U1T6 - Continuity of Cells

Question 1

How do most living organisms grow?

Answer 1

By increasing the number of cells they have. Cells divide.

Question 2

What are 2 types of cell division?

Answer 2

Mitosis + meiosis.

Question 3

What are the 3 main stages of the cell cycle?

Answer 3

Interphase (G1, S, G2), Mitosis/meiosis (Nuclear division) + Cytokinesis (Cell division)

Question 4

What happens to the nucleus during interphase?

Answer 4

Nucleus appears to be resting, Chromatin is dispersed throughout. Metabolic processes take place to prepare cell for its metabolic role + cell division.

Question 5

What happens during interphase?

Answer 5

Amount of DNA in nucleus doubles (New DNA synthesised + histone proteins made) new organelles made (Mitochondria), ATP store built up for nuclear division + spindle proteins synthesised.

Question 6

What are the 3 growth phases of interphase?

Answer 6

G1 phase, S phase + G2 phase.

Question 7

What is the purpose of the 2 gap phases?

Answer 7

Give cell time to monitor internal + external environment to ensure all is ready for S Phase + Mitosis/meiosis. Cell can delay progress through G1 and go to G0 in unfavourable conditions.

Question 8

Describe the checkpoints which exist within the cell cycle.

Answer 8

If growth phases haven’t been carried out properly, checkpoint stops cell dividing so cell is destroyed. Some genes code for these, one is a growth factor receptor which is on the cell surface membrane + once the growth factor is present, the cell can detect it and it can proceed.

Question 9

What happens during mitosis?

Answer 9

Chromosomes present as chromatids which were formed during interphase are separately + distributed to 2 daughter nuclei.

Question 10

What are the 4 phases of mitosis?

Answer 10

Prophase, metaphase, anaphase + telophase.

Question 11

What happens in animal cells during prophase (Mitosis)?

Answer 11

Centrioles divide + move to opposite ends (poles) of cell. Protein microtubules develop from each centriole, forming spindle fibres, some of which extend from pole to pole. Towards end of prophase, each chromosome exists as 2 chromatids held together by centromere. Nucleolus disappears + nuclear membrane breaks down so chromatid pairs are free in cytoplasm.

Question 12

What is the difference in prophase in plant + animal cells (Mitosis)?

Answer 12

In plant cells, there are no centrioles so the spindle forms independently.

Question 13

Describe the process of cytokinesis in animal cells.

Answer 13

Cleavage furrow forms as cell surface membrane invaginates + cell splits into 2.

Question 14

Describe the process of cytokinesis in plant cells.

Answer 14

Cell plate laid down along cell centre which eventually becomes cell wall (Middle lamella + primary cell wall) Golgi apparatus synthesis materials needed for new cell wall.

Question 15

Give an example of a mitotic poison + its use.

Answer 15

Vincristine which inhibits mitosis/cell division.

Question 16

Why are mitotic inhibitors used in cancer treatments?

Answer 16

Cancer cells can metastasize through continuous mitotic division. This interrupts cell division as 2 sets of fully formed chromosomes are supposed to separate into daughter cells.

Question 17

What do antimetabolites do?

Answer 17

Induce dell death during S phase of cell cycle when they’re incorporated into RNA/DNA or inhibit enzymes needed for nucleic acid production.

Question 18

Give an example of an antimetabolite + its use.

Answer 18

Uracil is pyrimidine nitrogenous base using in nucleic acid synthesis. 5’Fluorouracil prevents DNA synthesis during S phase of cell cycle.

Question 19

How are chromosomes organised?

Answer 19

Contain 1 long single molecule of DNA. 46 chromosomes in human cell so 46 individual DNA molecules, each being 4m long. To prevent entanglement in nucleus, DNA are coiled around histones.

Question 20

What is a human karyotype like?

Answer 20

All chromosomes from each pair are similar in size, except for sex chromosomes.

Question 21

What would happen if a diploid sperm fertilised a diploid egg?

Answer 21

There would be 46 pairs of chromosomes in the fertilised egg - double the normal number.

Question 22

Why do we have inherited characteristics?

Answer 22

Zygotes divide by mitosis producing diploid cells with identical chromosomes which carry the same genes as those in the zygote, this is why we have inherited characteristics.

Question 23

What is meiosis for, where does it take place, what does it result in, where are the gametes made?

Answer 23

Sexual reproduction + genetic variation, reproductive organs (Ovaries + testes), 4 haploid gametes which aren’t genetically identical by dividing twice, testes + ovaries in humans or anthers + ovules in plants.

Question 24

In a chromosome, is a gene on the dark or light band?

Answer 24

The dark band.

Question 25

What happens during meiosis interphase?

Answer 25

DNA content of cell doubles + new cell organelles are formed.

Question 26

What does the 2 chromosomes in each bivalent being pulled apart during anaphase 1 ensure?

Answer 26

One chromosome from each homologous pair ends up in a daughter cell.

Question 27

What does cytokinesis produce at end of Meiosis 1?

Answer 27

2 daughter cells (1st division) with haploid number of chromosomes. Number of chromosomes in each cell has been halved at end of meiosis 1.

Question 28

What is the main goal for meiosis? What does this depend on?

Answer 28

For a gamete to contain one of the chromosomes from a homologous pair. Chromosome in gamete depends on how chromosomes line up on the equator at metaphase 1.

Question 29

What is independent assortment important for?

Answer 29

Genetic variation in the next generation.

Question 30

How many chromosomes do humans have?

Answer 30

23 pairs.

Question 31

Before crossing over, what is the state of the chromatids of each chromosome?

Answer 31

They are identical, possessing the same genes + alleles.

Question 32

At the G1 checkpoint, what must be ensured about the cell?

Answer 32

Cell has reached a critical size, enough nutrients available for next stage, necessary growth factors in place + no DNA damage.

Question 33

G0: Lymphocytes

Answer 33

Many lymphocytes are in G0. They only move out of this state if triggered to do so by presence of specific antigens.

Question 34

Describe the G2 checkpoint.

Answer 34

At end of G2 phase, cell checks that DNA replication has taken place accurately + no DNA damage.

Question 35

What happens at the metaphase checkpoint?

Answer 35

Cell checks that all chromosomes have properly attached to spindle fibres.

Question 36

What are the main differences between mitosis and meiosis?

Answer 36

Meiosis only takes place in reproductive organs, involves 2 divisions creating 4 daughter cells + chromosome arrangements in daughter cells are both different from each other + the parent cell.

Question 37

What happens to cells from the primary tumour?

Answer 37

Shed + carried around body by circulatory system, producing a secondary tumour. (metastases)

Question 38

What is DNA unzipping inhibited by?

Answer 38

Drugs adriamycin + cytoxan. If 2 DNA strands can’t be exposed then DNA replication can’t take place.

Question 39

What happens if there’s a faulty checkpoint?

Answer 39

Certain gene mutations can cause a faulty
receptor to be produced, which is always in the ‘on’
state, whether the growth factor is present or not.
The cell repeatedly goes through the whole cell
cycle, dividing continuously.

Question 40

Describe how vincristine works.

Answer 40

It interferes with mitosis in rapidly dividing cells. It binds
to tubulin, which forms the microtubules of the spindle. When vincristine is bound to tubulin, the microtubules cannot be formed + so anaphase can’t take place. Chromatids therefore cannot be pulled apart. It is a mitotic poison. Can affect rapidly dividing
epithelium in intestine + bone marrow.

Question 41

Describe how 5’flouracil works.

Answer 41

Inhibitor of enzyme necessary for DNA replication. Interferes with nucleotide production carrying thymine so few nucleotides are available. DNA replication can’t be completed when it’s present so is an ‘antimetabolite’.

Question 42

How many chromosomes in a gamete?

Answer 42

22 autosomes + 1 sex chromosome.

Question 43

What are 2 methods of genetic shuffling used in meiosis?

Answer 43

Crossing over during prophase 1 + independent assortment during metaphase 1,

Question 44

What is the difference between metaphase in meiosis and mitosis?

Answer 44

In meiosis, they line up in bivalents + chromatids are not separated.

Question 45

Explain how mitotic poisons contribute to the treatment of cancer.

Answer 45

They stop mitosis occurring successfully/fully and so the tumour cells cannot divide.

Question 46

What happens during the G1 checkpoint?

Answer 46

Checks for DNA damage, cell size, availability of nutrients + presence of growth factors.

Question 47

What happens during the G2 checkpoint?

Answer 47

DNA replication + cell size.

Question 48

What are centrioles?

Answer 48

The paired structures from which spindle fibres originate in animal cells.

Question 49

What is the behaviour of chromosomes from prophase 1 to prophase 2?

Answer 49

Chromosomes are in homologous pairs, they exchange gene during crossing over at chiasmata and line up along cell equator in recombinant pairs. Spindle fibres attach to centromere and chromosomes separate before a new nuclear envelope is formed.

Question 50

How do chiasmata result in genetic variation?

Answer 50

They are the part where 2 chromatids join together and exchange DNA sections during crossing over and form recombinant chromosomes.