cell division Flashcards
(22 cards)
what is mitosis
nuclear division that produces 2 genetically identical daughter cells for growth, repair and asexual reproduction
what are the stages of the cell cycle
interphase
mitosis
cytokinesis
what happens in interphase
G1 - cell growth and organelle replication
S - semi conservative replication
G2 - cells grow more
what do the checkpoints before and after S phase do
error check to minimise mutation
can result in early cell death / apoptosis
what are the stages of mitosis
prophase
metaphase
anaphase
telophase
what happens in prophase
chromosomes condense and become visible - two sister chromatids joined by a centromere
nuclear envelope breaks down
centrioles move to opposite poles
spindle fibres form
what happens in metaphase
chromosomes align along equator
spindle fibres attach to centromere
what happens in anaphase
spindle fibres contract
sister chromatids pulled to opposite poles, splitting the centromere
what happens in telophase
chromosomes uncondense and a new nuclear envelope forms around each set of chromosomes
what are the steps for a root tip squash experiment
prepare temporary root tip mount
focus an optical microscope on the slide and count the number of cells in the field of view as well as the number of cells undergoing mitosis
calculate mitotic index - proportion of cells undergoing cell division in a sample
how do you create a temporary root tip mount for a root tip squash
place root in hydrochloric acid to stop mitosis
stain with a dye that binds to DNA in chromosomes
macerate tissue using needle
press down a coverslip at a 45 degree angle and obtain a single layer of cells
how do prokaryotic cells divide
binary fission
genetic information replicates → large loop of chromosomal DNA and plasmids -> DNA moves to opposite ends of the cell
cell grows bigger → cytoplasm divides → new cell wall synthesised.
cytoplasm completely splits in two (cytokinesis)
two new cells formed → clones other than varying plasmids
how do viruses replicate
bind to receptors on membranes of host cells → attachment proteins
releases capsid (containing nucleic acids and enzymes) into cell
single strand of nucleic acid converted into double-stranded DNA → integrated into the host cell’s genome
host cell’s ribosomes translate viral DNA into viral proteins → assembled into viral particles
what is meiosis
nuclear division that forms 4 haploid cells, involving 2 rounds of cell division
what does meiosis do
ensure the chromosome number between generations is constant and is a source of genetic diversity and variation
what is crossing over and when does it occur
prophase 1
when chromosomes are aligned on the equator in close proximity, non-sister chromatids can cross over at chiasmata
the exchange of alleles between sister chromatids leads to new allele combinations
what is independent assortment and when does it happen
metaphase 1 and 2
random alignment of chromosomes along the equator → random of assortment of chromosomes in gametes
what are the 3 ways meiosis increases genetic diversity
crossing over
independent assortment
random fusion of gametes
what is chromosome non-disjunction
homologous chromosomes don’t separate properly during meiosis (anaphase 1 or 2)
→ gametes have abnormal number of chromosomes → genetic disorders ie down syndrome
what enzyme unwinds the DNA double helix in semi-conservative replication
DNA helicase
how does one strand act a template
free nucleotides in the nucleoplasm are attarcted to the exposed bases via complementary base pairing
what does DNA polymerase do
catalyses the formation of phosphodiester bonds between adjacent nucleotides
