr Effect.