A Glance on Genetics - II

In this presentation…… Part 1 – DNA Part 2 – RNA Part 3 – Operations on Genes

Part 1 DNA

Some DNA can jump DNA responds to signals from outside the cell DNA is only the beginning for understanding the human genome DNA and proteins are key molecules of the cell nucleus One gene makes one protein A gene is made of DNA Bacteria and viruses have DNA too DNA is packaged in a chromosome A gene is a discrete sequence of DNA nucleotides There is a phosphate group in nucleotide along with sugar molecule whereas no phosphate group exists in nucleoside

This is an example of a gel electrophoresis run.. Each column was loaded with a different mixture. The mixtures are then separated vertically by their charge and size. The gel is then stained, producing dark bands where a molecule of a given size or charge is present in a mixture. In this gel, the columns marked with a - are a control group. The band marked with an arrow is filled only in the + columns.

Electron microscope view of human chromosomes

Human chromosomes

Structure of DNA

The DNA molecule is shaped like a twisted ladder, is a double helix, was found in 1953 by Watson and Crick

Alpha Helix

Beta Sheet/Strand

A half DNA ladder is a template for copying the whole

Forms of DNA structure

DNA is a linear polymer of four nucleotides viz., deoxy Adenosine monophosphate (abbreviated A), deoxy Thymidine monophosphate (abbreviated T), deoxy Guanosine monophosphate (abbreviated G), and deoxy Cytidine monophosphate (abbreviated C)

Double helix maintains a constant width because purines always face pyrimidines in the complementary A-T and G-C base pairs. The sequence in the figure is T-A C-G A-T G-C

Base pairing provides the mechanism for replicating DNA

Part 2 RNA

Some viruses store genetic information in RNA RNA was the first genetic molecule RNA is a very similar polymer of Adenosine monophosphate, Guanosine monophosphate, Cytidine monophosphate, and Uridine monophosphate Uridine monophosphate, abbreviated U, is a nucleotide functionally equivalent to Thymidine monophosphate RNA is an intermediary between DNA and protein The RNA message is sometimes edited RNA was discovered after DNA RNA occurs in the nucleus as well as in the cytoplasm Ribosomes are 2/3 RNA (a type of RNA known as ribosomal RNA or rRNA) and 1/3 protein

Cells of developing embryos contain high levels of RNA RNA has ribose sugar instead of deoxyribose sugar. The base uracil (U) replaces thymine (T) in RNA Most RNA is single stranded, although tRNA forms a “cloverleaf” structure due to complementary base pairing There are 61 different tRNAs, each having a different binding site for the amino acid and a different anticodon. For instance, for the codon UUU, the anticodon is AAA Energy for binding the amino acid to tRNA comes from ATP conversion to adenosine monophosphate (AMP) mRNA molecules are long containing ,000 nucleotides

Part 3 Operations on Genes

Biochemical reactions are controlled by enzymes, and often are organized into chains of reactions known as metabolic pathways Genes undergo different operations called mutation, cross over, local twist and variation Mutations are changes in genetic information, usually only one bit Variation modifies the encoded value by a small increment or decrement Crossover exchanges a contiguous fragment of an individual There could be single crossover, two point crossover or uniform crossover

Some types of mutations are automatically repaired Replication is of three types viz., conservative, semi- conservative and dispersive In conservative replication, an entirely new DNA strand is produced In semi-conservative replication, two DNA molecules are produced, each of which is composed of one-half of the parental DNA along with an entirely new complementary strand In dispersive replication, the parental strands are broken and a mix of old and new fragments of each stand of DNA are reassembled