Cell Structure and Organisation PDF

Cell Biology DR. AAINAA AMIR Cell Structure and Function Overview of Cells Definition The cell is the basic structural, functional, and biological unit of all living organisms Types of Cells Prokaryotic Cells: Simple, smaller cells without a nucleus (e.g., bacteria). Eukary...

Cell Biology DR. AAINAA AMIR Cell Structure and Function Overview of Cells Definition The cell is the basic structural, functional, and biological unit of all living organisms Types of Cells Prokaryotic Cells: Simple, smaller cells without a nucleus (e.g., bacteria). Eukaryotic Cells: Complex, larger cells with a nucleus (e.g., plant and animal cells). Major Components of a Cell Major Components of a Cell Cell Membrane Structure: Phospholipid bilayer with embedded proteins (Plasma Membrane) Function: Controls the movement of substances in and out of the cell; provides protection and support. Cytoplasm Structure: Jelly-like substance that fills the cell, composed mostly of water, salts, and proteins. Function: Site of many metabolic activities; holds organelles in place. Nucleus Structure: Membrane-bound organelle containing DNA Function: Control cell activities; stores genetic information. Major Components of a Cell Mitochondria Structure: Double-membrane organelle with inner folds called cristae. Function: Powerhouse of the cell; produces energy (ATP) through cellular respiration. Ribosomes Structure: Small particles made of RNA and proteins; found free in the cytoplasm or attached to the endoplasmic reticulum. Function: Site of protein synthesis.  Major Components of a Cell Endoplasmic Rough ER: Studded with Reticulum Types: ribosomes; involved in (ER) protein synthesis and modification. Smooth ER: Lack ribosomes; involved in lipid synthesis and detoxification processes. Function: Acts as a transport network for molecules destined for specific modifications and destinations.  Major Components of a Cell Golgi Apparatus Structure: Stacks of flattened membranous sacs. Function: Modifies, sorts, and packages proteins and lipids for storage or transport out of the cell.  Major Components of a Cell Lysosomes (in animal Structure: Membrane-bound cells) organelles containing enzymes. Function: Breaks down waste materials and cellular debris; involved in cell digestion and recycling. Major Components of a Cell Chloroplasts (in plant Structure: Double-membrane cells) organelles containing chlorophyll. Function: Site of photosynthesis; converts solar energy into chemical energy (glucose).  Major Components of a Cell Vacuoles Structure: Large, membrane-bound sacs. Function: Stores nutrients, waste products, and helps maintain turgor pressure in plant cells. Major Components of a Cell Cytoskeleton Structure: Network of protein filaments (microfilaments, intermediate filaments, microtubules). Function: Maintains cell shape, provides mechanical support, and aids in cell movement and division. Specialized Cell Structures Cilia and Flagella Structure: Hair-like structures (cilia) or tail-like structures (flagella) extending from the cell surface. Function: Movement of the cell or movement of substances across the cell surface. Cell Wall (in plant cells, fungi, and some prokaryotes) Structure: Rigid layer outside the cell membrane, primarily composed of cellulose in plants. Function: Provides structural support and protection; maintains cell shape. Centrioles (in animal cells) Structure: Cylindrical structures composed of microtubules. Function: Play a role in organizing microtubules during cell division (mitosis).  Functions of Cells The set of life- sustaining chemical reactions within the cells, including Metabolism catabolism (breaking down molecules) and anabolism (synthesizing new molecules). Functions of Cells The process by which cells build proteins based on Protein genetic instructions, involving Synthesis transcription (in the nucleus) and translation (at the ribosomes).  Functions of Cells Cells convert nutrients into energy in the form of ATP , primarily through Energy Production processes like glycolysis, the Krebs cycle, and oxidative phosphorylation in the mitochondria. Functions of Cells Cells replicate their DNA and divide to produce Cell new cells through Division mitosis (for growth and repair) or meiosis (for reproduction). Functions of Cells Cells communicate with each other through Cell signaling pathways involving receptors and Communication signaling molecules, coordinating functions and responses to the environment. Difference Between Plant and Animal Cells Plant Cells Have a cell wall, chloroplasts, and a large central vacuole. Usually rectangular or square-shaped Animal Lack a cell wall and chloroplasts; have Cells smaller, more numerous vacuoles. Usually round or irregularly shaped. Cell Organelles and Their Roles Nucleus Role Functions The control Stores genetic center of the information cell, containing Coordinates cell the cell’s DNA. activities such as growth, metabolism, protein synthesis, and cell division.  Mitochondria Role Functions Generates ATP (adenosine triphosphate) The powerhouse of the cell. through cellular respiration. Regulates cellular metabolism Plays a role in apoptosis (programmed cell death).  Ribosomes Role Functions Synthesizes The protein proteins by factories of the cell translating mRNA. Found free-floating in the cytoplasm or attached to the rough endoplasmic reticulum (RER). Endoplasmic Reticulum (ER) Types Functions Rough ER (RER): RER: Synthesizes Studded with and processes ribosomes. proteins for Smooth ER (SER): secretion or Lacks of membrane ribosomes. insertion. SER: Synthesizes lipids, detoxifies drugs and poisons, and stores calcium ions.  Golgi Apparatus The packaging Modifies, sorts, and distribution and packages center of the proteins and cell. lipids received Role Functions from the ER. Forms lysosomes. Involved in the transport of lipids around the cell. Lysosomes The digestive Contains enzymes Role Functions system of the cell. that break down waste materials, cellular debris, and foreign pathogens. Involved in autophagy (the process of digesting damaged cell parts). Peroxisomes Role Functions Breaks down fatty acids and amino acids. The detoxification centers of the cell. Detoxifies harmful substances like hydrogen peroxide. Cytoskeleton Microfilaments: Made of actin, involved in muscle contraction and cell movement. Components Intermediate filaments: Provide structural support. Microtubules: Involved in cell division, movement of organelles, and maintaining cell shape. Maintains the cell’s shape Functions Facilitates cell movement Organizes the internal structure of the cell.  Plasma Membrane The boundary that separates the cell from its environment. Role Controls the movement of substances in and out of the cell. Maintains the cell’s homeostasis. Involved in cell signaling and cell- Functions to cell-communication.  Chloroplasts (only in plant cells) Role The site of photosynthesis Functions Converts light energy into chemical energy (glucose). Contains the pigment chlorophyll, which absorbs light energy.  Vacuoles Storage and maintenance of cell tugor. Role Store nutrients, waste products, and other substances. Functions Maintains pressure within the plant cell, contributing to cell structure. Cell Wall (only in plant cells, fungi, and some prokaryotes) Role Functions Provides support and protection. Maintains the shape of plant cells. Protects against mechanical stress. Composed of cellulose in plants, chitin in fungi, and peptidoglycan in bacteria.  Centrosomes and Centrioles Organizes microtubules and provides Role structure for Facilitates cell Functions the cell. division by organizing the mitotic spindle. Ensures the proper distribution of chromosomes to daughter cells during cell division. Cell Division (Mitosis, Meiosis)  Cell Division Overview Cell division is a biological There are two main types of cell process in which a parent cell division: divides into two or more Mitosis: Division for growth, repair, and daughter cells. It is essential for asexual reproduction. growth, repair, and reproduction Meiosis: Division for sexual reproduction, leading to the formation of gametes. in organisms. Mitosis Purpose Mitosis results in the production of two genetically identical daughter cells from a single parent cell. It is used for growth, tissue repair, and asexual reproduction in some organisms. Phases of Mitosis 1. Interphase The cell prepares for division by replicating its DNA and organelles. Interphase includes three sub- phases: G1 Phase: Cell grows and performs normal functions. S Phase: DNA is replicated. G2 Phase: Cell prepares for mitosis, synthesizing necessary proteins. Phases of Mitosis 2. Prophase Chromatin condenses into visible chromosomes, each consisting of two sister chromatids. The nuclear membrane begins to disintegrate. The mitotic spindle, composed of microtubules, starts to form.  Phases of Mitosis 3. Metaphase 4. Anaphase Chromosomes Sister align at the cell’s chromatids are equatorial plane, pulled apart to known as the opposite poles of metaphase the cell by the plate. shortening of Spindle fibers spindle fibers. attach to the Each pole centromeres of receives an the identical set of chromosomes. chromosomes. Phases of Mitosis 5. Telophase Chromosomes de-condense back into chromatin. The nuclear membrane re-forms around each set of chromosomes. The mitotic spindle disassembles. Phases of Mitosis 6. Cytokinesis The cytoplasm divides, forming two separate daughter cells. In animal cells, a cleavage furrow forms to split the cell. In plant cells, a cell plate forms, leading to the creation of a new cell wall. Meiosis Meiosis consists of two successive divisions: Meiosis I and Meiosis II. Meiosis I 1. Prophase I Chromosomes condense, and homologous chromosomes pair up in a process called synapsis, forming tetrads. Crossing over occurs, where homologous chromosomes exchange genetic material, increasing genetic diversity. The nuclear membrane breaks down, and spindle fibers form. Meiosis I 2. Metaphase I Tetrads align at the metaphase plate. Spindle fibers attach to the centromeres of homologous chromosomes. Meiosis I 3. Anaphase I 4. Telophase I and Cytokinesis Homologous chromosomes Chromosomes reach the are pulled to opposite poles, and the cell divides poles, reducing the into two haploid cells. chromosome number by Each cell contains half the half. number of chromosomes, Sister chromatids remain but each chromosome still attached. consists of two chromatids. Meiosis II 1. Prophase II 2. Metaphase II Chromosomes Chromosomes align condense again. at the metaphase Spindle fibers form plate in each haploid in each of the two cell. haploid cells. Spindle fibers attach to the centromeres. Meiosis II 3. Anaphase II 4. Telophase II and Cytokinesis Sister chromatids are Chromatids reach the pulled apart to opposite poles, and nuclear poles in each cell. membranes re-form around each set of chromatids. The cells divide, resulting in four genetically unique haploid cells (gametes). Key Differences Between Mitosis and Meiosis Chromosome Number: Mitosis produces diploid cells (2n), while meiosis produces haploid cells (n). Genetic Diversity: Mitosis results in genetically identical cells, whereas meiosis increases genetic variation through crossing over and independent assortment. Number of Divisions: Mitosis involves one division, producing two cells. Meiosis involves two divisions, producing four cells. Function: Mitosis is used for growth, repair, and asexual reproduction, while meiosis is used to produce gametes for sexual reproduction.