A Tour of the Cell - Biology Textbook PDF

Chapt er 4 A Tour of the Cell © 2016 Pearson Education, Inc.  The Two Major Categories of Cells All cells have several basic features. They are all bounded by a thin plasma membrane. Inside all cells is a thick, jelly-like fluid called the cytosol, matrix of cytoplasm s...

Chapt er 4 A Tour of the Cell © 2016 Pearson Education, Inc.  The Two Major Categories of Cells All cells have several basic features. They are all bounded by a thin plasma membrane. Inside all cells is a thick, jelly-like fluid called the cytosol, matrix of cytoplasm surrounding organelle -in which cellular components are suspended. All cells have one or more chromosomes carrying genes made of DNA. All cells have ribosomes, tiny structures that build proteins according to the instructions from the genes. Most organelles are found in both animal and plant cells. But there are some important differences. Only plant cells have chloroplasts (where photosynthesis occurs). Only animal cells have lysosomes (bubbles of digestive enzymes © 2016 Pearson Education, Inc. Figure 4.3 IDEALIZED ANIMAL CELL Centriole Not in most Ribosomes plant cells Lysosom Cytoskeleton e Plasma membrane Nucleus Cytoplasm Mitochondrion Rough endoplasmic Smooth reticulum (ER) endoplasmic IDEALIZED PLANT CELL Golgi reticulum (ER) Cytoplasm apparatus Cytoskeleton Central vacuole Not in Cell wall animal cells Mitochondrion Chloroplast Nucleus Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic Channels between cells reticulum (ER) Golgi apparatus BioFlix Animation: Tour of a Plant Cell © 2016 Pearson Education, Inc. BioFlix Animation: Tour of an Animal Cell © 2016 Pearson Education, Inc.  Structure/Function: The Plasma Membrane Separates the living cell from its nonliving surroundings. Composed mostly of phospholipids group together to form a two-layer sheet called a phospholipid bilayer. Each phospholipid is composed of two distinct regions: 1. a “head” with a negatively charged phosphate group and 2. two nonpolar fatty acid “tails.” –hydrophobic Tail- (i) prevents unwanted polar ions and molecules to pass in the cell (ii) restricts the movement of water soluble molecules to pass out (Eg (amino acids glucose) Fluid mosaic model of membrane Proteins -suspended in the phospholipid bilayer of most membranes Help regulate traffic across the © 2016 Pearson membrane and perform other Education Structure/Function: The Plasma Membrane The plasma membrane is a fluid mosaic: fluid because molecules can move freely past one another and a mosaic because of the diversity of proteins in the membrane. Animal cells lack cell walls and Cell surfaces - Plant cells have a cell wall most secrete a sticky coat called the made from extracellular matrix (ECM) cellulose fibers. ECM-Fibers made of the protein collagen hold cells together in tissues and can have protective and supportive functions. Plant cell walls protect the cells, In addition, the surfaces of most animal cells maintain cell shape, and contain cell junctions, structures that connect keep cells from absorbing too much cells together into tissues, allowing the cells to water-avoid bursting function in a coordinated way. Cells are connected via channels passing through cell walls –joining Functions of membranes to our human skin. cell walls of cells and also allow water (a) detect stimuli, and other small molecules to move between cells. © 2016 Pearson (b)engage in gas exchange, and Education, Inc. (c) serve as sites of excretion and absorption. Animation: Tight Junctions © 2016 Pearson Education, Inc.  The Nucleus : Genetic Control of the The Cell nucleus is the control center of the cell. Contains DNA (contain genes) that stores the Nuclear envelope Nuclear information necessary to produce a particular pore protein. Chromatin fiber separated from the cytoplasm by a double membrane called the nuclear envelope. Nucleolus Pores - allow certain materials to pass between the nucleus and the surrounding cytoplasm long DNA molecules and associated proteins form fibers called chromatin. Each long chromatin fiber constitutes one chromosome. The nucleolus is a prominent structure within the nucleus and © 2016 Pearson the site where the components of ribosomes Education, Inc.  Ribosom es Ribosomes are protei synthes responsible for n is. In eukaryotic cells, the components of are made in the nucleus and then transported through the pores of the nuclear envelope into the cytoplasm structurally identical, some suspend inare ribosomes the cytosol, making Ribosomes attached ed tha remain within the fluid of proteins to endoplasmic reticulum visible as t the cell. tiny dark blue dots Others are attached to the outside of the nucleus to endoplasmic reticulum, making proteins that are incorporated into membranes or secreted by the © 2016 Pearson Education, Inc. How DNA Directs Protein DNA Production DNA transfers its coded Synthesis of information to a molecule mRNA in the nucleus called messenger RNA (mRNA). mRNA mRNA exits the nucleus through pores in the nuclear envelope and Movement of travels to the cytoplasm, mRNA into where it binds A ribosome to a moves cytoplasm via nuclear pore Ribosome ribosome. along the mRNA, translating the genetic message into a protein Synthesis of protein in the Protein with a specific amino cytoplasm acid sequence. © 2016 Pearson Education, Inc. The Endomembrane System: Manufacturing and Distributing Cellular Products The endomembrane system-internal network of membranes in a cell consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, and vacuoles. These membranous physically o organelles are either connected linked by r made of , sacs vesicles membrane. © 2016 Pearson Education, Inc. Figure 4.3 IDEALIZED ANIMAL CELL Centriole Not in most Ribosomes plant cells Lysosom Cytoskeleton e Plasma membrane Nucleus Cytoplasm Mitochondrion Rough endoplasmic Smooth reticulum (ER) endoplasmic IDEALIZED PLANT CELL Golgi reticulum (ER) Cytoplasm apparatus Cytoskeleton Central vacuole Not in Cell wall animal cells Mitochondrion Chloroplast Nucleus Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic Channels between cells reticulum (ER) Golgi apparatus The Endoplasmic Reticulum The endoplasmic reticulum (ER) - one of the main manufacturing facilities in a cell. connected to the nuclear envelope composed of interconnected rough and smooth ER that have different structures and functions. Cells specializing in the production of proteins - have a larger amount of rough ER (With ribosomes attached) Cells producing lipids (fats) and steroid hormones - have a greater amount of smooth ER. Some products manufactured by rough ER are chemically modified and then packaged into transport vesicles- Vesicles - sacs made of membrane that bud off from the rough ER. These transport vesicles may be dispatched to that otherfunction asindigestive locations the cell. © 2016 Pearson enzymes. Education, Inc. Figure 4.12 3 Secretory 4 Vesicles bud off proteins depart. from the ER. 2 Proteins are modified in the ER. Transpor Ribosome t vesicle 1 A ribosome links amino acids. Protein Rough ER Polypeptide  Smooth ER The smooth ER lacks surface ribosomes - produces lipids, including steroids (hormones in the adrenal cortex and endocrine glands) Cells of ovaries and testis –enriched with SER- produce steroid sex hormones detoxifying a number of organic chemicals converting them to safer water-soluble products. Large amounts of smooth ER are found in liver cells – Enzymes of SER functions to detoxify products of natural metabolism (drugs /antibiotics) It contains enzymes that catalyze a number of reactions ; that can make lipid- soluble drugs and metabolic wastes into water-soluble, so that these (drugs and waste) can easily be expelled out of the body. To assist with this, smooth ER can double its surface area within a few days, returning to its normal size when  Figure 4.11 contains enzymes that catalyze a number of reactions ; that can make lipid- soluble drugs and metabolic wastes into water-soluble, so that these (drugs and waste) can easily be expelled out of the body. Nuclear envelope Ribosomes Rough ER Smooth ER Figure 4.13 “Receiving” side of the Golgi apparatus T r a n s 1 the Golgi apparatus p o New r vesicle t 2 forming v e Transpor s 3 t Colorized SEM i vesicle c from the l “Shipping” side of Golgi e Plasma the fGolgi apparatus membrane apparatus r New vesicle forming o m The Golgi apparatus -works in partnership with the ER and r o receives, refines, stores, and distributes u chemical g The Golgi Apparatus The Golgi apparatus consists of a stack of membrane plates. Products made in the ER reach the Golgi apparatus in transport vesicles. Proteins within a vesicle are usually modified by enzymes during their transit from the receiving to the shipping side of the Golgi apparatus. The shipping side of a Golgi stack is a depot - finished products can be carried in transport vesicles to other organelles or to the plasma membrane. © 2016 Pearson Education, Inc. Lysosom es A lysosome is a membrane-enclosed sac of digestive enzymes found in animal cells. Most plant cells do not contain lysosomes, they contain lytic vacuoles. Enzymes in a lysosome can break down large molecules such as proteins, polysaccharides, fats, and nucleic acids. © 2016 Pearson Education, Inc.  Lysoso Digestive enzymes mes have several types of digestive Lysosome functions. Digestion Many single-celled protists engulf Lysosomes nutrients infuse tiny with the food vacuoles, exposing Food vacuole the food to digestive cytoplasmic enzymes. sacs called food vacuoles. A lysosome digesting food Small molecules that result from this digestion, such as amino acids, leave the lysosome and nourish the cell. Lysosomes can also destroy harmful bacteria, engulf and digest parts of another organelle, and sculpt tissues during embryonic © 2016 Pearson development, helping to form structures Education, Inc. Figure 4.14- 2 Lysosome Digestion Vesicle containing damaged organelle (b) A lysosome breaking down the molecules of damaged organelles Lysosom es lysosomes are important to cell function and human health - hereditary disorders called lysosomal storage diseases. A person with such a disease is missing one or more of the digestive enzymes normally found within lysosomes and has lysosomes that become engorged with indigestible substances, which eventually interfere with other cellular functions. Most of these diseases are fatal in early childhood. © 2016 Pearson Education, Inc.  Vacuol es Vacuoles are large sacs made of membrane that bud off from the ER or Golgi apparatus. Certain freshwater protists have contractile vacuoles - pump out excess water that flows into the cell from the outside environment. Paramecium, amoeba The contractile vacuole acts to regulate the quantity of water inside of a cell. In fresh water environments - the concentration of solutes inside the cell is high concentration than outside the cell (i.e., the environment is hypotonic ). water flows from the environment into the cell by osmosis. © 2016 Pearson Education, Inc. Figure 4.16 Rough ER Golgi apparatus Transpor t vesicle Transport vesicles carry enzymes and other proteins from the rough ER to the Plasma Golgi for processing. membrane Lysosomes carrying digestive enzymes can fuse with other Secretory vesicles. protein Some products are Vacuoles store some secreted from the cell. cell products. Figure 4.15- 1 A vacuole filling with water LM A vacuole contracting LM (a) Contractile vacuole in Paramecium Vacuol es A central vacuole can account for more than half the volume of a mature plant cell. The central vacuole of a plant cell is a versatile compartment that may store organic nutrients, absorb water, and contain pigments that attract pollinating insects or poisons that protect against plant-eating animals. © 2016 Pearson Education, Inc. Energy Transformations: Chloroplasts and Mitochondria A cell converts energy obtained from the environment to forms that the cell can use directly. Two organelles act as cellular power stations: 1. chloroplasts and 2. mitochondria. © 2016 Pearson Education, Inc. Chloropla sts Most of the living world runs on the energy provided by photosynthesis. Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar and other organic molecules. Chloroplasts are unique to the photosynthetic cells of plants and algae and the organelles that perform photosynthesis. © 2016 Pearson Education, Inc.  Chloropla sts Chloroplasts are divided into compartments by two membranes, one inside the other. The stroma is a thick fluid found inside the innermost membrane. Suspended in that fluid is a network of membrane- enclosed disks and tubes, which form another compartment. The disks occur in interconnected stacks called grana that resemble stacks of poker chips. The grana are a chloroplast’s solar power packs, the structures that trap light energy and convert it to chemical energy. © 2016 Pearson Education, Inc. Figure 4.17 Inner and outer membranes Space between membranes Granum S tr o m a (f lu id in TEM c hl o Mitochond ria Mitochondria are found in almost all eukaryotic cells, are the organelles in which cellular respiration takes place, and produce ATP from the energy of food molecules. Cells use molecules of ATP as the direct energy source for most of their work. © 2016 Pearson Education, Inc. Mitochond ria An envelope of two membranes encloses the mitochondrion, and the inner membrane encloses a thick fluid called the mitochondrial matrix. The inner membrane of the envelope has numerous infoldings called cristae. The folded surface of the membrane includes many of the enzymes and other molecules that function in cellular respiration and creates a greater area for the chemical reactions of cellular respiration. © 2016 Pearson Education, Inc. Figure 4.18 Outer TEM membrane Inner membrane Cristae Matrix Space between membranes Some different cells have different amounts of mitochondria because they need more energy. the muscle has a lot of mitochondria, the liver does too, the kidney as well, and to a certain extent, the brain, which lives off of the energy those mitochondria produce. Mitochond ria Mitochondria and chloroplasts contain their own DNA that encodes some of their own proteins made by their own ribosomes. Each chloroplast and mitochondrion contains a single circular DNA chromosome that resembles a prokaryotic chromosome and can grow and pinch in two, reproducing themselves. © 2016 Pearson Education, Inc. Mitochond ria mitochondria and chloroplasts evolved from ancient free-living prokaryotes that established residence within other, larger host. This phenomenon, where one species lives inside a host species, is a special type of symbiosis. Over time, mitochondria and chloroplasts likely became increasingly interdependent with the host, eventually evolving into a single organism with inseparable parts. © 2016 Pearson Education, Inc. The Cytoskeleton: Cell Shape and Movement The cytoskeleton-cell skeletal system is a network of fibers extending throughout the cytoplasm and serves as both skeleton and “muscles” for the cell, functioning in support and movement. Just like bony skeleton in body help in fixing organs- cytoskeleton provide anchorage and reinforcement to many organelle in a cell Example- Nucleus is held in place by a cage of Cytoskeletal filaments Lysosome –reach food vacuole by gliding along © 2016 Pearson microtubule track Education, Inc.  Cytoskeleton -provides mechanical support to the cell and helps a cell maintain its shape. Filaments & fibers Made of 3 fiber types Microfilaments Microtubules -hollow tubes of protein. Intermediate filaments- thinner and solid. Microtubule, microfilaments and intermediate filaments are all interconnected within the cytoplasm of the cell. Maintaining Cell Shape A cell’s cytoskeleton is dynamic. It can be quickly dismantled in one part of the cell by removing protein subunits and re-formed in a new location by reattaching the subunits. Such rearrangement can provide rigidity in a new location, change the shape of the cell or even cause the whole cell or some of its parts to move. Amoeboid crawling ,WBC movement © 2016 Pearson Education, Inc. Cilia and Flagella In some eukaryotic cells, microtubules are arranged into structures called flagella and cilia Extensions from a cell that aid in movement. Eukaryotic flagella propel cells through an undulating, whiplike motion. They often occur singly, such as in human sperm cells, © 2016 Pearson Education, Inc.  Cilia and Flagella Cilia (singular, cilium) are generally shorter and more numerous than flagella and move in a coordinated back-and-forth motion, like the rhythmic oars of a crew team. Both cilia and flagella propel various protists through water. On cells lining the human trachea, cilia help sweep mucus with trapped debris out of the lungs. Tobacco smoking – can inhibit or destroy these cilia © 2016 Pearson Cilia lining the respiratory tract Education, Inc. Animation: Cilia and Flagella © 2016 Pearson Education, Inc. Cilia and Flagella human sperm rely on flagella for movement - problems with flagella can lead to male infertility. Some men with a type of hereditary sterility also suffer from respiratory problems because of a defect in the structure of their flagella and cilia. © 2016 Pearson Education, Inc. Molecule Movement & Cells Passive Transport Active Transport Endocytosis (phagocytosis & pinocytosis) Exocytosis Passive Transport No energy required Move due to gradient differences in concentration, pressure, charge Move to equalize gradient High moves toward low Types of Passive Transport 1.Diffusion 2.Osmosis 3.Facilitated diffusion  Diffusio n and Liquids have random Gases movement of molecules (due to their Kinetic Energy) and due to their constant motion they tend to mix together. Ex. A sugar cube dissolves in a glass of Water Ex: Oxygen and carbon dioxide. Oxygen is taken into the cells and Molecules move to equalize carbon dioxide is given out as a concentration waste product  Osmo Net Movement of molecules (diffusion) across sis a selectively permeable membrane is called Osmosis. Special form of diffusion of water It can be defined as movement of water molecules from higher concentration to lower concentration flows from lower solute concentration Often involves movement of water Into cell Out of cell  Solution Differences & Cells solvent + solute = solution Hypotonic- Outside solvent will flow into cell Solutes in cell more than outside Isotonic Solutes equal inside & out of cell For example Sponges, Jellyfishes etc. are isotonic in oceanic conditions. Hypertonic- Solutes greater outside cell Fluid will flow out of cell Examples of Osmosis Swelling of Brain cells in response to excess water. Plants also exhibit osmosis-Turgid Lettuce cells—Crisp when they absorb water Salad dressing exhibit osmosis. Osmoregulation – water balance is maintained –fresh water fish has kidneys and gills –prevent excess build up of water Humans can suffer consequences of osmoregulation- dehydration - fatigue Too much water – water intoxication –overdilution of necessary ions Dialysi s To remove wastes from blood in patients with malfunctioning kidney Blood passed through series of tubes with semipermeable membrane Toxins diffuse into the surrounding fluid and the cleansed blood returns to the patients.  Facilitated Diffusion Differentially permeable membrane Channels (are specific) help molecule or ions enter or leave the cell Channels usually are transport proteins (aquaporins 1.Protein binds with molecule facilitate the 2.Shape of protein changes movement of 3.Molecule moves across water) membrane No energy is used glucose molecules- too large to fit in membrane pores Active Transport Molecular movement Requires energy (against gradient) Example is sodium-potassium pump 3 Na+ is pumped out of the cells up a concentration gradient 2 K+ are pumped into the cells up a concentration gradient  Endocyto sis Movement of large material Particles Organisms Large molecules Process – 1.Plasma membrane Movement is into cells surrounds material 2.Edges of membrane meet Types of endocytosis bulk-phase 3. Membranes fuse to form vesicle Forms of (nonspecific) Endocytosis : receptor-mediated Phagocytosis – cell eating Pinocytosis – cell drinking -engulfing liquids - useful (specific) hormones are released in this manner. Energy is used – active process Here the sacs formed are very small, compared with those formed during Phagocytosis- is the process of engulfing large particles, such as cells. Eg: protozoa engulf food and WBC engulf bacteria by wrapping them with membrane and taking them into the cell. Hence WBCs are called phagocytes. When phagocytosis occurs, the material to be engulfed touches the surface of the cell and causes a portion of the plasma membrane to be indented. The indented plasma membrane is pinched off inside the cell to form a vacuole containing the engulfed material. Inside the cell the vacuole fuses with the lysosomes and the enzymes of the lysosomes degrade the contents on the vacuole. Pinocytosis- is the process of engulfing liquids and the materials dissolved in the liquids. waste , useful hormones are released in this manner. Energy is used – active process Here the sacs formed are very small, compared with those formed during phagocytosis. Receptor mediated endocytosis- is the process in which molecules from the cells surroundings bind to receptor molecules on the plasma membrane. The membrane then folds in and engulfs these molecules. Example :transport of Insulin into animal cells Iron is carried through blood tightly bound to transferrin protein carrier – membrane has receptors proteins for transferrin Exocytosis: occurs in the same manner as endocytosis. Membranous sacs containing materials from the cell migrate to the plasma membrane and fuse with it. This results in the sac contents being released from the cell.  Exocyto sis of Reverse endocytosis Cell discharges material Vesicle moves to cell surface Membrane of vesicle fuses Materials expelled