UNIT 7: MOLECULAR GENETICS

INDEX1.DNA2.Replication3.The Expression of Genetic Information4.The Human Genome5.Genetic Engineering6.Biotechnology

1. DNA

Genes •Are located on chromosomes•Are the basic units of inheritance that carry genetic information•Consist of DNA (deoxyribonucleic acid)

In 1953 Watson and Crick proposed the double helix model of the DNA molecule.

Their discovery was based in one X-ray picture taken by Rosalind Franklin. However,only Watson, Crick and Wilkins were awarded with the Nobel prize in 1962, when shehad already died because of ovarian cancer.

Rosalind Franklin. Picture 51

1.1 Basic components of DNA

A molecule of DNA is formed from units called NUCLEOTIDES

P nitrogenous

Adenine

Thymine

Guanine

Cytosine

NUCLEOTIDE

Nucleotides join together through the phosphate building a strand (a chain of nucleotides)

1.2 Structure of DNA

DNA is made up of two chains of nucleotides. Both chains are joined togetherthrough the nitrogenous bases.

Hydrogen bonds

The link between bases follows the next pattern:

A and T are complementaryG and C are complementary

G-C

A-T

The two strands are twisted around each other in the shape of a double helix.

It is packed inside the nucleus.

Video doble helix structure Watson and Crick: https://www.youtube.com/watch?v=VegLVn_1oCERap https://www.youtube.com/watch?v=35FwmiPE9tI

1.3 Cell Cycle

Phase G1Cell growth

(protein synthesis)

Phase S Replication of DNA

Phase G2Preparation

for cell division

Mitosis

Cytokinesis

2. Replication of Genetic Information

After mitosis every daughter cell receives an identical copy of the mother cell’s genetic information.

For this to happen, the DNA needs to copy itself before mitosis begins (phase S).

Replication is the process by which DNA duplicates itself.

https://www.youtube.com/watch?v=5qSrmeiWsuc 3DNA Replication Cartoonshttps://www.youtube.com/watch?v=TNKWgcFPHqw 4DNA replication 3D

Replication must be very precise. Otherwise, mutations could appear. Different enzymes (like DNA-polymerase) perform the replication.

Steps

1. The double helix opens up and the two strands separate.

2. New complementary nucleotides are attached to each of the bases of both strands, forming two new strands.

3. At the end, there are 2 identical copies of DNA. Each one has a strand from the original DNA and a new strand.

This is why it is called SEMICONSERVATIVE REPLICATIONPage 127 activity 2, 3, 5, 6, 7, 9, 10

http://www.nobelprize.org/educational/medicine/dna_double_helix/dnahelix.html

http://www.learningliftoff.com/high-school-science-dna-replication/#.VtxuWPnhDIU

Games:

3. The Expression of Genetic Information Introduction

A. Proteins

Proteins are made up of molecules called amino acids.

There are 20 amino acids which make up all proteins.

Proteins have structural and physiological functions and they are the molecules responsible for the characteristics of the body.

A gene is a piece of DNA that contains the information to synthesize a specific protein.

B. RNA (ribonucleic acid)

It is made up of nucleotides, but instead of thymine there is Uracil.

Types

Messenger RNA (mRNA)

Copy of the information that is in a specific part of

the DNA

Ribosomal RNA (rRNA)

Ribosomes are made up of RNA

Transfer RNA (tRNA)

It transports the amino acids to the

ribosomes.

3.1 Protein Synthesis

This process is performed in two stages:

Transcription (It takes place inside the nucleus)

DNA cannot leave the nucleus.The specific piece of information needed is copied onto another molecule: Messenger RNA

StagesThe double helix of DNA opens

up.

Only one DNA strand is copied.

A RNA strand is produced.

The mRNA leaves the nucleus and arrives to the cytoplasm.

The double helix of DNA opens up.

Only one DNA strand is copied.

RNA polymerase synthetizes the RNA reading 3’ 5’ and creates the new RNA always 5’3’

T - A - C - G - G - C - T - A - C - A - T - G

Example of transcription:

DNA3’ 5’

Activity: Write the corresponding RNA sequence

T-A-C-T-T-T-G-G-C-G-A-T-A-C-AA-T-G-A-A-A-C-C-G-C-T-A-T-G-T

3’

5’

5’

3’

TEMPLATEDNA

3’mRNA A-U-G-A-A-A-C-C-G-C-U-A-U-G-U5’

Transcription (by the RNA polymerase)

A - U - G - C - C - G - A - U - G - U - A - CmRNA5’ 3’

mRNA leaves the nucleus and arrives to the cytoplasm.

Translation (It takes place in the cytoplasm, in the ribosomes)

The ribosome translates the information carried on the mRNA into a chain of amino acids (protein).

1. mRNA positions itself on a ribosome, starting with its 5’ side .

Stages:

5’

2. tRNA transports free-floating amino acids in the cytoplasm to the ribosome, in the order indicated by the mRNA.

It reads the nitrogenous bases in groups of three (codons).

3. Each tRNA is specific to an amino acid.

4. The ribosome moves along the mRNA and joins amino acids together in the appropiate order.

Each amino acid is coded by one or more codons.

https://www.youtube.com/watch?v=gG7uCskUOrA 5 From DNA to Protein

3.2 The Genetic Code

It is the relationship between the sequence of nitrogenous bases in DNA and the amino acids in the corresponding protein.

Characteristics•It is universal•Every living being uses the same mechanism.•The ribosomes can read every mRNA, although it does not belong to this cell.

•The same amino acid can be coded by more than one codon.•All proteins start with Metionine, this means every specific mRNA has a starting point which is AUG.•There are some codons which code for “stop”.Activities 11-20 (all) page 131

Write the sequence of the protein synthesized from the next DNA:

T-A-C-C-C-T-C-G-G-G-C-A-T-A-A-T-A-G-A-T-TA-T-G-G-G-A-G-C-C-C-G-T-A-T-T-A-T-C-T-A-A

3’

3’5’

5’

1st step: transcription mRNA

A-U-G-G-G-A-G-C-C-C-G-U-A-U-U-A-U-C-U-A-A5’ 3’

2nd step: translation protein

Met-Gly-Ala-Arg-Ile-Ile

4. The Human GenomeThe genome is the organism’s complete set of genes.

In order to know someone’s genome we have to know:

The whole sequence of nitrogenous bases in DNA

Location and function of all the genes Relationship between genes

In 2003 the sequence of nucleotides in the human genome was located.

•Diagnosis of genetic disease•Gene therapy (modify genes)•Medicines which can be personalised

Applications of mapping the

human genome

5. Genetic EngineeringIt consists of techniques to manipulate genetic material in order to change an organism’s traits.

General technique

1. Location of the gene.

2. Isolation of the gene using restriction enzymes, which cut the DNA in specific places.

3. Introduction of the gene in a vector (bacterium or virus) to transport it.

Vector’s DNA + the gene = RECOMBINANT DNA

4. Insertion of the recombinant DNA into a cell in order to be expressed.

Vector: bacterium

Vector: virus

Uses of genetic ingeneering

Biological research

Researching diseases

Police investigations

Suspects and victims of crimes

Paternity tests

Historical and archaeological

studies

Gel electrophoresis

Suspects and victims of crimes

6. BiotechnologyIt is the technology which uses living beings to create improved

products.

Making bread, dairy products, alcoholic drinks

Making vaccines and antibiotics

Treating rubbish or polluted water

Uses of modern biotechnology

A. Agriculture and farming

Cloning: obtaining genetically identical organisms

Dolly was the first mammal to be cloned(1996)https://www.youtube.com/watch?v=-Qry1gYYDCA Dolly the Sheep

Genetically modified organisms: organism (animal, plant…) which has a gene from another organism so that it can express a new trait.

Bt gene is a gene belonging to a bacteria which produces resistance to some insects.It the plant carries it it cannot be eaten by insects.

Risks of genetic engineering• Modified organisms could

spread and reach the nature and human beings

• Seed control by multinationals (patents)

• Possible allergies to new genes

B. Biomedical Uses

Production of insuline, antibiotics, vitamins…

https://www.youtube.com/watch?v=_ob1c-n_oNY&list=PL4473936D327B7C69 Genetic Engineering 7 Wonders of the Microbes

prevention of genetic diseases substitution of defective genes beforethey are transmitted to the gametes.

gene therapy curing genetic diseases, like cystic fibrosis

GlossaryRecombinant DNA PlasmidRestriction enzymeVectorDNA polymerase

Page 137, activities 21, 24, 25, 28, 29Page 138 activities 1, 3, 4, 5