The word cell comes from the Latin “cella”, meaning small room. It was coined by Robert Hooke in his book Micrographia (1665), in which he compared the cork cells he saw through his microscope to the small rooms monks lived in.
All organisms are made of cells. The cells is the simplest collection of matter that can live. A cell is chemical system that is able to maintain its structure and reproduce. Cell structure is related to cell function. All cells derive from a common descending cell, stem cells.
Cell structure is related to cell function
Here are a few examples of tissues in a human body:
They are small because they need to facilitate passive diffusion (no energy required). These molecules need to diffuse from a higher potential down a gradient to a lower potential.
For effective diffusion: A small volume & a big surface area
There are two main techniques:
This helps us to determine the functions of organelles & the interaction of molecules:
Common features in all cells include:
| Prokaryote | Eukaryote |
|---|---|
| Lack membrane-bound organelles (nucleus, mitochondria) | Have membrane-bound organelles (nucleus, mitochondria) |
| DNA – nucleoid | DNA – packed within the nucleus and organized in chromosomes |
| Mostly monocellular organisms (bacteria, archaea) | Mostly multicellular organisms (Plants, animals, fungus) |
| Quite small (1–10 μm) | Much bigger than prokaryotic cells (10–100 μm) |
Diagram coming soon
This is the outer layer of the cell
Functions of the membrane proteins include:
This is at the centre of the cell and is surrounded by the nuclear envelope. It is perforated by nuclear pores which are channels that regulate molecular traffic into and out of the organelle. A nucleus also contains Chromatin which is the genetic material of the cell (DNA) wrapped around proteins. In the centre go the nuclei is the nucleolus and this contains the genetic material for producing ribosomes.
Nucleotides are the building block of DNA They have:
Changing the base = changes the type of nucleotide. There are two types of nitrogenous bases:
To form the double helix:
Is a network of sacs directly contacted with the nucleus. These sacs are continuous & interconnected – one single lumen/ cisternal space. This allows molecules to be selectively transferred between nucleus-ER-cytoplasm. There are two types of ER:
Is a system of cisternae that synthesize carbohydrates. It receives newly synthesized proteins from the rough ER and puts the finishing touches on synthesis.
These organelles are the ‘powerhouses’ of the cell. It is made up of folded membranes (cristae) inside a membrane. ATP production occurs in the inner membrane where enzymes catalyze the respiration of pyruvic acid to ATP. Their main function is the conversion of the potential energy of food molecules into ATP (“oxidative phosphorylation”, “Krebs Cycle”):
C6H12O6 + 6O2 + 6H2O → 12H2O + 6CO2 + (36)ATP
These are the waste bins of the cell. They contain digestive enzymes and have an extremely low pH to break down foreign particles or damaged organelles.
Collection of filaments and cylinders that provide structural support, mobility, organization:
Tissue is mainly comprised of cells and a matrix. The matrix is composed of fibrous proteins and, usually, a clear gel variously known as ground substance, tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel. In cartilage and bone it can be rubbery or stony in consistency. The ground substance contains water, gases, minerals, nutrients, wastes, and other chemicals. There are many different types of tissues, examples include:
| Type | Definition | Locations |
|---|---|---|
| Epithelial | Tissue composed of layers of closely spaced cells that cover organ surfaces, form glands, and serve for protection, secretion, and absorption | Epidermis Inner lining of digestive tract Liver and other glands |
| Connective | Tissue with more matrix than cell volume, often specialised to support, bind together, and protect organs | Tendons and ligaments Cartilage and bone Blood |
| Nervous | Tissue containing excitable cells specialised for rapid transmission of coded information to other cells | Brain Spinal Cord Nerves |
| Muscular | Tissue composed of elongated, excitable cells specialised for contraction | Skeletal muscles Heart (cardiac muscle) Walls of viscera (smooth muscles) |
Chapter 2 to be completed soon