DNA -UNIT 1 Flashcards
What does DNA nucleotide contain
- phosphate
- deoxyribose sugar
- base
Why is it important for DNA strands are organised?
DNA strands are thousands of times longer than the length of a cell so need to be arranged to prevent tangling
How is DNA organised to prevent tangling>
Molecules of DNA are tightly coiled around proteins (histones)
What is semi-conservative
DNA replication Is when each daughter molecule of DNA contains one original strand and one newly synthesised strand
What happens at the recognised starting points for DNA replication
- DNA is UNWOUND and UNZIPPED to form two template strands
- this means that the HYDROGEN BONDS between the complementary base pairs BREAK and the TWO STRANDS SEPERATE exposing bases of the original DNA strand
Describe the role of DNA Polymerase?
- needs a primer to start replication
- adds complementary DNA nucleotides to the 3’ end (deoxyribose end of DNA strand)
Describe the role of ligase?
enzyme that joins DNA fragments together
What is a primer and importance to DNA polymerase
- A primer is needed to tell DNA polymerase where to start replication
- -single stranded sequence of nucleotides formed at the 3’ end of the template DNA strand
Formation of leading strand
- DNA molecule unwinds and unzips exposing bases
- A primer binds to the 3’ end of the leading strand
- Free DNA nucleotides stair to pair with exposed bases on the template strand in a complementary fashion
- DNA polymerase starts adding DNA nucleotides to the 3’ end forming a sugar phosphate backbone
Formation of lagging strand
- primers bind to the lagging strand and the DNA polymerase adds DNA nucleotides onto the strand
- DNA formed on lagging strand consists of short fragments and replication takes place in a DISCONTINOUS manner
- DNA ligase joins the fragments together
Key requirements for DNA replication
- DNA TEMPLATE
- PRIMER
- 4 TYPES OF FREE DNA NUCLEOTIDES
- ENZYMES
- ATP FOR ENERGY
