5 - The mitotic cell cycle

Question 1

What is a chromatid?

Answer 1

One of 2 identical copies of a replicated chromosome, made up of a very long, condensed DNA molecule (made up of a series of genes)

Question 2

What is the centromere?

Answer 2

The region of a chromosome that holds sister chromatids together. Serves as an attachment point for spindle microtubules during cell division.

Question 3

What are chromosomes made up of?

Answer 3

Chromatin

Question 4

What is a chromosome?

Answer 4

A structure within a cell containing DNA that has been packaged and organised into a more compact form. (Humans have 46 chromosomes, grouped into 23 pairs.)

Question 5

What are sister chromatids?

Answer 5

2 (identical) chromatids that make up the double structure of a chromosome. joined at centromere.

Question 6

What is chromatin?

Answer 6

The tightly coiled combination of DNA and histone proteins

Question 7

What are histones?

Answer 7

Proteins which DNA is tightly wound around in order to condense DNA so it fits into the nucleus + is more space efficient.

Question 8

What are telomeres? Refer to their structure.

Answer 8

Protective structures at the ends of the chromatids in chromosomes made of non-coding DNA (does not contain genes) that is made up of short base sequences that are repeated many times. One strand is rich in guanine and the other is rich in cytosine.

Question 9

State the components that make up a chromosome.

Answer 9

DNA, histone proteins, sister chromatids, centromere, telomeres

Question 10

What is the purpose of mitosis?

Answer 10

Produce 2 genetically identical daughter cells for:
Growth,
Cell replacement/tissue repair,
Asexual reproduction.

Question 11

Does the cell continue growing during the nuclear division (mitosis) phase of the cell cycle?

Answer 11

No.

Question 12

What does the S stand for in S phase?

Answer 12

Synthesis.

Question 13

What does the G stand for in G1 and G2 phase?

Answer 13

Gap

Question 14

How is the movement between phases of the cell cycle triggered?

Answer 14

Chemical signals called cyclins.

Question 15

What happens during cytokinesis?

Answer 15

1 - Cell membrane cleavage furrow forms,
2 - Cell divides and one nucleus moves into each cell → two genetically identical daughter cells
* In animals - cytoplasm constricts between the 2 nuclei
* In plants - a new cell wall is formed.

Question 16

Outline what happens during telophase

Answer 16

1 - Chromosomes decondense and can no longer be observed,
2 - New nuclear envelopes form around each set of chromosomes → two new nuclei, each with one copy of each chromosome

Question 17

Outline what happens during anaphase

Answer 17

(Requires energy from ATP hydrolysis)
1 - Spindle fibres contract, centromeres divide,
2 - Sister chromatids separate into two distinct chromosomes and pulled to opposite poles of the cell (appear as ‘V’ shapes facing each other),
3 - spindle fibres break down.

Question 18

Outline what happens during metaphase

Answer 18

Sister chromatids line up at cell equator attached to the mitotic spindle by their centromeres

Question 19

Outline what happens during prophase

Answer 19

1 - chromosomes condense and become visible,
2 - nuclear membrane disappears,
3 - centrioles move apart,
4 - spindle fibres form.

Question 20

Name the stages of mitosis

Answer 20

1 - Prophase,
2 - Metaphase,
3 - Anaphase,
4 - Telophase.

Question 21

Outline what happens during interphase

Answer 21

G1 - Cell makes RNA, enzymes + other proteins required for growth
S - DNA replicates → creates 2 identical sister chromatids
G2 - Newly synthesised DNA is checked + errors are usually repaired. organelles divide. cell continues growing. other preparations made (e.g. production of tubulin protein → makes microtubules for mitotic spindle)

Question 22

Outline the stages of the cell cycle

Answer 22

1 - interphase.
2 - Nuclear division (mitosis or meiosis)
3 - cytokinesis (cell division)

Question 23

What is the cell cycle?

Answer 23

Regulated cycle of division with intermediate periods of growth

Question 24

What is telomerase?

Answer 24

An enzyme found in most cells that adds additional bases at each end to elongate telomeres.
Not found in specialised cells → ageing.

Question 25

Why are telomeres needed?

Answer 25

The copying enzyme responsible for DNA replication is unable to run to the end of the DNA molecule - stops short of the end. If telomeres weren’t there, important genes would be lost.

Question 26

State the role of telomeres

Answer 26

Act as a ‘buffer’ region of non-essential DNA to ensure that no genes are lost during cell division - allows for continued replication of a cell.

Question 27

Name of the process in which stem cells develop into specialised cells

Answer 27

Differentiation

Question 28

Word for the ability of a stem cell to differentiate into more specialised cell types

Answer 28

Potency

Question 29

Suggest some uses of stem cells

Answer 29

1 - Repair of damaged tissue,
2 - drug testing on artificially grown tissues,
3 - treating neurological diseases e.g. Alzheimer’s or Parkinson’s,
4 - researching developmental biology e.g. formation of organs/embryos

Question 30

Where can stem cells be found in humans?

Answer 30

Bone marrow, skin, gut, heart, brain.

Question 31

Name and define the four types of stem cell

Answer 31

1 - Totipotent - can develop into any cell type including the placenta and embryo.
2 - Pluripotent - can develop into any cell type excluding the placenta and embryo.
3 - Multipotent - can only develop into a few different cell types.
4 - Unipotent - can only develop into one type of cell.

Question 32

What are stem cells?

Answer 32

Cells that can divide (by mitosis) an unlimited number of times. Each new cell has potential to remain a stem cell or differentiate into a specialised cell.

Question 33

Why do cancerous cell continue to divide?

Answer 33

They don’t respond to signals from other cells.

Question 34

How do oncogenes arise?

Answer 34

From carcinogens (agents which cause cancer)

Question 35

Why is metastasis dangerous?

Answer 35

Can be very difficult to detect, locate and remove secondary cancers.

Question 36

What is metastasis?

Answer 36

Malignant tumour cells can break off the tumour and travel through the blood and/or lymphatic system → invade other tissues → form secondary growths in other parts of the body. Metastasis is the spread of cancer by this movement.

Question 37

How do malignant tumours spread through the body?

Answer 37

Malignant tumour cells can break off the tumour and travel through the blood and/or lymphatic system → invade other tissues → form secondary growths in other parts of the body

Question 38

How can malignant tumours interfere with the organ/tissue where they started to grow? (example)

Answer 38

Example - could block the intestines, lungs or blood vessels.

Question 39

What is a malignant tumour?

Answer 39

A tumour which spreads through the body, invading and destroying other tissues — cause cancer.

Question 40

What is a benign tumour?

Answer 40

A tumour which does not spread from its original site — does not cause cancer. E.g. warts

Question 41

What do most mutations result in?

Answer 41

Early cell death or cell is destroyed by body’s immune system or formation of cancer.

Question 42

What is an oncogene?

Answer 42

A mutated gene which causes cancer

Question 43

What is a tumour?

Answer 43

An irregular mass of cells

Question 44

Why is the regulation of the cell cycle important?

Answer 44

Irregular growth of cells where growth or repair is not required can result in the formation of cell masses (tumours). This may lead to cancer.