Biological Functions of Proteins and DNA Replication

Biological Functions of Proteins

Structural Function

Proteins are essential components of plasma membranes, working alongside phospholipids and cholesterol. There are two main types of membrane proteins: peripheral proteins, located on the exterior or interior surfaces, and integral proteins, which are housed within the phospholipid bilayer.

Why is the water molecule a dipole? It is because electrons are closer to the more electronegative oxygen atom, resulting in positive and negative charges for hydrogen and oxygen respectively.

Enzymatic Function

Enzymes are globular proteins that catalyze metabolic reactions. A catalyst is a substance that accelerates chemical reactions. In our organism, only enzymes can perform this function. While chemical reactions can be accelerated by increasing temperature or pressure, this is not possible within the human body; therefore, enzymes are necessary.

Contractile and Transport Functions

Contractile Function: This is carried out by muscular proteins that constitute the myofibrils of striated muscle.

Transport Function: This includes Hemoglobin (Hb), the protein in red blood cells that carries oxygen from the lungs to the cells and transports carbon dioxide in the reverse direction.

Defense and Hemostatic Functions

Defense Function: This is performed by immunoglobulins (antibodies), which are responsible for eliminating foreign substances or microorganisms that enter through various pathways, such as the digestive system. These proteins defend us against viruses and bacteria and reject tissues that are not our own.

Hemostatic Function: This involves blood coagulation, which is carried out by the protein fibrin.

DNA Transcription and Protein Synthesis

DNA stores all the information required to build and maintain our bodies. Specifically, nucleotides are the "letters" of the recipe used to create proteins. However, DNA is located in the cell nucleus, while proteins are manufactured in the ribosomes.

During transcription, messenger RNA (mRNA) copies one of the DNA strands (the codogenic strand). The mRNA then leaves the nucleus and attaches to a ribosome. As the ribosome moves along the mRNA, transfer RNA (tRNA) brings the corresponding amino acids to synthesize the protein.

Once the mRNA transcript leaves the nucleus and is coupled to a ribosome, the encoding is always performed by mRNA, never by tRNA.

DNA Replication and Genetic Code

DNA molecules carry the information necessary to develop a cell or an individual and are the only molecules capable of self-replication. DNA performs its function through a chemical code known as the genetic code. The reading and expression of this code results in specific protein synthesis. Furthermore, genes can be deliberately manipulated using genetic engineering techniques.

Chromatin and Chromosomes

Chromatin is a fibrillar structure built from DNA and proteins within the nucleus. Before a cell divides, the DNA must double so that each daughter cell receives the same amount of genetic material. This process is known as DNA replication.

Chromosomes represent the compaction of chromatin required for cell division. The number of chromosomes varies depending on whether the cell is a somatic cell or a reproductive cell.