Cell Structure and Function PDF

Cell Theory 1- Cells are the smallest structural and functional unit of organisms 2- All organisms are composed of cells 3- All cells come only from preexisting cells (Cell division)  Characteristics of a Cell  Store information  Make and Use energy  Capable of movement ...

Cell Theory 1- Cells are the smallest structural and functional unit of organisms 2- All organisms are composed of cells 3- All cells come only from preexisting cells (Cell division)  Characteristics of a Cell  Store information  Make and Use energy  Capable of movement  Sense environmental changes  Can duplicate (growth, repair, reproduction & development)  Capable of self-regulation (homeostasis)  Build molecules (proteins, carbohydrates, fats, nucleic acids) Types of cells Prokaryote Eukaryotes Bacteria cells Animal cells Plant cells  Prokaryotes vs. Eukaryotes Prokaryotic Eukaryotic Cells Cells < 10 µm Size 10-100 µm Does not have a true Nucleus Has a true membrane nucleus. Only a nucleoid bound nucleus Has no membrane bound Membrane Has membrane bound organelles bound Organelles organelles One circular piece of DNA DNA Many linear pieces of with no proteins DNA with proteins Small ribosomes Ribosomes Large ribosomes All Prokaryotes are Number of cells Eukaryotes are either unicellular unicellular or multicellular Asexual only through Reproduction Sexual and asexual binary fission through mitosis & meiosis  Three important Cell Regions 1- Cell membrane: 2- Nucleus This is the outermost The control center of boundary on the cell. the cell that contains the DNA (deoxyribonucleic acid) which directs the functioning of the cell. 3- Cytoplasm: The part between the cell membrane and the nucleus It contains a liquid called cytosol. Within the cytosol are organelles which are special structures that carry out different cell functions.  Three important Cell Regions As well, two other important terms are: 1- Intracellular which refers to the area inside of the cell. 2- Extracellular which refers to the area outside of the cell.  Why study cells?  Cells Tissues Organs Bodies Bodies are made up of cells. Cells do all the work of life.  How study cells? We study cells using biochemistry techniques. Cell fractionation - Isolating organelles - Homogenization - Ultracentrifugation  Cell Fractionation APPLICATION: Fractionate cell components based on size and density. TECHNIQUE: Cells are homogenized in a blender. The resulting homogenate is centrifuged. Differential centrifugation results in a series of pellets, each containing different cell components RESULTS: Using microscopy to identify the organelles in each pellet Using biochemical methods to determine the metabolic functions of the organelles.  Organelles in eukaryotic cells The Cell Membrane Structure The cell membrane is also known as the plasma membrane. It is composed of two layers of phospholopids. It is called the phospholipids bilayer because it is made of these two layers A phospholipid is a type of fat composed of: Aqueous environment Phosphate head 1- A hydrophilic “water-loving” phosphate head that faces the aqueous Fatty acid tails environment. 2- Two hydrophobic water-fearing” Aqueous environment fatty acid tails which face other fatty acid tails  The Cell Membrane Structure Besides the phospholipid bilayer, the cell membrane also contains: proteins, sterols and sugars within the bilayer which help it perform specific functions. This model of the membrane is called the fluid mosaic model.  The Cell Membrane Function The cell membrane has several important functions: 1- It forms a physical barrier to protect the inside of the cell from outside environment. 2- It controls the transport of substances into and out of the cell. This is possible because the membrane is semi-permeable.  The Cell Membrane 3- It plays a role in cell-to-cell communication. 4- It is an attachment surface for cell walls, other cells and the intracellular cytoskeleton.  Organelles of the Cell  Organelles do the work of cells  The basic set of organelles found in most animal cells. http://image.tutorvista.com/content/feed/tvcs/Cell20organelle.jpg - Nucleus - Endoplasmic reticulum - Golgi apparatus - lysosomes - Mitochondria - Peroxisomes - Ribosomes Model Animal Cell  Cell organelles are of 2 types Membranous Organelles 1. Endoplasmic Non-Membranous reticulum. Organelles 2. Mitochondria. 1. Ribosomes 3. Golgi. 2. Cytoskeletal 4. Lysosomes. structures  Organelles of the Cell  Many cell organelles are connected through the endomembrane system  Many of these organelles work together in: -Synthesis -Storage, and -Export molecules.  The Nucleus: Information Central Structure  The nucleus is the largest cellular organelle in animals.  The nucleus is composed of: 1- Nuclear Membrane 2- Nucleoplasm 3- Nucleolus 4- Chromatin and Chromosomes  Structure The Nucleus 1-Nuclear Membrane  It surrounds and protects the contents of the nucleus  It consists of double layer of membrane and it contains nuclear pores.  It contains nuclear pores which permit exchange between nucleoplasm & cytoplasm. The Nucleus Structure 2- Nucleoplasm  The liquid within the nucleus.  It is similar to the cytosol within the cytoplasm 3- Nucleolus  is a "sub organelle" of the cell nucleus.  Made up of a combination of rRNA and proteins.  Site of ribosomes synthesis.  The nucleolus loses its identity during cell division.  The Nucleus Structure The nucleus is composed of: 4- Chromatin and chromosomes  Strands of DNA wrapped around proteins called histones create chromatin.  There are two types of chromatin: 1- Euchromatin, is the less compact DNA form, and contains genes that are frequently expressed by the cell. http://2.bp.blogspot.com/_HtLvymcBlKo/TJJ18_Eq-bI/AAAAAAAAAA8/l6AyC3lzG2Y/s1600/2.png  The Nucleus Structure  Chromatin forms chromosomes when it condenses into easily visible strands during cell division  Chromosome Structure Structure a. Nuclesosomes – Core of DNA wrapped around 8 histone proteins plus linker DNA b. Solenoid – coiling of nucleosomes like phone cord c. Chromatin fiber – series of nucleosomes d. Metaphase chromosomes  http://ccftp.scu.edu.cn:8090/Downl Each human cell contains 46 chromosomes (except sperm or egg cells)  Anucleated and polynucleated cells 1- Anucleated cells contain no nucleus and are therefore incapable of dividing to produce daughter cells. 2- Polynucleated cells contain multiple nuclei.  In humans, skeletal muscle cells, called myocytes, become polynucleated during development  Multinucleated cells can also be abnormal in humans. Cells arising from the fusion of monocytes and macrophages, known as giant multinucleated cells, sometimes accompany inflammation and are also implicated in tumor formation. Giant-cell tumor of the bone (GCTOB) is a relatively uncommon tumor of the bone. It is characterized by the presence of multinucleated giant cells (osteoclast-like cells). Malignancy in giant-cell tumor is uncommon and occurs in about 2% of all cases. Multinucleated giant cells due to an infection. Biomedical importance Functions The nucleus of a eukaryotic cell stores DNA and directs the cell's activities.  Nucleus contains the biochemical processes involved in the Replication of DNA before mitosis.  Involved in the DNA repair.  Transcription of DNA – RNA synthesis. The nucleus contains a variety of proteins: 1- Enzymes mediate transcription.  RNA polymerases that synthesize the growing RNA molecule.  Topoisomerases that change the amount of supercoiling in DNA. 2- Enzymes involved in regulating the transcription.  Transcription factors that regulate expression. Nuclear transport  Small molecules can enter the nucleus without regulation  Macromolecules: RNA and Proteins are actively transported across the nuclear membrane with regulation by the nuclear pore complexes Assembly and disassembly of the nucleus  During its lifetime a nucleus may be broken down: o The process of cell division. o As a consequence of apoptosis  Disorders of nucleus  Defective nucleoli (singular = nucleolus) have been implicated in several rare hereditary diseases, mostly neurodegenerative disorders such as Alzheimer’s and Huntington’s disease.  Parkinson’s disease may be caused by oxidative stress within cells due to defective nucleoli.  Antibodies to certain types of chromatin organization, particularly nucleosomes, have been associated with a number of autoimmune diseases, such as systemic lupus erythematosus, and multiple sclerosis These are known as anti-nuclear antibodies (ANA). Nucleus Summary  Cytoplasm:  It is jelly-like substance containing water and miniral salts.  Acts as a medium where biochemical reactions and most living processes occur within the cell. Enzymes (glycolytic pathway) All the machinery for protein synthesis (mRNA, transfer RNA, enzymes, and other factors) Oxygen, CO2, electrolytic ions, low molecular weight substrates, metabolites, waste products, etc  Contains organelles with different cell functions.  The Endoplasmic Reticulum: Biosynthetic Factory  Endoplasmic reticulum (ER) is a network of membranes throughout the cytoplasm of the cell.  There are two kinds of endoplasmic reticulum: Smooth and rough. Rough ER is embedded with ribosomes on cytoplasmic side. Smooth ER Rough ER membrane Is lacks attached ribosomes continuous with the nuclear envelope surrounding the nucleus  Although physically interconnected, smooth and rough ER differ in structure and function. Biomedical importance Smooth Endoplasmic Reticulum many metabolic processes (synthesis & hydrolysis) 1- Lipids biosynthesis: synthesizes lipids, phospholipids as in plasma membranes, and steroids 2- Detoxification: the detoxification of alcohol, and other potentially harmful substances. 3- Sequestration of Ca++: Some smooth ER helps store and release calcium ions. Rough ER  The ER system serves as a location for the proteins- synthesizing ribosomes.  Directs molecules towards single places. o Intracellular storage (eg, in lysosomes and specific granules of leukocytes), o Provisional intracellular storage of proteins before exocytosis o Integral membrane proteins.  Sends proteins to the Golgi apparatus.  Synthesis of other organelles (lysosomes & Peroxisomes). signal sequences direct proteins to the correct organelle.  proteins destined for the ER possess an N-terminal signal sequence that directs them to that organelle,  whereas those destined to remain in the cytosol lack this sequence.  recombinant DNA techniques can be used to change the location of the two proteins Golgi Apparatus: finishes, sorts, and ships cell products  3 main structures can be observed under EM :  Flattened vesicles.  secretory vesicles.  Microvesicles.  The main structural unit of Golgi apparatus is a flattened membrane vesicle described as GOLGI SACCULE.  Each stack of saccules in Golgi complex possess 1. Forming face(Cis–face) 2. Maturing face(Trans-face)  Biomedical importance  Serves as a molecular warehouse and finishing factory for products manufactured by the ER. - Products travel in transport vesicles from the ER to the Golgi apparatus. - One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock. Biomedical importance - Products are modified as they go from one side to the Golgi apparatus to the other side - Prepares for “shipment” in vesicles from trans face to other sites 1- Vesicles for transport (the secretion of proteins from the cells(hormones, plasma proteins, and digestive enzymes). 2- Vacuoles for storage. 3- lysosomes for find out later https://youtu.be/iA8hFSHS6Ho  Shipping and sorting done by the Golgi complex is a very important step in protein synthesis.  If the Golgi complex makes a mistake in shipping the proteins to the right address, certain functions in the cell may stop.  Defects in various aspects of Golgi function leads to 1. Congenital glycosylation disorders. 2. Muscular dystrophy. 3. Diabetes. 4. Cancer. 5. Cystic fibrosis.