Chapter 3.3: DNA structure
* Subcomponents of DNA are called DNA nucleotides
* DNA nucleotide composed of: phosphate group, deoxyribose sugar, and one of four nitrogenous bases
* Four nitrogenous bases (base of nucleotide) is made of:
PURINES adenine and guanine
(double II (triple III complimentary base
H bond)II H bond) III pairing PYRAMIDINES thymine and cytosine
DNA is double stranded and each strand is composed of nucleotides where the sugar of one nucleotide is covalently bonded to the phosphate group of the next nucleotide.
* Each strand of DNA is composed of nucleotides covalently linked:
- Bases are read in groups of three
- Send instruction for cell
- Switch genes on and off
- Make proteins and enzymes
DNA is described as having two antiparallel strands because the two strands are aligned in opposite directions.
In a double-stranded DNA molecule there is a sugar phosphate backbone outside and the base on the inside Chapter 3.4: DNA replication
DNA replication doubles the quantity of DNA and also ensures that there is an exact copy of each DNA molecule.
Two important molecules for DNA replication:
- enzymes (including helicase and DNA polymerase)
- free nucleotides (not yet bonded)
Helicase = enzyme that initiates separation into two single strands. It breaks down hydrogen bonds so that there becomes two separate DNA strands. Each single strand can now be used to replicate the original double stranded DNA molecule.
When existing DNA strands are used as a template for new strands of DNA, it makes use of complementary base pairing as the split forms two complementary strands.
DNA replication is called semiconservative as each resulting DNA molecule is actually an “old” strand now paired with a “new” strand, therefore no DNA molecule is ever completely new.