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DNA and Genes
Thing to find out:
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What is DNA?
The Genetic code
The Human genome
Passing on the genomic information
Inheritance patterns
Diversity of Life
• All biological
systems are
composed of the
same types of
molecules
• Similar
organization
priciples are used
at the cellular level
The Cell
• Basic component of
life
• Two main categories,
prokarytic and
eukaryotic cells
• Differences in the
nucleus
• Prokaryotes lack a
defined nucleus and
have a simplified
internal structure
• Eukaryotes have
membrane limited
nucleus and more
complicated internal
structure
• Three branches of
life
• Genetic material is located to the nucleus
• The genetic information is stored in
Deoxyribonucleic acid, DNA
• DNA contains all the information needed to
build an individual
What is DNA needed for?
•Genetic information
is used for gene expression
•Information of a gene is
transferred from DNA and
converted to protein
•RNA molecules work as
messangers
•Proteins are the biological
workers
•Information of the DNA is copied by
directing the synthesis of a RNA molecule
in a process called transcription
•RNA directs the
protein synthesis in a
translation
•Protein’s 3D structure
determines it’s function
•Information can
transfer only in one
direction
DNA (Deoxyribo Nucleic Acid)
•DNA is a polymer of nucleotide monomers
•2’-deoxyribose sugar
Base part
•Four bases:
•Adenine, A
•Guanine, G
•Thymine, T
•Cytosine, C
• Together a sugar and
a base are called
a nucleoside
Sugar part
Four bases...
Purine bases
• Adenine and
guanine
• Two carbon rings
Pyrimidine bases
• Thymine and
cytosine
• A single carbon
ring
DNA chains
• Nucleosides are
joiden together with
phospsodiesteri bond
• Sequence of bases
vary  genetic
information
• Chains are extremely
long!
DNA Molecules
• DNA molecules are
composed of two
polynucleotide
chains
• Double helix,
twisted in right
handed way
• Twists a full circle
in every 10 bases
•”ladder-structure”
–Bases = steps
–Sugars and phosphates =
suporting pilars
•Two nucleotide chains
run in opposite
directions  chemical
direction
Complementary Pairing
• Bases interact with other bases
• Purines with two carbon rings interact only
with single ring pyrimidines  Space
between the chains is limited.
• AT
• GC
• Complementary pairing  Vital for
retainins of the genetic information!
•Interaction is stabilized by
hydrogen bonds
•A-T bond  two hydrogen bonds
•G-C bond  three hydrogen bonds
The Genetic Code
• Describes how base sequences are
converted to protein sequence
• DNA sequence is divided into series of
units of three bases  a codon
• One codon is spesific to one amino
acid ( structural component of
protein)
• The four bases can
form 64 codons
• 20 amino acids are
found from the
nature
• Codons hava also
alternative
functions needed
to regulate protein
synthesis
•Right reading frame is obligatory!!!
•Sequence of human HCR gene, which assosiates with psoriasis
atgtttccac cttcaggttc cactgggctg attcccccct cccactttca agctcggccc
ctttcaactc tgccaagaat ggctcccacc tggctctcag acattcccct ggtccaaccc
•Many different reading frames can be used, but only one is the right one
•Transleate tools can found form the internet
Frame 1
The right one
Met F P P S G S T G L I P P S H F Q A R P L S T L P R Met A P T W L S D I
PLVQ
Frame 2
C F H L Q V P L G Stop F P P P T F K L G P F Q L C Q E W L P P G S Q T F
PWSN
Frame 1
G L D Q G N V Stop E P G G S H S W Q S Stop K G P S L K V G G G N Q
P S G T Stop R W K H
Genes
• Genetic information is encoded in the base
sequence of the DNA
• A gene : DNA sequence that encodes amino
acid sequence of a protein
• Beside the coding area, also other elements
are needed  control elements and ”empty
areas”
• Genes vary a lot in size
•Genes are separeted from each others by
sequences which function is unknown
•Only other strand of the DNA carries
biological information  template strand
•Potential to store biological information is
enormous
Chromosome
Condenced scaffold
fibers connected to
chromosome scaffold
chromatin fibers
chromatin
DNA
Mutations
• Mutations are alterations in DNA sequence
• Many chemical and physiological agents
and errors in DNA replication
• Cells can repaire some mistakes
•Once introduced and not repaired,
changes in DNA sequence are
made permanent by DNA replication
Sequence variations:
Single nucleotide polymorphims:
Alteration of a single base 
1. Causes an alteration in the amino
acid that the codon codes
2. Does not cause alteration on the
amino acid that the codon codes
3. Alters codon in the way that it
becomes stop-codon for protein
synthesis
• Frameshift mutation: insertion/deletion
of bases  reading frame is alterered
The Human Genome
The different types
of sequences that
make up the total
DNA of a human cell
The Human genome...
• 3 billion base pairs
• about 30000 genes
• 23 chromosome pares  46 chromosomes
• 25 % of the DNA is gene related
• Only 5 % encodes proteins
• Genes include exons and introns
• Beside coding areas also additional secuences are found
Two important terms...
Phenotype: The outlook of an organism
Genotype: The genetic information written in the DNA
Phenotypes
Genotype
GCCAAGAATGGCTCCCACC
T
GGCTCTCAGACATTCCCCT
GGTCCAACCCCCAGGCCAT
CAAGATGTCTCAGAGAGGC
GGCTAGACACCCAGAGACC
TCAAGTGACCATGTGGGAA
CGGGATGTTTCCAGTGACA
GGCA
Genotype
ATGTTTCCACCTTCAGGTTCC
ACTGGGCTGATTCCCCCCTC
C
CACTTTCAAGCTCGGCCCCT
T
TCAACTCAGAGAGGCGGCTA
GACACCCAGAGACCTCAAGT
GACCATGTGGGAACGGGATG
Passing on the genetic information:
• Information passed on in the sexual reproduction
• Needed for new characteristics to develope
All somatic cells
• 46 chromosomes
• Diploid cells, 2n
Sperm cell
• 23 chromosomes
• Haploid cell, n
Egg cell
• 23 chromosomes
• Haploid cell, n
Fertilization:
+
n
n
Fertilized egg
• 2n
• 46 chromosomes
Mitosis
• Every cell division
• The number of chromosomes
does not change
• DNA dublicates before entering
the mitosis
• Takes 1-2 hours
Meiosis
• Nuclear division
• Only in gamete formation
• Results formation of the haploid
gametosytes
• Mature gametocytes have 23
chromosomes (n)
Humans
•46 chromosomes ( 44 autosomes, 2 sex chromosomes)
•X and Y –chromosomes
•XX  female
•XY  Male
The chromosome pare:
• A locus
• An allele
• Heterozygous (Aa)
• Homozygous (AA or aa)
•We have two copies of each gene, one from the mother
and one from the father  Genotype
• Dominant character: only one allele needed to cause the
phenotype (heterozygous)
• Recessive character: both allels needed to cause the
phenotype (homozygous)
Inherited diseases
• DNA mutations are significant in development of diseases
• Inherited diseases are caused by mutations passed from
a parent to a offspring
• Monogenic diseases: disease is caused by mutation in
one gene
•Multifactioria diseases: disease is caused by co-operative
action of different mutations in different genes and
environmental factors
• Mendelian inheritance: Presence or absence depends
of the genotype at the single locus
Autosomal dominant inheritance:
Autosomal recessive inheritance:
X-chromosome linked recessive inheritance:
X-chromosome linked dominant inheritance: