Eukaryotic Cell Structure and Function PDF

• An eukaryotic cell has internal membranes, which partition the cell into compartments. • These membranes also participate in metabolism as many enzymes are built into membranes. ee • The general structure of a biological membrane is a double layer of phospholipids and diverse proteins. • Each...

• An eukaryotic cell has internal membranes, which partition the cell into compartments. • These membranes also participate in metabolism as many enzymes are built into membranes. ee • The general structure of a biological membrane is a double layer of phospholipids and diverse proteins. • Each type of membrane has a unique combination of lipids and proteins for its specific functions. – Ts For example, those in the membranes of mitochondria function in cellular respiration. Plant & Animal Cells • Similarities – Both are eukaryotic cells – Both contain similar organelles – Both are surrounded by cell membrane Plant & Animal Cells • Differences – Plants have • Cell wall – provides strength & rigidity and is not found in animal cells. • Have chloroplasts that is photosynthetic and are not found in animal cells. – Animals have • Organelle lysosomes, centriols and flagella are not found in plants. • Centrioles have important role in cell division. 1. The nucleus: Contains the cell’s genetic library • The nucleus contains most of the genes in an eukaryotic cell as it is the repository for genetic material. • The nucleus is separated from the cytoplasm by a double membrane called nuclear envelope. • It directs activities of the cell. • The nuclear membrane contains pores that allow large macromolecules and particles to pass through. • The nuclear membrane is maintaining the shape of the nucleus. mm • The nucleus contains “chromatin fiber” which is made up of DNA and proteins. • When the cell prepares to divide, the chromatin fibers coil up and condensed to be seen as “chromosomes”. • Each eukaryotic species has a characteristic number of chromosomes. - A typical human cell has 46 chromosomes, but sex cells or gametes (eggs and sperm) have only 23 chromosomes. I • The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA). – The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific protein. • Nucleolus is a dark region involved in production of ribosomes. 2. Ribosomes: build the cell’s proteins • Ribosomes are RNA-protein complexes composed of two subunits (large and small) that join and attach to messenger RNA to carry out protein synthesis. • So, it is the site of protein synthesis • Ribosome assembly begins in the nucleolus and is completed in the cytoplasm • In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits. • The subunits pass through the nuclear pores to the cytoplasm where they combine to form ribosomes. • Cells that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes. more protein • 1) 2) mffosiome Types of Ribosomes:Free ribosomes are suspended in the cytosol and synthesize proteins that function within the cytosol. Bound ribosomes are attached to the outside of the endoplasmic __ reticulum. – These synthesize proteins that are either included into membranes or for secretion outside the cell. 3- The Endomembrane System a) The endoplasmic reticulum is a manufacturer membrane and performs many other biosynthetic functions. b) The Golgi apparatus finishes, sorts, and ships cell products. c) The Lysosomes are digestive compartments. d) The Vacuoles have diverse functions in cell maintenance. A)- The endoplasmic reticulum (ER) (intracellular highway) • Largest internal membrane, Composed of Lipid bilayer • Serves as a system of channels from the nucleus • Functions in storage and secretion • There are two types of ER those are different in structure and function. 1. Smooth ER looks smooth because it lacks ( does not have ) ribosomes. 2. Rough ER looks rough because ribosomes (bound ribosomes) are attached to its outside. Rough Smooth The smooth ER: • It is Smooth as it lacks the associated ribosomes. • It is rich in enzymes and plays a role in metabolic processes. • Its enzymes synthesize lipids (oils, phospholipids and steroids) including the sex hormones. 0 • Extensive in the liver, it helps in detoxifying drugs and poisons The rough ER: • It is “rough” because of the associated ribosomes (sites of protein synthesis) • It is especially abundant in those cells that secrete proteins such as digestive glands and antibody-producing cells. Is • These secretory proteins are packaged in transport vesicles that carry them to their next stage. C)- Lysosomes are digestive components • The lysosome is a membrane-bounded sac of enzymes that digests macromolecules. • Lysosomal enzymes work best at pH = 5 (acidic). 0 • The lysosomal enzymes are synthesized by rough ER and then transferred to the Golgi then to lysosomes. ER Golgi lysosome y Function of Lysosomal enzymes 1) They hydrolyse proteins, fats, polysaccharides, and nucleic acids. 2) Can destroy the cell by autodigestion (autophagy). 3) Can fuse with food vacuoles to digest food, (when a food item is brought into the cell by phagocytosis). 4) Can also fuse with another organelle or part of the cytosol. This process of autophagy called recycling which renews the cell. s 5. They digest unwanted particles. 6. They help white blood cells to destroy bacteria. Functions of peroxisomes so 1- Hydrogen peroxide (H2O2) is a poison, but the peroxisome has enzyme that converts H2O2 to water. 2- Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria for fuel. 3- They detoxify alcohol and other harmful compounds. Thus, it exists extensively in the liver cells. 4- Initiate the production of phospholipids, which are typically used in the formation of membranes.