Introduccion A La Celula

CHAPTER 1:
STRUCTURE AND FUNCTION
OF THE CELL

INTRODUCTION TO THE CELL
Both living and non-living things are composed of molecules made from chemical elements such as
Carbon, Hydrogen, Oxygen, and Nitrogen. The organization of these molecules into cells is one
feature that distinguishes living things from all other matter. The cell is the smallest unit of
matter that can carry on all theprocesses of life.
1. Every living thing - from the tiniest bacterium to the largest
whale - is made of one or more cells.
2. Before the C17th, no one knew that cells existed, since they are
too small to be seen with the naked eye. The invention of the
microscope enabled Robert Hooke, (1665) and Anton van
Leuwenhoek (1675) to see and draw the first ‘cells’, a word coined
by Hooke todescribe the cells in a thin slice of cork, which
reminded him of the rooms where monks lived.
3. The idea that all living things are made of cells was put forward
in about 1840 and in 1855 came ‘Cell Theory’ – i.e. ‘cells only
come from other cells’ – contradicting the earlier theory of
‘Spontaneous Generation’
Cell Theory consists of three principles:
a. All living things are composed of one ormore cells.
b. Cells are the basic units of structure and function in an organism.
c. Cells come only from the replication of existing cells.
CELL DIVERSITY
Not all cells are alike. Even cells within the same organism show enormous diversity in size, shape,
and internal organization. Your body contains around 1013 to 1014 cells of around 300 different cell
types, which we broadly classifyinto 4 groups.
CELL SIZE
1. A few types of cells are large enough to be seen by the unaided eye. The human egg (ovum) is
the largest cell in the body, and can (just) be seen without the aid of a microscope.
2. Most cells are small for two main reasons:
a). The cell’s nucleus can only control a certain volume of active cytoplasm.
b). Cells are limited in size by their surface area to volumeratio. A group of small cells has a
relatively larger surface area than a single large cell of the same volume. This is important
because the nutrients, oxygen, and other materials a cell requires must enter through it surface. As a
cell grows larger at some point its surface area becomes too small to allow these materials to enter
the cell quickly enough to meet the cell's need. (= Fick’s Law –something you need to learn well).
Rate of diffusion α Surface Area x Concentration Difference
Distance

CELL SHAPE
Cells come in a variety of shapes – depending on their function:The neurones from your toes to your head are long and thin;
Blood cells are rounded disks, so that they can flow smoothly.
INTERNAL ORGANIZATION
1. Cells contain a variety of internal structures calledorganelles.
2. An organelle is a cell component that
performs a specific function in that cell.
3. Just as the organs of a multicellular organism
carry out the organism's life functions, the
organelles of a cell maintain the life of the cell.
4. There are many different cells; however,
there are certain features common to all cells.
5. The entire cell is surrounded by a thin cell
membrane. Allmembranes have the same
thickness and basic structure.
6. Organelles often have their own membranes
too – once again, these membranes have a similar structure.
7. The nucleus, mitochondria and chloroplasts all have double membranes, more correctly
called envelopes.
8. Because membranes are fluid mosaics, the molecules making them up – phospholipids and
proteins - move independently. Theproteins appear to ‘float’ in the phospholipids bilayer and thus
membranes can thus be used to transport molecules within the cell e.g. endoplasmic reticulum.
9. Proteins in the membrane can be used to transport substances across the membrane – e.g. by
facilitated diffusion or by active transport.
10. The proteins on the outside of cell membranes identify us as unique.

Prokaryotes v....