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DNA and Genes
Things to find out:
• What is DNA?
• The Genetic Code
• The Human Genome
Diversity of Life
• All biological
systems are
composed of the
same types of
molecules
• Similar
organization
principles are used
at the cellular level
The Cell
• Basic component of
life
• Two main categories,
prokarytic and
eukaryotic cells
• Differences in the
nucleus
• Prokaryotes: no
defined nucleus and
a simplified internal
structure
• Eukaryotes:
membrane limited
nucleus and
complicated internal
structure
• Three branches of
life
• Genetic material is located in nucleus
• The genetic information is stored in
Deoxyribonucleic acid, DNA
• DNA contains the information needed to build
an individual
What is DNA needed for?
• Genetic information is
transferred from DNA and
converted to protein
•RNA molecules work as
messengers
•Proteins are the biological
workers
•Information of the DNA is copied to a RNA
molecule in transcription
•RNA directs the
protein synthesis in a
translation
•Protein’s 3D structure
determines it’s function
•Information transfer
only in one direction
DNA (Deoxyribo Nucleic Acid)
•a polymer of nucleotide monomers
•2’-deoxyribose sugar
•Four bases:
•Adenine, A
•Guanine, G
•Thymine, T
•Cytosine, C
Sugar part
Base part
Four bases...
Purine bases
• Adenine and
guanine
• Two carbon rings
Pyrimidine bases
• Thymine and
cytosine
• A single carbon
ring
DNA chains
• Nucleotides are
joined with
phosphodiesteri bond
• Sequence of bases
vary  genetic
information
• Extremely long
chains!
DNA Molecules
• Two polynucleotide
chains are joined
• Double helix,
twisted in right
handed way
• Full circle in every
10 bases
•”ladder-structure”
–Bases = steps
–Sugars and phosphates =
supporting pilars
•Two nucleotide chains
run in opposite directions
chemical direction
(5´-3´)
Complementary Pairing
• Bases pair with other bases
• Space between the chains is limited 
Purines with two carbon rings pair only with
single ring pyrimidines
A+T
G+C
• Complementary pairing is vital for the use and
storage of the genetic information!
•Interaction is stabilized by
hydrogen bonds
The Genetic Code
• Describes how nucleotide sequence is
converted to protein sequence
• Unit of three nucleotides = a codon
• A codon codes for a specific amino
acid (structural component of protein)
• The four bases can
form 64 different
codons
• 20 amino acids are
found from the
nature
• Regulatory codons
•Right reading frame is obligatory!
•Part of the sequence from psoriasis associated gene HCR
atgtttccac cttcaggttc cactgggctg attcccccct cccactttca agctcggccc
ctttcaactc tgccaagaat ggctcccacc tggctctcag acattcccct ggtccaaccc
• Three different reading frames can be used, but only one is the right one
•Translate tools are found from 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
Chromosome
Condenced scaffold
fibers connected to
chromosome scaffold
chromatin fibers
chromatin
DNA
Genes
• A gene: DNA sequence that is needed to encode
amino acid sequence of a protein
• Composed of exons, introns and different control
elements
• Exon – protein coding sequence
• Intron – intervening sequence
• Genes vary a lot in size:
Humans: average 3000bp
largest 2.4 million bp
•Genes are separated by sequences with
unknown function
•Only one strand of the DNA carries
biological information  template strand
•Potential to store biological information is
enormous
That’s all for this time!
The Human Genome and Inheritance
The Human genome...
The different types of sequences that make up
the total DNA of a human cell
• 3 billion base pairs
• about 22 000 genes
• Only 2 % of the DNA encode proteins
• Genes include exons and introns
• Beside coding areas also additional secuences are found
• 50 % repeated sequences (”junk DNA”)
• 23 chromosome pairs  46 chromosomes
• 44 autosomes, 2 sex chromosomes
• X and Y –chromosomes
• XX  female
• XY  Male
Chromosomes carrying
the same genes are
called homologous
Mutations
• Alterations in DNA sequence
• Some are part of normal DNA variation
• Caused by chemical and physiological agents
and errors in DNA replication
• Cells can repaire some mistakes
• If not repaired changes in DNA sequence
are made permanent by DNA replication
Point mutations:
Single base mutations:
1. Missense mutation: leads to
an amino acid change
2. Silent mutation: does not
change the amino acid
3. Nonsense mutation: causes
premature stop-codon
• Frameshift mutations:
insertion/deletion
dublication
translocation
Altered reading frame
 Severe impacts on protein structure
Passing on the genetic information:
• Information passed on in the sexual reproduction
• Needed for new characteristics to develop
• Offspring recieve genes by inheriting chromosomes
Two important terms...
Phenotype: The outlook of an organism
Genotype: The genetic information written in DNA
Phenotypes
Genotype
GCCAAGAATGGCTCCCACC
T
GGCTCTCAGACATTCCCCT
GGTCCAACCCCCAGGCCAT
CAAGATGTCTCAGAGAGGC
GGCTAGACACCCAGAGACC
TCAAGTGACCATGTGGGAA
CGGGATGTTTCCAGTGACA
GGCA
Genotype
ATGTTTCCACCTTCAGGTTCC
ACTGGGCTGATTCCCCCCTC
C
CACTTTCAAGCTCGGCCCCT
T
TCAACTCAGAGAGGCGGCTA
GACACCCAGAGACCTCAAGT
GACCATGTGGGAACGGGATG
All somatic cells
• 23 chromosome pairs
(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
A chromosome pare:
• A locus
• An allele
Mitosis
• Division of somatic cells
• Products two daughter cells from
one parent cell
• The number of chromosomes
does not change
• DNA duplicates before entering
the mitosis
• Takes 1-2 hours
Meiosis
• Only in gamete formation
• One diploidic parent cell produces
four haploid gametosytes
• Mature gametocytes have 23
chromosomes (n)
Crossing over:
• Chromatids change parts
between homologous chromatids
during the meiosis
• Causes redistribution of heridary
material between the homologous
chromosomes
 number of genes doesn’t
change
 new allele combinations
are formed
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 one mutation in
one gene
• Multifactiorial diseases: disease is caused by interaction
of different mutations and environmental factors
• Mendelian inheritance: Presence or absence of the
phenotype depends on the genotype at a single locus
• Dominant character: only one allele needed to cause the
phenotype (heterozygous)
• Recessive character: both allels needed to cause the
phenotype (homozygous)
Autosomal dominant inheritance:
Aa
aa
Aa
aa
Aa
Autosomal recessive inheritance:
aa
Aa
aa
Aa
Aa
aa
aa
Aa
AA
X-chromosome linked recessive inheritance:
X-chromosome linked dominant inheritance: