A cell is the smallest functioning unit in the body therefore can only be seen through a microscope, the human body contains over 100 trillion cells
Most cells will include a nucleus, cell membrane or cell wall and also cytoplasm and cytoskeleton which hold the cell together
Cells will group together to form tissue and those tissues form vital organs such as the heart and brain
Cells contain organelles which carry out specific roles which make the human body function in a normal state; these can include aerobic respiration or generating energy
Excretion – Excretion is the process where a cell gets rid of its waste and toxins that could be damaging to it; these are removed through its cell membrane
Reproduction- Cell reproduction is the process where a cell divides to create new cells, when a cell divides, it makes a copy of all of its chromosomes, which are coiled strands of DNA, and sends an identical copy to the new cell that is created, “reproduction is also the ability to reproduce and pass genetic information onto offspring”. (https://www.sciencelearn.org.nz/resources/14-characteristics-of-living-things)
Growth – Growth is the increase in size of either a cell or an organism within its lifetime, for example a human is constantly growing from when it’s a baby to a fully grown adult.
Nutrition- Nutrition is needed for every living organism as it is absorbed into the body and turned into an energy source for the body to use during growth and for replacement of damaged tissues.
Movement – Movement is where something has moved from one place to another and can either be internal (within the cell, where organelles are being transferred) or external (where the actual limbs are able to move, contract muscles, run etc.)
Sensitivity – Sensitivity is the ability that an organism has to identify changes within its environment.
Mitochondria – Mitochondria is the site of cellular respiration through chemical reactions that start in the cytoplasm and are completed in the mitochondria, the cell converts energy from food molecules into ATP which is used for the overall function of the body. As energy conversion takes place in mitochondria we are able to find a larger amount in muscle cells as they are continually used to move the body and require the large amount of energy whereas red blood cells lack mitochondria as they utilise the space within the cell to store oxygen, showing that each cell has adapted to its function within the body.
Cell membrane –The cell membranes function is to contain and maintain the cell and its contents, it protects the cell contents and also controls the entry and exit of substances.
Endoplasmic Reticulum- There are two types of ER that have different functions, rough ER contains ribosomes along its membrane and is where protein is manufactured and modificated whereas smooth ER doesn’t have ribosomes and is responsible for lipid synthesis and a variety of metabolic processes such as drug detoxification.
Ribosomes- Ribosomes are the site of protein synthesis within a cell; they act as an assembly line where mRNA, which is the original DNA blueprint, is taken from the nucleus and used to assemble proteins from amino acid.
Golgi apparatus – The Golgi apparatus modifies proteins and fats built in the endoplasmic reticulum and prepare them for export to the outside of the cell. Both rough ER and the Golgi apparatus work together and are vital in the excretion process as the body needs to remove toxins that could cause harm, as protein is created in rough ER, the transition vesicle is made and the vesicle floats through the cytoplasm to the Golgi apparatus and is absorbed, from there the vesicle moves to the cell membrane and the molecules are released out of the cell.
Microtubules- Microtubules are part of the cytoskeleton, the motor proteins, such as myosin, move along actin filaments causing cytoskeleton fibres to slide alongside one another and this is the action between microtubules and proteins which produce cell movement.
Centrioles – Centrioles are self-replicating organelles made up of nine bundles of microtubules, they help in the formation of the spindle fibres that separate the chromosomes during cell division. Centrioles can only be only found in animal cells whereas microtubules can be found in both types of cell.
Lysosomes- Lysosomes are sacs containing digestive enzymes that can break down macromolecules in the cell using the process of hydrolysis. Lysosomes are bound by one singular membrane, this is similar to the Golgi apparatus and endoplasmic reticulum, whereas mitochondria are double membrane bound as they consist of inner and outer membranes.
Cytoplasm- Cytoplasm is a semi-fluid substance found inside the cell which cushions and protects the internal organelles; it allows movement of substances and is the source of raw materials for chemical reactions.
What is a prokaryotic cell?
Prokaryotic cells do not contain a true nucleus nor do they contain most other organelles whereas a eukaryotic cell contains a large number of organelles and a nucleus.
Their main feature is that their DNA is in the form of one single continuous strand which coils and loops within the cell and is known as the nucleoid. An example of a prokaryotic cell is bacteria ,as Prokaryotes have a higher metabolic rate it means they will have a higher growth rate and can multiply at a rapid speed, this is why bacteria spreads much quicker.
These are single celled and have single circular chromosomes, whereas eukaryotic cells can also be multi cellular and have multiple linear chromosomes
What is a Eukaryotic cell?
Eukaryotic cells have membrane bound organelles which include a nucleus, mitochondria, lipids etc., most prokaryotic cells will not contain these but some can contain ribosomes.
These cells are highly complex and contain a variety of organelles which all have specific functions, these cells are enclosed within animal, plant and fungi cells but prokaryotic cells can only be found in bacteria or archaea (archaea are extremophiles which means they like living in extreme conditions)
Eukaryotic cells are much bigger in size as they contain a much larger amount of DNA and prokaryotic cells are much smaller in size compared to eukaryotic cells which also means they don’t require a large number of organelles.
Similarities between Prokaryotic and Eukaryotic cells
Both types of cells contain DNA as genetic material
Both of these cells are able to reproduce
They both require chemical energy for some cellular processes
They both contain ribosomes, cytoplasm which is the cytoskeleton structure of each cell and have a plasma membrane
Viruses are acellular pathogens as they do not have a cell structure, but they are still able to infect a host and spread disease.
Viruses are non-living as they are unable to carry out the living processes self-sufficiently
They can only reproduce inside a host
Each type of virus will recognise and infect only specific hosts
Some viruses attack eukaryotic cells and others attack bacteria
Their structure consists of a small piece of nucleic acid, either DNA or RNA and is surrounded by a
Protein; viruses are also 50 times smaller than a bacteria cell
Core – The core contains DNA or RNA
Capsid – The capsid is a protective coat of protein, “it protects the nucleic acid from digestion by enzymes, it contains special sites on its surface that allow the virion to attach to a host cell and provides proteins that enable the virion to penetrate the host cell membrane. The capsid can also be injected into the infectious nucleic acid and into the cell’s cytoplasm”. https://micro.magnet.fsu.edu/cells/virus.html
Capsomeres- These are a subunit of the capsid which is an outer covering of protein that protects the genetic material of a virus, capsomeres self-assemble to form the capsid
Nucleocapsid – The nucleocapsid is the combined structure of the core and capsid
Envelope – The envelope is made from lipids and proteins; it is derived from the host cell membranes and can be found in HIV and Flu
How does a virus impact on a eukaryotic cell?
Viruses are able to penetrate through the cell membrane therefore docking proteins and insert their nucleic acid into the cell. This replication process is called the lytic pathway
The Lytic cycle
The lytic cycle is a type of viral reproduction which results in the lysis of the cell becoming infected
Firstly a virus needs a host cell for multiplication, it attaches itself onto the host cell which means it can gain access to the cell by breaking through the cell’s plasma membrane, the tail fibres of the virus and enzymes released are how it is able to enter into the cell.
The virus then releases its genetic material into the host cell, this could either be a single-stranded RNA or a double-stranded DNA, when this process is complete the cell is now said to be infected
Next the injected DNA or RNA then takes over the host cell’s genetic material and manipulates it so that it is able to replicate itself using the host cell. When DNA is injected the virus’s DNA transcribes itself into messenger RNA molecules, these molecules can control the host’s ribosomes which means the virus is able to replicate its own genetic material.
Now that the genetic material as well as viral parts is replicated, the host metabolism assembles new viruses, eventually the host cell is filled with viruses and the virus releases an enzyme that disintegrates the cell membrane from inside the cell, therefore destroying the host cell.
The viruses are individual and free now and each of these viruses will go and infect another host cell.
The Lysogenic Cycle
The lysogenic cycle is a viral reproduction method where the viral DNA is integrated into the hosts genome.
“The lysogenic cycle results in only a few virus copies being released at a time, but the host cell stay alive. That means the virus can survive and replicate inside a host for many years”. https://study.com/academy/lesson/lysogenic-cycle-of-a-virus-definition-steps-quiz.html
Once the virus’s genetic material is inserted, it attaches itself to the host’s, some viruses may not immediately start multiplying or replicating after infecting the cell, this means that the virus can stay dormant, a virus can survive for many years in a dormant state without affecting regular activities of the host cell.
The cell membrane is a semi-permeable membrane that surrounds the cells cytoplasm.
The main role of the cell is to contain and maintain the cell as a functional unit
The plasma membrane is made from a bilayer of phospholipid molecules studded with protein, this is also seen as fluid mosaic model.
The cell membrane is made up of different component, which include phospholipid molecules, bilayer structure and intrinsic and extrinsic proteins.
Phospholipid bilayer structure
A phospholipid molecule is made up of a phosphate head and 2 fatty acid tails, the fatty acids are non-polar and carry no overall electrical charge but the phosphate head is polar making it positively charged.
So the phosphate group of phospholipids is attracted to the water both inside and outside the cell as water has an imbalanced charge.
Whereas the fatty acids are repelled by water and so they face towards each other and away from the water.
Intrinsic and Extrinsic proteins
Extrinsic membrane proteins are entirely outside of the membrane, but are bound to it by weak molecular attractions (ionic, hydrogen, and/or Van der Waals bonds). Intrinsic membrane proteins, the class we are mainly interested in, are embedded in the membrane. Many of them extend from one side of the membrane to the other and are referred to as transmembrane proteins