DNA Structure and Replication replication replication Building block

DNA Structure and Replication, replication, replication

Building block of DNA the Nucleotide • 1 phosphate • 1 deoxyribose sugar • 1 of 4 nitrogen bases • • Adenine A Thymine T Cytosine C Guanine G

The back bone of the DNA Ladder • Sides of the DNA Ladder are made of: • Phosphate molecules • Deoxyribose sugars: five sided sugars missing one oxygen

Number the carbons • The carbons in the deoxyribose sugar are numbered clockwise. The phosphodiester bond occurs between the 5’ carbon of one sugar and the 3’ carbon of the next sugar.

Linkage • This back bone of DNA is linked together by strong covalent bonds called Phosphodiester bonds. This is done by removing a water molecule

Antiparallel Strands in the Double Helix • The rungs of the ladder are nitrogen base pair. • To ensure they are pointing towards the middle • The sides of the ladder are going in opposite directions. • This is called antiparallel. • Look at the #s on the carbons at • the end of each strand. • We call this the three prime 3’ end • And a five prime 5’ end.

The rungs of the ladder complimentary • The rungs of the DNA double helix are held together by weak hydrogen bonds. They are easily made and easily broken. • G always pairs with C • 3 h-bonds • A always pairs with T • 2 h-bonds • This is called complimentary base pairing • A & G have 2 rings (Purines) and C&T have 1 ring (Pyrimidines) • This ensure that the rungs of the ladder are always 3 rungs wide

Now you know • DNA Deoxyribonucleic acid is: • Double helix • Antiparallel • And complimentary • Soon you will also learn… • It is semi conservative.

Replication Make new friends but keep the old one is silver and the other gold • DNA has 2 things that it can do: • Copy itself • Make proteins Replication Protein synthesis • Replication is semi-conservative. DNA uncoils and each of the old strands makes a new complimentary copy.

Enzymes the body’s workers • Every step of the DNA replication is helped by and enzyme. • Enzymes are proteins that speed up reactions. They end in “-ase”. 1. Helicase Unwinds the double helix by breaking the hydrogen bonds

2. Binding proteins hold the replication fork open

3. Primer is attached to 3’end and provides a place for polymerase to attach.

4. Polymerase • Just for fun here’s what it looks like.

Polymerase can extend the new DNA strand by adding free floating base pairs to the 3’ end.

Polymerase can also proof read and fix mistakes

Leading strand lagging strand. • Because Polymerase can only add to a 3’ end one side of the DNA is copied in a continuous strand. This is the leading strand. • The other side has to restart over and over as the DNA uncoils. • laying down a new primer and a short piece of DNA each time. • It looks like a dotted line. This is the lagging strand the pieces are Okazaki fragments.

5. Ligase • Ligase follows along after polymerase. • It makes the phosphodiester bonds in the back bone. • It and ties the Okazaki Fragments together on the lagging strand. • Here it is in a nut shell.

Tah Dah! Make new friends but keep the old one is silver and the other gold Semi conservative: Each new strand of DNA Keeps one old parent strand Makes one new daughter strand

Here it is again