The Cell and Cell Cycle - OCR Lesson 3 PDF

THE CELL AND THE CELL CYCLE Lesson 3  Objectives: The students will have a better understanding of the cell organelles functions and will be aware that almost all cells undergo a cycle: The students will be able to: 1. Define cell 2. Identify the t...

THE CELL AND THE CELL CYCLE Lesson 3  Objectives: The students will have a better understanding of the cell organelles functions and will be aware that almost all cells undergo a cycle: The students will be able to: 1. Define cell 2. Identify the types of cell 3. Identify the different parts of the cell 4. Compare the functions of the parts of the cell 5. Identify the different stages of the cell cycle THE CELL The cell is the An organism can functional unit of be unicellular or living organisms multicellular Single celled vs. Multicellular organisms: An organism can be unicellular or multicellular The cells of multicellular organisms, such as humans, show a great variety of functional and morphological specializations--- EVOLUTION DIFFERENTIATION- the process by which cells assume specialized structure and function II. Parts of the Cell and their Function A. Cell Boundaries PLASMA MEMBRANE - External lipid membrane - Aka Plasmalemma - Function: Dynamic interface with the external environment - For transfer of nutrient and metabolites - Attachment of the cell to adjacent cells and extracellular matrix - Communication with the external environment PLASMA MEMBRANE ✓ Cell layer composed of bilayer of phospholipid molecules that are amphipathic ✓ Because of Amphipathic nature, phospholipids in aqueous solution will spontaneously form of a bilayer 1. Polar- hydrophilic (water loving), head, glycerol conjugated to a nitrogenous compound 2. Non-Polar – hydrophobic (water hating), tail, two-long chain fatty acids PLASMA MEMBRANE FLUIDY AND FLEXIBILITY- Increased by the presence of UNSATURATED fatty acids, which prevent close packing on the hydrophobic cell Cholesterol molecule is amphipathic and have a kinked conformation- for the prevention of overly dense packing of the phospholipid fatty acid tails. It mediates the flow of both materials and information into and out of the cell, a function of vital importance to the cell. NUCLEUS Largest organelles in the cell Control center of the cell, containing the "blueprint" Composition: DNA (20% of its mass) Protein (nucleoprotein) Some Ribonucleic acid (RNA) Nuclear RNA includes mRNA, tRNA, and rRNA NUCLEI Heterogenous structures with electron- dense and electron-lucent (light) areas Heterochromatin- dense areas (tightly- coiled inactive chromatin) Euchromatin- electron-lucent nuclear material that is active in RNA synthesis HETEROCHROMATIN and EUCHROMATIN- are called CHROMATIN NUCLEOLUS Sites of ribosomal RNA synthesis and ribosome assembly Ribosomal RNA and proteins, synthesized in the cytoplasm and imported back into the nucleus, are assembled into subunits The subunits then passed backed to the cytoplasm to aggregate the complete ribosomes. CYTOPLASM AND DIFFERENT CELL ORGANELLES Cytoplasmic organelles are suspended in fluid medium called Cytosol in which many metabolic reactions take place. Within the cytosol– the cytoskeleton Cytoskeleton- provides structural support for the cells and its organelles, as well as providing mechanism for transfer of materials within the cell and movement of the cell itself. Microfilaments ❑narrowest ❑diameter of about 7 nm ❑made up of many linked monomers of a protein called actin, combined in a structure that resembles a double helix. ❑also known as actin filaments. ❑come together to form linear, rod-like bundles, but they can also form branching networks with the assistance of proteins that anchor new side branches. ❑Actin is a key part of the cytoskeleton and is found in virtually all types of eukaryotic cells. Key Role: serve as tracks for the movement of a motor protein called myosin, which can also form filaments Intermediate Filaments ❑ A type of cytoskeletal element made of multiple strands of fibrous proteins wound together. ❑ Average diameter of 8 to 10 nm ❑Unlike microfilaments, which are always made of actin, intermediate filaments come in a number of different varieties, each one made up of a different type of protein monomer ❑ One familiar protein that forms intermediate filaments is keratin, a fibrous protein found in hair, nails, and skin ❑ found in many types of animal cells, but typically not in plants or fungi. Microtubules ❑the largest of the three types of cytoskeletal fibers - diameter of about 25 nm. ❑made up of tubulin proteins arranged to form a hollow, straw-like tube, and each tubulin protein consists of two subunits, α- tubulin and β-tubulin. ❑ Microtubules, like actin filaments, are dynamic structures, and they can grow and shrink quickly by the addition or removal of tubulin dimers. Microtubules have directionality, meaning that they have two ends that are structurally different from one another. Centrosome, Centrioles ❑A structure found near the nucleus of animal cells, serves as a microtubule-organizing center. ❑ It contains a pair of hollow, rod-like structures that lie perpendicular to each other. ❑ Each centriole is a cylinder of nine triplets of microtubules, with nontubulin proteins to hold the triplets together. ❑Anchor and initiate microtubules, and these proteins give the centrosome its microtubule- organizing capabilities. It surrounds centrioles ❑Plant and fungal cells don’t have centrosomes with centrioles, but they do have microtubule- organizing centers that play similar roles. Centrioles They play a vital role in facilitating the reproduction of cells. They engage in the arrangement of mitotic spindles during cell division. It aids in cytokinesis. It organises the microtubules in the cytoplasm. They regulate the position of the nucleus and other organelles in the cell. Flagella, Cilia ❑Flagella (singular, flagellum) are long, hair-like structures that extend outward from the plasma membrane and are used to move an entire cell ❑Cilia (singular, cilium) resemble flagella, but are shorter and can generally be divided into two different categories: motile cilia and primary cilia. ❑Like flagella, motile cilia generate power by beating, but unlike flagella, they are usually found in large numbers on the cell surface. ENDOPLASMIC RETICULUM (ER) extensive system of flattened membrane bound tubules, saccules, and flattened cisterns. compartmentalizes the cytoplasm in which increases the surface area for biochemical synthesis The endoplasmic reticulum (ER) plays an important role in the modification of proteins and synthesis of lipids. It consists of a network of membranous tubules and flattened sacs. The sacs are referred to as cisternae, a general term for membrane structures that come in stacks and have a flattened-pancake structure, and we will see that the Golgi also has cisternae.  ❑Found near the nucleus and typically forms large, flat sheets. As the ribosomes attached to the rough ER Rough synthesize proteins, they feed the newly forming polypeptide chains ER into the lumen inside the rough ER. ❑Another important role of the rough ER is to synthesize new phospholipids for cell membranes.  Key Role: ❑It produces lipids, including phospholipids, cholesterol and steroids, and glycolipids (lipids with carbohydrate groups attached). ❑Enzymes that assemble these lipids manufacture their products on the smooth ER’s membrane, Smooth where hydrophobic molecules can be sheltered from the surrounding watery (hydrophilic) ER environment. ❑ Detoxification: substances like drugs and toxic byproducts of metabolism are modified by enzymes that reside in the smooth ER, making them more water-soluble and easier for the body to remove. ❑Smooth ER is as a storage tank for calcium ions, which function in cell signaling. Golgi Apparatus made up of a series of flattened stacked pouches called cisternae. It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. responsible for transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations. Mitochondria The process of making ATP using the chemical energy found in glucose and other nutrients is called cellular respiration, and its oxygen-requiring steps take place inside the mitochondria. are oval-shaped organelles with two membranes: an outer one, surrounding the entire organelle, and an inner one, with many invaginations (inward protrusions) called cristae that maximize surface area. Lysosome is a membrane-bound cell organelle that contains digestive enzymes. Lysosomes are involved with various cell processes. They break down excess or worn-out cell parts. They may be used to destroy invading viruses and bacteria ** to remove waste as well as destroying a cell after it has died, called autolysis. Peroxisome Peroxisomes are organelles that sequester diverse oxidative reactions and play important roles in metabolism, reactive oxygen species detoxification, and signaling. Oxidative pathways housed in peroxisomes include fatty acid β- oxidation, which contributes to embryogenesis, seedling growth, and stomatal opening.  Ribosomes - minute cytoplasmic organelles composed of two subunits which consist of a strand of RNA (ribosomal RNA, rRNA) with associated ribosomal proteins. Align mRNA strands so that transfer RNA (tRNA) molecules may be brought into position and their amino acids added sequentially to the growing peptide chain. Chloroplast Chloroplasts are organelles found in plants and photosynthetic algae (protists), and their job is to carry out photosynthesis. In the process of photosynthesis, light energy is collected and used to synthesize sugars from carbon dioxide, and oxygen is released as a by-product. The CELL CYCLE Cell Division Dividing cells are needed in order to study chromosomes Cytogenetic abnormalities result from errors in cell division. 2 types: MITOSIS – Division of somatic cells MEIOSIS- division that occurs only on gametic cells Important notes: Some of the daughter cells progressively specialized and eventually produce the terminally differentiated cells. Most tissues however retain a population of relatively undifferentiated that are able to divide and replace the differentiated cell population as required. In the fully developed organism, the terminally differentiated cells of some tissues lose their ability to undergo mitosis In contrast, the cells of certain other tissues undergo continuous cycle to mitotic division throughout the lifespan of the organism replacing cells lost during normal wear and tear. Between these extremes are cells that do not normally divide but retain the capacity to undergo mitosis should the need arise (facultative dividers) APOPTOSIS CELL DEATH Cell division and differentiation are balanced by cell death both during the development and growth of the immature organism and in the mature adult. The liver Only human internal organ capable of natural regeneration of lost tissue Only 20% of an adult's liver is needed to serve as liver allograft for an infant or small child. Adult-to-adult liver transplantation has been done using the donor's right hepatic lobe, which amounts 60% of the liver. The CELL CYCLE AKA CELL DIVISION CYCLE Series of events that takes place in a cell leading to its division and duplication (replication) Last about 17-18 hours The interval between mitotic divisions or transition of a cell from one interphase through cell division and back to interphase. GAP 1 (G1) Longest 9 hours Chromosomes exist as single chromatids Cells are metabolically active Protein synthesis takes place A cell might be permanently arrested at this stage if it does not undergo further division. - G0 Gap zero GAP 1 (G1) Protein Synthesis 1. TRANSCRIPTION site: nucleus ❑DNA is copied in a complimentary piece of messenger RNA (mRNA) ❑Controlled by RNA Polymerase – enzyme ❑RNA polymerase attaches to a promoter region ❑RNA polymerase moves off the template strand at a termination sequence to complete the synthesis of a mRNA molecule ❑mRNA carrying the information necessary to synthesize of a specific protein, is transferred from the nucleus into the cytoplasm of the cell, where it then associates with ribosomes. GAP 1 (G1) 2. Translation site: Ribosomes - a chain of amino acid is synthesized by using the newly transcribed mRNA molecule as a template with the help of third ribonucleic acid, transfer RNA (tRNA) - Ribosomes read mRNA one codon at a time - Transfer RNA molecules transfer the specific amino acids to the synthesizing protein chain. This process is continued until a stop codon is reached. - New protein is then releases into the cell environment and the ribosomes split apart. SYNTHESIS (S) Last about 5 hours This is when the DNA synthesis occurs DNA replicates itself and the chromosome then consist of two identical sister chromatids. Steps: INITIATION– REPLICATION and TERMINATION Some DNA replicates early in the S phase and some replicates later.  GAP 2 (G2) Last about 3 hours During this phase, the cell prepares to undergo cell division. The completion of G2 represents the end of interphase MITOSIS (M) The Final Step in the cell cycle Last only 1-2 hours Process by which cells reproduce themselves, creating two daughter cells that are genetically identical to one another and to the original parent cell. End