Lecture 1 Cell Structure PDF

Introduction to Human Biology 1 Cell Structure 1  Eukaryotic Cell components 1. Nucleus Contains DNA packaged as chromatin (DNA wrapped around histone proteins). Nucleus is the most visible feature of a cell under the light microscope. Nu...

Introduction to Human Biology 1 Cell Structure 1  Eukaryotic Cell components 1. Nucleus Contains DNA packaged as chromatin (DNA wrapped around histone proteins). Nucleus is the most visible feature of a cell under the light microscope. Nucleus also contains one or more nucleoli (singular nucleolus). Nucleus contains nucleoplasm/karyoplasm, similar to cytoplasm. Nucleus Is surrounded by a double membrane called the nuclear membrane. Nucleus contains almost all of the cell’s genetic/hereditary information. (DNA is also found in mitochondria and in the chloroplasts of photosynthetic organisms). https://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html DNA packaging https://www.youtube.com/watch?v=eYrQ0EhVCYA 2 Diagrams for illustration purposes Epigenetics, histone acetylation 2. Nuclear envelope/membrane - Double membrane structure that separates the nucleus from the cytoplasm. The Outer membrane of the nuclear membrane folds out into the cytoplasm forming the endoplasmic reticulum (ER). Nuclear Pores in the nuclear membrane control the movement of materials into and out of the nucleus. The Nuclear membrane is covered on the outside with ribosomes (bound ribosomes). 3. Nucleolus is one or more dark-staining condensed regions of chromosomes that are involved in the assembly of ribosomes. 3 Diagrams for illustration purposes 4. Endomembrane system Protein translocation a. Plasma membrane b. Endoplasmic Reticulum (ER) c. Golgi apparatus d. Vacuoles, vesicles, lysosomes e. and endosomes Nuclear membrane (already This system of membranes co-operate functionally. Many materials are moved around the cell described) by the endomembrane system, including some proteins. https://www.youtube.com/watch ?v=tNEYtfvmRsc 4 Diagram for illustration purposes  Two types of membrane transport: 1. Passive diffusion 2. Energy-dependant transport 1/17/202 5 1 4. Endomembranes in Eukaryotic Cells a. Plasma membrane The plasma membrane is a semi-permeable/selectively permeable barrier which separates the inside of the cell from the external environment. b. Endoplasmic reticulum (ER); A series of enclosed, interconnected channels and sacs called cisternae. There are two forms of ER: Rough endoplasmic reticulum (rER): is covered with ribosomes. Rough ER is the site of new membrane synthesis for the cell. Smooth ER (sER) has NO ribosomes. Smooth ER has the following functions; 1. Synthesis of membrane components such as fatty acids and phospholipids 2. Synthesis of steroid hormones 3. Metabolism of carbohydrates 4. Detoxification of poisons (e.g. in liver cells) 6 4. Endomembranes in Eukaryotic Cells c. Golgi Apparatus The Golgi Apparatus is composed of a number of flattened, disk-like vesicles stacked together and located near the rER (rough endoplasmic reticulum). This apparatus plays a very important role in the modification and packaging of proteins that are made on ribosomes attached to the rough ER (called bound ribosomes). Transport vesicles fuse with one side of the Golgi and leave from the opposite side. Sorts and modifies lipids and proteins as they move from the cis side of the Golgi to the trans side. Functions: Modify, sort, package and some manufacture /synthesis. The mail centre of the cell!! Diagram for illustration purposes 7 7 4. Endomembranes in Eukaryotic Cells d. Vacuoles A vacuole is a space or cavity in the cytoplasm that is enclosed by a single membrane, therefore they are membrane bound organelles. Vacoules are usually much larger than vesicles. Vacuoles can be derived from ER and the Golgi complex. Their specific functions vary. Functions depend on the cell type, in plants:  Temporary storage organelles for proteins, nutrients, water, sugars, etc.  Store wastes and poisons to prevent toxicity to the cytoplasm. (used to defend against predation)  Internal strength - Turgor: Central vacuole in plants, take up water, enabling plant cells to increase in size and also provide rigidity to leaves and stems.  In animals, vacuoles are involved in exocytosis and endocytosis (secretory, excretory & storage functions) processes. (i) Vesicles: Small membrane-enclosed transport units that can transfer molecules between different cellular 8 compartments. They can fuse with other cell membranes. “Shuttle vehicle”! 4. Endomembranes in Eukaryotic Cells (ii) Lysosomes - digestive compartments (0.1-1.2microns) Membrane-enclosed spheres bound by a single membrane. Contain as many as 40 different Enzymes. These enzymes work best in an acid pH 4.5. Function in cell: 1. Digest other types of cells by phagocytosis. 2.Recycle cellular materials that have exceeded their life-time and recycle the cells own organic material by autophagy. A damaged organelle can be broken down and recycled allowing cells to renew themselves. (iii)Endosomes are a membrane-bound compartment inside eukaryotic cells. Endosomes provide an environment for material that are taken into cells by receptor mediated endocytosis to be sorted before it reaches the lysosome. (iv) Secretory vesicles. Transport molecules to the cell membrane for secretion. 5. Mitochondria (Breaking down fuel molecules and capturing energy in cellular respiration. Process glucose generate ATP) Mitochondria are the sites of cellular respiration, a process that generates ATP, the energy molecule of the cell. All eukaryotic cells contain mitochondria. Each mitochondrion is about 1–10 µm long. Structure: Mitochondria are large organelles containing circular DNA and are surrounded by a double membrane. The inner membrane is highly folded, folds are called cristae. The membranes divide the mitochondrion into two compartments, the central matrix, and the intermembrane space. DNA, in the form of a circular molecule, is found in the matrix. Mitochondrial DNA encodes many of the components for mitochondrial function, while nuclear DNA encodes for the remaining components. 10 Diagram: Draw and label 5. Mitochondria Diagram: Draw, label and describe the structure and function of the mitochondria 11 6. Peroxisomes - oxidative organelles Peroxisomes (found in plant and animal cells). All peroxisomes break down fats and amino acids into smaller molecules that can be used for energy production by mitochondria. Peroxisomes are cytoplasmic vesicles in which occur metabolic reactions occur that transfer hydrogens from various substrates to Oxygen and produce hydrogen peroxide (H2O2) as a by-product. H2O2 is highly reactive and toxic and is rapidly broken down by the enzyme catalase. 1/17/2021 Diagram for illustration purposes 12 7. Ribosomes (typical Bacterial cell 10,000-20,000 ribosomes –Woese S. American) Translate the DNA genetic code into proteins (made of RNA and protein). Composed of two parts (subunits). Eukaryotic ribosomes: Composed of a 60S and a 40S subunits that come together during protein synthesis to form an 80S ribosome. Prokaryotic ribosomes: Composed of a 50S and a 30S subunit that come together during protein synthesis to form a 70S ribosome. Ribosomes occur in the cell either free in the cytoplasm or bound to the ER these ribosomes 1. Plasmadestined produce proteins membrane for; 2. Nuclear membrane 3. Lysosomes 4. Golgi 5. Vacuoles 6. Secretory vesicles Both free and bound ribosomes are involved in protein synthesis, but differ in the final destination of their proteins. Free ribosomes synthesise proteins that are destined to be enzymes used in the cytoplasm (cytoplasmic enzymes), mitochondrial and chloroplast enzymes. http://highered.mheducation.com/sites/0072507470/student_view0/chapter3/animation how_translation_works.html Translation 13 For illustration purposes 8. Cytoplasm: Cytoplasm is the region in eukaryotic cells between the cytoplasmic membrane and nuclear membrane. It contains all the cell's internal sub-structures (organelles) except the nucleus. Liquid part  Cytosol. It is the site of almost all of the chemical activity occurring in a eukaryotic cell. 9. Nucleoplasm: Similar to the cytoplasm of a cell, the nucleus contains nucleoplasm (nucleus sap) or karyoplasm. 10. Cytosol: The aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended. 14 11. Cytoskeleton The cytoskeleton consists of; Microtubules Intermediate fibres Microfilaments (Together maintain cell shape, anchor organelles, and cause cell movement) The cell diagrams shown here represent intestinal epithelial cells with finger-like projections, the microvilli. The location and appearance of cytoskeletal fibres in different cell types Diagram for illustration purposes 12. CENTRIOLES AND CENTROSOMES A centriole is a small, cylindrical structure composed of microtubules, which are specialised protein filaments. In animals, some algae, and fungi, a pair of centrioles acts as a microtubule organising centre (MTOC) for the assembly of the spindle fibres that pull homologous chromosomes to opposite poles during cell division. Centrioles are not found in plants. 16 Diagram for illustration purposes 13. Locomotor structures Cilia and Flagella Cilia and flagella are cell structures that are structurally similar but are differentiated based on their function and/or length. Cilia are short and there are usually many (hundreds) cilia per cell. Flagella are longer and there are fewer flagella per cell (usually one to eight). https://www.youtube.com/watch?v=2lA2faVXt7A Cilia and flagella Diagram for illustration purposes 14. Extracellular matrix (controls how cells relate/interact with each other) The meshwork surrounding animal cells and secreted by the cells. Support: Holds cells together, provides physical strength. A scaffold for cells to attach and grow in as in tissue. Fills spaces between cells of tissues. Communication/regulation. Guides cell division, growth and development. By communicating with a cell through proteins called integrins, the ECM can regulate the cells behaviour - changing the set of proteins being made by the cell at any particular time and therefore altering a cells function. ECM largely determines how a tissue looks and functions. 18 14. Extracellular matrix (controls how cells relate/interact with each other) 19 In multicellular organisms eukaryotic cells are attached and communicate with each other through junctions. Ions and small polar molecules flow freely Hemidesmosomes: promoting the adhesion of epithelial cells in animal tissues to the underlying basement membrane. 20 Diagram for illustration purposes Plant Cell - same organelles as an animal cell, plus a few more. Be able to draw, label, describe functions of each component. Plastid Mitochondria Choloroplast Cytoso l Golgi apparatus Smooth endoplasmic Central vacuole reticulum Vesicl Plasmodesma e Cell wall Rough endoplasmic Plasma reticulum membrane Nuclear pore Chromatin (DNA) Nucleus Nucleolus Nuclear envelope Ribosomes Free ribosome Plant Cell – Practice Slide! Plastids: A double-membrane organelle found in the cells of plants, algae and some other eukaryotic organisms. Plastids manufacture and storage of important chemical compounds in autotrophic eukaryotes. Chloroplasts: Have a common evolutionary origin and possess a double-stranded circular DNA molecule. Contain the green pigment chlorophyll, 70S ribosomes, circular DNA, enzymes involved in protein synthesis. Chloroplasts are surrounded by a double membrane composed of an outer membrane and an inner membrane. Stroma (containing an aqueous fluid filled space). Thylakoids - hollow membranous sacs. Lumen - space inside a thylakoid. Grana (granum singular), stacks of thylakoids. Thylakoid membranes contain chlorophyll and other pigments that capture sunlight and CO2 and water make with sugar and O2 (by photosynthesis). ATP synthesis occurs in chloroplasts and mitochondria. Label and describe the structure of chloroplast 6CO2 + 6H2O  C6H12O6 + 6O2 Sunlight 23 Cell Wall Fungal cells: A cell wall that contains chitin Algae: Glycoproteins and polysaccharides Bacteria: Peptidoglycan Archaebacteria Glycoprotein, : pseudopeptidoglycan, Diatoms have a cell or polysaccharides). wall composed of biogenic silica Plant Cells have an extracellular matrix. 24 Diagrams for illustration  25 Diagrams for illustration  Generalised Prokaryotic cell. Be able to draw, label, describe function of components 1/17/2021 26 26 Endosymbiotic Theory: Process by which prokaryotes gave rise to the first eukaryotic cell is known as endosymbiosis. Proposed in1967. The theory proposes that cells became more complex when certain ancient prokaryotic cells ingested other cells with which they established a symbiotic relationship. 1. A free-living prokaryote was engulfed by an ancestral host eukaryotic cell as an endosymbiont. 2. This proteobacterium inside the ancestral eukaryote becomes a mitochondrion. 3. Later an ancestral non-photosynthetic eukaryote with a mitochondrion takes up a photosynthetic prokaryote - a cyanobacterium. 4. This photosynthetic prokaryote gives rise to what we know today as a chloroplast. http://www.sumanasinc.com/webcontent/animations/content/organelles.html Endosymbiotic theory 27  Evolution of eukaryotes through endosymbiosis Thus it seems that at least two lines of prokaryotic descent are represented in the eukaryotic cell evidence that at this time there were organisms evolving along different paths, two of these represented now inside eukaryotic cells! Diagram for illustration purposes Factors that support the endosymbiotic theory for mitochondria and chloroplasts in cells and how eukaryotic cells may have evolved from prokaryotic cells. (Occurred about 2bya) Both mitochondria and chloroplasts have; 1. Inner membrane of both organelles have enzymes and transport systems similar to those found in the plasma membrane of prokaryotes. 2. Circular DNA molecule. 3. Their DNA molecule is not associated with histone proteins as in eukaryotes. 4. Have 70S ribosomes like all prokaryotes. 5. Reproduction by binary fission like prokaryotes. 6. Both organelles are similar in size to the general size of bacteria. 7. Have two membranes, inner one thought to be derived from membrane of engulfed prokaryote, the outer membrane from the host eukaryote. 29 The End! 33