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EVERYTHING ABOUT
CELLS
Cell is the fundamental unit of life. Inside a human body, cells can be specialized in structure and function while still sharing some the same organelles or structure. Cell composes tissue, tissue composes organ, organ composes organ system, and organ system composes the human body as whole
Parts of the cell
1.Cell Membranes
It is semipermeable allowing some substances to pass through it while excluding others. It is made up of protein and lipids. It is a membrane that surrounds the cell
2. Cytoskeleton
A system of fibers that not only maintains the structure of cells but also allows it to move and change shape. The cytoskeleton is made up of microtubules, intermediate filaments, and microfilaments, along with proteins that anchor them tie them together.
3. Cytoplasm
Separated from the extracellular
environment by the plasma membrane
It is the place where most
metabolic activity occur, in here incorporated materials are broken down, new proteins are generated, and new phospholipids are produced.
4. Nucleus
Contains the DNA (genetic code for the cell). Is positioned in the middle of the cell Turns the copies of DNA code into RNA which cytoplasm used to make proteins.
5. Endoplasmic Reticulum
Plays an important role in protein
and lipid production
Is made up of large folded sheets
of membranes that occupy vast expanses of the cytoplasmic compartment.
Endoplasmic reticulum comes in 2
types:
Rough ER
Is covered in ribosomes, the organelles for protein synthesis, which gives the ER rough appearance.
Smooth ER
Does not contain ribosomes and is the site of lipid synthesis Materials from the ER are transported in membrane-bound spheres referred as vesicles that move toward and fuse with membranes of the Golgi apparatus.
6. Golgi Apparatus
A cell structure made up of flat saclike layers. Is essential for sorting proteins and packaging them for specific targets
As vesicle fuse together on their incoming side, they form a new layer termed the cis face of Golgi. Like an assembly line these layers are moved higher and higher in the stack stacks of the Golgi as new cis layers are added. At the opposite side of the stacks, the trans face or last layer, breaks up into transport vesicles and shuttles material to its target. Some materials will be shipped to the plasma membrane, while others will be placed into the vesicles going to other membrane- bound organelles, such as the mitochondria.
7. Vesicles
In addition to transport vesicles of the endomembrane system, other vesicles are essential for proper cellular function. Specialized vesicles: Lysosomes are spheres of enzymes that break down proteins, carbohydrates, or fats. Peroxisomes contains hydrogen peroxide and are prominent in liver and kidney cells where hydrogen peroxide detoxifies ethanol and breaks down fatty acid.
8. Mitochondria
Is an organelle that creates energy used by the cell. It’s composed of a double membrane system, much like the nuclear membrane. It also possesses DNA. The mitochondrial genome encodes for over 30 genes whose products play essential roles in metabolism and energy production. Capsule like shape, the outside membrane of mitochondria is flat over the surface of the structure while the inner membrane is folded (to increase surface area) into sheets, which is referred as cristae. Proteins in the inner membrane creates an electron transport system where protons or hydrogen ions are transported from the interior of the mitochondria called the matrix, to the intermembrane space between the inner and outer membranes. The energy of the flowing Hydrogen ion is used to produce ATP (Adenosine triphosphate), the molecules that all cells of the human body use for energy.
9. Ribosomes
Ribosomes are complex structures,
containing many different proteins and at least three ribosomal RNAs.
They are the site of protein
synthesis.
The ribosomes that are attached to
endoplasmic reticulum synthesize all transmembrane proteins, most secreted proteins, and most proteins that are stored in the Golgi apparatus, lysosome, and endosomes. These proteins typically have a hydrophobic signal peptide at one end.
chromatids are pulled by the spindle fibers toward one of the centrioles: 46 to one, 46 to the other. Following this movement, the chromosomes are called as daughter chromosomes, and the set at one pole is identical to the set opposite pole. But the cell is not ready yet to divide
4. TELOPHASE:
A fresh nuclear membrane is reassembled around each set of chromosomes. The spindles dissolves which free the daughter chromosomes.
Cytokinesis
Near the end of telophase, proteins called actin begin to form a belt that extends around the equator of the cell. As cytokinesis continues, the actin ring decreases in size resulting to a narrow waist of the cell called as cleavage furrow. This constriction continues until the 2 resulting daughter cells are separated one another into identical but independent cells.
Meiosis
Not all human cells divide by mitosis. During sexual reproduction, sperm and egg cells must be divided in half so that each cell contains only 23 chromosomes rather 46. Thus, while mitosis is often referred to as cloning, meiosis is called a reduction division
Types of Cells
There are around 200 different kinds of cells inside the human body. They look and function differently, but most share some certain structures or organelles like nucleus and cell membrane. Here are some:
- Red blood cells – lack a nucleus and carry as much oxygen as it can.
- Nerve cells – carry electrical signals between brain and all parts of body.
- Epithelial cells – line the surfaces of cavities of the body to form a tight barrier.
- Adipose cells – stores molecules of fat that insulate the body and can be turned into energy.
- Skeletal muscle cells – arrange into fibrous bundles that contracts to move muscles.
- Reproductive cells – the female egg and male sperm combine to form a new embryo.
- Photoreceptor cells – line the back of the eye and responds to light falling on them.
- Hair cells – pick up sound vibration being transmitted through the fluid of the inner ear.
- Stem cells – are the foundation for the body’s repair mechanisms, which makes them potentially useful in helping repair damage in the body
because they can specialized into different types of cells.
Cell death
Apoptosis - When cells reached the natural end of their life cycle they undergo, a deliberate series of events that causes the cell to dismantle itself, shrink, and fragment. Necrosis - Cell can also die prematurely due infections or toxins. This causes a process in which the cell’s internal structure detaches from its membrane, causing the membrane to burst and the cell to die.
