Acidos
Nucleicos
1
Ácidos nucléicos
• Ácidos nucléicos : un biopolímero que contiene
tres tipos de monómeros unidos
• Una base orgánica heterociclo nitrogenado aromático
derivado de purina y pirimidina
• Un azúcar monosacárido D-ribosa o 2-deoxi-D-ribosa
• ácido fosfórico
• su nombre viene de que son muy abundantes en los
núcleos celulares y de su carácter ácido
• El más importente es el DNA que es el material
genético.
• En la siguiente diapositiva se muestra el nombre
y abreviaturas de algunas bases nitrogenadas
2
Bases Purina/Pirimidina
O
O
4
3
N
2
HN
5
6
N
O
O
1
6
1
2
N
N
8
N
3
4
N9
Purina
H
N1
O
O
N
N
N
N1
H
Citosina (C)
NH2
7
5
N
H
Timina (T)
H
Uracil (U)
Pirimidina
CH3
HN
N1
NH2
N
H
Adenina (A)
N
HN
H2 N
N
N
H
Guanina (G)
3
Nucleósidos
• Nucleósido: son glucósidos cuya base son las
nitrogenadas indicadas, contienen D-ribosa o 2deoxy-D-ribose unidas a la bases por un enlace
-N-glicosídico
4
Nucleósidos
• Uridina
uracilo O
HN
-D-ribosido
1
O
5'
HOCH2
4'
H
N
O
H
H
Enlace -N glicosídico
1'
H carbono
anomérico
HO
OH
Uridina
3'
2'
5
Nucleótidos
• Nucleótido: un nucleósido con una molecula de
acido fofórico está esterificado con el -OH del
monosacarido, más comúnmente el 3’-OH o el
5’-OH
6
Nucleótidos
• Adenosina 5’-monofosfato (AMP)
NH2
N
O
5'
- O- P - O- CH
2
-
H
N
O
H
O
H
3'
HO
N
OH
N
1'
H
7
Nucleótidos
• Deoxitimidina 3’-monofosfato (3’dTMP)
O
CH3
HN
5'
HOCH2
H
O
O
H
H
3'
O
H
P
O
O
N
1'
H
-
O
8
Aciclovir & AZT
O
N
HN
H2 N
HOCH2
O
HN
N
N
O
HOCH2
O
H
H
H
Aciclovir
(Dibujado para ver
su semejanza con la
2-deoxyguanosina
H
N
O
H
H
CH3
H
H
N3
H
Azidotimidina (AZT)
9
DNA - 1° Estructura
• Ácidos Deoxirribonucleicos (DNA): un biopolímero (polinucleótido) constituido por los ácidos
desoxiadenílico, guanílico, citidílico y timidínico
unidos por enlaces de éster fosfórico entre 3’-OH
de una 2-deoxi-D-ribosa y el 5’-OH de la siguiente 2-deoxi-D-ribosa. Son cadenas monótonas alternándose D-ribosa con fosfato y diferenciándose sólo en las bases colaterales a esa cadena.
• Estructura Primaria :la secuencia de bases en el
DNA determina su especificidad funcional y la
información genética que almacena.
10
DNA – Estructura 1ia; TG
O
Extremo 5´fosforilado
CH3
HN
O
-
O
5'
O- P - O- CH2
-
O
N
O
O
H
1'
H
H
2' H
O
H
N
HN
N
H2 N
N
5'
O= P
O
CH2
-
O
H
O
H
H
2' H
Extremo 3´libre 3'
OH H
1'
11
Estructura - 2° DNA
• Estructura secundaria : es el ordenamiento de las
cadenas de ácidos nucleicos
• Hélice Doble : el DNA forma una doble hélice de
dos cadenas complementarias con las vueltas a
la derecha. Las bases están situadas hacia el interior de la hélice, en planos perpendiculares al
eje, y los grupos de fosfórico están hacia el exterior.
• Este modelo de doble hélice fue propuesto por
James Watson y Francis Crick en 1953 en base a
diagramas de rayos X y a las equivalencias A=T y
G=C de las bases.
12
T-A Pareja de Bases
• El mejor factor estabilizante es la pareja de bases T-A
y entre C-G
Timina
Adenina
13
T-A Pareja de Bases
14
C-G Pareja de Bases
Citosina
Guanina
15
C-G Pareja de Bases
16
Formas del DNA
• B-DNA
•
•
•
•
es la forma predominante en solución acuosa diluida
hélices con las vueltas a la derecha
34 Å por 10 pares de bases; 20 Å de espesor
surco menor de 12 Å y el mayor de 22 Å
• A-DNA
• una helice diestra, pero de mayor espesor que B-DNA
• 29 Å por 10 pares de bases
17
DNA – Estructura 3ia
• EstructuraTerciaria : el arreglo de todos los
átomos de ácido nucleico en la tercera
dimensión, comúnmente referido como
superenrollado
• Circular DNA: un tipo de ADN double-stranded en
el que 5 ' y 3 ' los finales de cada soporte son
unidos según enlaces de fosfodiester (Fig 19.10)
• Cromatina:consists de herida de moléculas de
ADN alrededor de las partículas de histones en
una estructura parecida a una cuenta
18
Ácidos Ribonucleicos (RNA)
• RNA son similares al DNA en los que tambien son
largas cadenas enroyadas de nucleotidos unidos
por grupos de fosfodiester siendo el 3’-OH de
una pentosa y el 5’-OH de la próxima. However,
• the pentose unit in RNA is -D-ribose rather than
-2-deoxy-D-ribose
• the pyimidine bases in RNA are uracil and cytosine
rather than thymine and cytosine
• RNA is single stranded rather than double stranded
19
RNA
• RNA molecules are classified according to their
structure and function
Type
Molecular Weight
Range (g/mol)
Number of
Nucleotides
Percentage
of Cell RNA
mRNA
25,000 - 1,000,000
75 - 3,000
2
tRNA
23,000 - 30,000
73 - 94
16
rRNA
35,000 - 1,100,000
120 - 2904
82
• Ribosomal RNA (rRNA): a ribonucleic acid found
in ribosomes, the site of protein synthesis
20
RNA
• Transfer RNA (tRNA): a ribonucleic acid that
carries a specific amino acid to the site of protein
synthesis on ribosomes
O
t RNA- O- P- O- CH2
Oamino acid, bound
as an ester to its
specific tRNA
H
O
H
O
C O
C
H
R
Ba s e
H
H
OH
NH3 +
21
RNA
• Messenger RNA (mRNA): a ribonucleic acid that
carries coded genetic information from DNA to
the ribosomes for the synthesis of proteins
• present in cells in relatively small amounts and very
short-lived
• single stranded
• its synthesis is directed by information encoded on
DNA
• a complementary strand of mRNA is synthesized along
one strand of an unwound DNA, starting from the 3’
end
22
RNA
• Transcription: the synthesis of mRNA from DNA
DNA template
3'-A-G-C-C-A-T-G-T-G-A-C-C-5'
5'-U-C-G-G-U-A-C-A-C-U-G-G-3'
mRNA
23
El Código Genético
• Codon: a triplet of nucleotides on mRNA that
directs incorporation of a specific amino acid into
a polypeptide sequence
24
5'
U
C
A
G
U
UUU
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
AUG
GUU
GUC
GUA
GUG
Phe
Phe
Leu
Leu
Leu
Leu
Leu
Leu
Ile
Ile
Ile
Met
Val
Val
Val
Val
C
UCU
UCC
UCA
UCG
CUU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG
Ser
Ser
Ser
Ser
Pro
Pro
Pro
Pro
Thr
Thr
Thr
Thr
Ala
Ala
Ala
Ala
A
UAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
AAU
AAC
AAA
AAG
GAU
GAC
GAA
GAG
Tyr
Tyr
Stop
Stop
His
His
Gln
Gln
Asn
Asn
Lys
Lys
Asp
Asp
Glu
Glu
G
UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG
Cys
Cys
Stop
Trp
Arg
Arg
Arg
Arg
Ser
Ser
Arg
Arg
Gly
Gly
Gly
Gly
25
3'
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
The Genetic Code
• Properties of the Code
• only 61 triplets code for amino acids; the remaining 3
(UAA, UAG, and UGA) signal chain termination
• the code is degenerate, which means that several
amino acids are coded for by more than one triplet.
Leu, Ser, and Arg, for example, are each coded for by
six triplets
• for the 15 amino acids coded for by 2, 3, or 4 triplets, it
is only the third letter of the codon that varies. Gly, for
example, is coded for by GGA, GGG, GGC, and GGU
• there is no ambiguity in the code; each triplet codes for
one and only one amino acid
26
Sequencing DNA
• Restriction endonuclease: an enzyme that
catalyzes hydrolysis of a particular
phosphodiester bond within a DNA strand
• over 1000 endonucleases have been isolated and their
specificities determined
• typically they recognize a set sequence of nucleotides
and cleave the DNA at or near that particular sequence
• EcoRI from E. coli, for example, cleaves as shown
cleavage here
EcoRI
5'
G-A-A-T-T-C----- 3'
5'
G +
5'- A-A-T-T-C----27
3'
Sequencing DNA
• examples of endonucleases
Recognition
Enzyme Sequence
Recognition
Enzyme Sequence
AluI
AG CT
HpaII
C CGG
BalI
TGG CCA
Mbol
GATC
FnuDII CG CG
Not I
GC GGCCGC
HeaIII GG CC
SacI
GAGCT C
28
Sequencing DNA
• Polyacrylamide gel electrophoresis: a technique
so sensitive that it is possible to separate nucleic
acid fragments differing from one another in only
a single nucleotide
• Chain termination or dideoxy method: a method
developed by Frederick Sanger for sequencing
DNA molecules
29
DNA Replication
• the sequence of nucleotides on one strand is copied as
a complementary strand to form the second strand of
double-stranded DNA
• this synthesis is catalyzed by the enzyme DNA
polymerase
• DNA polymerase will carry of this synthesis in vitro
using single-stranded DNA as a template, provided the
four dNTPs and a primer are present
• because the new DNA strand grows from the 5’ to 3’
end, the primer must have a free 3’-OH group to which
the first nucleotide of the growing chain is added
30
Chain Termin. Method
• The key is addition of a 2’,3’-dideoxynucleoside
triphosphate (ddNTP) to the synthesizing medium
O
O
O
O- P - O- P - O- P - O- CH2
OO- OH
H
O
Ba s e
H
H
H
H
A 2',3'-dideoxynucleoside triphosphate
(ddNTP)
• synthesis terminates at any point where a ddNTP
becomes incorporated
31
Chain Termin. Method
• a single-stranded DNA of unknown sequence is mixed
with primer and divided into four separate reaction
mixtures
• to each mixture is added all four dNTPs, one of which
is labeled in its 5’- phosphoryl group with P-32
• also added are DNA polymerase and one of the four
ddNTPs
• when polyacrylamide gel electrophoresis of each
reaction mixture is completed, a piece of x-ray film is
placed over the gel to detect gamma radiation from the
decay of P-32
• the base sequence of the complement to the original
single-stranded template is read directly from the
32
bottom to top of the developed film
Descargar

Introduction to Organic Chemistry 2 ed William H. Brown