Summary
Highlights
The video introduces the 'Life Science Biology' topic for the 2026 TYT exam, emphasizing a comprehensive review of core biological concepts. It highlights the importance of analyzing past exam questions to understand ÖSYM's question styles. The main common characteristics of living things discussed include cellular structure, nutrition, excretion, respiration, movement, adaptation, metabolism, response to stimuli, organization, and reproduction. The video also stresses the importance of recognizing alternative terminologies used in exams.
Cellular structure is presented as a fundamental characteristic, defining a cell as the smallest structural and functional unit of life. Organisms can be unicellular or multicellular. Cells are classified into prokaryotes (lacking a nucleus and membrane-bound organelles) and eukaryotes (having a nucleus and membrane-bound organelles). Nutrition involves obtaining energy from food. Organisms are categorized as producers (autotrophs), consumers (heterotrophs), or both (e.g., Euglena). Autotrophs can be photoautotrophs (using light for photosynthesis) or chemoautotrophs (using chemical energy for chemosynthesis).
Respiration is crucial for producing ATP to sustain life. It can be aerobic (with oxygen) or anaerobic (without oxygen), and fermentation is another ATP production mechanism. Excretion is the process of removing metabolic waste products from the body or cells. It's important to note that digestion is not a common characteristic of all living things, unlike excretion. Movement refers to changes in position or location, which can be passive or active. All living things move, but not all exhibit active movement (e.g., plants).
Living organisms respond to internal and external physical and chemical stimuli. Metabolism encompasses all chemical reactions in a living organism, divided into anabolism (synthesis, building up) and catabolism (breakdown, breaking down). Basal metabolism is defined as the minimum energy required to sustain life. Homeostasis, or internal balance, is the ability to maintain stable internal conditions despite external changes, such as regulating blood sugar levels.
Adaptation refers to inherited traits that enhance an organism's survival and reproduction in its environment. Organization describes how living things are structured in a hierarchical manner, from atoms to the entire organism. Growth in unicellular organisms involves an increase in size and mass, while in multicellular organisms it also includes an increase in cell number. Development is the maturation of tissues and organs to perform their functions. Reproduction is the process of creating new individuals, essential for the continuation of the species but not strictly necessary for an individual's survival. It can be asexual or sexual.
The 'HASRET' acronym (Hücre zarı, ATP, Sitoplazma, Ribozom, Enzim, DNA, RNA) represents structures common to all living things. All organisms perform protein synthesis due to the ubiquity of ribosomes. The video then transitions to basic biological compounds, dividing them into inorganic (water, minerals, acids, bases, salts) and organic (carbohydrates, lipids, proteins, enzymes, hormones, vitamins, nucleic acids, ATP) molecules. Inorganic compounds are not typically energy sources, except for chemosynthesis.
Water is a crucial inorganic compound due to its properties as a solvent, its role in waste removal, thermoregulation (sweating), and as a medium for enzymatic activity (requiring at least 15% water). Its cohesive and adhesive properties are important for transport in plants and animals. Water's freezing property insulates aquatic life. Minerals are essential inorganic regulators, participating in enzyme structure as cofactors and contributing to various bodily functions, but do not provide energy.
The concepts of monomers (small building blocks) and polymers (large molecules formed from monomers) are explained. Monomers are small enough to pass through cell membranes without digestion, while polymers are not. Dehydration synthesis reactions (anabolism) involve joining monomers to form polymers, releasing water. Hydrolysis reactions (catabolism) involve breaking down polymers into monomers, consuming water. Not all reactions that use or produce water are necessarily hydrolysis or dehydration, respectively.
Carbohydrates are organic molecules that serve as primary energy sources, structural components, and play a role in cell recognition. They are not regulatory. They contain glycosidic bonds. They are classified into monosaccharides (single sugars), disaccharides (two sugars), and polysaccharides (many sugars). Monosaccharides like glucose, fructose, and galactose are monomers. Disaccharides (maltose, lactose, sucrose) and polysaccharides (starch, glycogen, cellulose, chitin) are larger molecules.
Monosaccharides include 5-carbon sugars (ribose, deoxyribose, found in nucleic acids) and 6-carbon sugars (glucose, galactose, fructose). Disaccharides are formed by combining two monosaccharides (e.g., glucose + glucose = maltose; glucose + galactose = lactose; glucose + fructose = sucrose). Polysaccharides are large polymers of glucose. Starch is a plant energy storage, glycogen is animal/fungal/bacterial energy storage, cellulose is plant cell wall structural, and chitin is found in insect exoskeletons and fungal cell walls. Chitin is unique among carbohydrates for containing nitrogen.
Lipids are the second energy source used after carbohydrates during prolonged fasting, providing more energy per gram due to their higher hydrogen content. They are large molecules but not true polymers. They contain ester bonds (except for steroids). Lipids are vital for cell membrane structure and as regulatory molecules. Key types include triglycerides (storage fats, formed from glycerol and three fatty acids), phospholipids (structural, forming cell membranes), and steroids (regulatory, sex hormones, cholesterol).
Proteins are fundamental structural components and are the third energy source used. They are polymers of amino acids linked by peptide bonds. The sequence, number, and arrangement of amino acids determine protein diversity. Amino acids have a central carbon, an amino group, a carboxyl group, and a variable 'R' group. Proteins exist in four structural levels: primary (linear sequence), secondary (local folding), tertiary (3D shape), and quaternary (multiple polypeptide chains). Functional proteins primarily exist in secondary, tertiary, or quaternary structures.
Denaturation is the irreversible or reversible alteration of a protein's 3D structure, leading to loss of function, caused by factors like heat or extreme pH. Renaturation is the process of a denatured protein regaining its original structure and function. Notably, denaturation affects the higher-order structures (secondary, tertiary, quaternary) but generally preserves the primary structure (peptide bonds and amino acid sequence).
Enzymes are biological catalysts that speed up biochemical reactions by lowering activation energy. Most enzymes are proteins. They are reusable and highly specific to their substrates, following a 'lock and key' mechanism. Enzymes generally work reversibly (except digestive enzymes) and in teams, where the product of one enzyme-catalyzed reaction can be the substrate for another. Enzymes can be active (suffix '-az') or inactive (proenzymes, suffix '-ojen').
Enzymes can be simple (protein-only) or conjugated (protein part - apoenzyme - plus a non-protein helper part - cofactor). Cofactors can be inorganic (minerals) or organic (vitamins, called coenzymes). Factors influencing enzyme activity include temperature (optimum temperature, denaturation at high temps), pH (optimum pH), substrate concentration, enzyme concentration, and substrate surface area. An important concept is that enzymes increase reaction rate but do not change the total amount of product formed; they only affect the rate at which it forms.
Vitamins are organic, essential (mostly), non-energy-providing, and regulatory molecules. They act as coenzymes. Vitamins are categorized into water-soluble (B, C) and fat-soluble (A, D, E, K). Deficiencies can lead to specific health issues (e.g., night blindness from Vit A, scurvy from Vit C). Hormones are organic regulatory molecules, secreted by specific cells and acting on target cells. Both plant and animal hormones play crucial roles in growth, development, and metabolic regulation.
ATP is the primary energy currency of the cell, an organic molecule. It's produced and consumed only by living cells, and all living things utilize ATP. ATP cannot be stored or transferred between cells; each cell produces its own. ATP synthesis (phosphorylation) involves adding an inorganic phosphate to ADP, releasing water. ATP consists of adenine, ribose sugar, and three phosphate groups. The high-energy phosphate bonds store chemical energy for cellular processes. Reactions that release energy are exergonic (e.g., respiration), while reactions that require energy are endergonic (e.g., muscle contraction).
Nucleic acids (DNA and RNA) are found in all living things and carry genetic information. They are polymers of nucleotides. A nucleotide consists of a nitrogenous base, a 5-carbon sugar (ribose in RNA, deoxyribose in DNA), and a phosphate group. Nitrogenous bases are adenine, guanine (purines), and cytosine, thymine (pyrimidines in DNA), or uracil (pyrimidine in RNA). Glycosidic bonds link the base to the sugar, and ester bonds link the sugar to the phosphate. Phosphodiester bonds connect nucleotides within a single strand, while weak hydrogen bonds connect complementary bases between strands.
DNA is a double-stranded helix. Adenine pairs with thymine (two hydrogen bonds), and guanine pairs with cytosine (three hydrogen bonds). The number of adenine equals thymine, and guanine equals cytosine in a DNA molecule. DNA replication (self-duplication) is semi-conservative; helicase separates the strands, and DNA polymerase synthesizes new complementary strands. The 'Kedi Geni' (Cat Gene) acronym (Kromozom, DNA, Gen, Nükleotit) helps remember the hierarchical organization of genetic material from largest to smallest.
RNA is typically single-stranded. It contains adenine, uracil, guanine, and cytosine, with ribose as its sugar. RNA synthesis (transcription) is catalyzed by RNA polymerase. There are three main types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). rRNA is the most abundant and is a component of ribosomes. mRNA generally lacks hydrogen bonds, while tRNA and rRNA can form them within their single strand due to folding. Proteins and nucleic acids are synthesized according to genetic codes (DNA template).