Genetics molecules like DNA and RNA have the ability to carry genetic instructions and replicate themselves perfectly. DNA contains genes which provide the code for protein production. The genetic code is expressed through transcription of DNA to mRNA and translation of mRNA to proteins. DNA replication ensures genetic information is preserved as cells divide. Mutations can occur through changes in DNA sequence or structure and generate genetic variability in populations.

1. GENÉTICA MOLECULAR
LOS ÁCIDOS NUCLEICOS Y SU
EXPRESIÓN

2. 1. Conocer y comparar los distintos tipos de ácidos nucleicos:
a) Composición.
b) Función.
2. El ADN como portador de la información genética:
a) Qué es un gen.
3. Conocer como se expresa la información genética.
a) El código genético.
b) Los procesos de transcripción y traducción.
4. La conservación de la información genética:
a) La replicación del ADN.
b) Las mutaciones, generación de variabilidad, soluciones (evolución) y
problemas.
OBJETIVOS:

3. 1. Los ácidos nucleicos: ADN y ARN
3. El ADN y la genética molecular:
a) El concepto de gen.
b) La replicación del ADN.
c) Las mutaciones genéticas y sus tipos.
2. Expresión de la información genética:
a) El código genético.
b) Transcripción: de ADN a ARN
c) Traducción: de ARN a proteínas
CONTENIDOS:

4. Nucleic acids
A few key events
DNA as an acidic
substance present
in nucleus was first
identified by
Friedrich Meischer
in 1868
In 1953, James Watson and
Francis Crick, described a very
simple but famous Double Helix
model for the structure of DNA.
She study X-ray diffraction of DNA
The diffraction
pattern she
obtained suggested
several
structural
features of DNA

5. Genetics molecules
• Genetics molecules has the ability to carry instructions.
• Genetics molecules should have the ability to be self-
copied perfectly, over and over again.

6. Nucleic acids struture
• Nucleics acids are polymers of small repeating
units calles nucleotides.
• Components of a nucleotide are:
- Base.
- Phosphate
- Sugar

7. Nucleic acids struture
• Nucleics acids are polymers of small repeating
units calles nucleotides.
• Components of a nucleotide are:
- Base.
• There are five kinds of nucleotides
• There are two mind kinds of nucleics acids
 DNA
 RNA
- Phosphate
- Sugar

8. The Nitrogenous Bases
 THEY ARE DIVIDED INTO TWO GROUPS
• Pyrimidines and purines
 Purines
• Adenine
• Guanine
 Pyrimidines
• Thymine
• Cytosine
 The rings are not only made of carbon

9. Nitrogenous bases of DNA & RNA

10. Nucleotide
Nucleoside
Base
Phosphate
Sugar
X=H: DNA
X=OH: RNA
Base always
attached here
Phosphates are
attached here

11. HH
OH
O
CH2
Base
Phosphate
Ribose
OH
5′
4′ 1′
3′ 2′
O
O
P
O–
O
HH
A, G, C or U
HH
H
O
CH2
Base
Phosphate
Deoxyribose
5′
OH
4′ 1′
3′ 2′
OO
O
P
O–
HH
DNA Nucleotide RNA Nucleotide
A, G, C or T
Nucleotides

12. Nucleotides are linked together by covalent bonds
called phosphodiester linkage.
Sugar
Base
P
Sugar
Base
P
1
2
3
4
5
1
2
3
4
5
A chemical bond that
involves sharing a pair of
electrons between atoms in
a molecule.
DNA. Deoxyribonucleic acid

13. NH2
N O
N
O
N O
N
Adenine (A)
Guanine (G)
Thymine (T)
BasesBackbone
Cytosine (C)
O
HH
H
H
HH
O
OO
O–
P CH2
O–
HH
H
H
H
HH
O
OO
O
P CH2
O–
NH2
N
N
H
N
N
HH
H
HH
O
OO
O
P CH2
O–
NH2
H
N
N
N
H
N
HH
HOH
HH
O
OO
O
P CH2
O–
Single
nucleotide
Phosphodiester
linkage
Sugar (deoxyribose)
Phosphate
3′
5′
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
5′
4′ 1′
2′3′
CH3
The primary structure of DNA
is the sequence of linked
nucleotides
5’ end
3’ end
5’
3’
A shorthand notation for this sequence is
ACGTA

15. The secondary structure of DNA is the
anti-parallel double helix
Salient features of the Double-helix structure of DNA:
 It is made of two polynucleotide chains, where the backbone
is constituted by sugar-phosphate, and the bases project inside.
 The two chains have anti-parallel polarity. It means, if one
chain has the polarity 5’→3’, the other has 3’→5’
G
T
C
A
5’ 3’
C
A
T
G

16.  The bases in two strands are paired through hydrogen bond (H-bonds)
forming base pairs (bp). Adenine forms two hydrogen bonds with
Thymine from opposite strand and vice-versa. Similarly, Guanine is
bonded with Cytosine with three H-bonds.
 Hydrogen bond: A chemical bond consisting of a hydrogen atom between two
electronegative atoms (e.g., oxygen or nitrogen) with one side be a covalent bond
and the other being an ionic bond.
 Based on the observation of Erwin Chargaff that for a double stranded
DNA, the ratios between Adenine and Thymine; and Guanine and
Cytosine are constant and equals one.
DNA Double Helix & Hydrogen bonding
3 Hydrogen bonds 2 Hydrogen bonds

17. A T U C G
30%
Ratios between nucleotides in a double strand of DNA
Ratios between nucleotides in a double strand of DNA
30% 0% 20% 20%
A T U C G
28% 28% 0% 22% 22%
ADN
A T
G C
ARN
A U
G C
*Chargaff´s rule

18. Experimental level Conceptual level
For each type of cell, extract the
chromosomal material. This can be
done in a variety of ways, including the
use of high salt, detergent, or mild alkali
treatment. Note: The chromosomes
contain both DNA and protein.
1.
Remove the protein. This can be done in
several ways, including treament with
protease.
2.
Hydrolyze the DNA to release the bases
from the DNA strands. A common way
to do this is by strong acid treatment.
3.
Separate the bases by chromatography.
Paper chromatography provides an easy
way to separate the four types of bases.
(The technique of chromatography is
described in the Appendix.)
4.
Extract bands from paper into solutions
and determine the amounts of each base
by spectroscopy. Each base will absorb
light at a particular wavelength. By
examining the absorption profile of a
sample of base, it is then possible to
calculate the amount of the base.
(Spectroscopy is described in the
Appendix.)
5.
Compare the base content in the DNA
from different organisms.
6.
Solution of
chromosomal
extract
DNA
DNA +
proteins
Individual
bases
Origin
Protease
Acid
A
A
AA
A A
A
A
C
C
C C C CC
G
G G
G G GG
TT T
T
T
T
T
T
G
G
G
C
C
C
yErwin Chargaff’s Experiment
By Himanshu Dev
VMMC & SJH

19. The Data
By Himanshu Dev
VMMC & SJH

20. Major
groove
Minor
groove
20 Å
34 Å
The secondary structure of DNA

21. Nucleotides are linked together by covalent bonds
called phosphodiester linkage.
Sugar
Base
P
Sugar Base
P
RNA. Ribonucleic acid
Usually single stranded and
helical in structure.
But double stranded also
present in some viruses.
Nucleotides are:
• Guanine, adenine.
• Cytosine, uracil.

22. RNA VS DNA

23. Types of RNA
 In all prokaryotic and eukaryotic organisms, three main classes of RNA
molecules exist:
1) Messenger RNA(m RNA)
2) Transfer RNA (t RNA)
3) Ribosomal RNA (r RNA)
 The other are:
 small nuclear RNA (SnRNA),
 micro RNA(mi RNA) and
 small interfering RNA(Si RNA) and
 heterogeneous nuclear RNA (hnRNA).

24. Messenger RNA (m-RNA)
All members of the class function as messengers carrying the information in a gene to
the protein synthesizing machinery
The coding region or sequence encodes for the synthesis of a protein.
A gene is a locus (or region) of DNA which contains information to
build a protein.
A gene is the basic physical and functional unit of heredity.

25. The central dogma of molecular biology has been described as
"DNA makes RNA and RNA makes protein”

26. Transfer RNA are the smallest of three major species of RNA
molecules
They transfer the amino acids from cytoplasm to the protein
synthesizing machinery, hence the name tRNA.
There are at least 20 species of tRNA one corresponding to
each of the 20 amino acids required for protein synthesis.
Transfer RNA (t-RNA)
1) Primary structure- The nucleotide
sequence.
2) Secondary structure- Each single t-
RNA shows extensive internal base
pairing and acquires a clover leaf
like structure. The structure is
stabilized by hydrogen bonding
between the bases.
3) Tertiary structure
Structure

27. Ribosomal RNA (rRNA)
 Ribosomal ribonucleic acid (rRNA) is the RNA component of
the ribosome, and is essential for protein synthesis in all living
organisms.
 rRNA component performs the peptidyl transferase (peptide
bond formation) activity and thus is an enzyme (a ribozyme)

28. The genes expression
Transcription and translation
DNA
Protein
mRNA
Location Process
Nucleus
Cytoplasme
o RER
Transcription
Translation

29. Transcription
1.Initiation:
Promotor, contains the
transcription start point.
2.Elongation:
Transcription factors and RNA
polymerasa II
Growing RNA strand, from 5’ to 3’
3.Terminatio:
DNA duplex reforms
A gene is the stretch of DNA,
or transcription unit, that is
transcribed to RNA
Transcript
(newly synthesized mRNA)
Splicing, 5´Cap & Poly A tail

30. Translation
In translation, messenger RNA
(mRNA) - produced by
transcription from DNA - is
decoded by a ribosome to
produce a specific amino acid
chain, or polypeptide.
Is the process in which
cellular ribosomes
create proteins.
Protein
mRNA
Cytoplasme
o RER

31. Translation
The genetic code
A. The genetic code is redundant.
• More than one codon can specify
the same amino acid.
A. The genetic code is degenerate.
• In most instances the third base is
the degenerate base.
A. The genetic code is nearly universal.
• Living beings has the same code,
only a few rare exceptions have
been noted.
• Encode the same 20 amino acid
with the same 64 triplets.
There are 20 amino acid, but 64 bases combinations or 64 tRNAs
The genetic code is the set of rules by which information encoded within genetic
material (DNA or mRNA sequences) is translated into proteins by living cells.
So codons and amino acids are linked with by the genetic code
The genetic code is the set of rules by which information encoded within genetic
material (DNA or mRNA sequences) is translated into proteins by living cells.
So codons and amino acids are linked with by the genetic code

32. 1. Initiantio:
Ribosomes assembles
around mRNA (Firts
tRNAmet
)
2. Elongation:
tRNA transfers amino acids.
The ribosome moves to the
next codon
3. Termination:
When a stop codon is
reached, the
ribosome realease
the protein
Translation have directionality, begins at 5’ end of mRNA. 5’ 3’

33. SUMMARIZING

34. Replication
Step one:
- An enzyme called Helicase breaks the hydrogen bonds between the bases of the two
antiparallel strands forming a replication fork.
- DNA Gyrase (also called Topoisomerase) relieves tension that builds up as a result of
unwinding.
- Single strand binding proteins (SSBs) help to stabilise the single stranded DNA.

35. Replication
Step two:
- RNA polymerase (also known as RNA Primase) synthesizes short RNA
nucleotides sequences that act as primers (starters). These essentially provide a
starting point for DNA replication.

36. Replication
Step three:
- DNA Polymerase III can now start synthesising the new DNA strand using free DNA
nucleotides. However, DNA polymerase can only read the original template (parent strand)
in the 3’ → 5’ direction (making DNA 5’ → 3’). This is not a problem on the leading strand.
- On the lagging strand DNA polymerase synthesise short fragments of DNA in-between
each of the RNA primers.

37. Replication
Step four:
- DNA Polymerase I now removes the RNA primers and replaces them with DNA
- DNA Ligase joins the DNA fragments of the lagging strand together to form one
continuous length of DNA.

38. Replication windows
Replication fork Replication fork

39. ADN / DNA ARN / RNA
Nucleotide / Nucleotido
Nucleoside / Nucleosido
Deoxirribose / Desoxirribosa
+
Nitrogenous bases
(A, G, C, T)
Ribose / Ribosa
+
Nitrogenous bases
(A, G, C, U)
+
Fosfato ℗
Double helix mRNA, rRNA, tRNA

40. The central dogma of molecular biology has been modified
Virus ARN
Reverse
transcription
Protein
Prion
Ribozymes
RNA

41. MUTATIONS
Types of mutations – 1.Genetics:
There are many different ways that DNA can be changed, resulting in
different types of mutation.
Substitution
A substitution is a mutation that exchanges one base for another.
Such a substitution could:
Insertion
Insertions are mutations in which extra base pairs are inserted into
a new place in the DNA
Deletion
Deletions are mutations in which a section of DNA is lost.
1. Change a codon to one that encodes a different amino acid and
cause a small change in the protein produced.
2. Change a codon to one that encodes the same amino acid and
causes no change in the protein produced.
3. Change an amino-acid-coding codon to a single "stop" codon
and cause an incomplete protein.
A mutation is a change in DNA: genes, chromosomes or genomes

42. MUTATIONS
Types of mutations – 2. Chromosomals:
A chromosome mutation is an change that occurs in a chromosome.
These changes are most often brought on by problems that occur
during meiosis or by mutagens (chemicals, radiation, etc.).
Chromosome mutations can result in changes in the number of
chromosomes in a cell or changes in the structure of a chromosome.
Chromosome Structure
a) Translocation: The joining of a piece of a chromosome to a non-
homologous chromosome.
b) Deletion: This mutation results from the breakage of a chromosome in
which the genetic material becomes lost during cell division.
c) Duplication: Duplications are produced when extra copies of genes are
generated on a chromosome.
a) Inversion: In an inversion, the broken chromosome segment is reversed
and inserted back into the chromosome.

44. MUTATIONS
Types of mutations – 3.Genomics:
a) Aneuploidy (Aneuploidía): Is the presence of an abnormal number of
chromosomes in a cell, for example a human cell having 45 or 47
chromosomes instead of the usual 46.
 Monosomy: refers to lack of one chromosome of the normal
complement. Monosomy of the sex chromosomes (45,X) causes
Turner syndrome.
 Trisomy: Down syndrome, trisomy 21. Edwards syndrome, trisomy
18. Patau syndromed, trisomy 13. Klinefelter syndrome, sexual
trisomy XXY
 Moploidy or haploidy, is the state where all cells have just one
set of chromosomes beyond the basic set.
 Poliploidy (Poliploidía), is the state where all cells have multiple
sets of chromosomes beyond the basic set, usually 3 or more.
Specific terms are triploid (3 sets), tetraploid (4 sets), pentaploid
(5 sets)…
b) Euploidy (Euploidía), is the state of a cell or organism having one or
more than one set of the same set of chromosomes
Chromosome Number Changes

45. The causes of mutations
Mutations happen for several reasons:
1. DNA fails to copy accurately.
1. External influences: Mutations can also be caused by exposure
to specific chemicals or radiation
Cells employ an arsenal of editing mechanisms to correct mistakes
made during DNA replication.

46. The effects of mutations - Evolution
Somatic mutations, occur in non-reproductive cells and won't be passed onto
offspring.
Germ line mutations, occur in reproductive cells like eggs and sperm. The only
mutations that matter to large-scale evolution are those that can be passed on to
offsprin.
http://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_05
Some regions of DNA control other genes, determining when and where other
genes are turned "on". Mutations in these parts of the genome can substantially
change the way the organism work or is built. A mutation in a gene "conductor"
can cause a cascade of effects in the behavior of genes under its control.
Little mutations with big effects: Mutations to control genes