6.2 Mitosis

Question 1

Importance of mitosis

Answer 1

Mitosis: nuclear division
–> ensures both daughter cells are genetically identical (exact copy of parent DNA and same no of chromosomes)
–>essential for growth, replacement and repair of tissues
–> necessary for asexual reproduction (one parent multicellular organisms e.g. ameoba)

Question 2

Chromosomes

Answer 2

Each DNA molecule (chromosome) is converted into two identical DNA molecules (chromatids)

Question 3

How are chromatids joined?

Answer 3

region called centromere (need chromatids together during mitosis so that they can be precisely manoeuvred and segregated equally

Question 4

Late G2:

Answer 4

DNA has already been copied, chromosomes consist of 2 connected copies (sister chromatids- not clear/ still in long, uncondensed form)

-copy of centrosome is made (2 centrosomes)
-plants do not have centrosomes with centrioles (different microtubule organising centre)

Question 5

Chromatin fibres

Answer 5

complex made up of various proteins, RNA and DNA

Question 6

Early Prophase:

Answer 6

-chromosomes begin to condense (chromatin fibres begin to coil and condense)

-mitotic spindle begins to form

-nucleolus (area of nucleus where ribosomes are made) disappears

Question 7

Mitotic spindle

Answer 7

made of microtubules, strong fibres that help organise chrosomes and move them during mitosis

Question 8

Late Prophase (Prometaphase)

Answer 8

-chromosomes condense even more very compact)

-nuclear envelope breaks down, releasing chromosomes

-mitotic spindle grows and some microtubules begin to capture chromosomes
-two centrioles migrate to opposite poles of cell

Question 9

centrioles

Answer 9

cylinder bundles of proteins helping in the formation of the spindle

Question 10

Spindle fibre anatomy

Answer 10

Microtubules can bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid

Microtubules that are bound are called kinetochore microtubules
–>unbound ones can grab onto microtubules from opposite poles, stabilising them
–> Asters can form: when more microtubules extend from each centrosome towards the edge of cell

Question 11

Metaphase

Answer 11

spindle captures all chromosomes and lines them up along the metaphase plate
–> two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles

Question 12

Anaphase

Answer 12

sister chromatids separate and are pulled to opposite ends
–> protein glue that held sister chromatids together is broken (now singular chromosome)
–> unattached microtubules elongate and push apart, separating pole and making cell longer

Question 13

What is the essential organelle for pulling apart sister chromatids

Answer 13

motor proteins
–> molecular machines that can ‘walk’ along microtubule tracks, carrying cargo

Question 14

cytosol

Answer 14

liquid found inside of cells. It is the water-based solution in which organelles, proteins, and other cell structures float.

Question 15

Telophase

Answer 15

Cell is nearly done dividing and it starts to re-establish its normal structures as cytokinesis takes place
–> mitotic spindle is broken down into its building blocks
–> two new nuclei form, one for each set of chromosomes
–> nuclear membranes and nucleoli form
–> chromosomes begin to decondense & return to their stringy form

Question 16

Cytokinesis (animal)

Answer 16

division of cytoplasm to form two new cells, overlaps with telophase
animal cells: cytokinesis is contractile, pinching the cell in two like a coin purse and draw string
–>’drawstring’ is a band of filaments made of a protein called actin// pinch crease= cleavage furrow

Question 17

Cytokinesis (plants)

Answer 17

plant cells: cannot pinch because they have a cell wall and are too stiff// a cell plate forms down the middle, splitting it into two
–> vesicles from golgi apparatus begin to assemble in same place as metaphase plate
–> they fuse together and with the cell surface membrane before dividing in two