2 - Nucleic Acids

• 3.1.5.1 - State what the main 2 types of nucleic acids are?

  & thus briefly explain what the function of both types is each.

  • DNA & RNA are both types of nucleic acids (which are found in all living cells and both CARRY IMPORTANT INFORMATION)

  1. DNA is used to store genetic information

  2)Whereas RNA (ribonucleic acid) is used to transfer genetic information from the DNA to the ribosomes
• 3.1.5.1 - Describe how DNA holds genetic information in all living cells?

  • Genetic information is carried in the linear sequence of nucleotides in DNA
  • Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds between G-C and A-T base pairs.
• 3.1.5.2 - Describe how RNA transfers genetic information from DNA to the ribosomes?

  • Messenger RNA (mRNA) molecules carry the coding sequences for protein synthesis and are called transcripts
  • ribosomal RNA (rRNA) molecules form the core of a cell's ribosomes (the structures in which protein synthesis takes place)
  • transfer RNA (tRNA) molecules carry amino acids to the ribosomes during protein synthesis.
• 3.1.5.2 - What forms ribosomes?

  Ribosomes are formed from RNA and proteins.
• 3.1.5.2 - State what 3 things make up nucleotides?

  & thus how does DNA & RNA link to nucleotide?

  A nucleotide is made from;

  1. a pentose sugar
  2. a nitrogen containing organic base
  3. a phosphate group

  • & thus DNA & RNA are polymers of nucleotides
• 3.1.5.2 - Describe what is contained within a DNA nucleotide?

  1. The pentose sugar in a DNA nucleotide is called deoxyribose
  2. Each DNA nucleotide has the same sugar and a phosphate group
  3. However, the base on each nucleotide can vary

  • 4 bases are; adenine (A), thymine (T), cytosine (C) & guanine (G)

  
• 3.1.5.2 - Describe what is contained within a RNA nucleotide?

  1. The pentose sugar in a RNA nucleotide is called a ribose sugar
  2. Each RNA nucleotide has the same sugar and a phosphate group
  3. The base on each nucleotide can vary

  • 4 bases are; Adenine (A), Uracil (U), Cytosine (C) & Guanine (G)

  
• 3.1.5.2 - Explain when a phosphodiester bond is formed?

  A phosphodiester bond is formed from a condensation reaction of 2 nucleotides joining together between the phosphate group of one nucleotide and the sugar of another.

  
• 3.1.5.2 - Describe what the structure of a DNA molecule consists of?

  DNA has a double helix structure with;

  • 2 polynucleotide chains
  • That are held together by 2 hydrogen bonds between A & T, and 3 hydrogen bonds between C & G
  • thus 2 antiparallel polynucleotide strands twist to form the DNA double-helix

  
• 3.1.5.2 - Describe what the structure of a RNA molecule consists of?

  RNA is a relatively short polynucleotide chain

  • as it is made from a single polynucleotide chain (rather than a double one)
  • & thus it is shorter than most DNA nucleotides
• 3.1.5.2 - Explain why many scientists had previously doubted that DNA actually carried the genetic code?

  • Many scientists during the 1st observation of DNA in the 1800s doubted DNA could actually carry the genetic code because it has a relatively simple chemical composition
  • Instead, they argued that genetic information must be carried by proteins as they are more “chemically varied”
• 3.1.5.2 - State and explain what process ensures genetic continuity between generations of cells?

  • Semi-conservative replication is the method whereby DNA replicates itself before cell division, so that each new cell has the full amount of DNA
  • It’s called semi-conservative as half of the strands in each new DNA molecule are from the original DNA molecule (thus meaning that there is genetic continuity between generations of cells)
• 3.1.5.2 - Describe what the process of semi-conservative replication consists of?

  1. The enzyme DNA helicase breaks the hydrogen bonds between bases on the 2 polynucleotide strands (causing the double helix to now separate into 2 separate strands)
  2. Each exposed polynucloetide strand then acts as a template to which complementary free nucleotides bind by specific base pairing
  3. Condensation reactions join the nucleotides of the new strands together - catalysed by the enzyme DNA polymerase

  • thus each new DNA molecule now has 1 strand from the original DNA molecule & 1 new strand
• 3.1.5.2 - Explain what issue people previously had with Watson and Crick’s theory of semi-conservative replication?

  & thus what are the names of the 2 scientists that proved this belief wrong & briefly describe how they did this?

  1. people were unsure whether DNA replication was semi-conservative or “conservative” (if the method was conservative then the original DNA strands would stay together & the new DNA molecules would contain 2 new strands)
  2. & thus scientists Meselson & Stahl proved this idea wrong by using 2 isotopes of nitrogen & samples of bacteria (as DNA contains nitrogen)
• 3.1.5.2 - Briefly describe how Meselson & Stahl used 2 different isotopes of nitrogen to prove that DNA replicated via semi-conservative replication

  • Meselson and Stahl's experiment proved the incorrect idea of “conservative“ replication wrong by growing their bacterias DNA in two different environments one after another.
  • So when the bacteria with old DNA material replicated in the new environment, half its DNA would be from the old material and the other half would be made of new material from the new environment
  • thus showing the DNA had split into two template strands
• 3.1.6 - Describe what is used to make ATP (adenosine triphosphate) and thus link this to why this is done?

  • the energy released from glucose during respiration is used to make ATP
  • this is because plant and animal cells can’t get its energy directly from glucose (when energy is first released from glucose during respiration)
  • instead, once ATP is made it diffuses to the part of the cell that needs energy
• 3.1.6 - Define what is meant by a ‘nucleotide derivative’?

  & thus describe how ATP links to a nucleotide derivative?

  A nucleotide derivative is a modified form of a nucleotide.

  & thus ATP is made from the nucleotide base adenine, combined with a ribose sugar and 3 phosphate groups.

  
• 3.1.6 - State what ATP is broken down into when energy is needed by a cell?

  & thus explain what reaction this is done via?

  • When energy is needed by a cell, ATP is broken down into ADP (adenosine diphosphate) and Pi (inorganic phosphate)
  • This is done via a hydrolosis reaction, as a phosphate bond is broken and energy is released.
  • This reaction is catalysed by the enzyme ATP hydrolase
• 3.1.6 - What is significant about ATP hydrolysis?

  • ATP hydrolysis can be ”coupled” to other energy-requiring reactions in the cell
  • thus meaning that the energy released can be used directly to make the coupled reaction happen, rather than being lost as heat
• 3.1.6 - What is significant about the released Pi (inorganic phosphate)?

  The released inorganic phosphate can also be added to another compound, which often makes the compound more reactive.

  • this process is known as phosphorylation
• 3.1.6 - Describe how ATP can be re-synthesised?

  • ATP can be re-synthesised in a condensation reaction between ADP & Pi
  • This happens during both respiration and photosynthesis, & is thus catalysed by the enzyme ATP synthase

  
• 3.1.7 - Describe what water is?

  Water is a major component of cells.
• 3.1.7 - State what many metabolic reactions involve?

  & thus explain how water is an important metabolite?

  • Many metabolic reactions involve a condensation or hydrolosis reaction
  • & thus water is an important metabolite as;

  1. A hydrolysis reaction requires a molecule of water to break a bond
  2. & a condensation reaction releases a molecule of water as a new bond is formed
• 3.1.7 - Explain how water is a good solvent?

  • Due to many important substances within metabolic reactions being ionic
  • it means that they’re made from 1 positively charged atom/molecule & 1 negatively charged atom/molecule & as water is a polar molecule;
  • the positive end of a water molecule will be attracted to the negative ion
  • & the negative end of a water molecule will be attracted to the positive ion
  • thus meaning that the ions will get totally surrounded by water molecules (& dissolve)

  
• 3.1.7 - Explain how water having a high specific heat capacity can buffer changes in temperature?

  • Water has a high specific heat capacity as the hydrogen bonds between molecules can absorb a lot of energy, & thus a lot of energy is required to heat it up
  • This is beneficial for organisms living under water as the temperature under water is likely to be more stable than on land (thus making it a good habitat)
  • The water inside organisms also remains at a stable temperature, meaning that a constant internal body temperature can be maintained
• 3.1.7 - Explain why water has a high latent heat of vaporisation?

  & thus why is this beneficial for living organisms?

  • Water has a high latent heat of vaporisation as a lot of energy is used up when water evaporates (vaporises)
  • This is beneficial for living organisms as it means they can use water loss through evaporation to cool down (eg: sweat) without losing too much water
• 3.1.7 - Explain how water having strong cohesion between its water molecules is beneficial?

  • Strong cohesion helps water flow, thus making it useful for transporting substances
  • Strong cohesion also means that water has a high surface tension when it comes into contact with air (& thus is the reason why sweat can form droplets, which evaporate from the skin to cool an organism down)
• 3.1.8 - Describe what an inorganic ion is and include where it can be found?

  • An inorganic ion is one which doesn’t contain carbon
  • There are inorganic ions in solution, in the cytoplasms of cells and in the body fluids of organisms
• 3.1.8 - What is significant about each type of ion?

  • Each ion has a specific role depending on its properties
  • An ion’s role determines whether it is found in high or low concentrations
• 3.1.8 - Describe what the role is of iron ions?

  • Iron ions are an important part of haemoglobin, as it is the Fe2+ that actually binds to the oxygen in haemoglobin
  • Haemoglobin is made up of 4 different polypeptide chains, each with an iron ion (Fe2+) in the centre
  • Thus, when oxygen is bound, the Fe2+ ion temporarily becomes an Fe3+ ion until oxygen is released
• 3.1.8 - Describe what the role is of hydrogen ions?

  • Hydrogen ions determine pH as pH is calculated based on the concentration of hydrogen ions (H+) in the environment
  • & thus the more hydrogen ions present, the lower the pH (& the more acidic the environmen)
• 3.1.8 - Describe what the role is of sodium ions?

  • Sodium ions help transport glucose and amino acids across membranes
  • (A molecule of glucose or an amino acid can be transported into a cell alongside sodium ions, which is known as co-transport)
• 3.1.8 - Describe what the role is of phosphate ions?

  • Phosphate ions are an essential component of ATP & DNA and this is as;
  • When a phosphate ion is attached to another molecule, it’s known as a phosphate group
  • & DNA, RNA and ATP all contain phosphate groups
  • It’s the bonds between phosphate groups that store energy in ATP