BIOLOGICAL MOLECULES 3

Chemical tests and Nucleic acids

Jorge Melo

Monosaccharides

Disaccharides

Polysaccharides

Recap

What name is given to the carbohydrate in which n is 6 5 3

State 2 different functions of the carbohydrates

Simple carbohydrates are combined to form disaccharides, what else is produced?

This is a hydrolysis reaction.

Objectives

List different types of biological tests

Describe the basic structure of DNA

List DNA properties

Distinguish between RNA and DNA

Explain why DNA is so important

Mind map

Chemical tests

DNA History

DNA properties

RNA

DNA polymerase

Chemical tests

Biuret test

Test to detect proteins

A positive test will show a purple ring

Peptide bond

Benedict's test

Test for reducing sugars

A positive for reducing sugars is a brick-red precipitate

Reducing sugars

Non reducing sugars(sucrose)

Iodine solution

Test for starch

A positive test for amylose (starch) is a blue-black colour

Emulsion test

Test for lipids

Cloudy white emulsion is formed

Ethanol (alcohol)

Nucleic acids

What is DNA after all??

Is it so Important?

And RNA?

History of DNA

Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA

Proteins were composed of 20 different amino acids in long polypeptide chains

History of DNA

Fred Griffith worked with virulent S and nonvirulent R strain Pneumoccocus bacteria

He found that R strain could become virulent when it took in DNA from heat-killed S strain

Study suggested that DNA was probably the genetic material

22

Griffith Experiment

copyright cmassengale

History of DNA

She was able to deduce that the phosphate groups of DNA must be positioned on the outside of the molecule

This work was of vital importance to the later discovery of the double helix.

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

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

They built the first DNA model using Franklin’s X-rays

History of DNA

DNA Stands for:

Deoxyribonucleic acid

Made up of subunits called nucleotides

Nucleotide: 1. phosphate group 2. 5-carbon sugar 3. Nitrogenous base

DNA nucleotide

OO=P-O O

Phosphate Group

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

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

DNA Two strands coiled

called a double helix

Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds

Center made of nitrogen bases bonded together by weak hydrogen bonds

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

NitrogenousBase (A,T,G or C)

“Rungs of ladder”

“Legs of ladder”

Phosphate &Sugar Backbone

30

Antiparallel Strands One strand of

DNA goes from 5’ to 3’ (sugars)

The other strand is opposite in direction going 3’ to 5’ (sugars)

copyright cmassengale

DNA 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

Nitrogen Bases

PURINES1. Adenine (A)

2. Guanine (G)

PYRIMIDINES3. 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 CT A

BASE-PAIRINGS

CG

H-bonds

T A

Questions What is meant by:

complementary rule

Antiparallel

Chargaff's rule

What is the sequence of: AGTCCAATGCTAGGCTAA

Genetic Diversity… Different

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

RNA

Stands for: Ribonucleic acid

Polynucleotide

Usually single stranded

RNA

Made up of nucleotides containing the base pairs A, U, C, G

Replication theories

Semiconservative Model of Replication

Idea presented by Watson & Crick The two strands of the parental molecule

separate, and each acts as a template for a new complementary strand

New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

Parental DNA

DNA Template

New DNA

Helicase

DNA polymerase

Questions

Gene

Name given to some stretches of DNA and RNA that encode for a peptide

Stands for:Ribonucleic acid

Central dogma of life