DNA Structure and Replication

Mrs. Gamari

Oswald and Avery cont’d

Oswald and Avery

Experimental Evidence

Nucleic Acids

Compounds that contain phosphate and nitrogen in addition to carbon, hydrogen, and oxygen.

Examples of nucleic acids:DNARNA

DNA’s shape is often referred to as a “double helix”

1.8 meters of DNA must fit into the nucleus of human cells.

Since cells are so small, and the nucleus even moreso, the DNA must curl up and coil to fit into such a small space.

Think about curly hair vs. straight hair… when you pull at the piece of hair, it becomes straight and longer. When released, the piece of hair appears to get shorter when it curls up, taking up less space.

Structure of DNA

Long chain of repeating units called nucleotides.

A nucleotide has 3 main parts: 5-carbon sugar

Deoxyribose (DNA) or ribose sugar (RNA)

Phosphate group Nitrogenouse base

A, C, G, T/U

Science Aid: DNA Structure and Replication

scienceaid.co.uk/biology/genetics2/dna.html

A Nucleotide

DNA

DNA is double-stranded and its shape resembles a ladder.

The sides of the ladder are made up of repeating sugar and phosphate groups.

The rungs of the ladder are made of 2 bases bonded together by hydrogen bonds.

Latest from the Labs: Cells and DNA

info.cancerresearchuk.org/.../cellsanddna/

The DNA molecule needs to coil and fold-up so that it can fit into the small nucleus.

The Ladder The Double Helix

Base Pairing Rules

DNA has 4 different nitrogenous bases: adenine, guanine, cytosine, and thymine.

The bases always pair the same way in a DNA molecule…unless a mutation occurs.

Adenine always pairs with Thymine (2 H bonds) A-T

Cytosine always pairs with Guanine. (3 H bonds) C-G

Science Aid: DNA Structure and Replicationscienceaid.co.uk/biology/genetics2/dna.html

DNA is really a pattern of repeating nucleotides.

A DNA Sequence

http://68.90.81.6/ScienceTAKS/Integration/DNA%20&%20RNA.htm

Purines and Pyrimidines

Guardian Angels are Pure, with Two Wings

Orientation of Molecule

Antiparallel – Read strand 5’ to 3’. The other strand is oriented in the opposite direction with the 3’ end across from the 5’ end.

Concepts in Motion

Try it out!

Below is one strand of a DNA molecule

GATTACA

Determine the “complementary” strand of that same DNA molecule

Practice – use your “Nucleotide Kits” to build DNA molecules with complementary strands to the sequences below.

GTATAGCCAGAG

CTGTAGAGCTAGCAT

CGCCTAACTAGTTAGG

CHECK FOR UNDERSTANDING:

Name the 3 parts of a nucleotide.

Describe the structure of DNA using the ladder analogy.

Adenine pairs with __________ Guanine pairs with __________

DNA Replication

What does the term “replication” mean?

Why would the cell need to replicate its DNA?

Where does DNA replication take place?

Semiconservative Replication

Parental strands separate and serve as templates for new strands of DNA.

(Two new molecules of DNA are identical and each one has a new strand and an old strand)

Steps of Replication

DNA molecule unwinds with the help of enzyme.

Enzymes add complementary bases to build the new strands of DNA.

Enzymes seal the two strands (one old and one new) together.

Replication Process

DNA Replication Animation

Prokaryote and Eukaryote Replication

Replication Fork: location where DNA molecule is untwisted and the strands separate from one another.

How do prokaryote and eukaryote replication differ from one another?

DNA Replication

Honors Biology

Mrs. Gamari

DNA Replication

What does the term “replication” mean?

Why would the cell need to replicate its DNA?

Where does DNA replication take place?

Semiconservative Replication

Parental strands separate and serve as templates for new strands of DNA.

(Two new molecules of DNA are identical and each one has a new strand and an old strand)

Steps of Replication

DNA molecule unwinds with the help of enzyme.

Enzymes add complementary bases to build the new strands of DNA.

Enzymes seal the two strands (one old and one new) together.

Unwinding

DNA helicase – unwinds double helix (hydrogen bonds broken)

RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand

Base Pairing

DNA Polymerase adds the appropriate nucleotides to the new DNA strand according to the code of the template strand.

Nucleotides are added to the 3’ end of the new DNA strand. Extended/Built 5’ to 3’..

Leading strand (5’-3’) – strand is continuously built by the addition of nucleotides to the 3’ end towards the replication fork.

Lagging strand (3’-5’) – strand is discontinuously built. Elongates away from the replication fork. Small segments (Okazaki fragments ) are synthesized along template– could be 100 to 200 nucleotides long

Semidiscontinuous replication?

Replication Process

DNA Replication Animation

Advanced DNA Replication Animation

Joining

DNA polymerase removes the RNA primase.

DNA ligase links the segments/fragments together.

2 DNA molecules wind themselves back up into double helix

Prokaryote and Eukaryote Replication

Replication Fork: location where DNA molecule is untwisted and the strands separate from one another.

How do prokaryote and eukaryote replication differ from one another?

DNA Keychain Model Label original DNA molecule with 5’ and 3’ ends.

Label the leading/lagging strand. Mimic replication process by adding DNA

nucleotides continuously or discontinuously according to the strand.

Draw the correct number of hydrogen bonds between nitrogenous bases.

Label where covalent bonds are located. Draw key for your DNA model. Include bonds.