3.2.2 All cells arise from other cells Flashcards
Can all cells divide within multicellular organisms?
no
Stages of the cell cycle
-interphase
(G1, S, G2)
-cell division
(mitosis (PMAT), cytokinesis)
What stage of the cell cycle does DNA replication occur
-interphase
Interphase stages
G1 (GAP PHASE 1- growth) phase
- cell growth
- organelles replicate
S (Synthesis) phase
- DNA replication
G2 (GAP PHASE 2) phase
- spindle protein copied
- growth continues
M phase - MITOSIS
Mitosis
Definition
-mitosis is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell during DNA replication
Stages of cell division
Interphase (G1, S, G2) Prophase Metaphase Anaphase Telophase Cytokinesis
Mitosis/cell division
Process (full)
INTERPHASE -DNA is replicated └involving specific and complementary base-pairing -organelles are replicated -ATP content is increased
PROPHASE
- chromosomes shorten and thicken/condense
- and become visible
- they now consist of two chromatids
- joined by a centromere
- nuclear envelope breaks down
METAPHASE
- spindle forms
- the chromosomes line up at the middle/equator of the cell
- the centromere of the chromosomes attaches to spindle
- the centromere splits
ANAPHASE
- spindle fibres shorten
- sister chromatids separate
- and move to opposite poles of the cell
CYTOKINESIS
- chromosomes uncoil
- nuclear envelope reforms
What is interphase
Preparation for cell division
Interphase
-DNA is replicated
└involving specific and complementary base-pairing
-organelles are replicated
-ATP content is increased
Prophase
- chromosomes shorten and thicken/condense
- and become visible
- they now consist of two chromatids
- joined by a centromere
- nuclear envelope breaks down
Metaphase
- spindle forms
- the chromosomes line up at the middle/equator of the cell
- the centromere of the chromosomes attaches to spindle
Anaphase
- the centromere splits
- spindle fibres shorten
- sister chromatids separate
- and move to opposite poles of the cell
Telophase
- chromosomes uncoil
- nuclear envelope reforms
Role of the centromere in mitosis
- holds chromatids together
- attaches chromatids to spindle
- allows chromatids to be separated and move to opposite poles in anaphase
Mitosis products
-two genetically identical daughter cells
Importance of mitosis
-growth
-replacing cells and repairing tissues
-asexual reproduction /cloning
└produces genetically identical cells
-maintains chromosome number in all cells
EQ: During stage S, the genetic information is copied and checked.
Suggest what might happen if the genetic information is not checked
- there may be a mutation or error in copying so faulty DNA produced
- and daughter cells will not receive identical genetic information
- so the daughter cells do not function/are not produced
EQ: Explain why the DNA in two sister chromatids is identical
-semi-conservative replication
- double helix unwinds
-strands unzip
-hydrogen bonds break between complementary bases in the polynucleotide strands
└using DNA helicase
-both strands act as a template
-free DNA nucleotides align
-complimentary base pairing occurs
- C to G (3 H bonds) and T to A (2 H bonds)
- hydrogen bonds reform
└DNA polymerase joins adjacent nucleotides in the condensation reaction
- sugar-phosphate back bone forms
└using phosphodiester bonds
EQ: How can you investigate Mitosis?
- stain a tip from a growing root
- add HCL
- put it in a water bath
- place a cover slip over
- push firmly to make it thinner
- now you can see it under a microscope
EQ: Mitotic index=
number of cells with visible chromosome/ total number of cells observed
Role of spindle fibres
- they attach to the centromeres of chromosomes in metaphase
- and they shorten and pull the sister chromatids to opposite poles in anaphase
Cytokinesis
Definition
- the division of the cytoplasm in mitosis
- produces two new genetically identical daughter cells
How is mitosis different to cytokinesis?
- mitosis is nuclear division producing two identical nuclei
- cytokinesis is cellular division producing two identical cells
What type of process is mitosis
A controlled process
How is mitosis a controlled process
Mitosis and the cell cycle are controlled by a number of genes
What can uncontrolled cell division lead to
the formation of tumours and of cancers
How is cancer the result of uncontrolled cell division?
Mitosis and the cell cycle are controlled by genes.
- normally, when cells have divided enough times to make enough new cells, they stop
- if there’s a mutation in a gene that controls cell division, the cells can grow out of control
- cells keep on dividing and form tumours
- cancer is a tumour that invades surrounding tissue
Cancer treatment areas
- controlling rate of cell division
- prevent DNA replication
- interfere with spindle formation in metaphase
What are 2 cell cycle targets of cancer treatments?
-Gl (cell growth and protein production)
└some chemical drugs in chemotherapy prevent the synthesis of enzymes needed for DNA replication, so the cell is unable to enter the synthesis phase (S), disrupting the cell cycle and forcing the cell to kill itself
-S phase (DNA replication)
└radiation and some drugs damage DNA. At several points in the cell cycle (including just before and during S phase) the DNA in the cell is checked for damage. If severe damage is detected, the cell will kill itself -preventing further tumour growth
How do prokaryotic cells replicate
Binary fission
Binary fission
Process
-the circular DNA and plasmids replicate
└the main DNA loop is only replicated once but plasmids can be replicated may times
-the cell gets bigger
-the DNA loops moved to opposite poles of the cell.
-the cytoplasm begins to divide
-new cell walls begin to form
-the cytoplasm divides
└two daughter cells are produced
└each daughter cell has one copy of the circular DNA but can have a variable number of copies of the plasmids
Binary fission
Products
-two new daughter cells
-each cell has one copy of circular DNA
└variable number of plasmids
Similarities between mitosis and binary fission
- chromosome DNA is replicated
- cytokinese occurs
- daughter cells have the same genetic information
- division of cytoplasm
Differences between mitosis and binary fission
- binary fission has:
- has no organelle
- no interphase
- no spindle fibres
How do viruses undergo cell division
-viruses do not undergo cell division
└as they are non-living
Virus replication
- viruses use their attachment proteins to bind to complimentary receptor proteins on the surface of host cells
- their genetic information is injected into the host cell
- genetic material and proteins are replicated by host cell machinery
- viral components assemble
- replicated viruses are released from host cell
How does the virus damage the host cell?
The replicated viruses build up inside the cell until they overtake the cell and it bursts, destroying the host cell.
-the viruses are then free to infect other cells.
What do viruses need to divide and why?
As viruses are acellular and non-living, they have no metabolic processes of their own.
They cannot replicate without a host cell.
Describe how viruses enter host cells.
- the attachment proteins attach to complimentary receptors on the surface of the cell
- the capsid fuses with the cell membrane and the nucleic acid DNA of the virus is injected into the host cell, where it enters the nucleus
What is the process of viral replication called?
-the lytic cycle
└because it results in the lysis of the host cell
