5 - A tour of the cell - Part Two
- 1. A Tour of the Cell PART TWO 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 • The Golgi Apparatus • Lysosomes • Vacuoles • Energy Transfer • Mitochondria • Chloroplast • Peroxisomes • The Cytoskeleton • Microtubules • Actin filaments • Intermediate filaments
- 4. Energy Transfer • Mitochondria are rod-shaped organelles: (1-10 μm) • Considered the power generators of the cell • Cellular Respiration: converting oxygen and nutrients into adenosine triphosphate (ATP). • By extracting energy from sugar, fat, etc. • Chloroplasts are lens-shaped organelles: (3-6 μm) • Found in plants and algae • Site of photosynthesis • The process of using sunlight to drive the synthesis of organic compound such as sugar from carbon dioxide and water
- 5. Energy Transfer • Endosymbiont Theory and Evolution origin of Mitochondria and Chloroplast • Endosymbiont is a cell living within another cell • Widely accepted theory, consistent with many structural features: • Two membrane surrounding them unlike members of endomembrane system • Ribosomes and circular DNA molecules • Autonomous organelles • Independent and grow and reproduce in the cell
- 6. Energy Transfer - Mitochondria • Found in almost all forms of life: Plants, animals, fungi, etc. • Population: depending on the level of metabolic activity of the cell • Structure: • Phospholipid bilayer with specific proteins • Soft outer membrane and inner membrane is convoluted with infoldings (Cristae) • Intermembrane space • Mitochondrial matrix • Full of different enzymes and DNA and ribosomes • Enzymes catalyze some of the steps of cellular respiration • Other enzymes are build into the inner membrane • Cristae infoldings => larger surface area => enhanced cellular respiration • Other properties: moving, changing shape, fusing and dividing in two
- 7. Energy Transfer - Chloroplast • Contains: Chlorophyll and enzymes and molecules of photosynthesis of sugar • Structure: • Chloroplast envelope • Outer membrane • Intermembrane space • Inner membrane • Thylakoids • Thylakoid lumen • Thylakoid membrane • Granum (pl. Grana) • Stroma (the fluid outside the thylakoids): • DNA • Ribosomes • Enzymes • Three compartments: • Intermembrane space • Stroma • Thylakoid space • The chloroplast is a specialized member of a family of closely related plant organelles called plastids.
- 8. Energy Transfer - Peroxisome • Peroxisomes contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen (O2), producing hydrogen peroxide (H2O2) as a by-product in different functions: • Uses oxygen to break fatty acids down into smaller molecules that are transported to mitochondria and used as fuel for cellular respiration. • In the liver, they detoxify alcohol and other harmful compounds by transferring hydrogen from the poisonous compounds to oxygen. • Contains an enzyme that cleaves H2O2 • Grow larger by proteins made in cytosol and ER • Increase in number by splitting in two at a certain size
- 10. The cytoskeleton • The eukaryotic cytoskeleton • Major Roles: • Mechanical support • Motility (both cell location and cell movement) • Manipulating the plasma membrane is phagocytosis • Composed of three types of molecular structures: • Microtubules • Microfilaments • Intermediate filaments
- 11. The Cytoskeleton
- 12. The cytoskeleton - Microtubules • Composed of tubulin dimers: • α Tubulin • Β Tubulin • Functions: • Shape and support (compression resisting) • Main tracks for organelles’ movement • Guide vesicles from ER to Golgi system • Chromosome separation during cell division
- 13. The cytoskeleton - Microtubules • In animal cells, they grow out of Centrosomes • Centrosome is a region near the nucleus • Structure: • A pair of centrioles • Maternal centriole • Daughter centriole • Each centriole is composed of nine sets of triplet microtubules arranged in a ring
- 14. The cytoskeleton - Microtubules • Cilia and Flagella are microtubule- containing extensions • Functions: • They can act as locomotor appendages, e.g. the sperm of animals have flagella • In a tissue, they can move fluid over the surface of the tissue e.g. the ciliated lining of the trachea (windpipes) sweeps mucus, containing trapped debris out of the lungs.
- 16. The cytoskeleton - Microtubules • Cilia and Flagella differences • Motile cilia usually occur in large numbers on the cell surface. • Flagella are usually limited to just one or a few per cell • Flagella are longer than cilia. • Flagella and cilia differ in their beating patterns. • A flagellum has an undulating motion like the tail of a fish. • Cilia have alternating power and recovery strokes, much like the oars of a racing crew boat • Cilia and Flagella Similarity • A common structure • A group of microtubules sheathed in an extension of the plasma membrane • Nine doublets of microtubules are arranged in a ring with two single microtubules in its center. “9+2” pattern. • The microtubule assembly of a cilium or flagellum is anchored in the cell by a basal body, which is structurally very similar to a centriole, with microtubule triplets in a “9 + 0” pattern.
- 17. The cytoskeleton - Microtubules • Cilia and Flagella Similarity • Flagella and motile cilia bending involves large motor proteins called dynein • Dynein and Kinesin are motor proteins for organelle and vesicle transport along microtubules in the cell, each with specific activity
- 19. The cytoskeleton – Microfilament • AKA Actin Filaments because of their globular actin subunits • A microfilament is a twisted double chain of actin subunits • Formation: • Linear filaments • Network filaments in association with certain proteins • Their structural is to bear tension (pulling forces) • The 3D structure (cortical microfilaments) helps support the cell’s shape.
- 20. The cytoskeleton – Microfilament & Motility • In animals actin Filaments and thicker filaments called myosin interact to cause muscle contraction. • In Amoeba and some WBCs localized contractions brought about by actin and myosin are involved in the amoeboid (crawling) movement of the cells • The cell crawls along a surface by extending cellular extensions called pseudopodia and moving toward them • In plant cells, actin-protein interactions contribute to cytoplasmic streaming, a circular flow of cytoplasm within cells
- 22. The cytoskeleton – Intermediate Filaments • Named after their diameter • Structures larger than actin filaments and smaller than microtubules • Only found in some cell of some animals, including vertebrates • Specialized for bearing tension (like microfilaments) • A diverse class of cytoskeletal elements • Unlike microtubules and microfilaments, each type is constructed from a particular molecular subunit belonging to a family of proteins whose members include the keratins • Involve in diverse functions: • Reinforcing cell shape and fixing the position of organelles • Nuclear lamina
- 23. The cytoskeleton