DNA Replication Flashcards
Nucleic acid
Monomer = nucleotide
Phosphate group
Sugar - pentose
Purine/pyrimidine
Phosphodiester bond
Links together 2 nucleotides by condensation reaction
Glycosidic bond
Bounds bases to sugar
Oligonucleotides
Short chains
Polynucleotides
Longer chains
Types of RNA
tRNA mRNA rRNA snRNA viral RNA
DNA
ds chains bound by H bonds between bases; formed by 2-deoxyribose & bases (A,G,C,T)
Linear
Circular
Both strands carry the same genetic information
RNA
Usually ss polynucleic chain, formed from ribose & bases (A,G,C,U)
DNA Conformation
Primary
Secondary
Tertiary
DNA Primary Structure
Sequence of bases in nucleic acid chain
DNA Secondary structure
Shape of polynucleic chain in space -> Watson/Crick’s pairing of complementary strands
RNA = helix, double helix, cloverleaf
DNA = linear/circular right handed double helix
DNA Tertiary structure
DNA is organized into chromosome
DNA Denaturation
By heat treatment or high pH
Causes ds helix to dissociate into ss
Reversible process of DNA denaturation
Hybridization
DNA Cleavage (depolymeration)
Breaking of covalent bond between nucleotides of DNA strands by specific enzymes (restrictive nucleases)
Condensation of DNA into chromosome
Nucleosome -> chromatin fibre -> loops of fibre -> mitotic chromosome
Cell mechanisms
Copying of genetic information from mother to daughter cells
Protection of genetic information against defects (mutations)
When is DNA replicated?
S (synthetic)
Leading strand
DNA strand continuously synthesised in 5’-3’ direction
Single RNA primer is used
Lagging strand
DNA strand at the opposite side from the leading strand
Synthesised in 5’-3’ direction in short segments known as Okazaki fragments
Multiple RNA primers are used
DNA replication
Results in 2 identical copies of DNA (each copy is made of 1 strand from original DNA & 1 strand from nucleotide pool)
Semiconservative replication
Each strand can serve as template for synthesis of new strand
What are telomeres?
Repeating sequences of 6 base pairs
Why do chromosomes have telomeres?
Prevent chromosome ends from fraying & sticking to each other, that would cause cancer or other diseases/death
Allow cells to divide without losing genes
Without telomeres, chromosomes ends would look like broken DNA & the cell would try to fix it or stop dividing
Why do telomeres get shorter each time a cell divides?
DNA polymerases add nucleotides only to 3’ end
RNA primer is removed from 5’ end leaving ssDNA segment that is degraded & thus DNA will get shorter with each round of DNA replication
Cells normally an divide about 50-70 times
Does anything counteract telomere shortening?
Enzyme telomerase adds tandem repeats of bases to end of DNA using RNA molecules as atemplate
Are telomeres the key to aging & cancer?
When cell divides more often telomeres become very short, cells do not divide & become inactive/die
It can escape this fate fate by activating enzyme tekomerase which prevents telomeres from getting even shorter
DNA Damage
By exogenous agents such as ionising radiation, genotoxic chemicals, endogenously generated reactive oxygen, mechanical stress on chromosomes
DNA mismatch repair
Correction of replication errors that result from DNA polymerase misincorporation
Base excision repair
Corrects mutagenic damage of DNA from deamination, depurination
Pyrimidine dimers
Caused by UV component of sunlight
DNA intrastrand crosslinks
Oxidative damage
Transposition
Translocation of DNA sequence by enzyme transposase
Intermolecular transpoisition
Between different DNA molecules
Intramolecular transposition
On the same DNA molecule, cause change in genetic information, can lead to inactivation of genes in which it is located
Transposon
“Jumping genes”
DNA sequence that can translocate
Retrotransposons
Genetic elements that move in the genome by being transcribed to RNA & then back to DNA by reverse transcriptase
Microsatellites
Simple sequence repeats
Polymorphic due to an increased rate of mutation compared to other neutral regions of DNA
Typically used as molecular markers in genetics, population studies, relationship studies
Minisatellites
Persone genome have different numbers of repeats, thereby making them unique
Genetic marker
DNA sequence that can be identified by simple assay
Common used types of genetic markers
STR
SNP
VNTR
RFLP
Nucleosome
DNA is wrapped around a core of 8 histone proteins that are linked by H1 histones to form nucleosome which helps supercoil chromosome & regulate transcription
rRNA
Catalytic part of ribosome
mRNA
Copy gene for translation
tRNA
Bring amino acid to ribosome
snRNA
RNA processing
DNA vs RNA
SBS
sugar, base, strand
DNA Replication processes
Initiation
Priming
Elongation
Termination
DNA Replication initiation
DNA strands unwound & separate
DNA Replication priming
RNA primers are added to act as initiation points for DNA synthesis
DNA Replication elongation
New complementary DNA strands are synthesised in a 5’-3’ direction
DNA Replication termination
Primers replaced & fragments joined
DNA Replication initiation enzyme
Helicase
DNA Replication priming enzyme
RNA primase
DNA Replication elongation enzyme
DNA polymerase III
DNA Replication termination enzyme
DNA polymerase I
DNA ligase
Leading strand
Polymerase moving towards replication fork
Can copy continuously
Lagging strand
Polymerase moving away from replication fork
Copies in short fragments (OKAZAKI)
Because it is constantly exposing new nucleotides
DNA mismatch
Right after new DNA has been made & its job is to remove & replace mis-paired bases
Base-pair excision
Mechanism that detect & remove damaged bases
Glycosylase
Group of enzyme that detect & remove damaged bases
Correction of pyrimidine dimers
Detects & corrects types of damage that distort the DNA double helix
Transposon
“Copy & paste”
Chunk of DNA that “jump” form 1 place to another within a genome
Require enzyme transposase
Retrotransposons
“copy & paste”
BUT copy is made from RNA no DNA
RNA copies are then transcribed back to DNA (reverse transcriptase) -> which are inserted into new locations in the genome
Satellite DNA
Fraction of a eukaryotic organism’s DNA that consists of large arrays of tandemly repeating, non-coding DNA
Main component of centromeres -> form heterochromatin
Tandem repeats
Occur in DNA when pattern of 1/more nucleotides is repeated & repetitions are directly adjacent to each other
Molecular marker
Fragment of DNA associated with location in genom
Identify particular sequence of DNA in pool of unknown DNA
