- large molecules\/macro-molecules<\/li>
- consist of one or more long chains of amino acids<\/li><\/ul>\n\n\n\n
Protein functions: <\/strong><\/p>\n\n\n\n
- catalysing metabolic reactions (enzymes in the TCA cycle\/glycolysis etc.)<\/li>
- transport molecules (carrying lipids, carbohydrates, hormones)<\/li>
- structural motifs (part of the cytoskeleton, giving shape to cells)<\/li>
- regulatory elements (p53, transcription factors, coactivator, corepressor)<\/li>
- enzymes involved in the cell cycle (DNA replication, repair) <\/li><\/ol>\n\n\n\n
<\/div><\/p>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN-1024x569.png\")
<\/a><\/figure>\n\n\n\nLevels of the protein organization<\/strong><\/h1>\n<\/span>\n\n\n
\n\n![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2022\/01\/PROT-1024x568.jpg\")
Figure 1. Levels of the protein organization<\/strong><\/figcaption><\/figure>\n<\/div>\n\n\n\n \n- Primary<\/strong> (AMINO ACID SEQUENCE)<\/li>
- Secondary <\/strong>(ALPHA HELIX \/ BETA- SHEETS \/ TURNS AND LOOPS)<\/li>
- Tertiary<\/strong> (THE 3D SHAPE OF THE FULLY FOLDED POLYPEPTIDE CHAIN (due to the side chain interaction))<\/li>
- Quaternary<\/strong> (ARRANGEMENT OF SEVERAL POLYPEPTIDE CHAINS (full conformation with the subunits)) (Figure 1.)<\/li><\/ol>\n<\/div>\n<\/div>\n\n\n<\/span>\n
Primary structure – amino acid sequence<\/strong><\/h2>\n<\/span>\n\n\n
STARTS every time with: <\/p>\n\n\n\n
- MET<\/strong> (Methionine – Sulphur containing essential amino acid)<\/em><\/li><\/ul>\n\n\n\n
The sequence is arranged together in the process called “translation” (cytosol) after the “transcription” has been done (nucleus).<\/p>\n\n\n\n
Altogether 21 amino acids can be involved in the sequence depending on the composition\/mRNA codon sequences.<\/p>\n\n\n<\/span>\n
Secondary structures – Alpha-helix and beta-sheets; turns and loops<\/strong><\/h2>\n<\/span>\n\n<\/span>\n
ALPHA-HELIX<\/strong><\/h3>\n<\/span>\n\n\n
- CONSECUTIVE STRETCH OF 5-40 AMINO ACIDS<\/li>
- 3.6 AMINO ACIDS DISTANCE PER TURN<\/li>
- STABILIZED BY H-BONDS<\/li>
- STABILITY IS INFLUENCED BY THE AA SEQUENCE<\/li><\/ul>\n\n\n\n
Gibbs energy<\/strong><\/p>\n\n\n\n
The Gibbs energy<\/em> (G) is a thermodynamic potential that is minimized when a system reaches the chemical equilibrium = stability at constant pressure and temperature.<\/p>\n\n\n\n
Regarding the STRUCTURES, the G value (delta-delta -G) represents the potential of the helix formation, which can be influenced by different amino acids (helix former\/breaker) (Figure 2).<\/p>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN2-1024x678.png\")
<\/a>Figure 2. Helix breaker and former amino acids<\/strong><\/figcaption><\/figure>\n\n\n\n SECO<\/strong>NDARY \u2013\u0392ETA-SHEET<\/strong><\/p>\n\n\n\n
- TWO OR MORE SEGMENTS OF A POLYPEPTIDE CHAIN LINE UP NEXT TO EACH OTHER, FORMING A SHEET-LIKE STRUCTURE <\/li>
- CAN BE ANTIPARALELL OR PARALLEL ORIENTED (Figure 3)<\/li>
- CONSISTS OF 5-10 AMINO ACIDS<\/li>
- STABILIZED BY H-BONDS<\/li>
- STABILITY IS INFLUENCED BY THE AA SEQUENCE<\/li><\/ol>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN3-1024x418.png\")
<\/a>Figure 3. Types of the beta-sheets <\/strong><\/figcaption><\/figure>\n\n\n\n SECONDARY \u2013\u0392ETA-TURNS (HAIRPINS)<\/strong><\/p>\n\n\n\n
- OCCUR FREQUENTLY WHENEVER STRANDS IN B-SHEETS CHANGE THE DIRECTION<\/li>
- 180\u00b0 TURN IS ACCOMPLISHED OVER FOUR AMINO ACIDS<\/li>
- STABILIZED BY A HYDROGEN BOND FROM A CARBONYL OXYGEN TO AMIDE PROTON THREE RESIDUES DOWN THE SEQUENCE<\/li>
- PROLINE IN POSITION-2 OR GLYCINE IN POSITION-3 ARE COMMON IN B-TURNS (Figure 4)<\/li><\/ol>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN4-1024x575.png\")
<\/a>Figure 4. Types of the turns<\/strong><\/figcaption><\/figure>\n\n\n\n SECONDARY \u2013 LOOPS<\/strong><\/p>\n\n\n\n
- CONNECT THE SECONDARY STRUCTURE ELEMENTS<\/li>
- HAVE VARIOUS LENGTH AND SHAPES<\/li>
- LOCATED AT THE SURFACE OF THE FOLDED PROTEIN AND THEREFORE MAY HAVE IMPORTANT ROLE IN BIOLOGICAL RECOGNITION PROCESSES<\/li>
- PROTEINS THAT ARE EVOLUTIONARY RELATED HAVE THE SAME HELICES & SHEETS (ALFA-AND BETA-STRUCTURES) BUT MAY VARY IN LOOP STRUCTURES<\/li><\/ul>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN5.png\")
Figure 5. Loops<\/strong><\/figcaption><\/figure>\n\n\n<\/span>\n TERTIARY – THE 3D SHAPE OF POLYPEPTIDE CHAIN<\/strong><\/h2>\n<\/span>\n\n\n
- TYPICALLY CONTAIN 100-150 AMINO ACIDS<\/li>
- CAN BY DISTINGUISH BETWEEN FIBROSOUS AND GLOBULAR TYPES<\/li>
- FIBROSOUS PROTEINS:
- TYPICALLY INSOLUBLE <\/li>
- MADE FROM A SINGLE SECONDARY STRUCTURE<\/li><\/ul><\/li>
- GLOBULAR PROTEINS:
- WATER-SOLUBLE <\/li>
- LIPID-SOLUBLE MEMBRANEOUS PROTEINS<\/li><\/ul><\/li><\/ul>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN6.png\")
Figure 6. Types of stuctures<\/strong><\/figcaption><\/figure>\n\n\n\n TERTIARY \u2013 FUNCTION – COLLAGEN<\/strong><\/p>\n\n\n\n
- MAIN STRUCTURAL PROTEIN IN THE EXTRACELLULAR MATRIX AND CONNECTIVE TISSUES IN THE BODY <\/li>
- CONSISTS OF AMINO ACIDS BOUND TOGETHER TO FORM A TRIPLE HELIX (Figure 7)<\/li><\/ul>\n\n\n\n
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN7-1024x611.png\")
Figure 7. Synthesis of the collagen<\/strong><\/figcaption><\/figure>\n\n\n<\/span>\n QUATERNARY – ARRANGEMENT OF SEVERAL POLYPEPTIDE CHAINS<\/strong><\/h2>\n<\/span>\n\n\n
- PROTEINS THAT ARE COMPRISED OF MORE THAN ONE POLYPEPTIDE CHAINS <\/li>
- EACH POLYPEPTIDE CHAIN IN SUCH A PROTEIN IS CALLED A SUBUNIT<\/li>
- TYPICAL EXAMPLE: HEMOGLOBIN WITH FOUR SUBUNIT (Figure 8)<\/li><\/ul>\n<\/span>
- Secondary <\/strong>(ALPHA HELIX \/ BETA- SHEETS \/ TURNS AND LOOPS)<\/li>
- Primary<\/strong> (AMINO ACID SEQUENCE)<\/li>
![\"\"](\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/02\/PROTEIN.png\")
<\/a><\/figure>\n\n\n