topic 2

• prokaryotic ribosomes are smaller than eukaryotic ribosomes, 70s
• eukaryotic ribosomes are bigger than prokaryotic, 80s
• there are three stages of interphase: G1, S and G2
• G1: when the cell grows and prepares for DNA replication, meaning it synthesises more mitochondria and ribosomes
• S-phase is the stage of the cell cycle where DNA replication occurs.
• G2 is where the cell prepares for mitosis and the replicated DNA is checked for mistakes which could contribute to mutations
• gram staining is used to differentiate between gram positive and gram negative bacteria
• gram-positive bacteria have a thick peptidoglycan layer and a thick cell wall. This structure means that the crystal violet will get stuck in this net-like structure, staining it purple.
• gram-negative bacteria have a thin peptidoglycan layer sandwiched between two membranes, this means the crystal violet would be washed out followed by the red stain which is not washed out, staining it red.
• lambda phage is formed of : a capsid shape, tail and double-stranded DNA. It infects bacteria
• tobacco mosaic virus is formed by: a capsid head shape, protein coat, and single-stranded DNA. It infects plants
• Ebola virus is formed of : a helical capsid, protein envelope and single-stranded RNA. It infects humans.
• HIV is formed of : a rod-shaped capsid and protein envelope and single-stranded DNA. This infects humans
• ethical issues of untested drugs are : there are unpredicted side effects and on animals, they would have no rights or say in their treatments
• the lytic cycle : the virus replicates inside the host cell and then bursts out
• the strucutre of the lytic cycle :

  1. attachment by using attachment particles from the virus
  2. entry of the viral DNA/RNA and degradation of the host DNA
  3. synthesis of the viral genomes and proteins inside the cell
  4. assembly of the virus from the new genetic code
  5. release of the virus and bursting of the host cell
• the latent cycle : the virus remains dormant until it activates again
• mitosis concludes with the formation of two identical daughter cells, each with a copy of the original nuclear DNA, making them diploid
• the latency cycle :

  1. a virus can become latent (dormant) within its host cell after the initial infection. This means that the virus has stopped reproducing viral particles.
  2. the virus can become reactivated due to factors such as stress, the virus will resume producing viral particles and will continue into the lytic cycle.
• the stages of mitosis : prophase, metaphase, anaphase, telophase
• Prophase : the nuclear envelope disintegrates and DNA condenses and shortens
• Metaphase : spindle fibres, formed from the centromeres, pull apart the chromatids to opposite sides of the cell
• Anaphase : spindle fibres disintegrate and the nucleus starts to form
• Telophase : the two daughter cells form and the DNA uncoils and the cells separates
• Cytokenesis : the nucleus forms and the membrane is formed creating 2 identical diploid daughter cells
• meiosis is the process where a single cell divides twice to produce four cells containing half of the original genetic information
• oogeesis : the process of egg formation in the ovary

  1. primordial germ cells divide by mitosis several times, forming multiple oogonia
  2. one of these oogonia will form the primary oocyte
  3. after 1 mitotic decision, one secondary oocyte and one polar body are formed
  4. the second mitotic division forms the ovum and one polar body from the secondary oocyte
• Spermatogensis : production of spermatozoa from spermatogonia

  1. primordial germ cells divide several times by mitosis to form spermatogonia
  2. these grow to form primary spermatocytes
  3. primary spermatocytes undergo meiosis 1 to form secondary spermatocytes
  4. these then undergo meiosis 2 to form spermatids which grow into spermatozoa
• fertilisation : the fusion of the nuclei of two gametes to form a zygote

  1. the sperm head contacts the zona pellucida and an acrosome reaction occurs, releasing digestive enzymes
  2. the head fuses with the egg cell membrane allowing the nucleus to enter
  3. the cortical reaction occurs to stimulate the zona pellucida to harden and prevent polysomy
• fertilisation in plants :

  1. after pollination the pollen grain begins to grow, forming a pollen tube down the style
  2. as the pollen tube grows, two haploid male nuclei move down the tube
  3. one of the nuclei, the generative nucleus, divides by mitosis to form two haploid male nuclei
  4. as the pollen tube reaches the ovule, the pollen tube nucleus (the other original male nucleus) breaks down
  5. one male nucleus fuses with the egg cell and the other fuses with the two polar nuclei forming triploid endosperm nuclei, forming the endosperm of the plant.
• cleavage : the division of the zygote into smaller cells called blastomeres
• nucleoid - region of DNA in the bacteria in the cytoplasm
• apoplast pathways - transport of water and ions through the cell wall
• symplast pathway - transport of water and ions through the cell membrane and plasmodesmata
• capsparian strip - waterproof
• vacuoles control the turgor pressure of the cell
• in meiosis 1 - homologous chromosomes match up inside the cell, one from each parent and cross over in prophase 1, resulting in recombinant chromosomes
• meisosis 2 - the same as mitosis but with recombinant chromosomes
• variations can occur in interphase or during crossing over in prophase 1