Tumors

A tumor is a generic term which refers to development within normal tissue, a newly formed tissue. It is caused by the dysfunction of cellular development.

Tumor types

we distinguish :

1- Benign tumors : are localized tumors, circumscribed and not generalizing (without metastases). They simply repress the surrounding tissues without invading and therefore have a limited volume. On the other hand, this variety of cells shows no morphological abnormalities (monstrosity). These tumors usually do not cause pathological problems in the patient.

Among the benign tumors, there is:

        The lipoma consisting of fatty tissue

        Fibroids (hard tumors)

2- malignant tumors or cancers: whose specificity is important multiplication and modification of cell morphology, and their ability to invade surrounding tissues or more distant (metastases). This variety of tumor is totally opposed to benign tumors: indeed, they are likely to have a very large volume and are poorly demarcated. On the other hand, malignant tumors tend to recur frequently after ablation. Among the malignant tumors, there are primary tumors and secondary tumors which are metastases.

Among the malignant tumors, there is:

        Carcinoid tumor

        Tumors of the urethra

        Breast tumor is either malignant or benign

Restriction enzymes

These are enzymes, mainly of bacterial origin, capable of cleaving double-stranded DNA (and whatever its origin) to specific locations (nucleotide sequences) called restriction sites usually 4 to 6 pairs of bases.

DNA sequences recognized by the restriction enzymes :

Nucleotide sequences recognized by restriction enzymes are usually called palindromic sequences. The palindromic sequences are sequences where the succession of nucleotides read in the sense 5'à3 '(left-right) for the first strand is the same as the sequence read in the right-left direction for the second strand (sense 5'à3 '). These palindromic sequences are most often consist of 4, 5 or 6 pairs.

Nomenclature of restriction enzymes :

Restriction enzymes have a specific nomenclature. Their name has several letters (3 or 4). The first letter in the name of the enzyme is capitalized, it corresponds to the gender of the bacterium from which the enzyme was derived. The second letter and the third letter (lowercase) correspond to the species of the bacteria from which the enzyme is extracted. There may be a fourth letter written in capital corresponding to the bacterial strain. Finally to complete, a Roman numeral indicating the order of characterization of these enzymes.

Examples:

Eco RI Extracted from Escherichia coli RYB, site recognized: G / AATTC

Sma I Extracted from Serratia marcescens, site recognized: CCC / GGG

PstI Extracted from Providencia stuartii, site recognized: CTGCA / G

Types of cuts made ​​by restriction enzymes :

Restriction enzymes can provide two types of cuts: cut with a blunt ends and cut with a sticky ends.

The blunt ends result in a break in the middle of the palindromic sequence. The cut of sticky ends  is a cut which is on either side of the center of symmetry. The restriction sites are identified in the DNA by restriction enzyme that cuts DNA in principle as many times as there are restriction sites. This is valid for a given restriction enzyme, for another enzyme, the cut will be in a different position on the DNA. The DNA is cut into variable fragments and this both bacteria circular DNA or plasmids that linear DNA.

 

Examples of blunt and sticky ends of 

Methylation of the restriction site and restriction enzyme inactivation :

Bacterial DNA contains restriction sites may be identified by restriction enzymes that the bacteria has. To avoid self-destruction, modification enzymes of bacterial DNA involve. These modification enzymes are bacterial methylases ( or Methylation enzymes). Methylation of cytosine (at 5 carbon) or adenine (at nitrogen 6) belonging to the restriction sites leads to inactivation of the corresponding restriction enzyme. This methylation can be carried on a base or several bases belonging to the restriction site. Bacterial methylases are very specific.

Stem cells

A stem cell is an undifferentiated cell capable of self-renewal, to differentiate into other cell types and proliferate in culture. Stem cells are derived either from the embryo or fetus, or adult tissues with or without transformation, they can also be obtained by nuclear transfer. Due to these properties, they can be used to regenerate or recreate the destroyed tissues : it is cellular therapy.

Stem cells are characterized by two main properties:

•           The ability to replicate in giving new stem cells. They share this property with cancer cells can multiply indefinitely;
•           The ability to transform sous une certaine pression chimique under some chemical pressure (in a given culture medium) to a differentiated mature cell: for example, a liver cell, pancreas, skin, etc..

Potentiality of stem cells :

All stem cells do not have the same potential of differentiation. Thus, we find :

Unipotent stem cell : able to provide only a single cell type (liver, skin, brain, etc..), but capable of self- regeneration, what distinguishes of precursor cells;

Multipotent stem cells : (fetal and adult cells) capable of giving born to multiple cell types, as myeloid stem cells of bone marrow which are at the origin of blood cells.

Pluripotent stem cells : (embryonic stem cells or induced pluripotent stem cells), derived from  an embryo from a 5 to 7 days or artificially obtained after transformation of adult cells, which may give born to more than 200 cell types representative of all body tissues ;

Totipotent stem cells : cells derived from the first divisions of the fertilized egg (until the fourth day), capable of giving born to all cell types of the body and the alone to allow full development of the individual.

embryonic stem cells

Cell elements

What's an animal cell?

A cell is the structural and functional element that makes up the tissues and organs of living beings. It contains the genetic information of the individual and it is the origin of biological creation. It is complex and consists of various elements allowing it to be autonomous, but in interaction with other cells. The living beings are created in the base of a single cell that divides by an iterative phenomenon (called mitosis) to compose the body. The multiplication of cells is a regulated phenomenon that allows the development of the body and different organs. Abnormal and uncontrolled cell proliferation is a fundamental element for the development of a cancer.

Animal cell composition

Cell elements: It is composed of:

• Plasma membrane :

All cells (eukaryotic and prokaryotic) are separated from their environment by a plasma membrane.

it determines what enters the cell and what comes out. Like all biological membranes, the plasma membrane has a selective perméablilité, means it allows certain substances to pass through more easily than others. The plasma membrane consists of a double lipid layers, wherein proteins are inserted.

• Cytoplasm :

the cytoplasm is mainly composed of water and therefore the whole cell activity is carried out in aqueous medium in which the different solutes are in solution and different organelles are in suspension.

The cytoplasm is the privileged place of intense biochemical activity and in which several metabolic ways find their origin. Thus chemical reactions  of catabolic type leading to energy release can occur in the cytoplasm and anabolic reactions such as the biosynthesis of big molecules such as proteins and glycogen may also occur in the cytoplasm.

• Cytoskeleton :

The cell shall maintain its shape and collapse resistance to the presence of an internal cytoskeleton. Note that the cytoskeleton is not, however, a rigid or articulated structure as the word "skeleton" may suggest. The cytoskeleton appears in the cytosol as an impressive scaffolding formed of fibrillar proteins called "fibrils" : these protein fibrils are not covered by a membrane envelope. There are two major types of different fibrils by their size and chemical composition,  microfilaments and microtubules in bundles or more complex training.

• Nucleus:

holds the genetic information of the cell and governs all cellular activity. It includes:

- The nuclear envelope: double membrane cytoplasmic type punctuated nuclear pores for the exchange with the cytoplasm.

- The nucleoplasm: colorless substance that fills the spaces of the nucleus. It has close to those properties of the cytoplasm.

- Chromatin: denser than the nucleoplasm, chromatin is formed of entangled filaments of DNA.

- The nucleolus: is a small dense mass without membrane.

• Endoplasmic reticulum:

intervened in the intracellular transport of different substances, it is smooth, or rough (granular) and, in the latter case, lined with ribosomes whose role is to synthesize proteins.

• Golgi apparatus ( Golgi complex):

Organelle in eukaryotic cells consisting of a stack of cisternae "baggies" flattened.

The Golgi apparatus receives proteins and lipids from the endoplasmic reticulum and redirects after processing and sorting, to a number of internal or external destinations in the cell.

• Ribosomes :

Ribosomes are organelles present in eukaryotic and prokaryotic cells. Ribosomes play an extremely important role: they assemble amino acids to form proteins which then go into the endoplasmic reticulum.

• Lysosomes :

Lysosomes are organelles in eukaryotic cells that contain a mixture of digestive enzymes used to degrade macromolecules.

Lysosomes are considered like "stomach" of the cell.

• Mitochondrion :

Organelles present in eukaryotic cells. The mitochondrion is constituted by a double membrane, the inner membrane is folded into a mitochondrial cristae.

Mitochondrions are organelles that produce energy in the cell. So mitochondrion have a central role in energy for the cell. They are the ones who perform cellular respiration.

• Centriole :

Centriole  is a cell element specific  of the animal cells.

it is cylinders formed of nine microtubules arranged in a circle. Each cell contains two of these organelles, located close to the nucleus. Centrioles play an important role in cell division.