Nucleotidos 2 ppt
-
Upload
francisco-romero -
Category
Documents
-
view
121 -
download
2
Transcript of Nucleotidos 2 ppt
Clase anterior:-Reglas de Chargaff- Datos de difracción de rayos X- Estructura de la doble hélice- Componentes: pentosa, fosfato y base nitrogenada- Tipos de bases nitrogenadas- Tipos de enlaces en la doble hélice- Estructuras alternativas de la doble hélice
Nucleic acids can adopt different conformations.
* B-DNA is found at low salt concentrations. It is believed to be the native conformation occurring in chromatin.right-handed helix; sugar pucker: C2'-endo; number of nucleotides per pitch: 10; h: 3.38 Å; t: +36°.
* A-DNA is found in solutions with higher salt concentrations or with alcohol addedright-handed helix; sugar pucker: C3'-endo; number of nucleotides per pitch: 11; h: 2.56 Å; t: +32.7°.
* Z-DNA occurs for alternating poly(dG-dC) sequences in solutions with high salt concentrations or alcohol.left-handed helix; G: syn-conformation; sugar pucker: C3'-endo; C: anti-conformation, sugar pucker: C2' endo; number of nucleotides per pitch: 6x2; h:
3.7x2 Å; t= -30°x2
* RNA occurs (contrary to DNA) almost exclusively in the A-conformation (or in a related A'-form).
http://www.imb-jena.de/IMAGE_DNA_MODELS.html
dA dG
T dC
dA dG
T dC
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
anti-conformation syn-conformation
In order for base-pairing to occur in a nucleic acid, the anti- conformation is
required.
dA dG
T dC
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
anti-conformation syn-conformation
In order for base-pairing to occur in a nucleic acid, the anti- conformation is
required.
In molecular biology, a wobble base pair is a non-Watson-Crick base pairing between two nucleotides in RNA molecules (codon-anticodon). The four main wobble base pairs are guanine-uracil, inosine-uracil, inosine-adenine, and inosine-cytosine (G-U, I-U, I-A and I-C). The thermodynamic stability of a wobble base pair is comparable to that of a Watson-Crick base pair.
A triple-stranded DNA is a structure of DNA in which three oligonucleotides wind around each other and form a triple helix. In this structure, one strand binds to a B-form DNA double helix through Hoogsteen or reversed Hoogsteen hydrogen bonds.
DNA triple hélice
The triplexes also form most readily within long sequences containing only pyrimidines or only purines in a given strand. Some triplex DNAs contain two pyrimidine strands and one purine strand; others contain two purine strands and one pyrimidine strand.
exotic DNA structure, known asH-DNA (Holiday junction) ,important during DNA recombination
A palindrome is a word, phrase, or sentencethat is spelled identically read either forward or backward;two examples are ROTATOR and NURSES RUN.
Secuencia palindrómica o palíndrome
DNA Replication
DNA replication is a semi-conservative process. One strand serves as the template for the second strand. DNA replication is initiated at a region on a chromosome called an origin of replication. An enzyme called DNA Helicase binds to the origin and unwinds the DNA in both directions from the origin.
Main types of RNAs
mRNAs
rRNAs
tRNAs
snRNAs
messenger RNAs, code for proteins.
ribosomal RNAs, components of the ribosome and catalyze protein synthesis.
transfer RNAs, carry specific amino acids to the elongating peptide chain during translation.
small nuclear RNAs, function in a variety of nuclear processes, including the splicing of pre-mRNAs.
RNA
Ribozimas
Otro “tipo” de ácido nucleico:
ssDNA
Funciones de los nucleótidos
Estructura del cAMP
Bromodeoxyuridine (5-bromo-2-deoxyuridine, BrdU) is a synthetic nucleoside that is an analogue of thymidine. BrdU is commonly used in the detection of proliferating cells in living tissues.
BrdU can be incorporated into the newly synthesized DNA of replicating cells (during the S phase of the cell cycle), substituting for thymidine during DNA replication.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Aciclovir- a guanine derivative, DNA polymerase inhibitor and antiviral
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Nucleótidos modificados
Pseudouridine (Ψ) was discovered to be the most abundant posttranscriptionally modified nucleotide in cellular RNAs in the 1950s
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
DNA metiltransferasas
Nucleótidos modificados
Pseudouridine (Ψ) was discovered to be the most abundant posttranscriptionally modified nucleotide in cellular RNAs in the 1950s
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
X
desaminación espontánea de citosina, se repara (DNA repair enzymes)
Xuracilo
Nucleótidos modificados
Pseudouridine (Ψ) was discovered to be the most abundant posttranscriptionally modified nucleotide in cellular RNAs in the 1950s
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
desaminación espontánea de 5-metil citosina genera timina
(una mutación tipo transición)
Dideoxy Nucleotides
• Lack an -OH group at the 3-carbon position
• Cannot add another nucleoside at that position
• Prevent further DNA synthesis
Reversible denaturation and annealing of DNA
Efecto Hipocrómico / Hipercrómico
• Bases in DNA absorb light at 260 nm.
• The close proximity of the bases in double-stranded DNA quenches some of theabsorbance- hypochromic shift.
• When the two strands separate, this quenching disappears and the absorbancerises 30-40% hyperchromic shift.
Denaturation of DNA Causes Hyperchromism
Ad
ap
ted
fro
m V
oe
t e
t a
l (1
99
9)
Fu
nd
am
en
tal o
f B
ioch
em
istr
y p
.73
9
50 70 90
1.3
1.2
1.1
1.0
Temperature (C)
Re
lativ
e a
bso
rba
nce
(2
60
nm
)
Tm
Tm: temperatura a la cual el 50% del DNA es cadena doble
Depende de factores como:
Composición nucleotídicaEntorno (fuerza iónica, pH,…)Largo (complejidad) de las cadenas a hibridar
G+C Content Is Proportional to Tm
70 80 90 100
1.4
1.2
1.0Re
lativ
e a
bso
rba
nce
(2
60
nm
)
Temperature (C)
Pneumococcus(38%) G+C E. coli (52%)
S. Marcescens(58%)
M. Phlei(66%)
Ad
ap
ted
fro
m G
arr
ett
& G
rish
am
(1
99
9)
Bio
che
mis
try
(2e
) p
.37
2
3 X 105 moléculas de gene copia única corresponden a:
Tamaño genoma (pb)1 µg DNA humano ~3 X 109
10 ng DNA levadura ~1.6 X 107
1 ng DNA E. coli ~ 4 X 106
0.3 pg pBSSK ~2.9 X 103
Cation Neutralizes Phosphate and Elevates Tm
60 70 80 90 100 110
100
80
60
40
20
0
Tm (C)
G +
C (
%)
0.15 M NaCl0.015 M Na citrate
0.01 M phosphate0.001 M EDTA
Adapted from Garrett & Grisham (1999) Biochemistry (2e) p.372
3’
5’
5’
3’
ß-cianoethylphosphoramidite
1.Desprotección Consiste en eliminar mediante un tratamiento ligeramente ácido, al grupo Dimetoxitritilo (DMT). Este grupo protege al Hidroxilo 5' terminal de la base (nucleótido) correspondiente.
2.Acoplamiento Una vez libre el grupo hidroxilo, se adiciona el siguiente nucleótido, en forma de ß-cianoetilfosforamidito, correspondiente a la sequencia deseada.
3.Bloqueo (capping) Concluído el paso de acoplamiento, se bloquean todos los hidroxilos que no reaccionaron (menor al 2% del total) con la nueva base, esto mediante una reacción de acetilación.
4.Oxidación Finalmente, el grupo fosfito internucleotídico se oxida a un grupo fosfato estable.
Síntesis química de oligonucleótidos
TAREA:
¿Qué es una topoisomerasa?
¿Tipos de topoisomerasa y cuál son sus funciones?