DNA and Genes

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DNA and Genes
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Thing to find out

• What is DNA?
• The Genetic code
• The Human genome
• Passing on the genomic information
• Inheritance patterns

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Diversity of Life

• All biological systems are composed of the same
  types of molecules
• Similar organization priciples are used at the
  cellular level

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The Cell

• Basic component of life
• Two main categories, prokarytic and eukaryotic
  cells
• Differences in the nucleus

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• 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

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• 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

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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

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• 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
• Proteins 3D structure determines its function
• Information can transfer only in one direction

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DNA (Deoxyribo Nucleic Acid)

• DNA is a polymer of nucleotide monomers
• 2-deoxyribose sugar
• Four bases
• Adenine, A
• Guanine, G
• Thymine, T
• Cytosine, C

Base part

• Together a sugar and
• a base are called
• a nucleoside

Sugar part
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Four bases...

• Pyrimidine bases
• Thymine and cytosine
• A single carbon ring

• Purine bases
• Adenine and guanine
• Two carbon rings

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DNA chains

• Nucleosides are joiden together with
  phospsodiesteri bond
• Sequence of bases vary ? genetic information
• Chains are extremely long!

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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

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• ladder-structure
• Bases steps
• Sugars and phosphates suporting pilars

• Two nucleotide chains run in opposite
  directions ? chemical direction

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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

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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)

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• 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

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• 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 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 P L V Q   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 P W S N   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
The right one
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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

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• 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

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Chromosome
Condenced scaffold
fibers connected to chromosome scaffold
chromatin fibers
chromatin
DNA
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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

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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

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• Frameshift mutation insertion/deletion of bases
  ? reading frame is alterered

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The Human Genome
The different types of sequences that make up
the total DNA of a human cell
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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

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Two important terms... Phenotype The outlook
of an organism Genotype The genetic information
written in the DNA
Phenotypes
Genotype
Genotype
GCCAAGAATGGCTCCCACCT GGCTCTCAGACATTCCCCTGGTCCAACCC
CCAGGCCATCAAGATGTCTCAGAGAGGCGGCTAGACACCCAGAGACCTCA
AGTGACCATGTGGGAACGGGATGTTTCCAGTGACAGGCA
ATGTTTCCACCTTCAGGTTCC ACTGGGCTGATTCCCCCCTCC CACTTT
CAAGCTCGGCCCCTT TCAACTCAGAGAGGCGGCTA GACACCCAGAGAC
CTCAAGT GACCATGTGGGAACGGGATG TTTCCAGTGACAGGCAG
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Passing on the genetic information

• Information passed on in the sexual reproduction
• Needed for new characteristics to develope

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• All somatic cells
• 46 chromosomes
• Diploid cells, 2n

Fertilization

n n

• Sperm cell
• 23 chromosomes
• Haploid cell, n

• Egg cell
• 23 chromosomes
• Haploid cell, n

• Fertilized egg
• 2n
• 46 chromosomes

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• Mitosis
• Every cell division
• The number of chromosomes
• does not change
• DNA dublicates before entering
• the mitosis
• Takes 1-2 hours

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• Meiosis
• Nuclear division
• Only in gamete formation
• Results formation of the haploid
• gametosytes
• Mature gametocytes have 23
• chromosomes (n)

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• Humans
• 46 chromosomes ( 44 autosomes, 2 sex chromosomes)
• X and Y chromosomes
• XX ? female
• XY ? Male

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The chromosome pare

• A locus
• An allele
• Heterozygous (Aa)
• Homozygous (AA or aa)

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• 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)

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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

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Autosomal dominant inheritance
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Autosomal recessive inheritance
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X-chromosome linked recessive inheritance
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X-chromosome linked dominant inheritance
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