Nucleic acids

• What are the monomers of nucleic acids?


  Nucleotides
• What are the three components of nucleotides?


  Pentose sugar, nitrogenous base, phosphate group
• Draw the structure of a nucleotide


  (Check answer)

  
• What are the two types of organic base?


  Purine and pyrimidine
• What is a purine?


  Class of organic bases, double ring structure, includes adenine and guanine
• What is a pyrimidine?


  Class of organic bases, single ring structure, includes cytosine, thymine and uracil
• What is the structure of a DNA nucleotide?


  Deoxyribose (pentose sugar), phosphate group, nitrogenous base (A, T, C or G)
• What is the structure of an RNA nucleotide?


  Ribose (pentose sugar), phosphate group, nitrogenous base (A, U, C or G)
• What is an endergonic reaction?


  A non-spontaneous reaction that requires an input of energy e.g. ATP formation
• What is an exergonic reaction?


  A spontaneous reaction that overall releases energy e.g. ATP hydrolysis
• What is complimentary base pairing?


  Hydrogen bonds form between complimentary purine and pyrimidine bases

  Two bonds form between A and T (or U)

  Three bonds form between G and C
• What is the structure of DNA?


  Double-stranded polymer of nucleotides twisted to form a double helix

  Nucleotides joined by phosphodiester bonds

  Hydrogen bonds form between complimentary base pairs

  Antiparallel strands
• Why are the strands of a DNA double helix described as 'antiparallel'?


  The complimentary strand run parallel in opposite directions, 5' to 3' and 3' to 5
• What is the structure of RNA?


  Single-stranded polymer of nucleotides

  Nucleotides joined by phosphodiester bonds

  Hydrogen bonds form between complimentary base pairs
• What are the three types of RNA found in cells?


  Transfer RNA (tRNA), messenger RNA (mRNA), ribosomal RNA (rRNA)
• What is the function of tRNA?


  To carry specific amino acids to the ribosomes
• What is the structure of tRNA?


  80 nucleotides

  Single helix

  Clover leaf shape

  Anticodon on one end, amino acid binding site on the other
• What is the function of mRNA?


  To carry genetic information from the nucleus to the ribosomes for protein synthesis
• What is the structure of mRNA?


  2000 nucleotides

  Single helix

  Unstable
• What is the function of rRNA?


  To associate with proteins in the cytoplasm to from ribosomes
• What is the structure of rRNA?


  1800 to 5000 nucleotides

  Two subunits: small and large
• What is semi-conservative replication?


  The replication of DNA to produce two new DNA molecules which both contain one new and one old strand from the original DNA molecules
• What is the role of DNA helicase in semi-conservative replication?


  To catalyse the unzipping of double-stranded DNA into two single strands, each of which acts as a template
• What is the role of DNA polymerase in semi-conservative replication?


  To catalyse the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand
• What is the genetic code?


  The rules by which triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain

  The genetic code is degenerate, universal and non-overlapping
• Why is the genetic code described as degenerate?


  As more than one triplet can code for a particular amino acid
• Why is the genetic code described as universal?


  As the same codons code for the same amino acids in almost all organisms
• What is meant by non-overlapping?


  Each base in a sequence is read once and is only part of one triplet
• What is the 'triplet code' for amino acids?


  A specific sequence of three nucleotides (a codon) on a molecule of DNA or RNA codes for a particular amino acid in protein synthesis
• What is an exon?


  A region of DNA that code for an amino acid sequence
• What is an intron?


  A non-coding sequence of DNA that is found between exons
• What is the difference between eukaryotic and prokaryotic genes?


  Eukaryotic genes are discontinuous with non-coding introns and coding exons, while prokaryotic genes are continuous with coding sequences only
• What is protein synthesis?


  The formation of proteins from amino acids through two stages: transcription and translation
• What is transcription?


  The first stage of protein synthesis: the formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA
• What is the process of transcription?


  DNA helicase unwinds a section of DNA, breaking hydrogen bonds between the DNA strands, antisense strand acts as a template

  RNA polymerase binds to the promoter region on a gene

  Free RNA nucleotides align to their complimentary bases

  RNA polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds

  RNA polymerase reaches stop codon and detaches, mRNA complete
• What is post-transcriptional modification?


  The removal of intron from pre-mRNA in eukaryotic cells by splicing
• What is translation?


  The second stage of protein synthesis that takes place in the ribosomes: mRNA is used as a template for the attachment of tRNA molecules with complimentary anticodons, amino acids carried on adjacent tRNA molecules are joined to form a polypeptide chain
• What is the process of translation?

  mRNA attaches to groove between subunits of ribosomes

  Ribosome moves along the mRNA until it reaches 'start' codon

  Amino acids-tRNA complex anticodon attaches to complementary mRNA codon by hydrogen bonding, another complex binds

  Peptide bonds form between adjacent amino acids in the complexes

  Ribosome moves along one codon and releases empty tRNA, process continues to form polypeptide chain until 'stop' codon is reached
• What is the 'one gene-one polypeptide' hypothesis?


  The theory that each gene encodes a single protein
• What happens to the polypeptide after translation?


  They are further modified by adding carbohydrates, lipids or phosphates

  Different polypeptides may be combined