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PROCARYOTİC &EUCARYOTİC CELLS. Prof. Dr. Gönül KANIGÜR. Microorganisms can be divided into 2 groups :. CELLS. The microscopic study of cells reveals 2 types of cells: prokaryotic and eukaryotic. Two Main Classes of Cells • Prokaryotic ( Bacteria and Archaea )

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Prof. Dr. Gönül KANIGÜR

Microorganisms can be divided into 2 groups :


  • The microscopic study of cells reveals 2 types of cells: prokaryotic and eukaryotic.

  • Two Main Classes of Cells

  • • Prokaryotic (BacteriaandArchaea)

  • – Pro = “Before”; Karyon = “Kernel”

  • – No nucleus, DNA coiled up inside cell

  • • Eukaryotic (Everything else)

  • – Eu = “True”

  • – DNA inside membraneboundorganelle inside

  • cell, thenucleus

Prokaryotic Cells are relatively simple

  • 1. Bacteria are prokaryotic cells

  • 2. 1-10 um in diameter, just visible with light microscopes.

  • 3. Metabolically diverse.

  • 4. No True Nucleus


  • Prokaryotes exhibit a variety of shapes

    • Most common

      • Coccus

        • Spherical

      • Bacillus

        • Rod or cylinder shaped

Cellular Structure

  • A typical bacterial (procaryotic) cell has the following basic structures :

    (1)Cell Wall,

    (2)Cell Membrane,


    (4)Nuclear Region


  • Bacterial cell wall

    • Rigid structure

    • Surrounds cytoplasmic membrane

    • Determines shape of bacteria

    • Holds cell together

    • Prevents cell from bursting

    • Unique chemical structure

      • Distinguishes Gram positive from Gram-negative

Cytoplasmic membrane

  • A.Structure

  • -A phospholipid bilayer with proteins

  • -contains carbonhydrates

  • -contains sterols

  • B-Function

  • -transport:simple diffusion,facilitated diffusion,osmosis and active transport

  • -Endocytosis:phagocytosis and pinpcytosis

Cellular Structure


  • Small particles composed of protein and ribonucleic acid (RNA).

  • A single cell may have as many as 10,000 ribosomes.

  • Part of the translation apparatus, synthesis of cell proteins take place upon these structures.


  • Ribosome

    • Involved in protein synthesis

    • Composed of large and small subunits

      • Units made of protein 40% and ribosomal RNA 60%

    • Prokaryotic ribosomal subunits

      • Large = 30S

      • Small = 50S

    • Small than eukaryotic ribosomes

      • Difference often used as target for antimicrobials

Cellular Structure

(4)Nuclear Region

  • Nuclear region is primitive in procaryotic cell, i.e. bacteria.

  • Procaryotic cells DO NOT possess a true nucleus.

  • The functions of the nucleus are carried out by a single long strand of deoxyribonucleic acid (DNA)

  • The nuclear region where the DNA is present is sometimes known as a nucleoid, NOT a nucleus.

  • Bacterial chromosome is not directly intereact with the proteins such as histons

  • DNA contents range from about 0.6 million to five milion bp.5000 proteins are coded from the chromosomal DNA

  • Bacteria may also contain plasmids,double stranded DNA molecules.they are not essential for growth and reproduction.

  • Plasmids carry functional genes that give certain properties of the bacterial cell for ex.drug rezistance .some bacteria are rezistance to some antibiotics.


Many bacteria are motile, able to move independently due to a special structure known as Flagellum (plural : Flagella)

Rigid tubular structure made of pilin protein

Found only in Gram negative cells


Sexual pili—joins bacterial cells for DNA transfer (conjugation)

Common pili—adhesion



I. Organisms and general properties

  • A. Organisms

    • 1. Microorganisms

      • Fungi

      • Protozoa

      • Algae

    • 2. Other

      • Higher plants

      • Animals

I. Organisms and general properties, cont.

  • B. General properties

    • More complex than procaryotes

    • Larger than procaryotes

    • Have a true nucleus

    • Have membrane-bound organelles

III. The cell wall and glycocalyx

  • A. Cell wall

    • Rigid structure

    • Found on plant cells

    • Not made of peptidoglycan, but of long polysaccharide, e.g., cellulose

  • B. Glycocalyx A carbohydrate-containing structure on the surface of a cell.

    • May strengthen membrane of animal cells.

    • Serves as an adhesin, i.e., holds adjacent cells together

Eukaryotic Cells Components

Cell Wall

  • contains cellulose

  • support and protection

    Cell membrane / Plasma membrane

  • Phospholipid bilayer with embedded proteins

  • boundary layer and transport


  • nuclear envelope, nucleoplasm, chromatin, nucleoli

  • storage and synthesis of genetic material.


  • Ribosome formation

IV. The cytoplasmic membrane

  • A. Structure

    • A phospholipid bilayer with proteins

    • Contains carbohydrates

    • Contains sterols

  • B. Function

    • Transport: simple diffusion; facilitated diffusion; osmosis; and active transport

    • Endocytosis: phagocytosis; and pinocytosis

VI. Organelles

  • Organelle A membrane-enclosed structure.

  • A. Nucleus

    • Has a double membrane with pores

    • Contains nucleoli where ribosomal RNA is synthesized

    • Contains chromatin: DNA + histones (basic proteins)

    • Chromosomes divide by mitosis.

  • İts diameter is aprox. 5um

  • İt contains genetic material of the cell.

  • The Dna content is l.5 x10 – 7 to 5xl0 -9 bp

  • 30.000 protein are coded.

  • The nucleus is the site of DNA replication and RNA synthesis.

V. Cytoplasm

  • The substance outside the nucleus and inside the plasma membrane

  • Similar in composition to that of procaryotes, but has a cytoskeleton that provides shape, support, and transport within cell

  • Cytoskeleton consists of:

    • Microfilaments

    • Intermediate filaments

    • Microtubules

VI. Organelles, cont.

  • B. Endoplasmic reticulum (ER)

    • Membrane network from nucleus to plasma membrane

    • Rough ER

      • Has ribosomes attached

      • Site of protein synthesis

    • Smooth ER

      • No ribosomes attached

      • Site of lipid synthesis

VI. Organelles, cont.

  • C. Golgi apparatus

    • Stacks of membranes in cytoplasm

    • Receives proteins & lipids from ER

    • Ends pinch off forming secretory vesicles

    • Transports proteins & lipids within cell

D. Ribosomes

  • The site of protein synthesis

  • In cytoplasm: 80S variety consisting of 60S & 40S subunits

  • In mitochondria:70S variety consisting of 50S & 30S subunits

G. Lysosomes

  • Contains hydrolytic enzymes

  • Especially important in phagocytes

. Organelles, cont.

  • H. Vacuoles - membrane bound cavities

    • Diverse functions:

      • Store proteins, sugars, etc.

      • Store metabolic waste

      • Store water (plant cells)

Organelles, cont.

  • E. Mitochondria

    • The site of respiration

    • Has 2 membranes:

      • Outer one has sterols

      • Inner one has no sterols,

      • Has DS circular DNA

    • Has 70S ribosomes

    • Replicates autonomously

VI. Organelles, cont.

  • F. Chloroplasts

    • The site of photosynthesis

    • In algae and other plant cells

    • Contain 70S ribosomes

    • Contain DS DNA

    • Replicate autonomously

  • An endosymbiotic orijin for these organels mitochondria,chloroplast) is now generally accepted

I. Centrioles

  • Near nucleus

  • Functions: cell division, and formation of cilia and flagella

II. Structures external to the cell wall

  • A. Flagella

    • Surrounded by the cytoplasmic membrane.

    • Contains microtubules in a 2 + (2 x 9) arrangement

    • Function: motility

    • Found on some protozoa and algae

    • Only a few per cell



Simple wall structure

Sterols in membrane

2 + (9x2) flagella

True nucleus




Peptidoglycan wall

No sterols in memb.

Flagellin in helix

No nucleus

No histones

VII. Comparisons


Several chromosomes

Membrane-bound organelles

80S ribosomes


One chromosome

No membrane-bound organelles

70S ribosomes

VII. Comparisons, cont.


1 chromosome

No membrane-bound organelles

70S ribosomes

Replicates autonomously


Multiple copies

no membrane-bound organelles

70S ribosomes

Replicates autonomously

VII. Comparisons, cont.


About 1- 8 m

Peptidoglycan wall

No sterols in membrane

No nucleus

No histones


About 1 m

No wall

No sterols in inner membrane

No nucleus

No histones

VII. Comparisons, cont.

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