3.2.2 - all cells arise from other cells Flashcards
what do eukaryotic cells which retain the ability to divide do?
show a cell cycle
what are the two main stages of the cell cycle?
interphase and mitotic (M) phase
what happens during interphase?
DNA replication occurs (chromosomes become two sister chromatids joined by centromere), chromosomes can’t be seen but see chromatin instead
what are the stages of interphase?
- G1 - stage of cell growth focusing on synthesis of proteins and organelles
- S - DNA is replicated
- G2 - synthesis of proteins specific to mitosis
what happens during mitosis?
a eukaryotic cell divides to produce two daughter cells, each with the identical copies of DNA produced by the parent cell in DNA replication
what are the four stages of mitosis?
prophase, metaphase, anaphase, telophase
what happens during prophase?
chromosomes condense and become visible
pair of centrioles move to each pole of cell
nucleolus disappears and nuclear membrane breaks down
what happens during metaphase?
mitotic spindle forms and connects centrioles to chromosomes
chromosomes line up along equator of cell
what happens during anaphase?
centromeres split in two allowing chromatids to separate
spindle fibres shorten pulling chromatids towards opposite poles of cell
what happens during telophase?
chromatids reach poles of cell (now chromosomes)
spindle fibres break down
nuclear membranes form and nucleoli appear to create two new nuclei
what happens during cytokinesis in animal cells?
a ring of actin filaments form around the equator of the cell then tighten to form a cleavage furrow, splitting the cell in two
what happens during cytokinesis in plant cells?
vesicles move to the equator, line up and fuse to form two membranes called the cell plate - a new cell wall is laid down between the membranes which fuses with the existing cell wall
why do plant cells carry out cytokinesis differently to animal cells?
they have a cell wall which can’t be broken
what is mitosis?
a controlled process
what can uncontrolled cell division lead to?
the formation of tumours and cancers
what are non-cancerous tumours called?
benign tumours
what are cancerous tumours called?
malignant tumours
what are the features of benign tumours?
grow relatively slowly
cells in them usually show normal specialisation and have a regular looking nucleus
don’t spread - cells produce adhesion molecules which cause cells to stick together
usually surrounded by capsule of tissue which keeps cells in place
how can benign tumours be harmful?
they can damage the tissue surrounding them by constantly growing
if they grow on or in an organ they can stop it from functioning properly
how can benign tumours be treated?
they are localised, so can usually be removed surgically (once removed, they are unlikely to occur again)
what are the features of malignant tumours?
they grow rapidly
cells often appear very abnormal - can lose specialisation and differentiation of original cells, and their nuclei can be larger and darker than those of normal cells (contain more DNA)
tumours aren’t surrounded by capsule - their growth extends into neighbouring tissue
cells don’t produce adhesion molecules - cells may break away from primary tumour and form secondary tumours (metastasis)
what happens in metastasis?
- the cell detaches from the primary tumour
- the cell enters the bloodstream
- the cell circulates in the bloodstream
- the cell leaves the bloodstream
- the cell forms a secondary tumour
how can malignant tumours be harmful?
secondary tumours will destroy many sites of healthy tissue
the tumours often release chemicals which have effects on the whole body, like fatigue and weight loss
how can malignant tumours be treated?
it may be possible to remove primary and secondary tumours through surgery
chemotherapy and radiotherapy are also used when there are many secondary tumours, or they are too small to detect
chemotherapy - toxic chemicals kill cancer cells
radiotherapy - targeted radiation kills cancer cells
how do prokaryotic cells divide?
binary fission
what happens in the process of binary fission?
- the circular DNA and plasmids found in a bacterial cell are replicated (DNA replicates from the origin of replication)
- a septum forms down the centre of the cell as the cytoplasm splits
- the cytoplasm divides fully producing two daughter cells - each one has a single copy of the circular DNA and a variable number of copies of plasmids
what does a bacterial growth curve look like?
what is happening at each stage on a bacterial growth curve?
Lag phase - bacteria are metabolically active but not dividing
Log phase - exponential growth occurs as bacteria replicate
Stationary phase - growth plateaus because rate of growth is equal to rate of death
Death phase - bacteria die (but not necessarily all because some may be resistant)
what is the principle of viral replication?
viruses inject their nucleic acid into a host cell, and the infected host cell replicates the virus particles
what happens at each stage in viral replication?
- attachment - the virus attaches to the surface of the host cell (attachment protein)
- entry - the viral DNA or RNA enters the host cell
- replication - viral DNA or RNA replicates and new viral proteins are made (forms new capsids)
- assembly - the new virus particles assemble
- release - the host cell lyses which releases the newly made virus particles
