DNA REPLICATION Flashcards
what makes up the backbone of nucleotides?
sugar and phosphate
Which nucleotide bonds are easier to break ?
G-C is harder to break due to 3 hydrogen bonds whereas A-T is easier to break due to 2 hydrogen bonds
what bonds hold the nitrogenous bases together ?
hydrogen bonds
where and how does initiation begin ?
begins at the origin of replication (ori) when certain inititor proteins binds and trigger unwinding of DNA
when does DNA replication occurs?
During the S phase of interphase each original strand seves as a template for the formation of a complementary new strand
How does RNA synthesis start ?
a short fragment of RNA primer must be created and paired with the template of the DNA strand
In what direction does DNA forms and how does it start ?
DNA strand will always be from 5’ to 3’
needs a primer to kickstart the DNA replication
DNA polymerase III attaches new nucleotides in the 5’ to 3’ direction
What is the second step of DNA Replication
Elongation
what keeps the single-strand from re-joining?
Helicase, Topoisomerase and single strand binding protein
direction of synsthesis of DNA ?
5’ to 3’
function of ligase ?
joins adjacent DNA strands; fixes the nicks
function of DNA polymerase ?
matches the correct nucleotides then joins adjacent nucleotides to each other
function of primase ?
provides an RNA primer to start polymerization; forming new strand of DNA
function of helicase and how does it happen ?
unwind the DNA by breaking the hydrogen bond between complementary base pair
What are the basic requirements for DNA Replication?
Substrates - 4 deoxynucleoside triphosphates; cleavage of the high energy phosphate bond provides the energy for the addition of the nucleotide Template - each strand of parental DNA serves as a template strand Replication Enzymes - Helicase , primase , DNA polymerase , Ligase
what are the key events in Interphase (s phase)
DNA has replicated but has not formed condense structure of chromosome - remain as loosely coiled chromatin
functions of DNA and RNA ?
DNA : stores genetic information
RNA : make proteins and help out in DNA replication
Phosphate groups are bond together by ?
phosphoanhydride bonds which are high energy bonds
Last step of DNA replication ?
Termination
what are the two causes of DNA damage and the effect ?
ENDOGENOUS CAUSE : reactive oxygen species produced from normal metabolic by-product
EXOGENUOS CAUSE : Radiation, UV light, plant toxins, virus, high energy radiation, mutagenic chemicals
-due to environmental factors and normal metabolic processes inside the cell
-Single/double stranded breaks in the DNA sugar-phosphate backbone
-nucleotide bases have been modified chemically
-DNA-cross-links ; a covalent linkage between two nulceotides of DNA
- can occur within the same strand or opposite strands od double stranded DNA (INTRASTRAND VS INTERSTRAND)
Accuracy of replication
1 mistake every 10^8 bases
what is leading and lagging strand ?
leading strand : runs in the 3’ to 5’ ; strand that is replicated continuously towards the replication fork
lagging strand : runs in the 5’ to 3’ ; strand that is replicated discontinuosly away from the replication fork
what are new segments of DNA called
Okazaki Fragments
what happens after new Okazaki fragments are formed
RNA primers are replaced by DNA with the help of DNA polymerase
In which it specifically removes the RNA primers via its 5’ to 3’ exonuclease activity
and fill up the gaps with new deoxyribonucleotides by the 5’ to 3’ DNA polymerase activity
Ligase helps to join new adjacent DNA fragments together by breaking the sugar-phosphate backbone between the new adjacent DNA fragments
what are the two classes of checkpoints genes?
PROTO-ONCOGENS : code for proteins that promote the cell cycle and prevent apoptosis
TUMOUR SUPPRESSOR GENES : code for proteins that inhibit the cell cycle and promote apoptosis
Mutation in these checkpoints can cause the cell to lose control of the cell cycle hence cancer - uncontrolled cell growth
At what point during normal DNA replication is genetic material lost from the telomeres?
Joining of Okazaki Fragments
