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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
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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