Molecular genetics (chapter 14)

Deoxyribonucleic acid (DNA)

An organic chemical or macromolecule that carries genetic information

• Each DNA molecule consists of 2 polynucleotide strands twisted about each other to form a double helix structure.

• DNA molecule is wrapped around the proteins known as his tines at various intervals to form chromatin thread.

• Chromatin threads in the nucleus condenses to form chromosomes during cell division.

Structure of DNA

• music unit of DNA molecules is nucleotides

• Each nucleotide is made up of sugar (Deoxyribose), a phosphate group and a nitrogenous base.

• There are 4 bases: Adenine, Thymine, Cytosine and guanine

• Nucleotides are buildings blocks of DNA. They join together to form long chains of polynucleotides.

• DNA is a double helix structure with anti-parallel polynucleotide chains

• Stage phosphate backbone with complementary base pairing.

• Complementary base pairing is an important feature in the DNA molecule.

• Aden in always pair with Thymine and Cytosine always pair with Guanine in a ratio of 1:1

• Fixed pairing of the bases is crucial for the accurate replication of DNA and for synthesis of specific polypeptide

Genes

A segment of DNA, consisting of a sequence of nucleotides that codes for a polypeptide or protein.

• Each gene stores a message that will determine how a protein should be made in the cell.

• The message stored in the gene is known as genetic code.

• Each protein contributes to the development of certain characteristics in the body.

• Many genes can be found in a DNA molecule

Transcription

• Transcription occurs in the nucleus of the cell.

• Nucleotides form hydrogen bonds corresponding base on the DNA template following the same complementary base pairing rules and a mRNA strand is formed. mRNA strands do not contain Thymine but Uracil

Translation

• Translation occurs in the cytoplasm.

• On the mRNA, every three bases is a codon= 3 bases =1 amino acids

• There are 20 types of amino acids found in the cytoplasm of humans

• Amino acids are arranged in the sequence specified by the order of the codons.

• The amino acids are then linked together, by peptide bonds, with the help of ribosome to form a polypeptide

• Hence, ribosomes are involved in the synthesis of polypeptide/proteins.

Genetic Engineering

• Genetic Engineering is a technique that is used to transfer genes from one organism to another. Individuals genes may be cut off from the cells of one organisms and then inserted into the cells of another organism of the same or different species

• Transgenic organism is an organism which contains genes from the same or different species.

Recombinant DNA technology

• Restriction enzymes: These enzymes are able to recognise specific sequence of DNA and cut the sequence. The action of restriction enzymes produces “sticky ends” of DNA which are single-stranded portions of DNA that are able to base pair with complementary unpaired DNA sequences. This allows two complementary unpaired DNA sequence from different sources to be joined together neatly.

Genetic engineering of human insulin

1. Cut plasmid and human insulin gene with the SAME Restriction enzyme. ( to produce complementary sticky ends)

2. Add DNA Ligase (to join the sticky ends of plasmid and insulin gene)

3. Transformation (inserting the recombinant DNA into another bacterium, E.coli, by applying heat shock or electric shock)

4. Grow Transgenic bacteria, E.coli, in Fermenter (bacteria divide and multiply, produce insulin from the human gene)

5. Kill the bacteria, burst the cells, and extract and purify the insulin

Human insulin production in large scale fermenters

• Transgenic bacteria a re mixed with a nutrient broth inside the fermenter.

• To culture the transgenic bacteria under optimum conditions, oxygen concentration, pH, temperature and the concentration of nutrients are carefully monitored by a computer.

• Transgenic bacteria multiply rapidly under the optimism conditions and thus produce large quantities of human insulin

• The bacteria are then removed from the nutrient broth and then burst open to release the human insulin.

• The human insulin is extracted and purified.

Good of genetic engineering

• MEDICINE: lower cost, mass production helps to lower the medicines. It does not induce allergic responses in patient as the insulin produces is exactly to human insulin

• FOOD QUALITY : improve nutritional quality of food.

• CROPS: improve yield and increase profit $$

BAD of genetic engineering

• Environment & Health hazards

• Economic, social & Ethical