Cells

• What happens during G1

  The cell is preparing to divide

  Growth 1 - Cell grows and recieves signal to divide. This is when the cell synthesises proteins for replication (protein synthesis is occuring)
• What happens during Synthesis in mitosis

  DNA replicates

  Chromosomes consist of 2 sister chromatids joined at centromere
• What happens during Gap 2

  Further cell growth and error checking of newly synthesised DNA
• What happens in interphase

  Divided into G1, G2 and S

  DNA is replicated by semi conservative replication the organelles are also replicated

  More ATP is produced to be used in cell division
• What is the cell cycle and what are its stages


  Cycle of division with immediate growth periods

  1. Interphase
  2. Mitosis or Meiosis (nuclear division)
  3. Cytokinesis (cytoplasmic division)
• What are the stages of mitosis


  Prophase

  Metaphase

  Anaphase

  Telaphase
• What happens during Prophase

  Chromosomes condense and become visible (prevents DNA tangling during cell division)

  Centrioles move to opposite poles of the cell

  Mitotic spindle starts to form

  Nuclear envelope and Nucleolus break down
• What happens during metaphase

  Centrosomes reach opposite poles

  Spindle fibres extend to form Centrosomes

  Chromosomes line up at equator (so are equidistant to centrosome poles)

  Each sister chromatid is attached to a spindle fibre from opposite poles

  
  

  Sister chromatids line up at the cell equator attached to the mitotic spindle by their centromeres
• What happens during anaphase


  Spindle fibres contract causing the centromeres to divide

  Sister chromatids seperate into 2 distinct chromosomes and are pulled to the opposite poles of the cell

  Spindle fibres break down

  This requires energy fro ATP hydrolyisi
• What happens during telophase

  Chromosomes arrive at opposite poles and begin to decondense

  New nuclear envelopes form around each set of chromosomes

  Spindle fibres break down

  Cytokinesis occurs = cytoplasm divides

  2 new nuclei each with 1 copy of each chromosome
• What are the two types of phagocyte

  Neutophils

  Macrophages (can become APC)
• What is a neutrophil

  white blood cells produced in bone marrow with multi-lobed nuclei - migrate via chemotaxis
• What are macrophages

  larger white blood cells made in bone marrow found in tissues where infection more likely - capable of antigen presentation
• Stages of Phagocytosis

  Opsonins attach to antigen on pathogen

  Phagocyte binds to opsonin allowing it to get closer to pathogen

  Pathogen is englufed

  Pathogen enclosed in phagosome this fuses with lysosomes to create phagolysosome

  Lysosomes contain Lysozymes which breaks down pathogen
• What is the link between protein structure and antigenic variation in an RNA based virus

  Change in RNA sequence may result in change of amino acid

  Causes primary structure to change

  Could alter secondary structure

  R groups on amino acids would be different and would alter ionic bonds in the tertiary structure of the protein

  Changing shape so no longer complementary to antibodies in memory cells
• How are phagocytes specialised to carry out phagocytosis

  Have well developed cytoskeleton to help them change shape to engulf the pathogen and move lysosomes around

  Many mitochondria to release energy required for cell movement

  Lots of ribosomes to synthesise the lysosome enzymes

  Lobed nucleus to help them squeeze through narrow gaps between cells in the tissues
• What is the role of APCs


  Enhances recognition by T helper cells which cannot directly interface with pathogens / antigens in body fluids
• What are the two types of specific immune responses

  Cell mediated

  Humoral response
• Co transport of sodium and glucose in the ileum (simple)

  Na+ actively transported out of epithelial cells and into bloodstream

  Na+ concentration lower in epithelial cells than lumen of the gut

  Transport of glucose / amino acids from lumen to epithelial cells is 'coupled' to facillitated diffusion of Na+ down electrochemical gradient
• What is the name of the fixed position occupied by a gene on a dna molecule

  Locus / Loci
• How is a gene a code for the production of a polypeptide (no transcription or translation)

  Because base / nucleotides

  In triplets

  Determines sequence of amino acid / primary structure in polypeptide
• How is HIV replicated once inside Th cells

  RNA converted into DNA using reverse transcriptase

  DNA inserted into (thelper cell) human DNA

  DNA transcribed into HIV mRNA

  This is translated into new viral proteins for assembly into viral particles
• cotransport of glucose in the ileum

  Na+ in the lumen of the ileum is at HIGH concentration

  Glucose in lumen of ileum at low concentration

  Na+ and glucose BOTH bind to cotransport molecule and enter epithelial cell

  Glucose moves into blood by facilitated diffusion down a concentration gradient

  Na+ is now at a low concentration in the epithelial cell and enters blood via sodium potassium pump via active transport requiring atp