Please enable JavaScript.
Coggle requires JavaScript to display documents.
NUCLEIC ACID AND REPLICATION (DNA Replication (DNA polymerase catalyses…
NUCLEIC ACID AND REPLICATION
Structure of nucleic acid
DNA
four heterocyclic bases
Purines :arrow_right: Adenine (A) and Guanine (G)
Pyrimidines :arrow_right: Thymine (T) and Cytosine (C)
:warning: A=T, G≡C(stronger)
backbone
2'-deoxyribose sugar polymers
Orientation
Forward 5' :arrow_forward: 3'
Reverse 3' :arrow_forward: 5'
the sugars backbone are connected by Phosphate
RNA
four heterocyclic bases
Thymine :arrow_forward: Uracil :check: Cytosine can spontaneously deaminate to get Uracil
backbone
ribose sugar polymers :arrow_right: more active :arrow_right: easier to break RNA for denaturing
Complementary base pairing
DNA & RNA can both form double helices (
including base pair with each other
)
fundamental to genetics and genetic analysis
:one:Replication :two:Transcription :three:Recombination :four: Repair :five:Translation
allows
hybridization
:arrow_right: anneal two nucleic acid single strands :warning: base pairing does not need to be perfect!
:pencil2: DNA bases are hydrophobic :arrow_right: tend to form structures that avoid the aqueous environment :arrow_right:
right handed double helix strand
DNA Replication
DNA strand are denatured
:arrow_right: Each strand serves as a
template
for complementary strand sythesis :<3:semi-conservative mechanism
It's
rapid
and
accurate
:warning: broadly true for all organisms
DNA polymerase
catalyses replication :!!: requires
A template strand
and
A set of dNTPs (A,C,G,T)
and
primer (short nucleic acid strand)
:warning: RNA PRIMER must be added on initially for replication to occur (generated by
RNA primase
) :check: DNA polymerase recognizes PRIMER
:no_entry: RNA PRIMER must be removed ad replaced by DNA strand by
different DNA polymerase
only synthesizes in 5' :arrow_right: 3' direction
:arrow_forward: new base must be added on 5' end
Lagging strand :cry: replication occurs
discontinuously
and
away
from the FORK
called
Okazaki fragments
each strand starts with a new PRIMER
DNA Ligase
seals the lagging strands together
Leading strand :smiley: replication occurs
continuously
and
towards
the FORK
In Eukaryote
:check:Replisomes must also disassemble
protein-DNA of nucleosomes
:check:has multiple replication origins
Proofreading
DNA polymerases contain
3’ → 5’ exonuclease activity
:arrow_right: removed the mispaired base at 3' end
DNA polymerase reinserts the correct base
:check:gives high accuracy in DNA replication
DNA replication initiation and termination
INITIATION
:ONE:
DnaA proteins
bind to specific 13-base-pair sequence (repeated 5 times) in
oriC
:two: In response to the binding DnaA proteins :arrow_right: the origin is
unwound
at
cluster of A and T nucleotides
(bc it's easier to be melt than GC)
:three: addtional DnaA proteins bind to newly unwound single-stranded regions
(to prevent the rebinding)
:arrow_right:
helicases
bind and unzip DNA at the FORK :warning: can ONLY break the H-bond but cannot inititate DNA unwinding
:four: The
replisome
(DNA polymerase and PRIMER) begins replication
Replication Fork
Replication begins at single point (AT bases) :arrow_right:
the origin of replication
The point at which the helix is unwound and being replicated :arrow_right: FORK
Each fork has both lagging and leading strands
Two regions
Unwound parental duplex
:!!: made by DnaA proteins and Helicases
Over wound region
:!!: supercoils region which in front of other :arrow_right: hard to unwind :arrow_right:
Topoisomerase
:arrow_forward:cuts DNA strands :arrow_forward:DNA rotates to remove the supercoils :arrow_forward: rejoins the DNA strand
acts at the head of replication FORK
TERMINATION
The start of last Okazaki fragment will NOT replicated
due to no PRMIER present :arrow_right: telomeres get shorter as :arrow_double_up: age