CELL - 1

INTRODUCTION

• Cell is the fundamental structural and functional unit of all living organisms.
• Robert hooke - seen 1st cell, and coined -CELL

• Antony Von Leeuwenhoek first saw and described a live cell.

• All organisms are composed of cells.
• organisms composed of a single cell --unicellular organisms
• And organisms composed of many cells--multicellular organism.

CELL THEORY

Schleiden and schwann

Robert virchow

AN OVERVIEW OF CELL

• Cells are surrounded by a cell membrane.
• In plants, cell membrane is surrounded by a cell wall.
• Inside each cell -- nucleus --chromosome -- DNA.
• Cells that have membrane bound nuclei -- eukaryotic 
• whereas cells that lack a membrane bound nucleus are prokaryotic.
• In both prokaryotic and eukaryotic cells, a semi-fluid matrix -- cytoplasm
• Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like
• Endoplasmic reticulum (ER)
• Golgi complex
• Lysosomes
• Mitochondria
• Microbodies and
• Vacuoles

SIZE AND SHAPE

• Mycoplasmas, the smallest cells-- 0.3 μm in length
•  bacteria 3 to 5 μm.
• The largest isolated single cell is the egg of an ostrich
• Human red blood cells - 7.0 μm in diameter.
• Nerve cells - the longest cells in human

PROKARYOTIC CELLS

• The prokaryotic cells are represented by bacteria, blue-green algae, mycoplasma and PPLO (Pleuro Pneumonia Like Organisms).

• The four basic shapes of bacteria are bacillus (rod like), coccus (spherical), vibrio (comma shaped) and spirillum (spiral).

• The fluid matrix filling the cell is the cytoplasm.
• The genetic material is basically naked, not enveloped by a nuclear membrane.
• In addition to the genomic DNA, extra small circular DNA outside the genomic DNA - Plasmid.
• Prokaryotes have something unique in the form of inclusions.
• A special membranous structure--  mesosome --extensions of plasma membrane into the cell form of vesicles, tubules and lamellae.

• Bacteria have a chemically complex cell envelope consists of a tightly bound three layered structure
• the outermost glycocalyx

• cell wall

• plasma membrane

• Bacteria can be classified into two groups on the basis of the differences in the cell envelopes and the manner in which they respond to the staining procedure developed by Gram

• In some prokaryotes like cyanobacteria, there are other membranous extensions into the cytoplasm called chromatophores which contain pigments.
• Bacterial cells may be motile or non-motile, if motile they have flagella.

• Bacterial flagellum is composed of three parts – filament, hook and basal body.

• Besides flagella, pili and fimbriae are also surface structures of the bacteria.
• The pili are elongated tubular structures made of a special protein.
• The fimbriae are small bristle like fibres sprouting out of the cell.