Topic: DNA Date: February 8, 2013

DNA structure and function and replication

Objective

SWBAT-Explain the key structural features of DNA as well as DNA’s function.

-Explain the key steps of DNA replication

Warm up

From yesterday’s lesson,

1. What are two things you learned about DNA’s structure?

2. What’s one thing that you found interesting?

The Structure and

Function of DNA

Prokaryotic cells lack a true nucleusExample: bacteria and archaea

Eukaryotic cells have a nucleus surrounded by a nuclear membraneExamples: ALL cells except bacteria and Archaea

These areas contain DNA

Instead it’s in the Nucleoid

I. DNA stands for DeoxyriboNucleic Acida. Deoxyribose= sugarb. Nucleic = located in the nucleus or

nucleoid (free floating in prokaryotes) c. Acid= acidic in nature

2. DNA is…a. found in the nucleus of the cellb. the genetic material in each cellc. the chemical that processes and determines

which proteins will be made by the cell.

3. DNA is made up of nucleotidesA. 5 Carbon sugar called deoxyriboseB. Phosphate groupC. One of 4 nitrogen bases

1. Adenine=A2. Thymine=T3. Cytosine=C4. Guanine=G

Many, many nucleotides make up a single DNA molecule

Types of Bases Purine-have two rings of carbon and

nitrogen atoms– Adenine– Guanine

Pyrimidine-have one ring of carbon and nitrogen atoms– Cytosine– Thymine

*Nucleotides are connected by attachment of the deoxyribose and the phosphates

4. DNA is in the form of a double helixa. The sides of the helix/ladder are the

alternating phosphate groups and deoxyribose sugars

b. The rungs are paired nitrogen bases

*Only certain nitrogen bases can pair up with each other:

Adenine pairs with thymine Cytosine pairs with guanine

C. The base pairs of the rungs (A-T& C-G) are held together by hydrogen bonds that are easily broken.

Label:Deoxyribose

Phosphatecytosine

guanine

thymine

adenine

Hydrogen bond

nucleotide

Write the letters for the matching nucleotides on the strand of DNA.

*Remember, Adenine always pairs with Thymine. Cytosine always pairs with Guanine.

ATTATACGTAGCTAGCTGATCGATCG TAATATGCATCGATCGACTAGCTAGC

The Functions of DNA

1. DNA contains the genetic message

(Morse Code) to be passed on to the next generation.

2. DNA is the template for RNA which is the template for proteins that determine a living organism’s traits.

3. DNA must replicate (for mitosis and meiosis)

A segment of DNA that codes for a specific trait is called a gene.

This is Gene.

The players

Helicase-separate nucleic acid strands DNA Polymerase I-can add new nucleotides to the 3’ end

of DNA, also replaces RNA primer with DNA in lagging strand

DNA Ligase-repairs single strand discontinuities RNA Primase-an enzyme that synthesizes short RNA

sequences called primers. These primers serve as a starting point for DNA synthesis by adding a 3’ starting point.

DNA Polymerase III-adds nucleotide from RNA primer to RNA primer (from the 3’ added by the RNA primase to the next primer)

DNA replication:Before a cell can divide, the

DNA must replicate.1.The hydrogen bonds holding

the bases together are broken

by Helicase (DNA is now single stranded.)

2. DNA polymerase III (an enzyme)

attaches the complementary base

pairs to the leading strand

3. On the lagging strand, DNA primase adds short RNA primers that provide a 3’ end

4. DNA Polymerase III adds nucleotides from the 3’ end of the RNA primer towards the next primer

5. DNA Polymerase I replaces DNA Polymerase III, and replaces the RNA primers with DNA nucleotides

6. Gaps between the 3’ and 5’ends of nucleotides are sealed by ligase

DNA Animation

://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork .swf

This is called semi-conservative

Replication.Original DNA

New DNA

1. 2. 3.

Original DNA

*DNA “unzips”•New bases attached with help of DNA polymerase.

Two Identical strands

Replicate this DNA strand:

C A T C A T C A T T A G T A G

G T A G T A G T A A T C A T C