dna dan rna unit struktural dalam sel
DESCRIPTION
DNA dan RNA UNIT STRUKTURAL DALAM SEL. Agustina Setiawati , M.Sc., Apt. Albert, 1994, Molecular Biology of the Cell, Mc Graw Hill. REFERENSI. Nucleus. Kromosom dalam sel. Chromosome. Kromosom tanpa histon. Each cell has 46 chromosomes (in 23 pairs) - PowerPoint PPT PresentationTRANSCRIPT
DNA dan RNAUNIT STRUKTURAL DALAM
SEL
Agustina Setiawati, M.Sc., Apt
REFERENSI
Albert, 1994, Molecular Biology of the Cell, Mc Graw Hill
Kromosom dalam selNucleus
Chromosome
Kromosom tanpa histon
Each cell has 46 chromosomes (in 23 pairs)
~30,000 genes are arranged along the 23 types of chromosomes
Genes come in homologous pairs
The location of a gene on a chromosome = locus.
Alternative forms of genes that influence a characteristic = alleles.
DNA Introduction, cont.
A gene pair of two same alleles (i.e., AA) = homozygous
A gene pair of two different alleles (i.e., AO) = heterozygous.
DNA Introduction, cont.
Genotype: The particular combination of genes present in the cells of an individual (AA or AO)
Phenotype: The physical trait such as, shape, color, blood type, etc.
E. Coli 4.7 x 106 1 Chromosom40 – 50 loop superkoil
Human 4 x 109
22 autosom yang berbeda 2 sex kromosom
Masing2 single linier DNA
Kromatin Merupakan material inti yg mengandung kode genetik
Kode genetik tsb tersimpan dlm kromosom
Bdsk daya serapnya thdp lar pewarna dibedakan mjd 2 : heterokromatin (menyerap wrn dg kuat) & eukromatin (kurang kuat menyerap wrn)
Heterokromatin merup btk rapat (condensed) dr kromatin, shg terlihat spt noda yg rapat. Bnyk terlihat saat sel istirahat, spt limfosit atau sel memori yg menanti antigen asing. Heterokromatin inaktif dlm transkripsi
Eukromatin bbtk halus, bnyk tdpt dlm keadaan aktif (sel aktif melakukan transkripsi).
Kromatin
Berdasarkan lokasinya kromatin dibedakan mjd 3 daerah : ◦Kromatin perinukleolar, berada di sekeliling
nukleolus◦Kromatin internukleolar, berada dlm nukleolus◦Kromatin periferal, berikatan dg selaput sel.
Kromatin nukleolar & periferal merup heterokromatin
KromatinDitinjau dr peranannya sbg materi genetik,
heterokromatin dibagi mjd 2 : heterokromatin fakultatif & heterokromatin konstitutif.
Heterokromatin konstitutif selamanya tdk aktif & tetap dlm keadaan mampat selama daur hdp sel
Heterokromatin fakultatif tdk selamanya berada dlm keadaan mampat. Pd saat ttt secara ajeg kromatin ini terurai & saat terurai mrk dpt disalin
Dr analisis kimia ternyata kromatin tdr dr DNA, RNA & protein. Protein yg tdpt di kromatin tdr dr 2 jenis : histon & non-histon
PROTEIN HISTON Histon merupakan protein bersifat sangat basa, yg
disebabkan oleh adanya asam amino lisin & arginin dlm jml cukup bnyk.
Protein non-histon tdpt lbh dr bbrts jns, bervariasi sesuai dg jenis selnya, mis. Aktin, tubulin, RNA polimerase, asetil transferase dll
146 pasang basa DNA, 1 oktamer histon. 8 buah histon mbtk oktamer yg tdr dr 4 psg masing2 : H2A, H2B, H3 & H4
Set 8 histon tsb dsbt nuklosome, 10 nm fibril nukleoprotein. Nukleosome dipisahkan oleh daerah antara 4 nm filamen DNA
DNA
CHROMOSOME
KromosomSblm pembelahan sel (stlh sintesis DNA), kromatin
mengalami pembelahan kondensasi mbtk individu kromosom metafase, yg nampak sbg sepasang kromatid (tampak spt 2 pasang lengan)
Kromosom Jmlh kromosom di dlm sel berbeda2 sesuai jns
organismenya Btk & ukuran kromosom selama mitosis berubah2 ,
sebag bsr memp 2 lengan & tdpt lekukan dsbt kinetokor / sentromer
Sentromer ini merup tempat melekatnya kromosom pd mikrotubul dr gelendong mitosis & sekaligus sbg pusat pergerakan kromosom pd stadium anafase.
Kromosom tanpa sentromer dsbt kromosom asentrik & umumnya gagal memisahkan diri selama pembelahan sel.
Kromosom saat interfase seakan2 hilang, yg tampak dlm nukleus hanya anyaman filamen halus, dsbt kromatin
Chromosome DNA
Gene 1
Gene 2
Telomeres
Telomeres
TTAGGG
Telomere Length Declines
0 35 65
1,500
3,000
8,000
Age (years)
Telomere length in base pairs(human white blood cells)
A HISTORY OF DNA
Discovery of the DNA double helixA. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)B. Rosalind Franklin - X-ray photo of DNA.(1952)C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)
SEE p. 292-293
DNA Double Helix
NitrogenousBase (A,T,G or C)
“Rungs of ladder”
“Legs of ladder”
Phosphate &Sugar Backbone
UNIT FUNGSIONAL DNA/RNA
Perbedaan struktur gula antara RNA dan DNA
Basa
DN
A/RN
A
IKATAN RANTAI DNA
IKATAN FOSFODIESTER
RNA is a polymer of ribonucleotides
ribose sugars Phosphodiester linkages Directional chain (5’ to 3’) 4 Bases
purines: adenine & guanine
pyrimidines: cytosine & uracil
pGCUAC
G
U
A
5’ end
3’ end
1’
2’3’
4’
5’
3’
OH
PO-CH2
O
H2N-CC
CHN
N
NCH
CO
N
O
O
O P O CH2
O
O
C
N
N
CHC
CH
NH2
OH
O
O
O P O CH2
O
N
CHCO
HN
CHCO
OH
NH2
C
CN
N
N
CH
C
NHC
O
O
O P O CH2
O
O-HOH
DNA/RNA BERSIFAT ANTIPARALEL
DNA vs. RNADNA Double HelixGula deoksiribosaAdenine pairs with
Thymine (A-T)Tetap ada di nukleus
RNARantai tunggalGula ribosaUracil replaces
Thymine!Ditransport ke
sitoplasma
2’-deoxyribose sugars Phosphodiester linkages Directional chain (5’ to 3’) 4 Bases
purines: adenine & guanine
pyrimidines: cytosine & thymine
DNA is a polymer of2’-deoxyribonucleotides
pGCTA
5’ end
3’ end
C
G
T
A
OPO-CH2
O
H2N-CC
CHN
N
NCH
CO
N
O
O
O P O CH2
O
O
C
N
N
CHC
CH
NH2
NH2
C
CN
N
N
CH
C
NHC
O
O
O P O CH2
O
OH
O
O
O P O CH2
O
N
CCO
HN
CHCO
CH3
1’
2’3’
4’
5’
3’
RNA is easily hydrolyzed under alkaline conditions
The reaction proceeds through a 2’,3’-cyclic monophosphate intermediate. Enzymatic hydrolysis of RNA by RNase proceeds through a similar intermediate. Because DNA lacks the 2’-OH group, it is stable under alkaline conditions.
..
..
O P O-CH2
O
OO
N
OHO
O P O CH2
OO
N
OHO
O P OO
...
OH
ON
OHO
O P OO
...
HOCH2
O
..
..
O P O-CH2
O
O
N
OOP
OO
H+
..
..
O P O-CH2
O
OO
N
OHO
O P OHO
mixture of 2’- and 3’- monophosphate derivatives
H2O
shortened RNA
RNA
Why does DNA contain T rather than U?
N
CHCO
HN
CHCO
CNH2
N
N
CHCO
CH
cytosine uracil
H2O
Cytosine deaminates non-enzymatically to form uracil. If this happens in DNA, it constitutes a mutation. A proof-reading system recognize the error, and replaces the U by C.
Deamination of cytosine is of little consequence in RNA, which is not the permanent repository of genetic information.
The phosphate groups of DNA and RNA are negatively charged
A phosphodiester group has a pKa of about 1, and so will always be ionized and negatively charged under physiological conditions (pH ~7).
Nucleic acids require counterions such as Mg2+, polyamines, histones or other proteins to balance this charge.
5’
3’
HO-CH2
ON
O
O P O CH2
OO
N
O
O P O CH2
OO
N
O
O P O CH2
OO
O-PO32
N
+M
+M
+M
+M
The sugars are always in the b-furanose (cyclic) form
5’
3’
HO-CH2
ON
OH
O P O CH2 ON
O
O
OHO
O P O CH2
OO
N
OHO
O P O CH2
OO
O-PO32
N
OH
N
3’ 1’
5’
4’
endo
C-2’ exo
The ring can adopt various puckered conformations in which C-2’ and C-3’ are in either exo or endo positions relative to the base and C-5’.
CH2OHH-C-OH
H-C-OH
H-C-OHH-C-OHH-C=O
ribose in its aldehyde form
b-furanose (ring) form
HO-CH2OH
OHOH
O
The nucleotide base can rotate with respect to the sugar
The bases can adopt either syn or anti conformations, but anti conformations are preferred.
syn-Adenosine
NH2
C
C N
N
NHC
C
NCH
OHOCH2
OH OH
NH2
C
CN
N
N
CH
C
NHC
OHOCH2
OH OH
anti-Adenosine
O
C
N
N
CHC
CH
NH2
OHOCH2
OH OH
syn-Cytosine anti-Cytosine
OHOCH2
OH OH
ON
N
CHC
NH2
HCC
3 TIPE DNA
BENTUK DNA
Base pairs fill the center of the helix; the phosphates ( ) are on the outside.
The B-form DNA helix has a diameter of about 20 Å
~20 Å
A base pair is more exposed to the solvent on one side (the “major groove”, at the top in these views) than the other (the “minor groove”, bottom).
B-form DNA consists of a right-handed double helix with antiparallel strands
34 Å (10 bp) per turn
major groove
minor groovemajor groove
minor
3.4 Å per bp
These dimensions are for DNA fibers. In solution, there are ~10.5 base-pairs per turn.
5’ 3’
5’3’
Melting and Renaturation of DNA
Renaturation driven by homologous base pairing
Untai ganda DNA A260 = 1.00Untai tunggal DNA A260 = 1.37Basa bebas A260 = 1.60
The two strands of the double helix separate reversibly at high temperatures
The temperature at which this “denaturation” or “melting” occurs depends on the pH and salt concentration, and increases with the GC content of the DNA. (The curves drawn here are schematic.)
100
80
60
40
20
0
% D
enat
ured
110100908070Temperature / o
C
40 50 70% GC60If the temperature is lowered, the strands recombine. The rate of reassociation is inversely proportional to the complexity of the DNA.
dsDNAssDNAnucleotides
dA
dC
dGdU
The conjugated p-electron systems of the purine & pyrimidine bases absorb strongly in the UV. (That’s why UV light is mutagenic and carcinogenic.)
The absorbance of double-stranded DNA (dsDNA) at 260 nm is less than that of either single-stranded DNA (ssDNA) or the free bases. This is called “hypochromism.”
Double-stranded and single-stranded DNA differ in their optical absorption at 260 nm
TERIMA KASIH