DNA

(Deoxyribonucleic Acid)

Genetic material of cells…

• GENES – units of genetic material that

CODES FOR A SPECIFIC TRAIT

• Called NUCLEIC ACIDS

• DNA is made up of repeating molecules

called NUCLEOTIDES

DNA Nucleotide

O

O=P-O

O

Phosphate

Group

N Nitrogenous base

(A, G, C, or T)

CH2

O

C1 C4

C3 C2

5

Sugar

(deoxyribose)

A HISTORY OF DNA

• Discovery of the DNA 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)

Watson & Crick proposed…

•DNA had specific pairing between the

nitrogen bases:

ADENINE – THYMINE

CYTOSINE - GUANINE

•DNA was made of 2 long stands of

nucleotides arranged in a specific

way called the “Complementary Rule”

DNA Double Helix

Nitrogenous

Base (A,T,G or C)

“Rungs of ladder”

“Legs of ladder”

Phosphate &

Sugar Backbone

DNA Double Helix

P

P

P

O

O

O

1

2 3

4

5

5

3

3

5

P

P

P O

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Nitrogenous Bases

• PURINES

1. Adenine (A)

2. Guanine (G)

• PYRIMIDINES

3. Thymine (T)

4. Cytosine (C) T or C

A or G

Chargaff’s Rule

• Adenine must pair with Thymine

• Guanine must pair with Cytosine

• Their amounts in a given DNA molecule will be

about the same.

G C T A

BASE-PAIRINGS

C G

H-bonds

T A

Genetic Diversity… • Different

arrangements of

NUCLEOTIDES in a

nucleic acid (DNA)

provides the key to

DIVERSITY among

living organisms.

The Code of Life…

• The “code” of the chromosome is the

SPECIFIC ORDER that bases occur.

A T C G T A T G C G G…

DNA is wrapped tightly around

histones and coiled tightly to form

chromosomes

DNA Replication • DNA must be copied

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

A-T, G-C

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

DNA Replication

• Semiconservative

Model:

1. Watson and Crick

showed: the two strands

of the parental molecule

separate, and each

functions as a template

for synthesis of a new

complementary strand.

. Parental DNA

DNA Template

New DNA

1. Why is replication necessary?

2. When does replication occur?

3. Describe how replication works.

4. Use the complementary rule to

create the complementary strand:

A---?

G---?

C---?

T---?

A---?

G---?

A---?

G---?

C---?

A---?

G---?

T---?

Replication Quiz

(1961) Watson & Crick proposed…

• …DNA controlled cell function by serving as a template for PROTEIN structure.

• 3 Nucleotides = a triplet or CODON

(which code for a specific AMINO ACID) See p.303

• AMINO ACIDS are the building blocks of proteins.

DNA Transcription

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

• Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids.

DNA Translation

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

We will

discuss details

of this on a

later date

Transcription/Translation Quiz 1. Why is transcription necessary?

2. Describe transcription.

3. Why is translation necessary?

4. Describe translation.

5. What are the main differences

between DNA and RNA.

AMAZING DNA FACTS…

• DNA from a single human

cell extends in a single

thread for almost 2 meters

long!!!

• It contains information

equal to some 600,000

printed pages of 500 words

each!!!

(a library of about 1,000 books)

LET’S REVIEW DNA…

1. List the conclusions Griffith & Avery,

Hershey & Chase drew from their

experiments.

2. Summarize the relationship between

genes & DNA.

3. Describe the overall structure of the

DNA molecule.

4. What are the 4 kinds of bases?