Cell Structure and Function.pdf
Transcript
Introduction to Cells https://newbiescience.files.wordpress.com/2013/11/70261_420x315-cb1375994886.jpg Session Learning Outcomes (SLOs) SLO# 1: Explain the cell theory and the basic cell structure SLO# 2: Compare the structure of a prokaryotic cell with...
Introduction to Cells https://newbiescience.files.wordpress.com/2013/11/70261_420x315-cb1375994886.jpg Session Learning Outcomes (SLOs) SLO# 1: Explain the cell theory and the basic cell structure SLO# 2: Compare the structure of a prokaryotic cell with the structure of a eukaryotic cell SLO# 3: Explain how cell fractionation is used to isolate the cell components. SLO# 1: Recognize organelles found in eukaryotic cells. SLO# 2: Identify the function and organization of the various organelles in eukaryotic cells. SLO# 3: Explain how the diseases are associated with specific cell-organelles. 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 1- A hydrophilic “water-loving” head phosphate head that faces the aqueous Fatty environment. acid tails 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. Lysosomes: Digestive Compartments Membrane-bound vesicles responsible for the intracellular digestion of both intra and extracellular substances. Enzymes & membrane of lysosomes are synthesized by rough ER & transferred to the Golgi apparatus for processing. The membrane serves to safely isolate these potent enzymes from the rest of the cell. Biomedical importance The enzyme content varies in different tissues according to the requirement of tissues or the metabolic activity of the tissue. Lysosomal membrane is impermeable and specific translocators are required. Contain lytic enzymes (Low pH) Digestion of large molecules Recycling of cellular resources Apoptosis The metabolites that result are transported either by vesicles or directly across the membrane. Cellular digestion ▪ Lysosomes carry out intracellular digestion by Phagocytosis ▪ Lysosomes help digest food particles engulfed by a cell. 1. A food vacuole binds with a lysosome. 2. The enzymes in the lysosome digest the food. 3. The nutrients are then released into the cell. Cellular digestion Digestive enzymes Lysosome Digestion Food vacuole Plasma membrane Cellular digestion Products of lysosomal digestion are released and reutilized. ▪ Indigestible material accumulates in the vesicles called residual bodies and their material is removed by exocytosis. ▪ Some residual bodies in non dividing cells contain a high amount of a pigmented substance called Lipofuscin. ▪ Also called age pigment or wear –tear pigment. Recycler ▪ Lysosomes also help remove or recycle damaged parts of a cell by autophagy. 1. The damaged organelle is first enclosed in a membrane vesicle. 2. Then a lysosome Fuses with the vesicle, Dismantles its contents, and Breaks down the damaged organelle. ▪ Autophagy is enhanced in secretory cells that have accumulated excess secretory granules. ▪Digested products from autophagosomes are reutilized in the cytoplasm. Lysosome Vesicle containing damaged mitochondrion Digestion Apoptosis = cell death - Critical role in programmed destruction of cells in multicellular organisms ▪ Auto-destruct mechanism “cell suicide” ▪ Some cells have to die in an organized fashion, especially During development ex: development of space between your fingers During embryonic development ex: if cell grows improperly this self-destruct mechanism is triggered to remove damaged cell cancer over-rides this to enable tumor growth Disorders of Lysosomes Tay-Sachs disease Lysosomes play an important role in the metabolism of several substances in the human body, and consequently many diseases have been ascribed to deficiencies of lysosomal enzymes ▪ Individual lysosomal enzymes are missing or inactive and this lead to the accumulation of that particular substance. ▪ lysosomes gets enlarged and they interfere the normal function of the cell. ▪ Diseases called lysosomal storage diseases which are usually fatal Most important is Tay-Sachs disease lipids build up in brain cells child dies before age 5. Endomembrane System: Relationships among the major organelles of the endomembrane system Ribosomes: Protein Factories Ribosomes are the structures where proteins are made. ▪ They are produced in the nucleolus ▪ Composed of rRNA and ribosomal proteins known as a Ribonucleoprotein ▪ Consists of a large subunit and a small subunit 1. In Prokaryotes: only free ribosomes; 70S ribosomes large: 50S subunit 1. Eukaryotes: free and Small: 30s subunit bound ribosomes; 80S ribosomes Large: 60S subunit. Small: 40S ▪ Some ribosomes are free ribosomes; others are bound. 1- Free ribosomes: Suspended in the cytoplasm (singly or in groups called polyribosomes) Involved in making proteins that function within the cytoplasm cell. 2- Bound ribosomes: Attached On the endoplasmic reticulum associated with nuclear envelope Associated with proteins packed in certain organelles or exported from the cell. Ribosomes make proteins for use in the cell and export Nucleus, Ribosomes, & ER Disorders of ribosomes Defects in the function of ribosomes may cause: 1. Anemia (5 infants in 1 million are affected) 2. Cartilage hair hypoplasia 3. Shwachman diamond syndrome.(1 child in every 100,000 is born with ribosomal disorder) 4. Dyskeratosis congenita (1 child in 1 million is affected) Mitochondria: factories of energy Consists of flattened membranous sacs called cisternae. Every type of cell has a different amount of mitochondria. Figure 1-18 Essential Cell Biology (© Garland Science 2010) ▪ The singular for mitochondria is mitochondrion. ▪ A mitochondrion is composed of: 1- Outer membrane (smooth) 2- Inner membrane (folded) 3- Matrix: (liquid within inner membrane) 4- Christae (folds of the inner membrane) 5- Intermembrane space (liquide between membranes) 6- Each one also has singular circular chromosomes as well as its own ribosomes which allow it to self replicate. Biomedical importance ▪The main function of mitochondria is to produce energy for the cell in a chemical process called cell respiration. Chemical formula for cellular respiration: C6H12O6 +O2 Co2 + H2o + ENERGY (ATP) Both the membranes have different appearance and biochemical functions: Outer membrane: Inner membrane: ▪ It is permeable to most ions ▪ It surrounds the matrix. and molecules which can ▪ It contains components of move from the cytosol to electron transport system. intermembranous space. ▪ It is impermeable to most ions including H, Na, ATP, GTP, CTP and to large Matrix: molecules. ▪ It is enclosed by the inner ▪ special carriers are present mitochondrial membrane. (ATP –ADP transport). ▪ Contains enzymes of citric acid cycle. Mitochondria plays a key role in aging (apoptosis) Mitochondria have a role in their own replication- they contain copies of circular DNA. Mitochondrial DNA has information for some mitochondrial proteins and some RNAs. This DNA is inherited maternally. Mitochondrial matrix contains some rRNA and some tRNA used in the translation of mRNA. mDNA encodes some enzymes, involved in oxidative phosphorylation Most mitochondrial proteins are derived from genes in nuclear DNA. Disorders of mitochondria ▪ Mutation rate in mt DNA is 10 times more. ▪ The mutations of mtDNA are more likely to cause muscular dysfunctions. ▪ The most mitochondrial deficiency diseases are characterized by muscular dysfunction. ▪ Because of their high-energy metabolism, skeletal muscle fibers are very sensitive to mitochondrial defects. ▪ These diseases typically begin with drooping of the upper eyelid and progress to difficulties in swallowing and limb weakness. ▪ Generally, in these diseases the mitochondria show morphological changes. Peroxisomes ▪ Called Peroxisomes because of their ability to produce or utilize H2O2. ▪ They are small, oval or spherical in shape. ▪ They have a fine network of tubules in their matrix. Peroxisomes ▪ About 50 enzymes have been identified. ▪ Enzymes synthesized by free ribosomes in cytoplasm. ▪ The number of enzymes fluctuates according to the function of the cells. ▪ Peroxisomes are relatively large in hepatocytes and kidney cells but very small in intestine cells so called microperoxisomes Biomedical importance ▪ Some peroxisomes use oxygen to break fatty acids down into smaller molecules that are transported to mitochondria and used as fuel for cellular respiration. ▪ Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen and produce H2O2. ▪ The H2O2 formed by peroxisomes is itself toxic, but the organelle also contains an enzyme (catalase) that converts H2O2 to water. Disorders of Peroxisomes ▪ A large number of disorders arise from defective peroxisomal proteins, because this organelle is involved in several metabolic pathways. ▪ The most common peroxisomal disorder is X-chromosome- linked adrenoleukodystrophy, caused by a defective integral membrane protein that participates in transporting very long- chain fatty acids into the peroxisome for oxidation. ▪ Accumulation of these fatty acids in body fluids destroys the myelin sheaths in nerve tissue, causing severe neurologic symptoms. ▪ Deficiency in peroxisomal enzymes causes the fatal Zellweger syndrome, with severe muscular impairment, liver and kidney lesions, and disorganization of the central and peripheral nervous systems. Summary mitochondria ▪make ATP energy lysosome ▪intracellular degradation from sugar + O2 Peroxisome cytoplasm oxidation of toxic contains many molecules metabolic pathways protein synthesis Golgi apparatus nucleus ▪modification, sorting, ▪protects DNA and packaging of ▪controls cell proteins and lipids vesicles ▪transport inside cells Endoplasmic Reticulum ▪storage ▪synthesis of most lipids cell membrane ribosomes ▪synthesis of proteins for ▪cell boundary ▪builds proteins distribution to many ▪controls movement organelles and plasma of materials in & out membrane ▪recognizes signals
