DNA - alevel biology

• Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), which is the chemical energy currency of cells.
• The mitochondrial matrix contains enzymes that catalyze reactions involved in ATP synthesis, such as oxidative phosphorylation.
• why is a membrane structure model called a fluid mosaic?

  Phospholipids and proteins are abks to move. And embedded proteins vary in structure and size.
• phospholipid bilayer


  a double layer of phospholipid molecules that form membranes in cells. Hydrophilic head and hydrophobic tail forms a hydrophobic region.
• Golgi apparatus

  modifies and packages proteins for export by the cell
• Why is cholesterol important?


  Reduces membrane fluidity and permeability (binds hydrocarbon tails together reducing spaces for diffusion).
• Unsaturated membrane


  A more liquid membrane as they have kinks in tails so are more loosely packed.
• Saturated membrane


  A more solid membrane as they are long and straight so more tightly packed.
• passive transport


  the movement of substances across a cell membrane without the use of energy by the cell
• active transport


  the movement of materials through a cell membrane using energy from ATP
• Diffusion


  Net movement of molecules/ions down a conc. gradient from a region of high conc. to low conc. through the phospholipid bilayer
• facilitated diffusion


  Net diffusion down a conc. gradient in which molecules pass through carrier or channel proteins in c.s.m.
• Osmosis


  The net movement of water molecules from a region of high water potential to a region of lower water potential across a partially permeable membrane (phospholipid bilayer).
• carrier protein


  a protein that transports substances across a cell membrane actively or passively.
• Cotransport


  Two substances move in the same direction at the same time e.g. sodium ions and glucose or sodium ions and amino acids.
• Rate of diffusion affected by

  Temperature, conc. gradient, surface area (due to microvilli).
• Carrier and channel proteins limit rate of diffusion


  Number of carrier/channel proteins becomes a limiting factor as they are limited- eventually working at their maximum rate.
• Rate of facilitated diffusion increased by

  Increasing temperature, increasing conc. gradient, increasing no. Of carrier/channel proteins.
• water potential gradient

  Maximum value is 0. More solute= lower water potential (becomes a negative value)
• plasmolyzed


  shrunken; solute concentration is higher outside (in solution of lower water potential) the cell cytoplasm. Cytoplasm peels away allowing solutions to enter (plants). Animal cells shrivel/ crenated.
• Lysis of cells

  In animals Water enters and cell membrane can not withstand pressure (no cell wall). Plant cells become turgid.
• active transport


  Molecules/ions moved across a membrane against their conc. gradient using specific carrier proteins.
• Factors that limit rate of active transport

  Number of carrier proteins, lack of ATP and any factor that reduces aerobic respiration e.g. respiratory poison.
• What molecules can cross the phospholipid bilayer (properties)?


  Small, non- polar, lipid soluble and no charge.
• What molecules can't cross the phospholipid bilayer (properties)?

  Larger, polar, water soluble and charged.
• Eukaryotic cells


  Have a membrane bound nucleus, ribosomes and other membrane bound organelles.
• Prokaryotic cells


  A cell that lacks a membrane bound nucleus or any other membrane bound organelles.
• Are eukaryotic cells bigger than DNA?

  No, prokaryotic cells are much smaller than eukaryotic cells.
• DNA in prokaryotic cells

  Circular DNA not associated with proteins.
• DNA in eukaryotic cells

  Linear DNA associated with proteins.
• binary fission


  the division of a prokaryotic cell into two offspring cells, each having a single copy of circular DNA and variable no. Of plasmids. Produce very large numbers in a short time (doubles around every 20 mins)
• Cytokinesis

  Division of the cytoplasm during cell division
• Pathogen


  a bacterium, virus, or other microorganism that can cause infectious disease. Pathogen between people not the disease.
• Vaccine

  Make us immune to disease, but don't stop us from being infected by pathogens.
• Types of foreign cell

  Pathogens, abnormal cells e.g cancer cells, transplanted cells or Toxins. Can be recognised and destroyed by our immune system.
• Foreign cells

  Recognised due to specific shaped proteins/ glycoproteins on surface called antigens.
• Antigen


  A molecule (often a protein/glycoprotein) that triggers an immune response.
• non-specific immune response

  Any type of pathogen or foreign cell destroyed. Immediate response. Involves wbc called phagocytes.
• Phagocytosis


  process in which phagocytes engulf and digest microorganisms and cellular debris.
• antigen presenting cells


  Present antigens from pathogen to specific lymphocytes called T helped cells.