Goal 2 - DNA and DNA Replication Notes
DNA - Why is it Important?
Discovery of the DNA double helix - ladder that has been twisted into a spiral
A. 1950’s
B. Rosalind Franklin - X-ray photo of DNA.
C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.
- DNA - genetic material passes from generation to generation.
- DNA - controls cellular activities by controlling the production of proteins and enzymes
- DNA - determines an organisms traits.
- DNA - holds the information for life.
Discovery of the DNA double helix - ladder that has been twisted into a spiral
A. 1950’s
B. Rosalind Franklin - X-ray photo of DNA.
C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.
What is DNA?
What is DNA?
Deoxyribonucleic Acid (DNA)
Nucleotide:
Phosphate group
5-carbon deoxyribose sugar
Nitrogenous base
Deoxyribonucleic Acid (DNA)
- DNA molecules are large made up of thousands of repeating units called nucleotides.
Nucleotide:
Phosphate group
5-carbon deoxyribose sugar
Nitrogenous base
Nitrogen Bases in DNA
Nitrogenous Bases
PURINES
BASE-PAIRINGS
Purines Pyrimidines Pairs
Adenine (A) Thymine (T) A = T
Guanine (G) Cytosine (C) C = G
Chargaff’s Rule
Adenine must pair with Thymine
Guaninemust pair with Cytosine
PURINES
- Adenine (A)
- Guanine (G)
- Thymine (T)
- Cytosine (C)
BASE-PAIRINGS
Purines Pyrimidines Pairs
Adenine (A) Thymine (T) A = T
Guanine (G) Cytosine (C) C = G
Chargaff’s Rule
Adenine must pair with Thymine
Guaninemust pair with Cytosine
- Their amounts in a given DNA molecule will be about the same.
DNA Structure
Antiparllel Double Helix
Complementary
Information
- Double Helix Model - developed by Watson and Crick
- DNA molecule made up of 2 connected chains of nucleotides forming a ladder-like structure.
- Side of ladder are made of alternating phosphate and deoxyribose molecules.
- Rung of ladder made up of pair of nitrogen bases bonded by hydrogen bonds.
Complementary
- Because the bases pair together in only one way, the two strands of a DNA molecule are complementary.
- If you know the order of the bases in one strand - you also know the order in the second.
Information
- Contained in the linear sequence of the bases in the polynucleotide chain
- DNA for all organisms has same structure, but difference sequences = different information
- A+T or G+C are different for different species
DNA Replication
DNA Replication
DNA Replication - Steps
Synthesis of new DNA
DNA Synthesis in both Strands
Semiconservative Model:
DNA Repair - Excision (cut) repair:
- DNA - can make EXACT copies of itself in a process called replication.
- Replication occurs during the process of mitosis and meiosis.
- Replication occurs for growth and repair
DNA Replication - Steps
- Enzyme breaks hydrogen between bases
- DNA helix unwinds - two strands separate (unzip)
- Free nucleotides from the cytoplasm enter the nucleus, where they bond to complementary bases on the DNA strands.
- Result - two identical DNA molecules that are EXACT copies of the original.
Synthesis of new DNA
- New DNA is synthesized by adding one nucleotide at a time
DNA Synthesis in both Strands
- Enzyme only works from 5’ to 3’
- Antiparallel - one goes 5’ to 3’; the other goes 3’ to 5’.
- New synthesis has to go in opposite directions.
Semiconservative Model:
- Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.
DNA Repair - Excision (cut) repair:
- Damaged segment is excised (cut) by a repair enzyme (there are over 50 repair enzymes).
- DNA polymerase and DNA ligase replace and bond the new nucleotides together.