MODULE-2-THE-PARTS-OF-THE-CELL-AND-THEIR-FUNCTIONS
Module 2: The Parts of the Cell and Their Functions
Overview of the Cell
All life processes in an organism are supported by cells.
Cells contain organelles that perform specific functions.
Cell Membrane
Composed of a phospholipid bilayer with embedded proteins and carbohydrates.
Semipermeable: regulates entry and exit of substances.
Present in both animal and plant cells.
Microvilli (fingerlike folds) increase surface area.
Cytoplasm
Enclosed by the cell membrane, contains cytosol (semifluid substance).
Suspends organelles and contains substances like electrolytes, metabolites, RNA, and synthesized proteins.
Cytoskeleton
Provides structure to the otherwise formless cytoplasm.
Consists of three major filaments:
Microfilaments: Roughly 7 nm in diameter, made of actin proteins, involved in cellular movements.
Microtubules: About 25 nm diameter, made of tubulin proteins, important in cell shape and transport.
Intermediate Filaments: About 10 nm in diameter, most stable and least soluble part of the cytoskeleton.
Centrioles
Involved in cell division; microtubules arrange to form centrioles.
Come in pairs and are oriented at right angles to each other.
Assist in the separation of chromosomes during cell division.
Surrounded by pericentriolar materials that help microtubule organization and spindle fiber formation.
Nucleus
Serves as the control center of the cell housing genetic material.
Comprised of several parts: nuclear envelope, nuclear membranes, perinuclear space, nucleoplasm, and nuclear pores.
Nucleolus
Membrane-free organelle within the nucleus, typically spherical.
Contains fibrils (DNA coding for ribosomal RNA) and granules (rRNA combined with proteins).
Ribosomes
Small dense structures crucial for protein assembly.
Found freely in cytoplasm, attached to the endoplasmic reticulum, or as polyribosomes.
Endoplasmic Reticulum (ER)
A membrane-bound organelle forming interconnected sacs called cisternae.
Rough ER: Ribosome-attached, appears rough due to ribosome presence.
Smooth ER: Lacks ribosomes, appears smooth, involved in lipid synthesis and detoxification.
Golgi Bodies
Membrane-bound organelles consisting of cisternae, involved in the modification and transport of proteins.
Cis Face: Faces the ER.
Trans Face: Faces cytoplasm/cell membrane.
Lysosomes
Membrane-bound organelles that originate from the ER, containing hydrolytic enzymes.
Fuses with phagosomes to digest microorganisms.
Mitochondrion
Double-membrane organelle, site of ATP (energy) synthesis.
Outer membrane covers the organelle; inner membrane folded to create cristae.
Contains matrix with enzymes for metabolic reactions.
Flagella and Cilia
Membrane extensions responsible for cellular locomotion.
Have a central axoneme structure composed of microtubules, connected to the basal body similar to centrioles.
Cell Wall (Plant Cells)
Additional covering outside the cell membrane, primarily made of cellulose.
Maintains plant cell shape, protects the cell, and regulates water uptake.
Plasmodesmata / Gap Junctions
Channels in the plant cell wall that enable communication and exchange of substances between adjacent cells.
Peptidoglycan (Bacterial Cell Walls)
Composed of amino acids and sugars, provides structure and protection to bacterial cells.
Gram-positive bacteria have thicker layers compared to Gram-negative ones.
Chitin (Fungi Cell Walls)
A nitrogen-containing polysaccharide similar to cellulose, provides structural support in fungal cells.
Chloroplast (Plant Cells)
Double-membrane organelle responsible for photosynthesis; converts sunlight, carbon dioxide, and water into glucose.
Contains stroma and thylakoids where chlorophyll captures light energy.
Vacuole
Found in both plant and animal cells; larger and more prominent in plant cells.
Summary of Animal and Plant Cell Features
Typical Animal Cell components: Lysosome, ribosomes, cytoplasm, centriole, smooth and rough ER, Golgi apparatus, mitochondria, peroxisomes, cell membrane.
Typical Plant Cell components: Cell wall, chloroplast, vacuole, plasmodesmata, ribosomes, cytoplasm, nuclear components.