topic 2.3 - cell cycle & division Flashcards
1
Q
what is the cell cycle & its 3 main stages
A
- cell cycle is a process in which cells divide into two identical daughter cells
- interphase
- mitosis
- cytokinesis
2
Q
interphase
A
- interphase - the period between active cell divisions when cells increase size and mass and replicate their DNA
- new DNA is produced, chromosomes replicate, new proteins, cytoplasm, cell organelles are synthesised
- ATP production increases at times to provide extra energy needed for cell to divide
~ 90% of the cell cycle
3
Q
G1, S, G2
A
- G1 - time between end of previous round of mitotic cell division and start of chromosome duplication.
grows and develops
very short - S - stage where chromosomes replicate and become double stranded chromatids.
CHROMATIDS - one strand of the replicated chromosomes pair that’s joined to other chromatid at the centromere. - G2 - time that organelles + materials needed for cell division are synthesised - need 2 for everything before cell divides.
4
Q
prophase
A
- chromosomes coil and condense - can take up stain and become visible
- each chromosome consists of 2 chromatids joined at centromere
- nuclear envelope breaks down and centrioles move to opposite poles and pull apart to from spindle fibres between them
5
Q
metaphase
A
- chromosomes line up along the equator
- each centromere pair attaches to the spindle fibres
6
Q
anaphase
A
- the centromere splits, separating the 2 chromatids into two separate ‘chromosomes’
- the chromatids from each old pair are drawn to opposite poles of the cell
- they cannot move - spindle moves them
- contraction of overlapping spindles cause them to move to opposite ends
7
Q
telophase
A
- spindle fibres break down and nuclear envelopes form around the 2 sets of chromosomes
- chromosomes uncoil & become less dense (long + thin) & harder to see
8
Q
cytokinesis
A
- happens after mitosis; division of cytoplasm
- plasma membrane folds inwards
- cell splits into 2 new identical diploid daughter cells
9
Q
what are cyclins
A
small proteins that build up during interphase and are involved in the control of the cell cycle by their attachment to cyclin-depending kinases
10
Q
what are cyclin-depending kinases - CDK’s
A
- cyclin-dependent Kinases (CDKs) are enzymes involved in the control of the cell cycle
- cyclin attach to CDKs and this cyclin/CDKs complex adds phosphate to other proteins, changing their shape and bringing about the next stage in the cycle
11
Q
what are the roles of mitosis
A
- growth
- repair
- reproduction
12
Q
what are some measure of growth?
A
- height
- head circumference
- mass (dry mass for fungi/plants not animals as they’ll die with no water)
13
Q
continuous growth
A
rapid period of growth until maturity is reached - growth slows and may stop.
(land animals, marine animals grow for life)
14
Q
discontinuous growth
A
- grow, stop, repeat.
- insects grow in series of steps/bursts.
- they shed one exoskeleton whilst new one is soft they expand their body by taking in air and water = ‘grow’
- then new skeleton hardens & water is released & there’s room for tissues to increase in mass/size
15
Q
asexual reproduction
A
- asexual reproduction involves only one parent
- results in genetically identical clones to each other & parent
16
Q
advantages vs disadvantages of asexual reproduction
A
ADV:
- don’t need to find mate so it’s easier
- gives rise to large numbers of offspring rapidly
- can replicate desired traits
DISADV:
- no variation
- if conditions change/disease comes = can cause total destruction to entire species
17
Q
asexual reproduction methods
A
- binary fission
- sporulation
- regeneration
- Budding
- Vegetative propagation
18
Q
binary fission
A
- mitosis followed by splitting of an individual
- 2 new individuals formed.
- most common in bacteria
19
Q
sporulation
A
- production of spores through mitosis
- spores land on suitable substrate
- spores grow into new organism
- spores are well suited to survive in adverse conditions
- most common in fungi and plants such as mosses
20
Q
regenration
A
- organisms replace lost body parts by producing new cells by mitosis
- lizard’s tails
21
Q
fragmentation
A
- can reproduce themselves asexually through fragments of their original body.
- starfish
22
Q
budding
A
- organisms produce a growth of ‘bud’ from their bodies through mitosis
- the bud eventually breaks of & forms a new independent organism genetically identical to parent.
- yeast / hydra animal
23
Q
vegetative propogation
A
- when parts of a plant extend out under soil (propagate from stem/leaf/root/bud) and give rise to a new plant
- e.g. farmers use it with plants/strawberries
24
Q
what are gametes and where are they produced?
A
- Gametes are sex cells
- haploid (23 chromosomes)
- contain half the number of chromosomes as the rest of the cells which make up our body
- when two gametes fuse during sexual reproduction, the fertilised egg ( zygote) contains the full number of chromosomes
- it is diploid = 46
25
difference between egg & sperm
- sperm = many, mini, mobile (can move)
- egg = few, fat/big, fixed/can’t move.
26
meiosis 1
- Prophase 1 - chromosomes condense with 2 chromatids joined at centromere; (crossing over occurs)
- Metaphase 1 - spindle fibres form and pair of chromosomes line up at equator/middle plate.
(independent assortment occurs)
- Anaphase 1 - centromeres DO NOT divide. one chromosome from each homologous pair move to opposite ends of cell = chromosome number in each cell will be half the original due to this.
- Telophase 1 - nuclear membrane re-forms and the cells begin to divide
27
meiosis 2
- Metaphase 2 - new spindles formed and chromosomes line up in metaphase plate/equator
- Anaphase 2 - centromere NOW divides and chromatids split & go to opposite ends of cell.
- Telophase 2 - nuclear envelope re-forms & cytokinesis occurs. results in 4 genetically different haploid daughter cells ( half number chromosomes as original diploid cell)
- haploid gametes formed
28
how does meiosis bring variation?
1. independent/random assortment
- chromosomes from parents are distributed to gametes completely randomly
- so new gamete can have nay amount of chromosomes from either parent
- this guarantees great variety in gametes
29
how does meiosis bring variation?
2. crossing over/recombination
- a large enzyme ‘cuts & joins’ bits of maternal and paternal chromatids together
- the chiasmata (points where chromatids break) are important in 2 ways:
1. exchange of genetic material = genetic variation
2. errors in the process leads to mutations - introduces new combinations into the genetic make-up of a species.
30
what is a chromosome mutation?
- changes to the number or structure of chromosomes during meiosis
31
types of chromosome mutations
1. translocation
2. deletion
3. inversion
4. non disjunction
32
mutation through translocation
- where a part of one chromosome breaks off and reattaches to another completely different chromosome
- can be balanced or unbalanced
- balanced -a piece is swapped between 2 different chromosomes
- unbalanced - one chromosome loses a part and doesn’t get another one in exchange whilst the other chromosome gains it.
33
mutations through deletion
deletion - a section of chromosome is removed resulting in loss of a large number of genes
34
mutations through insertion
inversion - a part of a chromosome flips its orientation with respect to the rest of the chromosome
35
non disjunction
- causes abnormal number chromosomes in all the cells
- 3 chromosome 21 - results in Down's syndrome
36
why do we need meiosis
- results in genetic variation
- because crossing over occurs and there is independent assortment
- it produces new combinations of alleles
- genetic variation allows organism to adapt to environmental changes
37
describe the process of crossing over
- homologous chromosomes line up
- chiasmata forms
- chromosomes break
- genetic information exchanged between chromatids
38
what is an allele
different version of a gene
39
how does meiosis result in genetic variation
- results in recombination of alleles
- chromosomes cross over
- independent assortment occurs
