Biology Chapter 6 Cell division, diversity, organisation

• The cell cycle


  series of events that cells go through as they grow and divide
• 3 main stages in the cell cycle

  interphase, mitosis, cytokinesis
• Interphase stages


  G1 (first growth phase), S (synthesis phase), G2 (second growth phase)
• Mitosis Phases


  prophase, metaphase, anaphase, telophase
• Mitosis


  division into two genetically identical daughter cells, identical to parent cell
• Meiosis


  division into 4 unique daughter cells with half the chromosomes of the parent cell
• What happens in G1?

  Cell growth and normal functions
• What happens in the S phase?

  DNA replication using energy from ATP
• What happens in the G2 phase?

  preparation for mitosis, DNA is checked for errors and damage in replication
• Cell cycle checkpoint


  a cellular mechanism that ensures that each stage of the cell cycle is completed accurately
• How many checkpoints are there in the cell cycle?

  four
• Checkpoint 1 of cell cycle


  At the end of G1 (growth 1) chromosomes checked for damage to allow cell to move onto S phase, if damage detected cell will not proceed to S phase until repaired
• Checkpoint 2 of cell cycle


  At the end of S (synthesis phase) all chromosomes are checked to see if they are replicated. Cell cycle stops if not
• Checkpoint 3 of cell cycle

  At the end of G2 (growth 2) check for DNA damage after replication, cell cycle stopped/delayed to repair damage
• Checkpoint 4 of cell cycle

  At the end of metaphase, chromosomes are checked to see if they are correctly attached to spindle fibres
• What is the G0 phase?


  If the cell does not receive the go ahead for G1, it goes to G0 where it does not replicate/divide
• What usually goes into G0?

  nerve tissue
• What happens to cells in G0?

  Carries out normal functions, but don't divide

  differentiate

  die
• Name two reasons cells go into G0?

  differentiation - cell becomes specialised and carries out particular function making it unable to divide

  DNA becomes damaged - cell division is no longer viable, cells can only divide a set number of times
• What is mitosis?


  Cell division that generates new cells for growth and repair. The division of one cell into two genetically identical daughter cells
• Importance of mitosis


  growth, repair, reproduction
• Stages of Mitosis


  prophase, metaphase, anaphase, telophase
• Why is interphase not part of mitosis?

  it is part of the cell cycle where division is not occurring
• What happens to the chromosomes in interphase?

  DNA is replicated and chromosomes duplicate
• Structure of chromatids and chromosomes

  - before duplication chromosomes exist as one chromatid

  - after replication, each chromosome is made from two sister chromatids joined at the centromere

  - the genetic info on each chromatids identical

  - DNA is uncoiled and not visible
• Prophase (mitosis)


  1. chromosomes slowly become more distinct and then are visible as two chromatids

  2. DNA undergoes supercoiling giving it a shorter more condensed structure

  3. centrioles divide and move to opposite sides of the poles

  4. nuclear envelope disintegrates and the nucleolus shrinks and disappears

  
• Metaphase (mitosis)


  1. centrioles send out microtubules that form spindle fibres

  - spindle acts as a framework to guide chromatid to opposite poles

  2. spindle fibres attach to centromere of each chromosome

  - chromosomes are now attached to poles of cell

  
• Anaphase (Mitosis)


  - centromere divides and chromatids on each chromosome pulled by their centromere to opposite poles of the cell

  - they are still attached to shortened spindle fibres and move to poles with help from motor proteins

  - when each chromatid reaches pole it is referred to as a chromosome

  - each pole has a full set of chromosomes identical to the other
• Telophase (mitosis)


  1. chromosomes reach poles and begin to uncoil and become less distinct

  2. a new nuclear membrane forms around each group of chromosomes

  3. new nucleoli form in each nucleus

  4. spindle fibres disintegrate
• Cytokinesis


  - last stage of cell division but not part of mitosis

  - cell divides to create 2 new daughter cells

  - cytoplasm near the equator tucks in splitting it and causes it to divide

  - in animal cells the plasma membrane fold inwards creating two dents that meet to form separate cells
• comparing animal and plant mitosis

  - plants do not have centrioles but still form spindle

  - in cytokinesis, vesicles from golgi form new cell membrane and cell wall
• asexual reproduction


  when a single organism produces offspring identical to itself
• one advantage and disadvantage of asexual reproduction

  advantage: quicker than sexual reproduction

  disadvantage: lack of variation means there is less resistance to disease
• What is budding in yeast cells

  - yeast producing asexually by process called budding

  - mitosis but division of cytoplasm occurs in different way
• Process of budding in yeast cells

  1. DNA replicates inside nucleus

  2. area of cell wall is weakened causing an extension of the cytoplasm and cell wall called bud to form

  3. ring of chitins forms at junction of cell and bud and when bud separates it remains as a scar

  4. nucleus migrates to bug region and undergoes mitosis without nuclear membrane breaking up

  5. one nucleus and organelles migrate to bud region

  6. cytokinesis is completed and a new cell wall between 2 cells forms

  7. new daughter cell grows to full and starts budding cycle again

  
• What is meiosis?


  a type of cell division that results in four haploid daughter cells with two steps

  1. meiosis 1 - first division just after chromosomes duplicate in interphase

  2. meiosis 2 - sister chromatids in two haploid cells divide again to create 4 gamete cells with either only maternal or paternal chromatids
• Gamete


  - genetically unique specialized cell involved in sexual reproduction

  - formed from meiosis
• Zygote


  fertilized egg containing 2 haploid gametes fused in sexual reproduction
• Haploid


  containing a single set of chromosomes
• Diploid


  2 sets of chromosomes