Biology Notes: Introduction, Lecture notes of Biology

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Introduction

to

cell biology

Caril Alvin kradril SHS general biology 1 Department of biology College of science Polytechnic university of the Philippines

OBJECTIVES:

 Explain the postulates of the cell theory;  Describe the structure and function of major and subcellular organelles;  Distinguish prokaryotic from eukaryotic cells according to their distinctive features;  Classify different cell types and specify the function(s) of each; and  Describe some cell modifications that lead to adaptation to carry out specialized functions.

SOME HISTORICALLY IMPORTANT EVENTS IN CELL BIOLOGY

 1590 – Zacharias Jansen A invented the compound microscope.  1665 – Robert Hooke B , using an improved compound microscope, examined cork and used the term “cell” to describe its basic units.  1650 to 1700 – Anton Van Leeuwenhoek C , using a good quality simple lens (mag. x 200 ), observed nuclei and unicellular organisms, including bacteria. In 1676 , bacteria were described for the first time as “animalcules”. A. B. C.

 1831 to 1833 – Robert Brown a described the nucleus as a characteristic spherical body in plant cells.  1838 to 1839 – Matthias Schleiden b (a botanist) and Theodore Schwann c (a zoologist) produced the “cell theory” which unified the ideas of the time by stating that the basic unit of structure and function in living organisms is the cell.  1840 – Jonnanes Purkinje d gave the name protoplasm to the contents of cells, realising that the latter were the living material, not the cell walls. o Later the term cytoplasm was introduced (cytoplasm + nucleus = protoplasm). a b c d

 1880 to 1883 – plastids , e.g. chloroplasts, discovered.  1890 – mitochondria discovered.  1898 – Golgi apparatus discovered.  1887 to 1900 – improvements in microscopes, fixatives, stains and sectioning. o Cytology † started to become experimental. o Embryology was studied to established how cells interact during growth of a multicellular organism. o Cytogenetics ‡, with its emphasis on the functioning of the nucleus in heredity, became a branch of cytology.

 1900 – Mendel’s work , forgotten since 1865 , was rediscovered giving an impetus to cytogenetics. o Light microscope had almost reached the theoretical limits of resolution, thus slowing down the rate of progress.  1930 s – Electron microscope developed, enabling much improved resolution.  1946 to present – Electron microscope became widely used in biology, revealing much more detailed structure in cells. o This “ fine ” structure is called ultrastructure.

II. CELLULAR ULTRASTRUCTURE AND FUNCTIONS

THREE (3) MAJOR COMPONENTS

 Different types of membranes differ in thickness but most fall within the range 5 - 10 nm, for example cell surface membranes are 7. 5 nm wide.  Membranes are lipoprotein structures (lipid + protein), with carbohydrates (sugar) portions attached to the external surfaces of some lipid and protein molecules. Typically, 2 – 10 % of the membranes is carbohydrate.  Summary of the Features of Biological Membranes

 The lipids spontaneously form a bilayer owing to their polar heads and non-polar tails.  The proteins are variable in function.  The sugar are involved in recognition mechanisms.  The two ( 2 ) sides of a membrane may differ in composition and properties.  Both lipids and proteins show rapid lateral diffusion in the plane of the membrane unless anchored or restricted in some way.

 Functions:  Provides mechanical support and protection.  It allows a pressure potential to be developed which aids in support.  It prevents osmotic bursting of the cell.  It is a pathway for movement of water and mineral salts.  Various modifications, such as lignification, for specialized functions.

 NUCLEUS

 Structure:  Largest cell organelle, enclosed by an envelope of two ( 2 ) membranes that is perforated by nuclear pores.  It contains chromatin which is the extended form taken by chromosomes during interphase.  It also contains a nucleolus.