Biology 1 PDF

# UNIDAD I ## BIOLOGÍA GENERAL ### 1.1. INTRODUCCIÓN - In nature, we find inanimate or inorganic beings and living beings or organic beings. - Biology is the science that studies living beings. - The term biology comes from the Greek "bios" which means life and "logos" which means study or science....

# UNIDAD I ## BIOLOGÍA GENERAL ### 1.1. INTRODUCCIÓN - In nature, we find inanimate or inorganic beings and living beings or organic beings. - Biology is the science that studies living beings. - The term biology comes from the Greek "bios" which means life and "logos" which means study or science. - The term was introduced in Germany in 1800 and popularized by the French naturalist Jean Baptiste de Lamarck in order to bring together a growing number of disciplines that referred to the study of living forms. - We can define biology as the branch of science that studies the structure of living beings, their vital functions, their evolution, their relationships with other living beings, and with the environment in which they develop. - The importance of biology for human beings is enormous. - The general laws of biology are applied in the solution of a variety of problems in many branches of the economy. - Thanks to the knowledge of heredity and mutation, successes have been achieved in agriculture, new species of highly productive crops, livestock, the production of antibiotics. - This process will play an important role in the face of a growing population, new diseases, polluting industry, and scientific justification is important for the rational use of natural resources, the source of our existence. ### 1.2. SUBDIVISIONS OF BIOLOGY - Living beings can be studied from many different points of view, biology is actually a set of different sciences called biological sciences: * **Botany**: studies plants. * **Zoology**: studies animals. * **Microbiology**: studies microorganisms. * **Anatomy**: studies organic structures and the relationship between them. * **Cytology**: studies cells. * **Histology**: studies tissues. * **Physiology**: studies vital processes and the functions of different organs and tissues. * **Biochemistry**: determines the chemical composition of living matter and the changes that occur. * **Embryology**: studies the development of an organism from fertilization to birth. * **Genetics**: deals with the phenomena of heredity and its variations. * **Taxonomy or Systematics**: studies the classification of living beings. * **Ecology**: studies the relationship of an organism with its environment. * **Paleontology**: studies fossil organisms. * **Parasitology**: studies parasites. ### 1.3. CHEMICAL COMPOSITION OF LIVING MATTER - The chemical composition of living matter is extraordinarily complex. - There are four chemical elements that are found in the greatest proportion as part of living beings, they are **oxygen, carbon, hydrogen, and nitrogen**. - These four elements make up over 90% of most living beings. - The remaining percentage is made up of elements such as phosphorus, sodium, zinc, sulfur, calcium, potassium, magnesium, and iron, among others. - The chemical compounds that make up living matter are divided into two main groups: **inorganic compounds**, among them water and minerals, and **organic compounds or biomolecules**, made up of **carbohydrates, lipids, proteins, vitamins, and nucleic acids**. - Of the total components of cells, water is the component that is found in the greatest amount (75-85%), between 2 and 3% are inorganic salts, and the rest are organic compounds derived from carbon atoms, which represent the molecules of life. #### 1.3.1. Carbohydrates - Carbohydrates or carbohydrates are compounds made up of carbon, hydrogen, and oxygen (CHO). - They are classified according to the number of monomers they contain: **monosaccharides, disaccharides, oligosaccharides, and polysaccharides.** - Their main function is that they constitute the main source of energy for the cell, and they are also important structural components of the cell wall and of intercellular substances. - They are also part of other compounds such as nucleic acids and glycoproteins. * **Monosaccharides**: are simple sugars with a general formula Cn(H2O)n. * According to the number of carbon atoms, they are classified into trioses, pentoses, and hexoses. * Some pentoses are ribose and deoxyribose, present in nucleic acids. * Some important hexoses are glucose, galactose, fructose, and mannose. * **Disaccharides**: are sugars formed by the union of two hexoses, with the loss of a water molecule. * Their general formula is C12H22O11. * The most important are lactose (milk sugar), formed by glucose and galactose; sucrose (cane sugar), formed by glucose and fructose; maltose (malt sugar), formed by two glucoses. * **Oligosaccharides**: are found linked to lipids and proteins, so they are part of glycolipids and glycoproteins in the organism. * **Polysaccharides**: result from the union of many monosaccharides with the corresponding loss of a water molecule. * By complete hydrolysis, they give rise to monosaccharide molecules. * The most important are **starch and glycogen**, which represent food reserves in plant and animal cells, respectively. * Another relevant polysaccharide is **cellulose**, the most important structural element in the plant cell wall. #### 1.3.2. Lipids - They are compounds formed by carbon, hydrogen, and oxygen (CHO), although in different proportions than these components appear in sugars. - They differ from other types of organic compounds because they are not soluble in water (hydrophilic) but in organic solvents (alcohol, ether).  - They are important because they constitute energy reserves and are structural elements of cell membranes. - The most common lipids in the cell are **triglycerides, phospholipids, glycolipids, and steroids**. * **Phospholipids**, major components of the cell membrane. * **Triglycerides (fats and oils)**, serve as energy reserves in animal and plant cells. * **Steroids** are complex molecules where **cholesterol** and **hormones** are found. #### 1.3.3. Proteins - They are organic macromolecules formed by carbon, hydrogen, oxygen, and nitrogen, mainly (CHON), although some have phosphorus, sulfur, iron, and copper. - Structurally, they are chains of amino acids linked together by peptide bonds. - They intervene in various essential vital functions, such as metabolism, muscle contraction, or the immune response. * According to the shape of the protein, they can be classified into two types: fibrous and globular. * **Fibrous proteins**: such as collagen, keratin, fibrinogen, and myosin. * **Collagen**: forms part of bones, skin, tendons, and cartilage. * **Keratin**: makes up the outer layer of the skin, hair, and nails in humans and scales, hooves, horns, and feathers in animals. * **Fibrinogen**: is the plasma protein of the blood responsible for coagulation. * **Myosin**: is responsible for muscle contraction. * **Globular proteins**: such as albumin, globulin, casein, hemoglobin, all enzymes, protein hormones, and antibodies. * **Albumins and globulins**: are soluble proteins abundant in animal cells, the serum blood, milk, and eggs. * **Hemoglobin**: is a respiratory protein that transports oxygen through the body; it is responsible for the intense red color of red blood cells. * **Enzymes**: are proteins that combine with other substances, called substrates, to catalyze the numerous chemical reactions of the organism. * **Protein hormones**: are secreted by endocrine glands, such as insulin by the pancreas, thyroxine by the thyroid. * **Antibodies**: are elements of the immune defense, they group together thousands of different proteins that are produced in the serum blood in response to antigens (substances or organisms that invade the body). #### 1.3.4. Nucleic Acids - They are macromolecules made up of units called nucleotides. - They transmit hereditary information and determine what proteins the cell produces. - There are two types of nucleic acids: DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). * **Deoxyribonucleic acid (DNA)**, is the genetic material of all cellular organisms and almost all viruses. * **Ribonucleic acid (RNA)**, is the genetic material of certain viruses (RNA viruses) and, in cellular organisms, is the molecule that directs the intermediate stages of protein synthesis. - A nucleotide is composed of a nitrogenous base (which can be purine or pyrimidine), a five-carbon sugar (ribose or deoxyribose), and a phosphate group. - There are fundamental differences between DNA and RNA: | Feature | Deoxyribonucleic acid (DNA) | Ribonucleic acid (RNA) | |---|---|---| | Localization | Mainly in the nucleus (Also in mitochondria and chloroplasts) | Mainly in the cytoplasm (Also in nucleolus and chromosomes) | | Pyrimidine bases | Cytosine Thymine | Cytosine Uracil | | Purine bases | Adenine Guanine | Adenine Guanine | | Pentose | Deoxyribose | Ribose | | Role in the cell | Genetic information | Protein synthesis | | Structure | Double helix, two long intertwined chains, one over the other. | A single chain and smaller. | ### 1.4. STRUCTURE AND PHYSIOLOGY OF THE CELL #### 1.4.1. The Cell - It is the basic unit of anatomical, physiological, and genetic structure of living beings. - It is the fundamental unit of the organism, varying in size and shape depending on the function it performs. - It consists of an external envelope that surrounds the cytoplasm called the cell membrane, in the central part (usually) the nucleus is found, which is surrounded by the nuclear membrane. * **Cell membrane**: is the outer membrane that limits the cell and separates its components from the extracellular fluid or external medium. * **Cell wall**: is a rigid structure that surrounds plant cells and bacteria. Animal cells do not have it. * **Plasma membrane**: is present in all cells without exception. Its function is to protect the cell and regulate the exchange between the cell and the surrounding medium, its function is permeability. Chemically, it is made up of a phospholipid double layer, "fluid mosaic model". * **Cytoplasm**: represents the internal medium of the cell: it is colloidal in appearance, transparent, and translucent. It contains organelles such as ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, centrioles, microtubules, lysosomes, etc. * **Nucleus**: Usually located in the central part, surrounded by the nuclear membrane, in it is found the genetic material DNA (deoxyribonucleic acid) which carries the hereditary message. Its function is to regulate the development and reproduction of the cell. - Functions of cellular organelles: * **Rough endoplasmic reticulum**: synthesis and transport of proteins. * **Smooth endoplasmic reticulum**: synthesis of lipids, carbohydrates, and transport of substances. * **Golgi apparatus**: intervenes in cell secretion and in the production of lysosomes. * **Lysosomes**: release hydrolytic enzymes. * **Peroxisomes**: carry out metabolic reactions and degrade hydrogen peroxide. * **Vacuole**: storage of reserve substances or cellular waste. * **Mitochondria**: cellular respiration and production of ATP energy. * **Plastids**: photosynthesis and storage of nutrients such as starch, oils, and proteins. * **Nucleolus**: intervenes in the formation of ribosomes. * **Centrioles**: formation and organization of microtubules that make up the spindle fibers in nuclear division. * **Ribosomes**: protein synthesis. * **Microtubules**: provide structural support. * **Cilia**: movement of materials outside the cell. * **Flagella**: cellular locomotion in microorganisms and male gametes. - In order to observe the cell, it is necessary to use mechanical instruments such as microscopes, which magnify the image several hundred times (depending on the type of microscope). - There are cells of very diverse shapes and sizes. - The smallest bacterial cells are less than a micrometer (1 micrometer is equal to one millionth of a meter) in length. - Plant cells are usually more than 100 micrometers long (reaching 2-5 cm in green algae) and have a polygonal shape because they are enclosed in a rigid cell wall. - Animal tissue cells are usually compact, between 10 and 20 micrometers in diameter, and have a deformable and almost always very folded surface membrane. #### **Prokaryote: cyanobacterium** - Bacteria and other prokaryotic cells lack most of the internal structures of eukaryotic cells. - Thus, the cytoplasm of prokaryotes is surrounded by a plasma membrane and a cell wall (as in plant cells), but there is no nuclear membrane and, therefore, no differentiated nucleus. - The circular DNA molecules are in direct contact with the cytoplasm. - They also lack mitochondria, the endoplasmic reticulum, chloroplasts, and the Golgi apparatus. #### **Eukaryote: animal cell** - The nucleus controls the activities that take place in the cell and contains the genetic material. - Mitochondria are organelles responsible for energy production. - Ribosomes, which can be found free floating in the cytoplasm or attached to the rough endoplasmic reticulum, produce proteins. - The Golgi apparatus modifies, groups, and distributes proteins, while lysosomes contain enzymes that digest certain substances. - The cell is surrounded by a lipid membrane that selectively allows some substances to pass into or out of the cell. ### 1.4.2. Classification of organisms and cells. - Living organisms were originally divided by Carl von Linnaeus into two kingdoms: Plantae (Plants) and Animalia (Animals). - However, the use of the microscope revealed the existence of a huge diversity of unicellular organisms whose anatomical and physiological characteristics did not fit easily into this two-kingdom classification system.  - This great diversity led the German biologist Ernst Haeckel to propose, in the 19th century, the creation of a third kingdom of living beings, Protista, which included those unicellular organisms with characteristics intermediate between plants and animals. - Whittaker proposed in 1969 the classification into five kingdoms that was later modified by the biologists Lynn Margulis and Marlene Schwartz. - The five-kingdom classification system that is most widely accepted is made up of the following five groups, which are detailed in the following table: | Kingdom | Main characteristics | Examples | |---|---|---| | Moneran | Prokaryotic unicellular organisms. | Bacteria | | Protist | Eukaryotic unicellular organisms and their most immediate descendants. | Algae, protozoa | | Fungi | Heterotrophic organisms that obtain their food by absorption. They do not perform photosynthesis. The cell wall usually contains chitin. | Yeasts, mushrooms | | Plant | Immobile organisms that perform photosynthesis. Cell wall composed of cellulose.| Mosses, ferns, trees | | Animal | Motile organisms without a cell wall. They ingest food. They have differentiated tissues.| Mollusks, fish, birds| #### **Cellular organization in prokaryotes and eukaryotes** - The table above shows that only prokaryotic cells (bacteria and blue-green algae) are prokaryotic cells, while all other members are organisms composed of eukaryotic cells. - **Eukaryotic cells**: are organisms whose cells have true nuclei, that is, separated from the cytoplasm by a well-differentiated double membrane. - **Prokaryotic cells**: are organisms whose nuclei are not enclosed by a nuclear membrane. All prokaryotes are unicellular organisms, most of them are bacteria, while eukaryotes can be unicellular, which include protozoa, and multicellular, which include fungi, plants, and metazoans. - The main difference between these two cell types is that prokaryotes do not have a nuclear envelope. ### 1.5. CELL DIVISION #### 1.5.1. Binary division: - The parent cell gives rise to two daughter cells that are identical, it is also called bipartition, it is when the cell begins to lengthen and then in the middle of it it presents a constriction, at the same time the same process is noticed in the nucleus. #### 1.5.2. Budding: - Also called budding, it consists of the appearance of a bulge or bud in a part of the cell surface. - Where part of the cytoplasm migrates, at the same time that the nucleus is introduced and is divided into two nuclei, one of which is left in the bud. - This type of cell division is common in yeasts and some ciliates. #### 1.5.3. Sporulation: - Consists of the formation of multiple daughter cells inside the parent cell, which are released by destruction of the membrane of this. - This type of cell division is observed in fungi, algae, and sporozoans. Sporulation is a type of multiple fission cell division. #### 1.5.4. Mitosis - It is an indirect asexual division. - It is the process by which daughter cells with the same number of chromosomes are generated, which are identical to each other and to their progenitors. - Somatic cells divide by mitosis. - The phases of mitosis are: * **Prophase**: The chromatin condenses to form chromosomes. * The nucleolus disappears. * The centrioles surrounded by the aster move towards the poles and form the mitotic spindle (acromotic spindle). * The nuclear membrane disintegrates. * **Metaphase**: Chromosomes attach to the spindle fibers through their centromeres and align in the middle zone, forming the equatorial plate. * **Anaphase**: The centromeres and the chromatids separate and migrate towards the poles. * **Telophase**: The chromosomes condense again, the nuclear membrane is restored from the endoplasmic reticulum. * The nucleoli reappear. * The mitotic spindle disappears. * Cytokinesis of the cytoplasm occurs in animal cells by constriction, and in plant cells the fragmoplast appears, which divides the cell, resulting in two diploid daughter cells. #### 1.5.5. Meiosis - It is an indirect asexual division, by which a reduction in the normal diploid number of chromosomes occurs, generating four haploid daughter cells that differ genetically from each other and from their ancestor. - Gametes or sex cells are generated by meiosis. - It consists of two divisions: the first and second meiotic divisions. - The first meiotic division is reductional and consists of: * **Prophase I**: * **Leptotene**: Chromosomes are distinguished as long filaments similar to a string of pearls; each pearl represents a chromomere. Each chromosome comprises two chromatids in "bouquet" arrangement. * **Zygotene**: Homologous chromosomes pair up in a process called synapsis. * **Pachytene**: Pairing is completed. Chromosomes contract longitudinally and shorten. Tetrads are formed, composed of two homologous chromosomes in close union and four chromatids. * **Diplotene**: Homologous chromosomes begin to separate, but the separation is not complete because the homologous chromosomes remain united by points of exchange called chiasmata. * Chiasmata are an expression of a genetic phenomenon called CROSSING OVER or recombination. * Chromosome segments with genes are exchanged between homologous chromosomes. * **Diakinesis**: Homologous chromosomes remain united at their ends (terminalization); the nucleolus disappears. * **Metaphase I**: Chromosomes are arranged on the equatorial plane. * **Anaphase I**: The sister chromatids of each homologue go to the respective poles. * **Telophase I**: Two haploid cells are formed. - The second meiotic division is equational, and consists of: * **Prophase II**: Formation of the spindle fibers * **Metaphase II**: Chromosomes are arranged on the equatorial plane. * **Anaphase II**: Sister chromatids migrate towards opposite poles. * **Telophase II**: Four haploid cells are formed in which each one has one chromatid. #### Differences between mitosis and meiosis - Mitosis is an equational process, its resulting cells have the same number of chromosomes, they are diploid, structurally they are identical to the parent cell, and it occurs in somatic cells. - Meiosis is a reductional process, its resulting cells have half the number of chromosomes as the parent cell, they are haploid, they are different, structurally, from the parent cell. It occurs in the gonads.