Introduction to Cell Biology

A. What is a cell - Water, carbon, elements.

C. What is the difference between elements?

E. What is interesting about Cell biology?

What is a cell?

Cells are structural units that make up plants and animals, also there many single cell organisms. What cells all have in common is they are small 'sacks' composed mostly of water. The 'sacks' are made from a phospholipid bilayer. The membrane is semi-permeable (allowing some things to pass in or out of the cell and blocking others), there are also other methods of transport that we will get into later.

So what is in a cell? The cell as we mentioned is a fluid like membrane that surrounds the contents of the cell. Each component will be discussed in more detail later.

Cells are 90% fluid (cytoplasm) which consists of free amino acids, proteins, glucose, and numerous other molecules. The cell environment (ie. the contents of the cytoplasm, and the nucleus, as well as, they way the DNA is packed) affect the gene expression/regulations, and thus are VERY important parts of inheritance, below are approximations of other components:

Elements:

59% Hydrogen (H)
24% Oxygen (O)
11% Carbon (C)
4% Nitrogen (N)
2% Others - Phosphorus (P), Sulphur (S), etc.

As far as molecules that make up the cell:

50% protein
15% nucleic acid
15% carbohydrates
10% lipids
10% Other

What is inside the cell is the cytoplasm which is:

Cytosol - a lot of water - all except the organelles.

Organelles (which also have membranes) in 'higher' eukaryote organisms:

Nucleus (in eukaryotes) - where genetic material (DNA) is located, RNA is transcribed.

Endoplasmic Reticulum (ER) - Important for protein synthesis. It is a transport network for molecules destined for specific modifications and locations. There are two types:

Rough ER - has ribosomes, and tends to be more in 'sheets'.

Smooth ER - Does not have ribosomes and tends to be more of a tubular network.

Ribosomes - half are on the Endoplasmic Reticulum, the other half are 'free' in the cytosol, this is where the RNA goes for translation into proteins.

Golgi Apparatus - important for glycosylation, secretion.

Lysosomes - Digestive sacks - the main point of digestion, these are only found in animal cells.

peroxisomes - Use oxygen to carry out catabolic reactions, in both plant and animals.

Microtubules - made from tubulin, and make up centrioles,cilia,etc.

Cytoskeleton - Microtubules, actin and intermediate filaments.

Mitochondria - convert foods into usable energy. (ATP production) A mitochondrion does this through aerobic respiration. They have 2 membranes, the inner membranes shapes differ between different types of cells, but they form projections called cristae. The mitochondrion is about the size of a bacteria, and it carries its own genetic material and ribosomes.

Vacuoles - More commonly associated with plants. Plants commonly have large vacuoles.

Found in Plants and not in animals:

Chloroplasts - convert light/food into usable energy. (ATP production)

Plastids -

Cell Wall - found in prokaryotic plants and it provides structural support and protection.

Size of Cells

Eukaryotes are typically 10 times the size of prokaryotic cells. Plant cells are on average some of the largest cells, which may be because of the large water filled vacuoles in some plant cells.

So, you ask, what are the relative sizes of biological molecules and cells?

These are all approximations:

Small

0.1 nm (nanometer) diameter of a hydrogen atom
0.8 nm Amino Acid
2 nm Diameter of a DNA Alpha helix
4 nm Globular Protein
6 nm microfilaments
10 nm thickness cell membranes
11 nm Ribosome
25 nm Microtubule
50 nm Nuclear pore
100 nm Large Virus
200 nm Centriole
200 nm (200 to 500 nm) Lysosomes
200 nm (200 to 500 nm) Peroxisomes
1 um (micrometer)
(1 - 10 um) the general sizes for Prokaryotes
1 um Diameter of human nerve cell process
2 um E.coli - a bacterium
3 um Mitochondrion
5 um length of chloroplast
6 um (3 - 10 micrometers) the Nucleus
9 um Human red blood cell
10 um
(10 - 30 um) Most Eukaryotic animal cells
(10 - 100 um) Most"eukaryotic" plant "cells"
90 um Amoeba
100 um Human Egg
1 mm (1 millimeter, 1/10th of a centimeter)
1 mm Diameter of the squid giant nerve cell
2 mm Diameter of a frog egg

Large

To be completed

What is the difference between elements/compounds?

The various elements that make up the cell are:

59% Hydrogen (H)
24% Oxygen (O)
11% Carbon (C)
4% Nitrogen (N)
2% Others - Phosphorus (P), Sulphur (S), etc.

The difference between these elements is their respective weights, electrons and in general their properties. A given element can only have so many other atoms attached. For instance carbon (C) had 4 electrons in its outer shell and thus can only bind 4 atoms, Hydrogen only has 1 electron and thus can only bind to one other atom. An example would be Methane which is CH4. Oxygen only has 2 free electrons, but will some times form a double bond, which is a 'ester' (which typically smell good or bad).

     Methane    Water   Methanol (Methyl Alcohol)
     -------    -----   -------------------------
        H       H   H      H
        |        \ /       |
      H-C-H       O      H-C-O-H
        |                  |
        H                  H

As far as molecules that make up the cell:

50% protein
15% nucleic acid
15% carbohydrates
10% lipids
10% Other

Here is a list of Elements, symbols, weights and biological roles.

ELEMENT (Symbol)Atomic Weight   Biological role

Calcium   (Ca)  40.1            Bone; muscle contraction
Carbon    (C)   12.0            Constituent(backbone) of
                                organic molecules
Chlorine  (Cl)  35.5            Digestion and photosynthesis
Copper    (Cu)  63.5            Part of Oxygen-carrying
                                pigment of mollusk blood.
Fluorine  (F)   19.0            For normal tooth enamel
                                development
Hydrogen  (H)    1.0            Part of water and all organic
                                molecules
Iodine    (I)  126.9            Part of thyroxine (a hormone)
Iron      (Fe)  55.8            Hemoglobin, oxygen caring
                                pigment of many animals
Magnesium (Mg)  24.3            Part of chlorophyll, the photo-
                                synthetic pigment; essential
                                to some enzymes.
Manganese (Mn)  54.9            Essential to some enzyme actions.
Nitrogen  (N)   14.0            Constituent of all proteins and
                                nucleic acids.
Oxygen    (O)   16.0            Respiration; part of water; and
                                in nearly all organic molecules.
Phosphorus(P)   31.0            High energy bond in ATP.
Potassium (K)   39.1            Generation of nerve impulses.
Selenium  (Se)  79.0            For the working of many enzymes.
Silicon   (Si)  28.1            Diatom shells; grass leaves.
Sodium    (Na)  23.0            Part of Salt; nerve conduction
Sulfur    (S)   32.1            Constituent of most proteins.
                                Important in protein structure:
                                Sulfide bonds are strong.
Zinc      (Zn)  65.4            Essential to alcohol oxidizing
                                enzyme.

What is living?

This is a topic that is been of many long discussions and it depends on your initial definitions. Some definitions are:

1. The quality that distinguishes a vital and functional being from a dead body or purely chemical matter.

2. The state of a material complex or individual characterized by the capacity to perform certain functional activities including metabolism, growth, and reproduction.

3. The sequence of physical and mental experiences that make up the existence of an individual.

Under these varying definitions life may or may not include a virus that is only 'alive' if it can insert its genetic material into a living cell. To me live is the substance that can react to its environment, grow, improve and reproduce. To have less of a definition would include to much to have more would not include some cells.

What is interesting about Cell biology?

What makes cell biology particularly interesting is that there is so much that is not understood. Cells are a complex system in and of themselves. And when you add to a individual cell its environment, whether that is the single celled organism or multicellular, there is a complex web reactions. One organism, like the human, can have the same genetic material in every cell, yet, there are over 200 types of cells in the human, that are different shapes, sizes and and carry out very different functions. And ALL of these cells were developed from 1 (one) cell.

Complexity

inter-relations of cells
Intra-relations of cells
The cell and its environment.

Its ability to Live and reproduce.
Its ability to grow and change.
It is what makes up you and the food you eat.

Go to Chapter 1, 'Types of Cells'

WWW Cell Biology Course Index

Go to back one.

Please send questions/comments/suggestions to: Mark Dalton at markwdalton@gmail.com.