2.1.3 Nucleotides And Nucleic Acids Flashcards
Describe the structure of a nucleotide
Phosphate group
Pentose sugar
Nitrogenous organic base
State the difference between an RNA nucleotide and DNA nucleotide
RNA has a ribose pentose sugar
DNA has a deoxyribose pentose sugar
Define purines
Purines are bases which contain double carbon ring structures.
Adenine and guanine are purines.
Define pyrimidines
Pyrimidines are bases which contain single carbon ring structures.
Thymine and cytosine are pyrimidines.
Outline the synthesis of polynucleotides
Condensation reaction between phosphate groups and carbons of pentose sugars form phosphodiester bonds between adjacent nucleotides.
This forms a sugar-phosphate backbone.
Outline the breakdown of polynucleotides
Hydrolysis reactions break phosphodiester bonds to release individual nucleotides.
Describe the structure of ATP and ADP
ATP
- Three phosphate groups
- Ribose sugar
- Nitrogenous base
ADP
- Two phosphate groups
- Ribose sugar
- Nitrogenous base
Describe the structure of DNA
Two strands of polynucleotides coil into a helix shape
Two strands are held together by hydrogen bonding between complementary base pairs
Two strands are parallel and run in opposite directions
DNA has a double helix, anti-parallel structure.
Explain complementary base pairing in a DNA molecule
Adenine and Thymine form two hydrogen bonds
Cytosine and guanine form three hydrogen bonds
Outline the process of semi-conservative replication
DNA molecule is separated into two single strands
Free DNA nucleotides will form hydrogen bonds with complementary base pairings
Adjacent nucleotides will form phosphodiester bonds
Two new DNA molecules are produced, consisting of one old strand and one new strand.
Explain the role of enzymes in semi-conservative replication
DNA helicase - separation of DNA strand by catalysing reactions that break down hydrogen bonds between complementary base pairs
DNA polymerase - Formation of sugar phosphate backbone by catalysing the formation of phosphodiester bonds between adjacent nucleotides
State the importance of DNA replication
Cells divide to produce more cells needed for growth or repair of tissues
Cells produced as a result of cell division are genetically identical to the parent cell and each-other.
Define mutation
Random and spontaneous change in the sequence of bases in a DNA molecule
Define genetic code, triplet codon, degenerate code, universal code, gene, non-overlapping code
Genetic code - DNA codes for sequence of amino acids
Triplet codon - three bases code for an amino acid
Degenerate code - several triplet codons code for one amino acid
Universal - all organisms use the same genetic code
Gene - a section of DNA that codes for a protein
Non overlapping - each nucleotide is only part of one triplet of bases
Outline the process of transcription, stating the roles of RNA polymerase and messenger (m)RNA
DNA molecule is separated into two strands
Free RNA nucleotides form complementary base pairing with exposed DNA bases
Adjacent RNA nucleotides form phosphodiester bonds catalysed by RNA polymerase
mRNA molecule detaches from DNA strand and leaves through nuclear pore
DNA double helix reforms
Outline the process of translation, stating the roles of transfer (t)RNA, ribosomes and messenger (m)RNA
mRNA binds to the ribosome from the start codon
tRNA with complementary anticodon binds to the start codon
tRNA carries the amino acid which corresponds to the codon of the mRNA
This repeats with another tRNA molecule
The adjacent amino acids form a peptide bond
The ribosome then moves along the mRNA , releasing the first tRNA and the process repeats until a stop codon is reached
What is produced as a result of translation?
A polypeptide.
The sequence of amino acids in a polypeptide is the primary structure of a protein.
What is the process of purifying DNA by precipitation?
Purpose: To isolate DNA from a mixture of cellular components.
Steps:
Cell Lysis: Break open cells to release DNA, often using a detergent to dissolve cell membranes.
Removal of Proteins: Add a protease or use salt (e.g., NaCl) to separate proteins from DNA.
Precipitation: Add alcohol (e.g., ethanol) to the solution. DNA is not soluble in alcohol and precipitates out of solution.
Isolation: Use a centrifuge or careful technique to collect the precipitated DNA. It can then be spooled or washed to remove impurities.
What aree the key concepts for the purification of DNA by precipitation
*DNA is insoluble in alcohol and can be precipitated by changing the solubility conditions.
*The role of salt - to separate proteins from DNA - and alcohol - DNA is insoluble in alcohol - in promoting DNA precipitation.
*The importance of maintaining cold temperatures to prevent DNA degradation.
