Cell Biology PDF

# CELL - The cell is the structural and functional unit of a living body. - Self replicating and fundamental unit of life. - Many cells group together to form tissues, many tissues group together to form organs, many organs group together to form organ systems and many organ systems group together...

# CELL - The cell is the structural and functional unit of a living body. - Self replicating and fundamental unit of life. - Many cells group together to form tissues, many tissues group together to form organs, many organs group together to form organ systems and many organ systems group together and co-ordinate to form a living body. - Some organisms consist of a single cells, unicellular and others are multicellular organism. | | | |---|---| | Cells | | | ↓ | | | Tissues | | | ↓ | | | Organs | | | ↓ | | | Organ systems | | | ↓ | | | Living organism | | ## FUNCTIONS OF CELL 1. **Ingestion and assimilation:** The cell ingests chemical substances like amino acids from intercellular or interstitial fluid. These substances are used to build up complicated substances like proteins. 2. **Growth and repair:** The ingested and digested materials are used to synthesize new protoplasm. This leads to increase in size and growth of the cell. Worn out parts of the cell are also replaced by this process. 3. **Metabolism:** This involves two processes: - **Anabolism:** In this process, the ingested and assimilated food material is used for growth and repair. - **Catabolism:** In this process, the food material is broken down to release energy for various functions of the cell. 4. **Respiration:** This involves transport of oxygen from lungs through blood to the tissues and removal of waste products like carbon dioxide. This is essential for the survival and functions of a cell. 5. **Excretion:** The cell eliminates waste products resulting from catabolism into interstitial fluid. Excretion is the removal of toxic substances and metabolic waste products. These products are carried by blood for elimination through lungs and kidneys, which are the major organs of excretion. 6. **Irritability and conductivity:** The cell is active by means of these two functions. The cell responds to any stimulus (like physical, chemical, thermal, electrical and mechanical) by contracting or the impulse is conducted as that occurs in a nerve cell. 7. **Reproduction:** After growing to an optimum size, the cell divides into daughter cells. Reproduction of cells occurs by two processes-"mitosis" and "meiosis". Mitosis occurs for replacing worn out cells or to replace those destroyed by disease. However, meiosis is another kind of cell division occurring in the sex organs - the testis and the ovary. In mitosis, each of the daughter cells formed have all the 46 chromosomes. But in meiosis, the sex cells or gametes are formed, which contain only 23 chromosomes. The male gamete is called spermatozoon and the female gamete is ovum. When fertilization occurs, that is when a spermatozoon fuses with an ovum, a "zygote" is formed, which develops into a new individual. # STRUCTURES OF CELL - Cells forms the structural unit of all tissues and organs of the body - Human cell is eukaryotic. - It consist of - Cell membrane - Cytoplasm - Endoplasmic reticulum - Golgi bodies - Peroxisomes - Mitochondria - Ribosomes - Centrosomes - Nucleus ## 1. CELL MEMBRANE - Thin pliable elastic outermost structure which envelops the cell. - It consists of bilipid layer with embedded proteins that are: - Integral Proteins - Peripheral proteins - **Function:** - The cell membrane separates the cell from its external environment, and is selectively permeable (controls what gets in and out). - It protects the cell and provides stability. Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials. - Carbohydrates are attached to proteins and lipids on the outer lipid layer. ## 2. NUCLEUS - The largest organelle in the cell. It is dark and round, and is surrounded by a double membrane called the nuclear envelope/membrane. - In spots the nuclear envelope fuses to form pores which are selectively permeable. - The nucleus contains genetic information (DNA) on special strands called chromosomes. - **Function:** - The nucleus is the "control center" of the cell, for cell metabolism and reproduction. - DNA helps in production. - RNA helps in protein synthesis. ## 3. ENDOPLASMIC RETICULUM - The Endoplasmic Reticulum is a network of membranous canals filled with fluid. - They carry materials throughout the cell. - The ER is the "transport system" of the cell. - There are two types of ER: - **Rough Endoplasmic Reticulum:** Reticulum is lined with ribosomes and is rough in appearance. - **Smooth Endoplasmic Reticulum:** Smooth endoplasmic reticulum contains no ribosomes and is smooth in appearance. - **Function:** - It helps in the synthesis of steroids, proteins etc. - It helps to concentrate the products of synthetic activities of cell - It provides a pathway for transporting various chemical ## 4. GOLGI BODIES - Golgi bodies are stacks of flattened membranous stacks (they look like pancakes). - The Golgi body temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi. - Golgi apparatus is to process and bundle macromolecules like proteins and lipids as they are synthesized within the cell. - **Function:** - It helps in packaging of secretory proteins - It helps in a synthesis of carbohydrates. - It helps in intracellular sorting of proteins. - Wrapping and Packaging department of the cell. - Site of formation of lysosomes. ## 5. MITOCHONDRIA - The mitochondria are round "tube-like" organelles that are surrounded by a double membrane, with the inner membrane being highly folded. - The mitochondria are often referred to as the "powerhouse" of the cell. - The mitochondrion releases food energy from food molecules to be used by the cell. This process is called respiration. - **Function:** - It is the main site of synthesis and storage of ATP. - It is the site for citric acid cycle, beta oxidation and urea cycle. - It perform the main function of conversion and transfer of cellular energy. - It contains special DNA and is self replicative. ## 6. LYSOSOMES - Lysosomes are the membrane bound vesicular organelles found throughout the cytoplasm. - The lysosomes are formed by Golgi apparatus. - The lysosome is also known as a suicide sac because it contains digestive enzymes. - Many small granules are present in the lysosome. - The granules contain the hydrolytic enzymes. - **Function:** - Function as the digestive system of the cell. - Intracellular digestion. - Malfunctioning of lysosomes. - Help in fertilization. - Removal of dead cells. ## 7. RIBOSOMES - Ribosomes complex molecule made of ribosomal RNA molecules and proteins. - Ribosomes factory for protein synthesis in cells. - The "rib" in ribosome comes from ribonucleic acid (RNA) which provides the instructions on making proteins. - Ribosomes are different from most organelles in that they are not surrounded by a protective membrane. - **Function:** - Decoding the message and the formation of peptide bonds. - The ribosome reads the sequence of the messenger RNA (mRNA) and, using the genetic code, translates the sequence of RNA bases into a sequence of amino acids. ## 8. VACUOLES - Vacuole is a membrane-bound cell organelle. - Vacuoles are generally small and help sequester waste products. - Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes. - **Function:** - Vacuoles help maintain water balance. - It can hold food for later use or waste for removal. ## 9. PEROXISOME - Peroxisome contain digestive enzymes for breakdown toxic materials in the cell and oxidative enzymes for metabolic - Peroxisome found in the cytoplasm of virtually all eukaryotic cells. - Peroxisomes are oxidative organelles. - **Function:** - Part in various oxidative processes. - part in lipid metabolism and catabolism of D-amino acids, polyamines and bile acids. - Initiate the production of phospholipids, which are typically used in the formation of membranes. ## 10. CENTROSOME - The centrosome is the major microtubule-organizing centre (MTOC) in eukaryotic cells. - A centrosome comprises two microtubule rings known as centrioles. - Centrosome is a structure that organizes microtubules during cell division. - Each centrosome contains "paired barrel-shaped organelles" called centrioles and a "cloud" of proteins referred to as the pericentriolar material. - **Function:** - Main function is to organize the microtubules and provide a structure to the cell. - Centrioles organize DNA during replication and divisions.