Interactive Summaries

Chapter 6: Proteins and Amino Acids

Amino Acids: The Building Blocks of Protein

Proteins are sequences of amino acids. There are different amino acids; are indispensable, meaning they cannot be made by the body or cannot be made in sufficient quantities to meet the body's needs. are dispensable, which the body can make if supplied with adequate nitrogen. and cysteine are both considered amino acids. If your intake of methionine is too low, your body needs cysteine from your diet to free methionine for protein formation. People with lack sufficient amounts of an enzyme that converts to tyrosine. These people must carefully monitor the amount of phenylalanine in their diets to avoid problems such as .

One amino acid is linked to the next by a . When this bond is created, the carboxyl group of one amino acid binds to the amino group of another amino acid. This reaction releases water in the process. An oligopeptide is a chain of amino acids; a polypeptide contains at least amino acids. Acidity, heat, and oxidation can disrupt the chemical forces that stabilize a protein’s shape causing it to .

Functions of Body Proteins

Proteins have structural and mechanical functions. , the most abundant protein in mammals, gives skin and bones their elastic strength. The proteins that turn energy into mechanical work are known as proteins. These proteins are also involved in cell division and sperm swimming. Proteins that catalyze chemical reactions without being used up are . are chemical messengers that are made in one part of the body but act on cells in other parts of the body. are blood proteins that attack and inactivate bacteria and viruses. If the body does not have enough protein to maintain normal levels of blood proteins, fluids will leak into surrounding tissues and cause edema. Proteins help maintain levels in body fluids, by serving as buffers; they donate hydrogen ions when conditions are alkaline. They pick up extra hydrogen ions when conditions are acidic and donate hydrogen ions when conditions are alkaline. More than 1/3 of the energy your body uses at rest is consumed by the sodium-potassium protein pump which controls cell volume and nerve impulses. If the diet does not provide enough energy to sustain vital functions, the body will sacrifice its own protein to make energy and glucose. To release energy from an amino acid, the body performs a process called .

Proteins in the Body

During protein synthesis cells use a specific length of the in a cell nucleus to create a special type of mRNA. gathers the necessary amino acids from cell fluid and carries them to the mRNA where enzymes bind amino acids to the growing chain. The major component of ribosomes is . Scientists believe that rRNA plays a major role in protein synthesis. Genetic defects can cause problems in protein synthesis. People with sickle- cell anemia have a defect in the amino acid sequences of their .

Amino acids, which are not bound into proteins and are found throughout the body in fluids and tissues, are collectively referred to as the . Of the approximately 300 grams of protein synthesized by your body each day are made from recycled amino acids.

Amino acids also make up non-protein molecules in the body such as certain vitamins and . Tyrosine for example is used to make melanin, a skin pigment, and thyroxin, a hormone that helps regulate metabolism.

We can use the balance of to see if the body is getting enough or too much protein. A positive balance indicates that the body is adding protein. Healthy adults have no net gain or loss of body protein and they simply excrete excess dietary protein.

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