What is a Cell?
Cells are the essential building blocks of all living things. It is the smallest unit of an organism that can carry out the function of life. Some cells are single, self-sustaining organism such as amoebas or bacteria. Other cells are a part of a multicellular organisms that cannot survive on its own; like animal cells.
The human body is made out of loads of cells. Cells have many segments, each with a different function to carry out. Some of those segments (organelles) are specialized structures that accomplish certain tasks within the cell.
Stem cells differ from all other kind of cells in the body. A stem cell is a cell that can either reproduce another stem cell or a specialized cell an infinitive amount of times. The specialized cells that can be produced have specific function related to where they are produced in the human body.
Researchers typically focus their study between tow type of stem cells; embryonic and adult or somatic cells.
The main difference between the two stem cell types is the cell’s mechanism for replicating. Embryonic stem cells can become any specialized cell type in the body since they are pluripotent. Adult or somatic stem cells can only replicate into the specialized cell type that they originated from (differentiation).
All stem cells, regardless of their source, have three general properties: they are capable of dividing and renewing themselves for long periods; they are unspecialized; and they can give rise to specialized cell types.
Mutations in specific genes of the cell caused by carcinogens can result in the abnormal production and function of a cell, which is mostly taken synonym with cancer cells. Cancer cells also have the ability to divide but they divide in an uncontrollable manner.
The 7 characteristics of life:
But what exactly classifies as being “alive”? Or a living something?
Since there is no universal definition of life, life is considered a characteristic of something that preserves, advances or reinforces its existence in its given environment. These characteristics display all or most of the following attributes.
• Movement
• Respiration
• Sensitivity
• Growth
• Excretion
• Reproduction
• Nutrition
All living organisms respond to their surrounding environment. For example, a plant bends its leaves towards the sun to get energy, if you step on a snake it may move or even snap at you (movement).
Also, organisms use a source of energy for their metabolic activities. Some organisms capture energy from the sun and convert it into chemical energy (photosynthesis); others use chemical energy in molecules they take in as food (cellular respiration).
Even the smallest organisms are very complex in its being and require multiple regulatory mechanisms to coordinate internal functions, respond to stimuli, and cope with environmental stresses.
In order to function correctly, cells need to have suitable conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions can change from one second to the next one. Organisms are able to maintain those internal states within a limited range almost constantly, despite environmental changes, through homeostasis.
Researchers also have found that there are borderline cases of life, such as viruses and viroid’s that prove that they also have the characteristics which we define life under.
Which makes defining what is living and what is not a very controversial subject.
Eukaryotic, Prokaryotic and Virus Cells
All living organisms are usually classified in prokaryotes or eukaryotes.
Prokaryotes and eukaryotes are well-known on the basis of their cellular characteristics since they are similar in serval ways.
Prokaryotic cells lack a nucleus and other membrane related structures known as organelles, while eukaryotic cells have both a nucleus and organelles.
Both types of cells are surrounded by cell membranes and both use DNA for their genetic information. Prokaryotes include several kinds of microorganisms, such as bacteria and cyanobacteria.
Eukaryotes include such microorganisms as fungi, protozoa, and simple algae.
Viruses are considered neither prokaryotes nor eukaryotes because they lack the characteristics of living things, except the ability to replicate which they can only accomplish in living cells. Viruses are only genetic information surrounded by a protein coat. They may contain external structures and a membrane.
A virus infects a cell, permitting the viral genetic information to fusion and thus creating new virus elements in the host cell.
There are many kinds of viruses. Those which infect humans are polio, influenza, herpes, smallpox, chickenpox, and human immunodeficiency virus (HIV) causing AIDS.
Cell Membrane
The cell membrane is like the gatekeeper of the cell. It provides structure and allows cells to act as specialized units. The phospholipid bilayer decides what molecules can move into or out of the cell (semipermeable) and is also responsible for maintaining the homeostasis and metabolism of the cell.
Some molecules which are lipid soluble can drift in and out, others require special structures to get in and out of a cell, while some molecules even need energy in form of ATP to get across a cell membrane.
There are two ways that molecules can be moved across the membrane; active transport and passive transport. Passive transport like diffusion uses no energy, while active transport requires energy to get done.
Diffusion happens when some of the particles move down their gradient. Which simply means that there is an imbalance in the concentration and the particle is trying to be evenly distributed everywhere. Water is most likely to be involved in diffusion since it can easily pass through cell membranes – also known as osmosis. Another diffusion can happen through the protein carrier molecules when the molecule is still too big to go through the phospholipid bilayer.
Sometimes the cell needs to move molecules against their gradient, which requires energy. That action usually takes place in the sodium/calcium pumps that help maintain resting potential in the cell. The proteins use the energy released in form of ATP, to pump sodium ions out (exocytosis) of and potassium ions into the cell (endocytosis). ATP is an energy molecule that gets broken down to release the energy that was stored in its chemical bonds when hydrolysis happens.
Cellular Metabolism
Catabolic Cellular Metabolism
Catabolic metabolism breaks down complex organic molecules into simpler molecules. These exergonic reactions are portrayed by the release of energy. Catabolism reduces protein, fat, and carbohydrates into amino acids, fatty acids, and simple sugars, separately. The energy released from catabolic reactions pushes anabolic reactions. It’s a process that undergoes three stages:
1. Breakdown of complex molecules into their basic building blocks.
2. Breakdown of the basic building blocks into even more simple metabolic intermediates.
3. “Burning” of the acetyl groups of acetyl-coenzyme by the citric acid cycle and oxidative phosphorylation to produce CO2 and H2O = energy is released.
Anabolic Cellular Metabolism
Anabolic metabolism combines simple substances into more complex substances, like when the cells combine amino acids into proteins to produce cells or tissues. Anabolic reactions are endergonic reactions.
Even tough catabolism and anabolism happen independently of each other, they are linked together. Without cellular metabolism, the body’s cells wouldn’t be able to break down or manufacture the combinations needed for energy, growth, function, and healing.