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Transcript
What is the difference between life and nonlife? Where does the line begin? All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function—The contraction of muscle cells allows you to move your eyes as you read this sentence. All cells are related by their descent from earlier cells—however, they have been modified in many different ways throughout the history of life on Earth. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Light Microscopes: visible light is passed through the specimen and then through glass lenses. The lenses bend in the light in such a way that the image is magnified. Magnification=the ratio of an object’s image size to its real size Resolution=a measure of the clarity of the image Light microscopes cannot resolve detail finer than 200 nm, the size of a small bacterium—that’s about 1,000 times the size of the object. Advantage: Light Microscopes can observe living organisms Red Blood Cells Pollen grain Above: Spider shown with a Scanning Electron Microscope Electron Microscopes were first invented in the 1950s. They focus a beam of electrons through a specimen or onto its surface. They have a resolution 100 X better than a light microscope. Disadvantage: Only nonliving material can be studied 10 m Human height Length of some nerve and muscle cells 0.1 m Chicken egg 1 cm Frog egg 100 µm 10 µm Most plant and animal cells Nucleus Most bacteria Note: The scale is logarithmic, each reference mark is a tenfold increase in size from the bottom to top 1 µm Mitochondrion 100 nm Smallest bacteria 10 nm 1 nm 0.1 nm Viruses Ribosomes Proteins Lipids Small molecules Atoms Electron microscope 1 mm Light microscope Most cells are between 1 and 100 micrometers in diameter (see light region of chart to the right . 1m Unaided eye The Size Range of Cells: All cells have a plasma membrane surrounding the cytosol (a semifluid, jellylike substance in which organelles are found. All cells contain chromosomes and ribosomes Variations in other components, however, can be found between cells. Prokaryotic cells are characterized by having No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles “Pro”=before “karyo”=kernel/nucleus Bacteria are Prokaryotic Eukaryotic cells have DNA enclosed by a membrane in the nucleus. “Eu”= True In addition, they have other membrane-bound organelles in the cytoplasm Generally, they are much larger than prokaryotic cells All organisms except bacteria have eukaryotic cells Size is a general aspect of cell structure that relates to function Limits to cell size are due to the logistics of carrying out cell functions Having organelles to move materials around allows eukaryotic cells to be larger than prokaryotic cells. Elephants don’t have larger cells than other organisms—they just have more cells! Surface Area and Volume The surface area to volume ratio of a cell is critical. As the surface area increases by a factor of n2, the volume increases by a factor of n3 Small cells have a greater surface area relative to volume Why is this important to cells? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 6-9a A Typical Animal Cell: ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Flagellum Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Fig. 6-9b Nuclear envelope NUCLEUS Nucleolus Chromatin Rough endoplasmic reticulum A Typical Plant Cell Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Wall of adjacent cell Plasmodesmata CYTOSKELETON Cells need to build proteins Cells need energy Cells need to make more cells Proteins are macromolecules that are used by organisms for many different things: Building cell structures Transporting nutrients such as oxygen Enzymes speed up chemical reactions Hormones regulate functions of systems Defensive proteins guard against infection Responsive proteins communicate with other cells WOW! Lots of Work! The nucleus contains most of the genes in the eukaryotic cell It is generally the most conspicuous organelle in a eukaryotic cell The Nuclear Envelope encloses the nucleus Chromatin contains the DNA of the cell—it is organized into individual chromosomes. The nuclear envelope is a double membrane. It is perforated with pore structures. An intricate protein structure called a pore complex surrounds each pore. The Nucleus is like the “brain” of the cell—controlling most of the activities of the cell. How does it do this? By controlling what proteins are made. Proteins are the workhorse molecules of the cell—they are made by ribosomes. The nucleus contains the following organelles that are needed for protein synthesis: Nucleolus—builds rRNA and Ribosomes Chromosomes/Chromatin —contains strands of DNA Nuclear Membrane—has pores to allow mRNA to leave nucleus and go to ribosomes Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations: In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) DNA Controls the production of proteins in a series of steps that begins in the nucleus and ends at ribosomes. Remember: Proteins do the work of the cell. DNA directs which proteins are made. Ribosomes build the proteins. Take in nutrients Take in oxygen Build cell structures Remove wastes Make ATP Cells use many organelles to obtain, store, and release energy: plasma membrane, ER, Golgi Apparatus, Lysosomes, Mitochondria and Chloroplasts ATP “Endo”=inside Consists of: Nuclear Envelope, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Vacuoles, and the Plasma Membrane “Endo”=inside; “plasm”=liquid; “reticula”=intricate network ER is an intricate network of membranes that start at the nuclear membrane and continue throughout the cell to the plasma membrane. Smooth ER=no ribosomes attached Rough ER=ribosomes attached Smooth ER: Makes lipids Metabolizes carbohydrates Detoxifies poisons Stores calcium Rough ER: Because ribosomes are attached, many proteins are made here, especially glyco-proteins. (what are these?) Distributes proteins in vesicles (little membranebound bundles of proteins) Makes membranes for the cell Golgi Apparatus is a complex of flattened sacs of membranes (called cisternae). Function: Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles The Golgi is like the UPS store: It is the packaging and shipping center of the cell. “lysis”=to split Lysosomes are sacs of enzymes that can digest large molecules These enzymes can digest proteins, fats, polysaccharides, and nucleic acids— basically anything that enters the cell! They can even digest organelles in the cell Lysosomes may be called the “Stomach” of the cell; or even “The Suicide Sac” Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the molecules Autophagy: The lysosome can also digest damaged organelles These enzymes work best at pH 5 The lysosome makes its own enzymes The pH inside the lysosome stays at ph 5 because the transport proteins in the membrane pump in H+ ions. These enzymes don’t work well in the pH of the rest of the cell. Why? (so it won’t digest the cell if it leaks) White Blood Cells such as this one contain many lysosomes. They engulf bacteria and digest them. Lysosome diseases are often fatal. The enzymes in the lysosome may be defective…if so, when the lysosome takes in macromolecules, they may not get digested properly Undigested material builds up and lysosome gets larger & larger, eventually disrupting cells and organs. Tay-Sachs disease is a genetic disease that causes fat molecules to build up in the brain. Affected children usually die before age 3. Lysosomes can be used to kill cells when they are supposed to be destroyed Some cells have to die for proper development in an organism Apoptosis= “autodestruct” process; lysosomes break open & kill the cell. Why? Tadpoles lose their tails as they mature Fingers are fused in the human embryo Vacuoles are membrane-bound organelles whose functions vary—but most are used for storage of needed materials Food vacuoles: formed by phagocytosis, then store food to be broken down by lysosomes The central vacuole of mature plant cells develops from smaller vacuoles that come from the ER and Golgi apparatus. This organelle in plants stores proteins, sugars, ions and water. Some may contain pigments to give color to flowers. They may contain poisonous substances that keep the plant from being eaten. The membrane around the central vacuoles is called the tonoplast. Protists are fresh-water single-celled organisms. They live in an environment that causes water to constantly diffuse into their body. This could cause swelling and death. Contractile Vacuoles act like water pumps, continually pumping water out of the cell. Contractile Vacuoles in a Paramecium Mitochondria and Chloroplasts change energy from one form to another. Mitochondria are the sites for cellular respiration; Chloroplasts are the sites for photosynthesis. Mitochondrion Chloroplasts Mitochondria –where cellular respiration occurs. Where the chemical energy stored in sugars such as glucose is converted to ATP—a molecule that stores cellular energy. The “Powerhouse” of the cell Mitochondria have 2 membranes; the inner one is folded to increase the surface area. Enzymes attached to the membranes do the work of the mitochondria. Almost all eukaryotic cells have mitochondria—either one very large mitochondrion, or thousands of smaller ones. Which types of cells would have lots of mitochondria? Hint: Which cells need a lot of energy? Chloroplasts also have two membranes; the inner membranes form sacs that are stacked. In these membranes, chlorophyll (green pigment) traps sunlight energy. Chloroplasts, found in plants and algae are where photosynthesis occurs They convert the energy from sunlight into organic compounds such as glucose. “Little Green Sugar Factories” Both transform energy from one kind to another Both make ATP Both have double membranes Both are semiautonomous organelles—they can move, change shape, and divide Both have their own DNA and ribosomes—almost like independent cells-within-a-cell A peroxisome is a specialized metabolic compartment. Peroxisomes contain special enzymes that remove hydrogen from various substrates to form H2O2 (hydrogen peroxide). This process may detoxify poisons, or break down fuel for energy. Peroxisomes produce H2O2 as a by-product of many of the reactions in a cell. H2O2 is toxic, so the peroxisome has an enzyme, catalase, that breaks down H2O2. Organelles involved in organizing the cell so that it can divide are: Cytoskeleton Centrioles (in animal cells) The cytoskeleton is a network of fibers that organizes structures and activities in the cell. It gives the cell shape and support, much like the framework of a building holds it up and divides it into rooms. Besides giving shape to the cell, the cytoskeleton anchors the other organelles. It can be quickly dismantled in one part of the cell, then reassembled in a new location, changing the shape of the cell! The cytoskeleton consists of three types of structures: Microtubules, Microfilaments, and Intermediate filaments Vesicle ATP Receptor for motor protein Motor protein Microtubule (ATP powered) of cytoskeleton Microtubule Vesicles 0.25 µm By interacting with motor proteins, the cytoskeleton can move whole cells or just move parts of the cell around. Inside the cell, vesicles can travel to their destinations along “monorails” provided by the cytoskeleton. The cytoskeleton is composed of three main elements : 1.actin filaments (shown in red); also called microfilaments. 2.mictrotubules (gold) 3. intermediate filaments (blue) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hollow tubes made of Tubulin Function: maintains cell shape, cell motility (as in cilia or flagella), chromosome movement in cell division, organelle movement. Cilia Flagellum Tiny thread-like fibers made of 2 intertwined strands of actin Function: Maintains cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming, cell motility (as in pseudopodia), and cell division (cleavage furrow formation) Made of fibrous proteins supercoiled into thicker cables Function: maintenance of cell shape, anchoring nucleus and certain organelles In animal cells, microtubules grow out from a centrosome which is located near the nucleus. Within the centrosome is a pair of centrioles, each made of 9 sets of triplet microtubules. Centrioles in animal cells are essential for cell division. They are not found in plant cells. Cilia are hairlike extensions of certain cells that enable the cell to move or move fluid across the surface of the cell. Flagellum are singular long, tail-like extensions that also enable certaincells to move. Both cilia and flagella are made of microtubules. The cell wall is found outside the plant cell. Cell walls protect the plant cell, maintains its shape, and prevents excessive uptake of water. Cell walls are made mostly of microfibrils of cellulose. A young plant first secretes a relatively thin and flexible cell wall called the primary cell wall. Between primary cell walls of adjacent cells is the middle lamela, a thin layer rich in sticky polysaccharides called pectin. Some cells will add a secondary cell wall outside the primary cell wall. Wood is primarily secondary cell walls Plant cellulose cell walls from the ragweed plant anther (Ambrosia psilostachya). The rigid cell wall of plants is made of fibrils of cellulose embedded in a matrix of several other kinds of polymers such as pectin and lignin. Although each cell appears encased within a box, in fact primary cell walls are perforated permitting plasmodesmata to connect adjacent cells. Animal cells do not have cell walls, but they do have an elaborate extracellular matrix. The main ingredients are glycoproteins (the most abundant is collagen). Proteoglycans are proteins with many carbohydrate chains attached. Integrins are proteins embedded in the cell membrane that attach to the extracellular matrix. The main functions of the ECM: adhesion, support, regulation