Comprehensive Biology Notes: Proteins, Genetics, and Human Anatomy, and Physiology

Protein Structure and Classification

Proteins are sensitive macromolecules composed of amino acids. They easily lose their complex spatial structure, a process known as denaturation, which can be triggered by temperature changes, chemical influences, or mechanical impacts. Proteins are broadly divided into two categories: simple proteins (Proteins), which consist exclusively of amino acids, and conjugated proteins (Proteids), which contain amino acids combined with other compounds such as carbohydrates, lipids, or metal ions like $Fe^{2+}$.

Proteins perform the majority of biological tasks within an organism. They serve as enzymes (biochemical catalysts), signaling molecules (hormones), and structural components of the body, including bones, muscles, and nails. There are 20 different types of amino acids, and their specific sequence is encoded by DNA. This variety in sequences allows for the vast diversity of life forms.

The structural organization of proteins occurs at four levels. The primary structure is the linear sequence of amino acids connected by peptide bonds, often forming a polypeptide chain. The secondary structure refers to local arrangements like the alpha helix (a coiled shape) or the beta sheet (a pleated structure). The tertiary structure is the complete three-dimensional folding of the protein, which can be fibrous (fibrillar) or globular. Finally, the quaternary structure occurs when multiple protein chains (subunits) link together to form a larger complex, such as hemoglobin.

Proteins can be detected through specific chemical reactions. The Biuret test involves adding copper sulfate ($CuSO_4$) and sodium hydroxide ($NaOH$); a positive result for peptide bonds is indicated by a dark purple, non-homogeneous color. The Xanthoprotein reaction involves nitric acid, which reacts with the peptide bonds in egg white to produce a yellow color. When egg white is heated, it denatures, meaning its spatial structure changes and the colloid solution precipitates.

Genetic Modification and Biotechnology

Genetically Modified Organisms (GMOs) are used in agriculture (plant and animal breeding) and medicine. While they offer solutions for disease treatment and food production, they pose a risk of reducing the biodiversity of a given area, making populations less able to adapt to environmental changes. Gene therapy is a specialized application where defective genes are corrected using GMO techniques, often by intervening in stem cells so that the diseased cells do not continue to divide.

Cloning creates a genetic copy, resulting in a genetically identical individual. Natural cloning occurs through mitosis; examples include vegetative reproduction in plants (e.g., via leaves) or parthenogenesis (virgin birth). In laboratory cloning, such as the famous sheep experiment, the nucleus ($n$) is removed from an egg cell and replaced with the nucleus ($2n$) of a somatic (body) cell. This egg, now containing the new nucleus, is implanted into a surrogate mother. The resulting offspring resembles the donor of the somatic cell nucleus, though mitochondrial DNA is inherited solely from the maternal egg cell.

Genetic engineering involves direct intervention in the organization of genes. This includes gene transfer from one organism to another, creating transgenic organisms. In medicine, bacteria are engineered to produce human insulin or growth hormones. The process involves extracting DNA, isolating specific genes using enzymes, multiplying them through specialized techniques, and inserting them into the target organism using vectors like viruses. This often involves plasmids extracted from bacterial cells.

Mutations and the Human Genome

A mutation is a sudden, non-directed change in genetic material (DNA). It can be harmful, neutral, or beneficial. The impact depends on whether it occurs in a somatic cell or a germ cell (gamete). Germline mutations are hereditary and pass traits to the next generation. Somatic mutations affect only the individual and may lead to tumors if mutated cells begin to spread (metastasis).

Mutations are categorized by scale. Point mutations occur within a gene, affecting 1-2 bases, and can result in conditions like lactose intolerance. Chromosomal mutations involve changes in the number or structure of chromosomes. Mutagenic factors include radiation (UV rays, X-rays), chemical substances (dyes, industrial chemicals), and physical injuries to the DNA. While the body uses enzymes to repair mutations, a weakened immune system may fail to fix these damaged cells.

The Human Genome Project, launched in 1992, aimed to decipher the sequence of the 3 billion base pairs in human DNA. Findings showed that 99.9% of the genetic sequence is identical among all humans. DNA sequencing is now used for identification, solving crimes, determining family relationships, and treating cancer through genetic modification. Another important concept is penetrance, which is the percentage of individuals with a specific genotype who actually express the corresponding phenotype (trait or disease).

Determinations of Biological Sex

Biological sex is determined by several factors. Chromosomal sex (XX or XY) is decided at the moment of conception and leads to the development of primary reproductive organs. Hormonal sex is influenced by the secretion of testosterone or estrogen, which leads to secondary sexual characteristics. Intersexuality occurs when there is a mismatch, such as when chromosomes do not respond to testosterone. Additionally, psychosomatic sex refers to an individual's gender identity.

Enzymes and Protein Synthesis

Enzymes are protein catalysts that speed up biochemical processes by lowering the activation energy required for a reaction. They allow processes to occur at lower temperatures. Enzymes are highly specific; the structure of their active center determines which substrate they can binds to. Examples include amylase (breaks down starch), lipase (lipids), protease (proteins), and pepsin. Pepsin, found in the stomach, breaks down food proteins but only functions in an acidic, warm environment. Enzyme activity can be inhibited by methyl groups.

Protein synthesis occurs in two main stages: transcription and translation. During transcription, an mRNA copy of a DNA segment is made in the nucleus, chloroplasts, or mitochondria. The enzyme RNA polymerase unwinds the DNA at the promoter site and assembles bases to create pre-mRNA. This pre-mRNA contains coding sections (exons) and non-coding sections (introns). Through a process called splicing, introns are removed, and exons are joined to form the final mRNA, which then travels to the cytoplasm.

Translation occurs at the ribosome. The process begins with a start codon. tRNA molecules bring specific amino acids to the ribosome, matching their anticodons with the mRNA codons. Peptide bonds link the amino acids into a long chain. The process continues until a stop codon is reached, at which point the polypeptide chain detaches. Cytosolic proteins remain in the cytoplasm, while membrane proteins are integrated into the cell wall/membrane via the Golgi apparatus.

The Human Skeletal and Muscular Systems

The human skeleton provides structure and consists of the spine, chest, and limbs. The spine features cervical, thoracic (with ribs), lumbar, and sacral sections. The upper limbs include the clavicle, humerus, radius, ulna, metacarpals, and phalanges. The lower limbs consist of the pelvis, femur, tibia, fibula, and the bones of the foot. Bones connect in different ways: fused joints (sternum, pelvis, or skull sutures) allow no movement, while synovial joints (with ligaments and fluid) allow significant movement. Cartilaginous connections (e.g., ribs to sternum or intervertebral discs) allow limited movement.

Bone tissue consists of the periosteum (containing vessels and nerves to nourish the bone), the compact bone, and the spongy bone. Spongy bone contains red bone marrow, where red blood cells are produced and which transforms based on load. The medullary cavity contains yellow bone marrow, which can revert to a blood-forming state during emergencies.

Muscles, specifically striated muscles, are capable of great effort but fatigue easily. They are controlled by the nervous system via nerve-muscle connections. Muscle contraction is powered by ATP. According to the sliding filament theory, myosin attaches to actin, and as ATP is broken down, energy is released to pull the actin filaments, shortening the muscle. Biological oxidation provides energy: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + 38\,ATP$. In the absence of oxygen, glucose is converted to lactic acid and less ATP, which causes inflammation and soreness. Muscles store nutrients as glycogen, oxygen in myoglobin, and energy in creatine.

Muscles are attached to bones by tendons made of dense, fibrous connective tissue. Muscles work in groups: synergists (working together, like chest and abdominal muscles) and antagonists (working in opposition, like the biceps/flexor and triceps/extensor in the arm).

Circulatory and Lymphatic Systems

Blood is a fiber-free connective tissue, with the average human containing approximately 5 liters. It is composed of 55% plasma (water, ions, organic matter) and 45% formed elements. Formed elements include red blood cells (erythrocytes), which transport gases via hemoglobin and lose their organelles upon maturity ($4-5\,million/mm^3$); white blood cells (leukocytes), which serve as immune defense by engulfing or neutralizing pathogens ($4,000-6,000/mm^3$); and platelets, which are cell fragments vital for blood clotting ($150,000-350,000/mm^3$). The hematocrit value measures the ratio of plasma to formed elements.

The heart is a three-layered organ (pericardium, myocardium, endocardium) that functions tirelessly. It has four chambers: right/left atria and right/left ventricles. Valves ensure one-way flow: cuspid (atrioventricular) valves between atria and ventricles, and semilunar valves at the exits to the great vessels. The right side receives deoxygenated blood from the body, and the left side receives oxygenated blood from the lungs. The sinus node in the right atrium acts as the natural pacemaker ($72\,beats/min$ at rest). During one contraction, the heart pumps approximately $70\,ml$ of blood, meaning it circulates the entire 5-liter blood volume in about one minute (cardiac output).

Blood pressure is measured in two phases: systolic pressure ($120\,mmHg$) during ventricular contraction and diastolic pressure ($80\,mmHg$) during relaxation. The heart muscle itself is supplied by coronary arteries. The circulatory system is divided into the systemic (great) circuit, supplying the body, and the pulmonary (small) circuit, where gas exchange occurs in the lungs.

Blood clotting occurs when a vessel is injured. Platelets adhere to the site to form a temporary plug, then a fibrin mesh traps red blood cells to form a stable clot, a process taking about 6 minutes and requiring Vitamin K and $Ca^{2+}$. Inappropriate clotting can lead to thrombosis or embolism. The lymphatic system manages tissue fluid; excess fluid that does not return to the capillaries becomes lymph, which is transported back to the circulation by lymph vessels.

Common Diseases of the Systems

Musculoskeletal issues include joint wear (osteoarthritis), inflammation (arthritis), and osteoporosis (loss of bone density). Spiritual or lifestyle issues often lead to spinal problems like herniated discs or scoliosis. Tendonitis and carpal tunnel syndrome (nerve entrapment) are also common. Circulatory diseases include heart attacks (infarction), strokes (brain vascular accidents due to bleeding or blockage), and atherosclerosis (hardening of the arteries). Hypertension (high blood pressure) increases the risk of these events.