Week 2: DNA: replication, transcription and translation
Cells functionally specialize through expressing unique genes
Gene structure
Mechanisms of action of DNA and RNA polymerased
Protein synthesis
Regulation of gene expression in bacteria
Introduction to bioinformatics
DNA structure
DNA (deoxy-ribonucleic acid) is a polymer
The polymer is built form nucleotides (A, C, G, T)
Each nucleotide has a base (green), a sugar (blue) and a
phosphate (yellow)
The polymer has a direction (5’ to 3’)
Base complementarity ensures formation of a double helix
The backbone of a DNA chain connects nucleotides via their sugar
and phosphate groups
Adenine forms two hydrogen bonds with Thymine and Cystosine
makes three hydrogen bonds with Guanine
DNA is a double-helix. This helix has a major and a minor groove
Many DNA-binding proteins also bind to DNA through an interaction
of some of their alfa-helices with phosphate groups of the DNA
backbone
DNA replication
The chain is extended at its 3’ end
Synthesis occurs form 5’ to 3’ end
The template strand is “read” from 3’ end to 5’ end
Semi-conservative synthesis
Starts at fixed positions: the origins of replication initiation (ORI)
DNA synthesis by DNA polymerase
, Proofreading activity in DNA polymerase only 1 mistake every 107
nucleotides (human genome = 6,4x109 nucleotides)
DNA polymerase can only synthesize in 5’ to 3’ direction (how to
synthesis the other strand 3’ to 5’)
Solution
one half of the DNA
is replicated in
short strechtes, that
are later joined
Okazaki fragments
start from RNA
primer
o Primase joins
together two
ribonucleotides
o Primase synthesizes in 5’-3’ direction
o it forms a RNA primer
discontinuous synthesis: multiple enzymes
RNA primer removed by nucleases and replaced with DNA by repair
polymerase the end of the one strand and the beginning are
combined by DNA ligase
DNA helicase opens up the DNA strand for replication
A mechanism is needed for maintaining chromosome ends
Since Okazaki fragments start form RNA primer, which start at
random positions, and are themselves removed, it is impossible to
synthesize the lagging strand to the end
The and of a DNA strand ends with telomere which are repeat
sequences
Telomerase binds to template strand, it adds additional telomere
repeats completion of lagging strand by DNA polymerase (there is
a bit loss or extra length but it is not significant)
DNA = Deoxy-ribonucleic acid (RNA minus O)
Cells functionally specialize through expressing unique genes
Gene structure
Mechanisms of action of DNA and RNA polymerased
Protein synthesis
Regulation of gene expression in bacteria
Introduction to bioinformatics
DNA structure
DNA (deoxy-ribonucleic acid) is a polymer
The polymer is built form nucleotides (A, C, G, T)
Each nucleotide has a base (green), a sugar (blue) and a
phosphate (yellow)
The polymer has a direction (5’ to 3’)
Base complementarity ensures formation of a double helix
The backbone of a DNA chain connects nucleotides via their sugar
and phosphate groups
Adenine forms two hydrogen bonds with Thymine and Cystosine
makes three hydrogen bonds with Guanine
DNA is a double-helix. This helix has a major and a minor groove
Many DNA-binding proteins also bind to DNA through an interaction
of some of their alfa-helices with phosphate groups of the DNA
backbone
DNA replication
The chain is extended at its 3’ end
Synthesis occurs form 5’ to 3’ end
The template strand is “read” from 3’ end to 5’ end
Semi-conservative synthesis
Starts at fixed positions: the origins of replication initiation (ORI)
DNA synthesis by DNA polymerase
, Proofreading activity in DNA polymerase only 1 mistake every 107
nucleotides (human genome = 6,4x109 nucleotides)
DNA polymerase can only synthesize in 5’ to 3’ direction (how to
synthesis the other strand 3’ to 5’)
Solution
one half of the DNA
is replicated in
short strechtes, that
are later joined
Okazaki fragments
start from RNA
primer
o Primase joins
together two
ribonucleotides
o Primase synthesizes in 5’-3’ direction
o it forms a RNA primer
discontinuous synthesis: multiple enzymes
RNA primer removed by nucleases and replaced with DNA by repair
polymerase the end of the one strand and the beginning are
combined by DNA ligase
DNA helicase opens up the DNA strand for replication
A mechanism is needed for maintaining chromosome ends
Since Okazaki fragments start form RNA primer, which start at
random positions, and are themselves removed, it is impossible to
synthesize the lagging strand to the end
The and of a DNA strand ends with telomere which are repeat
sequences
Telomerase binds to template strand, it adds additional telomere
repeats completion of lagging strand by DNA polymerase (there is
a bit loss or extra length but it is not significant)
DNA = Deoxy-ribonucleic acid (RNA minus O)
