Eukaryotic Cell Structure and Functions.pptx

Eukaryotic Cell Structure and Functions

1. Eukaryotic Cell Structure & Functions

2. INTRODUCTION Eukaryotic Cells : The word Eukaryote which refer to any organism possessing eukaryotic cell is derived from the Greek word " eu karyon " in which " eu " means " true " and " karyon " means " nucleus ". A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotic organisms can be unicellular ( Protista ) or multicellular ( Fungi, Plantae & Animalia ) . Most eukaryotic cells also contain other membrane-bound organelles such as mitochondria, chloroplast, endoplasmic reticulum and Golgi apparatus etc .

3. Types of eukaryotic cells Figure 1: Eukaryotic cell - (a) Animal cell, (b) Plant cell (a) (b)

4. Classification of cell organelles Classification of cell organelles on the basis of presence or absence of membrane into three categories Cell organelles Endoplasmic reticulum (ER) Golgi apparatus Lysosomes Vacuoles Peroxisomes Mitochondria Chloroplast Nucleus Ribosomes Nucleolus Centrioles ( present in animal cell ) Cytoskeleton Single membrane Double membrane Without membrane

5. Cell membrane Outermost boundary of cytoplasm which separates the cell from external environment and controls the entrance & exit of molecules or ions. It has highly selective permeable . Several types of models have been put forward to explain the structure of cell membrane. The most accepted model explaining the structure of cell membrane is fluid mosaic model , proposed by Singer and Nicolson in 1972. Functions: - Play important role in various cellular activities, such as signal transduction, membrane trafficking as well as energy conversion. Figure 2: Fluid mosaic model of plasma membrane

6. Endoplasmic reticulum   Endoplasmic reticulum is a 3-dimentional, complicated and interconnected system of membrane-lined channels that run through the cytoplasm. ER divides the intracellular space into two compartments luminal (inside the ER) and extra-luminal ( cytoplasm). The ER is composed of the following three kind of structures ( i ) cisternae , (ii) tubules , (iii) vesicles . Two types: 1. Rough endoplasmic reticulum (RER) 2. Smooth endoplasmic reticulum (SER) Functions: RER- Synthesis of proteins . SER- Synthesis of fatty acid and phospholipids . Catabolism and detoxification of toxic substances. iii Figure 3: Endoplasmic reticulum

7. Golgi Apparatus The Golgi apparatus is a membrane bound organelle found in most cells. It is responsible for packaging protein into vesicles prior to secretion & therefore plays a key role in the secretary pathway. The Golgi is made of 5-8 folds called cisternae . It has two distinct faces i.e., forming face (cis region) and maturing face (trans region). The Golgi apparatus modifies proteins and lipids that is receives from the ER. This biochemical leaves the Golgi by exocytosis before being delivered to different intracellular or extracellular . Functions : - Processing of materials. - Packaging of materials. - Labeling and delivery of materials. Figure 4: Golgi apparatus

8. Lysosomes Lysosomes are small vesicles which are bounded by single membrane and contain hydrolytic enzymes in the form of minute crystalline or semicrystalline granules . They are also called acid hydrolyses because these digestive enzymes usually function in acidic medium or pH of 4-5 . Lysosomes are also called suicide bags because of the presence of large number of digestive enzymes or acid hydrolyses in them. Lysosomes shows polymorphism . Functions: - Digestion of intracellular and extracellular materials - Hormone secretion - Autophagy - kill or destroy their own cell through autolysis . - formation of acrosome of sperm. Figure 5: Lysosomes

9. Vacuole   Figure 6: Vacuole of a plant cell Vacuole is the membrane-bound space found in the cytoplasm. In plant cell the vacuoles can occupy up to 90% of the volume of cell. Mostly found in plant cell and fungi . However animal cells and protists also contain vacuoles. The vacuole is bound by a single membrane called tonoplast . Depending upon the contents & functions vacuoles are four types - ( i ) Sap vacuoles, (ii) Contractile vacuoles (iii) Food vacuoles (iv) Air vacuoles Functions: - Maintain the turgor pressure of cell - Vacuole store materials like water, food, nutrients and waste Products. - Molecular degradation and detoxification .

10. Ribosomes These are organelles without membrane, are granular and small dot like structure with a diameter of 15nm. They are made up to proteins (15%) and RNA (65%) . Ribosome formed of two unequal subunits- one larger subunit (dome shaped) and another smaller subunit (oblate-ellipsoid shape). Mg2+ ions is required for binding the two subunits. -In prokaryotes- 70S (50S and 30S)  -In eukaryotes- 80S (60S and 40S) Types of ribosomes :  (I)   Bound ribosomes - Attached to rough endoplasmic reticulum.   (ii)  Free ribosomes - Distributed in the cytoplasm. Function : - Play an important role in protein synthesis . Figure 7: Eukaryotic ribosomes

11. Mitochondria Mitochondria are double-membrane organelles that contain their own DNA and Ribosomes . Mitochondria are cell organelles of aerobic eukaryotes which take part in oxidative phosphorylation and Krebs cycle . They are called power houses of cell because they are the release of energy in aerobic respiration . A mitochondrion has two membranes : The outer membrane and inner membrane . The inner membrane of mitochondria has many folds and form layered structure called cristae . Functions: - Production of energy. - Synthesis of ATP. - help in building certain part of blood & hormones like testosterone and estrogen . - Play important role in the process of apoptosis. - Store and release of calcium . Figure 8: Mitochondria

12. Plastids Plastids are semi-autonomous organelles having DNA and double membrane envelope which store and synthesize various type of organic compounds. Depending upon their colour , plastids are of three main type- Plastids Chloroplast Chromoplast Leucoplasts • Contain chlorophyll and  carotenoid pigment. • Sites of CO2 assimilation. • Fat soluble carotenoid pigments present. • Gives part of plant yellow, orange or red colour  . • Protects against the Photo-oxidation. • Colourless plastids.   1. Amyloplasts : store starch 2. Elaioplasts : store lipid or fat 3. Aleuroplasts : store proteins

13. Chloroplast Functions: - Most important function of the chloroplast is to synthesize food through photosynthesis. - Absorbs light energy & converts into chemical energy . - Produces ATP through photosynthesis. - Produce NDPH & O2 by photolysis of water. Chloroplast are double-membrane organelles that contain their own DNA and Ribosomes . Chloroplasts are greenish plastids which possess photosynthetic pigments, chlorophyll and carotenoids, and take part in the synthesis of food. Chloroplasts has two membranes : The outer membrane     and inner membrane. A chloroplast has three parts - Envelope, matrix (stroma), & thylakoids. Figure 9: Structure of Chloroplast

14. Peroxisomes Peroxisomes are spherical, sac-like structures, bounded single membrane . They contain digestive enzymes for breaking down toxic materials in the cell & oxidative enzymes for metabolic activity. These contain 'peroxide' - producing enzymes (oxidases) and 'peroxide' - destroying enzymes (catalases) . Functions: - Perform β- oxidation process. - Degradation of toxic substances. - Major site of oxygen utilization in the cell. - Participate in the formation of myelin. - Play an important role in the formation of bile acids. - Accelerate gluconeogenesis from fat. Figure 10: Peroxisome

15. Nucleus Nucleus is a specialized double membrane bound protoplasmic body which contains all genetic information for controlling cellular metabolism and transmission to the posterity. A nucleus in the non-dividing or metabolic phase is called interphase nucleus. Nucleus envelope consists of two concentric membranes that are penetrated by nuclear pore complexes (NPC) . Small round granular structure present in nucleus called nucleolus . Functions: - Storage of genetic information. - Controls cellular activities like metabolism, protein synthesis, growth and cell division. - Synthesis of RNA. Figure 11: Nucleus

16. Cytoskeleton It is complex network of structures of various sizes present throughout the cytoplasm. They are three types :- ( i ) Microtubule, (ii) Intermediate filaments, (iii) Microfilament. 1. Microtubules: - Straight, hollow & tubular organelles without limiting membrane. - Determine the shape of cell. - Form spindle fibers. 2. Intermediate filaments: - Form network around the nucleus and extend to periphery of the cell. - Helps to maintain the shape of the cell. 3. Microfilaments: - Long & fine thread like structures. - Give structural strength to the cell. - Responsible for cellular movements . Figure 12: Types of Cytoskeletons