Year 2- Chapter 11-manipulating Genomes Flashcards
What is a genome
This is the minimum quantity of genetic material that contains one copy of all the genes of an individual or of a population or a species.
What is genomics
The application of the techniques of genetics and molecular biology to the mapping of genes on chromosomes and the sequencing of genes or complete genomes of organisms and viruses.
How is genomes measured in different species and the units
Genomes of many species have been sequenced, which means that the whole of the base sequence is known. All of them have double-stranded DNA so their size is measured in base pairs (bp), kilobase pairs (kbp), or megabase pairs (Mbp).
Which genomes are expressed well
Viral genomes are simple and prokaryotic genomes are smaller than eukaryotic genomes.
The control of gene expression in prokaryotes is much simpler than the control of eukaryotic genes. The genomes of eukaryotes have large quantities of DNA that are not transcribed or translated into proteins, but act to control gene expression. Also, eukaryotic genes have introns that are transcribed, but not translated.
What are introns
A segment of DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes
What is gene expression
This is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as tRNA or snRNA genes, the product is a functional RNA.
So there are genes that code for RNA molecules that conduct protein synthesis
Structure of HIV
A single-stranded molecule of RNA with 5000 bases and nine genes
E.coli structure
A single, circular molecule of double-stranded DNA with nearly 5 million base pairs and just over 4000 genes
How is nuclear DNA organised
Nuclear DNA is eukaryotic organisms is divided into regions that have different functions. For example, there are structural genes that code for the assembly of amino acids to make polypeptides.
How is a single gene in terms of its sequence of bases
Exons which are coding sequences (for proteins) are separated from non-coding introns. The gene for a beta polypeptide of haemoglobin has three exons and two introns and is 1605bp in length.
What happens to the structural genes
These are transcribed as mRNA which is then modified and then translated.
What happens to the other DNA structures
Other non-structural genes code for tRNA and rRNA. Some regulatory genes code for proteins that act as transcription factors and many code for forms of RNA that also control transcription and hence gene expression.
What are promoters
These are control sequences found at the site of binding of RNA polymerase at the start of transcription. There are long lengths of DNA that separate structural and regulatory genes. These used to be considered as junk DNA but now they are considered to have a function.
What are mtDNA and ctDNA
DNA in mitochondria are called mtDNA. DNA is chloroplasts are called ctDNA. These two organelles originated from prokaryotes and still possess what are essentially prokaryotic genomes with little non-coding DNA
What are polymerase chain reactions
There are three steps to this:
Denaturation
Annealing
Extension
What is denaturation
This occurs when hydrogen bonds between two polynucleotide strands are broken, thus separating the strands. This allows primers to gain access to the sequence of bases that are now exposed.
This process requires a temperature of 94 degrees centigrade for about 3 minutes.
What is annealing
The temperature in the cycle now decreases to 50-65 degrees centigrade. At this conditions, hydrogen bonds can form between the two types of oligonucleotide primer and the complimentary DNA sequence of bases.
What are the primers for?
The two primers are designed to bind to the region of DNA that is to be copied. Through complementary base pairing, one primer attaches towards the 5’ end of one strand and a different primer attaches towards the 5’ end of the other strand. These strands are antiparallel- one primer attaches at the ‘left’ of one strand and another primer attaches at the ‘right’ of one strand. The sequence of bases in each of the two primers is chosen carefully so that they bind to sequences just outside the region of DNA that is to be amplified (extended).
What are primers important
Necessary to identify sites where synthesis will take place and because DNA polymerase functions by adding nucleotides to an existing piece of double-stranded DNA.
What happens at the extension stage
DNA polymerase will add nucleotides to the primer. Therefore there will be an elongation as DNA polymerase builds up newly synthesised polynucleotide complementary to the template strands (similar to semi conservative replication). The DNA polymerase adds nucleotides to the 3’ end of the primer and synthesises the polynucleotide in the 5’ to 3’ direction. To do this dNTPs (deoxynucleotide triphosphates). This process requires a temperature of 72 degrees centigrade for 90 seconds.
How are phosphodiester bonds between nucleotides formed in the extension stage
The hydrolysis of a bond between the first and second phosphate groups of each dNTP provides the energy for the formation of a phosphodiester bond between the newly added nucleotide and the growing strand.
When and why are primers tagged with fluorescent molecules
So, DNA can be visualised and the progress of PCR monitored. This also allows the DNA to be analysed.
What is Taq polymerase
The bacteria, Thermus aquaticus is the source of heat-stable DNA polymerase Taq polymerase. This is used in the extension stage of PCR.
How many cycles can there be in the extension stage
Multiple
This is done by heating the new synthesised DNA molecules again. This separates the strands, making them available for copying again. Once, again this whole PCR cycle is conducted.