Nucleotides and Nucleic acids Flashcards
What are nucleic acids?
DNA and RNA
What are the monomers of nucleic acids?
Nucleotides
What is the structure of a nucleotide?
A phosphate group connected to the 5th carbon of a pentose sugar, connected via the 1st carbon to a nitrogenous base.
What different pentose sugars can nucleotides have?
Ribose or deoxyribose.
What different nitrogenous (organic) bases can nucleotides have?
Adenine, thymine, cytosine, guanine or uracil.
Which nitrogenous bases are purines and which are pyrimidines?
Adenine and Guanine are purines.
Cytosine, Uracil and Thymine are pyrimidines.
What is the difference between purines and pyrimidines?
Purines have 2 rings while pyrimidines have only 1.
Pyrimidines bind to purines.
Which bases form bonds and how do they bond?
G and C join with 3 hydrogen bonds.
A,T and U join with 2 hydrogen bonds.
What kind of reaction joins nucleotides and what bonds are formed?
Condensation reactions attach nucleotides forming phosphodiester bonds between the sugar (3rd carbon) and phosphate of each nucleotide. (forms the sugar-phosphate backbone of the nucleic acid)
What is an example of a phosphorylated nucleotide?
ATP and ADP are phosphorylated nucleotides.
ATP is just an adenine nucleotide with 2 extra phosphate groups.
Describe the structure of DNA.
2 complementary DNA strands run anti-parallel and are held together by weak hydrogen bonds. These anti-parallel strands twist forming a double helix.
What does anti-parallel mean?
The complementary DNA strands run in opposite directions. One is 5’ to 3’ and the other is 3’ to 5’.
What is the 5’ (five prime) end of a single DNA stand?
The end which is on the 5th carbon side of the pentose sugars that form the sugar-phosphate backbone.
What is the first step in DNA replication?
DNA helicase unwinds and unzips the DNA strands, breaking the weak H-bonds.
What is the second step in DNA replication?
DNA polymerase adds free, complementary nucleotides to the strands. Creating the leading and lagging strand.
What is the difference between the leading and lagging strand in DNA replication?
The leading strand is continuously copied by DNA polymerase while the lagging strand must be formed in okazaki fragments.
Why is there a leading and lagging strand in DNA replication?
DNA polymerase can only add nucleotides to the 3’ end (in the 5’ to 3’ direction).
Why is DNA replication called “semi-conservative”?
Each new DNA double helix contains one old strand from the original DNA molecule.
What is the nature of the genetic code?
Universal=(codons have the same meaning in all living organisms)
Triplet=(one codon is comprised of 3 nucleotides)
Degenerate=(more than one codon can code for each amino acid)
Non-overlapping=(each nucleotide is only part of one codon)
What is the difference in the genetic code between RNA and DNA?
RNA uses uracil instead of thymine.
What is a mutation in the genetic code?
A rare, random change in the genetic material, that can be inherited if the mutation affects gametes.
What is an example of a harmful mutation?
Sickle cell anaemia (amino acid valine translated instead of glutamate)
Why must transcription happen in protein synthesis?
DNA cannot leave the nucleus as it is too large to fit through the nuclear pore. (designed to protect the DNA)
How is DNA transcribed in protein synthesis?
Gene is exposed by unwinding and unzipping the double helix with DNA helicase.
RNA polymerase forms a complementary mRNA strand.
What is mRNA and what is its purpose?
messenger RNA, takes genetic information from the nucleus to the ribosome.
What happens in gene translation?
tRNA brings complementary anticodons and amino acids, which form weak H-bonds with the mRNA in the ribosome.
Peptide bonds form between adjacent amino acids, forming a polypeptide chain of amino acids which detaches from the mRNA as it is formed.
What is tRNA?
Transfer RNA, a single codon (anticodon) with the corresponding amino acid attatched.
How is the polypeptide chain formed into a protein after translation?
The chain is taken to the golgi apparatus, where it is modified, folded and packed forming a protein.
What is rRNA?
Ribosomal RNA, forms part of the ribosome.
