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4 - A tour of the cell - Part One
- 1. A Tour of the Cell PART ONE UNIVERSITY OF TEHRAN Ahmad V.Kashani, PhD
- 2. Outlines • Cells, Fundamental units of life • Tools and Techniques • Eukaryotes vs. Prokaryotes • Animal cell • Plant cell • Genetic instructions • Nucleus • Ribosomes • Endomembrane system • ER network • Rough ER • Soft ER • Endomembrane system • ER network • Rough ER • Soft ER • The Golgi Apparatus • Lysosomes • Vacuoles
- 3. Cells • Fundamental Units of life • Different types and functions: • Organisms • Single-celled e.g. Paramecium • Multicellular • Organs • Tissues • Cells • Organelles • Molecules
- 4. Tools and Techniques • Microscopes • Light Microscope (LM) • Brightfield • Phase contrast • Fluorescence • Etc. • Electron Microscope (EM) • SEM: 3-D surface image • TEM: Reveal internal structure • Biochemistry
- 6. Eukaryotes vs. prokaryotes Similarities: • Plasma membrane • Cytosol • Chromosomes • DNA • Ribosomes • RNA Differences: • Location of the DNA • Eukaryotes: nucleus • Prokaryotes: nucleoid • Membrane-bounded Organelles • Protein surrounded regions • Internal membrane • Specific composition for each organelle • Size • Eukaryotes: 10-100 μm • Prokaryotes: 1-5 μm
- 7. Animal cells
- 8. Plant cells
- 9. Genetic Instructions: Nucleus • Nucleus: contains most of the genes • Nuclear Envelope: a double membrane, each a lipid bilayer with associated proteins. • Pores • Nuclear Lamina: the nuclear side of the Envelope is a network of protein filaments (in animal cells, called intermediate filaments): • Maintains the shape of the nucleus • Mechanical support
- 10. Genetic Instructions: Nucleus – From DNA to Chromosome • Nucleosome: a structural unit of a chromosome, consisting of a length of DNA coiled around a core of histones. • Chromatin: The complex of DNA and proteins making up chromosomes, with primary function of more compact and denser packaging. • Heterochromatin • Euchromatin -> transcription • Chromosome: As a cell prepares to divide, chromosome coils become distinguishable under a microscope. • Nucleolus: • Ribosomal RNA (rRNA) DNA codes • Ribosomal subunits primary assembly
- 11. Genetic Instructions: Ribosomes: Protein Factories • Complexes made of ribosomal RNAs and proteins, carry out protein synthesis. • High rate of protein synthesis would result in more number of ribosomes. • Ribosomes build proteins in two cytoplasmic locales • Free ribosomes, suspended in the cytosol • Bound ribosomes, attached to the ER
- 12. Endomembrane System • Includes: • The nuclear envelope • The endoplasmic reticulum • The Golgi apparatus • Lysosomes • Various kinds of vesicles and vacuoles • plasma membrane • Functions: • Synthesis of proteins • Transport of proteins into membranes and organelles or out of the cell • Metabolism and movement of lipids • Detoxification of poisons
- 13. Endomembrane System • Endoplasmic reticulum (ER): An extension of nucleus membrane which consists of a network of membranous tubules and sacs called cisternae. • ER lumen (cavity) or cisternal space: the internal compartment of the ER • Two distinct regions and functions: • Rough ER (Have ribosomes) • Soft ER (Lack ribosomes)
- 14. Endomembrane System – Soft ER • The smooth ER functions in: • Synthesis of lipids and enzymes • Hormones • Sex hormones in vertebrates • Hormones from adrenal gland • Metabolism of carbohydrates • Detoxification of drugs and poisons • By adding hydroxyl group so that it becomes more soluble • Storage of calcium ions • Calcium pump in muscle cells
- 15. Endomembrane System – Rough ER • The Rough ER functions in: • Ribosomes of protein secreting cells are attached to rough ER. • Polypeptide chain is threaded into ER lumen through a pore formed by a protein complex • Primary process and folding in ER lumen • Further modifications e.g. glycosylation • Transport vesicles are bud-like bubbles that take protein-containing vesicles from transitional ER to another part of the cell. • Cell membrane factory
- 16. Endomembrane System – Golgi Apparatus • The Golgi apparatus consists of a group of associated, flattened membranous sacs (cisternae) • The two sides of a Golgi stack • The cis face (Receiving side) • The trans face (Shipping side) • Further modification of ER products during cis to trans transit
- 17. Endomembrane System – Golgi Apparatus • Further functions: • Modification and alteration of membrane phospholipids • Produce many polysaccharides e.g. pectins • Golgi products are in stages; each stage in a separate cisternae with unique enzymes. • the cisternae of the Golgi actually progress forward from the cis to the trans face, carrying and modifying their cargo as they move • Final vesicle before budding, is marked by some molecular tags as addresses or ZIP codes.
- 18. Endomembrane System – Lysosomes • A lysosome is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules. • Lysosomal enzymes work best in the acidic environment found in lysosomes • So, if leak into cytosol, they are not quite active • Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing
- 19. Endomembrane System – Lysosomes Phagocytosis Autophagy
- 20. Endomembrane System – Vacuoles • Vacuoles are large vesicles derived from the endoplasmic reticulum and Golgi apparatus • The vacuolar membrane (Tonoplast) is selective in transporting solutes; as a result, the solution inside a vacuole differs in composition from the cytosol. • Perform a variety of functions: • Contractile vacuoles by pumping excess water out of the cell and maintaining suitable concentration of ions and molecules. • In plants and fungi certain vacuoles carry out enzymatic hydrolysis (like lysosome in animal cells)
- 21. Endomembrane System – Vacuoles • In Plants: • Small vacuoles can hold reserves of important organic compounds, such as the proteins stockpiled in the storage cells in seeds • They protect the plant against herbivores by storing compounds that are poisonous or unpalatable to animals. • Some plant vacuoles contain pigments, such as the red and blue pigments of petals that help attract pollinating insects to flowers. • Central Vacuole: • Coalescence of smaller vacuoles • Inside solution is cell sap • Cell sap is plant’s main repository of inorganic ion such as potassium and chloride. • Major role in the growth of plant cells by absorbing water
- 22. Summary • Cells, Fundamental units of life • Tools and Techniques • Eukaryotes vs. Prokaryotes • Animal cell • Plant cell • Genetic instructions • Nucleus • Ribosomes • Endomembrane system • ER network • Rough ER • Soft ER • Endomembrane system • ER network • Rough ER • Soft ER • The Golgi Apparatus • Lysosomes • Vacuoles
- 23. Summary