ch6 - cell division and mitosis

what cells enter the cell cycle

eukaryotic cells

what two ways can eukaryotic cells divide

by mitosis or meiosis

what does the cell cycle consist of

interphase and cell division

what are the three stages during interphase

G1 > S > G2

what are the stages during cell division

mitosis/ meiosis > cytokinesis

what is the purpose of mitosis and why is it important

purpose = to create 2 genetically identical diploid daughter cells

important = for growth, tissue repair and asexual reproduction

what is the purpose of meiosis and why is it important

purpose = to create 4 genetically different haploid cells 

important = for sexual reproduction and genetic variation

what is a diploid cell and how many chromosomes does it contain? 

diploid = body cell

> contains 46 chromosomes

23mum & 23dad

how many copies do we have per chromosome in a diploid cell

per chromosome we have 2 copies = 2n

1set =mother

1set =farther

what is a haploid cell and how many chromosomes does it contain? 

haploid = gametes/ sex cell

> contains 23 chromosomes

how many copies do we have per chromosome in a haploid cell

per chromosome we have 1 copy = n

the first 22 pairs of chromosomes are called…

& are they identical or different between females and males?

autosomes

identical

what is the 23rd pair of chromosomes called & is it identical or different between females and males?

sex chromosomes

yes it is different

what is the 23rd chromosome for males and 23rd chromosome for females

males = XY

females = XX

what does homologous chromosomes mean 

a pair of chromosomes, one from the mother and one from the farther, that contain the same genetic information 

> HOWEVER each chromosome can contain different alleles

what is an allele

a different version of the same gene e.g. the gene for eye colour is the same however the colour can be different

can a chromosome be made up of one chromatid aswell as two chromatids?

yes - depending on which stage of the cell cycle, a chromosome can be made up of one or two chromatids

when will a chromosome be made up of two chromatids

when dna is replicated

when there are two chromatids that make up one chromosome what are they held by

the centromere

what does sister chromatids mean

when a chromosome is made up of two genetically identical chromatids 

what occurs during G1

-organelles are replicated

-cell increases in size

-proteins are synthesized

G1 CHECKPOINT

why is there are G1 checkpoint

to check if the cell is the correct size, has nutrients and there is no damage to DNA

what happens if a cell doesnt pass these checks

it will leave the cell cycle and enter G0 - which is permanent cell arrest

if a cell becomes specialised will it also leave the cell cycle

yes because it will no longer have the ability to divide

what cells can be stimulated to re-enter the cell cycle

lymphocytes

what occurs during S phase 

the dna in the nucleus is replicated 

> the individual maternal and paternal chromatids will make an identical copy of itself two form sister chromatids

> IN MEIOSIS each homologous chromosome will now be made up of maternal sister chromatids and paternal sister chromatids

what occurs during G2 phase

-cell continues to grow in size

-energy stores increase

G2 CHECKPOINT

why is there are G2 checkpoint

to check the newly replicated DNA has no damage, if there is damage the cell will try to repair it 

what 4 processes occur during the mitotic phase 

PMAT 

prophase

metaphase

anaphase

telophase

what occurs during prophase

1.chromatin condenses to form chromosomes (become shorter and thicker) to become visible 

2.nucleolus disintegrates and nuclear membrane breaks down meaning chromosomes are now free in the cytoplasm

3.(animal cells) centrioles separate and migrate to opposite ends of cells where they create spindle fibres by their spindle apparatus

3.(plant cells) have no centrioles but still have spindle apparatus

what occurs during metaphase

1.chromosomes align along the equator of the cell where metaphase plate is

2.spindle fibres are released and attach to the centromere of each chromosome

METAPHASE CHECKPOINT

what occurs during metaphase checkpoint

check if every chromosome is attached to a spindle fibre, mitosis will not proceed until this checkpoint is passed

what occurs during anaphase

1. spindle fibres will start to shorten back towards centrioles causing the centromere holding sister chromatids together to split so individual chromatids will be pulled to opposite poles 

does anaphase require energy

yes in the form of ATP

what occurs during telophase

1.each chromosome is now at opposite pole where they uncoil (become long and thin) into chromatin again

2.spindle fibres disintegrate, nuclear envelope forms around each group of chromatids and nucleolus forms within

what occurs during cytokinesis (in animal cells and plant cells)

cytoplasm splits in two to form 2 genetically identical daughter cells

(animal cells) cleavage furrow forms at the centre and cytoskeleton causes the cell surface membrane to draw inward until cell splits in 2 

(plant cells) vesicles from golgi apparatus assemble across centre and fuse with each other and cell surface membrane causing cell to split, new cell wall forms around cell surface membrane to complete division into 2 cells