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
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