Chapter 3.1 Flashcards
Genome
The whole of the genetic information of an organism
Gene
A heritable factor that consists of a length of DNA and influences a specific characteristic.
Chromosomes
Long stretches of DNA
Locus
A specific location of genes in a chromosome
Alleles
The various, specific forms of a gene that usually vary from each other by one or a few bases.
Mutations
Errors in DNA replication which lead to daughter cells being different from parent cells from changes in the DNA sequence. These lead to new alleles forming.
Causes of mutations
- Errors in DNA replication
- Exposure to chemicals or mutagens (if they cause tumorigenisis then they are carcinogens)
- Exposure to radiation
- Exposure to certain viruses
How does the DNA change in mutation?
They change the base sequence of DNA by replacing a base with another in substitution, deletion or addition
What is the result of mutations?
- Some occur in a stretch of DNA that does not code for a polypeptide.
- Some mutations in protein-coding genes cause no change because the genetic code includes multiple codons (triplets) for the same amino acid.
- Some, if an amino acid is changed, the polypeptide formed might work differently or not at all
The Human Genome project
Started in 1990, the Human Genome projected wanted to sequence all 3.2 billion base pairs in human DNA in 15 years. By 2003, it was achieved. It allowed people to find genetic defects that predicted certain diseases and allowed them the steps in order to overcome them. Insurance companies may also use this to determine how much to charge you. Medicine may also become more tailor based on the individual. Other genomes have also been sequenced, allowing more in other fields of science.
Comparison of the number of genes of humans (20,000) to…
Triticum aestivum - 100,000
Canis lupus familiaris - 19,000
Escherichia coli - 4000
Oryza sativa japonica - 35,000
Sickle Cell Anaemia symptoms
Symptoms, if not controlled, include:
- extreme pain
- weakness
- heart attack
- stroke
- pneumonia
- bone malformations
- death
What causes Sickle Cell Anaemia?
There is a gene on chromosome 11 called HBB; which codes for a beta subunit of haemoglobin, a polypeptide 146 amino acids long. A standard Hba gene is coded as GAG at the 6th triplet of the sense DNA strand. The Hbs gene, however, reads as GTG. A A is substituted by an T. Changing glutamic acid into valine.
Under standard conditions, Hbs and Hba are not that different. However, at low levels of oxygen for example, while the glutamic acid is hyrophilic and dissolves well in the red blood cell, valine is not. Subsequently, it polymerises to form long fibres which cause it to carry less oxygen and change the shape of the red blood cell to a sickle.
How does the sickle shape cause problems?
They can get stuck and clog blood vessels anywhere in the body, causing intense pain as blood supply fails. If this happens in the brain, the person could have a stroke. Sickled cells must be broken down and eliminated from the body, which strains the liver and causes a shortage of functioning red blood cells (anemia). New red blood cells must be made in the bone marrow to replace the cells lost, and the extra work can damage bone structure.
What can we do about sickle cell anaemia?
Sickling events are triggered by low levels of oxygen in the blood, dehydration, infection, and exposure to sudden temperature changes. A careful lifestyle and medicines can help greatly. Without treatment, most children with sickle cell anemia will die in infancy. With access to quality health care, individuals can usually lead normal and active lives, sometimes including healthy pregnancies.
