38
UNIT 7: MOLECULAR GENETICS

Unit7 Molecular Genetics

Embed Size (px)

Citation preview

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

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)

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

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 identicalcopy of the mother cell’s genetic information.

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

Replication is the process by which DNA duplicates itself.

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 fromthe original DNA and a new strand.

This is why it is called SEMICONSERVATIVE REPLICATION

Page 127 activity 2, 3, 5, 6, 7, 9, 10

3. The Expression of Genetic Information

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 tosynthesize 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 theinformation that isin a specific part of

the DNA

Ribosomal RNA (rRNA)

Ribosomes are made up of RNA

Transfer RNA (tRNA)It transports the

amino acids to theribosomes.

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

Stages

The double helix of DNA opens up.

Only one DNA strand is copied.

A RNA strand is produced.

The mRNA leaves the nucleusand 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-G-C-U-A-U-G-U

5’

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’

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

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

Each tRNA is specific to an amino acid.

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.

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 notbelong to this cell.

• The same amino acid can be coded by more than one codon.

• All proteins start with Metionine, this means, every specificmRNA has a strating 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

4. The Human Genome

The 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 nucleotidesin 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

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

6. Biotechnology

It 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

A. Agriculture and farming

Cloning: obtaining genetically identical organisms

Dolly was the first mammal to be cloned(1996)

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.

B. Biomedical Uses

Production of insuline, antibiotics, vitamins…

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