Kocaeli Health And Technology University Medical Biology and Genetics Lecture 2 2024 PDF

KOCAELİ HEALTH AND TECHNOLOGY UNIVERSITY FACULTY OF PHARMACY (ENGLISH) MEDICAL BIOLOGY and GENETICS Lecture-2 Origin and Evolution of Cells, Diversity of Life, Prokaryotes and Eukaryotes Assist. Prof. Dr. Seval ÇINAR se...

KOCAELİ HEALTH AND TECHNOLOGY UNIVERSITY FACULTY OF PHARMACY (ENGLISH) MEDICAL BIOLOGY and GENETICS Lecture-2 Origin and Evolution of Cells, Diversity of Life, Prokaryotes and Eukaryotes Assist. Prof. Dr. Seval ÇINAR [email protected] 2024 History of Life on Earth  The Origin and Evolution of Cells The current estimate for the age of the universe is approximately 13.8 billion years Our solar system formed about 4.6 billion years ago At its origin, Earth was sterile and anoxic **All present-day cells use the same genetic mechanisms. How did this first cell develop? It appears that life first emerged at least 3.8 billion years ago It was first suggested in the 1920s that simple organic molecules could form and spontaneously polymerize into macromolecules under the conditions thought to exist in primitive Earth’s atmosphere. At the time life arose, the atmosphere of Earth is thought to have contained little or no free oxygen, instead consisting principally of CO2 and N2. Such an atmosphere provides reducing conditions in which organic molecules, given a source of energy such as sunlight or electrical discharge, can form spontaneously.  Phospholipids are the basic components of biological membranes. The first cell is presumed to have arisen by the enclosure of self-replicating RNA in a membrane composed of phospholipids RNA (Ribonucleic acid) is generally believed to have been the initial genetic system, and an early stage of chemical evolution is thought to have been based on self-replicating RNA molecules →RNA world !! RNA can catalyze its own replication. DNA eventually replaced RNA as the genetic material.  →The evolution of metabolism Cellular life, in the form of Bacteria and Archaea (Prokaryotes), was emerged on Earth by 3.8 billion years ago The first cells obtained energy by glycolysis. In the initially anaerobic atmosphere of Earth, the first energy-generating reactions presumably involved the breakdown of organic molecules in the absence of oxygen. These reactions are likely to have been a form of presentday glycolysis—the anaerobic breakdown of glucose, with the net energy gain of two molecules of ATP The development of photosynthesis is generally thought to have been the next major evolutionary step Oxidative metabolism evolved: a mechanism for generating energy from organic molecules that is much more efficient than anaerobic glycolysis The use of H2O in photosynthetic reactions produces the by-product free O2; this mechanism is thought to have been responsible for making O2 abundant in Earth’s atmosphere, which occurred about 2.4 billion years ago. →The origin of Eukaryotes It is likely that some other organelles evolved from invaginations of the plasma membrane. For example, the nucleus is thought to have been formed by invaginations of the plasma membrane that surrounded the nucleoid of a prokaryotic ancestor. At least two organelles of eukaryotes, mitochondria and chloroplasts, arose by endosymbiosis (one cell living inside another) A symbiotic relationship where one organism lives inside the other is known as endosymbiosis. !! Mitochondria and chloroplasts originated by endosymbiosis. endosymbiosis →The origin of Eukaryotes mitochondria are thought to have evolved from aerobic bacteria living inside the archaeal ancestor of eukaryotes chloroplasts evolved from photosynthetic bacteria, such as cyanobacteria, living inside the ancestor to plants and green algae. The mitochondrial and chloroplast DNAs are replicated each time the organelle divides, and the genes they encode are transcribed within the organelle and translated on organelle ribosomes. Mitochondria and chloroplasts thus contain their own genetic systems, which are distinct from the nuclear genome of the cell and are more closely related to the genomes of bacteria than to the nuclear genomes of eukaryotes. Multicellular organisms then evolved from associations between unicellular eukaryotes, and division of labor led to the development of the many kinds of specialized cells that make up present-day plants and animals.  The three domains of cellular organisms are Bacteria, Archaea, and Eukarya. Bacteria and Archaea appeared first and Eukarya evolved later, diverging from the Archaea. LUCA, last universal common ancestor. THE CELLS  Cells are the basic structural, functional, and biological units of all living organisms. NOTE: All cells have a cytoplasmic membrane, cytoplasm, ribosomes, DNA genome. 1.Prokaryotic Cells: Structure: Prokaryotic cells are a type of unicellular organism. Generally smaller and simpler than eukaryotic cells. Lack a nucleus and membrane-bound organelles. Example: Prokaryotes include cells of two domains, the Archaea and the Bacteria The nucleoid is a region within the prokaryotic cell that contains all or most of the genetic material. The nucleoid lacks a membrane and is located within the cytoplasm Types of Prokaryotes: 1.Bacteria: The most well-known group of prokaryotes, with species that can be found in virtually every environment on Earth. They can be beneficial, such as those in human gut flora, or pathogenic, causing diseases. 2.Archaea: Another category of prokaryotes, often found in extreme environments (e.g., hot springs, salt lakes). They have distinct biochemical and genetic characteristics that differentiate them from bacteria.  2.Eukaryotic Cells: Structure: Larger and more complex. Contain a nucleus and various organelles Eukaryotes include cells of one domain: Eukarya. Types of Eukaryotic Cells: 1.Protists: A diverse group that can be unicellular or multicellular, including organisms like amoebas and algae. 2.Fungal Cells: Have a cell wall made of chitin; they can be unicellular (like yeast) or multicellular (like mushrooms). 3.Plant Cells: Have a rigid cell wall made of cellulose, chloroplasts for photosynthesis, and a large central vacuole. 4.Animal Cells: Lack a cell wall and chloroplasts; they have centrioles and lysosomes.  Prokaryotes and Eukaryotes Prokaryotes Eukaryotes Domain Archaea and Bacteria Eukarya Diameter of a typical cell 1-10 μm 10-100 μm Chromosome Single circular DNA molecule Multiple linear DNA Molecules, Circular mitochondrial DNA, Circular chloroplast DNA Ribosomes 70S 80S (bound to endoplasmic reticulum or free in the cytoplasm) (70S ribosome in mitochondria and chloroplast) Plasmids Present Rare Nucleus Absent Present Membrane-enclosed organelle Absent Present Reproduction Prokaryotic cells reproduce sexually or asexually asexually primarily through binary fission, where a single cell divides into two identical daughter cells. Cell wall Peptidoglycan Cellulose in plants, Chitin in fungi, cell wall absent in animal cells Common Cellular Components in Eukaryotes 1.Cell Membrane: A lipid bilayer that surrounds the cell, providing structure and controlling the movement of substances in and out (selectively permeable). 2.Nucleus: Contains the cell's genetic material (DNA) and is responsible for regulating activities such as growth and metabolism. 3.Cytoplasm: The gel-like substance within the cell membrane that contains organelles, where various cellular processes occur. 4.Ribosomes: Sites of protein synthesis, where amino acids are assembled into proteins. 5.Cytoskeleton: Eukaryotic cells have a well-developed cytoskeleton made up of microtubules, microfilaments, and intermediate filaments. The cytoskeleton provides structural support, aids in cell movement, and facilitates intracellular transport.  Common Cellular Components in Eukaryotes 6.Membrane-bound Organelles: 1. Mitochondria: Often referred to as the "powerhouses" of the cell, mitochondria are responsible for producing ATP through cellular respiration. 2. Endoplasmic Reticulum (ER): The ER is involved in the synthesis of proteins (rough ER) and lipids (smooth ER). Rough ER: Studded with ribosomes; involved in protein synthesis and processing. Smooth ER: Lacks ribosomes; involved in lipid synthesis and detoxification. 3. Golgi Apparatus: This organelle modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles. 4. Lysosomes: Containing digestive enzymes, lysosomes are involved in breaking down waste materials and cellular debris. 5. Peroxisomes: These organelles contain enzymes that metabolize fatty acids and detoxify harmful substances. 6. Vacuoles: Storage organelles; larger in plant cells for storing nutrients and waste products. NUCLEUS The nucleus is a membrane-bound organelle found in eukaryotic cells Often called the "control center" of the cell Typically the largest organelle in animal cells Contains genetic material (DNA) that directs cellular activities Structure of the Nucleus Double membrane: Outer and inner nuclear membranes Nuclear pores: Allow selective passage of molecules Nucleoplasm: Gel-like substance within the nucleus Chromatin: DNA and associated proteins Nucleolus: Site of ribosome production (A) An electron micrograph of a nucleus. (B) An electron micrograph illustrating the continuity of the outer nuclear membrane with the endoplasmic reticulum. (C) Schematic of the nuclear envelope. Nuclear Envelope Double-layered membrane surrounding the nucleus Outer membrane continuous with endoplasmic reticulum Inner membrane lined with nuclear lamina Functions: Protects genetic material Regulates nuclear-cytoplasmic transport  By separating the genome from the cytoplasm, the nuclear envelope allows gene expression to be regulated by mechanisms that are unique to eukaryotes. DNA replication, transcription, and RNA processing all take place within the nucleus, with only the final stage of gene expression (translation) localized to the cytoplasm. Whereas prokaryotic mRNAs are translated while their transcription is still in process, eukaryotic mRNAs undergo several forms of posttranscriptional processing before being transported from the nucleus to the cytoplasm. The presence of a nucleus thus allows gene expression to be regulated by posttranscriptional mechanisms, such as alternative splicing.  Nuclear Lamina Mesh-like network of intermediate filaments Lines the inner nuclear membrane Composed of fibrous proteins called lamins, along with associated proteins. Plant cells have a similar fibrous network comprising unrelated proteins. Lamins are a class of intermediate filament proteins; the other classes are found in the cytoskeleton Functions: Provides structural support Anchors chromatin and nuclear pore complexes Involved in gene regulation and DNA replication  Nuclear Pore Complex (NPC) Large protein structure embedded in the nuclear envelope Composed of approximately 30 different proteins called nucleoporins Electron micrograph showing nuclear pores Acts as a selective gateway for molecular traffic Allows passive diffusion of small molecules (