DNA Structure and replication
DNA Structure
 DNA (deoxyribonucleic Acid) carries the genetic code.
DNA Structure
 DNA (deoxyribonucleic Acid) carries the genetic code.
 Found in the chromosomes – it has a double helix
shape (like a twisted ladder)
DNA Structure
 DNA (deoxyribonucleic Acid) carries the genetic code.
 Found in the chromosomes – it has a double helix
shape (like a twisted ladder)
 The side strands are made of alternating sugar and
phosphate groups.
DNA Structure
 DNA (deoxyribonucleic Acid) carries the genetic code.
 Found in the chromosomes – it has a double helix
shape (like a twisted ladder)
 The side strands are made of alternating sugar and
phosphate groups.
 The ‘rungs’ are made of paired nitrogenous bases.
DNA Structure
 DNA (deoxyribonucleic Acid) carries the genetic code.
 Found in the chromosomes – it has a double helix
shape (like a twisted ladder)
 The side strands are made of alternating sugar and
phosphate groups.
 The ‘rungs’ are made of paired nitrogenous bases.
 Each strand of DNA is made of many repeating units
called nucleotides (a sugar, a phosphate, and a
nitrogen base)
DNA Structure
Phos
phate
Nitrogen base (any one of A, T, C, G)
Deoxyribose
Sugar
DNA Structure
 A always pairs with T (adenine and thymine)
 C always pairs with G (cytosine and guanine)
DNA Structure
 A always pairs with T (adenine and thymine)
 C always pairs with G (cytosine and guanine)
 The pairs are held together by weak hydrogen bonds
– therefore holding the 2 strands of DNA together.
DNA Structure
 A always pairs with T (adenine and thymine)
 C always pairs with G (cytosine and guanine)
 The pairs are held together by weak hydrogen bonds
– therefore holding the 2 strands of DNA together.
 The genetic code is the sequence of bases along one
strand – 3 bases = a triplet.
DNA Structure
 A always pairs with T (adenine and thymine)
 C always pairs with G (cytosine and guanine)
 The pairs are held together by weak hydrogen bonds
– therefore holding the 2 strands of DNA together.
 The genetic code is the sequence of bases along one
strand – 3 bases = a triplet.
 A triplet codes for a particular amino acid, and amino
acids together make proteins.
DNA Structure
 All the triplets that code for one complete protein
make up a gene.
DNA Structure
 All the triplets that code for one complete protein
make up a gene.
 Different sequences of bases along a gene can
produce proteins that are slightly different (eg. One
sequence would code for brown eyes, and one would
code for blue)
DNA Structure
 All the triplets that code for one complete protein
make up a gene.
 Different sequences of bases along a gene can
produce proteins that are slightly different (eg. One
sequence would code for brown eyes, and one would
code for blue)
 Different forms of a gene are called alleles.