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CHAPTER 4:CHAPTER 4:Expression Of Biological Expression Of Biological

InformationInformation(6 Hours)(6 Hours)

CHAPTER 4:CHAPTER 4:Expression Of Biological Expression Of Biological

InformationInformation(6 Hours)(6 Hours)

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CHAPTER 4:EXPRESSION OF BIOLOGICAL INFORMATION

4.1 DNA and Genetic Information (2 hrs)

4.2 DNA Replication (2 hrs)

4.3 Protein Synthesis (1½ hrs)

4.4 Lactose Operon (30 mins)

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4.1 DNA & Genetic Information

4.1.1 DNA structure – Watson and Crick Model4.1.2 DNA– as the carrier of genetic information4.1.3 Gene concept; one gene one polypeptide

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4.1: DNA Structure- Watson & Crick Model

DNA is a double-stranded polymer.

Each DNA molecule has 2 bonding:-

1) Phosphodiester linkage - has strong covalent bond.

2) Hydrogen bonding- maintained the helix shape- linked the 2 nitrogenous bases

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Nucleic Acid DNA RNA

Each nucleotide consists of:1 phosphate group

1 pentose sugar 1 organic/nitrogenous base

2 types of pentose sugar: Ribose : RNA Deoxyribose : DNA

DNA Structure

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There are 4 types of organic bases for DNA:-Purines ( double ringed structure ) Adenine (A) Guanine (G)

2. Pyrimidine ( two single ringed structure ) Cytosine (C) Thymine (T)

Adenine = ThymineGuanine = Cytosine

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DNA structure – Watson & Crick Model (Nobel Laureate)

Consist of 2 polynucleotide chains.Anti-parallel (opposite direction).Both chain are linked to the other by pairs of organic bases which are themselves joined by hydrogen bonds.

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O

CH2

Base

O P OH

O

OH

OH

1

23’

4

5’

• Phosphate group

• Pentose Sugar (5C)

• Organic Bases

Nucleotide Basic Structure

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DNA

DNA molecule structure

5`

oP

oP

oP

oP

P

o

P

o

P

o

P

o

C

T

G

A

A

T

G

C

5` 3`

3` Hydrogen bond

phosphodiester linkageHydrogen bond

10BASIC STRUCTURE OF DNA

11BASIC STRUCTURE OF DNA

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IF…….

So…

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DNA as the carrier of genetic information Characteristic that are required of genetic material, can be

able to: store information

replicate, in order to be in each cell of growing organism

control expression of traits

Encode the sequence of proteins

Change in a controlled away, in order to ensure survival of a species in a changing environment

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• There are experiments that were conducted to prove that DNA is the genetic material.

Griffith Experiment (1931)Hereditary Information Can Pass between

Organisms

Avery, MacLeod & McCarty Experiment (Avery et. al.(1944))

Find out that the transforming agent is the DNA

Beadle and Tatum Experiment (1941)Gene Concept : One gene One polypeptide

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The Griffith Experiment Discovery of Transformation  

Griffith injected mice with various strains of bacteria

Streptococcus pneumoniae (known as pneumococcus)• Virulent, coated bacteria (Smooth form) lethal to

mice  • Non-virulent, coatless strain (Rough form) not

lethal  • Coat necessary for infection  

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Wild type

Smooth, virulent

(IIIS)

Mutant type

Rough, non-virulent

(IIR)

Symbol of bacteria

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TRANSFORMATION (1931 F. GRIFFITH)

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Observation :

Conclusion: Living R cells are converted to S cells Transformation occurred

Question:• Was the “transforming agent” protein or DNA, or

what?

ControlsLiving S (smooth) cells + mouse = mouse deadLiving R (rough) cells + mouse = mouse healthy

Heat-killed S cells + mouse = mouse healthy

CombinationsHeat-killed S cells + Living R cells + mouse

= mouse dead

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-prove that the transforming principle is DNA

- Use purified DNA from types S (smooth) and was treated with:

* DNase : break down DNA* RNase : degrades RNA* Protease : degrades protein

The Avery et. al. Experiment

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Experiments carried out by Avery et. al.

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Conclusion:

The “transforming agent” was in fact DNA