(U1) Continuity Of Cells

Question 1

What are somatic cells?

Answer 1

Non-sex cells

Question 2

What are gametes?

Answer 2

Sex cells

Question 3

What are the parts of a chromosome called? (2)

Answer 3

• chromatids
• the centromere (centre where 2 chromatids are joined)

Question 4

Name the stages of the cell cycle in order

Answer 4

• mitotic (M) phase
• G₁ (gap) phase
• S (DNA synthesis) phase
• G₂ phase

Question 5

What does the mitotic phase consist of?

Answer 5

• mitosis
• then cytokinesis

Question 6

What is mitosis? In simple terms (2)

Answer 6

• Division of the nucleus
• during eukaryotic cell division

Question 7

What is cytokinesis? In simple terms (2)

Answer 7

• division of cytoplasm
• during eukaryotic cell division

Question 8

What does the Synthesis phase consist of? (2)

Answer 8

• DNA replication
• histone production

Question 9

What does the G₁ phase consist of? (2)

Answer 9

• synthesis of structural proteins and enzymes to perform its functions
• organelles develop e.g. Mitochondria

Question 10

What does the G₂ phase consist of?

Answer 10

Tubulin production (protein)

Question 11

What are the 4 stages of mitosis?

Answer 11

• prophase
• metaphase
• anaphase
• telophase

Question 12

Outline the events of the prophase of mitosis (5)

Answer 12

• chromatin (DNA) condenses around histones into chromosomes
• nucleolus disintegrates
• nuclear envelope disappears
• centrioles migrate to opposite poles and
• the microtubules of spindle fibres form

Question 13

Outline the events of the metaphase of mitosis. (2)

Answer 13

• microtubules of spindle fibres attach to the kinetochore of centromeres
• chromosomes are lined along the equator of the cell

Question 14

What are kinetochores? (3)

Answer 14

• protein complexes
• that bind to the centromeres of chromosomes
• to allow microtubules of the spindle fibre to attach

Question 15

Outline the events of the anaphase of mitosis. (3)

Answer 15

• microtubules of the spindle fibres contract
• centromere splits
• sister chromatids are pulled to opposite poles (sides of the cell)

Question 16

Outline the events of the telophase of mitosis. (3)

Answer 16

• nuclear envelope reforms around each new set of chromosomes
• chromosomes de-condense into chromatin (not visible under a light microscope)
• microtubules of spindle fibres disperse as they are broken down

Question 17

How does cytokinesis occur in animal cells? (5)

Answer 17

• protein microfilaments (actin) contract along the centre of the cell
• A cleavage furrow forms
• as the cell surface membrane invaginates
• eventually this spilts the cell in 2
• leaving 2 genetically identical daughter cells

Question 18

How does cytokinesis occur in plant cells? (4)

Answer 18

• golgi vesicles fuse to form a cell plate
• which is laid down along the equator (centre) of the cell
• Golgi apparatus helps synthesise materials needed to form a new cell wall
• the cell splits in 2

Question 19

Give another name for a cell membrane

Answer 19

Cell envelope (double membrane)

Question 20

Put the following structures in order of origin:

• spindle fibres
• microtubules
• centrioles

Answer 20

• centrioles
• spindle fibres
• microtubules

Question 21

What effect does the Synthesis phase have on:

• the amount of DNA
• the volume of the cell

Answer 21

• DNA doubles (due to replication)
• volume of the cell increases slightly

Question 22

What effect does end of a cell cycle have on:

• the amount of DNA
• the volume of the cell

Answer 22

• DNA halves
• volume halves

(Nucleus splits after mitosis - cell splits after cytokinesis)

Question 23

What is the name of the 2 broad divisions in meiosis

How many phases do each contain?

Answer 23

1. • Meiosis 1
   • Meiosis 2
2. 4 each + 2 cytokinesis (10 total)

Question 24

Outline the phases of meiosis 1 and 2

Answer 24

1. Meiosis 1:

• prophase 1
• metaphase 1
• anaphase 1
• telophase 1

2. Cytokinesis 1
3. Meiosis 2:

• prophase 2
• metaphase 2
• anaphase 2
• telophase 2

4. Cytokinesis 2

Question 25

Outline **prophase 1** of **meiosis** (**6**)

Answer 25

- **Chromatin** becomes **short and dense** (forms chromosomes) - ***Homologous** chromosomes* form **bivalents** - **Non-sister** *chromatids* meet at **chiasmata** and **exchange recombinant alleles** – ***genetic crossover*** - **Centrioles migrate** to *opposite poles* - **Microtubules** develop - **Nuclear envelope** *disintegrates*

Question 26

Outline **metaphase 1** of **meiosis** (**2**)

Answer 26

- **Bivalents** *attach* to **microtubules of spindle fibres** by *kinetochores* at **centromere** - **Bivalents** align at **equator** in a **random order** – **independent assortment**

Question 27

Outline **anaphase 1** of **meiosis** (**2**)

Answer 27

- *Microtubules* **contract** - Bivalents separate – whole chromosomes pulled to opposite poles – **haploid no. of chromosomes** formed

Question 28

Outline **telophase 1** of **meiosis** (**4**)

Answer 28

- **Cluster** of chromosomes go to **each pole** - **Spindle disintegrates** - **2 nuclear envelopes** form – *1 for each set* of chromosomes (at each pole) - **Nucleoli reappear**

Question 29

What are the only **differences** between **meiosis 2** and **meiosis 1**? (**4**)

Answer 29

- *prophase 2*: **spindle fibres** *form* at **right angles** *to original* - *metaphase 2*: **individual chromosomes** rather than bivalents - *anaphase 2*: **non-sister chromatids** *pulled to opposite poles* - not whole chromosomes - *telophase 2*: **2 nuclear envelopes** form around each **set of chromatids**

Question 30

What is the **purpose** of **checkpoints** in the **cell cycle**? (**3**)

Answer 30

- *Prevents* cell being the **wrong size** - *Prevents* **DNA** having **errors** when **replicating** - *Ensures* **chromosomes** *were* **arranged properly** in *metaphase*

Question 31

**Where** are the **checkpoints** in the **cell cycle**?

Answer 31

The end of: - G1 - G2 - Mitotic phase

Question 32

**What** does the ***G1* checkpoint check for**? (**4**)

Answer 32

- **DNA damage** - **Cell size** (i.e. organelles, macromolecules etc.) - *Supply* of **nutrients** (e.g. glucose) - *Presence* of **growth factors**

Question 33

**What** does the ***G2* checkpoint check for**?

Answer 33

- if **DNA replication** was **done properly** - **Cell size** (organelles, macromolecules etc)

Question 34

**What** does the ***mitotic* checkpoint check for**?

Answer 34

**Number** and **alignment** of *chromosomes*

Question 35

If a **cell doesn’t** *meet the* **requirements** of **checkpoints**, what happens? (**3**)

Answer 35

- cell **enters G0** (purgatorial phase), therefore **can’t replicate** - **errors** are **corrected** - cell is **allowed** to **replicate**

Question 36

**How** can **cancer occur** in the *cell cycle*? (**2**)

Answer 36

- due to a **mutation** in **bases in DNA** – *coding for* **wrong amino acid** –> **wrong protein** (*e.g. growth factor*) - This can cause **cells** to **divide uncontrollably** and **bypass G0**

Question 37

In the **cell cycle**, **where** are **cancer drugs** used? (**2**)

Answer 37

- synthesis phase - Mitotic phase

Question 38

In **S phase**, what **types of cancer drug** are used? Describe **how each work** and name an **example**

Answer 38

1. **unzipping inhibitors**: - **inhibit enzymes** *like DNA Helicase* so **replication can’t occur** - e.g. **adriamycin** and **cytoxan** 2. **Antimetabolites**: - **inhibit synthesis** of **nucleotides** - e.g. **5-fluorouracil** and **methotrexate**

Question 39

In **M phase**, what **type of cancer drug** is used? Describe **how they work** and name an **example** (**3**)

Answer 39

**Microtubule formation blockers**: - **bind** to **tubulin** - **chromatids can’t separate** - *anaphase can’t occur* - e.g. **vincristine** and **taxol**

Question 40

**How** does **vincristine** *slow down* the growth of a *tumour*? (**3**)

Answer 40

- vincristine **inhibits tubulin** - *prevents microtubules* being formed - *no spindle fibre* is formed