Structure And Replication Of DNA Flashcards
(28 cards)
structure of DNA
Double stranded
2 polynucleotide chains- anti parallel
Made up of nucleotides
Nucleotides contain 2-deoxyribose sugar, nitrogenous base and a phosphate group
Forming a phosphoribose backbone
When in the double helix DNA has major and minor grooves
What direction does DNA run in?
It run in a 5’ to 3’ direction
The 5’ has the phosphate group attached and the 3’ has a hydroxyl group
Which are the complementary base pairs?
How many hydrogen bonds are between each base pair?
Adenine-thymine
2 h bonds
Guanine- cytosine
3 h bonds
Which nitrogenous bases are the pyrimidines and which are the purines?
Pyrimidines are thymine and cytosine
These are smaller only one ring
Purines are adenine and guanine
These are larger they have two rings
Why is it good that hydrogen bonding between base pairs is relatively weak?
Able to split apart double helix during replication and during transcription
What bond binds the 2-deoxyribose sugar and the nitrogenous base?
N-glycosidic link
How does the phosphate group bind to the deoxyribose sugar?
Phosphate group binds to the 5 prime end of the deoxyribose sugar by a phosphodiester bond
What is the term for a 2-deoxyribose bonded to a nitrogenous base and what is this then called when a phosphate group is attached?
Nucleoside
Nucleotide
How is the phosphoribose backbone is formed?
A phosphate group will bind to an adjacent nucleotide by binding to the hydroxyl group on the 3’ carbon and will release water in a condensation reaction forming a 3’ to 5’ phosphodiester bond
Definition of DNA replication
What can it also be called?
When a cell divides and faithfully transfers the genetic information from one cell generation to the next
Also called asexual reproduction
Replication in prokaryotes
Single chromosome
Replicates
Two genomes will move to either end of the cell
Two daughter cells are formed in a process called partitioning that are identical
When does replication take place in the cell cycle
During S phase
What does semi conservative replication mean
One strand is the parental strand and the second strand is a new daughter strand
Parental strand acts as a template
Enzymes involved in DNA replication?
Helicase Primase DNA polymerase Exonucleases Gyrase Telomerase
Steps of DNA replication
Initiation
Helicase unwinds double helix and both strand are replicated at the same time
Elongation
DNA polymerase binds to RNA primer and lays down complementary base pairs for daughter strand using template strand
The role of helicase and what happens after helicase has unwound the double helix
Unwind the double helix by breaking the h bonds between complementary base pairing
Single binding proteins bind to either side of the replication fork to keep the replication fork in an open confirmation
What does primase do?
Lays down an RNA primer which acts as a tether for the DNA polymerase
Primase binds to both strands as both strands are being replicated
Role of DNA polymerase? What does it require? What direction does it work in?
Adds correct nucleotide bases and has proof reading capabilities so checks it lays down correct complementary base pairs, requires all four bases and a primer and templates, it works in a 5’ to 3’ direction
What is the role of exonucleases?
Cut out the RNA primer out and DNA polymerase then fills in the gap , they work in both directions
It identifies the primer as it is structurally different
What is the role of ligase?
Join final 2 nucleotides together with the 3’ 5’ phosphodiester bond if not you will have DNA damage
Which strand of DNA does RNA polymerase primer bind to?
3’ to 5’ strand as primase lays down the RNA primer in a 5’ to 3’ direction as primase works by adding nucleotides in 5’ to 3’ direction
Which strand is the leading strand in DNA replication
The leading strand is the 3’ to 5’ parental strand and the other strand is replicated discontinuously and is called the lagging strand
What is the discontinuous strand made up of and why is it discontinuous?
Okazaki fragments which are made after the leading strand because the parental strand is the 5’ to 3’ strand therefore the lagging strand has to wait for the hydrogen bonds to be broken so it can lay down the RNA primer for DNA polymerase to bind to the primer to then make the next part of the chain
Where does transcription happen during the cell cycle
During the gap phases as there is nothing happening
Happens in low amounts in S phase however this is dangerous as replication is happening so there is a higher chance of mutations
