Molecular Genetics

Sunday, Tuesday & Thursday

2-3

Molecular genetics

• A science that uses methods of genetics and

molecular biology to study the structure and function of genes. In addition, it studies how genes are genetically transferred from one generation to another.

Correlation of molecular genetics

with other sciences: • Cell biology – study structure and functions of

whole cell and its organelles • Physiology – study the functions of body tissues

and organs • Biochemistry- study cellular molecules (micro and

macro) and their inter-conversions inside the cell (metabolism).

• Molecular Biology - study structure and functions of macromolecules in the cell

• Molecular genetics - branch of molecular biology that study genes at the molecular level

Cell Biology

Physiology Anatomy

Biochemistry

Molecular Biology

Molecular Genetics

Clinical Applications of Molecular

Genetics • Identify sites of genetic variations that are linked

with certain human diseases.

• Use these genetic variations to understand the

molecular basis of pathology

• Apply genetic information to the diagnosis of

some diseases

• Use genetic knowledge to develop treatments for

particular human diseases

We Live In The Age Of Genetics

Gene is a region of DNA along the genome chromosomes which represents the molecular unit of heredity for a living

organism

Gene action

• Phenotype in the form of biological traits (characters), can be either apparent such as eye color or hidden (non-visible) like blood groups. However, all characters are determined by the type of proteins synthesized. These proteins are the product of gene expression during the process of gene action.

• genes contain all the genetic information needed to build up the phenotype characters of an organism and the expression of these phonotype characters is the result of gene action.

Size of the gene

• Average gene size is 103 - 104 base pairs , although they can be much larger, such as the human dystrophin gene (produces defective protein in muscular dystrophy) which is 2000 kb in size.

• E. coli has about 4,200 genes, not very many considering that at least 1,000 different enzymes are needed to carry out just the basic biochemical reactions in the cell. The smallest genome for a free-living organism is that of the bacterium Mycoplasma which encodes only 467 genes.

• Humans are at the other end of the spectrum of complexity and have about 20,000 - 25,000 genes.

Gene location on chromosome

• Each gene occupies a specific region on chromosome - called a gene locus. At the locus the gene is present in two different copies called Alleles that express single trait. These two alleles are inherited one from each parent. The alleles are expressed in the phenotype either as dominant or recessive trait.

Dominant

The allele that masks the effect of the other when present in the same cell.

Recessive

An allele masked by the other when both alleles present in the same cell. The recessive

allele is capable of producing its characteristics phenotype in the organism only when

present as a pair.

Gene arrangement

The gene structure contains regulatory regions, transcribed regions, and other functional sequence regions

A regulatory region called promoter usually present at the beginning of the gene which can initiate the starting of gene expression (mRNA transcription) from 5' to 3' direction..

Some genes have "strong" promoters that bind the transcription machinery well, and others have "weak" promoters that bind this machinery poorly. The low affinity for binding the transcription machinery causes the weak promoters to produce lower rate of transcription than the strong promoters. Structurally, eukaryotic promoters are much more complex than prokaryotic promoters.

• In prokaryotes the coding sequence is a continuous piece of DNA (not interrupted) and the majority of these genes are organized into operons which are group of genes whose products have related functions and transcribed as one unit.

• In eukaryotic genes are transcribed individually and the coding sequence(exons) is discontinuous and interrupted by long pieces of non coding sequence called introns which are transcribed but never translated into protein (they are spliced out before translation).

Gene expression

• In eukaryotes, promoters determine what portions of the DNA will be transcribed into mRNA. The pre-mRNA is then spliced into messenger RNA (mRNA) which is later translated into protein

• Whereas the chromosomes of prokaryotes are relatively gene-dense, those of eukaryotes often contain so-called "junk DNA", or regions of DNA that serve no obvious function. Simple single-celled eukaryotes have relatively small amounts of such DNA, whereas the genomes of complex multicellular organisms, including humans, contain an absolute majority of DNA without an identified function. Protein-coding DNA only makes up 2% of the total human genome.

• Repetitive DNA sequence (satellite DNA) noncoding sequences , regulatory sequence ,represent the major part of the eukaryotic genome which occupies 98% of total DNA.

Gene amplification Loss or rearrangement can alter a cell genome during an organism lifetime. In some cases an organism may make many additional copies of single gene or genes in preparation for an upcoming period of rapid protein production. After this period passes the extra genes are broken down back to nucleotides. This has been observed in amphibians and in the cells of cancer patients undergoing chemotherapy. The amplified genes in cancer cells may provide resistance to the anti-cancer drugs.

Gene families

• Gene family is a set of several similar genes,

formed by duplication of a single original gene, and generally with similar biochemical functions. One such family is the genes for human haemoglobin subunits; the ten genes are in two clusters on different chromosomes, called the α-globin and β-globin loci.

Recommended Textbooks

1. Concepts of Genetics 10th.Ed.

William S. Klug, Michael R. Cummings,

Charlotte A. Spencer & Michael A. Palladino

Publisher :PEARSON 2012

2. Essentials of Genetics 7th. Ed. 2010

Same Authors & Publisher

International Edition

ISBN-13: 978-0-321-66999-5

Assessment

• Mid-Term Exam On Wednesday 15/3

From 9-11 50 % of total

( 50 MCQs )

• Final Exam 50 % To be decided later ..