2.6 Cell division

Question 1

what is mitosis

Answer 1

A type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell

Question 2

what happens during interphase

Answer 2

• DNA is replicated + checked for errors in the nucleus
• Protein synthesis occurs in the cytoplasm
• Chloroplast grow + divide in plant and agal cell cytoplasm, increasing in number
• Mitochondria grow + divide

Question 3

what are the 3 stages of interphase

Answer 3

G1: The first growth phase and proteins from organelles are synthesised and the cell increases in size
S; The synthesis phase where DNA is replicated
G2: The second growth phase where the cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors

Question 4

What are the 2 stages of mitotic phase

Answer 4

1. Mitosis
2. Cytokinesis

Question 5

What is the G0 phase

Answer 5

This is the name of the stage where the cell leaves cycle either temporarily or permenantly.

Question 6

what are the reasons this happens

Answer 6

1) Differentiation - cell becomes specialised to carry out a particular function and can’t enter cell cycle again
2) DNA of a cell is damaged - The DNA of a cell may become damaged in which case it’s no longer viable for cell division and enters a period of cell arrest. The majority of normal cells only divide a limited number of times and eventually become senescent
3) As you age the number of scenscent cells increase which could cause age related diseases

Question 7

what is Quiescence

Answer 7

Few type of cells can be stimulated to go back into cell cycle

Question 8

what are checkpoints

Answer 8

Are control mechanisms in cell cycle to monitor + verify whether the processes at each phase of the cell cycle has been accurately completed before the cell is allowed to progress into the next phase

Question 9

what are the 3 checkpoints

Answer 9

1) G1 checkpoint is at the end of G1 before entry into S phase . It checks for ; cell size, nutrients, DNA damage, Growth factors

2) G2 checkpoint is at end of G2 with checks for ; cell size, DNA damage, DNA replication

3) Spindle Fibre assembly in metaphase and check if DNA is
distributed evenly

Question 10

what is ampoptosis

Answer 10

Programmed cell death

Question 11

what is hayflick’s limit

Answer 11

A normal cell can only replicate 40 - 60 times. This happens since the telomeres ( which protect DNA ) shorten and can no longer offer further protection so will stop further division and initiate cell death

Question 12

which 2 cells can go through division unlimited times

Answer 12

Stem Cells
Cancer Cells

Question 13

what is cancer

Answer 13

caused by mutation of games that regulate cell cycle uncontrolled growth of cells & forms tumour

Question 14

How to treat cancer

Answer 14

1. Prevent DNA replication
2. Inhibit metaphase-interfere with spindle fibres

Question 15

How is cancer mainly formed

Answer 15

there is a level of telomerase which is an enzyme which repairs the telomeres. This enables the cells to continue to divide more times than normal leading to a growth of cells

Question 16

how is the cell cycle regulated

Answer 16

The cell cycle is regulated by the PS3 protein

It can stop cell division, iniating cell death or causing DNA repair

It checks for DNA damage

PS3 suppresses tumour development by preventing a potential cancerous cell from passing on defective DNA to next generation cells

Question 17

what happens during interphase

Answer 17

-DNA is replicated
-Each DINA molecule ( chromosome ) is converted into 2 identical DNA molecules called chromatids
-The 2 chromatids join together at a region called centromere It’s important to keep chromatids together during mitosis so they can be properly + precisly manoeuvered + segregated equally , one each into 2 new daughter cells centromethe 2 chromosomes ( after replication ) one chromosome ( before replication )

Question 18

what happens during prophase

Answer 18

• Chromatin fibres begin to coll + condense to form chromosomes that will take up stains to become visible under a light microscope.
  -The nucleolus disappears + nuclear envelope membrane begins to break down
  -Protein microtubles form spindle fibres to link poles of the cell .
• The fibres forming the spindle are neccessary to move chromosomes into the correct position
  -In animals + some plant cells 2 centrioles migrate to opp poles of cells .
  -The centrioles are cyclinderical bundles of proteins to help formation of spindles
• Spindle- F attaches to specific areas on centromeres + start to remove the chromosomes to centre + nuclear envelope disappears fully

Question 19

What happens in metaphase

Answer 19

Chromosomes are moved by SF to form a plane in centre called the metaphase plate + held in position

Question 20

what happens in anaphase

Answer 20

• The centromers holding together the pairs of chromatids in each chromosome divide during anaphase .
• The chromatids in each chromosome are seperated to opp polls of cell by shortening SF
  -The characteristic ‘v’ shaped of the chromatids moving towards the poles is a result of them being dragged by their centromeres through the liquid cytosol

Question 21

What happens during telophase

Answer 21

• Chromatids hared reached the poles + are now chromosomes
  -2 set of chromosomes assemble at each pole
• nuclear envelope reforms around them
• Chromosomes start to uncoil + the nucleolus is formed

Question 22

what happens in Cytokinesis

Answer 22

Division of the cell into 2 seperate cells

Question 23

What is homologous Chromosome

Answer 23

where each nucleus contains matching sets of chromosomes.

Question 24

what is loci

Answer 24

actual location of the gene on a region of chromosome.

Question 25

what are alleles

Answer 25

Different versions of the same gene

Question 26

What happens in meiosis 1

Answer 26

The First Division is the reduction division when the pairs of homologous chromosomes are separated into two cells. Each intermediate cell will only contain one full set of genes instead of two, so they are haploid.

Question 27

What happens in Meiosis 2

Answer 27

The second division is like mitosis, and the pairs of chromatids present in each daughter cell are separated, forming 2 more cells. 4 haploid daughter cells of produced in total.

Question 28

What happens in P1

Answer 28

-DNA condenses and becomes visible as chromosomes

-DNA replication has already occurred, so each chromosome consists of two sister chromatids joined together by a centromere

-The chromosomes are arranged side by side in homologous pairs

-A pair of homologous chromosomes is called a bivalent

-As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur. The point at which the crossing over occurs is called the chiasma (chiasmata; plural)

-In this stage centrioles migrate to opposite poles and the spindle is formed

-The nuclear envelope breaks down and the nucleolus disintegrates

Question 29

what happens in M1

Answer 29

-The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres

-The maternal and paternal chromosomes in each pair position themselves independently of the others; this is independent assortment

-This means that the proportion of paternal or maternal chromosomes that end up on each side of the equator is due to chance

Question 30

What happens in A1

Answer 30

-The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle

-The centromeres do not divide

Question 31

What happens in T1

Answer 31

-The chromosomes arrive at opposite poles

-Spindle fibres start to break down

-Nuclear envelopes form around the two groups of chromosomes and nucleoli reform

-Some plant cells go straight into meiosis II without reformation of the nucleus in telophase 1

Question 32

What happens in C1

Answer 32

-This is when the division of the cytoplasm occurs

-Cell organelles also get distributed between the two developing cells

-In animal cells: the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half

-In plant cells, vesicles from the Golgi apparatus gather along the equator of the spindle (the cell plate). The vesicles merge with each other to form the new cell surface membrane and secrete a layer of calcium pectate which becomes the middle lamella. Layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell

-The product of cytokinesis in meiosis I is two haploid cells

Question 33

What happens in P2

Answer 33

-The nuclear envelope breaks down and chromosomes condense

-A spindle forms at a right angle to the old one

Question 34

What happens in M2

Answer 34

-Chromosomes line up in a single file along the equator of the spindle

Question 35

what happens in A2

Answer 35

-Centromeres divide and individual chromatids are pulled to opposite poles

-This creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell

Question 36

what happens in T2

Answer 36

-Nuclear membranes form around each group of chromosomes

Question 37

What happens in C2

Answer 37

Cytoplasm divides as new cell surface membranes are formed creating four haploid cell

Question 38

what is a stem cell

Answer 38

Cells that are undifferentiated & divides to form more stem cells that can then differentiate

Question 39

what is cell potency

Answer 39

A stem cell’s ability to differentiate into different cell types

Question 40

What is Totipotent

Answer 40

These stem cells differentiate into any type of cell a fertilised egg, or zygote, and eight or 16 cells from its first few mitotic divisions are totipotent cells, which are destined eventually to produce a whole organism, they can differentiate into extra embryonic tissue.

Question 41

what is pluripotent

Answer 41

These stem cells can form all tissue types, but not whole organisms. They are present in early embryos, another origin of the different types of tissue within an Organism.

Question 42

what is multipotent

Answer 42

These stem cells can only form a range of cells within a certain type of cells. Haematopoietic stem cells in bone marrow are multi potent because this gives rise to the various types of blood cells.

Question 43

what are 2 sources of stem cells

Answer 43

Embryonic
Adult (tissue) Stem Cells

Question 44

Embryonic stem cell

Answer 44

These cells are present at very early stage of embryo development and are totipotent. After about seven days a mass of cells called a blastocyst has formed and the cells are now in a pluripotent state. They remain in this state in the foetus until birth.

Question 45

Where are stem cells used

Answer 45

Heart disease
Type one diabetes
Parkinson’s disease
Alzheimer’s disease
Spinal injuries
The treatment of burns
Developmental Biology

Question 46

Adult Stem Cell

Answer 46

These cells are present throughout life from birth. They are found in specific areas such as bone marrow. They are multi potent, although there is growing evidence that they can be artificially triggered to become pluripotent, stem cells can also be harvested from the umbilical cord of newborn babies. The advantages of this source are the plentiful supply of umbilical cords, and that invasive surgery is not needed. These stem cells can be stored. In case they are ever needed.

Question 47

what are the ethical issues surrounding stem cells

Answer 47

-Embryo’s that were left over from fertility treatments were used as stem cells but there are many ethical issues and objections due to the embryo being destroyed
-This controversy is holding back progress that could lead to the successful treatment of many incurable diseases. The use of umbilical cord stem cells overcome these issues to a larger extent, but these cells are mainly multi potent, not pluripotent like embryonic stem cells, thus restricting to their usefulness.
-Adult stem cells can also be used, but they do not divide as well as umbilical stem cells and are more likely to have acquired mutations.
-Developments are being made towards artificially transforming tissue stem cells into pluripotent cells. This happens by genetically modifying adult stem cells to act like embryonic stem cells, so they are pluripotent.