DNA Structure and Function
Starr/Taggart’s
Biology:
The Unity and Diversity of Life,
Chapter 13
9e
Key Concepts:
• DNA contains the information of heritable
traits in all cells
• Each DNA strand consists of two strands of
nucleotides twisted together
• Hereditary information is encoded in the
sequence of nucleotides
• Nitrogen bases have specific pairing
arrangements
• DNA is replicated before a cell divides
Discovery of DNA Function
• Fred Griffith - Discovered hereditary
transformation
Discovery of DNA Function
• Griffith’s experiments
• Transfer of hereditary material from dead S
cells to living R cells (transformation)
DNA Structure
• Pairing
Arrangement
• Nucleotides
• Deoxyribose
• Phosphate Group
– A-T
• Nitrogen base
– C–G
– Adenine
A
– Guanine
G
– Thymine
T
– Cytosine
C
Amount of A=T and
C=G
Rosalind Franklin
Fig. 13.8, p. 220
James Watson and Francis Crick
1
6
2
7
13
14
19
20
3
8
4
9
15
10
16
21
22
5
11
12
17
18
X
Y
Fig. 13.1, p. 214
Structure of DNA
• DNA consists of two strands of
nucleotides held together at bases by
hydrogen bonds
– A=T and C=G
• The two strands twist into a double
helix.
• The two strands run in opposite
directions (anti-parallel)
– Each strand runs in a 5’ to 3’ direction
2-nanometer diameter, overall
distance between each pair
of bases = 0.34 nanometer
each full twist of the
DNA double helix =
3.4 nanometers
Fig. 13.7, p. 219
Unlocking the Secret to Heredity
• The structure of DNA allows for one strand
to act as a template for the other strand
– If you have one strand you automatically
know the sequence of base pairs for the other
strand.
• ACGCGCT
• TGCGCGA
Semi-conservative Replication
• DNA Replication is semi-conservative
• There are 3 enzymes that are used for
replicating a new strand of DNA
– Helicase
– DNA polymerase
– Ligase
Click to view
animation.
animation
DNA Replication and Repair
• Enzyme regulated
– Hydrogen bonds
break
– Attachment of
nucleotides to new
strands
– DNA polymerases
DNA ligases
– New strand is half
old, half new
Detailed Look at Replication
• Nucleotides can only be added in the 5’
to 3’ direction
• Leading Strand assembly is continuous
• Lagging strand discontinuous
Creating Clones
• Dolly the sheep was first mammal to be
cloned from a differentiated cell
– Nucleus from sheep udder cell was
transferred into enucleated unfertilized
egg
– Egg grew into sheep by mitotic divisions
• Mice and cows have now also been
cloned from adult cells
In Conclusion
• Hereditary information is located in DNA
• DNA consists of nucleotides
• DNA molecule consists of two nucleotide
strands twisted into a double helix
• The bases of DNA strands pair in a constant
fashion
• DNA of one species has specific nucleotide
sequences