CELL,CELL MEMBRANE,ENDOPLASMIC RETICULUM AND GOLGI APPARATUS

MBBS 1ST YEAR ...CELLULAR ORGANISATION CHAPTER FROM GK PAL TEXTBOOK....IT COVERS CELL DEFINITION,CELL MEMBRANE,ENDOPLASMIC RETICULUM AND GOLGI APPARATUS

1. CELLULAR ORGANISATION Dr. RENUKA MAKANA DEPARTMENT OF PHYSIOLOGY GMC ANANTAPURAM .

2. 1. What is the structural and functional unit of tissues ?

3. Ans. Cell is the structural and functional unit of tissues.

4. 2.What is the boundary of all animal cells ?

5. Cell membrane is the boundary of all animal cells

6. CELL MEMBRANE Cell membrane is the protective sheath of the cell. It exchanges materials between the cytoplasm and the external environment. It facilitates interaction between cells and helps in anchoring the cells to each other.

7. Fluid-Mosaic Model (Singer & Nicolson, 1972) Cell membrane is made of  phospholipid bilayer with proteins embedded in it. It’s called “fluid-mosaic” because lipids move freely, giving flexibility without losing structure. The fluidity of the membrane is mainly dependent on the lipid composition of the membrane.

8. Lipid Bilayer The major lipids in the cell membrane are phospholipids, glycolipids and cholesterol. The phospholipids are phosphatidylcholine, sphingomyelin, phosphatidylserine and phosphatidyl ethanolamine. Glycolipids are generally found in the outer layer.

9. Lipids are amphipathic  molecules as their head or polar region is  hydrophilic  and tail or nonpolar region is  hydrophobic.   Hydrophilic head of lipid molecules faces the aqueous phase from both inside and outside the cell. Cholesterol  is incorporated into the hydrophobic regions of the membrane, and serves to reinforce the lipid permeability barrier.

10. Functions of the Lipid Bilayer Acts as a selective (semipermeable) barrier between the cytoplasm and interstitial fluid . Controls movement of substances into and out of the cell. Lipid-soluble molecules (e.g., oxygen, alcohol ) pass through easily . Water-soluble molecules (e.g., urea, glucose ) pass through with difficulty . Maintains the cell’s internal environment and chemical balance . Provides a flexible yet stable structure for membrane proteins to function.

11. INTEGRAL PROTEINS OR TRANSMEMBRANE PROTEINS Channel Proteins → Form pores for water-soluble substances (e.g., glucose, electrolytes). Carrier Proteins → Transport molecules via facilitated diffusion (e.g., glucose transporter). Ion Pumps → Perform active transport using ATP (e.g., Na⁺–K⁺ ATPase ). Receptors & Enzymes → Outer side: act as receptors . Inner side: act as enzymes (e.g., G-proteins ). Antigenic Role → Glycoproteins act as cell surface antigens (e.g., blood group antigens ).

12. Peripheral Proteins Lightly attached to the inner or outer surface of the membrane. 1. Intrinsic Proteins (Inner Surface) Located on the cytoplasmic side of the membrane. Function as enzymes or anchor proteins for the cytoskeleton . Help maintain cell shape and structural stability. 2. Extrinsic Proteins (Outer Surface) Found on the outer side of the membrane. Function as cell adhesion molecules (CAMs) . Anchor the cell to the basal lamina and neighboring cells .

13. Membrane Carbohydrates The external surface of the cell membrane is loosely covered by a carbohydrate layer known as the cell coat or glycocalyx . Functions of the Glycocalyx : 1. Glycocalyx serves as a protective coat. 2.Permit temporary cell-to-cell adhesion. 3. Some carbohydrate molecules serve as receptors.

14. Functions of Cell Membrane 1. Cell membrane maintains a constant and distinctive intracellular environment , which is essential for functioning of the organelles. 2.Cell membrane maintains cell volume by actively transferring ions across it, especially by pumping sodium ions out of the cell. 3. In neurons and muscle cells, it maintains a potential difference between intracellular and extracellular surfaces, which enables cells to respond to various stimuli. 4. Cell membrane helps in recognizing foreign cells or antigens so that they can be destroyed by phagocytes .

15. MITOCHONDRIA

16. Mitochondria Mitochondria are the “ power house ” of the cell. They are Cigar ­shaped organelles whose shape, size and number vary in different tissues of the body. They are most abundant in cells that have high rate of metabolism, as in liver, cardiac muscle.

17. Mitochondrial Membranes Electron microscopy shows that each mitochondrion has two layers of membranes: the outer and inner membranes. Outer Mitochondrial Membrane : This forms a continuous envelop of the organelle.  Outer membrane consists mostly of phospholipids and cholesterol, and contains a specific membrane protein that forms “porin”.  Porins are channels that permit substances with molecular weight of less than10,000 to diffuse freely across the outer membrane.

18. Inner Mitochondrial Membrane: Rich in proteins ; lipid-to-protein ratio is 0.27 : 1 . Virtually impermeable to polar and ionic substances . Inner membrane forms folded structures called cristae . Cristae increase surface area for biochemical reactions. Rich in enzymes involved in the electron transport chain (ETC) and oxidative metabolism , including:  Cytochromes : b, c₁, c, a, a₃,  NADH dehydrogenase, Succinate dehydrogenase, Electron-transferring flavoprotein, Carnitine-palmitoyl transferase.

19. Mitochondrial Matrix The region enclosed by the inner membrane is called  matrix. An amorphous material fills the matrix, which contains enzymes involved in the Kreb’s citric acid cycle and Fatty acid oxidation . Matrix also contains several strands of DNA, ribosomes and enzymes for synthesis of proteins coded in the mitochondrial genome.

20. Functions The inner membrane contains the cytochromes of the electron transport system and the associated enzymes for oxidative phosphorylation . The TCA cycle takes place in the matrix.The end products of the citric acid cycle (Kreb’s cycle) are CO2, H2O and ATP. Like most components of the cell, mitochondria have a short lifespan and are constantly renewed. As they have strands of DNA they are capable of self ­replication as well as protein synthesis

21. Clinical box Mitochondrial diseases: The disease that affects mitochondrial energy transduction is called Luft’s disease .  The abnormality of mitochondrial DNA leads to cellular dysfunction called as mitochondrial cytopathy syndrome, which manifests with muscle weakness, degenerative lesions of the brain and high levels of lactic acid in blood.

22. Endoplasmic Reticulum The endoplasmic reticulum (ER) consists of a network of membranous tubules, vesicles, and flattened cisternae. The membranes of ER are continuous with the outer membrane of nucleus and are also connected with Golgi apparatus .  They are of two types: rough ER and the smooth ER.

23. Rough Endoplasmic Reticulum When surface of ER is studded with ribosome, the organelle is called rough ER (RER) as it gives a “rough” or “granular” appearance to it. RER are present in more number in cells that are actively involved in protein synthesis like acinar cells of pancreas and neurons. In neurons, the Nissl granules are modified RER. Functions of RER : 1. It is concerned with protein synthesis . Therefore, it is abundant in cells of endocrine glands and cells secreting digestive enzymes. 2. It also plays some role in the conjugation of carbohydrates with proteins to form glycoproteins, a function which it shares with the Golgi apparatus.

24. Smooth Endoplasmic Reticulum When ribosomes are not attached to the surface of ER, the organelle is called smooth ER (SER) or agranular ER as its surface has “smooth” or “agranular” appearance. Functions of SER 1. It is concerned with the synthesis of lipids. Hence it is abundant in cells that synthesize cholesterol, steroid Hormones and phospholipids. 2. In muscles, it is called sarcoplasmic reticulum, which is specialized for the storage of calcium ions that is released during excitation ­contraction coupling. 3. SER is part of intracellular transport system as it is continuous with the RER and Golgi apparatus. 4. It is also the site for the detoxification or neutralization of hormones and toxic substances.

25. Golgi Apparatus The Golgi apparatus (GA) is also known as Golgi complex or dictyosome.  It is present in all cells and generally is located close to the nucleus. It appears as flat discs that are dilated peripherally and stacked together in a bunch as stack of cisternae .  Anatomically and functionally it is closely associated with endoplasmic reticulum. Functionally GA two main regions: cis and trans. The region nearer to the nucleus is the cis face (cis Golgi) and the region close to the membrane is the trans face (trans Golgi) .

26. Major Functions of Golgi apparatus 1. It is the site for the packaging of secretory products into the secretory granules. Materials produced in rough ER travel through the lumen of smooth ER.  2. It is the site for the incorporation of carbohydrates into the newly synthesized proteins to form glycoproteins. 3. Lysosomal enzymes are formed in GA. 4. Transports material to other organelles and cell surface.

27. MULTIPLE CHOICE QUESTIONS  1.The Fluid-Mosaic Model of the cell membrane was proposed by: A. Robertson B. Singer and Nicolson C. Danielli and Davson D. Watson and Crick

28. 1.The Fluid-Mosaic Model of the cell membrane was proposed by: A. Robertson B. Singer and Nicolson  C. Danielli and Davson D. Watson and Crick

29. 2.The lipid-to-protein ratio in the average cell membrane is about: A. 1:1 B. 1:2 C. 0.9:1 D. 0.27:1

30. 2.The lipid-to-protein ratio in the average cell membrane is about: A. 1:1 B. 1:2 C. 0.9:1 D. 0.27:1

31. Membrane fluidity mainly depends on: A. Carbohydrate content B. Lipid composition C. Protein size D. Ribosome density

32. Membrane fluidity mainly depends on: A. Carbohydrate content B. Lipid composition C. Protein size D. Ribosome density

33. The major lipids of cell membranes include all except: A. Phospholipids B. Cholesterol C. Glycolipids D. Triglycerides

34. The major lipids of cell membranes include all except: A. Phospholipids B. Cholesterol C. Glycolipids D. Triglycerides

35. Lipid molecules are amphipathic, meaning they have: A. Both hydrophilic and hydrophobic parts B. Two hydrophobic ends C. Only nonpolar regions D. Only polar regions

36. Lipid molecules are amphipathic, meaning they have: A. Both hydrophilic and hydrophobic parts B. Two hydrophobic ends C. Only nonpolar regions D. Only polar regions

37. 10.The main function of the lipid bilayer is to: A. Produce ATP B. Serve as permeability barrier C. Synthesize proteins D. Transport ions actively

38. 10.The main function of the lipid bilayer is to: A. Produce ATP B. Serve as permeability barrier C. Synthesize proteins D. Transport ions actively

39. 11.Proteins that span the entire membrane are called: A. Peripheral proteins B. Integral proteins C. Cytoskeletal proteins D. Glycoproteins

40. Proteins that span the entire membrane are called: A. Peripheral proteins B. Integral proteins C. Cytoskeletal proteins D. Glycoproteins

41. 12.Integral proteins function as all except: A. Ion pumps B. Channel proteins C. Enzymes D. Structural microtubules 

42. 12.Integral proteins function as all except: A. Ion pumps B. Channel proteins C. Enzymes D. Structural microtubules 

43. Na⁺–K⁺ ATPase is an example of a: A. Channel protein B. Carrier protein C. Ion pump D. Receptor protein

44. Na⁺–K⁺ ATPase is an example of a: A. Channel protein B. Carrier protein C. Ion pump ✅ D. Receptor protein

45. 16.Intrinsic peripheral proteins are found on: A. Outer surface B. Inner surface C. Both sides equally D. None of these

46. 16.Intrinsic peripheral proteins are found on: A. Outer surface B. Inner surface ✅ C. Both sides equally D. None of these

47. . Extrinsic proteins function mainly in: A. Cell adhesion B. Active ion transport C. Protein synthesis D. Energy production

48. Extrinsic proteins function mainly in: A. Cell adhesion  ✅ B. Active ion transport C. Protein synthesis D. Energy production

49. The carbohydrate-rich outer layer of the membrane is called: A. Cell coat / Glycocalyx B. Myelin sheath C. Cell wall D. Cytoskeleton

50. The carbohydrate-rich outer layer of the membrane is called: A. Cell coat / Glycocalyx ✅ B. Myelin sheath C. Cell wall D. Cytoskeleton

51. Glycocalyx mainly consists of: A. Polysaccharides only B. Glycoproteins and glycolipids C. Phospholipids and cholesterol D. RNA and DNA

52. Glycocalyx mainly consists of: A. Polysaccharides only B. Glycoproteins and glycolipids ✅ C. Phospholipids and cholesterol D. RNA and DNA

53. The cell’s “powerhouse” is the: A. Golgi apparatus B. Nucleus C. Mitochondrion D. Endoplasmic reticulum

54. The cell’s “powerhouse” is the: A. Golgi apparatus B. Nucleus C. Mitochondrion ✅ D. Endoplasmic reticulum

55. Outer mitochondrial membrane contains: A. Porins B. Cristae C. Ribosomes D. Cytochromes

56. Outer mitochondrial membrane contains: A. Porins ✅ B. Cristae C. Ribosomes D. Cytochromes

57. Cristae increase: A. Volume of mitochondria B. Surface area for enzyme reactions C. Protein degradation D. Ion permeability

58. Cristae increase: A. Volume of mitochondria B. Surface area for enzyme reactions ✅ C. Protein degradation D. Ion permeability

59. The inner mitochondrial membrane is rich in enzymes like: A. Cytochromes and dehydrogenases B. Lipases only C. Kinases only D. Proteases only

60. The inner mitochondrial membrane is rich in enzymes like: A. Cytochromes and dehydrogenases ✅ B. Lipases only C. Kinases only D. Proteases only

61. Rough Endoplasmic Reticulum (RER) is abundant in: A. Cells producing steroid hormones B. Cells actively synthesizing proteins C. Cells involved in detoxification D. Muscle cells

62. Rough Endoplasmic Reticulum (RER) is abundant in: A. Cells producing steroid hormones B. Cells actively synthesizing proteins C. Cells involved in detoxification D. Muscle cells

63. Rough Endoplasmic Reticulum (RER) is abundant in: A. Cells producing steroid hormones B. Cells actively synthesizing proteins ✅ C. Cells involved in detoxification D. Muscle cells

64. Smooth Endoplasmic Reticulum (SER) is specialized for: A. Protein synthesis B. Lipid synthesis and detoxification C. DNA replication D. RNA transcription

65. Smooth Endoplasmic Reticulum (SER) is specialized for: A. Protein synthesis B. Lipid synthesis and detoxification ✅ C. DNA replication D. RNA transcription

66. The Golgi apparatus mainly functions in: A. ATP production B. Packaging and secretion of proteins C. DNA synthesis D. Fat storage

67. The Golgi apparatus mainly functions in: A. ATP production B. Packaging and secretion of proteins ✅ C. DNA synthesis D. Fat storage