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.