Module 2: Cell Division Flashcards
What are the 2 main phases in the cell cycle?
Interpahse
Mitosis
Why is it wrong to say interphase in the resting phase of the cell cycle?
Very active phase DNA replication occurs Production of enzymes and hormones Protein synthesis occurs Growth and replication of organelles e.g. mitochondria and chloroplasts
How many stages are in interphase? Name them
3 stages
G1, S and G2
Describe G1
1st growth phase
Cell gains size
Proteins synthesised
Organelles synthesised
Describe the S phase
DNA replication
Leads to production of genetically identical sister chromatids
In the nucleus
Describe the G2 phase
2nd growth phase
Proteins form spindle fibres
Checking of genetic material before mitosis for errors
Energy stores increased
What are the 2 stages of the mitotic phase?
Mitosis
Cytokinesis
What is the G0 phase?
The cell leaves the cell cycle either temporarily or permanently
What can cause a cell to enter the G0 phase?
1) Differentiation = cell no longer able to divide due to being specialised to carry out a particular function
2) DNA may be damaged = no longer viable - apoptosis - no longer able to divide and enters permanent cell arrest - majority of cells only divide a certain number of times before becoming senescent
3) Age = number of senscent cells increase
Which types of cell can enter the G0 phase and be stimulated to return to the cell cycle?
Lymphocytes in an immune response
What are checkpoints in the cell cycle?
Control mechanisms of the cell cycle to monitor and verify whether processes at each phase of the cell cycle have been accurately completed before progression into the next phase
Where are chckpoints found in the cell cycle?
G1 checkpoint at the end of G1 before entry into the S phase - if requirments not met entry into the G0 phase occurs
G2 checkpoint - before mitosis - ensure DNA has been replicated without error
Spindle fibre/ metaphase - all chromosomes should be attached to spindle fibres and be aligned - mitosis cannot occur without this
What happens to chromosomes during DNA replication in interphase?
Converted into 2 DNA molecules called chromatids, joined by a centromere.
What is the significance of mitosis?
Growth = produce genetically identical cells to allow multicellular organisms to grow
Tissue repair
Asexual reproduction = amoeba and plants like strawberries form runner and yeast cells (fungi) reproduce by budding
What is cell division in prokaryotes called?
Binary fission
What are the 4 stages of mitosis?
Prophase, metaphase, anaphase, telophase
Describe interphase
Replication of DNA and organelles, protein synthesis, increase in metabolic rate
Chromosomes not visible
Describe prophase
Chromosomes shorten and thicken - visible
Centrioles in the cytoplasm migrate to the poles and form spindle fibres
Nucleolus disappears
Nuclear membrane has disintergrated
Describe metaphase
Pairs of chromatids (chromosomes) line up along the equator/metaplate of the cell
Attached to spindle fibres by their centromeres
Describe anaphase
Spindle fibres shorten
Centromere splits
Sister chromatids pulled towards opposite poles of the cell by the centromere first
Gives a distinct V shape
Describe telophase
Chromatids (now chromosomes) reach the poles
New nuclear envelope forms
Cell now contains 2 genetically identical daugheter diploid nuclei
Describe cytokinesis for an animal
Cleavage furrow around the middle of the cell
Plasma membrane pulled inwards by the cytoskeleton util close enough to fuse aroudn the middle, forming 2 new genetically identical daughter diploid cells
Describe cytokinesis in plants
Not possible for a cleavage furrow due to a cell wall
Vesicles from the golgi assemble along the equator
Vesicles fuse with each other forming an end plate dividing the cell in two
New sections of the cell wall form along the new membrane
What is the significance of meiosis?
Production of haploid cells
Provide genetic varieation through independent assortment and crossing over
What is different about meisosis compared to mitosis?
Meiosis has 2 lots of cell division to produce 4 genetically identical haploid daughter cell
Mitosis has 1 cell division to procuce 2 genetically identical diploid daughter cells
Describe prophase 1 of meiosis
Chromosomes shorten and thicken - visible
Nuclear envelope disintergrates
Nucleolus disappears and spindle fibres form
Homologous pairs of chromosomes come together to form a bivalent
Non-sister chromatids from homologous chromosomes cross over at points called chiasmata -
What is the purpose of crossing over of non-sister chromatids?
Provides genetic variation by giving new allele combinations
Describe metaphase 1
Homologous pair of chromosomes arrange themselves along the equator of the cell
Independent assortment occurs
What is the purpose of independent assortment?
Means the combinations of chromosomes in daughter cells is random
Gives genetic variation
Describe anaphase 1
Homologous pairs of chromosomes separate
One chromosome from each pair are pulled to opposite poles by spindle fibres
Recombinant chromatids occur here whereby sections of DNA on sister chromatids from crossing over break off and exchange DNA
Provides genetic variation from new allele combinations
Describe telophase 1
Chromosomes assemble at the poles and the nucler membrane reforms
Does not occur in plants - straighth to metaphase 2
Chromosomes uncoil to form chromatin
Describe prophase 2
Chromosomes shorten and thicken by condensing - visible
Nuclear envelope disintergrates
Spindel fibre formation
Describe metaphase 2
Individual chromosomes arrange at the equator
Independent assortment and segregation of the chromatids occurs
Provides genetic variation
Describe anaphase 2
Spindle fibres contract
Centromeres separate
Chromatids move towards opposite poles
Describe telophase 2
Chromosomes uncoil and form chromatin
Nuclear envelope reforms and the nucleolus becomes visible
Cytokinesis occurs after this
What are the levels of multicellular organisation?
Specialised cells Tissues Organs Organ system Whole organism
Define differentiation
Process by which stem cells become specialised into different types of cell to carry out specific functions
Describe erythrocytes
Flattened bi-concave shape = increases surface area to volume ratio
Beneficial to role in the transport of oxygen around the body
No nuclei to increase space for haemoglobin
Flexible to move through narrow capillaries
Describe neutrophils
White blood cell in immune response
Muti-lobed nucleus = easy to move through gaps to reach sights of infection
Granular cytoplasm contains many lysosomes whith hydrolytic enzymes to kill pathogens
Describe sperm cells
Male gametes
Deliver genetic material to the female gamete
Flagellum to move and swim towards the egg cell/ovum
Many mitochondria in the middle to provide energy to swim
Acrosome on the head contains hydrolytic enzymes to digest the protective layers around the ovum for fertilisation
