Cell Structure

1. Cell Structure

3. Cell Theory • Every living organism is made up of one or more cells • The smallest living organisms are single cells • Cells are the functional units of multi-cellular organisms • All cells arise from preexisting cells

5. Cell Structure • Basic Features of All Cells • Features of Prokaryotic Cells • Features of Eukaryotic Cells

6. Cells Share Certain Basic Features • A cell membrane • Nucleic acid • A cytoplasm • Ribosomes

7. Cell Membrane

8. Function of Cell Membrane • Isolates the cell’s contents from external environment • Regulates the flow of materials into and out of the cell (i.e. selectively permeable ) • Allows interaction among cells

9. Structure of the Cell MembraneFluid-Mosaic Model • Consists of phospholipids and proteins • The head region of each phospholipid molecule “loves” water (i.e. is hydrophilic) • The tail region of each phospholipid “hates” water (i.e. is hydrophobic) • Phospholipids form a bilayer • Proteins are embedded in phospholipid bilayer

10. Fluid Mosaic Model of the Cell Membrane

12. Nucleic Acid • Deoxyribonucleic acid (DNA) has two functions: • DNA controls protein synthesis in the cell • DNA is replicated and passed on to progeny cells during reproduction

14. Cell Cytoplasm • Consists of all materials inside the plasma membrane • It is the “bulk” of the cell • It is the site of cell metabolism: • (1) breaking down complex molecules for energy and simple “building block” molecules • (2) synthesis of new cell structures

15. Animal Cell

16. Ribosome • Ribosomes are the sites of protein synthesis, where an RNA strand is translated into an amino acid sequence. • Protein synthesis is extremely important to cells, and so large numbers of ribosomes are found throughout cells (often numbering in the hundreds or thousands).

17. Ribosomes

18. Prokaryotes Eukaryotes

19. Prokaryotic Cells • Lack a nucleus (though DNA is concentrated in a region called the cell’s nucleoid) • Lack membranous organelles • Are small in size ( < 5 um ) • Many have cell walls • Belong to the Domain Archaea and Domain Bacteria

21. Eukaryotic Cell • DNA is housed in a membranous organelle called the nucleus • Membranous organelles exist in the cytoplasm and perform specific cell functions • A network of protein fibers called the cytoskeleton give the cell shape and stability • Cells are large in size (10 – 100 um)

22. Animal Cell

23. Plant Cell

24. Nucleus • Control center of the eukaryotic cell • Nucleus has three distinct parts: • (1) nuclear envelope: double membrane between nucleoplasm and cytoplasm • (2) nuclear pores: openings between nucleus and cytoplasm • (3) nucleoplasm: fluid portion of nucleus that contains DNA and nucleolus

26. Nuclear Envelope • Nuclear envelope is a double membrane • Isolates cytoplasm from nucleoplasm • Regulates flow of materials between cytoplasm and nucleoplasm • Outer nuclear membrane is continuous with cytoplasm’s endoplasmic reticulum

28. Nucleoplasm • Contains the hereditary molecule deoxyribonucleic acid (DNA) which always remains in the nucleus • Loose “non-condensed” strands of DNA are called chromatin (cell is not dividing) • Tight “condensed” strands of DNA are called chromosomes (cell is dividing)

30. Nucleolus • Present inside of nucleus as a distinct region • Consists of ribosomal RNA, protein, ribosomes and DNA • Nucleoli are the sites of ribosome synthesis in the cell

31. Nucleus of a Liver Cell

33. Endoplasmic Reticulum • A complex system of membranes present within the cytoplasm • Endoplasmic reticulum (ER) is continuous with the nuclear envelope and the plasma membrane • ER functions as an internal transport system for the cell

35. Endoplasmic Reticulum • There are two types of ER: • (1) smooth ER: lacks ribosomes on its surface • Involved in lipid synthesis • (2) rough ER: outside is studded with ribosomes • Involved in protein synthesis

37. Endo-membrane System

38. Golgi Complex • A set of specialized membranes derived from the ER • Looks like a stack of flattened sacs or vesicles • Receives contents from ER, modifies these products, and packages them for transport out of cell

39. Golgi Complex

40. Lysosome • A membranous sac (or vesicle) containing digestive enzymes • Enzymes used to break down complex molecules in the cell • Lysosomes’ enzymes derived from RER and lysosome’s sac derived from Golgi complex

41. Lysosome

42. Vacuole • Membranous sac used for storage of water, waste, nutrients in the cell • Plant cells tend to have one, large vacuole • Animal cells tend to have numerous, small vacuoles

43. Plant Cell Vacuole

44. Peroxisome • Similar to lysosome • Membrane-bound vesicle that contains enzymes • Enzymes are used to breakdown toxic substances to hydrogen peroxide • Hydrogen peroxide is broken down by catalase to produce water and oxygen

46. Mitochondrion • Double membrane organelle • Outer membrane is smooth • Inner membrane is highly folded (in order to increase inner surface area for cellular respiration) • Folds are called cristae (sing. crista) • Inner fluid portion of mitochondrion is called the matrix

47. Mitochondrion Structure

48. Mitochondrion • Space between inner and outer membrane is called the intermembrane compartment • Function of mitochondrion is the breakdown of complex molecules to release energy for the cell (cellular respiration) • All eukaryotic cells have mitochondrion

49. Muscle Cell Mitochondrion

50. Chloroplast • Present only in plants • Site of photosynthesis • Double membrane system encloses the fluid-filled space called the stroma • Membrane system within stroma is organized into interconnected, flattened sacs called thylakoids