Genetics and molecular biology
 

dear fellows

in the Botany paper II , genetics , evolution, molecular biology and plant physiology are the main areas.

as a fact paper I is of old version botany.
paper II is modern world sciences.

many students in css botany can not attempt genetics section well.

this is also indicated in FPSC's annual reports.



so I am going to start this thread.
disscussion on gentics and related topics will be carried out here.

Do participate actively


regards
M.Rizwan Anwar
student of Plant breeding and genetics
future plans: M phil in Biotechnology from NIBGE ( National institute of biotechnology and genetic engineering)
E mail: [email]***************@gmail.com[/email]

Dear I am also intrested to understand genetics because its very intresting and essential to understand before taking botony paper.

bro can u explain me the Structure and synthesis of DNA.

structure of DNA
 

Components of DNA

DNA is a polymer. The monomer units of DNA are nucleotides, and the polymer is known as a "polynucleotide." Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group. There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. The four nucleotides are given one letter abbreviations as shorthand for the four bases.

A is for adenine
G is for guanine
C is for cytosine
T is for thymine
Purine Bases

Adenine and guanine are purines. Purines are the larger of the two types of bases found in DNA.


The 9 atoms that make up the fused rings (5 carbon, 4 nitrogen) are numbered 1-9. All ring atoms lie in the same plane.

Pyrimidine Bases

Cytosine and thymine are pyrimidines. The 6 stoms (4 carbon, 2 nitrogen) are numbered 1-6. Like purines, all pyrimidine ring atoms lie in the same plane.

Deoxyribose Sugar

The deoxyribose sugar of the DNA backbone has 5 carbons and 3 oxygens. The carbon atoms are numbered 1', 2', 3', 4', and 5' to distinguish from the numbering of the atoms of the purine and pyrmidine rings. The hydroxyl groups on the 5'- and 3'- carbons link to the phosphate groups to form the DNA backbone. Deoxyribose lacks an hydroxyl group at the 2'-position when compared to ribose, the sugar component of RNA.
Nucleosides

A nucleoside is one of the four DNA bases covalently attached to the C1' position of a sugar. The sugar in deoxynucleosides is 2'-deoxyribose. The sugar in ribonucleosides is ribose. Nucleosides differ from nucleotides in that they lack phosphate groups. The four different nucleosides of DNA are deoxyadenosine (dA), deoxyguanosine (dG), deoxycytosine (dC), and (deoxy)thymidine (dT, or T).
Nucleotides

A nucleotide is a nucleoside with one or more phosphate groups covalently attached to the 3'- and/or 5'-hydroxyl group(s).

DNA Backbone

The DNA backbone is a polymer with an alternating sugar-phosphate sequence. The deoxyribose sugars are joined at both the 3'-hydroxyl and 5'-hydroxyl groups to phosphate groups in ester links, also known as "phosphodiester" bonds
Features of the 5'-d(CGAAT) structure:

Alternating backbone of deoxyribose and phosphodiester groups
Chain has a direction (known as polarity), 5'- to 3'- from top to bottom
Oxygens (red atoms) of phosphates are polar and negatively charged
A, G, C, and T bases can extend away from chain, and stack atop each other
Bases are hydrophobic
DNA Double Helix

DNA is a normally double stranded macromolecule. Two polynucleotide chains, held together by weak thermodynamic forces, form a DNA molecule.
Features of the DNA Double Helix

Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral
The two polynucleotide chains run in opposite directions
The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase
The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.
Base Pairs

Within the DNA double helix, A forms 2 hydrogen bonds with T on the opposite strand, and G forms 3 hyrdorgen bonds with C on the opposite strand.
dA-dT and dG-dC base pairs are the same length, and occupy the same space within a DNA double helix. Therefore the DNA molecule has a uniform diameter.
dA-dT and dG-dC base pairs can occur in any order within DNA molecules
DNA Helix Axis

The helix axis is most apparent from a view directly down the axis. The sugar-phosphate backbone is on the outside of the helix where the polar phosphate groups (red and yellow atoms) can interact with the polar environment. The nitrogen (blue atoms) containing bases are inside, stacking perpendicular to the helix axis.

DNA synthesis
 

There is a major difference between DNA polymerase and RNA polymerase: the RNA polymerase can synthesize a new strand whereas the DNA polymerase can only extend an existing strand. Therefore, to synthesize a DNA molecule, a short RNA molecule (~ 5 - 12 nucleotides) must be synthesize first by a special enzyme. The initiating RNA molecule is known as a primer, and the enzyme is called primase.

In addition to DNA polymerase and primase, DNA replication requires helicase and single strand binding protein (SSB protein). The role of helicase is to unwind the duplex DNA. SSB proteins can bind to both separated strands, preventing them from annealing (reconstitution of double-stranded DNA from single strands).

The replication mechanisms in both bacteria and eukaryotes are similar. However, eukaryotic DNA polymerases do not contain a subunit similar to the E. coli b subunit. They use a separate protein called proliferating cell nuclear antigen (PCNA) to clamp the DNA.
DNA polymerases can extend nucleic acid strands only in the 5' to 3' direction. However, in the direction of a growing fork, only one strand is from 5' to 3'. This strand (the leading strand) can be synthesized continuously. The other strand (the lagging strand), whose 5' to 3' direction is opposite to the movement of a growing fork, should be synthesized discontinuously.

Thanks to you sir. Kindly suggest me 1 or 2 books which cover all the syllabus of botany for css. I shall be very thankfull to you .

Dear senior Rizwan Anwar!
im searching for multiple choice questions with answer on the topic of Plant BREEDING, HORTICULTURE AND PATHOLOGY can u plz tell me any book or net resources.
Thanks.

[QUOTE=Zaree;591397]Dear senior Rizwan Anwar!
im searching for multiple choice questions with answer on the topic of Plant BREEDING, HORTICULTURE AND PATHOLOGY can u plz tell me any book or net resources.
Thanks.[/QUOTE]

It will be better to consult "General Agriculture" by "Akhtar Abbas" it contains all these three sections and if you want to study Plant Breeding and Genetics in detail then go for "Plant Breeding: Principles and Methods" by "B.D. Singh"
Wish you luck!
Regards!

Thanks a lot Syeda Bukhari for ur cooperation.

Thanks a lot Syeda Bukhari for ur cooperation one thing more that either is it theoratical book or MCQs based, coz I need only MCQs or objective type question book on the above topics.

[QUOTE=Zaree;591830]Thanks a lot Syeda Bukhari for [COLOR=DarkRed][B]ur [/B][/COLOR]cooperation one thing more that either is it theoratical book or MCQs based, [COLOR=DarkRed][B]coz [/B][/COLOR]I need only MCQs or objective type question book on the above topics.[/QUOTE]

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