1.2 DNA & Replication Flashcards
What is each strand of DNA made up of repeating units called
Nucleotides
How many components does each nucleotide have
3 different components
What does each component of nucleotides include
A phosphate group, a deoxyribose sugar and a base
What are the four chemical bases in DNA
Adenine, guanine, cytosine and thymine
Describe the structure of DNA
It’s doubled stranded and wound into a helix shape
What are nucleotides
Sub units which make up each strand of DNA
How are the nucleotides joined together
By a chemical bond where the deoxyribose of one nucleotide joins with the phosphate of another nucleotide called a sugar phosphate bond which forms a sugar phosphate backbone
How are the two strands held together
By weak hydrogen bonds which join the bases together
What does each base have
A specific complementary base partner
What do both strands of DNA have
A 5’ and a 3’ end running in opposing directions
What can the DNA strands be described as
Anti parallel
What does the 5’ end of the strand begin with
A phosphate
What does the 3’ end of a strand start with
A deoxyribose sugar
Why must the vast amount of DNA be packed
So it can fit into the cells nucleus
Where is DNA tightly coiled around
Protein molecules called histones and arranged into chromosomes
What is DNA replication
The process by which 2 identical DNA molecules are made from 1 parent molecule to make an exact copy of DNA
What is the first stage of DNA replication
The double helix of DNA unwinds and unzips with hydrogen bonds between bases breaking
What is the second stage of DNA replication
A primer attached to the complementary target sequence at the start of the sequence of bases to be replicated
What is the third stage of DNA replication
This allows the enzyme DNA polymerase to synthesise a new strand of DNA by adding nucleotides complementary to the template strand
What is the fourth stage of DNA replication
DNA polymerase only adds nucleotides to the 3’ end of the growing strand. This means that DNA polymerase works in a 5’ to a 3’ direction. One strand is replicated continuously and is known as the leading strand
What is the fifth stage of DNA replication
The other strand is synthesised in fragments in a 3’ to 5’ direction and is known as the lagging strand
What is the sixth stage of DNA replication
The fragments of the lagging strand are joined by the enzyme ligase
