2.2 All cells arise from other cells Flashcards
Name the stages of the cell cycle in eukaryotic cells
Stage 1 - interphase
Stage 2 - mitosis
Stage 3 - cytokinesis
Summarise stage 1 - interphase of the cell cycle in eukaryotic cells
● DNA replicates semi-conservatively (S phase)
○ Leading to 2 chromatids (identicalcopies) joined at a centromere
● Number of organelles & volume of cytoplasm increases, protein synthesis (G1 / G2)
Summarise stage 2 - mitosis of cell cycle in eukaryotic cells
● Nucleus divides
● To produce 2 nuclei with identical copies of DNA produced by parent cell
Summarise stage 3 - cytokinesis of the cell cycle in eukaryotic cells
● Cytoplasm and cell membrane (normally) divide
● To form 2 new genetically identical daughter cells
Describe the behaviour of chromosomes & role of spindle fibres in stage 1/ prophase
● Chromosomes condense, becoming shorter/thicker so visible
○ Appear as 2 sister chromatids joined by a centromere
● Nuclear envelope breaks down
● Centrioles move to opposite poles forming spindle network
● Spindle fibres start to attach to chromosomes by their centromeres
Describe the behaviour of chromosomes & role of spindle fibres in stage 2/ metaphase
● Spindle fibres attach to chromosomes by their centromeres
● Chromosomes align along equator
Describe the behaviour of chromosomes & role of spindle fibres in stage 3/ anaphase
● Spindle fibres shorten/contract
● Centromere divides
● Pulling chromatids (from each pair) to opposite poles of cell
Describe the behaviour of chromosomes & role of spindle fibres in stage 4/ telophase
● Chromosomes uncoil, becoming longer/thinner
● Nuclear envelopes reform =2 nuclei
● Spindle fibres / centrioles break down
Why do some eukaryotic cells not undergo the cell cycle?
● Within multicellular organisms, not all cells retain the ability to divide (eg. neurons)
● Only cells that do retain this ability go through a cell cycle
Explain the importance of mitosis in the life of an organism
Parent cell divides to produce 2 genetically identical daughter cells for:
● Growth of multicellular organisms by increasing cell number
● Replacing cells to repair damaged tissues
● Asexual reproduction
Describe how tumours and cancers form
Mitosis is a controlled process so:
● Mutations in DNA/ genes controlling mitosis can lead to uncontrolled cell division
● Tumour formed if this results in mass of abnormal cells
○ Malignant tumour= cancerous, can spread(metastasis)
○ Benign tumour= non-cancerous
Suggest how cancer treatments control rate of cell division
● Some disrupt spindle fibre activity/ formation
○ So chromosomes can’t attach to spindle by their centromere
○ So chromatids can’t be separated to opposite poles (no anaphase)
○ So prevents/slows mitosis
● Some prevent DNA replication during interphase
○ So can’t make 2 copies of each chromosome (chromatids)
○ So prevents/slows mitosis
What process do prokaryotic cells divide through?
binary fission
Describe the process of binary fission
- Replication of circular DNA
- Replication of plasmids
- Division of cytoplasm to produce 2 daughter cells
○ Single copy of circular DNA
○ Variable number of copies of plasmid
Describe how viruses replicate
1.Attachment proteins attach to complementary receptors on host cell
- Inject viral nucleic acid (DNA/RNA) into host cell
- Infected host cell replicates virus particles:
a. Nucleic acid replicated
b. Cell produces viral protein/capsid/enzymes
c. Virus assembled then released
