Proteins, Enzymes, and Carbohydrates

General Properties of Proteins

Proteins have diverse functions, including:

  • Enzymatic activity
  • Carrying capacity
  • Energy reserve
  • Contractile capacity
  • Structural support
  • Defensive or immune function
  • Regulatory properties

Some proteins incorporate non-protein substances, forming protein conjugates. The amino acid portion is called the prosthetic group. Glycoproteins, lipoproteins, and metalloproteins are the most important conjugated proteins.

General Structure of Proteins

Primary Structure: The amino acid sequence and location of disulfide bonds.

Secondary Structure: The spatial relationship between adjacent amino acids. This spontaneously takes the form of α-helix or β-sheet structures.

Tertiary Structure: The three-dimensional conformation of the polypeptide chain.

Quaternary Structure: The majority of proteins have more than one chain of amino acids. The union of these chains constitutes this structure. They are, therefore, multiple polypeptide chains. The possibility of forming quaternary structures only exists when there is more than one chain of amino acids.

Enzymes

Enzymes are catalysts of reactions in biological systems, increasing the speed of reaction of chemical substances. They are very specific and are composed primarily of protein.

Holoenzyme (enzyme) = protein portion or apo-enzyme + non-protein portion, co-enzyme or co-factor (when the non-protein portion is not a metal).

Enzymatic Function

Enzymes are very large molecules with abnormal shapes and a multitude of links: covalent and weak chemical bonds. The enzyme gives up energy to the substances that will produce the reaction (substrates). The energy comes from the rupture of weak bonds, which in turn causes changes in its structure. Upon reaction, the enzyme and substrate generate the product and the enzyme. Once the reaction is produced, the enzyme releases energy and absorbs it, thereby returning to its original structure and can re-produce the reaction with another substrate.

Characteristics of Enzymes

  • High catalytic activity
  • Reversibility to initial state after the catalytic cycle
  • Specificity to the type of chemical reaction and the substances involved
  • Regulation of enzyme activity by each cell
  • No change in the nature of the product (although involved in the reaction, the product is the same as if the enzyme did not act)

Factors Affecting Enzyme Activity

  • pH: Enzymes are very sensitive to pH.
  • Temperature: Within biological limits, higher temperature leads to higher enzyme activity.
  • Co-enzymes: Can increase or decrease activity.
  • Pro-enzymes or zymogens: They need a trigger to carry out the reaction.
  • Inhibitory phenomena: Ways of blocking the enzyme active site.

Functions of Carbohydrates

  • Act as structural and protective tissue
  • Lubricate bone joints
  • Cell-adhesion (oligosaccharides)
  • Create signaling systems that allow intercellular or intracellular localization of a substance. Serve to regulate where it should be placed, for example, a hormone.

Composition of Carbohydrates

From a molecular standpoint, carbohydrates are polyhydroxyaldehydes or polyhydroxyketones.

The proportion of atoms – C:H:O is 1:2:1. The proportion of H is twice that of O and C.

There are three main types:

  • Monosaccharides
  • Oligosaccharides: Consist of a small number of monosaccharides (under 10). Disaccharides (formed by 2 monosaccharides) are found here. There are 3 basic types of disaccharides:
    • Sucrose: glucose + fructose (sugar cane or beet)
    • Lactose: glucose + galactose (sugar of milk)
    • Maltose: glucose + glucose
  • Polysaccharides: Chains of hundreds or thousands of monosaccharides. The main component is glucose, but sometimes:
    • Form linear chains (cellulose)
    • Form highly branched chains (starch, glycogen)

Monosaccharides

A monosaccharide is an aldehyde (aldose) or ketone (ketose) with one or more hydroxyl groups. To designate names, the suffix -ose is used.

Often, we find carbon atoms with chiral symmetry.

Molecular Characteristics

  • Unbranched carbon chain, consisting of between 3 and 7 carbon atoms, united by single covalent bonds.
  • One of the carbons is attached by a double bond to an oxygen (ketose or aldose).
  • Each of the other carbons have hydroxyl groups or alcohol.

Fischer Projections

Fischer projections are a way to represent three-dimensional shapes of molecules in a plane. The first molecule designed was glyceraldehyde (the smallest monosaccharide).

Features

  • Made by convention: if we place the most oxidized group at the top, we actually get a tetrahedron.

The most important monosaccharides are aldoses and ketoses. Most of the naturally occurring monosaccharides are D chiral isomers; therefore, L-forms are usually manufactured artificially.

Epimería

: Epimer: are two sugars that differ only in the configuration of an atom of C.