unit7 molecular genetics
TRANSCRIPT
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
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’
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.
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.
Uses of genetic ingeneering
Biological research
Researching diseases
Police investigations
Suspects and victims of crimes
Paternity tests
Historical and archaeological
studies
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.
prevention of genetic diseases substitution of defective genes beforethey are transmitted to the gametes.
gene therapy curing genetic diseases, like cystic fibrosis