this is my own understanding , if u see any mistakes please feel free to contact me email : xanaf05@hotmail.com thnks

1. DNA
part 4
Prep by : Mohamed Abdukadir kalif
Mphil in Optometry

2. DNA chain

3. • In real life even alone man can not produce
child , and alone women can not give birth to
child without men .
• So as DNA , a single molecule of DNA can not
live alone it needs another molecule of DNA .
• So how is single chain DNA arranges another
chain of DNA ?

4. • To produce a child there is a need of man and
woman which are different living organisms
• so as the two chains of the DNA molecules ,
they are different from each other .
• Because mostly identical things don’t attract
each other except in some circumstances

5. • To arrange another chain of DNA
• Adenine bonds with thymine in upside down
way
• And the bond between them is called
hydrogen bonds
• Adenine and thymine have two hydrogen
bonds , and it is a weak bond

6. Adenine bond with thymine

7. • Guanine bonds with Cytosine in upside down
way , with three hydrogen bonds , and it is a
stronger bond

8. Guanine bond with Cytosine

9. Complete DNA chain

10. • The DNA molecules are not straight , they are twisted
, their nitrogenous bases are held together by
hydrogen bonds , and their wall is made of
phosphate and sugar , which is held together by
phosphodiester bonds .

11. • Most of the DNA are right hand twisted
• But also in some points it becomes left hand
twist
• So There are different forms that the DNA
twist.

12. B-form of DNA
• This is right handed twist
• It is only a DNA molecule twisting with
another DNA molecule
• There are ten (10) pairs of nucleotides in
complete 360’ degree turn
• And every pair is perpendicular to the central
axis

14. A-form of DNA
• Right handed twist
• It can be one molecule of DNA twisted with
another molecule of RNA , or it can be DNA
twisted with another DNA
• There are 11 pairs of nucleotide in complete
360’ degree turn
• It is slightly dehydrated , because of the more
pairs of nucleotide within 360’ degree turn

15. Z-form of DNA
• With in right handed long chain of DNA ,
suddenly some areas appear which are left
hand twisted , this sudden left hand twist
creates zigzag area , that area of DNA which
has gone in to reverse twisting is called Z-
FORM of DNA .
• There are 12 pairs of nucleotides in complete
360’ degree turn

16. To be continued