Cell Division, Diversity and Organisation - Chromosomes and Cell Cycle Flashcards
how is each chromatid held together
by the centromere
describe chromosomes during interphase
each DNA molecule makes a copy of itself
chromosomes are then composed of two identical chromatids
what are homologous pairs
one of each pair come from the father and from the mother (same genes, but possibly different alleles)
what are autosomes
the remaining chromosomes that aren’t sex chromosomes
how many sets of chromosomes do gametes have
one (haploid)
how many sets of chromosomes do body cells have
two (diploid)
what are the phases of the cell cycle
interphase (G1, S, G2)
prophase
metaphase
anaphase
telophase
describe interphase
- DNA is uncoiled and not visible during interphase
- DNA replication occurs (S) and DNA is checked for errors
- centrioles replicate (animal cells only) (G1 and G2)
- cell increases in size (more cytoplasm)
- new organelles produced
- cell is very active and large amounts of ATP required
- protein synthesis occurs
describe prophase
- chromosomes become visible as they shorten and thicken
- centrioles move to opposite ends (poles) of the cell
- microtubules develop from pole to pole forming spindle fibres
- nucleolus disappears (forms part of several chromosomes)
- nuclear envelope breaks down
describe metaphase
- centrioles reach the two poles
- chromosomes line up at the equator of the cell
- the spindle fibres attach to the centromere on each chromosome and pull the chromosomes to arrange them along the equator of the cell
describe anaphase
- the centromeres divide
- the spindle fibres contract and shorten, pulling the chromatids apart, centromere leading, towards opposite ends of the cell
describe telophase
- the chromatids have now reached the poles and can be regarded as distinct chromosomes
- the nuclear envelope reforms around each group of chromosomes
- the nucleolus reappears
- the chromosomes uncoil to form chromatin
describe cytokinesis in an animal cell
cell division involves furrowing and cleavage of the cytoplasm
where does cytokinesis begin in an animal cell
the edge of the cell
describe cytokinesis in a plant cell
cell division involves formation of a cell plate
where does cytokinesis begin in a plant cell
the middle of the cell
what are the four functions of mitosis
- asexual reproduction
- growth in multicellular organisms
- repair of tissues (same marking point)
- replacement of cells (same marking point)
why is it important that gametes contain the haploid number of chromosomes
- restores diploid number
- prevents doubling of chromosomes
What are checkpoints of the cell cycle
Monitor whether each stage of the cell cycle has been completed before the cell can proceed to the next step
What are the purposes of checkpoints
- prevent uncontrolled cell division leading to tumours
- detect and repair damage to DNA
- ensure cell cycle is not reversed
- ensure DNA is only copied once during each cell cycle
What are the three checkpoints of the cell cycle
- G1 checkpoint
- G2 checkpoint
- spindle assembly checkpoint
What does the G1 checkpoint check for
- cell size
- nutrients
- growth factors
- DNA damage
What does the G2 checkpoint check for
- DNA replication (no DNA damaged)
- cell size
What does the spindle assembly checkpoint check for
Chromosome attached to spindle fibre
What does the cell enter if a problem is found or DNA is damaged
G0 phase
What is G0 or resting phase
Cells leave the cell cycle permanently or temporarily
What happens during resting phase/why does it happen
- cell differentiation, once specialised some cells won’t undergo mitosis again
- if DNA is damaged (majority of cells have limited number of times they divide)
- lymphocytes, can start dividing again and re enter cell cycle
What happens if the damage can’t be repaired
Apoptosis
Where does mitosis take place in animal cells
Many cells are capable of mitosis
Where does mitosis take place in plant cells
Only special regions called meristems can undergo mitosis
Why can only meristems perform mitosis
Meristem cells have very thin cell walls. Older cell walls are thicker, meaning unable to undergo cytokinesis
Give examples of meristems
- Just behind root tips
- just behind shoot tips
- cambium
- buds
Compare cell division in plants and animal cells
- no centrioles present vs centrioles present
- cytokinesis starts from middle of the cell vs cytokinesis starts at edge of the cell
- occurs at meristems vs occurs throughout the body
How do yeast cells reproduce
Budding/asexual reproduction
Describe the process of cell division in yeast cells
- nucleus divides by mitosis
- cell swells on the side (bud develops)
- one nucleus moves into the swelling
- unequal distribution of cytoplasm
- cell wall forms
- two new cells formed (genetically identical)
How do prokaryote cells divide
Binary fission
Describe cell division in prokaryote cells
- the cell grows to its limit
- DNA replicates
- two new loops of DNA pulled to opposite poles of the cell
- cell divides into 2
- a new cell wall forms
What organelles within eukaryotes divide by binary fission
Chloroplasts, mitochondria
Suggest what might happen if the genetic information is not checked
- mutations
- faulty DNA
- daughter cell may not have identical genetic information
- do not function
Explain why the nuclei of most human cells contain 46 chromosomes
- two sets of chromosomes
- one from each parent
Explain why prokaryotic cells do not undergo meiosis
- no nucleus
- single chromosome
- need homologous chromosomes for meiosis
