Cell and Cell Structure Part-3

Cell organelles

  • They are living part of the cells having definite shape, structure and function bounded by plasma membrane.
  • There are single membrane bound, double membrane bound and non-membrane bound cell organelles. 

Endoplasmic Reticulum

  • It is a network of membrane-bound tubes and sheet which appears as long tubules or round or oblong bags (vesicles).
  • It plays a crucial part in interpreting the genetic information found in the nucleus.
  • Found in all cells except prokaryotes and human erythrocytes.
  • Smooth ER – They do not contain ribosome on their surface and therefore does not involve in protein synthesis. It helps in synthesis of fat molecules, lipid and detoxifying of poisonous molecules.
  • Rough ER - They do contain ribosome on their surface and involved in protein synthesis. They are made up of nucleic acid and proteins. They also involved in the modification and folding of proteins.
  • Function- Act as a cytoplasmic framework to provide surface for some of the biochemical activities, form endoskeleton of cell and serves as channel for the transport of material between various region of cytoplasm and between cytoplasm and nucleus.

Golgi Apparatus-

  • It was discovered by Camillo Golgi and often known as the cell's post office.
  • It consists of a system of membrane bounded fluid filled vesicles arranged parallel to each other in stacks called cisternae along with some large and spherical vesicles.
  • They package and transport the proteins throughout the cytoplasm.
  • It is not found in prokaryotes, mammalian RBC’s and sieve cells.
  • Function-Storage, modification, packaging and secretion of products in vesicles and also involved in the formation of lysosomes.

Lysosome

  • It is membrane-bound cell organelle containing strong digestive enzymes for intracellular digestion.
  • They are responsible for removing worn-out cell components and eliminating any foreign bacteria or viruses.
  • It is synthesized by Golgi body and enzyme found in it synthesized by Rough ER.
  • They are known as "suicide bags of the cell" because they are filled with potent enzymes that can digest cells.
  • Function-Kind of waste disposal system of the cell and mainly perform digestion.

Mitochondria

  • They are rod-shaped membrane bound organelle found in all eukaryotic cells except prokaryotes and mammalian RBC’s.
  • It is known as power house of the cell because it is responsible for the extracting energy from food through cellular respiration.
  • Outer membrane has specific protein while inner membrane is folded inside to form chamber called Cristae.
  • It is semi-autonomous organelle as it has its own DNA (mDNA) and ribosome.
  • Function-Produce, store and release the energy in the form of ATP which is known as currency of the cell and  they also a main site for cellular respiration in which ATP are produced.

Plastids

  • Only found in plants cells.
  • There are two types of plastids- chromoplast (coloured plastids) and leucoplasts (white or colourless plastids).
  • Plastid containing the pigment chlorophyll is called chloroplast which performs the function of photosynthesis. It also contains membranes known as thylakoids embedded in the stroma.
  • Leucoplasts are found primarily in organelles in which materials such as starch, oils and protein granules are stored.
  • Plastids also have their own DNA and ribosome.

Vacuoles

  • Vacuoles are large vesicles that contain either air or water and provide the cell its structural rigidity.
  • Mostly found in plants cells while in animals they are small or absent.
  • Function- Their main function is to ensure the rigidity of the cell and maintain its osmotic pressure.

Cell Division

  • Mitosis- A single cell divides into two identical daughter cells during the cell division process known as mitosis. The daughter cells are identical to the mother cells in terms of chromosomal number. It helps in tissue growth and repair in organisms.

  • Meiosis- It is a type of cell division that results in the production of four gamete cells and a half reduction in the number of chromosomes in the parent cell.