Chromatin: Chromatin is a complex of
DNA and proteins that forms chromosomes ,along with DNA and proteins RNA also present in chromatin.Chromatin is only found in eukayotic cell. Prokaryotic cells have a different organization of their DNA.Chromatin is thin fibrous and condensed structure.
Histones are the proteins which are present in the chromosomes. Amino acids, lysine and Arginine are abundant in Histones.
Histones are small and positively charged . Histones are divided into H1,H2a,H2b,H3,and H4 based on the Lysine and Arginine composition. Histones H2A, H2B, H3, and H4 come together to form a histone octamer,in core Histone. H1 is not not involve in core.H1 histones which is connecting linker.Positively charged Histones are bind with negatively charged DNA. DNA is negatively charged because of its phosphate molecule.The histones octamers and DNA together called as Nucleosomes.
Chromatin exists in two forms. One form, called euchromatin, is less condensed and can be transcribed. The second form, called heterochromatin, is highly condensed and is not transcribed.
The primary functions of chromatin are 1) to package DNA into a smaller volume to fit in the cell, 2) to reinforce the DNA macromolecule to allow mitosis, 3) to prevent DNA damage, and 4) to control Gene Expression and DNA replication.
Chromosomes:Chromosomes discovered by E.Strasburger in 1875.Chromosomes are condensed Chromatin Fibers. They are a higher order of DNA organization.Chromosomes are compact, thick and ribbon-like. The chromosomes cannot seen clearly in the nucleus,but able to seen during prophase in cell division.
Number ,size and shape of chromosomes: Number of chromosomes changes from organism to organism ,if chromosomes are paired that type are called Diploid chromosomes(2n), observe in somatic cell division. Chromosomes are not paired they are Haploid(n), observed in gametes.
wheat chromosomes 2n=42 .
size of the chromosomes measure at Metaphase.
Shape of the chromosomes are determine at Anaphase.
In eukaryotes chromosomes are divide into two categories autosomes and sex chromosomes.
Types of chromosomes based on position of centromere:
1.acrocentric :
In holocentric chromosomes, the centromere runs through the entire length of the chromosome. These chromosomes are very common in cells belonging to organisms in the animal and plant kingdom.
besides centromere ,chromosomes produces primary constrictions ,and secondary constrictions , which pinch off small fragments called satellite .this satellite remains attaches to the rest of the body. That chromosomes are called SAT chromosomes.
Terminal region of chromosomes are called telomeres,which protects chromosomes from breaks and fusion of broken fragments etc. If the length of the telomeres decrease too short, then that cell does not replicate that means cell became old.
Chromonema is the gene bearing portion of the chromosomes.this chromonema protected by matrix and pellicle.These two are non genetic materials and appears only at metaphase,that means nuleolus disappear. that means matrix and nucleolus both are interchangeable. when matrix disappears nucleolus appear.Nucleolus is a round body which present in side the nucleus and with out any membrane bounded.It makes ribosomes sub unites from proteins by using rRNAs.
When chromosomes are strain with acetocarmine,dark strain region called heterochromate and light strain region called euchromatin.
In heterochromatic regions contains three structure,chromomeres ,chromocentre and knob. Knobs are valuable chromosome markers for distinguishing chromsomes of related species and races.Certain region of chromosomes ,particularly those proximal to centromeres are constant, and are called Constitutive heterochromatic regions serving as chromosome markers.Other region called Facultative heterochromatine.
Chromosomes are 4 types depends up on number of centromeres.
1.Acetric chromosomes:
Histones are the proteins which are present in the chromosomes. Amino acids, lysine and Arginine are abundant in Histones.
Histones are small and positively charged . Histones are divided into H1,H2a,H2b,H3,and H4 based on the Lysine and Arginine composition. Histones H2A, H2B, H3, and H4 come together to form a histone octamer,in core Histone. H1 is not not involve in core.H1 histones which is connecting linker.Positively charged Histones are bind with negatively charged DNA. DNA is negatively charged because of its phosphate molecule.The histones octamers and DNA together called as Nucleosomes.
Chromatin exists in two forms. One form, called euchromatin, is less condensed and can be transcribed. The second form, called heterochromatin, is highly condensed and is not transcribed.
The primary functions of chromatin are 1) to package DNA into a smaller volume to fit in the cell, 2) to reinforce the DNA macromolecule to allow mitosis, 3) to prevent DNA damage, and 4) to control Gene Expression and DNA replication.
Cell CyclesCell DivisionMitosisMeiosisEukaryotic Gene and Gene Expression |
Chromosomes:Chromosomes discovered by E.Strasburger in 1875.Chromosomes are condensed Chromatin Fibers. They are a higher order of DNA organization.Chromosomes are compact, thick and ribbon-like. The chromosomes cannot seen clearly in the nucleus,but able to seen during prophase in cell division.
Number ,size and shape of chromosomes: Number of chromosomes changes from organism to organism ,if chromosomes are paired that type are called Diploid chromosomes(2n), observe in somatic cell division. Chromosomes are not paired they are Haploid(n), observed in gametes.
wheat chromosomes 2n=42 .
size of the chromosomes measure at Metaphase.
Shape of the chromosomes are determine at Anaphase.
In eukaryotes chromosomes are divide into two categories autosomes and sex chromosomes.
Types of chromosomes based on position of centromere:
1.acrocentric :
The location of the centromere in the acrocentric chromosome is
subterminal. This causes the short arm of the chromosome to become
really short making it very difficult to observe.2.Sub metacentric:
Centromere located towards at the end of the chromosome,they have a centromere that is located towards the end of the
chromosome. Thus, telocentric chromosomes have a 'rod' shaped
appearance. In some cases, the telomeres extend from both the chromosome
ends. The telocentric chromosome is not present in humans.
The arms of the submetacentric chromosome are said to be unequal in
length. This is because the kinetochore is present in the sub median
position. This gives rise to the 'L' shape of the submetacentric
chromosome.
3.Metacentric:
3.Metacentric:
The metacentric chromosome has its centromere centrally located
between the two arms. This gives the chromosome a typical 'V' shape that
is seen during the anaphase. The arms of this chromosome are roughly
equal in length. In certain cells, fusion of two acrocentric chromosomes
leads to formation of metacentric chromosome.
4.telocentric chromosomes:
4.telocentric chromosomes:
5.Sub telomcentric:
Chromosomes that have a centromere that is located closer to the end than the center, are called subtelocentric chromosomes.
6.Holocentric chromosome: In holocentric chromosomes, the centromere runs through the entire length of the chromosome. These chromosomes are very common in cells belonging to organisms in the animal and plant kingdom.
besides centromere ,chromosomes produces primary constrictions ,and secondary constrictions , which pinch off small fragments called satellite .this satellite remains attaches to the rest of the body. That chromosomes are called SAT chromosomes.
Terminal region of chromosomes are called telomeres,which protects chromosomes from breaks and fusion of broken fragments etc. If the length of the telomeres decrease too short, then that cell does not replicate that means cell became old.
Chromonema is the gene bearing portion of the chromosomes.this chromonema protected by matrix and pellicle.These two are non genetic materials and appears only at metaphase,that means nuleolus disappear. that means matrix and nucleolus both are interchangeable. when matrix disappears nucleolus appear.Nucleolus is a round body which present in side the nucleus and with out any membrane bounded.It makes ribosomes sub unites from proteins by using rRNAs.
When chromosomes are strain with acetocarmine,dark strain region called heterochromate and light strain region called euchromatin.
In heterochromatic regions contains three structure,chromomeres ,chromocentre and knob. Knobs are valuable chromosome markers for distinguishing chromsomes of related species and races.Certain region of chromosomes ,particularly those proximal to centromeres are constant, and are called Constitutive heterochromatic regions serving as chromosome markers.Other region called Facultative heterochromatine.
Chromosomes are 4 types depends up on number of centromeres.
1.Acetric chromosomes:
Acentric chromosomes are those that lack centromeres, i.e., the
centromere is totally absent on the chromosome. These chromosomes are
observed due to effects of chromosome-breaking process like irradiation.
2.Monocetric chromosomes:
Monocentric chromosomes are those that contain a single centromere.
This type of chromosome is present in most of the organisms. The
monocentric chromosomes can be called acrocentric, if the centromere is
located at the end of the chromosome. If the centromere is located
towards the center it is called metacentric chromosome. And, telocentric
chromosomes are those in which the centromere is present at the
chromosome's end.
3.Dicentric chromosomes:
3.Dicentric chromosomes:
Dicentric chromosomes are those that have two centromeres that are
present on its arms. These chromosomes are formed after two chromosomal
segments with a centromere each, are fused end to end. This causes them
to lose their acentric fragments, leading to formation of dicentric
chromosome.
4.Polycentric chromosomes :
Polycentric chromosomes are those that contain more than two
centromeres. These chromosomes are very common in plants.
