Introduction

All living things that can be found on earth with the exception of Viruses are made of cells. There are two main types of cell the relatively simple Prokaryotic cells such as bacteria and the more complex Eukaryotic cells that are found in plants, animals and fungi.

Prokaryotic Cells

The prokaryotic cell has no membrane bound organelles and no nucleus. The prokayote is a bacteria of which E.coli is a good example.

Cell Wall

The cell wall of the prokaryotic cell is made out of polysaccharides such as peptidoglycans. The role of the cell wall is to provide a strong wall to prevent the cell from bursting under osmotic pressure.

Plasma Membrane

As in eukaryotic cells this is a partially permeable membrane which determines which substances are allowed to leave and enter the cell. This membrane has a large surface area with many enzymes attached too it allowing it to be a surface for respiration and other reactions.

Slime Capsual

This is a layer of a slime like substance which protects the prokaryote

Flagella

These are outward projections from the prokaryote which enable the bacteria to be mobile. There is a structure similar to a motor which is found at the base of the flagellum causing it to rotate.

Bacterial Chromosome

This is where the DNA for the bacteria is found. In Bacteria the DNA is one long double helix which forms a circle. There is no nucleus so this chromosome sits in the cytoplasm.

Plasmids

These are small DNA molecules which are found in the cytoplasm separately from the Bacterial Chromosome. The genes which form antibiotic resistance are often found in the plasmids. Plasmids can be transmitted from one bacterium to another which is one of the mechanisms which has aided the growth in bacterial resistance to antibiotics.

Glycogen

Glycogen is the store of carbohydrate within the prokaryotic cell. It is stored in granules which are found in the cytoplasm. This can be broken down to form glucose which can used in respiration.

Lipids

This is another form of energy store which is found in the cytoplasm of prokaryotic cells. It is insoluble and so doesn’t need to be contained in anything.

Ribosomes

Ribosomes are also found in eukaryotic cells they are the protein factories of the cell. They read the genes encoded in the DNA and then turn them into proteins. The prokaryotic ribosomes are smaller than those found in the eukaryotic cell.

Eukaryotic Cells

The main difference between Eukaryotic and Prokaryotic cells is the existence in Eukaryotic cells of a ‘nuclear envelope surrounding the DNA. There are also a number of membrane bound organelles. Bellow are two examples of eukaryotic cells but there are many types.

Nucleus

The nucleus is the membrane-bound region which contains the DNA in a Eukaryotic cell. In the Eukaryotic cell DNA is found in chromosomes which are linear molecules joined together by histones. The nucleolus is a dark area in the nucleus which is where ribosomal RNA is being made.

Nuclear Envelope

The nuclear envelope is a double membrane which surrounds the DNA in a Eukaryotic cell. There are pores in the nuclear envelope which allows mRNA to leave the nucleus and enter the cytoplasm.

Rough Endoplasmic Reticulum

The Rough ER is is made up of a large number of connected compartments known as cisternae. There are ribosomes which are attached to the outside of the membrane. The role of the Rough ER is to make and then break up proteins which are then transported to other parts of the cell.

Smooth Endoplasmic Reticulum

The Smooth ER has a similar structure to the Rough ER but doesn’t have the ribosomes. It is used to synthesize steroid hormones and cholesterol.

Golgi Apparatus

This organelle is involved in the modification of proteins. The proteins arrive here in vesicles from the rough ER and have carbohydrates or other molecules added to them to make them more complex and suited for their role. The modified proteins are then packaged into vesicles and transported out of the cell by the process of exocytosis.

Mitochodria

Mitochondria are sometimes known as the power house of the cell, it is here where aerobic respiration is used to release energy from organic molecules such as glucose and make ATP. The mitochondria has a double membrane, the inner of which is folded to provide a large surface area.

Lysosomes

These are vesicles which contain hydrolytic enzymes. They can be exported out of the cell for the process of phagocytosis or used in the cytoplasm to break down organelles or proteins which are no longer needed.

Ribosomes

There have the same role that they have in prokaryotic cells they read ribosomal RNA and make it into the proteins needed.

Microtubules

These are found in both prokaryotic and eukaryotic cells. They are found throughout the cytoplasm and are made out of a protein called tubulin. The role of microtubules is to assist in the transports of the cellular organelles and assist with cell division.

Chloroplasts

These are only found in plant cells where they contain chlorophyll which is used to transform light energy into carbohydrates. It is not unusual for chloroplasts to contain starch granules for energy.

Cell Wall

The holes of the cell wall in Plant cells is similar to the role of the cell wall in a bacterium. It prevents the cell rupturing due to osmotic pressures. In a plant cell the cell wall is made out of cellulose which is a very strong fibre but is fully permeable the role of controlling what leaves and enters the cell is down to the cell membrane which is the same as the one found in prokaryotic cells.

Biology No Comments November 3rd, 2009