The Molecular Basis of Inheritance

Presented by: Marlett Ann R. de los Santos

Deoxyribonuccleic acid (DNA) • A nucleic acid

molecule that contains the genetic instruction used in the development and functioning of all living organisms.

Structure of a DNA

-DNA is a very large polymer made up of monomers called nucleotides. Each DNA nucleotide consists of a phosphate group, the sugar deoxyribose and a nitrogen base. The only difference among the four nucleotides of DNA is in their nitrogen bases.

The four nitrogen bases of DNA are the organic ring structures:

*adenine *guanine *cytosine *thymine Only the nitrogen bases of the nucleotides

vary. And the amounts of adenine and thymine nucleotides are equal likewise the amounts of guanine and cytosine nucleotides are equal too.

• The Watson-Crick model of DNA has two strands. The phosphate sugar chains form the backbone for each strand. The nitrogen bases of each strand pair with the other strand by hydrogen bonding. Adenine (A) always pair with thymine (T) and guanine (G) always pair with cytosine (C).

Because there are two strands in a spiral, the shape of DNA is described as double helix. The DNA double helix is sometimes compared to a twisted ladder. The sides of the ladder are the sugar phosphate backbones. The rungs are the pair of nitrogen bases.

It is the order of these bases that makes up the genetic code. Differences in the order give individuality to each organisms. When a cell divides, the DNA preserves this individuality by passing exact copies of itself to each new cell.

Ribonucleic acid (RNA)

- a nucleic acid of nucleotide monomers that plays several important roles in the processes that translate genetic information from DNA into protein products.

Roles of RNA

1. RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes.

2. RNA forms vital portions of ribosomes.

3. RNA acts as an essential carrier molecule for amino acid to be used in protein synthesis.

Structure of RNA

• Instead of the base thymine, RNA contains the nitrogen base uracil (U). Uracil pair with adenine pair with adenine just as thymine does in DNA. Thus, RNA contains the four bases adenine, uracil, cytosine and guanine.

• Like DNA, RNA is a nucleic made of bonded nucleotides. However, there are some important differences in the molecules. DNA contains the sugar deoxyribose, but RNA contains ribose, a slightly different sugar.

• Whereas, a DNA molecule takes the shape of a double helix, RNA are single-stranded.

Types of RNA

There are three main kinds of RNA found in organisms:

1. Messenger RNA (mRNA) – carries information specifying amino acid sequences of proteins from DNA to ribosomes.

2. Transfer RNA (tRNA) – serves as adapter molecule in protein synthesis; translates mRNA codons into amino acid.

3. Ribosomal RNA (rRNA) – plays catalytic (ribozyme) roles and structural roles in ribosomes.

How DNA replicates?

REPLICATION - the process by which

molecule is copied.

A model for DNA replication: the basic concept

a. The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.

b. The first step in replication is separation of the two DNA strands.

c. Each parental strands new serves as a template that determine the order of nucleotides along a new complementary strand.

d. The nucleotides are connected to form the sugar-phosphate backbone of the new strand and one new strand.

Does DNA replication follow the conservative, semi-conservative, or dispersive model?

Matthew Meselson and Franklin Stahl cultured E. coli bacteria for several generations on a medium containing nucleotide precursors labeled with a heavy isotope of 15N. The bacteria incorporated the heavy nitrogen into their DNA. The scientists then transferred the bacteria to a medium with only 14N, the lighter than the parental DNA made in the 15N medium. They distinguished the DNA by the difference in the densities through centrifuging DNA extracted from the bacteria.

a. Semi-conservative model - the two strands of the

parental molecule separate and each function as a template for synthesis of a new, complementary strand.

b. Conservative model - the two parental strands

reassociate after acting as templates for new strands.

c. Dispersive model - each strand of both

daughter molecule contain a mixture old and newly synthesized DNA.

Meselson and Stahl concluded that DNA replication follows the semi-conservative model by comparing their results predicted by each of the three models.

Protein Synthesis

Genes specify proteins via transcription and translation.

Transcription -is the synthesis of RNA under the

direction of DNA.Translation -is the actual synthesis of a

polypeptide, which occurs under the direction of mRNA.

The resulting RNA molecule is a faithful transcript of the genes protein-building instructions. Messenger RNA carries the genetic message from the DNA to the protein synthesizing machinery of the cell.

The cell must translate the base sequence of an mRNA molecule into the amino acid sequence of a polypeptide. The sites of translation are the ribosomes, complex particles that facilitate the orderly linking of amino acid into the polypeptide chains.

Why proteins could not simply be translated directly from DNA?• It provides protection for the

DNA and its genetic information.

• Using an RNA intermediate allows more copies of a protein to be made simultaneously and be translated repeatedly.

To summarize, cells are governed by a molecular chain of command:

DNA RNA PROTEIN

RECOMBINANT DNA or GENETIC ENGINEERING

Genetic engineering - the intentional production of new

genes and alteration of genomes by the substitution or addition of new genetic material.

Recombinant DNA - a DNA resulting from the insertion of a

sequence of genes from one organism into the DNA of another organism

Gene Splicing is the cutting of DNA by

enzymes and insertion of a piece of foreign DNA.

Gene Cloning is the production of multiple

copies of genes.

How to extract DNA in food?• Materials needed:

BananaTable salt Ethyl alcoholColorless shampooDistilled waterIce cubes

• Equipment needed:

BlenderCoffee filterTable spoonGraduated cylinderMedicine dropperTest tube w/ coverBeaker Bucket

• What to do?

Step 1. * In a blender, mix a ratio of one banana per 250 mL of

distilled water. * Blend for 15-20 seconds, until the mixture is a solution.Step 2. * In one of the 5 oz cups, make a solution consisting of 1 tsp.

of shampoo and two pinches of table salt. * Add 20 mL of distilled water or until the cup is 1/3 full.

Dissolve the salt and shampoo by stirring slowly with the plastic spoon to avoid foaming.

Step 3. * To the solution you made in step 2, add the three heaping

teaspoons of the banana mixture from step 1. Mix the solution with the spoon for 5-10 minutes.

Step 4.* While one member of your group mixes the banana solution,

another member will place a #2 cone coffee filter inside the second 5 oz plastic cup. Fold the coffee filter‘s edge around the cup so that the filter does not touch the bottom of the cup.

Step 5. * Filter the mixture by pouring into the filter and letting the

solution drain for several minutes until there is about 5 mL (covers the bottom of the cup) of filtrate to test.

Step 6. * Obtain a test tube of cold alcohol. For best results, the

alcohol should be as cold as possible.Step 7. * Fill the plastic pipette with banana solution.Step 8. * Add the solution to the alcohol. * Let the solution set for 2-3 minutes without disturbing it. It is

important not to shake the test tube.

• EXPECTED RESULTS

You can watch the white DNA precipitate out into the alcohol layer. DNA has the appearance of white, stringy mucus.

The End

thank you…