Cell Structure and Functions (PDF)

* THE CELL AND ORGANELLES II. Interior structure of cell – Cytoplasm viscous gel, enclosed within the cell membrane consist of cytosol (liquid component of the cytoplasm) and organelles cytosol - mixture of cytoskeleton filaments, dissolved molecules, and water each organelle has their...

* THE CELL AND ORGANELLES II. Interior structure of cell – Cytoplasm viscous gel, enclosed within the cell membrane consist of cytosol (liquid component of the cytoplasm) and organelles cytosol - mixture of cytoskeleton filaments, dissolved molecules, and water each organelle has their own cytoplasm function - serve as medium for most cellular activities  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton skeleton of cytoplasm made of filamentous protein network present in plant and animal cells a dynamic structure Functions ⮚ maintains cell shape, enables cellular motion ⮚ play important roles in intracellular transport and cell division  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton Three types of fibers: a) Microfilaments b) Microtubules c) Intermediate filaments  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton a) Microfilaments Functions ⮚muscle contraction ⮚Invovle in cell division (cytokinesis) ⮚movements of certain cells (eg: Amoeba, white blood cell) ⮚provide support major portion of cytoskeleton, two chains twisted around one another. long fibers but thin, diameter = 6-7 nm thinnest filaments, flexible and strong each subunit is made of actin (protein).  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton b) Microtubules Functions:– involved in many cellular processes:- - transport vesicle - provide cell shape and support - separate chromosomes during cell division  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton b) Microtubules straight, hollow rods (d = 25nm) made of β and α-tubulin (protein) part of the cilia and flagella of eukaryotic cells form spontaneously around centrosomes (microtubule organizing centre) unstable, easily assembled and disassembled * THE CELL AND ORGANELLES  * THE CELL AND ORGANELLES II. Interior structure of cell – Cytoskeleton c) Intermediate filaments Functions ⮚preventing excessive stretch of cells shape ⮚fix organelles position most durable and stable diameter varies, from 8 to 12nm made of vimentin (protein) example: keratin of the skin cell  * THE CELL AND ORGANELLES Exterior structure:- ⮚Cell wall (plants and bacteria) ⮚Plasma membrane ⮚Cilia and flagella Interior structure:- ⮚Cytoplasm ⮚Cytoskeleton (in eukaryotes) ⮚Organelles (in eukaryotes) – 3 groups:- ▪ Endomembrane system ▪ Mitochondria and chloroplast ▪ Ribosomes and nucleus  * THE CELL AND ORGANELLES II. Interior structure of cell – Organelles Class I: Endomembrane system a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and protein include - endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, endosomes, vacuoles (plant cell) and the cell membrane Endomembrane system  * THE CELL AND ORGANELLES Class I: Endomembrane system i. Endoplasmic reticulum (ER) endoplasmic = ‘within the cytoplasm’ reticulum = ‘a little net’ observed by electron microscope a network of membranous tubules, vesicles and flattened sacs called cisternae. ER separate cisternal space from cytosol  * THE CELL AND ORGANELLES Class I: Endomembrane system i. Endoplasmic reticulum (ER) function varies depending on the type of endoplasmic reticulum and the type of cell two main types:- Smooth ER and Rough ER the quantity of RER and SER in a cell can quickly interchange depending on metabolic needs  * THE CELL AND ORGANELLES i. Endoplasmic reticulum (ER) Rough Endoplasmic Reticulum (RER) membrane of RER is continuous with the outer layer of the nuclear envelope cisternae are flat and rough (studded with ribosomes that synthesis protein) ribosomes are not a stable part of RER  * THE CELL AND ORGANELLES i. Endoplasmic reticulum (ER) Rough Endoplasmic Reticulum (RER) Function Protein synthesis -ribosomes attached to its surface (sites of protein synthesis) Protein folding -helps in folding the newly synthesized proteins into their correct shapes and ensures quality control. Formation of SER and Golgi complexes -gives rise to the smooth endoplasmic reticulum, *proteins normally for export or membrane insertion * THE CELL AND ORGANELLES  * THE CELL AND ORGANELLES i. Endoplasmic reticulum (ER) Smooth ER found in a variety of cell types (both animal and plant) and it serves different functions in each cisternae are tubes-like, connected with RER, smooth surface Function – synthesis lipids - enzymes within SER catalyze various processes e.g. - In gut epithelial cells, enzymes of SER catalyze the synthesis of lipid, carbohydrate metabolism - In liver cells- enzymes detoxify drugs and toxin - In testes and ovary, enzymes produce sex hormones and steroid  * THE CELL AND ORGANELLES Class I: Endomembrane system ii. Golgi Apparatus named after Italian physician Camillo Golgi. made of a stack of flattened membranous sacs (cisternae) in mammalian cell, each consist of 5-6 cisternae, in plant 20 or more. cisternal space separated from cytosol by membrane abundant in an active cells  * THE CELL AND ORGANELLES Class I: Endomembrane system ii. Golgi Apparatus Function modify, sort and package the macromolecules that are synthesized by the cells for secretion purposes or for use within the cell e.g. protein added with carbohydrate, lipid, create lysosome  * THE CELL AND ORGANELLES Class I: Endomembrane system ii. Golgi Apparatus Process occurred: vesicles from RER fuse with cis face (receiving side) and release the contents contents are modified during the transit from cis to trans face by various enzymes, marked and sorted into batches, distribute to different destination in transport vesicles which bud from trans face (shipping side facing plasma membrane) vesicles move to plasma membrane, fused with it, released the contents out. vesicle remain as a permanent addition to plasma membrane Class I: Endomembrane system ii. Golgi Apparatus  Nucleus receive the information transcribe mRNA sent into cytoplasm RER cisternae are flat and rough studded with ribosomes that synthesis protein Ribosomes are not a stable part of RER Protein synthesized from ribosome enter the cisternal space (lumen) of RER, altered/changed by enzyme (carbohydrate molecules normally added → glycoprotein) secretory proteins - temporarily kept before being pack in vesicles and exported to Golgi apparatus proteins normally for export or membrane insertion. Golgi Apparatus a cis face is the receiving side located near ER vesicles from RER fuse with cis face and released the contents. contents are modified during the transit from cis to trans face by various enzymes, marked and sorted into batches, distribute to different destination in transport vesicles which bud from trans face (shipping side facing plasma membrane) transport/secretory vesicles move to plasma membrane, fused with it, and released the contents out. Thank you