Cell Structure - Chp4-Final PDF

Chapter 4 A Tour of the Cell © 2016 Pearson Education, Inc. 10 to 100 μm 0.1 to 5 μm The Microscopic World of Cells Cell theory states that all living things are composed of cells and that all cells come from earlier cells every cell in our body (and in...

Chapter 4 A Tour of the Cell © 2016 Pearson Education, Inc. 10 to 100 μm 0.1 to 5 μm The Microscopic World of Cells Cell theory states that all living things are composed of cells and that all cells come from earlier cells every cell in our body (and in every other living organism on Earth) was formed by division of a previously living cell © 2016 Pearson Education, Inc. What kind of organism do you think this is? And this one?? Valonia ventricosa, also known as bubble algae, sea grape, or sailor's eyeballs – one of the largest known UNICELLULAR organisms!! Caulerpa taxifolia, an algal species – green seaweed, often bred for use in aquariums – also consists of just a single cell with many nuclei!! In fact, it is the LARGEST KNOWN single-celled organism! PHOTOGRAPH BY UNIVERSAL HISTORY ARCHIVE/UNIVERSAL IMAGES GROUP VIA GETTY IMAGES - HTTPS://EDUCATION.NATIONALGEOGRAPHIC.ORG/RESOURCE/CELL-  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 surrounded by membranes). © 2016 Pearson Education, Inc. Figure 4.3 IDEALIZED ANIMAL CELL Centriole Not in most Ribosomes Lysosome plant cells Cytoskeleton Plasma membrane Nucleus Cytoplasm Mitochondrion Rough endoplasmic Smooth reticulum (ER) endoplasmic IDEALIZED PLANT CELL Golgi reticulum (ER) Cytoplasm apparatus Cytoskeleton Mitochondrion Central vacuole Not in Cell wall animal cells Nucleus Chloroplast Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic Channels between cells reticulum (ER) Golgi apparatus BioFlix Animation: Tour of an Animal Cell © 2016 Pearson Education, Inc. BioFlix Animation: Tour of a Plant Cell © 2016 Pearson Education, Inc.  CHROMATIN ORGANIZATION NUCLEUS  The Nucleus : Genetic Control of the Cell The nucleus is the control center of the cell. Contains DNA (contain genes) that stores the Nuclear envelope information necessary to produce a particular protein. Nuclear pore 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 the site where the components of ribosomes are made. © 2016 Pearson Education, Inc. Ribosomes Ribosomes are responsible for protein synthesis In eukaryotic cells, the components of ribosomes are made in the nucleus and then transported through the pores of the nuclear envelope into the cytoplasm Some ribosomes are suspended in the cytosol, making proteins that remain within the fluid of the cell. Ribosomes attached Others are attached to the outside of the nucleus & to endoplasmic the endoplasmic reticulum, making proteins that are reticulum visible as incorporated into membranes or secreted by the tiny dark blue dots cell. Both these types of ribosomes are structurally identical © 2016 Pearson Education, Inc. How DNA Directs Protein Production DNA 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 travels to the cytoplasm, where Movement of it binds to a ribosome. mRNA into cytoplasm via Ribosome nuclear pore A ribosome moves along the mRNA, translating the genetic Synthesis of protein in the Protein message into a protein with a cytoplasm specific amino acid sequence. © 2016 Pearson Education, Inc. Actively transcribing DNA (viewed under a microscope) The Endomembrane system 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 organelles are either physically connected or linked by vesicles, sacs made of membrane. © 2016 Pearson Education, Inc. 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 other locations in the cell. © 2016 Pearson Education, Inc. cells of the pancreas and digestive tract produce a high Figure 4.12 3 Secretory 4 Vesicles bud off proteins depart. from the ER. 2 Proteins are modified in the ER. Transport Ribosome 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 the assault has subsided detoxify overloads of ethanol derived from excess alcoholic drinking and barbiturates from drug overdose. © 2016 Pearson Education, Inc.  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  The Golgi Apparatus Rough ER “Receiving” side of the “Receiving” side of Golgi apparatus the Golgi apparatus Golgi apparatus Transport vesicles carry enzymes and 1 other proteins from Transport the rough ER to the vesicle Golgi for processing. “Shipping” side of the Golgi apparatus 2 Lysosomes carrying 3 digestive enzymes Plasma can fuse with other Colorized SEM membrane vesicles. “Shipping” side of Glogi apparatus Secretory protein Figure 4.13 The Golgi apparatus works in partnership with the ER and 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. Lysosomes 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 Lysosomes originate from vesicles that bud off from the Golgi apparatus Enzymes in a lysosome can break down large molecules such as proteins, polysaccharides, fats, and nucleic acids Lysosomes provide a safe compartment for breakdown of these molecules, without putting the cell’s other organelles and important molecules in danger of being broken down by these enzymes! © 2016 Pearson Education, Inc.  Digestive enzymes Lysosomes Lysosome have several types of digestive functions: Digestion 1) Many single-celled protists engulf nutrients in tiny cytoplasmic sacs called food vacuoles. Food vacuole Lysosomes fuse with the food vacuoles, exposing the food to digestive enzymes. 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 2. destroy harmful bacteria (e.g. WBCs - immunity), 3. engulf and digest parts of another organelle (recycling) and, 4. sculpt tissues during embryonic development, helping to form structures such as fingers. © 2016 Pearson Education, Inc.  A lysosome digesting food Digestive Lysosome enzymes In lower eukaryotes like Protista (Paramecium) Digestion Food vacuole Lysosome Digestive enzymes Digestion Vesicle containing damaged organelle A lysosome breaking down the molecules of damaged organelles In higher eukaryotes Lysosomes Lysosomes are important to cell function and human health as suggested by a group of 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 interferes with other cellular functions. Most of these diseases are fatal in early childhood For example, in Tay-Sachs disease, deficiency of a lipid-digesting enzyme results in accumulation of excess lipids in nerve cells, leading to their death. © 2016 Pearson Education, Inc. Vacuoles Vacuoles are large sacs made of membrane that buds off from the ER or Golgi apparatus. They have many types of functions in different cell types: 1) Certain freshwater protists like Paramecium, amoeba etc. have contractile vacuoles - pump out excess water that flows into the cell from the outside environment. The contractile vacuole acts to regulate the quantity of water inside the cell. In freshwater 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. The contractile vacuole acts as part of a protective mechanism that prevents the cell from absorbing too much water and possibly lysing (rupturing) through excessive internal pressure. © 2016 Pearson Education, Inc. Figure 4.15-1 A vacuole filling with water LM A vacuole contracting LM (a) Contractile vacuole in Paramecium Vacuoles 2) 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 like proteins, absorb water causing cells to expand, thus contributing to plant growth, and contain pigments (e.g., in cells of flower petals) that attract pollinating insects contain poisonous chemicals that protect against plant-eating animals/bugs (e.g., nicotine, caffeine etc.) 3) A food vacuole which buds into the cell from plasma membrane as a vehicle for ingesting food particles from outside © 2016 Pearson Education, Inc.  Rough ER “Receiving” side of the Golgi apparatus Golgi apparatus Transport vesicles carry enzymes and other proteins from the rough ER to the Transport Golgi for processing. vesicle “Shipping” side of the Golgi apparatus Lysosomes carrying digestive enzymes Plasma can fuse with other membrane vesicles. Secretory protein Energy Transformations: Chloroplasts and Mitochondria A cell converts energy obtained from the environment to forms that can be used directly by it Two organelles act as cellular power stations: 1. Chloroplasts, and 2. Mitochondria © 2016 Pearson Education, Inc. MITOCHONDRIA TEM Outer membrane Inner membrane Cristae Matrix Space between membranes Figure 4.18 MITOCHONDRIA Mitochodrial DNA (mtDNA) is circular unlike the linear nuclear DNA. It codes for proteins that are involved in cellular respiration. 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 Different cells have different amounts of mitochondria depending on their energy requirements the muscle cells have a lot of mitochondria, the liver does too, the kidney as well, and to a certain extent, the brain, which lives off the energy those mitochondria produce. © 2016 Pearson Education, Inc. MITOCHONDRIA 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 surface area in which more of these enzymes can be embedded, maximizing ATP output © 2016 Pearson Education, Inc. MITOCHONDRIA 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. These observations suggest that these two organelles could have originated from prokaryotic cells which were engulfed by larger cells and over time developed a symbiotic relationship © 2016 Pearson Education, Inc. MITOCHONDRIA 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.  Inner and outer CHLOROPLASTS membranes Space between membranes Stroma (fluid in Granum chloroplast) TEM Figure 4.17 CHLOROPLASTS 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 The organelles that perform photosynthesis They are unique to the photosynthetic cells of plants and algae © 2016 Pearson Education, Inc. CHLOROPLASTS 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, a network of membrane-enclosed disks and tubes forms 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 4.3 IDEALIZED ANIMAL CELL Centriole Not in most Ribosomes Lysosome plant cells Cytoskeleton Plasma membrane Nucleus Cytoplasm Mitochondrion Rough endoplasmic Smooth reticulum (ER) endoplasmic IDEALIZED PLANT CELL Golgi reticulum (ER) Cytoplasm apparatus Cytoskeleton Mitochondrion Central vacuole Not in Cell wall animal cells Nucleus Chloroplast Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic Channels between cells reticulum (ER) Golgi apparatus PLASMA MEMBRANE Structure/Function: The Plasma Membrane Composed mainly of phospholipids, which 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.” The hydrophobic tail - (i) Prevents unwanted polar ions and molecules to pass in the cell (ii) Restricts the movement of water-soluble molecules such as amino acids, glucose etc. out of the cell Certain proteins are suspended throughout the phospholipid bilayer of most biological membranes These help to regulate traffic across the membrane and perform many other functions © 2016 Pearson Education, Inc.  Structure/Function: The Plasma Membrane – Fluid Mosaic Model The plasma membrane is not a static sheet of molecules fixed in their place but a fluid mosaic: fluid because molecules can move freely past one another, and a mosaic because of the diversity of proteins in the membrane Functions of membranes are analogous to our human skin in some aspects: detect stimuli, engage in gas exchange, and serve as sites of excretion and absorption. © 2016 Pearson Education, Inc.  Cell surfaces Plant cells have a cell wall made from Animal cells lack cell walls and usually secrete a cellulose fibers, surrounding the plasma sticky coat called the extracellular matrix (ECM) membrane - A large network of proteins and other molecules that surround, support, and give Plant cell walls structure to cells and tissues in the body. protect the cells, ECM - Fibers made up of the protein collagen maintain cell shape, and which hold the cells together in tissues and can keep cells from absorbing too much also have protective and supportive functions. water to avoid bursting In addition, the surfaces of most animal cells Plant cells are connected via channels contain cell junctions, structures that connect passing through cell walls and joining their cells together into tissues, allowing the cells to cytoplasm with each other function in a coordinated way. These channels also allow water and other small molecules to move between cells – integrating them into a functional tissue © 2016 Pearson Education, Inc. Animation: Tight Junctions Collagen Cells embedded in an extracellular matrix of an animal cell © 2016 Pearson Education, Inc. Plant Cell: Plasmodesmata Various components of ECM Functions of membrane proteins (Chapter 5 of reference book) Functions of membrane proteins – Transport Passive Transport Active Transport Endocytosis (phagocytosis & pinocytosis) Exocytosis Biological membranes are selectively permeable!! Passive Transport No energy required Movement due to gradient differences in concentration, pressure, charge Movement in order to equalize gradient High moves toward low Can be of two types – diffusion or facilitated diffusion Types of Passive Transport - Diffusion A passive flow of substances down a concentration gradient Cell does not spend energy Only small molecules like gases, hydrophobic compounds, or even some polar molecules like ethanol can pass through Diffusion Gases and Liquids have random 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 carbon dioxide is given out as a waste product Molecules move to equalize concentration Application of passive diffusion - Dialysis 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. Types of Passive Transport – Facilitated Diffusion 1. A passive process 2. Down the concentration gradient 3. Passage through proteins – carrier proteins (or transporters) and channel proteins 4. Cell does not spend energy 5. Facilitated diffusion therefore allows polar and charged molecules to cross the plasma membrane Transport sugars, amino acids and Transport small molecules like water nucleosides. E.g., glucose transporter. (aquaporins) and ions (ion channels in nerves Transport is facilitated by change in and muscles). Highly selective (size), very fast shape of the protein. Facilitated Diffusion Differentially permeable membrane Channels help a specific molecule or ion to enter or leave the cell Channels usually are transport proteins 1.Protein binds with molecule (aquaporins facilitate 2.Shape of protein changes the movement of water) 3.Molecule moves across membrane glucose molecules- too large to fit in membrane No energy is used pores Solution Differences & Cells Solvent + solute = solution Hypotonic - Solutes present in higher concentration inside the cell Outside solvent will flow into cell Isotonic Solutes equal inside & out of the cell For example, sponges, jellyfishes etc. are isotonic in oceanic conditions Hypertonic - Solutes present in higher concentration outside the cell Fluid will flow out of cell Osmosis Net Movement of solvent (diffusion) across a selectively permeable membrane towards higher solute concentration. It can be defined as movement of water molecules from higher to lower concentration of water or from lower to higher concentration of solute Often involves movement of water Into the cell Out of the cell Examples of Osmosis Swelling of Brain cells in response to excess water. Plants also exhibit osmosis - Turgidity Lettuce cells—Crisp when they absorb water Salad dressing exhibit osmosis Osmoregulation – water balance is maintained –freshwater fish have kidneys and gills – prevent excess build up of water Humans can suffer consequences of disrupted osmoregulation: Drinking less water - Dehydration - fatigue Drinking too much water – water Intoxication –overdilution of necessary ions Both can be fatal Active Transport Molecular movement against the concentration/electrochemical gradient Requires energy (against gradient) provided by coupling with ATP hydrolysis Example is sodium-potassium pump – vital for nervous system 3 Na+ are pumped out of the cells against the concentration gradient 2 K+ are pumped into the cells against the concentration gradient Na+-K+ pump maintains osmotic balance and cell volume  Turgidity of guard cells controls the opening & closing of stomata, depending on water availability for the plant. This turgor is controlled by a combination of active & passive transport, with K+ ions being actively pumped into guard cell vacuoles to allow water inflow, making them turgid & inducing stomatal Endocytosis Movement of large sized materials like: Particles Organisms Large molecules into the cells Types of endocytosis bulk-phase (nonspecific) receptor-mediated (specific) Process – 1.Plasma membrane surrounds material 2.Edges of membrane meet 3. Membranes fuse to form vesicle Forms of Endocytosis : 1) 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 some 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. 2) Pinocytosis - is the process of engulfing liquids and the materials dissolved in the liquids, such as useful hormones. Energy is used – active process. Here the sacs formed are very small, compared with those formed during phagocytosis. Due to their small size, they are called vesicles 3) Receptor mediated endocytosis- is the process in which molecules from the cell’s surroundings bind to receptor molecules on the plasma membrane. The membrane then folds in and engulfs these molecules. Examples : transport of Insulin into animal cells Iron is carried through blood tightly bound to transferrin protein carrier – membrane has receptors proteins for transferrin Cholesterol uptake from blood by liver cells Exocytosis: occurs in the same manner as endocytosis, just reverse (inside to outside) 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 Many materials such as mucus, digestive enzymes and molecules produced by nerve cells, tears from tear glands etc. Exocytosis Exocytosis of neurotransmitters – brain Cell discharges material Vesicle moves to cell surface Membrane of vesicle fuses Materials expelled HUMAN SKELETON CYTOSKELETON The Cytoskeleton: Cell Shape and Movement The cytoskeleton-cell skeletal system is a network of protein 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 microtubule track Microtubules – guide movements of chromosomes when cell divides Give mechanical support to the cell © 2016 Pearson Education, Inc. Cytoskeleton - provides mechanical support to the cell and helps a cell maintain its shape. Filaments & fibers Made of 3 fiber types Microtubules -hollow tubes of protein Intermediate filaments Microfilaments - 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, whip-like 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 Education, Inc. Cilia lining the respiratory tract 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.