IB HL Biology > 1.6 Cell division > Flashcards

1.6 Cell division Flashcards

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1
Q

What are the three main stages the cell cycle is divided into?

A

1) Interphase
2) Mitosis
3) Cytokinesis

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2
Q

Diagram showing the three stages of the cell cycle

A
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3
Q

Interphase

A
  • Interphase is the most active as well as the longest phase of the cell cycle.
  • Cells will spend most of their life within this stage undergoing common cell processes such as metabolism, endocytosis, exocytosis, and using and obtaining nutrients.
  • It involves many processes that occur both in the nucleus and cytoplasm.
  • It encompasses three important phases of the cell cycle: G1 (Gap 1), S (synthesis), and G2 (Gap 2).
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4
Q

G1 location in the cell

A

-Takes place in the cytoplasm

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5
Q

G1 activities

A
  • The cell grows and functions, normally undergoing everyday processes.
  • Rapid protein synthesis takes place, allowing the cell to grow in size.
  • Proteins required for DNA synthesis (the next phase) are made.
  • Mitochondria and chloroplasts (in the case of plant cells) are replicated. This also continues in the S phase.
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6
Q

S location in the cell

A

Takes place in the nucleus

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7
Q

S activities

A
  • The amount of DNA doubles as DNA replication takes place.
  • The genetic material is duplicated but no chromosomes are formed yet.
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8
Q

G2 location in the cell

A

Takes place in the cytoplasm

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9
Q

G2 activities

A
  • Protein synthesis occurs to produce the proteins needed for cell division, such as microtubule proteins that will make up a mitotic spindle.
  • The cell is actively preparing for cell division.
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10
Q

Mitosis

A
  • Mitosis is the division of the nucleus into two genetically identical daughter nuclei.
  • It involves the separation of sister chromatids into individual chromosomes which are then distributed among the daughter nuclei.
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11
Q

Cytokinesis

A
  • Once mitosis has been completed, with the formation of two nuclei with identical sets of chromosomes, the cell enters cytokinesis.
  • In cytokinesis, the cytoplasm of a parental cell is divided between the two daughter cells.
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12
Q

What are cyclins?

A

Cyclins are a family of proteins that control the progression of cells through the cell cycle.

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13
Q

Function of cyclins in a cell

A
  • Cyclins and CDKs regulate the cell cycle
  • Cells cannot progress to the next stage of the cell cycle unless the specific cyclin reaches a certain concentration.
  • Cyclins bind to enzymes called cyclin-dependent kinases (CDKs) and activate them.
  • The activated CDKs then attach phosphate groups (phosphorylation) to other proteins in the cell.
  • The attachment of phosphate triggers the other proteins to become active and carry out tasks; in this case, specific to the phases of the cell cycle.
  • For example, Cyclin E, shown in purple in Figure 2, peaks just before the S phase and the peak leads to DNA replication.
  • DNA replication must occur before mitosis can begin.
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14
Q

What must occur before mitosis can begin?

A

DNA replication

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15
Q

Explain how cyclins and CDKs regulate the cell cycle

A
  • Depending on the presence and action of these proteins, the cell cycle can be fast or slow, and it may even stop altogether.
  • Mutations in genes that code for cyclins can lead to problems regulating the cell cycle, which may lead to cancer.
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16
Q

What are CDKs?

A

Enzymes called cyclin-dependent kinases

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17
Q

Diagram showing the fluctuations of different cyclins during the cell cycle.

A
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18
Q

What is a difference between a cell in the G1 phase and a cell in the G2 phase of the cell cycle?

A

A cell in the G2 phase has more mitochondria than a cell in the G1 phase.

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19
Q

Which cyclin affects all four phases of the cell cycle?

A

D cyclin

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20
Q

What are the three important phases in interphase?

A

G1 (Gap 1), S (synthesis), and G2 (Gap 2).

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21
Q

The process of mitosis is the division of ___. This involves separating the ___ that was replicated in ___

A

The division of the nucleus

DNA

The S phase.

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22
Q

Describe mitosis in eukaryotic cells

A
  • In eukaryotic cells, the separation of DNA is done through the formation of chromosomes.
  • Eukaryotic chromosomes consist of DNA that is tightly wound around proteins called histones.
  • Histones are basic (alkaline) proteins that form part of nucleosomes.
  • Many nucleosomes are coiled together in a specific pattern to form a structure called a chromosome.
  • During interphase, chromosomes are unpacked, so that protein synthesis and replication can take place. DNA is only visible during mitosis.
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23
Q

What are histones?

A

Histones are basic (alkaline) proteins that form part of nucleosomes.

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24
Q

Diagram of the relationship between chromosomes and supercoiling

A
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25
(Mitosis in eukaryotic cells) DNA is initially packaged by \_\_\_\_\_\_\_
- Histones to form chromatin, which undergoes further condensation to form the chromosome. - Thus, chromatin is a lower order of DNA organization, while chromosomes are a higher order of DNA organization.
26
What is the difference between chromosomes, sister chromatids, and chromatin?
- During interphase, DNA is present as chromatin. - Following prophase, the phase when DNA supercoiling takes place, the DNA is visible as a pair of sister chromatids that are identical to each other connected by a centromere. - After the sister chromatids are separated during anaphase, they are referred to as chromosomes.
27
When are sister chromatids created?
- During the S phase when DNA replication occurs. - The two chromatids are identical and are joined by a centromere.
28
When are sister chromatids created?
- During the S phase when DNA replication occurs. - The two chromatids are identical and are joined by a centromere.
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When do sister chromatids separate at the centromere?
- After anaphase - At this point they are referred to as chromosomes.
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Diagram of a chromosome consisting of two sister chromatids
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When does mitosis occur?
After the G2 phase
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How many stages does mitosis have?
Four
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What are the four stages of mitosis?
Prophase, metaphase, anaphase, and telophase. (PMAT)
34
Diagram of cell in prophase phase of mitosis
35
Events taking place during prophase
1) DNA supercoils, causing the chromatin to condense. 2) Nucleolus disappears. 3) Nuclear membrane disintegrates. 4) Spindle fibers (made of microtubules) start to form (and are completely formed by the end of prophase). 5) Centrioles (absent from plant cells) move to opposite poles.
36
Diagram of cell in metaphase phase of mitosis
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Events taking place during metaphase
1) Spindle fibers bind to the centromere of sister chromatids and cause their movement towards the equatorial plate. 2) Sister chromatids are aligned at the equatorial plate at the end of metaphase.
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Diagram of cell in anaphase
39
Events taking place during anaphase
-Sister chromatids are separated (now known as chromosomes) and pulled to opposite poles by the spindle fibres.
40
What is the shortest phase of mitosis?
Anaphase
41
Diagram of cell in telophase phase of mitosis
42
Events taking place during telophase
1) The chromosomes have reached the poles. 2) A nuclear membrane starts to reform at each pole. 3) A nucleolus appears in each new nucleus. 4) The spindle fibers disintegrate. 5) The cell elongates in preparation for cytokinesis. 6) In some cases, the invagination of the membrane is also visible (marking the beginning of cytokinesis).
43
Prophase under a light microscope and micrograph
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Metaphase under a light microscope and micrograph
45
Anaphase under a light microscope and micrograph
46
Telophase under a light microscope and micrograph
47
When drawing phases of mitosis, don't forget to show that \_\_\_\_\_
The nuclear membrane disappears in prophase (you can draw a dotted line) and chromosomes in the form of sister chromatids are formed.
48
When drawing metaphase, \_\_\_\_\_
Chromosomes should be labelled as sister chromatids
49
When drawing anaphase, chromosomes should be labelled as \_\_\_\_\_
Chromosomes, not chromatids.
50
When drawing anaphase, chromosomes should be labelled as \_\_\_\_\_
Chromosomes, not chromatids.
51
Mitotic index
The ratio of the number of cells in a population undergoing mitosis (prophase, metaphase, anaphase, or telophase) to the total number of visible cells.
52
The formula used to calculate the mitotic index is \_\_\_\_\_
(where P, M, A, and T refer to the number of cells at prophase, metaphase, anaphase, and telophase, respectively)
53
Show how you can determine the mitotic index from a micrograph
For instance, in Figure 5 below, there are 8 cells undergoing mitosis out of a total of 56 cells present, which gives a mitotic index of 8/56 (0.14). Remember you can only give an estimate of the mitotic index as it is sometimes hard to differentiate between cells at prophase and interphase.
54
When counting the cells to figure out the mitotic index, you should take into account only \_\_\_\_
- Those fully visible. - Since it is sometimes difficult to differentiate between cells in prophase and interphase, the mitotic index is only an estimate and should be expressed as a percentage.
55
Why is the mitotic index important?
- Because it indicates how many cells in a tissue are dividing at a given time. - In a tumor, where cell division is uncontrolled, the mitotic index is higher than in normal tissue. - We can therefore use the mitotic index to predict how quickly cancer could spread and the likely outcome in reducing cell proliferation of any treatment, such as chemotherapy.
56
What ensures that mitosis produces two genetically identical nuclei?
Sister chromatids are pulled apart and moved to opposite poles by spindle fibers.
57
A package of histones with DNA wrapped around them forms a spherical structure and is called \_\_\_\_\_
Nucleosomes
58
What is tumourigenesis?
The formation of a tumor (or several of them), which is defined as a mass of cells that divide uncontrollably.
59
What are the two types of tumors?
- Benign and malignant tumours. - It should be noted that not all tumours lead to cancer. - Cancer is caused by a malignant tumour.
60
Cancer is caused by \_\_\_\_\_
A malignant tumor.
61
What is a benign tumor?
- A benign tumor is usually localized and does not spread to other parts of the body. - Most benign tumors respond well to treatment.
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What is a malignant tumor?
- A malignant tumor is a cancerous growth that is often resistant to treatment. - It may spread to other parts of the body and sometimes recur after it has been removed.
63
When can a tumor form?
When the events of the cell cycle are disrupted because of a mutation in one of the cyclins, CDKs, or a protein associated with the cell cycle.
64
Give an example of how a tumor can form
- For example, p53 is a protein involved in the regulation of the cell cycle. - A mutation in the p53 gene can lead to tumor formation. - In fact, over 50% of all tumors have a mutation in the p53 gene.
65
A mutation in a single cell can trigger \_\_\_\_
- The beginning of a tumor. - The cell may have lost its ability to enter the G1-phase, and instead continues to divide rapidly. - The mutation is passed on to the daughter cells and a clump of cells starts to form. - When this uncontrolled growth continues, a tumor is formed.
66
Diagram showing tumor formation
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Cancer can occur in \_\_\_\_\_
Any organ or cell and hence in any part of the body.
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What is a mutation?
- A change in an organism’s genetic code. - A change in the base sequence of a certain gene can result in tumor formation. - However, some parts of a gene do not code for anything, so a mutation in these areas will not affect the organism. - So, not all gene mutations lead to uncontrolled cell division.
69
What are mutagens?
- These are agents that cause gene mutations. - Although not all mutations result in cancers, anything that causes a mutation has the potential to cause cancer.
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Examples of mutagens
- Chemicals that cause mutations that are referred to as carcinogens, such as asbestos or dioxin. - High-energy radiation, such as X-rays. - Short-wave ultraviolet light. - Some viruses such as hepatitis B.
71
What is an oncogene?
- A mutated gene that contributes to the development of a tumor. - In their normal, un-mutated state, oncogenes are called proto-oncogenes, and they help in the regulation of cell division.
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What is the difference between a primary and secondary tumor?
- Once abnormal cell division has started at a particular place in the body, a malignant primary tumour begins to form. - If left untreated, this may follow a particular development pathway to form secondary tumours. - We say that the tumour has metastasised.
73
Steps of a tumor being metastasized
1) Cancerous cells detach from the primary tumor. 2) Some cancerous cells gain the ability to penetrate the walls of lymph or blood vessels and so circulate around the body. 3) The circulating cancerous cells invade tissues at different locations and develop, by uncontrolled cell division, into secondary tumors.
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Diagram showing how metastasis can lead to secondary tumor formation
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Metastasis
The movement of cells from a primary tumor to other parts of the body where they develop into secondary tumors.
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What do tumors result from?
Uncontrolled cell division
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The DNA of a particular cell is damaged so that the cell continues to divide uncontrollably. What is the most likely result?
Tumor formation
78
What health issues can smoking cause?
- Lung cancer and a range of other types of cancers - Asthma - Stroke
79
History of the tobacco industry in relation to cancer
- The link between smoking and the incidence of cancer was once strongly denied by the tobacco industry. - Initially, research established a strong correlation, but this did not prove that smoking was the cause of the cancers. - Over many years of study, causal relationships between some of the compounds in cigarette smoke and tumorigenesis were established. - Only then did the tobacco industry grudgingly admit that the link existed.
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Graph showing the correlation between smoking and incidence of lung cancer.
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Graph showing the correlation between smoking and incidence of lung cancer after a smoker quits.
82
With increasing consumption of cigarettes, as well as the number of years a person smokes, the risk of \_\_\_\_
Developing lung cancer increases.
83
Name the phase of the cell cycle when DNA duplicates
S
84
What is the difference between a cell in the G1 phase and a cell in the G2 phase of the cell cycle?
A cell in the G2 phase would have more mitochondria than a cell in the G1 phase.
85
What is the function of cyclins?
Control of the cell cycle.
86
Miotic cells stained by fluorescent dyes.
87
Which cyclin increases to trigger the beginning of mitosis?
Cyclin B
88
Cytokinesis involves the formation of a cell plate in \_\_\_\_
Plant cells only
89
Though mitosis is similar for animal and plant cells, cytokinesis is \_\_\_
Very different due to the presence of a cell wall in plant cells.
90
What is cytokinesis?
It is the division of the parental cytoplasm between the two daughter cells after mitosis (though it often starts in telophase).
91
Diagram showing cytokinesis in animal cells vs. plant cells
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Cytokinesis in animal cells
1) A ring of protein (microfilaments) located immediately beneath the plasma membrane at the equator pulls the plasma membrane inward. 2) The inward pull on the plasma membrane produces the characteristic cleavage furrow. 3) When the cleavage furrow reaches the centre of the cells, it is pinched apart to form two daughter cells.
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Cytokinesis in plant cells
1) In plants, the Golgi apparatus forms vesicles that consist of material to build a new cell wall. 2) Vesicles merge and form the cell plate. 3) The cell plate grows and divides into two daughter cells.
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When does cytokinesis involve the formation of a cell plate?
It involves the formation of a cell plate in plant cells only.
95
State the name of the molecule that CDKs attach to proteins in order to activate them.
Phosphate group
96
How are CDKs activated?
- By the process of phosphorylation by a CDK-activating kinase. - It is false that cyclin-dependent kinases only require cyclins for their activation.
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What characteristic is specific to cytokinesis in animal cells?
The cleavage furrow is made by the inward pull on the plasma membrane.
98
A cell that is dividing too rapidly may have lost its ability to enter which part of the cell cycle?
G1
99
Metabolic reactions taking place during interphase.
1) DNA replication in the nucleus. 2) Protein synthesis in cytoplasm. 3) Reactions of cellular respiration.
100
What happens to chromosomes during interphase?
- They are unpacked, so that protein synthesis and replication can take place. - DNA is only visible during mitosis.
101
What are spindle fibers made of?
Microtubules
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Processes occurring during interphase (DOCTOR)
- DNA replication – DNA is copied during the S phase of interphase - Organelle duplication – Organelles must be duplicated for twin daughter cells - Cell growth – Cytoplasmic volume must increase prior to division - Transcription / translation – Key proteins and enzymes must be synthesized - Obtain nutrients – Vital cellular materials must be present before division - Respiration (cellular) – ATP production is needed to drive the division process
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