3.2.2 All cells arise from other cells

• What are the steps for virus replication? (4 steps)

  Step 1: Virus detects host cell by recognizing protein marker on its membrane.Virus attaches to cell using attachment proteins.Step 2: Virus injects genetic material into cell.Step 3: Cell reproduces the genetic material and reads it creating new viral proteins.Step 4: Virus leaves cell using some of the cells own membrane to form itself.
• What does the two daughter cells contain?

  Each contain an identical DNA loop but can contain a different number of plasmid copies.
• What are the steps for binary fission for prokaryotes? (4 steps)

  Step 1: DNA and plasmids replicate.Step 2: Cell elongates and DNA moves to the opposite poles of the cell.Step 3: Cytoplasm begins to divide and new cell walls begin to form.Step 4: The cytoplasm divide to produce two daughter cells. Each contain an identical DNA loop but can contain a different number of plasmid copies.
• What happens if the bacteria doesn't have a favorable environment and what can happen?

  If conditions become unfavorable (for example, when the bacteria eat all available food or their accumulated waste products become toxic), they stop dividing and eventually die off.
• What is the right environment for bacteria and what can happen?

  With the right environment (warm with lots of nutrients) bacteria can divide quickly.
• What can the daughter cells contain?

  The daughter cells have one copy each of the circular chromosome but the number of plasmids can vary.
• How does binary fission work?

  1. The circular chromosome and plasmids replicate.
  2. The cell gets larger and the DNA moves to opposite ends of the cell.
  3. The cytoplasm divides and new cell walls form.
• What is binary fission?

  Prokaryotic cells reproduce by splitting in two.
• How can some cancer therapies damage DNA?

  Radiotherapy and some chemotherapy drugs can damage DNA, if DNA is damaged the cell will not pass the check points in S phase. This will force apoptosis.Cells will not divide/Mitosis is prevented.
• How does cancer therapies work in terms of chemotherapy?

  Chemotherapy prevents the synthesis of enzymes required for DNA replication. This stops the cell cycle before the S phase as it cannot take place. If DNA cannot be replicated cells will not be able to divide.
• What treatments can target cancer cells?

  Immunotherapy and targeted therapy can help direct treatments to cancerous cells to reduce side effects and damage to the body.
• What are the treatments that are not targeted and why can't they target cancer cells?

  Radiation therapy and chemotherapy are not targeted. So treatments are not able to distinguish between cancer cells and other normal body cells that divide a lot.
• How can cancer treatments control the rate of cell division?

  Cancer treatments can control the rate of cell division in cancer cells by targeting the cell cycle and to try and stop it. This will kill the tumour cells and prevent them from dividing further. 
• What are malignant tumours?

  Cells that are cancerous and that can spread to other tissues and organs.
• What are benign tumours?

  Cells that are not cancerous and wont spread.
• What are the two tumour types?

  Benign Tumours and Malignant Tumours.
• How does the immune system prevent cells from developing into cancer?

  Some cells  can be identified as different to the rest of our cells, and the immune system will destroy them.
• How can apoptosis prevent cells from developing into cancer?

  A cell that is identified as having too many mutations to be fixed may be forced to undergo apoptosis, preventing it from passing on damaged genes.
• What is apoptosis?

  Programmed cell death 
• What are defence mechanisms are there to prevent the cells from developing into cancer?

  Apoptosis & The immune system
• How can the number of chance of mutations lead to cancer?

  The number or chance of mutations can be increased by being exposed to mutagens such as toxic chemical or ionising radiation.
• What is a mutation?

  A mutation is a random change to the base sequence of DNA that makes up a gene.They are natural, random and happen continuously (all the time).
• What is the most common cause of hereditary breast cancer?

  An inherited mutuation in the BRCA1 or BRCA2 gene.
• What does the rate of cell division depend on?

  The rate of cell division can depend on environmental factors (e.g. nutrients, oxygen, hormones - known as growth factors),and also genetics 
• Describe what happens in the telophase stage of mitosis?

  • Nuclear membranes reform around each group of newly divided chromosomes.
  • Nucleolus reforms.
  • Spindles disappear.
  • Chromosomes extend, becoming invisible.
• Describe what happens in the anaphase stage of mitosis?

  • Centromere of each chromosome splits.
  • One chromatid from each chromosome moves to centrioles at the poles of the cell.
• Describe what happens in the metaphase stage of mitosis?

  • Nuclear membrane has broken down.
  • Chromosomes align in the equator of the cell.
  • Each chromosome is attached to a spindle fibre by its centromere.
• Describe what happens in the prophase stage of mitosis?

  • Chromosomes condense.
  • Nucleolus disappears.
  • Nuclear envelope begins to break down.
  • Spindle fibres form.
  • Centrioles migrate apart.
• Describe what happens in the interphase stage of mitosis?

  • Chromosomes are not visible because the DNA is uncondensed.
  • The nucleolus is still visible.
  • Nuclear envelope is still intact.
  • The centrioles have replicated and may be visible.
• What are the stages of mitosis?

  InterphaseProphaseMetaphaseAnaphaseTelophase
• What does a chromosome consist of?

  A chromosome consists of two identical strands called chromatids, they are joined by a centromere.
• What are centrioles?

  Centrioles are paired barrel-shaped organelles located in the cytoplasm of animal cells near the nuclear envelope.
• What is cytokinesis?

  Cytokinesis is the final stage where the cytoplasm divides and two separate genetically identical cells are formed.
• What involves the division of the nucleus?

  Mitosis
• What happens in the S phase?

  • DNA replication 
  • Amount of DNA Doubles
• What happens in the G1 and G2 phase?

  • Cell growth
  • New proteins synthesized 
  • New organelles formed
• How many percentage does interphase take of the cell cycle?

  90%
• What also occurs in the interphase stage?

  • Cell growth 
  • DNA replication
• What happens to the DNA in interphase?

  The DNA is unwound as chromatin so the genes are accessible for transcription.
• What is interphase?

  The phase between divisions.