Post on 07-Jan-2017
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