Introduction to cell biology

What is a cell?

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.

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 - it is everything 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

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

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

What is the difference between elements/compounds?

59% Hydrogen (H)

24% Oxygen (O)

11% Carbon (C)

4% Nitrogen (N)

2% Others - Phosphorus (P), Sulphur (S), etc.

50% protein

15% nucleic acid

15% carbohydrates

10% lipids

10% Other

What is living?

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.

What is interesting about Cell biology?

Food for thought - to be discussed in the final chapters.

Biology is the understanding of complex systems. Which is how in basic terms how we get a functional system when things tend to move toward lower energy states. For example, if you took food scraps and left them in a compost pile they cells and proteins would break down to more basic compounds. The system maintains and generates new proteins. Without constantly breaking down and building new proteins, enzymes, DNA, cells, the larger system would break down.

Complexity - A cell is more like a balanced eco-system then a simple unit.

inter-relations of cells - between cells in multi-cellular or organisms there is communication, exchanges of information and needed resources. (like a red blood cell bringing oxygen, other cells producing a hormone, or one bacterium transferring a plasmid to another).

Intra-relations of a cell - Within a cell organelles, gene expression work together to maintain the cell.

The cell and its environment - The environment around the cell influences and is required at times how, when or if a gene is expressed. It is not as simplistic as the 'gene' causes A or B, it is the entire cell, the cells around and the larger environment.

Its ability to Live and reproduce.

Its ability to grow and change.

It is what makes up you and the food you eat.