PROKARYOTIC AND EUKARYOTIC CELL

PROKARYOTIC AND EUKARYOTIC CELL:

 

Cell basics:

·        All living organisms are composed and depend on cells to function normally.

·        Not all cells are alike.

·        There are two primary type of cells:

·        1.) Prokaryotic cells

         2.) Eukaryotic cells

 

 

 

Characterstics

Prokaryotic cell

Eukaryotic cell

1)

Occurence

Found in bacteria and

Found in all plants and

 

 

Blue Green Algae(BGA)

animals

 

 

 

Except bacteria and BGA.

 

 

 

 

2)

Size

1-10µm

10-100µm

3)

Cell wall

Present in most but

Animal cell lack cell wall but

 

 

not in all. In bacteria

plant cell wall is made up of

 

 

cell Wall is made up of

cellulose. In fungi cell wall is

 

 

polysaccharide,

made up of chitin.

 

 

Lipid and protein.

 

4)

Plasma membrane

Present

Absent

 

 

 

 

5)

Nucleus

Absent, nuclear region

present

 

 

is present where

 

 

 

genetic material

 

 

 

resides.

 

6)

Nuclear membrane

absent

present

7)

Chromatin with histone

absent

present

8)

Chromosome

Circular ring having a

Linear having centomere

 

 

centromere

 

9)

Number of chromosome

Each cell has only one

Number of chromosome

 

 

chromosome

depend upon the type of

 

 

 

organism

10)

Genetic material

Circular or linear, ds

Linear ds DNA genes

 

 

DNA only exons are

frequently interrupted by

 

 

present

intron sequences specially in

 

 

 

higher eukaryotes called

 

 

 

split genes.

11)

Plasmids

Absent

Rare

12)

Cell Organelles (mitochondria,

Absent

Present

 

endoplamic reticulum, golgi body,

 

 

 

lysosomes, chloroplast, centrioles,

 

 

 

microtubules)

 

 

13)

Ribosomes

70S lie freely in

80S, In plastids and

 

 

cytoplasm or engaged

mitochondria 70S present.


 

 

in protein synthesis.

 

14)

Flagella

Simple and composed

Complex 9+2 structure of

 

 

of flagellin protein

tubulin and other protein

15)

Respiration

Anaerobic respiration

Aerobic respiration but

 

 

 

some facultative anaerobes

 

 

 

present

16)

Photosynthetic enzymes

Bound to plasma

Enzymes packed in plastids

 

 

membrane as

bound by membrane

 

 

composite

 

 

 

chromatophores

 

17)

Sexual system

Transformation,

Both sexes involve in sexual

 

 

transduction or

participation.

 

 

conjugation

 

18)

Cell division

Does not show

Distinction present between

 

 

distinction between

phases.

 

 

interphase and M phase

 

19)

Duration of cell cycle

Cell cycle is short and

Duration is long and takes

 

 

takes 20-60 minutes to

12-24 hrs to complete.

 

 

complete.

 

20)

Pili and Fimbrae

Present

Absent

21)

Cyclosis or cytoplasmic streaming

Absent

Common

22)

Transcription

Occur in cytoplasm

Occur inside nucleus

 

 

 

 

 

 

 

 

 

 

 

 

 

Structure of prokaryotic cell


 

Prokaryotes derived from two words “Pro” means primitive and “karyon” means nucleus. Those organisms which possess primitive nucleus are known as prokaryotes. Prokaryotes are unicellular organisms. They are the earliest and most primitive forms of life on earth. Prokaryotes are able to live and thrive in extreme habitats like hydrothermal vents, hot springs, swamps, wetlands, guts of animals. Prokaryotes are known as gram negative bacteria. Prokaryotes are mainly of two types:

 

  1. Bacteria
  1. Archaeans

 

 

 

Components of Prokaryotic Cell

 

I.             Cell Wall:

Prokaryotes have rigid framework of murein or peptidoglycan (polysaccharide cross linked by peptide chains). Archeans do not have peptidoglycan in their cell wall. Cell wall protects the prokaryotes from adverse conditions or harsh environment of outside the cell and gives them a definite shape.

 

II.             Plasma membrane or Cell membrane:

Consist of phospholipid bilayer with associated protein. It holds all intracellular material and regulates movement of material in and out of the cell.

 

III.              Gl ycocalyx:

It is present in some bacteria and located outside of cell wall. It can be of two types:

 

i.             Slime layer: It helps stick to things and protect them from drying out particularly in hypertonic environment.

 

ii.              Capsule: Capsules allow bacteria to stick to things and encapsulated bacteria hide from host immune system or provide some protection

 

IV.  Cytoplasm: A gel like substance consists mainly of water. Cytoplasm also contains enzymes, salts, cell components and various organic molecules. All cellular components are suspended in cytolplasm.

 

V.  Cell Extensions: Two types of extensions are emerge out of cell:

i.             Flagella: It is a long whip like extension which helps in motility (able to move spontaneously and actively consuming energy in the process of cell movement)

ii.              Pilli or Fimbrae: Pilli is a hair like appendage present on the surface of cell. Pilli helps in transfer of plasmid from donor to recipient bacteria. Fimbrae is a protein rod (3-10nm in diameter).  It. helps bacterial cell adhere to each other.

 

VI.         Mesosomes: Structure of prokaryotic cell formed by invagination of plasma membrane. They serve as mitochondria of prokaryotes. Enzymes associated with respiration are located on the infoldings of mesosomes.

 

VII.         Genetic material: In prokaryotes DNA is found in condensed form in cell producing a darkened area called Nucleoid.

 

VIII.         Plasmid: Short piece of circular DNA which replicate autonomously are also found in prokaryotic cell.

 

IX.        Reserve Food: Lipid globules or glycogen granules are present as reserve food material in prokaryotes.

 

X.             Ribosomes: Here 70S type of ribosomes is present which are smaller than eukaryotic ribosomes. They are scattered in cytoplasm called as “Free ribosomes”. Bacterial ribosomes have half amount of ribosomal RNA and one third ribosomal protein.

 

XI.        Cytoskeleton: It’s recently been discovered that rod shaped bacteria and Archaeans possess cytoskeletal proteins. This provides structural support to cells and plays a key role in cell division.

 

 

 

 

Eukaryotic Cell Structure

 

Eukaryotes derived from two word “Eu” means true and “karyon” means nucleus i.e. those organisms which possess true nucleus are known as eukaryotes. They are more complex than prokaryotes. These organisms have membrane bound nucleus with many cell organelles to perform several cellular functions. A cell defined as eukaryotes if it has true membrane bound nucleus and has other membrane organelles that allow for compartmentalization of function. Some examples of eukaryotes are animals, plants, fungi (mushrooms), protists(algae, plankton etc.)

 

 

Components of eukaryotic cell:

i.  Plasma Membrane:

            It is a Semi-permeable membrane made of phospholipid and protein. It function as a barrier                           which regulating the movement of materials between inside and outside of cell.

 

ii.  Nucleus:

It is the largest and most visible cell organelle. Nucleus is surrounded by double layer of phospholipid bilayer called as nuclear envelope. Here genetic material is found in the form of DNA and stores all necessary information.

iii. Nuclear membrane:

Double layer that surrounds the nucleus and it play a role in entry and exit of material.

iv.  Ribosomes:

       Eukaryotic ribosomes are larger than prokaryotic ribosomes. Ribosomes are of 80S type which                contains twice the amount of rRNA and one third more ribosomal proteins than that of prokaryotes.


v.  Cytoplasm:

      Cytoplasm is a gel like substance in which all the cell organelles are suspended.

vi. Cell Wall:

Plants, algae and fungi have thick protective cell wall, which provide support, help in maintaining the shape of cell and prevent cell from external environment.

vii. Cilia and Flagella:

     They are covered with plasma membrane and supported internally with structural system of                     microtubules.

a. Flagella: Larger than cilia aid in movement.

b.Cilia:They are able to beat together in a coordinated manner and can also direct material outside of cell.

viii. Endoplasmic Reticulum:

      They are functioning as a factory for making and shipping proteins and lipids. It regulates the flow of       calcium inside and outside of cell. Endoplasmic reticulum are of two types:

Smooth E.R.- Endoplasmic reticulum covered with ribosomes

Rough E.R. – Endoplasmic reticulum which is not covered with ribosomes.

ix.   Mitochondria:

       It is known as the power house of the cell. It is the centre for ATP synthesis which provides energy         to the cell.

x.  Golgi body:

      It consists of flattened tubules and rounded vesicles which help in storing and transporting the                    proteins and lipids synthesized by E.R.

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