Chapter 6 Cell Cell – Cell-membrane, Cytoplasm and Nucleus Cytoplasm – Cytosol and Cell Organelles Nucleus – Nuclear Envelope, Nucleoplasm and Chromatin (DNA + Histones) Cell Membrane All cells are covered with a thin covering of a double layer of Phospholipids and associated Proteins present here and there. Each phospholipid has a polar (hydrophilic) head and non-polar (hydrophobic) tails. In the double layer the tails face each other forming a hydrophobic barrier which keeps water dissolved contents inside. Proteins may be Intrinsic – embedded in the lipid double layer and Extrinsic associated outside the lipid double layer.

Cytoplasm Cytoplasm is the living fluid part between cell membrane and nucleus. It has special structures called Cell Organelles in it. Cytosol is the matrix (formless) part of cytoplasm formed of water having dissolved or suspended substances in it. Cell Organelles are organ like each performing specific function/s but formed of molecules and membranes only (sub- cellular). Double Membrane bound Organelles: Mitochondria, Chloroplasts, Endoplasmic Reticulum, Golgi Body, and Nucleus. Single Membrane bound Organelles: Lysosomes, Peroxisomes, Vacuoles Organelles lacking any membrane: Ribosomes, Centrioles, Nucleolus Plant Cell versus Animal Cell Most Plant Cells have but most animal cells lack: Cell Walls outside cell membranes Chloroplasts give green color to plants and produce organic food Central Vacuoles maintain Turgor pressure Most Animal Cells have but most plant cells lack: Centriole help in cilia/flagella formation and spindle formation Lysosome have digestive enzymes helping in cellular digestion Flagella are locomotory organelles that help in movements from place to place Recap-1 Chapter 6 1. Cell is formed of ------, ------and ------2. Cytoplasm is formed of ------and ------3. Cell membrane has a ------bilayer 4. Proteins in cell membrane can be ------or ------5. Cell membrane is fluid due to ------6. Cell membrane forms a mosaic due to ----- 7. Cells must have a high ------to ------ratio 8. Heads of phospholipids are --- but tails are------9. Only plant cells have -----, ----- and ------. 10. Most animal cells have ------and ------.

Nucleus and Ribosomes 1 Genetic Control of the Cell Nucleus: is the most distinct structure inside cell visible with light microscope. It has inside it DNA having all the information needed to form and run the cell. The segments of DNA are called Genes. Nuclear Envelope: is formed of 2 membranes with a gap between them. It has a large number of Nuclear Pores usually bound by a nuclear complex. The pores are large enough to allow RNA and proteins to pass through. Nucleoplasm: is the matrix (formless) of nucleus and has a different composition than cytosol. Chromatin fibers: are very long molecules of DNA associated with proteins (Histones and other nuclear proteins). Each chromatin fiber, at the time of cell division, organizes into Chromosomes. Nucleolus: is present in the nucleus when the cell is not dividing. No membrane bounds it. It assembles both units of Ribosomes. Nucleus and Ribosomes 2 Transcription Translation DNA ------m-RNA ------ Protein A gene (DNA) produces m-RNA by transcription. The m-RNA comes out of nuclear pores into the cytoplasm. Here ribosomes attach one by one to m-RNA and synthesize a protein. t-RNA’s bring amino acids from cytosol to m-RNA – ribosome complex. Each ribosome has 2 sub-units larger (60S) and smaller (40S). r-RNA and ribosomal proteins form the ribosomal subunits. No membrane covers the ribosomal subunits. Ribosomal subunits join only around m-RNA for protein synthesis otherwise remain separate. At the time of cell division one DNA divides and produces 2 DNA molecules by replication. DNA replication leads to produce sperms and eggs (gametes). m-RNA = messenger RNA Replication t-RNA = transfer RNA DNA ------ DNA + DNA r-RNA = ribosomal RNA The Endomembrane System 1 Manufacturing and Distributing Cellular Products Endoplasmic Reticulum, Golgi Apparatus, Lysosomes and Vacuoles collectively form Endomembrane System. Endoplasmic Reticulum: is a system of double membranes in the form of tubes and sacs throughout cytoplasm (in between cell membrane and nuclear envelope). Main manufacturing facility. Functions include synthesis of proteins and lipids including steroids, detoxification, and cellular transportation. It transports materials inside the cell by transport vesicles. RER SER 1 Rough ER, ribosomes fixed 1 Smooth ER, no ribosomes 2 Synthesis of membrane proteins 2 Lipids, steroids 3 Synth of secretory proteins 3 Detoxification of drugs

The Endomembrane System 2 Golgi Apparatus = Golgi Body: is a stacks of flattened sacs called cisternae. A cell may have from a few to a few hundred of Golgi stacks. Golgi Apparatus receives transport vesicles from ER on one side, modifies received chemicals, can store them and packs them in secretory vesicles and releases them on shipping side. Lysosomes: are single membrane bound organelles rich in digestive enzymes, help in breakdown of large molecules like proteins, polysaccharides, lipids and nucleic acids. Lysosomes provide a safe place for digestion of large molecules without damaging molecules of the cell. A Lysosome joins a food vacuole to digest the materials inside vacuole. Lysosomes are absent in most plant cells. Vacuoles: are membrane bound sacs and pinch off from ER, Golgi Apparatus and cell membrane. Functions include endocytosis, exocytosis, maintain turgor pressure in a plant cell, transportation.

Mitochondria Mitochondria (sing. Mitochondrion): are the powerhouses of cells and the site for cellular respiration. Respiration is oxidation of food and chief source of energy for the cell. These are bound with double membrane, outer smooth and inner folded. Mitochondria have enzymes for breakdown glucose derivatives, fatty acids and amino acids. Mitochondria have Electron-Transport-System that generates ATP molecules by using the energy contained in H’s produced during breakdown of glucose. Mitochondria are found in plants, animals, fungi and protists. Chloroplasts

Chloroplasts like mitochondria are bound by double membranes and are found only in plant cells . These have the green plant pigment called Chlorophyll. Chloroplast have enzyme systems including electron transfer systems needed to convert energy of sunlight into chemical energy of glucose. These are sites of Photosynthesis that convert CO2 and H2O to Glucose by using the sunlight energy. They synthesize starch from glucose. The Cytoskeleton Cell Shape and Movement Maintaining Cell Shape: The shape of the cell is maintained by Intermediate Filaments, the thick ropes of twisted protein fibers, Microtubules, the hollow organelles and Microfilaments, the solid thinner organelles. These maintain the shape of cells and keep in position the nucleus. The framework of support is highly dynamic that can organize and dismantle really fast. Transport of organelles and molecules: Microtubules are the freeways used by organelles like lysosomes to move from one part of cell to another. Microfilaments are the roads/streets used by smaller things. The Cytoskeleton Cilia and Flagella: are the locomotory organelles of eukaryotes. These have an axis formed of 2 central microtubules and 9 peripheral microtubules expressed as 9+2. The axis is covered by cytoplasm and cell membrane. These utilize ATP to bend at any part and help in locomotion, cilia inside tracts help in moving mucous. For example, cilia in lungs, cilia in Paramecium, flagellum in Euglena and sperms.

Recap 2 Cells Chapter 6 1. DNA ------m-RNA ------Protein 2. ----- are power houses of cells and yield ATP molecules. 3. ----- are packaging centers of cells and have flattened vesicles. 4. ----- are the smallest organelles and present in both prokaryotic and eukaryotic cells. They help in ------synthesis in cells. 5. ----- have hydrolytic enzymes in vesicles and form from Golgi App 6. ---- are interconnected membranes and can be smooth or rough 7. In prokaryotic cells DNA lies in ---- but in eukaryotic cells it lies in---. 8. ------are 2 rod like structures at 90⁰ to each other. 9. Organelles like vesicles move along ------in cells. 10. ------help in photosynthesis in green parts of plants. 11. ---- and ---- are cytoskeletal structures present in cells. 12. RER synthesize ------and SER produce ------.