Photo 51 by Rosalind Franklin DNA Structure Replication

Photo 51 by Rosalind Franklin

DNA Structure & Replication The material of heredity

Overview Nucleic acids Nucleotide structure Types of nucleotides DNA structure Sugar-phosphate backbone Base pairs DNA vs. RNA DNA replication Leading strand Lagging strand Prokaryotic DNA replication

What are nucleic acids? Large, organic molecules (biomolecules) made of monomers called nucleotides

Recognize this picture?

Nucleotide Structure: Nitrogenous base Phosphate group Pentose sugar

Nucleotide Structure:

Types of Nucleotides:

Types of Nucleotides: This one is only in RNA

Types of Nucleotides: This one is only in RNA This one is only in DNA

DNA Structure X

DNA Structure The phosphate group is bonded to the sugar’s 5’ (five prime) carbon X

DNA Structure Another nucleotide adds on at the 3’ carbon The phosphate group is bonded to the sugar’s 5’ (five prime) carbon X

DNA Structure A phosphate group from another nucleotide binds to the 3’ carbon

DNA Structure A phosphate group from another nucleotide binds to the 3’ carbon This forms the sugarphosphate backbone

Purines bind to pyrimidines through Hydrogen bonds

Adenine binds to Thymine A T Guanine binds to Cytosine G C

Purines bind to pyrimidines through Hydrogen bonds These are complementary base pairs

Which base pair is stronger? A-T or G-C?

DNA Structure Summary DNA is a biomolecule composed of nucleotides Phosphate and sugar groups from different nucleotides bind together to form the sugar-phosphate backbone Base pairs from two complementary backbones are connected through hydrogen bonds This forms a double helix (twisted ladder) structure

DNA vs. RNA

DNA vs. RNA DNA: Deoxyribose RNA: Ribose

DNA vs. RNA DNA: RNA: Deoxyribose Ribose Thymine Uracil

DNA vs. RNA DNA: RNA: Deoxyribose Ribose Thymine Uracil Double-stranded Single-stranded* * usually. It can fold and form ds. RNA and viruses sometimes use ds. RNA

All of your cells have identical* copies of your DNA * mistakes and mutations happen

DNA Replication There is about 6 feet of DNA in every cell You started out as a single cell. . . how do all of your cells now have the same DNA?

DNA Replication 1. Helicase breaks H-bonds between base pairs and “unzips” DNA

DNA Replication 2. Primase lays down RNA primers (a short strip of RNA)

DNA Replication: Leading strand 3. DNA Polymerase sees the primer and knows to start working

DNA Replication: Leading strand 3. DNA Polymerase sees the primer and knows to start working 5’ 3’ It builds a new, complementary strand from 5’ to 3’ from the leading strand template

DNA Polymerase can only add nucleotides to the 3’ carbon

DNA Replication: Leading strand 3. DNA polymerase builds a new, complementary strand from 5’ to 3’ ?

DNA Replication: Leading strand 3. DNA polymerase builds a new, complementary strand from 5’ to 3’ 5’

DNA Replication: Leading strand 4. DNA Another DNA Polymerase (I) comes in to replace the RNA primer with 5. Ligase connects the primer-replacer to the rest of the strand

If DNA Pol can only synthesize 5’-3’. . . what about the other strand?

DNA Polymerase continuously building a new strand from 5’-3’ Helicase unwinding the DNA Primase making an RNA primer DNA Polymerase building 5’-3’ fragments called “Okazaki fragments”

DNA Replication: Lagging Strand The lagging strand is copied backward in short 5’-3’ segments These segments are called Okazaki fragments Everything else works the same as on the leading strand

Your book talks about Telomerase. You should read about it!. . . but I won’t test you on it.

DNA Replication in Prokaryotes have circular DNA This means they don’t need to do leading and lagging strands They also only have one place where replication starts. This is called the point of origin. Eukaryotes have many points of origin!

Do This Walkthrough! DNA Replication Walkthrough