What Role Do Proteins Play In The Cell Membrane – Proteins are the “workhorses” of the body and participate in many body functions. As we have already discussed, proteins come in all sizes and shapes, and each one is specifically structured for its specific function. This page describes some of the important functions of proteins. As you read through them, keep in mind that the synthesis of all these different proteins requires sufficient amounts of amino acids. As you can imagine, consuming a diet that is deficient in protein and essential amino acids can impair many of the body’s functions. (More on that later in the unit.)

The main types and functions of proteins are summarized in the table below, and the subsequent sections of this page give more details about each of them.

What Role Do Proteins Play In The Cell Membrane

Breaks down macronutrients into smaller monomers that can be absorbed; carry out steps in metabolic pathways to allow for nutrient utilization

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More than a hundred different structural proteins have been discovered in the human body, but the most abundant by far is collagen, which makes up about 6 percent of total body weight. Collagen makes up 30 percent of bone tissue and consists of large amounts of tendons, ligaments, cartilage, skin, and muscle. Collagen is a strong, fibrous protein composed mainly of glycine and proline amino acids. Within its quaternary structure, three protein strands twist around each other like a rope and then these collagen ropes overlap with others.

This highly ordered structure is even stronger than steel fibers of the same size. Collagen makes bones strong but flexible. Collagen fibers in the skin’s dermis provide it with structure, and the accompanying elastin protein fibrils make it flexible. Pinch the skin on your hand and then release; the collagen and elastin proteins in the skin allow it to return to its original shape. Smooth muscle cells that secrete collagen and elastin proteins surround blood vessels, providing the vessels with structure and the ability to stretch back after blood is pumped through them. Another strong, fibrous protein is keratin, an important component of skin, hair and nails.

Enzymes are proteins that carry out specific chemical reactions. An enzyme’s job is to provide a site for a chemical reaction and to reduce the amount of energy and time it takes for that chemical reaction (this is known as “catalysis”). On average, more than 100 chemical reactions take place in cells every second, and most of them require enzymes. The liver alone contains over 1,000 enzyme systems. Enzymes are specific and will only use specific substrates that fit into their active site, similar to the way a lock can only be opened with a specific key. Fortunately, an enzyme can fulfill its role as a catalyst over and over again, although it is eventually destroyed and rebuilt. All body functions, including breaking down nutrients in the stomach and small intestine, transforming nutrients into molecules a cell can use, and building all macromolecules, including protein itself, involve enzymes.

Figure 6.11. Enzymes are proteins. An enzyme’s job is to provide a place for substances to chemically react and form a product, reducing the amount of energy and time it takes to reduce it.

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VIDEO: “Enzymes,” by Amoeba Sisters, YouTube (August 28, 2016), 5:46 minutes. This video demonstrates the action of enzymes.

Are the chemical messengers produced by the endocrine glands. When an endocrine gland is stimulated, it releases a hormone. The hormone is then transported in the blood to its target cell, where it communicates a message to initiate a specific response or cellular process. For example, after eating a meal, your blood glucose levels rise. In response to the increased blood glucose, the pancreas releases the hormone insulin. Insulin tells the cells of the body that glucose is available and to take it up from the blood and store it or use it for making energy or building macromolecules. An important function of hormones is to turn enzymes on and off, so some proteins can even regulate the action of other proteins. Although not all hormones are made of protein, many of them are.

Adequate protein intake enables the basic biological processes of the body to maintain homeostasis (constant or stable conditions) in a changing environment. One aspect of this is fluid balance, so that water is properly distributed in the different compartments of the body. If too much water suddenly moves from the blood into a tissue, the results are swelling and possibly cell death. Water always flows from an area of ​​high concentration to an area of ​​low concentration. As a result, water moves to areas that have higher concentrations of others

, such as proteins and glucose. To keep the water evenly distributed between blood and cells, proteins are constantly circulating at high concentrations in the blood. The most abundant protein in blood is the butterfly-shaped protein known as albumin. The presence of albumin in the blood makes the protein concentration in the blood similar to that in cells. Therefore, fluid exchange between the blood and cells is not at an extreme, but rather is minimized to preserve homeostasis.

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Figure 6.12. The butterfly-shaped protein, albumin, has many functions in the body, including maintaining fluid and acid-base balance and transporting molecules.

Protein is also essential in maintaining proper pH balance (the measure of how acidic or basic a substance is) in the blood. Blood pH is maintained between 7.35 and 7.45, which is slightly basic. Even a slight change in blood pH can affect body functions. The body has several systems that keep the blood pH within the normal range to prevent this from happening. One of these is the circulating albumin. Albumin is slightly acidic, and because it is negatively charged, it balances the many positively charged molecules circulating in the blood, such as hydrogen protons (H)

), calcium, potassium and magnesium. Albumin acts as a buffer against abrupt changes in the concentrations of these molecules, thereby balancing blood pH and maintaining homeostasis. The protein hemoglobin also participates in acid-base balance by binding hydrogen protons.

Proteins also play an important role in transporting substances through the body. For example, albumin chemically binds to hormones, fatty acids, some vitamins, essential minerals and drugs, and transports them through the circulatory system. Each red blood cell contains millions of hemoglobin molecules that bind oxygen in the lungs and transport it to all the tissues in the body. A cell’s plasma membrane is usually not permeable to large polar molecules, so in order to get the necessary nutrients and molecules into the cell, many transport proteins exist in the cell membrane. Some of these proteins are channels that allow certain molecules to move in and out of cells. Others act as one-way taxis and require energy to function.

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Figure 6.13. Molecules move in and out of cells through transport proteins, which are either channels or carriers.

VIDEO: “The sodium-potassium pump,” by RicochetScience, YouTube (May 23, 2016), 2:26 minutes. This tutorial describes how the sodium-potassium pump uses active transport to move sodium ions (Na+) out of a cell, and potassium ions (K+) into a cell.

Proteins also play an important role in the body’s immune system. The strong collagen fibers in the skin provide it with structure and support, but they also act as a barrier against harmful substances. The immune system’s attack and destruction functions depend on enzymes and antibodies, which are also proteins. For example, an enzyme called lysozyme is secreted in the saliva and attacks the walls of bacteria, causing them to rupture. Certain proteins circulating in the blood can be directed to build a molecular knife that pierces the cellular membranes of foreign invaders. The antibodies secreted by white blood cells survey the entire circulatory system, looking for harmful bacteria and viruses to surround and destroy. Antibodies also trigger other factors in the immune system to seek out and destroy unwanted invaders.

VIDEO: “Specific Immunity, Antibodies,” by Carpe Noctum, YouTube (December 11, 2007), 1 minute. Watch this video to see how antibodies protect against foreign invaders.

Examples Of Protein In Biology And Diet

Some of the amino acids in proteins can be broken down and used to make energy. Only about 10 percent of dietary protein is catabolized each day to make cellular energy. The liver is able to break down amino acids to the carbon skeleton, which can then be fed into the citric acid or Krebs cycle. This is similar to the way glucose is used to make ATP. If a person’s diet does not contain enough carbohydrates and fats, their body will use more amino acids to make energy, which can impair the synthesis of new proteins and destroy muscle proteins if caloric intake is also low.

Not only can amino acids be used directly for energy, but they can also be used to synthesize glucose through gluconeogenesis. Alternatively, if a person eats a high protein diet and eats more calories than their body needs, the extra amino acids will be broken down and converted into fat. Unlike carbohydrates and fat, protein does not have a specialized storage system to be used later for energy.

Proteins that help speed up or facilitate chemical reactions in the body; they bring two compounds together to react,

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