NUCLEIC ACIDS, ATP, GENETIC INFORMATION, PROTEIN SYNTHESIS & ENZYMES

Question 1

DNA and RNA comparison

Question 2

DNA double helix and replication

Answer 2

• Polynucleotides are polymers made up of many nucleotide
  monomers joined together by a series of condensation
  reactions, forming phosphodiester bonds.
• The DNA double helix is held together by hydrogen (H) bonds
  between complementary base pairs.
  ◦ 2 H bonds between Adenine & Thymine
  ◦ 3 H bonds between Cysteine and Guanine
• Semi conservative replication is the method in which DNA
  replicates, creating two molecules of DNA that consist of one
  original DNA strand and one newly synthesised DNA strand.
  ◦ DNA helicase breaks H bonds
  between the two strands
  ◦ Free nucleotides complementary
  base pair to the exposed strands
  ◦ DNA polymerase catalyses
  condensation reactions to join
  adjacent nucleotides, forming
  phosphodiester bonds.

Question 3

genetic information

Answer 3

• In prokaryotic cells, DNA molecules are short, circular and not
  associated with proteins.
• In eukaryotes, the nucleus contains very long, linear DNA
  molecules associated with proteins, called histones. Together a
  DNA molecule and its associated proteins form a chromosome.
• The mitochondria and chloroplasts of eukaryotic cells also
  contain DNA which, like the DNA of prokaryotes, is short,
  circular and not associated with protein.
• The genome is the full set of DNA found in an organism.
• The proteasome is the full range of proteins that can be
  synthesised from the genome.
• A gene is a section of DNA that code for polypeptides and
  functional RNA and are located at a fi xed locus on a DNA molecule.
• A sequence of three DNA bases, called a codon, codes for
  a specifi c amino acid. The genetic code is universal, nonoverlapping and degenerate.
• In eukaryotes, sections of the nuclear DNA do not code for
  polypeptides (introns). Exons are sections of DNA that code for
  amino acid sequences.

Question 4

ATP

Answer 4

• 3 phosphate groups, one adenine base and a ribose sugar group
• ATP hydrolyzed to ADP using ATP hydrolase which releases energy
• ATP is formed in a condensation reaction from ADP using ATP synthase requiring energy

Question 5

protein synthesis

Answer 5

• Structure of tRNA & mRNA:
• Transcription is the process of making messenger RNA From a DNA template.
• DNA helicase breaks the hydrogen bonds between the DNA helix, free RNA nucleotides base pair with the exposed DNA template strand.
• In prokaryotes, transcription results directly in the production of
  mRNA from DNA.
• In eukaryotes, transcription results in the production of premRNA; this is then spliced to form mRNA.
• Translation is the process of making proteins by forming a specific sequence of amino acids based on coded instructions in mRNA. RNA polymerase catalyzes phosphodiester bonds between adjacent RNA nucleotides and the mRNA strand detaches, allowing the DNA helix to reform.
• mRNA attaches to a ribosome on the rough endoplasmic reticulum,
  tRNA carries the corresponding amino acid to each codon on the mRNA one at a time, with an enzyme catalysing the formation of a peptide bond between amino acids using ATP, until a stop codon is reached and the peptide is released, folding into its tertiary structure.

Question 6

enzymes

Answer 6

• Enzymes are biological catalysts that speeds up the rate of reaction
  and remains unchanged and reusable at the end of the reaction.
• They lower the activation energy of the reaction.
• The lock and key model proposed that each substrate is a key that only fits a specific lock or enzyme. The alternative induced fi t model has been proposed
• The specificity of enzymes is due to the tertiary structure of its
  active site, allowing complementary binding to substrates.
• Enzymes catalyse both intracellular and extracellular reactions
  that determine structures and functions from cellular to whole
  organism level.
  ◦ Catalase intracellularly breaks down hydrogen peroxide into
  water and oxygen
  ◦ Amylase is secreted from the salivary glands and pancreas to
  extracellularly break down starch. Requires Cl–
  cofactor
  ◦ Trypsin is secreted from the pancreas to extracellularly break
  down proteins
• Some enzymes are synthesised in an inactive precursor form
  and need to be activated e.g. another enzyme removes part of
  the molecule in trypsin, forming the correct active site shape
• Some enzymes require a cofactor, which is a substance which
  must be present to enable an enzyme to catalyse a reaction at
  the appropriate rate.
  ◦ A prosthetic group is permanently bound e.g. Zn2+ bound to
  carbonic anhydrase
  CO2 + H2O –> H2CO3 –> H+ + HCO3-
  ◦ A coenzyme forms temporary associations and are derived
  from vitamins.