Mr McAlonan - DNA Flashcards
What is semi conservative replication
- For DNA to replicate , the double helix structure has to unwind and then separate into two strands , so the hydrogen bonds holding the complementary bases together must be broken.
- Free DNA nucleotides will then pair with their complementary bases which have been exposed as the strands separate .
- Hydrogen bonds are formed between them.
- Finally , the new nucleotides join to their adjacent nucleotides with phosphodiester bonds.
In this way two new molecules of DNA are produced .
Each one consists of one old strand of DNA and one new strand .
This is known as semi conservative meaning half the same replication .
What are the roles of enzymes in the replication
- DNA replication is controlled by enzymes a day of proteins that act as catalysts for biochemical reactions. Enzymes are only able to carry out the function by recognising and attaching to specific molecules or particular parts of the molecules.
- Before replication can occur, the unwinding and separating of the two strands of the DNA double helix is carried out by the enzyme DNA helicase. It travels along the DNA backbone. catalysing reactions that break the hydrogen bonds between complementary base pairs as it reaches them. This can be thought of as the strand ‘unzipping’. is
- Free nucleotides pair with the newly exposed bases on the template strands during the ‘unzipping’ process. A second enzyme, DNA polymerase catalyses the formation of phosphodiester bonds between these nucleotides.
What are the 5 stages of DNA replication
a) A representative portion of DNA, which is about to undergo replication.
b) An enzyme, DNA helicase, causes the two strands of the DNA to separate.
c) DNA helicase completes the separation of the strand. Meanwhile, free nucleotides that have been activated are attracted to their complementary bases
d) Once the activated nucleotides are lined up, they are joined together by DNA polymerase (bottom three nucleotides). The remaining unpaired bases continue to attract their complementary nucleotides.
e) Finally, all the nucleotides are joined to form a complete polynucleotide chain using DNA polymerase. In this way, two identical molecules of DNA are formed. Each new molecule of DNA is composed of one original strand and one newly formed molecule - semi-conservative replication.
What are some of the replication errors that can occur
Sequences of tenses are not always matched exactly, and an incorrect sequence may occur in the newtły-copied strand. These errors occur ily spontaneously and lead to a change in the sequence of randomly and bases, known as a mutation
What is the genetic code
DNA is contained within the cells of all organisms and scientists determined that this molecule was the means by which genetic information was passed from one generation to the next. But how does this happen? Scientists understood that DNA must carry the instructions or blueprint needed to synthesise the many different the lagging strand has to be located in proteins needed by these organisms.
Proteins are the foundation for the different physical and biochemical characteristics of living things.
They are made up of a sequence of amino acids, folded into complex structures.
Therefore DNA must ade for a sequence of amino acids. This is called the genetic code
What is a triplet code
The instructions that DNA caric are contained in the sequence of bases along the chain of nucleotides that make up the two strands of DNA.
The code in the base sequences is a simple triplet code. It is a sequence of three bases called a codon. Each codon codes for an amino acid.
A section of DNA that contains the complete sequence of bases teodums) to code for an entire protein is called a gene
The genetic code is universal all organisms use this same code. although the sequences of bases coding for each individual proteins will be different
What is a Degenerate code
there are four different bases, which means there are 64 different base triplets or codons possible (4 or 4 x 4 x 4). This includes one codon that acts as the start codon when it comes at the beginning of a gene, signalling the start of a sequence that codes for a protein. If it is in the middle of a gene, it codes for the amino acid methionine. There are also three ‘stop’ codons that do not code for any amino acids and signal the end of the sequence.
Having a single codon to signal the start of a sequence ensures that the triplets of bases (codons) are read ‘in frame’. In other words the DNA base sequence is ‘read’ from base 1, rather than base 2 or 3. So the genetic code is non-overlapping.
As there are only 20 different amino acids that regularly occur in biological proteins, there are a lot more codons than amino acids. Therefore, many amino acids can be coded for by more than one codon,
