CELL STRUCTURE AND ORGANIZATION

Cell Structure and Organization

 

1) Cell: Structure and functional unit of life of all living organisms.

2) Cytology: The branch of biology which deals with the study of cell is called cytology.

3) Mycoplasm: The smallest known living cell (size 0.3 micrometre in length).

4) Cell theory: Cell theory was proposed by Schwann and Schleiden according to which body of all living organisms are made up of cells.

5) Rudolf Virchow: Explained for the first time that new cells are formed by cell division from the pre-existing cells.

6) Totipotency: It is the capacity or the potential of living nucleated cells to differentiate and divide to form any other type of cell and thereby a completely new organism.

7) Prokaryotic cell: It has chemically complex protective cell envelop. However, it does not have a well-defined nucleus and other membrane-bound cell organelles.

8) Cell envelop: Cell envelop is a three-layered structure with outer glycocalyx,    middle cell wall, and inner plasma membrane

9) Gram staining: The most followed staining method is ‘Gram staining’ for bacteria developed by Danish bacteriologist Hans Christian Gram.

10) Pili: These are the outgrowth of plasma the membrane which helps in intercellular communication.

11) Fimbriae: It helps in attachment of the organism to substratum.

12) Mesosomes: Infolding of the cell membrane into the cytoplasm of the bacterial cell is called mesosomes which help in cell wall formation and DNA replication.

13) Chromatophores: Some bacteria especially photosynthetic cyanobacteria show longer extensions of plasma membrane called chromatophores. They carry photosynthetic pigments.

14) Ribosome:  The cytoplasm contains dense particles called ribosomes helping in protein synthesis. It is also known as a protein factory.

15) Eukaryotic cell: The cell in which the nucleus has a definite nuclear membrane are known as Eukaryotic cells. These cells exhibit the presence of membrane-bound cell organelles. e.g. Cells of Protists, Plants,  Animals, and Fungi.

16) Cell wall: It is a rigid, supportive and protective outer covering of the plasma membrane of plant cells, fungi and some protists.

17) Middle lamella layer: It is thin and lies between two adjacent cells. It is the first structure formed from the cell plate during cytokinesis. It is mainly made up of pectin, calcium, and magnesium pectate. The softening of ripe fruit is due to the solubilization of pectin.

18) Primary wall: It is present in young plant cell

19) Secondary wall: It is present inner to the primary wall.

20) Plasmodesmata: Plasmodesmata are cytoplasmic bridges between neighbouring cells.

21) Cell membrane / Plasma membrane: It is a thin quasi-fluid (semi-solid) structure present extracellularly around protoplast and intracellularly around most of the cell organelles in the eukaryotic cell.

22) Fluid mosaic model: It is the most accepted model of the cell membrane. It was proposed by Singer and Nicholson in 1972. According to this model, plasma membrane is made up of phospholipid bilayer and proteins. Proteins are like icebergs in the sea of lipids.

23) Hydrophilic: The substance which hates water is called a hydrophilic substance.

24) Hydrophobic: The substance which loves water is called a hydrophobic substance.

25) Amphipathic: The molecule having both hydrophilic and hydrophobic parts are called as an amphipathic molecule. 

26) Selective permeable: The membrane which allows only selected substances to move in and out the cell is called a selective permeable membrane.

27) Active transport: The movement of ions or molecules against the concentration gradient (from lower to higher concentration) is called active transport. It requires energy. So, ATP is utilized.

28) Passive transport: The movement of ions or molecules with the concentration gradient (from higher to lower concentration) is called passive transport. It does not require the expenditure of energy.

29) Cytoplasm: The colloidal jelly matrix which forms the ground substance of cell is    called cytoplasmic material or cytosol.

30) Cyclosis: The streaming movement of cytoplasm is known as cyclosis.

31) Endomembrane system: Nuclear membrane, endoplasmic reticulum, Golgi complex, lysosomes and various types of vesicles and vacuoles form a group and are together considered as the endomembrane system of the cell.

32) Endoplasmic Reticulum(ER): The little network within the cytosol is present in all eukaryotic cells except for ova and mature red blood corpuscles are called the endoplasmic reticulum.

33) Smooth ER: The endoplasmic reticulum which doesn’t have ribosome on its surface is called the smooth endoplasmic reticulum. It helps in the synthesis of lipid, detoxification of drugs and poisons, and storage of calcium ions.

34) Rough ER: The endoplasmic reticulum which has a ribosome on its surface is called is called the rough endoplasmic reticulum. It helps in protein synthesis.

35) Golgi complex: Golgi complex or Golgi apparatus or Golgi body; various terms are used to denote this assembly, manufacturing cum packaging, and transport unit of the cell.

36) Lysosome: It is single membrane structure contain hydrolytic enzyme and        capable of digesting carbohydrate-protein lipid and nucleic acid.

37) Vacuoles:  Vacuoles are membrane-bound sacs prominently found in plant cells. It occupies 90% of the total volume of the cell.

38) Tonoplast: The vacuoles are bound by a semipermeable membrane, called tonoplast.

39) Microbodies:  These are minute membrane-bound sac which contains types      of enzymes e.g Sphaerosomes, Peroxisomes, etc.

40) Glyoxysomes: These membrane-bound organelles contain enzymes that   convert fatty acids to sugar.

41) Mitochondria: These are important cell organelles involved in aerobic respiration. Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs). It is also called power house of the cell

42) Oxysomes:  Inner membrane of mitochondria bears numerous particles - Oxysomes (F1-F0/ Fernandez - Moran / Elementary particles /  mitochondrial particles). The Head acts as an enzyme ATP    synthase and foot as a proton channel. Oxysomes are involved in proton pumping and ATP synthesis.

43) Plastids: These are double-walled organelles containing DNA, RNA, and 70S ribosomes.

44) Leucoplast: These do not contain any pigment e.g Elaioplast.

45) Elaioplast : Oil storing leucoplast is called elaioplast e.g Cotyledons of Ricinus.

46) Amyloplast : Starch Storing leucoplast are called amyloplasts E.g Stem Tuber of Potato.

47) Aleuroplast: Protein storing leucoplast are aleuroplast E.g Cotyledons of the bean.

48) Chromoplast : Contains pigments other than chlorophylls like carotene, xanthophyll.

49) Chloroplast: Chloroplasts contain green pigment - chlorophyll along with other enzymes that help in the production of sugar by photosynthesis.

50) Thylakoid: Inside the cavity of the inner membrane of the chloroplast there is another set of membrane sacs. These are called thylakoids. Thylakoids are arranged in the form of stacks called grana (singular: granum).

51) Frets or stroma lamellae: The membranous tubules that connect grana are called stroma lamella.

52) Ribosomes:  Protein factories of the cell are called a ribosome.

53) Polyribosomes: Free ribosome come together and form chains called        polyribosomes for protein synthesis.

54) Nuclear envelope: The double-walled delimiting membrane of the nucleus is called a nuclear envelope.

55) Nucleopore: The nuclear membrane is not continuous. At places, there are small openings called a nucleopores or nuclear pore.

56) Karyolymph: Karyolymph or nucleoplasm is the matrix of the nucleus which      contains various substances like nucleic acids, protein molecules mineral and salts.

57) Nucleolus: Nucleus containing body is called the nucleolus. It is made up of rRNA and ribosomal proteins and it is best known as the site of ribosome biogenesis.

58) Chromatin material: The thread-like structure which is a complex of DNA and protein found in a eukaryotic cell is called chromatin material.

59) Euchromatin: Euchromatin is lightly packed region of chromosome or chromatin that is enriched in genes and is often genetically more active is called euchromatin.

 

60) Heterochromatin: Heterochromatin is a densely packed region of chromosome or chromatin that contain more proteins and less DNA and are genetically inert, are called heterochromatin.

61) Cytoskeleton: Network of fibrils present throughout the cytoplasm is called the cytoskeleton. It consists of microtubules, microfilaments, and intermediate filaments.

62) Cilia: Membrane-bound protoplasmic extension that occurs on the free surface of the cell. They are of small size and many in number.

63) Flagella: It is a long whip-like structure that helps some unicellular to move and are few in number.

64) Sheath: Covering membrane of cilia and flagella are called sheath.

65) Axeoneme: Core of cilia and flagella is called an axoneme. It posses 11 fibrils running parallel to the long axis. It shows 9 peripheral doublets and two single central fibrils (9+2).

66) Centriole & Centrosome: Centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in the most eukaryotic cell. It helps in the assembly of the spindle apparatus during cell division.