Structure of DNA & RNA, DNA replication Flashcards
What three components are individual nucleotides made up of
- A pentose sugar
- A phosphate group
- A nitrogen containing organic base (A,T,C,G)
How are individual mononucleotides joined to form a polynucleotide
They are joined as a result of a condensation reaction between the deoxyribose sugar of one mononucleotide and the phosphate group of another. The bond formed is a phosphodiester bond.
In what order are the pentose sugar, phosphate group and base joined in a nucleotide
Pentose sugar in the middle joined onto the base and phosphate group either side.
Describe the structure of RNA
RNA is a single, relatively short polynucleotide chain in which the sugar is always ribose and the organic bases are adenine, guanine, cytosine and uracil.
Summarise the function of each of the three types of RNA
1) One type of RNA transfers genetic information from DNA to the ribosomes.
2) ribosomes are made of proteins and another type of RNA
3) A third type of RNA is involved in protein synthesis.
Describe the structure of DNA
- DNA consists of two strands of polynucleotides forming a double helix shape.
- In DNA, the pentose sugar is deoxyribose and the organic bases are adenine, thymine, cytosine and guanine.
- The hydrogen bonds that hold the double helix together form between complementary bases.
Which bases pair and form hydrogen bonds in
- Adenine and Thymine
- Cytosine and Guanine
Why is DNA a stable molecule
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix.
- Hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights. As there are three hydrogen bonds between cytosine and guanine, the higher the proportion of C—G pairs, the more stable the DNA molecule.
Describe how the DNA molecule is adapted to carry out its functions
- It is a very stable structure which normally passes from generation to generation without significant change. Most mutations are repaired, so persistent mutations are rare.
- Its two separate strands are joined only by hydrogen bonds which allows it to separate during DNA replication and protein synthesis.
- It is an extremely large molecule and therefore carries an immense amount of genetic information.
- By having the base pairs within the cylinder of the deoxyribose-phosphate backbone, the genetic information is to some extent protected from becoming corrupted by outside chemical and physical forces.
- Base pairing leads to DNA being able to replicate and to transfer information as mRNA.
What are the two main stages in cell division
- Nuclear division
- Cytokinesis
What is nuclear division and what are the two types
Nuclear division is the process by which the nucleus divides. This could be via mitosis or meiosis
What is cytokinesis
Cytokinesis follows nuclear division and is the process by which the whole cell divides.
What is the model of DNA replication that is generally accepted
The semi-conservative model of DNA replication
What are the four requirements for semi-conservative replication to take place
1) the four types of nucleotide each with their bases of A,T,C or G must be present
2) Both stands of the DNA molecule act for a template for the attachment of these nucleotides.
3) The enzyme DNA polymerase
4) A source of chemical energy is required to drive the process.
Describe the process of semi-conservative DNA replication
1) The enzyme DNA helicase breaks down the hydrogen bonds linking the base pairs of DNA
2) As a result the double helix separates into its two strands and unwinds.
3) Each exposed polynucleotide strand then acts as a template to which complementary free nucleotides bind by specific base pairing.
4) Nucleotides are joined together in a condensation reaction by the enzyme DNA polymerase to form the ‘missing’ polynucleotide strand on each of the two original strands of DNA
5) Each of the new DNA molecules contains one of the original DNA strands- ie semi-conservative model.
