Nucleic Acids-Topic Two

• What are nucleic acids?


  Biological macromolecules that store and transmit genetic information.

  Examples are ribonucleic acid (RNA) and deoxyribose (DNA).
• What is the structure of a nucleotide?


  consists of a sugar molecule, a phosphate group, and a nitrogenous base. Bases include; adenine, guanine, thymine, cytosine and uracil, which is only found in RNA.
• How are nucleic acids joined?

  ~Pentose sugar, phosphate group and organic bases are joined as a result of condensation reactions to form a single nucleotide (mononucleotide)

  ~The bond formed between the deoxyribose sugar and the phosphate group is called a phosphodiester bond.

  ~New structure is called a dinucleotide

  ~The continued linking of mononucleotides in this way forms a long chain known as a polynucleotide.
• What is the structure of RNA?

  RNA is a single-stranded molecule composed of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, and uracil).
• Who discovered the structure of DNA?

  James Watson and Francis Crick in 1953.
• What is the structure of DNA?

  The structure of DNA is a double helix, consisting of two strands of nucleotides (polynucleotides) that are connected by hydrogen bonds. The pentose sugar is deoxyribose and the bases are adenine, guanine, thymine and cytosine.
• What bases pair together?

  ~Adenine with thymine; complementary base pairs

  ~ Cytosine with guanine; complementary base pairs

  ~They attach by hydrogen bonds
• The double helix structure of DNA

  ~Ladder-like arrangement of two-polynucleotide chains being twisted

  In this way, the uprights of phosphate and deoxyribose wind around one another to form a double helix. They form the structural backbone of the DNA molecule.
• Why is DNA a stable molecule?

  Double helix structure and hydrogen bonding between base pairs.

  ~The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix. • Hydrogen bonds link the organic base pairs forming bridges (rungs) between the phosphodiester uprights. As there are three hydrogen bonds between cytosine and guanine, the higher the proportion of C- G pairings. the more stable the ONA molecule.
• What is the function of DNA?

  ~The function of DNA is to store and transmit genetic information.

  ~DNA is the hereditary material responsible for passing genetic information from cell to cell and generation to generation. In total, there are around 3.2 billion base pairs in the DNA of a typical mammalian cell. This vast number means tha t there is an almost infinite variety of sequences or bases alo ng the length of a DNA molecule. Tt is this variety that provides the genetic diversity within living organisms.
• How is DNA adapted to its function?

  ~It is a very stable structure which normally passes from generation to generation without change. Only rarely does it mutate.

  ~Its two separate strands are joined only with hydrogen bonds, which allow them to separate during DNA replication & protein synthesis.

  ~Base pairing leads to DNA being able to replicate and to transfer information as mRNA.

  ~It is an extremely large molecule and therefore carries an immense amount of genetic information.
• What is nuclear division?


  The process by which the nucleus of a cell divides, resulting in the formation of two daughter nuclei. Two types; meiosis and mitosis
• What is cytokinesis?


  Cytokinesis is the process by which a cell divides its cytoplasm and organelles into two daughter cells.
• What must happen before a cell divides?

  DNA replication. This ensures that all the daughter cells have the genetic information to produce the enzymes and other proteins they need.
• What is semi-conservative replication?

  DNA replication where each new DNA molecule consists of one original strand and one newly synthesized strand.
• What are the requirement to semi- conservative replication?

  ~Four types of nucleotide, each with bases of adenine, guanine, cytosine, thymine must be present

  ~Both strands of DNA molecule must acts as a template for attachment of the nucleotides

  ~Enzyme DNA polymerase

  ~A source of chemical energy is required to drive the process
• What is ATP?


  Adenosine triphosphate
• What is the structure of ATP?

  ATP (adenosine triphosphate) consists of an adenine base, a ribose sugar, and three phosphate groups.
• How does ATP store energy?

  ~ATP is a nucleotide and has three phosphate groups, which are the key to how it stores energy.

  ~The bonds between these groups are unstable & have low activation energy so are easily broken.

  ~ When broken they release a lot of energy
• What is the ATP equation?

  ATP + (H2O) > ADP + Pi + E

  Adenine phosphate + Water > Adenine Diphosphate + Inorganic Phosphate + Energy

  ~As water is used to convert ATP to ADP, known as hydrolysis. The reaction is catalysed the enzyme ATP hydrolase (ATPase)
• What is the synthesis of ATP?

  ~Cellular respiration.

  ~Conversion of ATP to ADP is reversible & energy can be used to add an inorganic phosphate to ADP to re-form ATP according to the equation.

  ~Reaction is catalysed by ATP synthase

  ~Water is removed so it's a condensation reaction
• What is the synthesis of ATP?

  ~In chlorophyll-containing plant cells during photosynthesis (photophosphorylation)

  ~ in plant and animal cells during respiration (oxidative phosphorylation)

  ~ in plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation).
• What is the role of ATP?

  ~Energy currency

  ~Immediate energy source so cells don't store large quantities of ATP

  ~Each ATP molecule releases less energy than each glucose molecule. ~The energy for reactions is therefore released in smaller, more manageable quantities rather than the much greater, and therefore less manageable, release of energy from a glucose molecule.

  ~The hydrolysis of ATP to ADP is a single reaction that releases immediate energy. The breakdown of glucose is a long series of reactions and therefore the energy release takes longer.
• What energy requiring processes in cells is ATP used in?

  ~Metabolic process; energy needed to build macromolecules from their basic units.

  ~Movement; energy needed for muscle contraction, for the filaments of muscle to slide past each other

  ~Active transport; energy to change shape of carrier proteins in plasma membranes

  ~Secretion; needed to form lysosomes necessary for secretion of cell products

  ~Activation of molecules; inorganic phosphate released used to phosphorylate other compounds to make them reactive.
• What is the dipolar water molecule?

  A water molecule that has both positive and negative poles
• What is water and hydrogen bonding?

  ~Intermolecular attraction

  ~Different poles attract, and therefore the positive pole of one water molecule will be attracted to the negative pole of another water molecule. The attractive force between these opposite charges is called a hydrogen bond . Although each bond is fairly weak (about one-tenth as strong as a covalent bond), together they form important forces that cause the water molecules to stick together, giving water its unusual properties.
• What is specific heat capacity of water?

  ~4.18 J/g°C

  ~Water molecules stick together so need more energy (heat) to separate. So the boiling point of water is higher than expected.

  ~Without its hydrogen bonding, water would be a gas (water vapour) at temps commonly found on Earth

  ~It takes more energy to heat given mass of water

  ~Water then acts as a buffer against certain temperature variations making the aquatic environment a temperature-stable one.
• What is latent heat of vaporisaion of water?


  ~2260 kJ/kg

  ~Hydrogen bonding between water molecules means that it requires a lot of energy to evaporate 1 gram of water. This energy is called the latent heat of vaporisation.

  ~Evaporation of water such as sweat in mammals is therefore a very effective means of cooling because body heat is used to evaporate the water.
• What is cohesion and surface tension in water?


  ~The tendency of molecules to stick together is known as cohesion. With its hydrogen bonding, water has large cohesive forces and these allow it to be pulled up through a tube, such as a xylem vessel in plants.

  ~In the same way, where water molecules meet air they tend to be pulled back into the body of water rather than escaping from it. This force is called surface tension and means that the water surface acts like a skin and is strong enough to support small organisms such as pond skaters
• What is the importance of water to living organisms?

  Water is the main constituent of all organisms - up to 98% of a jellyfish is water and mammals are typically 65% water. Water is also where life on Earth arose and it is the environment in which many species still live.
• Water in metabolism?


  ~Water is used to break down many complex molecules by hydrolysis e.g. proteins to amino acids

  ~Water is also produced in condensation reactions

  ~Chemical reactions take place in an aqueous medium

  ~Water is a major raw material in photosynthesis
• Water as a solvent?


  Water readily dissolves other substances;

  ~Gases like oxygen & carbon dioxide

  ~Wastes like ammonia & urea

  ~Inorganic ions & small hydrophilic molecules like amino acids, monosaccharides and ATP

  ~Enzymes, whose reactions take place in solution
• What are other important features of water?


  ~Evaporation cools organisms & allows them to control their temperature

  ~Not easily compressed & so provides support

  ~Transparent & so aquatic planta can photosynthesis and light rays can penetrate the jelly-like fluid that fills they eye & reach the retina
• What are inorganic ions?


  ~Ions that do not contain carbon and are not derived from living organisms.

  ~Found in organisms where they occur in solution in the cytoplasm of cells and in body fluids

  ~May be in concentrations that range from very high to very low
• What is the function of inorganic ions?


  ~Specific function a particular ion performs is related to it properties

  ~Inorganic ions are charged particles that are not part of a larger organic molecule. These ions can be positively charged (cations) or negatively charged (anions) and play important roles in biological processes such as muscle contraction, nerve impulses, and fluid balance.