3.2.2 All cells arise from other cells Flashcards
What are the three stages of the cell cycle ?
- Interphase (G1, S, G2)
- Nuclear division (mitosis)
- Cell division (Cytokinesis)
What is interphase and what are the three main stages?
organelles double and DNA replicates but the cell continues to carry out normal functions
Stages = G1, S, G2
What occurs during the G1 stage of interphase ?
- Cells make RNA, enzymes and proteins for growth
- A signal is received telling the cell to divide
What occurs during the synthesis stage of interphase ?
*** DNA in the nucleus replicates **(each chromosome has two identical sister chromatids)
relatively short stage
What occurs during the G2 stage of interphase ?
- **cell continues to grow and the new DNA that has been synthesises is checked **
- other substances needed for division are also made (eg proteins)
Define mitosis
a eukaryotic cell divides to produce two genetically identical daughter cells
- each with identical copies of the DNA produced by the parent cell
Two divisions - Diploid daughter cells (complete set of chromosomes)
Give the three main uses of mitosis
- growth of multicellular organisms
-
repair and replacement of cells -produce new cells with an identical structure and function
3.** asexual reproduction **- genetically identical diploid daughter cells
Describe what happens during prophase
- chromosomes condense and become visible (when stained)
- Nuclear envelope breaks down
- Nucleolus breaks down
- **centrioles move to opposite poles **and spindle fibres emerge from the centrioles- form a spindle aparatus
spindle fibres = protein microtubules
Describe the composition of the chromosomes in prophase
two identical sister chromatids joined at the centromere
(the chromosomes are replicated during the synthesis stage of interphase)
Each chromatid contains one DNA molecule
Centromere - site of attachment for spindle fibres
Describe what happens during metaphase
- centrioles reach the opposite poles
- **Spindle fibres reach the chromosomes **and attach to centromeres
- chromosomes are pulled along the spindle apparatus and** line up along the cell equator**
Describe what happens during anaphase
- spindle fibres retract, which puts tension on the centromere
- centromere divides in two - separates the sister chromatids
- Chromatids are pulled to opposite poles
- They are now called **chromosomes **again
This stage requires energy from the mitochondria
Describe what happens during telophase
- chromosomes reach the opposite poles
- they begin to decondense/uncoil (no longer visible)
- spindle fibres break down
- nuclear envelope reforms - two new nuclei
Each chromatid now contains one DNA molecule which will replicate itself during interphase before the next division
Describe what happens during cytokinesis
the **cytoplasm divides **forming two genetically identical daughter cells
How does cytokinesis vary in animal and plant cells ?
Animal
- cleavage furrow forms to separate the daughter cells
Plant
- cell plate forms at the equator, stimulating the production of new cell walls
State the difference between diploid and haploid cells
Diploid
- Two sets of chromosomes (46 in humans - 23 pairs)
- Two diploid cells produced in mitosis
Haploid
- Single set of chromosomes (23 total)
- Four haploid cells produced during two divisions in meiosis
What is the function of spindle fibres ?
separation of sister chromatids and movement of chromosomes during mitosis
Define mutation
a change in the base sequence of an organisms DNA
- can cause uncontrolled cell division and tumour formation
Define benign vs malignant
Benign - do not spread from the original site
Malignant - invade surrounding tissue
What are the four main stages of cancer development ?
1.** Oncogenes** (mutated genes that cause cancer) arise due to carcinogens
2. cancer cells** divide uncontrollably by mitosis**
3. malignant tumour cells can break off and** travel through the blood/lymphatic system to form secondary growths**
4. invasion of other tissues interupts normal functioning
Define metastasis
spreading of cancer cells to other parts of the body, forming secondary growths
Why does cancer treatment often involve blocking some parts of the cell cycle ?
disrupts cell division, which inhibits cancer cell growth
Which two parts of the cell cycle are typically targeted during chemotherapy ?
- G1 phase - prevents synthesis of enzymes for DNA replication
- Metaphase (interferes with spindle formation) - prevents chromatids lining up, so they cannot divide
Wht are the issues with targeting the cell cycle during cancer treatment ?
- also disrupts the cell cycle of normal cells
- so can result in sickness and hair loss
However cancer cells divide more rapidly so are damaged to a greater extent
Define binary fission
a form of asexual reproduction in which the organism divides into two genetically identical copies
occurs in prokaryotic cells
Describe the three main stages of binary fission
- **circular **DNA and plasmids replicate (DNA replicates once, plasmids many times)
- DNA loops move to opposite poles
- **cytoplasm divides into two **and a new cell wall - forms daughter cells
Each daughter cell has ONE DNA loop and a variable number of plasmids
Describe the three main stages of viral replication
Viruses are non-living so cannot undergo cell division themselves
- ATTACHMENT - **attachment proteins **(on the virus) bind to the complementary receptor proteins on the host cell
- ENTRY - viral DNA is injected
- REPLICATION - viral DNA provides the instructions for the host cell to produce nucleic acids, enzymes and structural proteins which form the new viruses**
- Host cell bursts - releasing the new viruses
When are chromosomes visible?
prophase, metaphase, anaphase and telophase
(in interphase they are decondensed and so not visible)
