2.1.3 nucleic acids Flashcards
what are the 2 types of nucleic acids?
DNA and RNA
what are the roles of nucleic acids?
storage and transfer of genetic information, synthesis of proteins
what elements are inside nucleic acids?
C, H, O, N, P
what are the components of a nucleotide?
pentose sugar, a phosphate group (PO4 2-) that is inorganic and acidic, a nitrogenous base
what are the bonds that form the sugar phosphate backbone? how are they formed?
phosphate group at the fifth carbon of the penrose sugar (5’) forms a covalent bond with the OH group at the third carbon (3’) of the penrose sugar of an adjacent nucleotide.
what sugar is in DNA and how is it different to the sugar in RNA?
DNA has deoxyribose which has one fewer oxygen atoms than ribose in RNA
What are pyrimidines?
smaller bases which contain single carbon rings (thymine and cytosine)
what are purines?
larger bases which contain double carbon rings structures (adenine and guanine)
how many hydrogen bonds do A and T form?
2
how many hydrogen bonds do C and G form?
3
how are the 2 strands of the DNA double helix held together?
hydrogen bonds between bases and they run antiparallel to each other
what does complementary base pairing mean?
A and T always bonded together and C and G always bonded together meaning DNA always has equal amounts of complementary bases
what does RNA do?
plays an essential role in the transfer of genetic information from DNA to the ribosomes to make proteins
How is an RNA molecule different to a DNA molecule?
ribose sugar is used instead of deoxyribose and the base thymine is replaced by uracil
what happens to RNA after protein synthesis?
the RNA molecules are degraded in the cytoplasm. phosphodiester bonds are hydrolysed and RNA nucleotides are released and reused
Explain the process of extracting DNA from a plant.
•grind sample in a mortar and pestle to break down cell walls.
•mix sample with detergent to break down cell membrane releasing the contents of the cell into solution.
•add salt to to break down hydrogen bonds between DNA and water molecules
•add protease to break down proteins associated with DNA
•add a layer of ethanol on top of the sample causing DNA to precipitate out of solution
•DNA will be seen as white strands forming between the layer of sample and alcohol
why is DNA replication semi conservative?
2 new molecules of DNA are produced each consisting of one parent strand of DNA and one new synthesised strand of DNA
what does DNA helicase do?
it travels along the DNA backbone catalysing reactions that break the hydrogen bonds between complementary base pairs. can be thought of as unzipping the DNA molecule
what does DNA polymerase do?
free nucleotides pair with the now exposed bases on the template strands and polymerase catalyses the formation of phosphodiester bonds between nucleotides
Explain DNA replication.
•DNA helicase causes the two strands of DNA to separate by breaking hydrogen bonds
•free nucleotides that have been activated are attracted to their complementary bases
•once bases have been paired, the nucleotides are joined together by DNA polymerase forming phosphodiester bonds.
•finally, all new nucleotides are joined together to form a complete polynucleotide chain.
•2 new molecules of DNA are formed each identical to the original
What is continuous replication?
the strand that is unzipped from 3’-5’ as polymerase can only unzip DNA in one direction. 3’-5’ is continuously replicated as the strand unzips
what is discontinuous replication?
when the strand is unzipped 5’-3’ so DNA polymerase has to wait until a section of the strand has unzipped and then work back along the strand. this results in DNA being produced in sections callled okazaki fragments which then have to be joined
what is a mutation?
a change in the genetic material which may affect the phenotype of the organism
