Definition of DNA and RNA & it's structure pdf

What is DNA and RNA . It's basic structure

1. Structure of DNA
(Lecture # 2)
Ms. Saba Saeed
Lecturer
M.Phil.(Biochemistry)

2. WhatisDNA?
•Deoxyribonucleicacid
•Twopolynucleotidechainsthatcoil
aroundeachothertoformadouble
helix.
•Carryinggeneticinstructionsfor
thedevelopment,functioning,
growthandreproductionofall
knownorganisms.
•Itisacomplexmoleculethat
contains alloftheinformation
necessarytobuildandmaintainan
organism.

3. DiscoveryofDNA
•In1869,FriedrichMiescherdiscoveredin
thecellnucleusamixtureofcompounds
thathe callednuclein.
•Themajorcomponentofnucleinis
deoxyribonucleicacid(DNA).
•By the end of the 19
th
century, chemists
learnedthegeneralstructureofDNAand
ofa relatedcompound,ribonucleicacid
(RNA).

4. Cont….
•Botharelongpolymers—chainsofsmall
compoundscallednucleotides.
•Eachnucleotideiscomposedofasugar,a
phosphategroup,andabase.
•Thechainisformedbylinkingthesugars
tooneanotherthroughtheirphosphate
groups.

5. StructureofDNA-thebuilding block
•Bythemid-1940s,biochemistsknew
thefundamentalchemicalstructuresof
DNAandRNA.
•WhentheybrokeDNAintoits
componentparts,theyfoundthese
constituentsto benitrogenousbases,
phosphoricacid,andthesugar
deoxyribose(hencethename
deoxyribonucleicacid).
•Similarly,RNAyieldedbasesand
phosphoricacid,plusadifferentsugar,
ribose.

6. ComponentsofNucleicacid
NitrogenousBases
•The fourbasesfoundinDNAare
adenine(A),cytosine(C),guanine(G),
andthymine(T).RNAcontainsthe
same bases,exceptthaturacil(U)
replacesthymine.
•Thestructuresofthesebasesreveal
thatadenineandguaninearecalledas
purines(doublering structure).
•Cytosine,thymineanduracilarecalled
as pyrimidines(singleringstructure).

7. NitrogenousbasesofDNA
•There are four nitrogenous
basesfoundinDNAare
1.Adenine
2.Guanine
3.Cytosine
4.Thymine

8. NitrogenousbasesofRNA
•There are four nitrogenous
basesfoundinRNAare
1.Adenine
2.Guanine
3.Cytosine
4.Uracil

9. ComplementaryBases
Thenitrogenousbasesin DNAare:
•Adenine always makes pair with thymine (complementary
toeachother).
•Guanine always makes pair with cytosine (complementary
toeachother).

10. ComplementaryBasePairing

11. Sugars
•BothDNAandRNAcontains5
carbonsugar(pentosesugar).
•The5carbonsugarinRNAiscalled
asribose,whereas5carbonsugar
inDNAiscalledasdeoxyribose.
•Theydifferatonlyoneplace.
Ribose contains a hydroxyl (OH)
groupincarbon2-position
•Deoxyribose lacks the oxygen and
simplyhas ahydrogen(H),
represented by the vertical line.
Hencethenamedeoxyribose.

12. PhosphateGroup
•Phosphate group is identical in
bothDNAandRNA.
•Phosphate group is attached at 5
carbon of the pentose sugar in
bothDNAandRNA.

13. Nucleoside
•ThebasesandsugarsinRNAand
DNA are joined together into
unitscallednucleosides.
•In nucleic acids, the bases are
covalently attached to carbon 1
of the pentose sugar ring, to
formanucleoside.
•Thebondbetweenthebasesand
the sugarsisthe glycosylic (or
glycosidic)bond.

14. Nucleotide
•Nucleosidewitha phosphategroup
is called as nucleotide. The
phosphategroupattacheswiththe
pentose sugar at carbon number 5
by phosphodiesterbond.
•An ester is an organic compound
formedfromanalcohol(bearinga
hydroxylgroup)andanacid.

15. Cont….
•In the case of a nucleotide, the
alcohol group is the 5'-hydroxyl
groupofthesugar,andtheacidis
phosphoric acid, which is why we
call theester aphospho-ester.
•Thesearecalledphosphodiester
bonds because they involve
phosphoricacidlinkedtotwo
sugars.

16. Positionofphosphategroupand nitrogenousbase
withpentosesugar
•Thenitrogenousbases(adenine, guanine,cytosine,thymineand
uracil)attach withpentosesugaratits carbonnumber1.

17. •In pyrimidines, the nitrogenous
baseslikethymine,cytosine and
uracil attach with 1
stcarbon of
pentose sugar with their 1
st
nitrogen.
•In purines, the nitrogenous bases
likeadenineandguanineattach
with 1
stcarbon of pentose sugar
withtheir 9
thnitrogen.
•The bond between the pentose
sugarandnitrogenousbaseis
calledas glycosidicbond.

18. •The phosphategroupattacheswith pentosesugaratcarbon
number5.
•The bondbetween thephosphoricacidandpentosesugaris
calledas phospho-esterbond.

19. Nucleotide

20. PhosphodiesterbondofNucleotides
•Onenucleotideisattached
with other nucleotide via
phosphodiesterbond.

21. HowDNA strandsform?

22. DNA,adoublehelicalstructure..
•DNAisadoublehelicalstructure.
•TwostrandsofDNAareanti-paralleltoeach other.
•TwostrandsofDNAcoilaroundeachotherandtherearetenbases
perturn.
•TwostrandsofDNAjointogether viahydrogenbondingbetweenthe
nitrogenousbases.
•Adenosine&thymine (twohydrogenbonds).
•Cytosine&guanine(threehydrogenbonds).
•Thepentosesugarandphosphategroupmakethebackboneofthe
DNA,the nitrogenousbasesareinsidethe helix.

23. DNA bothstrandsrun anti-paralleltoeach other