DNA replication Flashcards
What is DNA?
DNA is a polymer
What does it mean by “dna is a polymer”
meaning it consists of repeated subunits – molecules – in this case nucleotides
What bonds connect nucleotides together?
phosphodiester bonds.
How is the DNA polymer chain formed?
the DNA polymer chain is formed by the sugar part of one nucleotide being covalently bonded to the phosphate group of the next nucleotide (phosphodiester bond) – and so on…
How are dna strands held together?
DNA strands are held together by hydrogen bonds between the nucleotides.
These bonds are formed between the sugar and phosphate molecules of adjacent nucleotides, creating a double helix structure.
What does DNA consist of?
Polymerised dNTPs
What are the bases of DNA?
The bases are nitogen-containing ring compounds, either pyrimidines or purines.
What bases are pyrimidines?
uracil, cytosine, thymine
What bases are purines?
Adenine, guanine
How many rings does a pyrimidine have?
1 ring
How many rings does a purine have?
2 rings
How are nucleotides added to a growing chain of DNA?
nucleotides are added on to a growing chain of DNA by the release of pyrophosphate (PPi) after the addition of a nucleotide – the remaining phosphate group then forms a phosphodiester bond.
so adjacent nucleotides on a DNA strand are joined by covalent bonds on the sugar phosphate backbone
Adjacent nucleotides on a DNA strand are joined by…
covalent bonds on the sugar phosphate backbone
What does a nucleotide consist of?
Base [nitrogenous]
Phosphate group
Sugar
Nucleotides are the subunits of…
nucleic acids.
What are the subunits of nucleic acids?
nucleotides.
DNA is a polymer of nucleotides consisting of…
…adenine (A), cytosine (C), guanine (G) and thymine (T)
How many strands in a DNA molecule?
DNA molecules are double-stranded
How do the two strands in a DNA molecule pair together?
the two strands ‘pair’ together with complementary sequences forming the pairs
What are the two types of groove in DNA molecule?
Minor groove
Major groove
What bonds hold the bases together?
Hydrogen bonds
eg: hydrogen bond between G and C
What direction does DNA run in?
5 prime to 3 prime
On left, 5 down to 3
On right 5 up to 3.
In double stranded DNA, how do bases pair together?
in double stranded DNA A always pairs with T and C always pairs with G.
the two strands are paired because of hydrogen bonds (H bonds)
How many hydrogen bonds between A and T?
2 H bonds
In a molecule of water…
…an oxygen (O) atom shares electrons with 2 hydrogen (H) atoms
Do oxygen or hydrogen atoms pull electrons toward their nucleus more strongly?
oxygen atoms pull electrons towards their nucleus more strongly than hydrogen atoms - more electronegative
Oxygen atoms are more […] than hydrogen atoms.
Oxygen atoms are more electronegative the hydrogen atoms.
Due to oxygen atoms pulling electrons towards their nucleus more strongly than hydrogen atoms (being more electronegative the hydrogen), what has happened to the charge of the overall water molecule?
because of this the water molecule has a charge difference across the molecule
Why is there a charge difference across water molecules?
Oxygen atoms more electronegative than hydrogen atoms.
because the atoms within water molecules have a net charge difference…
…adjacent molecules attract one another and hydrogen bonds form between the H atom of one molecule and the O atom of an adjacent molecule - intermolecular forces
you can think of the bonding in DNA as …
…analogous to the simple case in water
define adjacent
next to or near to something. eg: a neighbour.
Where are covalent bonds located in relation to bases?
Covalent bonds are located between adjacent bases within a single strand in the dna molecule.
Hydrogen bonds are between bases which connect the TWO strands together within dna molecule.
What happens to electrons in covalent bonds?
electrons shared.
What are the strength level of covalent bonds?
strong bonds.
What are the strength level of hydrogen bonds?
weak bonds
unwinding of the double helix makes…
…two single strands
polymerisation depends upon…
…the presence of a template strand.
What does unwinding of the dna double helix and polymerisation require?
requires dNTPs, a polymerase, Mg2+ and a free 3’ OH end
For any cell to reproduce it first must?
copy its genetic material.
What does the genetic material of a cell contain?
the genetic material contains the blueprint for making all the proteins a cell needs - without it the daughter cells cannot function
How does dna replicate?
DNA replicates by copying itself – each strand of the double helix contains the information to make a duplicate strand – because DNA molecules pair by complementary base pairing.
this is called semi-conservative replication
Describe DNA polymerisation:
DNA is polymerised by a complex of proteins at the replication fork:
1 – DNA polymerase – catalyses the addition of bases to the 3’ end
2 – Topoisomerase – unwinds the helix to prevent torsion
3 - Helicase – melts the double stranded molecule
4 - DNA primase – makes short RNA primers (gives a free 3’ end)
5 - Single stranded binding proteins – prevents premature annealing
6 - DNA ligase – joins Okazaki fragments on the lagging strand
