all cells arise from other cells

• in eukaryotic cells where is DNA found

  within the nucleus
• what does DNA look like in eukaryotic cells

  linear + associated with proteins (histones)

  = form chromosomes
• in prokaryotic, DNA is found

  in the region called the nucleiod as a single, loop within the cytoplasm

  = not associated with proteins
• what happens in preparation for cell division

  DNA is replicated and the chromosomes condense

  = each duplicated chromosome has 2 chromatids which separate during division
• what is chromatids


  one of two identical "sister" parts of a duplicated chromosome

  
  

  - 2 sister chromatids = 1 chromosome
• what is the centromere

  narrow part of the duplicated chromosome, where the 2 chromatids are most closely attached

  
• what is mitosis


  the division of a cells nucleus into 2 genetically identical nuclei

  = followed by the dividing of the cytoplasm + CSM to form 2 genetically identical daughter cells
• what is mitosis needed for

  1. growth

  2. repair + replacement of damaged tissues

  = relies on stem cells:

  - can divide by mitosis

  - can differentiate into specialised cells

  3. asexual reproduction
• what is the purpose of the cell cycle

  prevent cell division when its not needed + make it happen when it is
• what are the 3 stages of the cell cycle

  interphase, mitosis, cytokinesis
• stage 1 - interphase summary

  - DNA replication

  - replication of organelles + production of proteins (eg. enzymes)

  - cell grows in mass
• stage 2 - mitosis summary

  - nucleus divides

  - separation of chromatids

  = PMAT
• stage 3 - cytokinesis summary

  - division of cell membrane + cytoplasm

  - produces 2 genetically identical daughter cells
• interphase


  - chromosomes are copied exactly in DNA replication

  - ATP is synthesised

  = provides energy for cell division

  - proteins (eg. enzymes) + organelles (eg. mitochondria, ribosomes) are synthesised

  - cell grows in size + mass
• what are the 4 stages of mitosis

  prophase, metaphase, anaphase, telophase
• prophase (longest stage)


  - chromsomes condense

  = become shorter, thicker + visible through supercoiling

  - each chromosome is in the form of 2 identical chromatins joined at the centromere

  = this is due to replication in interphase

  - nuclear envelop breaks down + nucleolus disappears

  - chromosomes now lie freely in the cytoplasm

  - centrioles move to opposite poles of the cell, forming spindle fibres across it

  = they extend to the equator of the cell

  
• metaphase


  - chromosomes move to the equator (middle) of the cell

  - the spindle fibres from each pole become attached to the of the centromeres chromosomes
• anaphase


  - spindle fibres contract

  - centromeres split + the pairs of sister chromatids separate + are pulled to opposite poles of the cell

  - the chromatids assume a "V" shape

  - a complete set of chromosomes are therefore found at each pole

  = this process requires AT that is provided by mitochondria around the spindle fibres
• telophase


  - chromatids reach their respective poles + uncoil

  = become thin + long again

  = forming chromatin

  = no longer visible

  - each pole receives identical copies of each chromosome

  - the spindle fibres break down

  - nuclear envelope + nucleolus reforms around each group of chromosomes at each pole

  = forming two nuclei (genetically identical)
• cytokinesis


  - a contractile ring forms causing the CM + cytoplasm to divide forming 2 genetically identical daughter cells

  - cell enters interphase again
• what is chromatin made up of

  DNA wrapped around histone proteins
• what is cancer


  a group of diseases caused by a growth disorder of cells

  = abnormal cell division
• what is cancer caused by

  damage to the genes that regulate mitosis + the cell cycle leading to uncontrolled division + growth of cells
• what is a tumour

  Group of abnormal cells that develop + constantly expand in size
• what are the 2 types of tumours

  benign and malignant
• characteristics of benign tumours

  - Slow growth

  - confined to a particular area/tissue/organ

  - often harmless, unless growing in confined space

  = eg. brain tumours can "press" on healthy tissue

  - can be removed surgically
• characteristics of malignant tumours

  - cancerous

  = can spread to other tissues/organs around the body

  
  

  - primary tumour

  = enter bloodstream or lymphatic system

  = form secondary tumours

  = metastasis
• what is metastasis


  cancer cells leaving a tumor and invading other parts of the body
• why do tumours cause harm

  a growing tumour will invade healthy tissue causing:

  
  

  - pressure on surrounding cells which affects normal function

  = eg. brain tumour

  
  

  - pressure on blood vessels supplying healthy tissues

  
  

  - pressure on airways within the lungs
• causes of cancer (5)

  1. genetic factors

  2. carcinogens

  = eg. tobacco smoke

  3. age

  4. environmental factors

  = eg. UV radiation, X rays

  = damage to DNA

  5. viruses

  = HPV - cervical cancer

  = hepatitis - liver cancer
• why do cells divide my mitosis

  to increase size of the tissue during growth to to replace dead cells and repair tissues
• what is rate of mitosis affected by

  - environment of the cells

  - growth factors

  = eg. human growth hormone

  = produced by one type of cell + travel to the other
• what is mitosis controlled by

  2 types of regulatory gene:

  
  

  - tumour suppressor genes

  - oncogenes
• what is a risk linked with these regulatory genes

  a mutation to one of these genes results in uncontrolled mitosis

  = this will eventually form a tumour
• what does the treatment of cancer often involve

  killing dividing cells by blocking a part of the cell cycle

  = leading to no cell division

  = cancer stops growing
• how does drugs used to treat cancer (chemotherapy) disrupt the cell cycle

  1. prevents the DNA from replicating

  2. inhibiting metaphase by interfering with spindle formation
• issue with chemotherapy


  it targets all rapidly dividing cells so will kill some healthy cells too

  = eg. in hair follicles + lining of small intestines
• how do bacteria divide

  binary fission
• explain binary fission


  1. single loop of DNA replicates + both copies attach to the cell membrane

  = plasmids also replicate

  
  

  2. cell membrane begins to grow + elongate between the 2 DNA molecules whilst beginning to pinch inwards, dividing the cytoplasm into 2

  
  

  3. a new cell wall forms between the 2 molecules of DNA, dividing the original cell into 2 genetically identical daughter cells, each with a single copy of the circular DNA + a variable number of copies of the plasmids

  
• do viruses undergo cell division


  No as they're non-living