Chapter 4 Cell Structure and Function Sections 1-6

Transcription

1 Chapter 4 Cell Structure and Function Sections 1-6

2 4.1 Food For Thought E. coli O157:H7A, strain of bacteria that causes severe illness or death, occasionally contaminates foods such as ground beef and fresh vegetables Outbreaks, which occur with disturbing regularity, also have severe economic impacts Food growers and processors are now using procedures that they hope will reduce E. coli O157:H7 outbreaks

3 E. coli O157:H7

4 4.2 Cell Structure The cell is the smallest unit that shows the properties of life All cells have a plasma membrane and cytoplasm, and all start out life with DNA

5 Components of All Cells Plasma membrane Controls substances passing in and out of the cell DNA containing region Nucleus in eukaryotic cells Nucleoid region in prokaryotic cells Cytoplasm A semifluid mixture containing cell components

6 Organelles Organelles are structures that carry out special metabolic functions inside a cell Membrane-enclosed organelles compartmentalize tasks such as building, modifying, and storing substances

7 Prokaryotic and Eukaryotic Cells Eukaryotic cell Cell interior is divided into functional compartments, including a nucleus Prokaryotic cell Small, simple cells without a nucleus

8 A A prokaryotic cell. cytoplasm DNA plasma membrane nucleus B A eukaryotic (plant) cell. Only eukaryotic cells have a nucleus. Figure 4-2 p54

9 ANIMATED FIGURE: Overview of cells To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

10 Preview of Cell Membranes Lipid bilayer A double layer of phospholipids organized with their hydrophilic heads outwards and their hydrophobic tails inwards Many types of proteins embedded or attached to the bilayer carry out membrane functions

11 cell s exterior plasma membrane cell s interior Figure 4-3 p54

12 Constraints on Cell Size Surface-to-volume ratio restricts cell size by limiting transport of nutrients and wastes

13 The Cell Theory Emerges Van Leeuwenhoek was the first to describe small organisms seen through a microscope, which he called animalcules and beasties Hooke was the first to sketch and name cells Brown was the first to identify a cell nucleus

14 Cell Theory The cell theory, a foundation of modern biology, states that cells are the fundamental units of life In 1839, Schleiden and Schwann proposed the basic concepts of the modern cell theory All organisms consists of one or more cells A cell is the smallest unit with the properties of life Each new cell arises from division of a preexisting cell Each cell passes its hereditary material to its offspring

15 Take-Home Message: How are all cells alike? All cells start life with a plasma membrane, cytoplasm, and a region of DNA, which, in eukaryotic cells only, is enclosed by a nucleus The surface-to-volume ratio limits cell size and influences cell shape Observations of cells led to the cell theory: All organisms consist of one or more cells; the cell is the smallest unit of life; each new cell arises from another cell; and a cell passes hereditary material to its offspring

16 4.3 How Do We See Cells? Most cells are micrometers in diameter, about fifty times smaller than the unaided human eye can perceive One micrometer (μm) is one-thousandth of a millimeter, which is one-thousandth of a meter We use different types of microscopes to study different aspects of organisms, from the smallest to the largest

17 Table 4-1 p56

18 Modern Microscopes Light microscopes Phase-contrast microscopes Reflected light microscopes Fluorescence microscopes Electron microscopes Transmission electron microscopes Scanning electron microscopes

19 path of light rays (bottom to top) to eye prism that directs rays to ocular lens ocular lens objective lenses specimen stage condenser lens illuminator focusing knob light source (in base) Figure 4-5a p56

20 incoming electron beam condenser lens specimen on grid objective lens projective lens phosphor screen Figure 4-5b p56

21 ANIMATED FIGURE: How a light microscope works To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

22 ANIMATED FIGURE: How a light microscope works To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

23 Different Microscopes, Different Characteristics

24 Relative Sizes human eye (no microscope) largest organisms small animals frog eggs 100 m 10 m 1 m 10 cm 1 cm 1 mm 100 µm

25 Relative Sizes light microscopes electron microscopes most eukaryotic cells most bacteria mitochondria, chloroplasts viruses molecules of life small molecules DNA carbohydrates proteins lipids 10 µm 1 µm 100 nm 10 nm 1 nm 0.1 nm

26 Take-Home Message: How do we see cells? Most cells are visible only with the help of microscopes Different types of microscopes reveal different aspects of cell structure

27 4.4 Introducing Prokaryotes Bacteria and archaea are the prokaryotes ( before the nucleus ), the smallest and most metabolically diverse forms of life Bacteria and archaea are similar in appearance and size, but differ in structure and metabolism

28 General Prokaryote Body Plan Cell wall surrounds the plasma membrane Made of peptidoglycan (in bacteria) or proteins (in archaea) and coated with a sticky capsule Flagellum for motion Pili help cells move across surfaces Sex pilus aids in sexual reproduction

29 General Prokaryote Body Plan Ribosomes Organelles upon which polypeptides are assembled Nucleoid An irregularly shaped region of cytoplasm containing a single, circular DNA molecule Plasmids Small circles of DNA carry a few genes that can provide advantages, such as resistance to antibiotics

30 General Prokaryote Body Plan 7 flagellum 1 cytoplasm, with ribosomes 2 plasma membrane 3 DNA in nucleoid 4 capsule 5 6 cell wall pilus

31 ANIMATED FIGURE: Typical prokaryotic cell To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

32 Bacteria

33 Archaeans

34 Biofilms Although prokaryotes are all single-celled, few live alone Biofilm Single-celled organisms sharing a secreted layer of polysaccharides and glycoproteins May include bacteria, algae, fungi, protists, and archaeans

35 Dental Plaque: A Biofilm

36 Take-Home Message: How are bacteria and archaea alike? Bacteria and archaea do not have a nucleus. Most kinds have a cell wall around their plasma membrane; the permeable wall reinforces and imparts shape to the cell body The structure of bacteria and archaea is relatively simple, but as a group these organisms are the most diverse forms of life; they inhabit nearly all regions of the biosphere Some metabolic processes occur at the plasma membrane of bacteria and archaea; they are similar to complex processes that occur at certain internal membranes of eukaryotic cells

37 4.5 Introducing Eukaryotic Cells All protists, fungi, plants, and animals are eukaryotes Eukaryotic ( true nucleus ) cells carry out much of their metabolism inside membrane-enclosed organelles Organelle A structure that carries out a specialized function within a cell

38 Importance of Organelles Membranes around eukaryotic organelles control the types and amounts of substances that enter and exit them Such control maintains a special internal environment that allows the organelle to carry out its particular function Some metabolic pathways take place in a series of different organelles

39 Components of Eukaryotic Cells

40 Components of Eukaryotic Cells

41 Cytoskeleton microtubules microfilaments intermediate filaments (not shown) Mitochondrion Cell Wall Chloroplast Central Vacuole nuclear envelope nucleolus DNA in nucleoplasm Nucleus Ribosomes Rough ER Plasmodesma Smooth ER Golgi Body Plasma Membrane Lysosome-Like Vesicle Figure 4-12a p61

42 3D ANIMATION: Tour of an Animal Cell

43 cell wall vacuole central vacuole plasma membrane chloroplast mitochondrion nucleus B Photosynthetic cell from a blade of timothy grass. Figure 4-11b p60

44 Rough ER Modifies proteins made by ribosomes attached to it Smooth ER Makes lipids, breaks down carbohydrates and fats, inactivates toxins Golgi Body Finishes, sorts, ships lipids, enzymes, and proteins Lysosome Digests, recycles materials Stepped Art p64

45 vacuole plasma membrane mitochondrion nucleus A Human white blood cell. Figure 4-11a p60

46 Take-Home Message: What do eukaryotic cells have in common? All eukaryotic cells start life with a nucleus and other membrane-enclosed organelles

47 ANIMATION: Common eukaryotic organelles To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

48 4.6 The Nucleus All of a eukaryotic cell s DNA is in its nucleus The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm The nuclear envelope controls when DNA is accessed

49 Table 4-2 p60

50 nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER Figure 4-13a p62

51 nuclear envelope DNA nucleolus nuclear pore nucleoplasm cytoplasm ER Figure 4-13b p62

52 The Nuclear Envelope Nuclear envelope Two lipid bilayers pressed together as a single membrane surrounding the nucleus Outer bilayer is continuous with the ER Nuclear pores allow certain substances to pass through the membrane

53 Structure of the Nuclear Envelope

54 B Each nuclear pore is an organized cluster of membrane proteins that selectively allows certain substances to cross it on their way into and out of the nucleus. nuclear pore A The outer surface of this nuclear envelope was split apart to reveal the pores that span the two lipid bilayers. Figure 4-14ab p63

55 nuclear pore nuclear envelope (two lipid bilayers) cytoplasm Figure 4-14b p63

56 ANIMATED FIGURE: Nuclear envelope To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

57 The Nucleoplasm and Nucleolus Nucleoplasm Viscous fluid inside the nuclear envelope, similar to cytoplasm Nucleolus A dense region in the nucleus where subunits of ribosomes are assembled from proteins and RNA

58 Chromosomes Chromatin All DNA and its associated proteins in the nucleus Chromosome A single DNA molecule with its attached proteins During cell division, chromosomes condense and become visible in micrographs Human body cells have 46 chromosomes

59 A Condensed Chromosome

60 Take-Home Message: What is the function of the cell nucleus? A nucleus protects and controls access to a eukaryotic cell s DNA The nuclear envelope is a double lipid bilayer. Proteins embedded in it control the passage of molecules between the nucleus and the cytoplasm