Molecular Genetics Genetics, GEN 301

Genetics Molecular

A A. Abugabal

GEN 301

The Aims of the course Acquire the students with

good basic grounding in the molecular structure, organization and function of genetic material

To distiguish between different types of molecular markers

To critically appraise the different methods used in molecular mapping

To study the application of genetic analysis in different organisms

Assessment DetailsMethods of Assessment Weighting%

Project

Quizzes

Assignments

Mid-Term

Lab Work

Final Exam:

7%3%5%20%25%40%

•Assessment Details:

Introduction The history of genetics is quite extensive.

It has taken the work of many brilliant scientists to finally conceive the structure of the DNA molecule or to even conceive it as the hereditary material life.

In this opening genetics section it is important to understand scientists' achievements.

Appreciate and understand their method, do not get caught up in history and dates.

The History of Molecular Genetics

The early contributions: setting the stage

Gregor Mendel: mid 1800’s

Gregor Mendel1865 Gregor Mendel

By studying pea plants,

discover the basic rules of heredity of garden pea.

Characteristics are inherited in discrete units (later called genes)

An individual organism has two alternative heredity units for a given trait (dominant trait vs. recessive trait)

Major events in the history between1800 - 1870

1869 Johann Friedrich Miescher discovered DNA and named it

nuclein.Johann

Miescher

1881 Edward Zacharias showed chromosomes are composed of nuclein.

Major events in the history of Molecular genetics 1880 - 1900

1899 Richard Altmann renamed nuclein to nucleic acid.

By 1900, chemical structures of all 20 amino acids had been identified

1902 - Emil Hermann Fischer wins Nobel prize: showed amino acids are linked and form proteins

Emil Fischer

Major events in the history of Molecular Biology 1900-1911

Thomas Hunt Morgan Worked at Columbia University;

later at CalTech Studied fruit fly eye color,

determining that trait was sex-linked

Won the Nobel Prize in 1933 for his work on chromosomes and genetics

1911 – Thomas Hunt Morgan discovers genes on chromosomes are the discrete units of heredity

Thomas Morgan

The early contributions: setting the stage

early 1900’sStudied fruit fly eye color, determining that trait was sex-linked1911 –

Thomas Hunt Morgan discovers genes on chromosomes are the discrete units of heredity

Won the Nobel Prize in 1933 for his work on chromosomes and

genetics

The early contributions: setting the stage

By this point, it was known that genetic material was located on a chromosome

This genetic material was in discrete units called genes

All Life depends on 3 critical molecules

DNA

RNA

Protein

Components Involve in Molecular Biology

By this stage , It was NOT known whether the gene was simply a protein, or whether it was composed of DNA

A Brief History

Since the late 1950s and early 1960s, molecular biologists have learned to

Characterize, isolate, and manipulate the molecular components of cells and organisms, which are:

1. DNA, the storage of genetic information

2. RNA3. Proteins, the major structural

and enzymatic type of molecule in cells.

Discovery of DNA 1930’s

Various experiments identify chromosomes as the source of genetic information

Chromosomes are composed of mainly proteins and deoxyribonucleic acid (DNA)

The DNA molecule was considered too simple to be important so proteins were thought to carry the genetic information

The Molecular Basis of Inheritance

Evidence that DNA is a genetic

material

Came from

Fred Griffith (1928) – Experiments with pneumonia and bacterial transformation determined that there is a molecule that controls inheritance.

Oswald T. Avery (1944) - Transformation experiment determined that DNA was the genetic material responsible for Griffith’s results (not RNA).

Erwin Chargaff (1947) – noted that the the amount of A=T and G=C and an overall regularity in the amounts of A,T,C and G within species.

Hershey-Chase Experiments (1952) – discovered that DNA from viruses can program bacteria to make new viruses.

Important Early Discoveries

Frederick Griffith

Late 1920’s Frederick Griffith from Britain worked with bacteria

“Streptococcus pneumoniae”

Defined the term, “TRANSFORMATION”

In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA

Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria

1952, Hershey-Chase Bacteriophage Experiment

Hershey and Chase concluded that the injected DNA of the phage provides the genetic information that makes the infected cells produce new viral DNA and proteins, which assemble into new viruses.

Griffith 1928 & Avery 1944:

DNA (not RNA) is transforming agent.

Hershey-Chase 1953:

DNA (not protein) is the genetic material.

- RNA (not protein) is genetic material of some viruses,- but no known prokaryotes or eukaryotes use RNA as their genetic material.

Alfred HersheyNobel Prize in Physiology or Medicine

196922

Conclusions about these early experiments:

THE RACE IS ON! Who discovers the double helix?

Linus Pauling

Won Nobel prize in chemistry in 1954 for work in chemical bonding;

Nobel peace prize in 1962 for his campaign against above-ground nuclear testing

He also worked on the structure of DNA, but came up with a TRIPLE HELIX

He thought DNA was 3 strands with the phosphates on the inside

DNA Structure based on Two primary sources of information:

X-ray diffraction studies of Rosalind Franklin & Maurice H. F. Wilkins to study the structure of DNA.

The diffraction pattern can be used to deduce the three-dimensional shape of molecules.

Edwin Chargaff

1950 – Edwin Chargaff find Cytosine complements Guanine and Adenine complements Thymine

What about?Rosalind Franklin

Franklin and Wilkins

Their results using X-ray crystallography gave Watson and Crick the necessary information they needed to come up with the double helix structure Width of the helix Spacing of the nitrogenous bases DNA molecule was made up of two strands, forming a

double helix

James Watson and Francis Crick

1953 proposed the Double Helix Model based on two sources of information

1. Base composition studies of Erwin Chargaff• indicated double-stranded DNA consists of• ~50% purines (A,G) and ~50% pyrimidines (T, C)

• amount of A = amount of T and• amount of G = amount of C (Chargraff’s rules)

• %GC content varies from organism to organism

Examples: %A %T %G %C %GCHomo sapiens 31.0 31.5 19.1 18.4 37.5Zea mays 25.6 25.3 24.5 24.6 49.1Drosophila 27.3 27.6 22.5 22.5 45.0Aythya americana 25.8 25.8 24.2 24.2 48.4

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Structure of DNA

Structure of DNA

James D. Watson/Francis H. Crick 1953 proposed the Double Helix Model based on two sources of information:

2. X-ray diffraction studies by Rosalind Franklin & Maurice Wilkins

Conclusion-DNA is a helical structure with distinctive regularities, 0.34 nm & 3.4 nm.

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Two sources of information

Francis H.Crick

Watson, J.D. and F.H. Crick, “Molecular Structure of Nucleic Acids.

1962 :Nobel Prize in Physiology and Medicine

Conclusion-DNA is a helical structure with

distinctive regularities, 0.34 nm & 3.4 nm.

James D.Watson

Major events in the history of Molecular Biology 1950 - 1952

1950s – Mahlon Bush Hoagland first to isolate tRNA

1952 – Alfred Hershey and Martha Chase make genes from DNA

Mahlon Hoaglan

d

1941 – George Beadle and Edward Tatum identify that genes make proteins

George

Beadle

Edward Tatum

1956 George Emil Palade showed the site of enzymes manufacturing in the cytoplasm is made on RNA organelles called ribosomes.

George Emil

Palade

Major events in the history of Molecular Biology 1970

1970 Howard Temin and David Baltimore independently isolate the first restriction enzyme

• This means that: DNA can be cut into reproducible pieces at specific site by restriction enzymes called endonuclease

• The pieces can be linked to bacterial vectors and introduced into bacterial hosts.This is called (gene cloning or recombinant DNA technology)

Major events in the history of Molecular Biology 1970- 1977

1977 Phillip Sharp and Richard Roberts demonstrated that pre-mRNA is processed by the excision of introns and exons are spliced together.

Phillip Sharp

Richard Roberts

Major events in the history of Molecular Biology 1986 - 1995 1986 Leroy Hood:

Developed automated sequencing mechanism

1986 Human Genome Initiative announced

1995 Moderate-resolution maps of chromosomes 3, 11, 12, and 22 were published

These maps provide the locations of “markers” on each chromosome to make locating genes easier

Leroy Hood

Major events in the history of Molecular Biology 1995-1996

1995 John Craig Venter: First bacterial genomes sequenced

1995 Automated fluorescent sequencing instruments and robotic operations

1996 First eukaryotic genome-yeast-sequenced

John Craig Venter

Molecular Biology 1997-1999

1999 First human chromosome (number 22) sequenced

Molecular Biology 2000-2001

• 2001 International Human

Genome Sequencing published

the first draft of the sequence

of the human human genome

Major events in the history of Molecular Biology

Major events in the history of Molecular genrtics 2003- Present

April 2003 Human Genome Project Completed

Mouse genome is

sequenced.

April 2004 Rat genome sequenced.

Next-generation sequencing – genomes being sequenced by the dozen

Molecular genetics Molecular genetics is the field of biology and genetics that

studies the structure and function of genes at a molecular level.

Molecular genetics employs the methods of genetics and molecular biology to elucidate molecular function and interactions among genes. It is so called to differentiate it from other sub fields of genetics such as ecological genetics and population genetics.

Molecular genetics helps in understanding developmental biology, genetic mutations that can cause certain types of diseases.

Through utilizing the methods of genetics and molecular biology, molecular genetics discovers the reasons why traits are carried on and how and why some may mutate.

Thank you