A View of the Cell CHAPTER 7

Transcription

1 A View of the Cell CHAPTER 7

2 CELL THEORY Before microscopes, people thought diseases were caused by curses and supernatural spirits They had no idea microorganisms, such as bacteria and viruses existed When the microscope was invented, scientists discovered cells exist Cells are the basic units of living organisms

3 CELL THEORY Anton van Leeuwenhoek (Dutch) used the first simple light microscope in the 1600s It had one lens Gradually, lenses got better Compound light microscopes use a series of lenses to magnify objects in steps Can magnify up to 1500 times The microscopes we use in the lab

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6 CELL THEORY Robert Hooke (1600s, English) used a light microscope to study cork, the dead cells of oak bark He saw small, geometric shapes that reminded him of the small rooms monks lived in called cells Cells are the basic units of all living things

7 CELL THEORY Matthias Schleiden (1830s, German) discovered that all plants are made of cells Theodor Schwann (German) discovered that all animals are made of cells Rudolf Virchow discovered that all cells come from existing cells All these scientists (plus others) contributed ideas that are now summed up in what we call the cell theory

8 CELL THEORY 1. All organisms are composed of one or more cells. 2. The cell is the basic unit of structure and organization of organisms. 3. All cells come from preexisting cells.

9 ELECTRON MICROSCOPES Electron Microscopes let us see a much greater magnification than light microscopes They use beams of electrons to produce images Scanning Electron Microscope Used for scanning 3- D surfaces

10 ELECTRON MICROSCOPES Transmission Electron Microscope Used for scanning interior structures of cell The best TEM can produce an image meters big (that s half as big as a hydrogen atom)

11 TYPES OF CELLS Organelles are small, specialized structures within cells Many, but not all are surrounded by membranes Prokaryotes are organisms that do not have membrane-bound organelles (biology.arizona.edu) Kingdom Monera ( now split into Eubacteria & Archaebacteria) Eukaryotes are organisms that do have membrane-bound organelles Kingdoms Animalae, Plantae, Fungi, Protista

12 TYPES OF CELLS Robert Brown (Scottish) observed that eukaryotic cells have a prominent structure, the nucleus the nucleus manages cellular functions Rudolf Virchow concluded that this prominent structure was responsible for cell division

13 SECTION 1 REVIEW 1. How has the history of microscopes influenced the study of cells? 2. What are the three parts of the cell theory? 3. What is the difference between a light microscope and an electron microscope? 4. What is the difference between a prokaryote and a eukaryote?

14 THE PLASMA MEMBRANE Cells must maintain proper conditions within itself to function The plasma membrane is a flexible boundary between the cell and its environment It allows a steady supply of nutrients into and out of the cell at the appropriate levels The bouncer The plasma membrane is selectively permeable This means that it allows some molecules to pass through while keeping others out. Like a screen in a window

15 THE PLASMA MEMBRANE Phospholipids The head is polar, or slightly charged It is hydrophilic (likes water) The tail is nonpolar, or not charged It is hydrophobic (repels water) The phospholipids arrange themselves form a bilayer with the fatty acid tails forming the interior and the heads facing both the watery external environments and inside the cell

16 PLASMA MEMBRANE The plasma membrane is called a phospholipid bilayer Arranged in this manner, a barrier is created that is water-soluble at its outer surfaces and water-insoluble in the middle Keeps out both water soluble and water insoluble molecules

17 PLASMA MEMBRANE The current model of the plasma membrane is called the fluid mosaic model. The phospholipids actually move around like a fluid. The other components of the membrane (proteins, carbohydrates, cholesterol, etc.) move around as well

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19 PLASMA MEMBRANE Cholesterol helps to stabilize the phospholipids by preventing their fatty acid tails from sticking together Transport proteins move span the membrane and move needed substances or waste materials through the plasma membrane Other proteins and carbohydrates that stick out help cells to identify surface signals and other cells These proteins play an important part in protecting cells from infection

20 SECTION 2 REVIEW 1. What is a phospholipid? 2. Why is the cell membrane a bilayer? 3. What does polar and nonpolar mean? 4. What are the specialized parts of the cell membrane? 5. Why is the cell membrane referred to as fluid mosaic?

21 CELL WALL Fairly rigid structure located outside the plasma membrane of some cells that provides additional support and protection Plants, fungus, most bacteria The cell wall is very porous, made of a tough mesh of fibers Like framing of a house

22 NUCLEUS Membrane-bound (called nuclear envelope) organelle that contains the directions to make proteins Boss Nuclear pores allow passage through the nuclear envelope Chromatin - uncondensed strands of DNA When cell is dividing, DNA condenses into chromosomes Nucleolus - organelle within the nucleus that make ribosomes Small machine factory

23 ORGANELLES Ribosomes are the sites where the cell produces proteins according to the directions of DNA One organelle without a membrane small machines on assembly line Cytoplasm/Cytosol is the clear, gelatinous fluid inside the cell Acts as a medium for things to move around in the cell Organelles can t fly

24 ORGANELLES The endoplasmic reticulum (ER) is arranged in a series of highly folded membranes suspended in the cytoplasm In general, ER is involved in the movement of materials throughout the cell The factory floor Rough ER has ribosomes, which is where protein synthesis takes place Smooth ER has no ribosomes and is involved in numberous biochemical activities, including the production and storage of lipids

25 ORGANELLES The Golgi apparatus is a flattened stack of tubular membranes that modifies the proteins The Golgi sorts proteins into packages and packs them into membranebound structures called vescicles for later transport Shipping Department

26 ORGANELLES Vacuoles are membrane-bound compartments for temporary storage of materials Store food, enzymes, water, waste Plant cells have one very large vacuole storage

27 ORGANELLES Lysosomes are organelles that contain digestive enzymes Digest old organelles, food, viruses, bacteria, etc. janitor Can fuse with a vacuole to dump waste or give enzymes Lysosomes digest a tadpole s tail

28 ORGANELLES Plastids are a group of organelles used for storage Named for the color or pigment they contain Chloroplasts are organelles that capture light energy and convert it to chemical energy (photosynthesis occurs here) Plastid containing chlorophyll, which actually traps the light and gives plants green color solar panels

29 ORGANELLES Mitochondria are membrane-bound organelles in plant and animal cells that transform stored chemical energy into a usable form for the cell (ATP) power generator Has an outer and inner highly folded membrane ATP produced on inner folds

30 ORGANELLES The cytoskeleton forms a framework for the cell A network of tiny rods and filaments beams or columns holding factory up Cytoskeleton is constantly changing its shape Microtubules are thin, hollow cylinders made of protein Microfilaments are smaller, solid protein fibers Give support for cell Provide highway system for organelles to move throughout cell

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32 ORGANELLES Centrioles are organelles made up of microtubules that play a part in cell division In animals and most protists Cilia are short, numberous projections that look like hairs Made of microtubules and help organelles move and feed Flagella are longer projections that move in a whip-like motion Made of microtublules - help with movement Cells usually only have 1 or 2

33 ANIMAL CELL

34 PLANT CELL

35 SECTION 3 REVIEW 1. How are highly-folded membranes an advantage for the functions of cellular parts? 2. Name an organelle that has highly-folded membranes. 3. If a cell synthesizes large quantities of protein molecules, which organelles might be numerous in that cell? 4. A cell s digestive enzymes are enclosed in a membranebound organelle. Why? 5. Compare and contrast the functions of a cell wall to the functions of a plasma membrane. 6. What are the functions of the cytoskeleton? 7. Why are mitochondria and chloroplasts referred to as energy transporters?

36 OSMOSIS What is diffusion? (review) Osmosis is the diffusion of water across a selectively permeable membrane This maintains homeostasis in the cell

37 CELLS IN AN ISOTONIC SOLUTION Isotonic solution - the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell Water does go in and out of the cell, but there is no net change in concentration

38 CELLS IN A HYPOTONIC ENVIRONMENT Hypotonic solution - the concentration of dissolved substances is lower in the solution outside the cell than the concentration inside the cell Therefore, water moves through the plasma membrane into the cell Pressure increases inside against the cell membrane and Animal cells may burst Plant cells become more firm as they expand against the cell wall. (grocery stores)

39 HYPOTONIC

40 CELLS IN A HYPERTONIC SOLUTION Hypertonic solution - the concentration of dissolved substances outside the cell is higher than the concentration inside the cell Water moves out of the cell In animals, cells shrivel In plants, membrane shrink away from cell wall

41 OSMOSIS LAB

42 PASSIVE TRANSPORT The movement of molecules across a membrane by diffusion (no energy required) Facilitated Diffusion is passive transport across the cell membrane using proteins Transport proteins form a channel to allow specific molecules to flow across Carrier proteins change shape to allow a substance to pass through the plasma membrane

43 FACILITATED DIFFUSION

44 ACTIVE TRANSPORT The movement of materials through a membrane against a concentration gradient Requires energy Carrier proteins have a specific shape to allow them to bind with specific molecules Then then change shape (with energy) so molecule can be transported across Carrier protein resumes original shape

45 ACTIVE TRANSPORT

46 TRANSPORT OF LARGE MOLECULES Endocytosis - process by which a cell surrounds and takes in material from its environment Membrane forms around material and engulfs it Exocytosis - the expulsion of materials from a cell (wastes, hormones) Membrane surrounds material and takes it to membrane, opens up.

47 ENDOCYTOSIS Exocytosis

48 SECTION REVIEW 1. What factors affect osmosis? 2. How do animal and plant cells react differently in a hypotonic solution? 3. How are facilitated diffusion and active transport similar? How different? 4. How do carrier molecules facilitate transport of molecules across a membrane? 5. A paramecium expels water when in freshwater. What kind of internal environment does it have?

49 DIVERSITY OF CELLS Unicellular Organisms Single celled organisms Fulfill all characteristics of life in one cell More than half of all life Multicellular Organisms Individual cells cannot live by themselves Through cell specialization, cells each perform specialized functions (eg muscle cells, neural cells, red blood cells, etc.) Protozoa

50 LEVELS OF ORGANIZATION IN LIFE Cells the smallest unit of life E.g. cardiac muscle cell Tissue a group of similar cells that perform a particular function E.g. cardiac muscle tissue Organs groups of tissue working together to perform a function E.g. - muscle

51 LEVELS OF ORGANIZATION IN LIFE Organ System a group of organs working together to perform a specific function E.g. cardiovascular system Organism an entire living thing E.g. you (probably)

52 REVIEW 1. What is the difference between a unicellular organism cell and a cell in a multicellular organism? 2. What is cell specialization? 3. List the 5 levels of organization in life. 4. Give an example of each of the 5 levels of organization in life.