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