DNA Structure and Function

1
DNA Structure and Function

• Oak Ridge High School
• Biology
• DNA Structure Function
• Chapter 10

2
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

3
Discovery of DNA Function

• Griffiths experiments
• Transfer of hereditary material from dead S cells
  to living R cells

4
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

5
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.

6
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.

7
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.

8
DNA Structurea Summary

• Nucleotides
• Deoxyribose
• Phosphate Group
• Nitrogen base
• Purines
• Adenine A
• Guanine G
• Pyrimidines
• Thymine T
• Cytosine C

• Pairing Arrangement
• A - T
• C G

9
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.

10
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 AT
  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.

11
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.

12
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.

13
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

14
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.

15
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

16
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