3.2.2 All cells arise from other cells Flashcards
what is the purpose of mitosis?
- asexual reproduction
- growth of tissues
- replacement of lost cells
- repairing damaged tissue
what are the three stages of the cell cycle?
- interphase
- mitosis
- cytokinesis
what happens during interphase?
- cell grows/elongates
- DNA is uncondensed and replicated so each cell will have the same amount
- organelles are replicated
what are the three stages of interphase?
- G1 (gap 1)
- S (synthesis)
- G2 (gap 2)
chromosomes are not ____ during interphase because?
- visible
- DNA is uncondensed
what happens during the G1 phase?
cell elongates and new organelles and proteins are made
what happens during the S phase?
cell replicates its DNA
what happens during the G2 phase?
cell keeps elongating and proteins needed for cell division are made
what is a centromere?
holds two sister chromatids together
what are the four stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
what happens during prophase?
- chromosomes condense and become visible (DNA is coiled tightly around proteins called histones)
- nucleolus disappears
- nuclear envelope breaks down
- centrioles separate and move to opposite poles of the cell
- centrioles start to produce spindle fibres
what happens during metaphase?
- chromosomes align along the equator of the cell
- spindle fibres released from centrioles attach to the centromere and chromatids
what happens during anaphase?
- spindle fibres retract and pull the centromere and chromatids towards the opposite poles
- this causes the centromere to divide in two and the individual chromatids are pulled to each opposite pole
- CHROMATIDS SEPARATE, CHROMOSOMES DO NOT SEPARATE
- requires ATP which is provided by respiration
what happens during telophase?
- chromosomes are now at each end of the cell and become longer and thinner again
- nuclear envelope begins to reform around each new group of chromosomes
what happens during cytokinesis?
- cytoplasm divides
- two genetically identical diploid cells are formed
what happens during binary fission?
- circular DNA loop is replicated
- plasmids are replicated
- cytoplasm divides
what is cancer?
mutations in the genes that control cell division can cause cells to grow out of control
what is a mutation?
a change to the base sequence of DNA
what causes mutations?
- mutagens such as ionising radiation from UV rays
- carcinogenic chemicals
how are cancer cells different to normal cells in structure and function?
they either die through apoptosis or can be destroyed by the immune system
how are tumours formed?
uncontrolled cell division causes cells to keep on dividing and they layer on top of each other
how tumours can harm the body?
- can cause blockages which damage organs they grow in
- they can cause damage to other organs
why do tumours need their own blood supply?
- rate of cell division is very high which requires lots of oxygen
- however, blood supply often cannot meet oxygen demand
- so tumours suffer from low oxygen
what are the two types of tumours?
benign and malignant
what are the characteristics of benign tumours?
- tumour grows slowly and is kept in one place
- do not invade other tissues and start tumours in other organs
what are the characteristics of malignant tumours?
- grows quickly
- will invade other tissues and can break off and spread around the body causing tumours in other organs (metastasis)
what is the key difference between benign and malignant tumours?
malignant tumours metastasise, benign tumours do not
how do cancer treatments generally work?
they control the rate of cell division by targeting the cell cycle to try to stop it
what is the problem with cancer treatments?
- they cannot distinguish between cancer cells and normal body cells so kill both
- however, cancer cells have a faster rate of cell division so are more likely to be affected by cancer treatment
what are 3 examples of cancer treatments?
- chemotherapy
- radiotherapy (and some chemotherapy drugs)
- drugs which prevent spindle fibres from forming
how does chemotherapy work?
- prevents the synthesis of enzymes required for DNA replication
- stops the cell cycle before the S phase
how does radiotherapy work?
- damage DNA
- so the cell will not pass through the checkpoints in the S phase
- forces the cell to kill itself (apoptosis)
how do viruses replicate (long)?
- virus detects host cell by recognising protein markers on its membrane
- virus attaches itself to the cell using attachment proteins
- virus injects genetic material into the cell
- cell replicates the genetic material and makes new viral proteins
- virus leaves cells by bursting it (lysis) using some of the cell’s membrane to form itself
how do viruses replicate (short)?
- inject their nucleic acid into the host cell
- infected host cell replicates the virus particles
