Post on 19-Jan-2016
DNA Structure & Replication
Objectives
• To explain how instructions in DNA lead to different cells and result in cells being able to perform certain tasks in an organism
• Identify the building blocks and nitrogenous bases (A, T, G, C and U) of nucleic acids
Who Discovered DNA?• 1952 Rosalind Franklin-studied DNA molecule
using x-ray diffraction • 1953 Watson and Crick- developed double
helix model
What is DNA?
• Although the environment can influence how an organism develops, DNA determines the organism’s TRAITS.
• Determines the structure of the proteins.• Contains the instructions for LIFE!• DEOXYRIBONUCLEIC ACID!• Prokaryotic and Eukaryotic cells depend on
DNA to determine function.
What does DNA look like?
• DNA– Phosphate group
• One phosphorous atom• Four O2 atoms
– Deoxyribose (simple) sugar• Give DNA it’s name
– Nitrogenous Base• Adenine (A)• Guanine (G)• Cytosine (C)• Thymine (T)
DNA StructureNucleotides make up the DNA Each nucleotide is held together by hydrogen bonds!Hydrogen bonds are easily broken.
DNA Structure
• Double Helix • Twisted ladder structure • Sides have alternating
phosphate sugar groups• “Rungs of a DNA ladder”“Chargoff’s rule”
A = T & C = G(Complementary
Base Paring)
DNA Replication
• DNA must be copied before the cell can divide (mitosis or meosis)
• Without replication, new cells would only have ½ the DNA of their parents.
• Survival, growth, and reproduction would be impossible
• Prokaryotic and Eukaryotic cells depend on DNA replication to ensure each daughter cell will receive same genetic instruction as parent cell.
• Because of base pairing, we can predict the sequence of bases on a different strand.
• During replication, each strand serves as a template (or pattern)
• Enzymes break apart the DNA at the hydrogen bonds.
• The old strand is paired with each complementary base generating a complementary strand.
• DNA runs 3” to 5” (leading strand) ; DNA replicates 5” to 3” (lagging strand)
https://www.youtube.com/watch?v=27TxKoFU2Nw
Why does sequence matter?
• The sequence of nucleotides creates the specific genetic information.
• Different sequence = different function.
• ATTGAC is not the same as TCCAAA.• The closer a sequence is related to another,
the more similar the organisms are to one another
Knowledge Check
• What is DNA?• DNA determines an organism’s ____________• What does DNA stand for?• What are the 4 nitrogenous bases?• Pair the following nitrogenous bases with their
matching bases: AAAT CGATATC TTCCGCT