Molecular Biology Tutorials

Folded Fibre Model of Chromosomes


Dupraw model of chromosome

Folded Fibre Model of Chromosome
(The Ultra-structural Organization of DNA and Histone Proteins in the Chromosomes)

The chromosomes of eukaryotic organisms are a complex structural organization of DNA and proteins. The exact structural organization of proteins and DNA to form the chromatin material (or chromosomes during cell division) is a curious question in the scientific community. This curiosity becomes a wonder when we realize the total length of DNA in a single cell and size of the nucleus in which this DNA is residing. For example, in a diploid human cell, there will be 46 chromosomes. The DNA in all these 46 chromosomes when joined together, it will have a distance of about 2.2 meters. Thus, the average length of DNA in a single chromosome will be 4.8 cm or 48,000 µm (2.2 X 100/46). On an average, the human chromosome at its metaphase stage is about 6 µm long. This means the 48,000 µm long DNA strand is heavily folded to from the 6 µm long chromosome with a packing ratio of about 8000 : 1. The exact folding pattern of DNA is a highly debated concept.  For explaining the structural organization of DNA and proteins in the chromosome, various theories have been put forward by different scientists. DuPraw Folded Fibre Model and Nucleosome Model are the two such models trying to explain the ultra-structural organization of DNA and proteins in the chromosome. The present post describes the significance of Folded Fibre Model of Chromosomes and its merits and demerits.

Folded Fibre Model of Chromosome

Ø  The Folded Fibre Model of chromosome was proposed by DuPraw in 1965.

Ø  He published this model based on his studies on human chromosomes using electron microscope.

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Molecular Biology Tutorials

Karyotype and Idiogram: Definition and Importance of Karyotype Test (Karyotyping) in Human


what is karyotyping

(image source: wikipedia)

Karyotype, Karyotyping and Preparation of Idiogram

What is a Karyotype?

All species are characterized by a set of chromosomes to carry their genetic information. The chromosomal composition of each species has a number of characteristics. The Karyotype is a set of characteristics that identifies and describes a particular set of chromosome. These characteristics which are described by a karyotype are:-

(1).  The chromosome number

(2).  Relative size of different chromosomes

(3).  Position of centromere and length of chromosomal arms

(4).  Presence of secondary constrictions and satellites

(5).  Banding pattern of the chromosome

(6).  Features of sex chromosomes

What is Karyotyping? How to Prepare the Karyotype of Human?

Ø  The process of preparation of the karyotype of a species is called Karyotyping.

Ø  Karyotyping is now most commonly used in clinical diagnosis and clinical genetics.

Ø  Karyotype is prepared from the microphotographs of metaphase chromosomes.

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Molecular Biology Tutorials

Classification of Chromosomes based on Position of Centromere and Length of Chromosomal Arms

how chromosomes are classified

Classification of Chromosomes Based on Position of Centromere and Length of Arms

Ø  The size and shape of the chromosomes are variable in the different phases of cell cycle.

Ø  Chromosomes in the interphase of cell appear as thin, coiled, elastic and thread-like structures.

Ø  This thread-like stainable interphase chromosome is called chromatin.

Ø  During the mitotic or meiotic cell division, the chromatin materials become thicker in their width and shorter in their length.

Ø  Chromosomes in the metaphase stage of cell division show maximum condensation.

Ø  Each metaphase chromosome contains a centromere (primary constriction).

Ø  The centromere divides the chromosome into two parts called chromosomal arms.

Ø  The small arm of the chromosome is denoted as ‘p’ – arm, whereas the large arm is denoted as the ‘q’ – arm.

Ø  When chromosomes are represented as a karyotype or ideogram, each chromosome is arranged in such a way that the ‘p’ arm is positioned above the centromere and the q arm is represented below the centromere.

Ø  The position of centromere and the relative size of chromosomal arms are used as a criterion for a morphological classification of chromosomes.

Ø  This morphological classification is an important karyotypic feature of an organism.

Classification of chromosome

Ø  Based on the position of centromere and length of chromosomal arms, the chromosomes are classified into 4 groups:

(1).      Telocentric chromosomes

(2).      Acrocentric chromosomes

(3).      Sub-metacentric chromosomes

(4).      Metacentric chromosomes

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mcq biology

DBT BET JRF Exam 2017 Model Questions with Answer Key and Explanations Part 1


dbt bet 2017 free online test

image source wikipedia

DBT BET JRF Exam, 2017
Model Question Paper with Answer Key and Explanations

(Biology / Life Sciences MCQ: Multiple Choice Questions)

(1).  _____ can serve as an alternative to ethidium bromide to stain DNA for detection on gels

a.       Mitomycin C
b.      Acridine orange
c.       SYBR Green I
d.      Acriflavine

(2). _____ is a sensitive technique to find out the number of template molecules originally present in a PCR reaction.

a.       Hot start PCR
b.      Real time PCR
c.       AP PCR
d.      Reverse Transcriptase PCR

(3).  Using __________ it is possible to generate fluorescence in quantitative PCR reactions

a.       TaqMan probes
b.      Molecular beacons
c.       Scorpion probes
d.      All of the above

(4). For whole genome amplification, creating very long DNA products ________ method can be employed with great success

a.       MDA
b.      PEP
c.       iPEP
d.      DOP

(5).  ________ polymerase has the ability to add ~70,000 nucleotides every time it binds to primer and has a very low error rate.

a.       Taq polymerase
b.      Tli polymerase
c.       Pfu polymerase
d.      Bacteriophage ϕ 29 polymerase

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Botany lecture notes

Kerala PSC Botany Lecturer Exam 2017 Model Question Paper 3/3


psc botany lecture questions

Kerala PSC Botany Lecturer / Assistant Professor Model Question Paper 2017 Part 3/3

Model/Sample Question Paper of Kerala PSC Botany Lecturer/Assistant Professor Recruitment Examination to be conducted by Kerala Public Service Commission Question for the appointment of Botany Lecturer/Assistant Professor in Government Colleges of Kerala under the Directorate of Collegiate Education, Trivandrum, Kerala. Questions are in MCQ (Multiple Choice Questions) format.

Botany Lecturer Test: Model Questions Set – 3/3

(1). The concept of raising the profile of a particular species to successfully leverage more support for biodiversity conservation of biodiversity is denoted as:

a.       Keystone species concept
b.      Flagship species concept
c.       Umbrella species concept
d.      Indicator species concept

(2). Gelatinous fibres are:

a.       Long sclerenchymatous cells with highly lignified secondary wall
b.      Short sclerenchymatous cells with slightly lignified secondary wall
c.       Fibres with cellulosic secondary cell wall
d.      Fibres with hemicellulosic secondary cell wall

(3). Which of the following is a C3 plant?

a.       Maize
b.      Sugarcane
c.       Sorghum
d.      Rice

(4). The wrong rejection of a true null hypothesis is denoted as:

a.       Type I error
b.      Type II error
c.       Type III error
d.      Type IV error

(5). Carl Woese is best known for his contribution in:

a.       Gene mapping
b.      Three domain system of classification
c.       Genetic engineering
d.      Shotgun sequencing

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