CELL �Structure and Functional unit of all living organism

Approx 40 MARKS

CHARACTERISTICS OF LIVING ORGANISMS

LEVELS OF ORGANISATION

LEVELS OF ORGANISATION

What is cell ?

• Structural & functional unit of all living organisms.

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What are the different types of cells are existed?

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• Prokaryotes (pro - primitive, karyote - nucleus)
• Mesokaryotes
• Eukaryotes (Eu - true)

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How cell is in living state ? - Energy

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• Metabolic reactions - various chemical reactions occurs inside the cell

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• Reactions - cytoplasm (Glycolysis) & Mitochondria (Krebs cycle, Electron transport chain)

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What does the cell consist of ?

• Cell Membrane & Cell Wall
• Protoplasm = Cytoplasm + Nucleoplasm
• Cytoplasm – Cell Organelles = Cytosol
• Cell organelles
• Chloroplast
• Mitochondria – Powerhouse of the cell
• Vacuoles
• Endoplasmic Reticulum - protein and lipid producer of cell
• Golgi Apparatus

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STRUCTURE OF CELL

• Nucleus - control center of cell

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• Nucleus - nucleoplasm (fluid inside nuclear membrane) + nucleolus

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• Chromosomes(2 sister chromatids) - DNA, RNA, histone and non histone proteins �

MICROSCOPE

• To study cell & sub-cellular structure

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• “SCOPE” in Studying MICROscopic organelles - Hence named MICROSCOPE

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• Light microscope - low magnification & enough resolution

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• Electron microscope - higher magnifications & higher resolution

SCALE OF MICROSCOPE

CELL SHAPE

• Cells differ – size, shape & activities
• E.g., Mycoplasma - Smallest cell (0.3 μm) in length
• No cell wall & survive without oxygen
• Bacteria - 3 to 5 μm
• Largest isolated single cell - Ostrich egg (1.5 kg)

Mycoplasma

Ostrich egg

CELL SHAPE

• Human RBC - 7.0 μm in dia
• Round & Biconcave

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• Nerve cells - longest cells

• Disc - like, Polygonal, Columnar, Cuboid, Thread like, or even irregular
• Shape of cell vary with specific function

E g., Tracheid (Elongated cell) - transport of water & mineral salts

CELL SIZE

Human RBC

Nerve cell

CELL SIZE AND SHAPE

SURFACE : VOLUME RATIO

Factors - limits cell size or volume :

• Nucleo - cytoplasmic ratio - determines the range of control of metabolic activities by nucleus

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• Ability of oxygen & other materials to reach every part of the cell

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• Ability of waste particles to reach outside

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• Rate of metabolic activity

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• Ratio of surface area to volume of cell

DISCOVERY OF CELL

• In 1665, Robert Hooke – cork cells under microscope.

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• Observed “Honey – comb” named as CELLULAE or CELLS

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• He wrote a book called “MICROGRAPHIA”

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• 1665 - Robert Hook - discovery of cell

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• 1674 - A. Van Leeuwenhoek - studied living cells for the first time

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• 1831 - Robert Brown - discovered Nucleus in a cell

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• (1838 - 39) - M.J.Schleiden & Schwann - Cell Theory

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• 1855 - Rudolf Virchow - Stated “Omnis cellula e cellula ”

CELL THEORY

• Three scientists:
• Malthias Schleiden (1838) - in plants
• Theodore Schwann (1839) - in animals
• Rudolf Virchow (1855)

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CELL THEORY

• Schleiden & Schwann together formulated “CELL THEORY“

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• All organisms are made up of cells

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• Contains genetic material - parents to daughter cells

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• All metabolic reactions take place inside the cells

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Drawback:

Did not explain “How new cells are formed ?“

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MODERN CELL THEORY modified hypothesis �

• Schleiden, Schwann and Rudolf Virchow (1855) - German physician

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• He explained cell division (TOTIPOTENT)

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• New cells are formed from pre-existing cell

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• Omnis Cellula e Cellula

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EXCEPTION TO CELL THEORY

• Bacteria & cyanobacteria
• No nucleus
• Many cell organelles – absent

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• Acellular organism - Monera & Protista, Xanthophytes (Vaucharia) Phycomycetes (Rhizopus)

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• Viruses, viroids & prions (obligate parasites)

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• RBC cells & tracheids - without nucleus but still they survive

TYPES OF CELLS

• Undifferentiated (stem cells)
• Unspecialized cell - power of division

e g : Apical meristem, zygote

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• Differentiated (post mitotic cells)
• Specialized cell - perform specific functions
• By switching ON (INDUCERS) & OFF (REPRESSORS) of Particular genes

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• Dedifferentiated
• Differentiated cell - revert to growth and division

E g : Healing of wounds, Regeneration in animals & plants

CLASSIFICATION BASED ON NO. OF CELLS

• Unicellular organisms E.g Bacteria and Archea
• Independent existence

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• Multicellular organisms E.g Fungi, Yeast, Animals

CLASSIFICATION OF CELLS BASED ON NUCLEUS

• Prokaryotes

(pro - primitive, karyote - nucleus)

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• Mesokaryotes

(meso - intermediate, karyote - nucleus)

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• Eukaryotes

(Eu - true, karyotes - nucleus )

PROKARYOTES

• Organisms with primitive nucleus (i.e., No TRUE nucleus)

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• DNA - without histone proteins

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• E.g : Bacteria, Blue green algae (BGA ), Mycoplasma, Rickettsiae and Spirochaetae.

BGA

PROTEOBACTERIUM

• Proteobacteria - major group (phylum) of bacteria.

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• Includes wide variety of pathogens - Escherichia (E.coli), Salmonella, Vibrio, Helicobacter,…

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• Others are free-living & includes bacteria(nitrogen fixation)

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MESOKARYOTES

• 1966, Dodge and his co-workers proposed mesokaryotes
• Intermediate between pro & eukaryotes
• Contains Nucleus & Nuclear membrane but no histones
• Divides through Amitosis
• Protozoa like Noctiluca, some phytoplanktons like Gymnodinium, Peridinium & Dinoflagellates (representatives of mesokaryotes)

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Noctiluca scintillans

Sparkling Light in Sea Water

EUKARYOTES

• Eukaryotes - E.g., Protists, Plants, Animals, Fungi

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• Cytoplasm - compartmentalized with Membrane bound organelles

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• Few organelles - Endosymbiosis (cell living inside another cell)

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DIFFERENCES

ENDOSYMBIOTIC THEORY

ENDOSYMBIOSIS

PROKARYOTIC CELLS

• Bacteria, Archae (Extermophiles) & BGA (Cyanobacteria)

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• Mycoplasma - PPLO (Pleuro Pneumonia Like Organisms)

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• Basic shapes of bacteria
• Bacillus (rod),
• Coccus (spherical),
• Vibrio (comma shaped) and
• Spirillum (spiral)

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FEATURES OF PROKARYOTES

• All prokaryotes have a cell wall surrounding the cell membrane except Mycoplasma

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• Cell envelope – 3 layers

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• Mesosomes – Infoldings

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• Flagella – motility

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• Pili - conjugation

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• Fimbriae - attachment

• No nucleus - Naked genetic material - No Nuclear membrane - contains genomic DNA

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• Plasmid DNA (extra chromosomal circular DNA) - confers certain unique phenotypic characters - e.g., Resistance to antibiotics - used for rDNA technology

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• Chromatophores - membranous extensions - cyanobacteria - contain Pigments

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• Only Ribosomes - present

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• Membrane bound organelles - absent

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MESOSOMES

• Special Membranous structures

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• Extensions of plasma membrane in the form of vesicles, tubules and lamellae.

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Functions:

• Cell wall formation
• DNA replication and distribution to daughter cells
• Respiration - Enzyme secretion processes
• Surface area

Enzyme content

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FLAGELLA, PILI AND FIMBRIAE

• Flagella - Locomotion / Motility.
• Flagella - filament, hook and basal body.
• Pili and Fimbriae - Do not play a role in motility.
• Sex Pilus - For conjugation (Transfer of genetic material)
• Fimbriae - bristle like fibers sprouting out of the cell. Help attachment to rocks in streams also to the host tissues

PLASMID

• Plasmids are extra-chromosomal
• Double stranded
• Circular
• Self-replicating
• Autonomous elements

BACTERIAL CHROMOSOMES

• Single circular DNA molecule, tightly coiled
• Not enclosed in a membrane

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• This genetic material is called Nucleoid or Genophore

Questions

Rickettsiae belong to which types of cells?

1. Mesokaryotes
2. Prokaryotes
3. Eukaryotes
4. None of the above

Questions

Nuclear membrane is present in which of the organisms?

1. Mesokaryotes
2. Prokaryotes
3. Eukaryotes
4. Both a and c

ANIMAL CELL

PLANT CELL

DIFFERENCE BETWEEN PLANT & ANIMAL CELL