The Components and Structure of DNA

DNA
– deoxyribonucleic acid
 Deoxyribose – simple sugar in DNA
 DNA is made up of nucleotides
 Nucleotide
– made of simple sugar, phosphate and a nitrogen base

4 Nitrogen Bases in DNA
1. adenine
purines – double ring
2. guanine
3. cytosine
pyrimidines
– single ring
4. thymine
 Nucleotides join together to form long chains

Phosphate and deoxyribose form the backbone of the chain (sides of the ladder)
 Nitrogen bases for the steps of the ladder
 The amount of adenine equals thymine

The amount of guanine equals cytosine
Phosphate
Hydrogen Bond
Deoxyribose
Nitrogen Base
Nucleotide
1

History of DNA

Rosalind Franklin and Maurice Wilkins worked on the structure of DNA based on xray crystallography (pictures of DNA by x-rays).
 James Watson and Francis Crick were also working on the structure of DNA
 These scientists were trying to be the first to discover and prove the structure of
DNA because they knew it would be one of the most important discoveries in the
20 th century.
 1953 Watson and Crick proposed that DNA is made of two chains of nucleotides joined together by nitrogen bases
 two bases are held together by hydrogen bond
 two strands are complementary

complementary base pairing
 A and T
 C and G
 DNA is shaped in a double helix
A-A-G-C-T-T-G-C-C-A-T-C-A-G-T-G-G-A-C-G-T-A-C-C-G-T-
The Importance of Nucleotide Sequences
 All living organisms are composed of A, T, C, G
 How can organisms be so different from each other if their genetic material is made of the same four nucleotides?
 Differences in organisms are from the sequence of the four different nucleotides and how many nucleotides

The closer the relationship between two organisms the greater the similarity in their order of DNA nucleotides
 Scientists use nucleotide sequences to:

Determine evolutionary relationships among organisms
 Determine whether two people are related
 Determine if DNA from a crime scene matches the DNA of a suspected criminal
Replication of DNA
 Before a cell can divide by mitosis or meiosis it must first make a copy of its chromosomes
 DNA Replication
– DNA is copied

All organisms undergo replication
How DNA Replicates
 During replication each strand serves as a pattern to make a new DNA molecule
 The end result is the formation of two DNA molecules that are identical (duplicated chromosome)
2


Steps of Replication
1. Enzyme, DNA helicase, breaks the hydrogen bonds between nucleotides, this
“unzips” the DNA molecule
2. Free nucleotides in the nucleus bond to the single strands. Enzyme, DNA polymerase glues the new strands together.
3. This continues until the entire molecule has been unzipped and replicated
4. Each new strand formed is a complement of one of the originals or parent strand.
5. Two DNA molecules that are identical
6. Proofreading enzymes check the strand for mistakes and repair enzymes fix any mistakes that occur
3

The Components and Structure of DNA
 DNA –
 Deoxyribose –
 DNA is made up of _______________
 Nucleotide –

4 Nitrogen Bases in DNA
1.
purines
–
2.
1.
pyrimidines
–
2.

Nucleotides join together to form long chains
 _______________ and _______________ form the backbone of the chain (sides of the ladder
 ____________ ____________ are the steps of the ladder

The amount of _______________ equals _______________
 The amount of _______________ equals _______________
4

History of DNA

Rosalind Franklin and Maurice Wilkins worked on the structure of DNA based on xray crystallography (pictures of DNA by x-rays).
 James Watson and Francis Crick were also working on the structure of DNA
 These scientists were trying to be the first to discover and prove the structure of
DNA because they knew it would be one of the most important discoveries in the
20 th century.
 1953 Watson and Crick proposed that DNA is made of two chains of nucleotides joined together by nitrogen bases


 complementary base pairing


 DNA is shaped in a ____________ ____________
DNA A – A –G –C –T –T –G –C –C –A –T –C –A –G –T –G –G –A –C
The Importance of Nucleotide Sequences

 How can organisms be so different from each other if their genetic material is made of the same four nucleotides?
 Differences in organisms are from the _______________ of the four different nucleotides and how _______________ nucleotides
 The closer the relationship between two organisms the greater the similarity in their order of DNA nucleotides
5


Scientists use nucleotide sequences to:
 Determine ___________________ relationships among organisms
 Determine whether two people are __________________
 Determine if DNA from a crime scene _____________ the DNA of a suspected criminal
Replication of DNA
 Before a cell can divide by mitosis or meiosis it must first make a copy of its chromosomes
 DNA Replication –

All organisms undergo replication
How DNA Replicates

During replication each strand serves as a pattern to make a new DNA molecule
 The end result is the formation of 2 DNA molecules that are _______________
(duplicated chromosome)
 Steps of Replication
1. Enzyme _______ ____________, breaks the hydrogen bonds between nucleotides, this “__________” the DNA molecule
2. Free _______________ in the nucleus bond to the single strands. Enzyme,
_______ ____________ glues the new strands together.
3. This continues until the entire molecule has been unzipped and replicated.
4. Each new strand formed is a _______________ of one of the originals or parent strand.
6

5. Two DNA molecules are ________________
6. ________________ enzymes check the strand for mistakes and ____________ enzymes fix any mistakes that occur
7

8

9