Hereditary Breast Cancer Essay is a disease caused by mutations on breast cancer
suppresser genes (ACCV Pg.17). Mutations allow normal cells to divide abnormally
(ACCV Pg.13). Resulting cells divide faster as they do not specialize and form
useless lumps of cells called malignant tumours (ACCV Pg.
13). Genetic Screening
is the process where Deoxyribonucleic Acid (DNA) fragments are analyzed for a
specific gene. The purpose is to identify individuals carrying disease causing
genes so they can change their life style and also help invent a cure (ACCV
Pg.20). This is done by amplifying DNA withdrawn from an individual, then
specific gene mutations are targeted using the Electrophoresis process. The two
genes, BRCA1 and BRCA2 isolated in 1994 and 1995 respectively are breast cancer
suppresser genes (Internet 1).
BRCA1 is located on chromosome 17q21 and BRCA2 on
13q(Internet 2). A person that possesses certain mutations to these genes has an
increased risk of up to 80-90% in developing breast cancer (Internet 3). The
cost of genetic screening ranges among several hundred to several thousand
dollars depending on the tests performed and can take several weeks to many
months from the initial blood sample (Internet 4). Public acceptance of genetic
screening for severe disease causing genes in early childhood is high (New
Scientist Pg. 14). Many people argue for less debilitating diseases that
discrimination will occur against individuals carrying those genes (New
14). In human cells there are 22 pairs of autonomic chromosomes
and two sex chromosomes. These chromosomes contain information for protein
synthesis. DNA stores this information by a sequence of nucleotides. There are
four different nucleotides that construct DNA. They all contain a 5 ring carbon
sugar (Deoxyribose), a phosphate molecule and one of four nitrogenous bases.
base names are Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). Adenine
is complementary to Thymine and Guanine to Cytosine. The arrangements of a
series of nucleotides are genes. Hereditary Breast Cancer is an autosomal
dominant disease (Internet 3), meaning only one parent needs to carry the trait
expression in the parents offspring. The disease is cause by mutations found on
the BRCA1 or 2 tumour suppresser genes (Internet 3). BRCA1 has 24 exons
distributed over a genomic region of 81 kilobases long and located on
chromosome17q21 (Internet 3) Exon 11 being the largest that codes for 61% of a
protein, 1863 amino acids and 5592 nucleotides long (ACCV Pg.
irrelevant information known as introns found on BRCA1 range in size from 403
base pairs to 9.2 kilobases (Internet 3). Over 100 disease-associated mutations
have be identified to this gene (Internet 3) 21 of these found in exon 11 (ACCV
Pg. 17). These mutations code for a stop signal causing protein truncation (ACCV
17). BRCA2 has mutations that function the same as BRCA1 (ACCV Pg. 18).
BRCA2 has been linked to hereditary breast cancer and increases the risk for
male breast cancer. (ACCV Pg. 18).
BRCA2 is located on chromosome 13q12(Internet
2). Little additional detail about this gene is available. Testing for BRCA2 is
not widely available except within the research laboratory. There are two
distinctive stages in protein synthesis of BRCA1, transcription and translation.
Transcription is the synthesis of messenger Ribonucleic Acid (mRNA). The enzyme
RNA polymerase initiates transcription by separation of DNA strands.
nucleotides then bind to their complementary DNA nucleotides of the BRCA1 gene
to form a mRNA strand. The mRNA is different to the DNA strand of the BRCA1 gene
as Uracil (U) replaces Thymine and is complementary to Adenine. The resulting
mRNA strand detaches from the BRCA1 gene before the DNA Ligase enzyme joins the
DNA strands together. Splicing of the mRNA occurs to remove introns (Raven 440).
The mRNA now only contains exons, that are primary transcripts of the gene. The
mRNA strands leave the nucleus through nuclear pores to undergo Translation the
second stage of protein synthesis.
Translation occurs at the ribosome found in
the cytoplasm, where production of the tomour suppresser protein from mRNA
occurs. A ribosomal RNA molecule with in the ribosome binds to the
“start” sequence of the mRNA strand. The ribosome then moves the mRNA
strand through 3 nucleotides adding an amino acid. This process continues until
the ribosome encounters a “stop” signal at this point it disengages
from the mRNA and releases the completed suppresser protein. Genetic screening
can allow testing DNA to determine if an individual carries mutated forms of the
BRCA1 gene. DNA collection is the first stage to screen for the BRCA1gene.
blood cells withdrawn from a blood sample contain the needed .