cell cycle

Question 1

state the relationship between cell division and nuclear division

Answer 1

cell division involves both nuclear division and cytokinesis

Question 1

define mitosis and meiosis

Answer 1

• mitosis: process by which a nucleus divides to produce 2 daughter nuclei containing identical sets of chromosomes to the parent nucleus
• meiosis: process by which a nucleus divides to produce 4 daughter nuclei, each containing half the number of chromosomes of the parent nucleus

Question 2

how does DNA become chromatin?

Answer 2

DNA is coiled around proteins to form a nucleosome, and a group of nucleosomes are intensely coiled together to form chromatin

Question 3

define centromere

Answer 3

region of chromosome that holds two sister chromatids together after DNA replication

Question 4

define homologous chromosomes

Answer 4

a pair of chromosomes with the same gene loci, length, centromere position and shape which determine the same characteristics, and pair with each other during Prophase I of meiosis

Question 5

describe prophase (mitosis)

Answer 5

• chromosomes become visible due to condensation of chromatin, consisting of 2 sister chromatids joined at centromere
• (in animal cells) centrioles migrate to opposite poles of the cell
• nucleolus and nuclear envelope disintegrate

Question 6

describe metaphase (mitosis)

Answer 6

• chromosomes are attached to spindle fibres at their centromeres
• chromosomes arrange themselves 90 degrees to spindle axis, at the equator of the cell

Question 7

describe anaphase (mitosis)

Answer 7

• centromere of each chromosome divides, separating sister chromatids of the chromosome
• sister chromatids move to opposite poles of the cell, centromeres first, due to shortening of spindle fibres

Question 8

describe telophase (mitosis)

Answer 8

• sister chromatids reach respective poles of the cell
• chromsomes uncoil and become chromatin
• spindle fibres break down
• nucleolus and nuclear envelope reform

Question 9

describe what happens during interphase

REMEMBER THAT INTERPHASE IS NOT PART OF MITOSIS/MEIOSIS (it’s only part of the CELL CYCLE)

Answer 9

• cell prepares for division
• occurence of cell growth, DNA replication and the cell synthesises proteins and new organelles for mitosis
• chromatin has yet to condense, so not chromosomes are visible

Question 10

describe cytokinesis

Answer 10

• cytoplasm of cell divides into two parts

Question 11

why is mitosis important? explain how it achieves this

Answer 11

maintains genetic stability
- mitosis results in daughter cells genetically identical to parental cell
- before mitosis, DNA replication occurs to produce a duplicated chromosome where 2 sister chromatids are held at the centromere
- during metaphase, the duplicated chromosomes arrange themselves at metaphase plate/equator
- during anaphase, the sister chromatids separate and move to opposite poles of the cell

Question 12

describe

2 ways mitosis ensures diploid number

Answer 12

1. replication of chromosomes doubles amount of DNA during interphase, which is halved at telophase
2. arrangement of chromosomes at equator of cell in mitosis ensures even distribution of chromosomes between daughter cells

Question 13

what are the 3 core functions of mitosis?

Answer 13

• growth and development of multicellular organism
• replacement of worn-out body parts
• basis of asexual reproduction

Question 14

contrast non-sister and sister chromatids

Answer 14

• non-sister: 2 chromatids of homologous chromosomes (usually refer to it like this)
• sister: 2 chromatids of the same chromosome

Question 15

define/describe the term chiasma

Answer 15

x-shaped structure formed between non-sister chromatids of homologous chromosomes, the site where corresponding sections of non-sister chromatids of homologous chromosomes break and rejoin, where a portion of one non-sister chromatid is exchanged with an equivalent portion of the other during crossing over, enabling exchange of genetic material

Question 16

define crossing over

Answer 16

exchange of corresponding alleles between non-sister chromatids of homologous chromosomes

Question 17

describe prophase I

Answer 17

• chromosomes become visible due to condensation of chromatin
• ⭐ homologous chromosomes pair up through synapsis, each pair constituting a bivalent
• ⭐ chiasmata may form between non-sister chromatids of a pair of homologous chromosomes, where crossing over occurs
• (in animal cells) centrioles migrate to opposite poles of the cell
• nucleolus and nuclear envelope disintegrate

“⭐” shows distinguishing trait between meiosis I and mitosis

Question 18

describe metaphase I

Answer 18

• chromosomes are attached to spindle fibres at their centromeres
• bivalents⭐ arrange themselves 90 degrees to spindle axis, forming 2 rows ⭐ at the equator of the cell
• ⭐ where the arrangement of chromosomes of each bivalent is completely random

“⭐” shows distinguishing trait between meiosis I and mitosis

Question 19

describe anaphase I

Answer 19

• homologous chromosomes separate ⭐ and move to opposite poles of the cell, centromeres first, due to shortening of spindle fibres

“⭐” shows distinguishing trait between meiosis I and mitosis

Question 20

describe telophase I

Answer 20

• chromosomes ⭐ reach respective poles of the cell
• DOES NOT HAPPEN: chromsomes uncoil and become chromatin
• spindle fibres break down
• nucleolus and nuclear envelope reform

(AFTER MEIOSIS I - not part of telophase)
- if cytokinesis takes place, 2 daughter cells result, each with haploid number of chromosomes

“⭐” shows distinguishing trait between meiosis I and mitosis

Question 21

describe prophase II

Answer 21

• centrioles migrate to opposite poles of the cell (assuming present)
• nucleolus and nuclear envelope disintegrate (assuming Telophase I and interphase occurred)
• ⭐ spindle fibres develop perpendicular to spindle axis of Meiosis I

“⭐” shows distinguishing trait between meiosis I and II

Question 22

describe metaphase II

Answer 22

• chromosomes are attached to spindle fibres at their centromeres
• chromosomes arrange themselves 90 degrees to NEW spindle axis, at the equator of the cell

same as mitosis, except “NEW” spindle axis

Question 23

describe anaphase II

Answer 23

• centromere of each chromosome divides, separating the TWO (not sister) chromatids of the chromosome
• (NOT sister) chromatids move to opposite poles of the cell, centromeres first, due to shortening of spindle fibres

same as mitosis, except NOT sister

Question 24

describe telophase II

Answer 24

- chromatids reach respective poles of the cell, ⭐ they become **chromosomes of daughter cells** - chromsomes **uncoil** and become chromatin - **spindle fibres** break down - **nucleolus and nuclear envelope** reform

Question 25

what are the functions of meiosis?

Answer 25

* produces **haploid gametes** for **sexual** reproduction, where the **nuclei of haploid gametes fuse** together during **fertilisation** to **restore the diploid number** of chromosomes in the **zygote** (otherwise fusion of diploid gametes would result in doubling of chromosomes for each successive sexually reproduced generation) * gives rise to **genetic variation** which is essential for **evolution**, as it allows **natural selection** to operate and ensures species can adapt to and survive changing environmental conditions

Question 26

how does meiosis bring about genetic variation?

Answer 26

results in **new combination of alleles** due to: * **crossing over** of non-sister chromatids of homologous chromosomes in **Prophase I** * random arrangement and **independent assortment** of homologous chromosomes during **metaphase I**, and **separation** of these chromosomes at **anaphase I**

Question 27

contrast mitosis and meiosis in at least 3 ways

Answer 27

1. DNA replicates once and **nucleus divides** once | DNA replicates once but **two successive nuclear divisions** 2. **crossing over** does not occur | likely to occur 3. chromosomes form **single row** | **two rows** at equator of the cell at **metaphase** | **metaphase I** 4. **2 | 4** daughter cells formed 5. daughter cells have **same number | half the number** of chromosomes as parent cell 6. **pairing up of homologous chromosomes** does not occur during Prophase | occurs during Prophase I 7. **homologous chromosomes** are not | are **separated** during **Anaphase | Anaphase I**

Question 28

what is cancer?

Answer 28

diseases due to **uncontrolled cell division**

Question 29

what is unique about cancer cells?

Answer 29

1. do not **stop reproducing** 2. do not exhibit **contact inhibition** 3. do not exhibit **cell adhesion** 4. do not **become specialised**, remain **undifferentiated** 5. **stimulate growth of blood vessels toward itself** 6. **able to metastasise** ## Footnote Research Cities Can Support Vital Missions

Question 30

how does cancer develop?

Answer 30

* **accumulation of DNA mutation** across successive generations of cells, with genes involved in **regulation of cell cycle** * cells **divide uncontrollably**, giving rise to a **tumour**

Question 31

distinguish benign and malignant tumours

Answer 31

* *benign*: **only found in one location** and can be removed surgically * *malignant*: cells are able to undergo **angiogenesis and metastasis**, and are **cancerous** as they can **travel to other parts of the body** to form **secondary tumours**

Question 32

distinguish early and late interphase

Answer 32

early: DNA has **not yet** replicated late: **DNA replication has occurred**

Question 33

# state what stages of meiosis are happening at each point in the [graph](https://drive.google.com/file/d/1kJiMux9b6ctDhU4m2w_Vi2ZfWuFSTcuo/view?usp=sharing) do 1 for each for if the y-axis was DNA content "per nucleus" and "per cell" | distinguish early/late interphase and telophase

Answer 33

[answer](https://drive.google.com/file/d/1D_ozPeiJlO17q6DEQTK3qIj-h6_nDv4n/view?usp=sharing)

Question 34

# state at what stage of nuclear division does the nuclear envelope reform

Answer 34

(late) telophase