Lecture 4 - Introduction to Cell Biology 23-24.pdf
- 1. Introduction to CELL BIOLOGY Ms. Nasir., Z.J. GENERAL BIOLOGY I –BIO 101.
- 2. LECTURE OUTCOME By the end of this session, you should be able to: • Describe the cell theory • Describe cell structures with their specific functions • Describe with the aid of a diagram, the different types of cells and their modifications • Explain the evolution of cells
- 3. CELL SIZE
- 4. Introduction A cell is a chemical system that is able to maintain its structure and reproduce. Cell Theory: • Basic unit of life; all chemical reactions that makes us alive happens in the cell • All cells arrives from existing cells • Is a building block for all living organisms: • Unicellular • Multicellular: • Each type of cell with a specific function • Immune cells fight against pathogens Cell components: • Membrane – boundary • Cytoplasm – contains organelles • Nucleus – contains DNA
- 5. CELL TYPES Cells types: • Prokaryotic cells: bacteria • Do not have nucleus, however, have DNA • 10x smaller • Eukaryotic cells: • Animal cells • Plant cells This figure shows the generalized structure of a prokaryotic cell.
- 6. PROKARYOTIC CELLS • Prokaryotes are single-celled organisms of the domains Bacteria and Archaea. • All prokaryotes have plasma membranes, cytoplasm, ribosomes, and DNA that is not membrane-bound. • Most have peptidoglycan cell walls, and many have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1 to 5.0 μm. • As a cell increases in size, its surface area-to-volume ratio decreases. If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume • few or no membrane enclosed spaces within the cytoplasm • no nucleus - DNA is in a region called the nucleoid • DNA is circular and naked (has no protein associated with it)
- 7. EUKARYOTIC CELLS • Like a prokaryotic cell, a eukaryotic cell has a plasma membrane, cytoplasm, and ribosomes, but a eukaryotic cell is typically larger than a prokaryotic cell, has a true nucleus (meaning a membrane surrounds its DNA), and has other membrane- bound organelles that allow for compartmentalizing functions. • The plasma membrane is a phospholipid bilayer embedded with proteins. The nucleus’s nucleolus is the site of ribosome assembly. We find ribosomes either in the cytoplasm or attached to the cytoplasmic side of the plasma membrane or endoplasmic reticulum that perform the protein synthesis. • Mitochondria participate in cellular respiration. They are responsible for the majority of ATP produced in the cell. Peroxisomes hydrolyze fatty acids, amino acids, and some toxins. Vesicles and vacuoles are storage and transport compartments. In plant cells, vacuoles also help break down macromolecules.
- 8. EUKARYOTIC CELLS • Animal cells also have a centrosome and lysosomes. The centrosome has two bodies perpendicular to each other, the centrioles, and has an unknown purpose in cell division. Lysosomes are the digestive organelles of animal cells. • Plant cells and plant-like cells each have a cell wall, chloroplasts, and a central vacuole. The plant cell wall, whose primary component is cellulose, protects the cell, provides structural support, and gives the cell shape. Photosynthesis takes place in chloroplasts. The central vacuole can expand without having to produce more cytoplasm.
- 9. EUKARYOTIC CELLS • Components: 1. Plasma Membrane - And a Cell wall in plants, yeast 2. Nucleus 3. Cytoplasm • Organelles: • Mitochondria • Ribosomes • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Peroxisomes • Cytoskeleton • Vacuoles (plants) • Chloroplast (plants) This figure shows (a) a typical animal cell and (b) a typical plant cell.
- 10. CELL STRUCTURE AND FUNCTION
- 11. 1. PLASMA MEMBRANE Components: • Lipids • Double layer of phospholipids • and cholesterol & other lipids • Proteins • Carbohydrates • Attached to either lipids or proteins • Function • Allows selective passage in & out the cell The plasma membrane is a phospholipid bilayer with embedded proteins. There are other components, such as cholesterol and carbohydrates, which can be found in the membrane in addition to phospholipids and protein.
- 12. Membrane enclosed spaces allow cell functions to be compartmentalized and isolated from other functions. Prokaryotes lack membrane enclosed spaces in their cytoplasm. • Some prokaryotes are photosynthetic. The biochemical machinery for trapping light energy is contained within a highly folded plasma membrane.
- 13. 2. THE NUCLEUS Structure: • Nuclear membrane – envelope • Nuclear pores – allows passage in & out • Surrounded by rough endoplasmic reticulum • Nucleoplasm – inside the nucleus • Contains: • the nucleolus – where rRNA is made • DNA – under the form of chromatin The outermost boundary of the nucleus is the nuclear envelope. Notice that the nuclear envelope consists of two phospholipid bilayers (membranes)—an outer membrane and an inner membrane—in contrast to the plasma membrane, which consists of only one phospholipid bilayer. (credit: modification of work by NIGMS, NIH)
- 14. Chromosome - “colored body” consists of both DNA and protein - seen as chromosomes when highly condensed in preparation for cell division At other times the DNA and protein are threadlike and called . The most common proteins are histones. DNA is coiled around histones in a regular pattern that produces structures called nucleosomes.
- 15. 3. ENDOPLASMIC RECTICULUM ER structure: made of membranes as boundary • Two types: • Rough ER (RER) – has ribosomes attached to their surfaces on the membrane • Made of flatten vesicle and attached to the nuclear envelope • Role in modifying proteins • Smooth ER (SER) – shaped as tubules • Role in storage of calcium ions (Ca+), synthesize lipids, steroid hormones, carbohydrates The endomembrane system works to modify, package, and transport lipids and proteins. It also covers a large surface area for enzymatic action. (credit: modification of work by Magnus Manske)
- 16. 4. GOLGI APARATUS Structure: • Flatten big vesicles or sacs • Have two faces • Trans face – Receiving face towards the ER and nucleus • Cis face – Releasing face towards the cell plasma membrane Function: • Modifies proteins, lipids The Golgi apparatus in this transmission electron micrograph of a white blood cell is visible as a stack of semicircular flattened rings in the lower portion of this image. Several vesicles can be seen near the Golgi apparatus. (credit: modification of work by Louisa Howard; scale-bar data from Matt Russell)
- 17. 5. LYSOSOME • The Golgi Apparatus also forms lysosomes • Lysosomes - vesicles filled with digestive enzymes - used for intracellular digestion Structures: • membranous vesicle • Containing enzymes and low pH • Role as “garbage disposal” by removing any broken organelles, pathogens etc. • In Macrophages (a type of white blood cells) A macrophage has phagocytized a potentially pathogenic bacterium into a vesicle, which then fuses with a lysosome within the cell so that the pathogen can be destroyed. Other organelles are present in the cell, but for simplicity, are not shown.
- 18. THE ENDOMEMBRANE SYSTEM A system of structures of different shapes made of membranes; Function: Role in making and modifying proteins and lipids; It includes: Plasma membrane, nuclear envelope, RER, SER, Golgi apparatus, lysosomes The endomembrane system works to modify, package, and transport lipids and proteins. (credit: modification of work by Magnus Manske)
- 19. 6. RIBOSOMES Structure: • Organelles not made of membranes • Made of rRNA and proteins • Attached to RER or free in the cytoplasm • Roundly shape Function: • Function in synthesizing proteins
- 20. 7. MITOCHONDRIA “powerhouse” or “energy factories” function in making ATP (chemical energy) from food Structure: oval-shaped vesicles, made of two membranes • Outer membrane • inner membrane – with folds called cristae • Intermembrane space and the matrix Function: • The site of oxygen consumption within cells • Have their own DNA that is similar to prokaryotic DNA • Have their own ribosomes that are similar in constructionto prokaryotic ribosomes • Synthesize many, but not all, of their own proteins • Mitochondria replicate by binary fission - similar toprokaryotic cell division • This transmission electron micrograph shows a mitochondrion as viewed with an electron microscope. Notice the inner and outer membranes, the cristae, and the mitochondrial matrix. (credit: modification of work by Matthew Britton; scale-bar data from Matt Russell)
- 21. 8. CHLOROPLASTS Structure: Vesicle with two membranes: • inner and outer • Stroma – inside the chloroplast • Thylakoids – flatten vesicles inside the stroma • Organized in stacks called grana • Made of • membrane boundary – contains green pigments or chlorophylls • lumen Function: • Role in photosynthesis – transforming solar energy into food (chemical energy) This simplified diagram of a chloroplast shows the outer membrane, inner membrane, thylakoids, grana, and stroma.
- 22. CHLOROPLASTS have their own DNA, similar to prokaryotic DNA Can synthesize many of their own proteins using prokaryote-like ribosomes Synthesize many, but not all, of their own proteins Replicate through division similar to prokaryotic cell division Chloroplasts can take on other functions synthesize and store starch in roots and tubers have pigments and give fruits ripened color
- 23. CELL PROTECTION Protection against tension and compression • Extracellular matrix (ECM) – animals • Made of protein collagen and glycoproteins (sugar + protein) • The extracellular matrix consists of a network of substances secreted by cells. • Cell wall – plant cells • Made of carbohydrates like pectin
- 24. Plants have cell walls made of cellulose. During cell division plant cells build dividing walls between the two new cells called the cell plate. An adhesive layer - the middle lamella - is laid down between the new cell walls Cell walls can be thickened through the addition of materials to the inside of the primary cell wall.
- 25. CYTOSKELETON • It is composed of A SCAFFOLDING OF proteins assembled into 3 different types: • Microtubules – made of tubulin proteins • helps with: • transporting vesicles/organelles within the cell, • mitotic spindle (in cell division), • movement of cells (see flagellum, cilia) • Intermediate filaments – helps with the shape of the cells • Example: Keratin • Microfilaments – made of actin proteins • helps with: • movement of cells (see pseudopods), • contraction in the muscle cells, • Cleavage furrow during Cell division Microfilaments, intermediate filaments, and microtubules compose a cell’s cytoskeleton.
- 26. Plant Cells have, in addition to the collection of organelles found in other groups, a central vacuole for storage and for producing pressure inside the the cell. The central vacuole is usually filled with water and solutes. A high solute concentration draws water into the vacuole, expanding the vacuole and the cell. Because plant cells are enclosed by a cell wall, the expansion of the vacuole can exert pressure on the cell without causing the cell to burst.
- 27. CILIAAND FLAGELLUM • More on this visit YouTube video: Cilia and flagella • Cilia – many in number, size: short, hair-like • Helps in movement of cells or substances (mucus) • Flagellum – 1 or 2 on cell surface; very long • Helps in movement of cells Bacteria often have flagella with a single protein core (flagellin) that they can use to move in a rotary corkscrew like fashion The rotary motor of prokaryotic flagella is powered by proton flow through the cell membrane. Rotating structures are rare in nature.
- 28. ENDOSYMBIOSIS & EVOLUTION • Symbiosis = living together • Mitochondria and chloroplasts are organelles that in the past were independent organisms (i.e. bacteria) living outside the cells. • Proofs: 1 circular DNA, ribosomes, binary division • For more details, please watch this YouTube video: Endosymbiosis