Key Points
Key Points
- Both prokaryotic and eukaryotic cells have a plasma membrane, cytoplasm and ribosomes. Prokaryotic cells have a single circular chromosome in a nucleoid, while eukaryotic cells have a defined nucleus whereby multiple chromosomes are surrounded by a nuclear membrane. Prokaryotic cells are typically smaller than eukaryotic cells. The increased size of eukaryotic cells results in the need for more complex, membrane bound organelles to allow compartmentalisation of chemical processes within the cell. In most circumstances archaea and bacteria are prokaryotic while plant, animal and fungi are eukaryotic although there are some intermediate types of microorganisms.
- Cells are the basic functional and structural units of life and compose all living organisms, which is why understanding cell physiology, especially in the absence of healthy functioning, is important. The main regions in all cells include the plasma membrane, cytoplasm, and nucleus (or nucleoid in prokaryotic cells).
- The plasma membrane encloses the cytoplasm and internal cell structures in all cells and displays selective permeability whereby some molecules can pass through the membrane into and out of the cell, and others are inhibited. The plasma membrane structure is often described in terms of the fluid mosaic model, in reference to the fluid movement of membrane components and the mosaic like composition of the membrane which includes various lipid and protein components. The embedded components contribute to permeability of the plasma membrane, allowing the controlled movement of molecules into and out of the cell.
- The cytoplasm is a gel-like substance that is composed of water and dissolved chemicals important for growth.
- Genetic information is organised into genes that are arranged on chromosomes and plasmids. In eukaryotic cells, chromosomes are contained within the nucleus, separated from the cytoplasm by the nuclear membrane. Prokaryotic DNA and DNA-associated proteins are concentrated within the nucleoid region of the cell. Nucleoid-associated proteins assist in the organisation and packaging of the chromosome. DNA is important for the regulated construction of proteins necessary for cell growth and replication.
- Various cell processes and organelles contribute to cell function and movement, dependent on the cell type and individual requirements of the cell. This includes energy production, production and packaging of proteins and cellular defence mechanisms.
- When a cell is worn out, damaged or lacking required nutrients, they can be broken down and the individual components of the cell reused by the body. This process is known as autophagy.
- When cell replication occurs, the cytoplasm is equally divided between the two resulting daughter cells. This is known as cytokinesis.
- Deoxyribonucleic acid (DNA) is a double helical structure composed of two bound strands of nucleotides. The complete complement of DNA in a cell is referred to as its genome. Prokaryotes have a single, double-stranded DNA molecule that forms a loop or circle, while in eukaryotes several double-stranded, linear DNA molecules bind with proteins to form complexes known as chromosomes.
