The biological cell
A cell is the smallest unit of living organism, the building block of life.
Some organisms, like bacteria, are really made of one microscopic cell. Others, like humans, are made of lots and lots of different cells.
Let's start by looking at 2 different types:
1. Prokaryotic cells: these cells have no nucleus or membrane-bound organelles (organelles are like mini-organs inside the cell). They have 3 areas:- The cytoplasm, which is the inside of the cell. It contains the genetic material (DNA), and ribosomes which take part in protein sythesis.
- The cell envelope- quite literally what envelopes the cell. Innermost is the plasma membrane, responsible for filtering material in and out of the cell, and other things like energy production. Then comes the cell wall, which is for structure and additional protection. Finally a capsule on the outside which makes up the outer surface of the cell.
- Additional apparatus/appendages, like a flagellum, which is a tail-like extension which grants the cells movement.
Prokaryotic cells are usually cells that make up bacteria. Complex organisms are composed of eukaryotic cells.
2. Eukaryotic cells: These cells have a nucleus and membrane bound organelles. They're much larger than prokaryotic cells. They're also a lot more structured, as you'll soon see. Complex animals and plants are made of these.
The eukaryotic cells may have outer appendages, like flagellum or cilia, which are tiny hair-like extensions used for a variety of actions. Some of them (particularly plant cells) have a cell-wall which provides structure and support, but some (animal-cells) don't have one. All cells however have a cellular membrane responsible for what goes in and out of the cell, as well as for communication between different cells.
- Nucleus- A structure that has a double membrane. Inside the nucleus you'll find the DNA and genetic material of the cell, safely stored.
- Endoplasmic reticulum- a network of tubular organelles used as space for creating, storing and transporting things throughout the cell. Smooth endoplasmic reticulum is used for lipids, carbs, and more. Rough endoplasmic reticulum contains ribosomes and is used for proteins.
- Ribosomes- find both within the cells and on rough ER, these are the structures where proteins are synthesized. Proteins are the material almost everything in the cell is made out of.
- Golgi apparatus- an organelle used to process and package macromolecules such as proteins and lipids. It produces vesicles, which are sacs used to carry things out of the cell.
- Lysosomes- organelles that contain digestive enzymes used to break down waste within the cell.
- Mitochondria- organelles where glucose (cell's food) is broken down to provide the cell with energy used to carry out different functions.
- Chloroplasts- organelles found only in plant cells, which use sunlight to produce energy through photosynthesis.
- Vacuoles- found primarily in plant cells, these are used mostly for storage.
Cells are complex, but they're what moves and sustains us, and all other plants and animals. They're a mini-system inside the larger system that makes up a body. The various organelles within a cell interact to sustain the cell much in the same way our different organs interact to sustain our bodies.
The 3 primary functions of concern with cells in general are: cell growth and metabolism (cellular respiration and photosythesis), cell division (mitosis and meiosis leading to genetics), and protein synthesis.
That's all for this time!
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