Basic Cell Biology for Understanding Genetics
Introduction to Eukaryotes, Prokaryotes, Chromosomes & Cell Division
Oct 26, 2008
Basic cell biology, such as how cells grow and divide, is important in the understanding of genetics. The journey begins with two basic groups of organism (life form) – eukaryotes and prokaryotes.
Eukaryotic and Prokaryotic Cells
Eukaryotic cells have nuclei, functioning structures (organelles) that safely house the cell’s genetic material. These organelles are in a fluid called cytosol, surrounded by a plasma membrane that allows nourishment to enter. Humans are eukaryotes, alongside other animals, plants, fungi and protists.
Other important organelles in eukaryotic cells include:
- Mitochondria – these organelles supply the cell energy, sourced from the body’s intake of food.
- Chloroplasts – in plants, these organelles process energy from sunlight into sugars that feed the cell.
Prokaryotic cells, on the other hand, do not have nuclei. They do contain a little genetic material, which floats in the cell’s cytosol, protected only by a cell wall. These cells also have a plasma membrane. Prokaryotes are the planet’s most common life forms (bacteria and archaea are examples).
The Human Body: Somatic Cells and Sex Cells
Body cells, or somatic cells, share common features such as nuclei and mitochondria. However, somatic cells have different roles in the running of the human body and so do vary. For example erythrocytes (red blood cells) carry oxygen to the body’s tissues whereas osteoblasts (a type of bone cell) are responsible for bone formation.
Sex cells are required for sexual reproduction, the biological process resulting in a new organism. In humans, male sex cells are called sperm and female sex cells are called eggs (ova). A fertilised egg (zygote) contains genetic material from both sex cells – all the information required to grow into a human adult.
Inside Cells: Genes, DNA and Chromosomes
What is genetic material? Put simply, genes are defined as the basic units of heredity, and are made up of a molecule called DNA (deoxyribonucleic acid). Chromosomes are condensed structures of DNA and proteins, residing in an organism’s cell. In prokaryotes, chromosomes are usually circular, and in eukaryotes, linear.
Chromosomes vary from one species of organism to another. Humans have 46 chromosomes in total, divided into 23 pairs, half of which came from the mother, and the other half from the father. Gender is determined by sex chromosomes called X and Y. Males have an X and a Y chromosome, whereas females have 2 X chromosomes.
Cell Division: Mitosis, Meiosis and Binary Fission
Cells can only be made by other cells, through a process called cell division. There are a few different types:
- Mitosis – somatic cells use this division, for example, when worn out or damaged cells need replacing. In short, the parent cell’s nuclear DNA is copied into two new, identical cells called daughter cells, each of which get 23 pairs of chromosomes.
- Meiosis – a more complex type of cell division, occurring only in sex cells. Two divisions occur to result in four daughter cells, each containing half the number of chromosomes of the parent cell, and therefore not identical.
- Binary fission – this is how prokaryotic cells divide. The cell splits in two, creating two identical daughter cells. This is similar to, but much simpler, than mitosis.
For a more detailed looked into mitosis and meiosis, read Mitosis & Meiosis Comparison. Read Biology of Prokaryotic & Eukaryotic Cells for links to useful articles on cell biology.
Sources
"What is a cell?", Genetics Home Reference website, accessed 26th October 2008, no author specified.
The cells, tissue and organisations of the body, Anatomy and Physiology (9th edition), published by Ross and Wilson in 2001, authors Anne Waugh and Alison Grant.
 |
