DNA

Composed of deoxyribose sugar, phosphate and base

Connect the sugar (deoxyribose) with the phosphate of two nucleotides together foriming the sugar-phosphate backbone of dna strand

Weak bond that joins complimentary bases on opposite sides of dna

Marks the end of a dna strand. Has either a deoxyribose sugar (3’) or phosphate (5’) at the end forming a double helix

Structure of DNA — nucleotides (deoxyribose sugar, phosphate and base), sugar–phosphate backbone, base pairing (adenine–thymine and guanine–cytosine), by hydrogen bonds and double stranded antiparallel structure, with deoxyribose and phosphate at 3’ and 5’ ends of each strand respectively, forming a double helix.

The base sequence of DNA forms the genetic code.

Prior to cell division, DNA is replicated by a DNA polymerase. DNA polymerase needs primers to start replication. A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add DNA nucleotides.

DNA polymerase adds DNA nucleotides, using complementary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming, ie in the 5’ to 3’ direction

DNA is unwound and hydrogen bonds between bases are broken to form two template strands. DNA polymerase can only add DNA nucleotides in one direction resulting in the leading strand being replicated continuously and the lagging strand replicated in fragments.

Fragments of DNA are joined together by ligase.

Strand of dna which is replicated continuously from 3’ to 5’ end

Strand of dna which is replicated in fragments from 3’ to 5’ end

Polymerase chain reaction (PCR) amplifies DNA using complementary primers for specific target sequences.

• DNA is heated to between 92 and 98°C to separate the strands. • It is then cooled to between 50 and 65°C to allow primers to bind to target sequences. • It is then heated to between 70 and 80°C for heat-tolerant DNA polymerase to replicate the region of DNA. Repeated cycles of heating and cooling amplify the target region of DNA.

PCR can amplify DNA to help solve crimes, settle paternity suits and diagnose genetic disorders.

In PCR, primers are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified.

A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add DNA nucleotides