Cell Introduction YouTube Lecture Handouts

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Cell: An Introduction

Introduction

• Lamarck: no body can have life, if no cells

• Cytology: Study of form, structure & composition of cell

• Cell Biology: Deals with structure, chemistry & functioning of cell

• Unicellular: Amoeba, bacteria, yeast, acetabularia – independent existence & perform all essential functions

• Multicellular: made of many cells (new born infant - cells to 100 trillion in 60 kg man)

• Large organism – not have large-sized cells but more cells

Cell

• Structural unit

• Functional Unit

• Building blocks

• Smallest unit capable of independent existence

• Totipotent: Single cell can form whole organism

• Cell Tissue Organ Organ System (division of labour)

• Pasteur – life originates from life

• Haeckel – nucleus stores and transmits hereditary

Microscope

• 1^st by Zacharias Janssen – 1590

• Modified by Galileo

• Then by Robert Hooke – new microscope – study of cork cells

• Hooke – book – Micrographia- honey comb structure called it cellula

• Malphighi – called it saccules & utricles

• Leeuwenhoek – 1^st to observe, describe & sketch free living cell

• Robert Brown – disc. nucleus in cell

• Dujardin – living semifluid substance as sarcode

• Purkinje & von Mohl – called sarcode as protoplasm

• Schwann – disc. cell membrane

• Nageli & Cramer – named it as cell membrane

Cell Theory

• By Schleiden & Schwann

• Schwann – animal cells don’t have cell wall

• Organism made of cells

• Cells are units of structure and function of living organisms

• New cells from pre-existing cells

• Each cell has protoplasm

• All cells are alike in chemistry & physiology

• Activity of organism are sum total of activities of cell

Modern Cell Theory or Cell Doctrine

• All living beings have cells

• Cells are units of structure & function

• Cell can survive independently, organelle cannot

• Cells have fundamental similarity

• Life exists in cells

• Cells can be modified (elongated in muscle & nerve cell)

• Cell grows & multiplies

• Life passes to next generation as cell

• New cells from pre-existing cells

• All cells have common ancestry

• Cells are totipotent

• No organism can have activity that is absent in its cell

Objections to Modern Cell Theory

• Virus are a cellular

• Some organisms – body is not differentiated in cells (e.g. rhizopus)

• Protozoa have uninucleate differentiated body

• Bacteria & cyanobacteria don’t have nucleus

• RBCs & sieve tube cells are without nucleus

• In skin & cork – protoplasm is replaced by nonliving material

Surface Volume Ratio

Small cells – higher surface volume ratio

Types of Cells

• Undifferentiated / Stem Cells: Unspecialized and have power of division – stem apical meristem

• Differentiated / Post-mitotic Cells: Specialized for better organization and avoid duplication

• Dedifferentiated Cells: Differentiated cell which revert to undifferentiated state and loose specialization - cork cambium of plant, healing of wound, regeneration in animals and vegetative propagation in plants

Compartmentalization of Cellular Life

• Separation from extracellular medium

• Selective permeability

• Accumulation

• Interconnections

• Recognition

• Communication & exchange

• Intracellular compartmentalization

Cell Sizes

• Smallest cell – Mycoplasma

• RBC is 7 in diameter

• Lymphocytes are 6

• Kidney, liver and intestine are 20-30

• Longest human cell – nerve cell of 90 cm

• Egg cells are large sized cells – store food for embryo

• Avian eggs are largest

Cell Shapes

• Surface cells – flat

• Cortex – polygonal

• RBC – biconcave

• Nerve cells – long

• Sperms – tail for mobility

Prokaryotic & eukaryotic cells (to be discussed in next lesson)

-Manishika