Key processes- last minute panic deck

• Transcription:


  Hydrogen bonds between DNA bases break,

  Only one DNA strand acts as a template,

  Free RNA nucleotides align by complementary base pairing,

  In RNA uracil base pairs with adenine,

  RNA polymerase joins adjacent RNA nucleotides,

  by phosphodiester bonds,

  Pre-mRNA is spliced to form mRNA
• Translation:


  mRNA attaches to ribosomes,

  tRNA anticodons bind to complementary mRNA codons,

  tRNA brings a specific amino acid,

  Amino acids join by peptide bonds,

  With the use of ATP,

  tRNA released after amino acids join to the polypeptide,

  The ribosomes moves along the mRNA to form the polypeptide.
• Transport of sugars in plants stem:

  At source sucrose is actively transported into the phloem tube,

  By companion/transfer cells,

  This lowers the water potential in phloem + water enters by osmosis,

  Produces high hydrostatic pressure,

  Mass flow towards sinks/roots.
• How does a Mutation lead to a non-functional protein:

  A mutation changes the DNA nucleotide bases,

  This changes the amino acid sequence,

  Altering the positions of hydrogen bonds,

  Changing the 3D tertiary structure of the protein.
• Explain a decrease in biodiversity:


  Removes plant species,

  Reducing food sources,

  Reducing habitats.
• cellulose:


  Long, straight/unbranched chains of beta glucose,

  Joined by H bonds,

  Form microfibrils,

  Provide rigidity/strength.
• Starch:


  Helical so compact,

  Insoluble so osmotically inactive,

  Branched so glucose is easily released for respiration,

  large molecule so cannot leave across cell membrane.
• Glycogen:


  Highly branched easily broken for fast source of energy,

  alpha glucose,

  Insoluble.
• Reducing sugars food test:

  Heat in benedict solution,

  Red/green/orange colour shows maltose/reducing sugar
• Non-reducing sugars food test:

  Heat with acid and neutralise,

  Heat with benedict solution,

  Red precipitate/colour.
• Co-transport:


  co-transport,

  uses hydrolysis of ATP,

  Sodium ion and protein bind to the protein,

  Protein change shape to move sodium ion/protein across the membrane.
• Induced fit:

  Before reaction active is not complementary to substrate,

  Shape of active site changes as enzyme-substrate complex forms,

  Bending bonds in substrate lead to a reaction..
• Starch food test:

  Iodine,

  blue/black
• Lipids food test:

  add ethanol,

  shake,

  add water,

  white emulsion positive
• Proteins food test:

  Buiret,

  Lilac purple
• Semi-conservative replication:


  DNA helicase breaks H bonds/seperates strands,

  Both strands act as a template,

  Free nucleotides attach,

  By complimentary base pairing (AT and GC)

  DNA polymerase joins nucleotides,

  H bonds reform,

  One old strand and one new/semi-conservative replication.
• Xerophyte adapted to reduce water loss:

  Thick cuticle - reduces water loss by evaporation,

  Rolling up of leaves - so stomata are on the inside +traps local humidity/air with a high water potential so no water loss,

  Hairs - traps moist air next to leaf, reducing water potential gradient,

  Stomata in pit/grooves - traps moist air,

  Reduced SA:V of leaves (cactus spines) - reduces SA for respiration.
• Adaptations of leaf for rapid diffusion:


  Short diffusion pathway - cells close to stoma,

  Lots of air spaces - gases can diffuse into more mesophyll cells,

  Large SA of mesophyll cells - rapid diffusion.
• Ventilation (Inspiration/breathing in):

  External intercostal muscles contract + internal intercostal muscles relax,

  Ribs move up and out increasing thorax volume,

  Diaphram muscles contract moving down, flattening and increasing thorax volume,

  Air pressure in lungs less than atmospheric pressure,

  Air force in by higher external atmospheric pressure.
• Ventilation (expiration/breathing out):

  Internal intercostal muscle contract + external intercostal muscles relax,

  Ribs move down and in + diaphram relaxes and moves up = decreasing volume of thorax,

  Air pressure in alveoli is more than atmospheric pressure so forces air out.
• Water

  • High specific heat capacity - buffers heat changes in organisms and makes sure large bodies of water don't change as quickly as land protecting aquatic organisms
  • Large latent heat of vaporisation - animals able to sweat so can keep cool as water evaporates of surface and plants cooled by evaporation
  • Strong cohesion - allows water to move up the xylem as continuous stream
  • Important solvent - allows substances dissolved in water to be transported around living organisms
  • A metabolyte - Hydrolysis important in digestion and condensation important in synthesis of molecules/proteins
• t cell:


  •        Pathogen enters the body and is engulfed by a phagocyte which can act as an antigen presenting cell (APC)

  •        APC processes and presents the antigen

  •        T cell receptor binds to APC

  •        T cells divide and differentiate via mitosis

  •        T Helper cells release cytokines that stimulate and activate B cells to divide and make antibodies

  •        They also stimulate phagocytosis

  •        T killer cells are cytotoxic and kill infected cells by making holes in their cell surface membrane

  •        T memory cells are also made and remain in the blood 
• •        Once the B Cell is activated by a APC it differentiates by mitosis into either a plasma cell or a B memory cell

  •        B plasma cells produce and release antibodies

  •        Antibodies are specific to the pathogen and bind, cause agglutination transporting the pathogens to the phagocyte


  b cell:
• HIV


  • Inserts RNA and reverse transcriptase into the T Helper cell
• HIV


  • Attaches to receptors on CD4 T helper cells
• HIV replication


  1. Reverse transcriptase causes production of HIV DNA from RNA

  2. Viral DNA inserted into human DNA

  3. Protein synthesis occurs

  4. Viral HIV particles made and leave cell by exocytosis, destroying T helper cell

  5. Viral particles go on to infect more cells
• T killer cells come

  Destroy infected T helper cells
• Reduction of T helper cells

  Cannot activate B cells or stimulate phagocytosis, cannot fight infection
• Transpiration


  1. Water vapour evaporates from the leaf

  2. This lowers the pressure at the top

  3. Ions are actively transported into the roots, this lowers the water potential of the root hair cells so water follows by osmosis

  4. This creates a high hydrostatic pressure at the bottom on the xylem

  5. Water moves from a high to low pressure – mass flow
• Water molecules


  • They are attracted to each other due to cohesive forces caused by hydrogen bonding
  • They are attracted to the walls of the xylem due to adhesive forces caused by hydrogen bonding
• cohesion tension thoery:

  •        What is lost from the leaf by transpiration

  •        This lowers the water potential of the mesophyll cells


  •        Water is pulled up the xylem in a continuous column

  •        As water  molecules stick together because of H-bonding – cohesion

  •        Water molecules are attracted to the sides of the xylem – adhesion

  •        Pull the xylem in – narrower 
• How does oxygen in the air reach capillaries surroundig the alveoli?

  Trachea, bronchi, bronchioles,

  Down pressure gradient,

  Down diffusion gradient,

  Across alveolar epithelium,

  across capillary endothelium.
• Explain how human gas exchange is adapted for efficient gas exchange?

  Large SA - numerous alveoli/capillaries where exchange occurs,

  Narrow capillaries slow down flow of blood - more time for diffusion/reduces diffusion pathway,

  Concentration gradients maintained by ventilation/flow of blood through capillaries