Download Cell Division and Mitosis

DNA Structure and Function
Oak Ridge High School
Biology:
DNA Structure & Function
Chapter 10
Key Concepts:
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
DNA contains the information of heritable
traits in all cells
Discovery of DNA Function
Griffith’s experiments
Transfer of hereditary material from dead
S cells to living R cells
Evidence for DNA as The
Substance for Heredity
Radioisotope
incorporated into
protein and picked
up by
bacteriophage
Viral DNA inside
the cell picked up
radioisotope
Hershey – Chase
Experiment
 Bacteriophage viruses contain
DNA core and Protein outer coat
 Steps using RadioIsotopes
 Tag DNA-Phosphate
 Tag Protein-Sulfur
 Infection
 Blending
 Centrifugation
Only phosphate detected inside cells,
sulfur remains outside cell.
Therefore DNA is genetic material.
DNA Inside the Nucleus
A cells DNA is
contained inside the
cells nucleus.
Each chromosome is
a coiled mass if DNA
and protein.
The DNA molecule is
a tightly coiled double
helix.
Nucleotide Structure
 DNA helix is made up of
four bases, Adenine,
Guanine, Cytosine, &
Thymine.
 A nucleotide consists of a
phosphate, Sugar, &
Nitrogen base.
 These bases form a
“ladder” like structure
that is twisted.
DNA Structure
a Summary
Nucleotides
Deoxyribose
Phosphate Group
Nitrogen base
Purines
• Adenine A
• Guanine G
Pyrimidines
• Thymine T
• Cytosine C
Pairing
Arrangement
A - T
C – G
DNA Nucleotide
Sequence Codes for Alleles
 Look at the replication fork to
the right.
 The strand on the left reads
TGCCATCCTA……
 Each three base sequence is a
codon and codes for a specific
amino acid.
 If there was a different DNA of
the same species the same
sequence might read TGCAAT
CGTA…… and code for a
protein that would produce a
different allele.
DNA Structure Continued
 The DNA side groups are arranged in
alternating sets of phosphate and sugar
molecules. One side is 5’-3’ and the other
side is 3’ - 5’.
 Base pairs make up the rungs of the ladder
A—T and G– C. The genetic code is
arranged as sets of three base codes
together. For example AAA, CGC, ATC, CCC,
would all code for four different amino acids.
 Each gene and therefore allele has a
different sequence which codes for a
different protein that is expressed in the
organism; as the persons phenotype.
Central Dogma
 DNA can be replicated by
using one side of the
molecule as a template to
copy a new side.
 RNA, know as mRNA can
be transcribed from a
DNA strand. This mRNA
will then leave the
nucleus to find a ribosome
in the cytoplasm.
 mRNA coded message
can be translated into a
protein sequence.
DNA Replication
 Enzyme regulated
 Helicases unwind parent stand
 Binding proteins stabilize
complementary strands by breaking
hydrogen bonds between nitrogen base
pairs.
 DNA Polymerase enzymes bind to the
complementary strands and copy each
side of the original “old” strand in the 5’
- 3’ direction. Each strand acts as a
template for “new” base pairs to attach
according to base paring rules.
 DNA Ligase binds the new bases to the
old bases so that each strand is half old
and half new and are identical.
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
 In this replication fork the
helicases have unwind the
DNA.
 Binding proteins are
breaking the base pairs.
 DNA polymerase is copying
each strand; one side
continuous and the other in
smaller fragments.
 DNA ligase binds smaller
fragments together to
produce identical copies.
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
In Conclusion
 Enzymes unwind the two strands of DNA
and assemble a new strand during DNA
replication
 Resulting new DNA molecule has an old
strand and a new strand
 Some of the enzymes in DNA replication
also repair DNA

developed by M. Roig & S. Iverrson