CELL AND ITS ORGANELLES PDF

# Cellular Level of Organisation ## Structure and Functions of Cell **Cell:** A living structural and functional unit enclosed by membranes. ### Three major parts of a cell: 1. **Plasma Membrane:** Outer surface that separates the cell's internal environment from the external; regulates flow of...

# Cellular Level of Organisation ## Structure and Functions of Cell **Cell:** A living structural and functional unit enclosed by membranes. ### Three major parts of a cell: 1. **Plasma Membrane:** Outer surface that separates the cell's internal environment from the external; regulates flow of materials in and out of a cell. 2. **Cytoplasm:** Region between the plasma membrane and nucleus that consists of all the cellular contents. * **Cytosol:** Fluid portion of cytoplasm with suspended particles. * **Organelles:** * **Cytoskeleton:** A network of protein filaments throughout the cytosol. * **Microfilaments:** Thinnest. Made of protein actin. Prevalent at the cell's periphery. * Function: Movement-muscle contraction, cell division, all locomotion. Provide mechanical support for basic strength of the cell. Shape of cells like villi. * **Intermediate filaments:** Thicker than microfilaments. Made of several proteins. * Function: Stabilize position of organelles such as nucleus. Help cell-cell attachments. * Help cells to cope with mechanical stress. * **Microtubules:** Long, unbranched hollow tubes. Made of the protein tubulin. Assemble in the organelle. Provide mechanical functions and determine cell shape and movement. * **Centrosome:** Located near the nucleus. Consists of two centrioles and pericentriolar material. * These tubulin complexes are centers for growth of mitotic spindle which plays a role in cell division. * During cell division, the centrosome replicates and goes to each cell for ensuring cell replication. * **Cilia and Flagella:** Motile projections of the cell surface. * **Cilia:** Hair-like projections from the surface of the cell. Each cilium contains a core of 20 microtubules surrounded by a plasma membrane. * Movement: Cilia cause movement of fluid along the cell's surface. * **Flagella:** Longer than cilia. It has wave patterns of movement. E.g., sperm cell's movement. * **Ribosomes:** Sites of protein synthesis. Contains two subunits that are made separately in the nucleolus. They only join together in the cytoplasm when released. * **Freeribosomes:** Synthesize proteins in the cytosol. * **Attached ribosomes:** Attached to nuclear membrane or endoplasmic reticulum. Synthesize proteins for organelles, plasma membrane, or for export from the cell. * **Endoplasmic Reticulum:** Extends from the nuclear envelope into the cytoplasm. * **Rough ER:** Attached to the nuclear membrane. Studded with ribosomes. Synthesize proteins, glycoproteins, and phospholipids. These proteins may be incorporated into the membrane (membrane proteins), membrane of organelles (organellar proteins) or secreted via exocystosis (secretory proteins). * **Smooth ER:** Extends from the rough ER. Lacks ribosomes. Doesn't synthesize proteins. Synthesize fatty acids and phospholipids. Detoxify drugs. Remove glucose-6-phosphate from glycogen. Store and release calcium, especially in muscle cells. * **Golgi Complex:** Consists of 3-20 cisternae. Converging face of cisternae faces rough ER (cis face). Concave face (trans face or unit) faces plasma membrane. * Receives and modifies proteins produced by rough ER in transporter vesicles. * Lies between entry and exit. * Adds carbohydrates to proteins to form glycoproteins. Adds lipids to form lipoproteins. * Packages the proteins for transport in secretory or membrane vesicles. * **Lysosomes:** Vesicles that form from the Golgi complex. Contain all kinds of digestive hydrolytic enzymes. * Lysosomal enzymes help recycle worn-out cellular structures. Involved in autophagy. * **Peroxisomes:** Contain oxidases (remove hydrogen atoms) from various organic substances such as fatty acids and alcohol. * Peroxisomes are very abundant in liver cells where detoxification of alcohol and other substances takes place. * A byproduct produced in the process of oxidation is hydrogen peroxide (H2O2), which is a potentially toxic compound. * Peroxisomes also contain catalase which decomposes H2O2. * **Proteasomes:** Involved in destruction of damaged or faulty proteins. Contain proteases: enzymes that breakdown proteins to peptides. * **Mitochondria:** Powerhouse of the cell. Produce ATP through aerobic respiration. * Active cells in muscles, liver, kidneys use ATP at a high rate and thus have a large number of mitochondria. * Outer membrane * Inner membrane * Intermembrane space (fluid-filled spacer) * Cristae (folds) Provide enormous surface area for aerobic phase of cellular respiration that produce ATP * Matrix: Mitochondrial matrix (fluid-filled cavity). Enzymes for the matrix are present in the matrix. * Like peroxisomes, mitochondria can self-replicate. * They have their own ribosomes in the matrix for synthesis of proteins for mitochondrial functions. * Have their own DNA: circular DNA (double helix). Contains 37 genes. These genes control synthesis of ribosomal RNA, 22 transfer RNA, and 13 proteins that build mitochondrial components. * Genes of mitochondria are only inherited from the mother because the head of the sperm that penetrates and fertilizes the oocyte normally lacks most organelles such as mitochondria, ribosomes, endoplasmic reticulum, Golgi complex. Unlike genes in the nucleus, genes from both father and mother. * **Nucleus:** Contains the cell's hereditary units present in the nucleus. * **Nuclear Envelope:** A double membrane that separates the nucleus from the cytoplasm. * **Outer layer:** In continuation with rough ER. * **Nuclear Pores:** Multiple in number. Control the movement of substances between the nucleus and cytoplasm. * **Nucleolus:** One or more spherical bodies inside the nucleus. Produce ribosomes. Made up of protein, DNA, and RNA. * Nucleoli are sites of synthesis of rRNA and assembly of rRNA and proteins into ribosomal subunits. * **Genes:** Cell's hereditary units present in the nucleus. * **Human Somatic Cells:** Have 46 chromosomes; 23 inherited from each parent. * **Chromosomes:** Each chromosome is a long molecule of DNA that is coiled together with several proteins. * **Chromatin:** Complex of DNA, proteins, and some RNA that appears as a diffuse granular mass. * Histone Proteins: Double stranded DNA wrapped twice around 8 histone proteins. * Nucleosome * Linker DNA (string beads) * Contromere * Condensed chromatin (fiber) * **Chromosomes:** Consist of genes that control cellular structure and direct cellular functions. * All eukaryotes have a nucleus.