Nucleic Acid Structure

DNA and RNA

Where are Nucleic Acids located?

• In the nucleus– DNA stays – RNA can leave

Nucleus

DNA and RNA Structure

DNA• Double Helix• Nucleotide Strands

– Basic Building Block of DNA

– Composed of• Sugar (Deoxyribose)• Phosphate group• Base (A, T, G or C)

RNA• Single Strand• Nucleotide strands

– Basic Building Blocks of RNA

– Composed of• Sugar (Ribose)• Phosphate group• Base (A, U, G, or C

Create the appropriate nucleotides.

DNA and RNA

• Backbone– Alternating sugar and

phosphates

What are the bases?

Purines Pyrimidines

Place your nucleotides in two piles: purines and pyrimidines.

Which nucleotide are we missing? Why?

Which bases join together?

DNA

• A with T– Purine with pyrimidine

• G with C– Purine with pyrimidine

• How are they joined?– Hydrogen Bonds

• These strands are complements! Allowing for DNA replication to take place.

RNA

• Remember Single Strand

• RNA pairs with DNA– A (DNA) with U (RNA)– T (DNA) with A (RNA)– G (DNA) with C (RNA)– C (DNA) with G (RNA)

• How are they joined?– Hydrogen Bonds

Line Up

• 5’ to 3’– Antiparallel

Create your DNA strand.

Why?

DNA Replication

• Double Helix– Base pairs?

• Antiparallel?– 5’-3’– 3’-5’

• Replication is semi-conservative?

DNA Characteristics

Begin replication on your strand.

What has to happen first?

DNA Replication

Step 1Double Helix needs to be

unwound and unzippedCreates a replication

bubble / forkDNA Helicase

– What is that?

Creates a leading and lagging strandLeading – replication

occurs continuouslyLagging – occurs in

fragments called Okazaki fragments

Step 2How does replication know where to begin?

RNA Primase– Lays down a primer

RNA – ribonucleic acid (both oxygens, uracil instead of thymine, single strand)

• Step 3– DNA Polymerase

• Lays down complementary base pairs– 5’ 3’

» The replicated strand always starts from the phosphate end and replicates towards the sugar end.

• Continues until done

• Step 4– DNA Polymerase changes the RNA Primer to DNA

DNA Replication

• Step 5– Ligase comes in and fills the Okazaki

fragment gaps.

• What are we left with?

• Why do we call it semi-conservative again?

DNA Replication

Create a flow chart of DNA ReplicationStart from the very beginning.

Your sequence is– 5’-TGCACGAATG-3’

Create a Double Helix using that sequence– You have a template to trace from the picture handout I gave

youWhen you unwind make sure you show the structure of

each nucleotide– Use the template from the picture handout I gave you.

Make sure you show everything in detail of what is going on.

Make sure you have an explanation of what is going on under each picture.

Be neat and detailed.Due Tomorrow.

Your Turn