DNA(Deoxyribonucleic Acid)

A HISTORY OF DNAA HISTORY OF DNA

• Discovery of the DNA double helixDNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.(1952)

C. Watson and Crick - described the DNA molecule from Franklin’s X-ray.(1953)

DNA History

• Avery – Discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation to the next.

More DNA History

• Hershey-Chase – Concluded that the genetic material in bacteria was DNA not proteins

• Watson & Crick – created the double helix model for DNA.

Structure of DNA

• DNA is a long molecule made up of units called nucleotides.

• Each nucleotide is made up of three parts: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base (Nitrogen Containing).

• The backbone of DNA is formed by sugar and phosphate groups of the nucleotide.

• The nitrogenous base stick out from the sides and can be joined together in any order, meaning that any sequence of bases is possible.

DNA NucleotideDNA Nucleotide

OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

DNA Double HelixDNA Double Helix

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

DNA Double HelixDNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Nitrogenous BasesNitrogenous Bases

• PURINESPURINES

1. Adenine (A)Adenine (A)

2. Guanine (G)Guanine (G)

• PYRIMIDINESPYRIMIDINES

3. Thymine (T)Thymine (T)

4. Cytosine (C)Cytosine (C) T or C

A or G

Chargaff’s Rules

• Chargaff discovered how the nitrogenous bases bond together.

• He discovered that Adenine always bonds with Thymine and that Cytosine always bonds with Guanine.

BASE-PAIRINGSBASE-PAIRINGS

CG

H-bonds

T A

Genetic Diversity…Genetic Diversity…• Different Different

arrangements of arrangements of NUCLEOTIDESNUCLEOTIDES in a in a nucleic acid (DNA) nucleic acid (DNA) provides the key to provides the key to DIVERSITYDIVERSITY among among living organisms.living organisms.

The Code of Life…The Code of Life…

• The “code” of the chromosome is the The “code” of the chromosome is the SPECIFIC ORDERSPECIFIC ORDER that bases occur. that bases occur.

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

DNA is wrapped tightly around histones and coiled tightly to form

chromosomes

DNA DNA ReplicationReplication• DNA must be copiedDNA must be copied

• The DNA molecule produces The DNA molecule produces 2 2 IDENTICALIDENTICAL new complementary new complementary strands following the rules of strands following the rules of base pairing: base pairing:

A-T, G-CA-T, G-C

•Each strand of the Each strand of the original DNA serves as original DNA serves as a template for the new a template for the new strand strand

DNA Replication

• During DNA replication, the DNA molecule separates into two strands, then produces two new complimentary strands following the rules of base pairing (Chargaff Rules). Each strand of double helix of DNA serves as a template, or model, for the new strand.

How It Occurs

• DNA replication is carried out by a series of enzymes.

• The enzymes unzip the DNA molecule creating two strands that serve as templates.

• Complimentary bases are added to the strands, for example a strand of DNA with the bases ATTCGAG would have a complimentary strand of TAAGCTC.

Replication Continued

• Each new DNA molecule has one new stand and one strand from the original molecule.

• The enzyme DNA polymerase, the principal enzyme, “proofreads” the new DNA strands, helping to maximize the odds that each molecule is a perfect copy of the original.

Use the complementary rule to create the complementary strand:

A---?G---?C---?T---?A---?G---?A---?G---?C---?A---?G---?T---?

Use the complementary rule to create the complementary strand:

A---TG---CC---GT---AA---TG---CA---TG---CC---GA---TG---CT---A

DNA DNA Transcription OverviewTranscription Overview

• DNA can “unzip” DNA can “unzip” itself and itself and RNARNA nucleotides match nucleotides match up to the DNA up to the DNA strand.strand.

• Both DNA & RNA Both DNA & RNA are formed from are formed from NUCLEOTIDESNUCLEOTIDES and and are called are called NUCLEICNUCLEIC acids.acids.

Transcription – Step I

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

Template DNA Strands

Transcription – Step II

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

Template DNA is Matched Up with Complementary mRNA Sequences

Transcription – Step III

mRNA leaves nucleus and goes to ribosomes

U G C A U A G C G C A U

A C G U A U C G C G U A

DNA DNA Translation OverviewTranslation Overview

• The cell uses The cell uses information from information from “messenger” RNA “messenger” RNA to produce proteinsto produce proteins

tRNA structure

• 3-base code (triplet) is an “anticodon”

• Attached amino acid that is carried from cytoplasm to ribosomes

• Amino acids make up the protein

Prokaryotes & DNA

• In prokaryotes, DNA molecules are located in the cytoplasm of the cell.

• Most prokaryotic DNA is a single circular molecule that contains nearly all the cell’s genetic information.

Eukaryotes & DNA

• Many eukaryotes have 1000 times as much DNA as prokaryotes.

• DNA is located in the nucleus in the form of chromosomes.

• Chromosomes are DNA wound tightly around proteins called histones.

AMAZING DNA FACTS…AMAZING DNA FACTS…

• DNA from a single human DNA from a single human cell extends in a single cell extends in a single thread for almost 1-2 meters thread for almost 1-2 meters long!!!long!!!

• It contains information It contains information equal to some 600,000 equal to some 600,000 printed pages of 500 words printed pages of 500 words each!!! each!!! (a library of about 1,000 books)(a library of about 1,000 books)

DNA Length

• E. Coli have about 4,639,221 base pairs. It is about 1.6mm in length. This sounds small until you realize the bacteria is only 1.6µm in diameter.

• Thus DNA must be wrapped tightly to fit into cells. Imagine fitting 900 feet of rope into a backpack.