Human cells

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Last Updated: Saturday, 19 October 2024 23:18
Published: Saturday, 05 October 2024 00:24
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Human cells:

Before we dive into human cells, let's look at basic cell in general.

Cells:

Cell is the structural and functional unit of life. Cells have genes in them that decides how the cell is going to grow over time, and pass it's characteristics to new cells that develop from it. Cells reproduce through a process of cell division, in which the parent cell divides into two or more daughter cells and passes its genes onto a new generation. Though almost all life consists of cells, some life such as Viruses are non cellular. However, whether virus should be considered living being or not is controversial. They have been described as "organisms at the edge of life"  because they possess genes, evolve by natural selection, and replicate by making multiple copies of themselves through self-assembly. However, viruses do not metabolise and they require a host cell to make new products.

We'll mostly be talking about uni cellular and multi cellular life. Before that we will learn a bit about cell.

Video on cell structure => https://www.youtube.com/watch?v=URUJD5NEXC8

There are two kinds of cells, both of which consist of Cytoplasm enclosed within a membrane and contain many biomolecules. All cells have 3 things in common => cell membrane (to protect cell), cytoplasm (a jelly like liquid) and a genetic material (usually within a nucleus which determines what the cell is going to be like). The 2kind of cells are:

  • Prokaryotes: Prokaryotes are single celled organisms that lack a nucleus and other membrane bound organelles (organelles are little organs within cells). The word prokaryote comes from the the word pro meaning before and karyon meaning nut o kernel. Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell. Prokaryotes are asexual, reproducing without fusion of gametes. Link: https://en.wikipedia.org/wiki/Prokaryote
  • Eukaryotes: Eukaryotes are single or multi celled organisms that have a nucleus. All animals, plants, fungi, and many unicellular organisms, are eukaryotes. The word eukaryote comes from the the word eu meaning good and karyon meaning nut or kernel. Besides the presence of a nucleus, eukaryotes also contain other membrane-bound organelles such as mitochondria and Golgi apparatus. Mitochondria is the main powerhouse of the cell. Eukaryotes developed around 2 Gya. Link: https://en.wikipedia.org/wiki/Eukaryote. Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion.
    • mitosis reproduction (asexual): In mitosis, one cell divides to produce two genetically identical cells.
    • meiosis reproduction (sexual): In meiosis, DNA replication is followed by two rounds of cell division to produce four haploid daughter cells that act as sex cells or gametes. Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from  genetic recombination during meiosis.

Sizes: Size of atom is about 0.2 Angstrom. Small molecules are about a nm. Proteins are about 10nm, while Viruses are about 100nm. Single cells start from about 1um, while multi cellular organisms are upto few mm. This link shows relative size of cells: https://en.wikipedia.org/wiki/Bacteria#/media/File:Relative_scale.svg

Plant and animal cell:

Video in detail (Intro to cell structure) => https://www.youtube.com/watch?v=vwAJ8ByQH2U

Cells will need to talk to each other if they need to transport information. In between the cells, we have a fluid called interstitial fluid. Interstitial fluid is mostly water with other dissolved substances in it like salt, sugar, protein, waste etc.The fluid inside the cell is called cytoplasm, but inside is referred to as cytosol. The cell membrane surrounding the cell separates these 2 fluids, but allows mechanism for solutes (or particles in interstitial/cytosol fluid) to flow in or out of the cells.

Intracellular and Extracellular fluids => https://courses.lumenlearning.com/suny-ap2/chapter/body-fluids-and-fluid-compartments-no-content/

Cell Membrane structure => https://www.youtube.com/watch?v=fJfTDc3WzQ8

Cell Membrane is made of molecules called phospholipids. Read more about it in Biology section. The bilayer phosphid forms a very close knit structure so that no external molecules can pass thru, unless they are very small in size and non polar (by being non polar, they can get inside to the tail of phospholipd molecule which is nonpolar). Besides the phospholipd bilayer structure, a cell membrane contains few more structures:

  • Chloesterol => controls what can pass thru the cell
  • Proteins => They behave like openings in the cell membrane and control what bigger particles can pass thru them.
  • Carbohydrates => Involved in cell identification

Transport across a membrane => https://www.youtube.com/watch?v=J5pWH1r3pgU

Receptors:

These protein structure in the membrane that we saw above allow movement of solutes in or out of the cells. They are called as receptors. They are selective as to what they will allow to pass depending on the protein structure. A cell has multipe of these protein receptor and each is selective. Different kind of cells have different receptors, i.e heart cells have different receptors than lung cells.