1. Cell structure and function Chapter 3

2. Processes of Life
Growth
Reproduction
Responsiveness
Metabolism

3. Prokaryotes Do not have membrane surrounding their DNA; no nucleus
Lack various internal structures bound with phospholipid membranes
Small; ~1.0 µm in diameter
Simple structure
Comprised of bacteria and archaea

4. Eukaryotes Have membrane surrounding DNA; have nucleus
Have internal membrane-bound organelles
Are larger; µm in diameter
Have more complex structure
Comprised of algae, protozoa, fungi, animals, and plants

5. Comparing Prokaryotes and Eukaryotes
Figure 3.2a

6. Comparing Prokaryotes and Eukaryotes
Figure 3.2b

7. External Structures of Prokaryotic Cells
Glycocalyces
Flagella
Fimbriae and pili

8. Glycocalyces
Gelatinous, sticky substance surrounding the outside of the cell
Composed of polysaccharides, polypeptides, or both
Two types
Capsule
Slime layer

9. Capsule Composed of organized repeating units of organic chemicals
Firmly attached to cell surface
Protects cells from drying out
May prevent bacteria from being recognized and destroyed by host

10. Example of Capsule
Figure 3.4a

11. Slime Layer Loosely attached to cell surface Water soluble
Protects cells from drying out
Sticky layer that allows prokaryotes to attach to surfaces

12. Example of Slime Layer
Figure 3.4b

13. Flagella Are responsible for movement
Have long structures that extend beyond cell surface
Not all prokaryotes have flagella

14. Bacterial Flagella Structure
Composed of filament, hook, and basal body
Flagellin protein (filament) is deposited in a helix at the lengthening tip
Base of filament inserts into hook
Basal body anchors filament and hook to cell wall by a rod and a series of either two or four rings of integral proteins
Filament capable of rotating 360º

15. Bacterial Flagella Structure
Figure 3.5a

16. Bacterial Flagella Structure
Figure 3.5b

17. Arrangements of Bacterial Flagella
Figure 3.6a

18. Arrangements of Bacterial Flagella
Figure 3.6b

19. Arrangements of Bacterial Flagella
Figure 3.6c

20. Function of Bacterial Flagella
Rotation propels bacterium through environment
Rotation can be clockwise or counterclockwise; reversible
Bacteria move in response to stimuli (taxis)
Runs – movements of cell in single direction for some time due to counterclockwise flagellar rotation; increase with favorable stimuli (positive chemotaxis, positive phototaxis)
Tumbles – abrupt, random, changes in direction due to clockwise flagellar rotation; increase with unfavorable stimuli (negative chemotaxis, negative phototaxis)

21. Bacterial Movement

22. Fimbriae and Pili Nonmotile extensions Fimbriae
Sticky, proteinaceous, bristlelike projections
Used by bacteria to adhere to one another, to hosts, and to substances in environment
May be hundreds per cell and are shorter than flagella
Serve an important function in biofilms

23. Fimbriae Versus Flagella
Figure 3.9

24. Pili Long hollow tubules composed of pilin
Longer than fimbriae but shorter than flagella
Bacteria typically only have one or two per cell
Join two bacterial cells and mediate the transfer of DNA from one cell to another (conjugation)
Also known as conjugation pili or sex pili

25. Pilus Versus Fimbriae
Figure 3.10

26. Prokaryotic Cell Wall
Provides structure and shape and protects cell from osmotic forces
Assists some cells in attaching to other cells or in eluding antimicrobial drugs
Animal cells do not have; can target cell wall of bacteria with antibiotics
Bacteria and archaea have different cell wall chemistry

27. Bacterial Cell Wall
Most have cell wall composed of peptidoglycan; a few lack a cell wall entirely
Peptidoglycan composed of sugars, NAG, and NAM
Chains of NAG and NAM attached to other chains by tetrapeptide crossbridges
Bridges may be covalently bonded to one another
Bridges may be held together by short connecting chains of amino acids
Scientists describe two basic types of bacterial cell walls: gram-positive and gram-negative

28. Gram-Positive Cell Wall
Relatively thick layer of peptidoglycan
Contains unique polyalcohols called teichoic acids
Some covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane
Retains crystal violet dye in Gram staining procedure; appear purple
Acid-fast bacteria contain up to 60% mycolic acid; helps cells survive desiccation

29. Gram-Negative Cell Walls
Have only a thin layer of peptidoglycan
Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)
May be impediment to the treatment of disease
Following Gram staining procedure, cells appear pink

30. LPS Union of lipid with sugar Also known as endotoxin
Lipid portion known as lipid A
Dead cells release lipid A when cell wall disintegrates
May trigger fever, vasodilation, inflammation, shock, and blood clotting
Can be released when antimicrobial drugs kill bacteria

31. Periplasmic Space Located between outer membrane and cell membrane
Contains peptidoglycan and periplasm
Contains water, nutrients, and substances secreted by the cell, such as digestive enzymes and proteins involved in transport

32. Bacterial Cell Walls
Figure 3.13a

33. Thick layer peptidoglycan
Teichoic acid
Lipoteichoic acid
Gram Positive Cell Wall

34. Bacterial Cell Walls
Figure 3.13b

35. Outer Membrane
LPS-lipopolysaccharide (Endotoxin)
Porins
Periplasm
Gram Negative Cell wall

36. Archael Cell Walls Do not have peptidoglycan
Cell walls contain variety of specialized polysaccharides and proteins
Gram-positive archaea stain purple
Gram-negative archaea stain pink

37. Prokaryotic Cytoplasmic Membrane
Referred to as phospholipid bilayer; composed of lipids and associated proteins
Approximately half the membrane is composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channels
Integral proteins
Peripheral proteins
Glycoproteins
Fluid mosaic model describes current understanding of membrane structure

38. Phospholipid Bilayer of Cytoplasmic Membrane
Figure 3.14

39. Cytoplasmic Membrane Function
Controls passage of substances into and out of the cell; selectively permeable
Harvests light energy in photosynthetic prokaryotes

40. Control of Substances Across Cytoplasmic Membrane
Naturally impermeable to most substances
Proteins allow substances to cross membrane
Occurs by passive or active processes
Maintains a concentration gradient and electrical gradient
Chemicals concentrated on one side of the membrane or the other
Voltage exists across the membrane

41. Passive Processes of Transport
Diffusion
Facilitated diffusion
Osmosis
Isotonic solution
Hypertonic solution
Hypotonic solution

42. Effects of Solutions on Organisms
Figure 3.18

43. Active Processes of Transport
Active Transport
Utilizes permease proteins and expends ATP
Uniport
Antiport
Symport
Group Translocation
Substance chemically modified during transport

44. Cytoplasm of Prokaryotes
Cytosol – liquid portion of cytoplasm
Inclusions – may include reserve deposits of chemicals
Ribosomes – sites of protein synthesis
Cytoskeleton – plays a role in forming the cell’s basic shape
Some bacterial cells produce dormant form called endospore

45. Endospores Hardiest of all life forms
For escape from unfavorable environmental conditions
Germination = return to the vegetative state from the spore state
NOT reproductive (1 cell forms 1 endospore which return to reform 1 cell)

48. External Structure of Eukaryotic Cells
Glycocalyces
Never as organized as prokaryotic capsules
Helps anchor animal cells to each other
Strengthens cell surface
Provides protection against dehydration
Function in cell-to-cell recognition and communication

49. Eukaryotic Cell Walls
Fungi, algae, plants, and some protozoa have cell walls but no glycocalyx
Composed of various polysaccharides
Cellulose found in plant cell walls
Fungal cell walls composed of cellulose, chitin, and/or glucomannan
Algal cell walls composed of cellulose, proteins, agar, carrageenan, silicates, algin, calcium carbonate, or a combination of these
…..NO peptidoglycan

50. Eukaryotic Cytoplasmic Membrane
All eukaryotic cells have cytoplasmic membrane
Is a fluid mosaic of phospholipids and proteins
Contains steroid lipids to help maintain fluidity
Controls movement into and out of cell

51. Cytoplasm of Eukaryotes – Nonmembranous Organelles
Flagella
Cilia
Ribosomes
Cytoskeleton
Centrioles and centrosome

52. Flagella Shaft composed of microtubules
May be single or multiple; generally found at one pole of cell
Do not rotate, but undulate rhythmically

53. Cilia Shorter and more numerous than flagella
Coordinated beating propels cells through their environment
Also used to move substances past the surface of the cell

54. Ribosomes Larger than prokaryotic ribosomes (80S versus 70S)
Composed of 60S and 40S subunits

55. Cytoskeleton Extensive Functions
Anchor organelles
Movement of organelles
Movement during endocytosis and amoeboid action
Produce basic shape of the cell
Made up of tubulin microtubules, actin microfilaments, and intermediate filaments composed of various proteins

56. Centrioles and Centrosome
Centrioles play a role in mitosis, cytokinesis, and in formation of flagella and cilia
Centrioles composed of microtubules
Centrosome – region of cytoplasm where centrioles are found

57. Cytoplasm of Eukaryotes – Membranous Organelles
Nucleus
Endoplasmic reticulum
Golgi body
Lysosomes, peroxisomes, vacuoles, and vesicles
Mitochondria
Chloroplasts

58. Nucleus Often largest organelle in cell
Contains most of the cell’s DNA
Semiliquid portion called nucleoplasm
One or more nucleoli present in nucleoplasm; RNA synthesized in nucleoli
Nucleoplasm contains chromatin – masses of DNA associated with histones
Surrounded by double membrane composed of two phospholipid bilayers – nuclear envelope
Nuclear envelope contains nuclear pores

59. Endoplasmic Reticulum
Netlike arrangement of flattened, hollow tubules continuous with nuclear envelope
Functions as transport system
Two forms
Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis
Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; transports proteins produced by ribosomes

60. Rough and Smooth Endoplasmic Reticulum
Figure 3.32

61. Golgi Body
Receives, processes, and packages large molecules for export from cell
Packages molecules in secretory vesicles that fuse with cytoplasmic membrane
Composed of flattened hollow sacs surrounded by phospholipid bilayer

62. Golgi Body
Figure 3.33

63. Lysosomes, Peroxisomes, Vacuoles, and Vesicles
Store and transfer chemicals within cells
May store nutrients in cell
Lysosomes contain catabolic enzymes
Peroxisomes contain enzymes that degrade poisonous wastes

64. Mitochondria Have two membranes composed of phospholipid bilayer
Produce most of cell’s ATP
Interior matrix contains 70S ribosomes and circular molecule of DNA

65. Chloroplasts
Light-harvesting structures found in photosynthetic eukaryotes
Have two phospholipid bilayer membranes and DNA
Have 70S ribosomes

66. Endosymbiotic Theory
Eukaryotes formed from union of small aerobic prokaryotes with larger anaerobic prokaryotes; smaller prokaryotes became internal parasites
Parasites lost ability to exist independently; retained portion of DNA, ribosomes, and cytoplasmic membranes
Larger cell became dependent on parasites for aerobic ATP production
Aerobic prokaryotes evolved into mitochondria
Similar scenario for origin of chloroplasts

67. Endosymbiosis Theory of eukaryotic cell evolution

68. Endosymbiont theory of Eukaryotic evolution
Evidence in support of the hypothesis
Mitochondria and chloroplasts contain their own DNA
They contain their own ribosomes which are very similar to prokaryotes
They divide independent of the cell and by binary fission
Size, etc. etc