Cell Structure

1. Cell Structure Kathy Huschle Northland Community and Technical College

2. Cells • fundamental units of all living systems • are a self-contained system • only come from pre-existing cells n - nucleus

3. Comparison: prokaryotic cells vs eukaryotic cells • similar in chemical composition and chemical reactions • prokaryotic cells lack membrane-enclosed organelles, including a nucleus • eukaryotic cells have membrane-enclosed organelles and a membrane bound nucleus • prokaryotic cell walls contain peptidoglycan, eukaryotic cell walls do not

4. Cell StructureProkaryotes • prokaryotes contain • cytoplasmic membrane • cytoplasm • cell wall • external cell wall surface layers • filamentous protein appendages • internal structures

5. Prokaryotic: cytoplasmic membrane • semi permeable barrier • encloses the cytoplasm • regulates flow into and out of cell • selective permeability

6. Cytoplasmic Membrane

7. Prokaryotic: cytoplasmic membrane • composed of a phospholipid bilayer embedded with protein

8. Prokaryotic: cytoplasmic membrane • 2 parts to the phospholipid molecule • phosphate: hydrophilic • attracted to water • lipid: hydrophobic • repelled by water

9. Prokaryotic:cytoplasmic membrane

10. Prokaryotic: cytoplasmic membrane • membrane proteins • passageway for larger molecules • act as sensors for the cell, allowing it to adjust to it’s changing environment membrane protein

11. Transport Across Cytoplasmic Membrane • osmosis • solute is restricted • water will move until equilibrium is reached • high to low concentration

12. Transport Across Cytoplasmic Membrane • plasmolysis: cells shrink • lysis: cells burst cell lysis plasmolysis Between the shrinking protoplasm and the neighboring cells remain strands of cytoplasm.

13. Transport Across Cytoplasmic Membrane • diffusion • concentration gradient (high to low) • substance move from high concentration to low concentration • move until equilibrium is reached

14. Facilitated Transport Across Cytoplasmic Membrane • facilitated diffusion/passive transport • substances are moved by transporter proteins from high to low concentration

15. Facilitated Transport Across Cytoplasmic Membrane

16. Facilitated Transport Across Cytoplasmic Membrane • active transport • substances are moved by transporter proteins from low to high concentration • cell has to expend energy for this to happen

17. Facilitated Transport Across Cytoplasmic Membrane • group translocation • molecules are chemically modified during passage across cytoplasmic membrane • energy is expended

18. Prokaryotic: cytoplasmic membrane • membrane can be destroyed by antimicrobial agents and alcohol • resulting in leakage of the cell contents Cell lysis

19. Cytoplasm • cytoplasm • semi-fluid substance • contains internal cell structures and solutions • made up of mostly water with organic and inorganic molecules • DNA and ribosomes are found here Cytoplasm

20. Cell Wall • surrounds the cytoplasmic membrane • not a regulatory structure like cytoplasmic membrane • not selectively permeable • anything that can fit ,can pass through the cell wall

21. Cell Wall • maintains characteristic shape • rigid wall compensates for flexibility of membrane and keeps cell from assuming a spherical shape • provides a rigid platform for surface appendages • flagella, pili, cilia emanate from the wall and extend beyond it • counters the effects of osmotic pressure • strength of the cell wall keeps the cell from bursting when intracellular osmolarity is greater than extracellular osmolarity

22. Cell Wall • the cell wall of all bacteria are not identical • cell wall composition is an important factor in analysis and differentiation of bacteria • clinically the cell wall • contributes to ability to cause disease • is a site of action for antibiotics

23. Cell Wall • 2 major types of walls • Gram-positive • Gram-negative

24. Gram Positive Cell Wall • thick peptidoglycan layer • peptide • amino acids • cross linked • glycan • sugar • 90% of the cell wall ispeptidoglycan

25. Gram Positive Cell Wall • teichoic acid • makes the Gram positive cell wall acidic • cell walls do not degrade as easily

26. Gram Negative Cell Wall • more complex than the Gram positive cell wall • 2 distinct structures • peptidoglycan layer • outer membrane • held together by lipoproteins

27. Gram Negative Cell Wall • peptidoglycan layer • 10% of cell wall • bonded to lipoproteins • located between outer membrane and the cytoplasmic membrane • area called the periplasmic space • because of the minimal amount of peptidoglycan, Gram negative cells are more vulnerable to mechanical breakage

28. Gram Negative Cell Wall • periplasmic space • contains a high concentration of degrading enzymes • large number of transport proteins

29. Gram Negative Cell Wall • outer membrane • outer extremity of cell • semipermeable • restricts passage of materials based mostly on size • unique to Gram-negative bacteria • contains endotoxin lipopolysaccharide (LPS)

30. Gram Negative Cell Wall • outer membrane • strong negative charge assists in evading phagocytosis • provides a barrier to certain antibiotics (for example, penicillin), digestive enzymes and detergents • contains porins • channels that allow for the passage of molecules like amino acids, sugars, peptides Porins in Mycobacteriums smegmatis

31. Gram Negative Cell Wall • outer membrane • LPS (lipopolysacharide) • releases an endotoxin when in bloodstream or gastrointestinal tract which causes fever and shock • blocks passage of large molecules • increased barrier to • antibiotics

32. Gram negative and Gram positive cell walls Gram negative Gram positive

33. Atypical Cell Walls • Mycoplasma • bacterial genus that naturally lacks a cell wall • acid-fast staining is used to identify this cell type • Archaea • lack peptidoglycan in their cell walls Mycoplasma

34. Cell Surface Layers • attached to cell wall • provides another protective surface for the cell • composed of polysaccharide, polypeptide or both

35. Cell Surface Layers • glycocalyx • provides protection or assists in attachment • capsule • slime layer

36. Cell Surface Layers • capsules • distinct and gelatinous • antiphagocytic • protect from dehydration

37. Cell Surface Layers • slime layer • disorganized and loosely attached

38. Cell Surface Attachments • fimbriae • assist the cells adhere to surfaces

39. Cell Surface Attachments • pili • specific attachment processes • allow bacteria to attach to cells and grow on surface Pili

40. Cell Surface Attachments • conjugation pili • transfer of extrachromosomal DNA between donor and recipient conjugation pili

41. Cell Surface Attachments • flagella • propel the cell E. coli

42. Prokaryotic Internal Structures • chromosome • nucleoid region • contains the DNA of the bacterial cell

43. Prokaryotic Internal Structures • plasmids • small macromolecule of DNA • limited amount of genetic info • not necessary for cell function • may carry information that is advantageous to the cell • drug resistance to certain antibiotics

44. Prokaryotic Internal Structures • ribosomes • structures where proteins are made • can be inhibited by certain antibiotics

45. Prokaryotic Internal Structures • endospores • resting structures formed by some bacteria for survival during adverse environmental conditions • germination results in leaving the dormant stage and once again becoming a typical, multiplying cell (vegetative cell) B. Subtilis forming endospores

46. Prokaryotic Internal Structures • genus Bacillus and Clostridium are two common disease causing bacteria that produce endospores as needed • Bacillus • B. anthracis, causative agent for anthrax • Clostridium • C. tetani, causative agent for tetanus Clostridium tetani Bacillus anthracis

47. Prokaryotic Review

48. Cell StructureEukaryotes • larger • internal structures more complex • membrane bound organelles • membrane bound nucleus • cell wall is usually much simpler in structure than a prokaryotic cell wall

49. Cytoplasmic MembraneEukaryotes • similar in structure and function to the prokaryote cell • transport across the membrane includes • simple diffusion • facilitated diffusion • osmosis • active transport • endocytosis

50. Cytoplasmic MembraneEukaryotes • endocytosis • eukaryotic cells only • engulf substance Soil protozoa engulfing a bacillus bacteria.