Download File

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 freeliving 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.
Gene expression
• 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).
• In eukaryotes, promoters determine what portions of
the DNA will be transcribed into mRNA. The premRNA 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 ..