chemistry proteins Flashcards
(8 cards)
protients
Proteins make up more than half of the organic material in the body and have many different jobs. Some proteins help build body parts (like muscles and skin), while others are important for how cells work. Just like carbs and fats, proteins are made of carbon, hydrogen, and oxygen, but they also have nitrogen and sometimes sulfur, which makes them special.
amino acids of protiens
Proteins are made from amino acids, which are like building blocks.
There are 20 different amino acids used in your body to build proteins.
Every amino acid has two key parts:
An amine group (–NH₂), which is basic.
An acid group (–COOH), which is acidic.
What makes each amino acid different is the R-group, which can vary in size, charge, or chemical makeup.
For example:
If the R-group has another acid group, the amino acid is more acidic.
If the R-group has a sulfhydryl group (–SH), it can help hold the protein’s shape by bonding with other amino acids.
So in short, amino acids all share a core structure but have different R-groups that give them unique properties and help form the structure and function of proteins.
amino acid sequence
Amino acids are joined together in chains to form polypeptides (fewer than 50 amino acids); proteins (more than 50 amino acids); and large, complex proteins (50 to thousands of amino acids). Because each type of amino acid has distinct properties, the sequence in which they are bound together produces proteins that vary widely both in structure and function. To understand this more easily, think of the 20 amino acids as a 20-letter alphabet. The letters (amino acids) are used in specific combinations to form words (a protein). Just as a change in one letter of any word can produce a word with an entirely different meaning (flour → floor) or one that is nonsensical (flour → fluur), changes in amino acids (letters) or in their positions in the protein allow literally thousands of different protein molecules to be made.Proteins can be described in terms of four structural levels. The sequence of amino acids composing each amino acid chain is called the primary structure. This structure, which resembles a strand of amino acid “beads,” is the backbone of a protein molecule in which the chemical properties of each amino acid will affect how the protein folds.The folding is crucial because a protein’s shape determines its function.
the diffrent shapes of amino acid other then linear
Most proteins do not function as simple, linear chains of amino acids. Instead, they twist or bend upon themselves to form a more complex secondary structure. The most common secondary structure is the alpha (α)-helix, which resembles a metal spring (Figure 2.18b). The α-helix is formed by coiling of the primary chain and is stabilized by hydrogen bonds. Hydrogen bonds in α-helices always link different parts of the same chain together.
In another type of secondary structure, the beta (β)-pleated sheet, the primary polypeptide chains do not coil, but are linked side by side by hydrogen bonds to form a pleated, ribbonlike structure that resembles the pleats of a skirt or a sheet of paper folded into a fan (see Figure 2.18b). In this type of secondary structure, the hydrogen bonds may link together different polypeptide chains as well as different parts of the same chain that has folded back on itself.
“In an alpha helix, the primary amino acid chain coils into a spiral shape, held together by hydrogen bonds between nearby amino acids. In a beta-pleated sheet, the chain folds back and forth, and hydrogen bonds form between parallel or antiparallel segments, creating a sheet-like structure that looks like a pleated skirt.”
These are both examples of secondary structures in proteins, stabilized by hydrogen bonds.
territory amino chains
this relates to even simples amino chains Many proteins have tertiary structure (ter′she-a″re), the next higher level of complexity. Tertiary structure is achieved when α-helical or β-pleated regions of the amino acid chain fold upon one another to produce a compact ball-like, or globular, protein (Figure 2.18c). The unique structure is maintained by covalent and hydrogen bonds between amino acids that are often far apart in the primary chain. Finally, when two or more amino acid chains (polypeptide chains) combine in a regular manner to form a complex protein, the protein has quaternary (kwah′ter-na″re) structure (Figure 2.18d).
Although a protein with tertiary or quaternary structure looks a bit like a crumpled ball of tin foil, the final structure of any protein is very specific and is dictated by its primary structure. In other words, the types and positions of amino acids in the protein backbone determine where hydrogen bonds can form to keep water-loving (hydrophilic) amino acids near the surface and water-fearing (hydrophobic) amino acids buried in the protein’s core so the protein remains water-soluble.
fibrous proteins
Based on their overall shape and structure, proteins are classed as either fibrous or globular proteins (Figure 2.19). The strandlike fibrous proteins, also called structural proteins, appear most often in body structures. Some exhibit only secondary structure, but most have tertiary or even quaternary structure. They are very important in binding structures together and providing strength in certain body tissues. For example, collagen (kol′ah-jen) is found in bones, cartilage, and tendons and is the most abundant protein in the body (Figure 2.19a). Keratin (ker′ah-tin) is the structural protein of hair and nails and the material that makes skin tough.
Globular proteins
Globular proteins are mobile, generally compact, spherical molecules that have at least tertiary structure. These water-soluble proteins play crucial roles in virtually all biological processes. Because they do things rather than just form structures, they are also called functional proteins; the scope of their activities is remarkable (Table 2.6). For example, some proteins called antibodies help to provide immunity; others (hormones) help to regulate growth and development. Still others, called enzymes (en′zīmz), regulate essentially every chemical reaction that goes on within the body. The oxygen-carrying protein hemoglobin is an example of a globular protein with quaternary structure (Figure 2.19b).
The fibrous structural proteins are exceptionally stable, but the globular functional proteins are quite the opposite. Hydrogen bonds are critically important in maintaining their structure, but hydrogen bonds are fragile and are easily broken by heat and excesses of pH. When their three-dimensional structures are destroyed, the proteins are said to be denatured and can no longer perform their physiological roles. Why? Their function depends on their specific three-dimensional shapes. Hemoglobin becomes totally unable to bind and transport oxygen when blood pH becomes too acidic, as we stated earlier. Pepsin, a protein-digesting enzyme that acts in the stomach, is inactivated by alkaline pH. In each case, the improper pH has destroyed the structure required for function.
So yes — globular proteins do the work, while fibrous proteins build the body.
enzymes
are functional proteins that act as biological catalysts. A catalyst is a substance that increases the rate of a chemical reaction without becoming part of the product or being changed itself. Enzymes can accomplish this feat because they have unique regions called active sites on their surfaces. These sites “fit” and interact chemically with other molecules of complementary shape and charge called substrates (Figure 2.20). While the substrates are bound to the enzyme’s active site, producing a structure called an enzyme-substrate complex, they undergo structural changes that result in a new product. Whereas some enzymes build larger molecules, others break things into smaller pieces or simply modify a substrate. Once the reaction has occurred, the enzyme releases the product. Because enzymes are not changed during the reaction, they are reusable, and the cells need only small amounts of each enzyme. Think of scissors cutting paper. The scissors (the enzyme) are unchanged while the paper (the substrate) is “cut” to become the product. The scissors are reusable and go on to “cut” other paper.
Substrate: This is the molecule the enzyme works on (like paper for scissors).
Enzyme’s Active Site: This is a specially shaped area on the enzyme where the substrate fits—like a key fits into a lock.
Enzyme-Substrate Complex: When the substrate binds (attaches) to the enzyme’s active site, they form a temporary partnership called the enzyme-substrate complex.
Structural Change: While the substrate is bound to the enzyme, the enzyme helps it change—either by:
Breaking it apart (e.g., cutting a molecule in two),
Joining it with something else, or
Rearranging its atoms.
Product: After the reaction, the changed substrate becomes a new product (the final molecule).
Enzyme Reuse: The enzyme releases the product and stays unchanged, ready to repeat the process with a new substrate.
Enzymes are capable of catalyzing millions of reactions each minute. However, they do more than just increase the speed of chemical reactions; they also determine just which reactions are possible at a particular time. No enzyme, no reaction! Enzymes can be compared to a bellows used to fan a sluggish fire into flaming activity. Without enzymes, biochemical reactions would occur far too slowly to sustain life.
Most chemical reactions in your body could happen on their own, but they’d be way too slow to keep you alive.
Enzymes act like a match to dry wood — the wood could burn eventually, but the match makes it happen faster and at the right time.
Although there are hundreds of different kinds of enzymes in body cells, they are very specific in their activities, each controlling only one (or a small group of) chemical reaction(s) and acting only on specific substrates. Most enzymes are named according to the specific type of reaction they catalyze. For example, hydrolases add water, and oxidases cause oxidation. (In most cases, you can recognize an enzyme by the suffix -ase in its name.)
The activity of different enzymes is controlled in different ways. Many enzymes are produced in an inactive form and must be activated in some way before they can function. In other cases, enzymes are inactivated immediately after they have performed their catalytic function. Both events are true of enzymes that promote blood clotting when a blood vessel has been damaged. If this were not so, large numbers of unneeded and potentially lethal blood clots would be formed.
