2.1.6 - cell division, cell and organisation Flashcards
what are the 4 stages of the cell cycle
G1, S, G2 and M (mitosis)
what happens in G1
the cell grows and inc size
transcription of DNA to mRNA
organelles duplicate
biosynthesis happens
what is biosynthesis
where the enzymes needed for the other stages are made
what gene controls G1
p53 (tumour suppressor gene) controls this phase and stops excess growth
what can happen if the p53 gene doesn’t control the cell growth
cell may grow too much and develop into a tumour which could be cancerous
what happens at the early G1 checkpoint
if the cell isn’t progressing properly, it enters G0
what happens at G0
the cell enters to be repaired or sometimes it may have to stay there permanently
what are the reasons that a cell may enter G0 permanently
if it has differentiated into a cell that doesn’t go through mitosis
if the DNA is beyond repair
what happens to a cell in G0 if it is beyond repair
apoptosis (controlled cell death)
senescence (cell ages until death)
what happens at the G1/S checkpoint
if the cell is damaged, it won’t enter the S phase
what happens in the S phase (replication phase)
the DNA duplicates
why is the S phase rapid
to reduce the chance of mutations
what is the order of the genes that are duplicated in the S phase
- housekeeping genes (genes switched on in all cell types)
- genes active in that cell type
- genes normally switched off in that cell type
what happens at the DNA synthesis checkpoint
checks that DNA is replicated properly before entering G2
what happens in G2
additional growth
energy stores replenished
cytoskeleton dismantled
organelles arranged in the cytoplasm
what happens at the G2/M checkpoint
final check before mitosis and special chemicals are produced to help from spindle fibres
what is the M phase
where mitosis happens
what happens at the M checkpoint
happens 1/2 way through mitosis
the cell won’t enter anaphase if chromosomes aren’t attracted to spindle fibres
what happens during cytokinesis
cell membranes and cytoplasm divide to produce 2 genetically identical daughter cells
what happens during prophase in mitosis
- chromosomes condense
- the nuclear envelope breaks down into vesicles
- the spindle fibres are formed
what is each chromosome in prophase made of and how is it held together
each chromosomes is made of 2 sister chromatids which are held by a centromere
what makes spindle fibres
the centrioles make tubulin which makes up the spindle fibres
what happens during mitosis metaphase
- chromosomes align along the equator (metaphase plate)
- spindle fibres attach to centromeres
what happens in mitosis anaphase
- sister chromatids pulled apart to opposite poles of the cell
- centromere divides
- chromatids are called chromosomes again
how are the sister chromatids pulled apart
by the motor proteins ‘walking’ along the spindle fibres
what happens during mitosis telophase
nuclear membrane reforms from vesicles
spindle fibres disappear and chromosomes uncoil
why is the nuclear membrane kept in vesicles
because it saves energy rather than rebuilding from scratch
what are the mitosis daughter cells identical to
the parent cell and eachother
the parent ell of meiosis is diploid. What does that mean
there are 2 copies of each chromosome one each from the mother and father
what happens in meiosis prophase 1
chromosomes condense
nuclear membrane breaks down into vesicles
centrioles make spindle fibres
the chromosomes are made of sister chromatids held by a centromere
recombination occurs
what is recombination
non sister chromatids wrap around each other and exchange sections of DNA
what is the bivalent
the 2 non sister chromatids crossing over
what is the chiasma
the specific part where the 2 non sister chromatids cross over during recombination
what happens in meiosis metaphase 1
homologous pairs (still crossed over) line up at the equator
spindle fibres attach to centromere
independent assortment of chromosomes and independent segregation of chromosomes
what is independent assortment of chromosomes
homologous pairs align randomly at the equator and could be on either side
what is independent segregation of chromosomes
how they line up on the equator which determines how they are pulled apart during anaphase
what happens during meiosis anaphase 1
homologous chromosome pairs pulled to opposite poles by motor proteins
each chromosome made of 2 non sister chromatids
centromeres still holding chromatids together
crossed over section pulled apart
what happens during meiosis telophase 1
2 new nuclei form from the vesicles
spindle fibres disappear
chromosomes uncoil
what is the purpose of meiosis 1
halves the chromosome number
what happens in meiosis prophase 2
nuclear membrane breaks down into vesicles
chromosomes condense
centrioles make spindle fibres
chromosomes still made of 2 chromatids
are the chromatids in the chromsomes during prophase 2 sister or non sister
non sister due to the crossing over in prophase 1
what happens in meiosis metaphase 2
chromosomes line up at the equator
spindle fibres attach to centromere
random assortment and random segregation occur
what is random assortment of chromatids
chromatids are arranged randomly and either side can be facing either pole
what is random segregation of chromatids
how they arrange themselves along the equator determines how they are pulled apart in anaphase 2
what happens in anaphase 2
chromatids pulled to opposite poles by motor proteins walking along spindle fibres
centromere divides
what happens during telophase 2
spindle fibres disappear and nuclear membrane reforms
what is the end product of meiosis
4 genetically non identical daughter cells that are different to the parent and each other
what is the purpose of meiosis 2
separates chromatids and each nucleus has the correct number of chromosomes and genetic material
what is variation caused by
independent assortment and segregation, random assortment and segregation, random fertilisation
where do embryonic stem cells come from
2-5 day old embryos
what can embryonic stem cells differentiate into
any cell in the body
where are adult stem cells from
from certain locations in the body - eg bone marrow
pros of embryonic stem cells
can differentiate into any cell
uses ‘wasted’ embryos from IVF
cons of embryonic stem cells
ethical issues
destroying embryo
expensive
immunosuppressants needed
pros of adult stem cells
no rejection as own cells used
no immunosuppressants needed
no embryos involved
cons of adult stem cells
only found in certain locations
can only differentiate into the type of cell where it is found
can be painful to extract
what are stem cells
undifferentiated cells that can express all genes and can self renew
what is totipotent
can differentiate into any cell in the body and placental cells
what is pluripotent (embryonic)
any cell in the body but not placental
what is multipotent (adult)
can only be limited cell types
multipotent animal stem cell example
bone marrow - can only become blood cells and genes switch on/off to determine type of blood cell
multipotent plant example
meristem - inner meristem is xylem and outer meristem is phloem. the level of hormones determine if it is xylem or phloem
what are induced pluripotent stem cells
created by programming differentiated cells to switch on/off key genes which enables them to become undifferentiated
made from the patients own cells so no rejections so no immunosuppressants needed
