D2.1

Question 1

Cell Division and Cell Cycle

What is Cytokinesis?

Answer 1

• The splitting of the cytoplasm to create two daughter cells from one parent cell.
• Each daughter cell has an adequate amount of cytoplasm
• This is the last step of cell division (genetic material already divided)

Question 2

Cell Division and Cell Cycle

What is a cleavage Furrow?

Answer 2

• In early stages of cytokineses –> plasma membrane pulls inwards at the equator/centre of the cell
• Uses a ring of contractile protiens inside the membrane that gather at the center
• The region of pinching at the centre is the cleavage furrow

Question 3

Cell Division and the Cell Cycle

Cell plate?

In cytokinesis for plants

Answer 3

• Cell plate begins with a layer of vesicles
• Vesicles fuse - this layer of fused vesicles at the equator is the cell plate –> goes on to form new cell wall

Question 4

Cell Division and the Cell Cycle

Chromatids?

Answer 4

• When a chromosome copies an indetical copy, the two identical copies attached to one another by proteins
• New daughter cells resulting from cell division must have a full set of DNA (46 chromosomes) hence the chromosomes need to replicate before division.

Question 5

Cell Division and the Cell Cycle

What is DNA condensation?

Answer 5

• Prior to division, DNA is tightly wrapped into nucleosomes - nucleosomes then linked (condensed).
• Note: DNA needs to be less tightly wrapped around histones so genes are accesible for transcription.

Question 6

Cell Division and the Cell Cycle

Cell Cycle?

Answer 6

• Series of events leading up to cell division
• Must firstly, grow, replicate their DNA, and prepare for division.
• These stages (interphase) and stages of division themself (prophase, anaphase, metaphase, telophase) make up cell cycle.

Question 7

Cell Division and the Cell Cycle

What is interphase?

Answer 7

• Stages prior to division
• Growth, DNA replication and preparation
• Divided into three phases of G1, S, and G2
• 90% of cell cycle in comprised of these stages

Question 8

Cell Division and the Cell Cycle

Cell proliferation?

Answer 8

• Rapid increase in the no. cells
• Occurs when the rate of cell division exceeds rate of cell death
• Faciliates growth and repair of damaged tissue

Question 9

Cell Division and the Cell Cycle

DNA Division: Binary Fission

Prokaryotes do cell division via mitosis

Answer 9

• DNA divided in prokaryotes that lack a nucleus referred to as binary fission
• Process in distinct from complex division of eukaryotic chromosomes
• Circular DNA is repliacted then separated

Question 10

Cell Division and the Cell Cycle

DNA Division: Mitosis

Answer 10

• DNA is linear and contained in nucleus divided by mitosis
• 4 stage process involving arranging linear chromosomes centrally so they can be separated
• Ensures daughter cells have one set of chromosomes

Question 11

Cell Division and the Cell Cycle

DNA Division: Meiosis

Answer 11

• When DNA is divided to produce gametes
• As gametes join together to make zygotes - need one copy of each chromosome instead of two
• This form of division results in reduction of genetic material, requires a unique form of division involving two stages of divisions (meiosis 1 and 2)

Question 12

Cell Division and the Cell Cycle

Constrast cytokinesis in plant vs animal cells

Answer 12

• Animal: lack of cell wall makes division in cytoplasm straightforward, inside pinches, cleavage furrow made from contractile proteins.
• Plants: instead of pinching, cell plate forms from merging vesicles, perimeter of cell plate forms 2 membranes, inside of vesicles forms new cell wall.

Question 13

Cell Division and the Cell Cycle

Explain how Oogenesis is an example of unequal cytokinesis.

Answer 13

• Formation of egg cells - goal to create one large egg with many organelles to support zygote
• Hence, DNA divides evenly but cytoplasm divides unevely to create one large egg cell and 3 polar bodies

Question 14

Cell Division and the Cell Cycle

Explain how Budding is an example of unequal cytokinesis.

Budding in yeast

Answer 14

• Nucleus divides evenly, creating two identical nuclei.
• But, new daughter cell takes small amoung of cytoplasm
• Cell wall repairs creating a scar on intial cell
• Cells don’t have to double in size prior to division

Question 15

Cell Division and the Cell Cycle

What is the structure of sister chromatids?

Answer 15

• Before cell division, DNA replicates
• The two identical strands of DNA are then joined prior to being separated in mitosis.
• Held together by cohesion loops, then spindle fibres attach to kinetochore proteins to break them apart.

Question 16

Cell Division and the Cell Cycle

What is the G1 phase?

First phase of interphase

Answer 16

• The cell grows in size
• Accumulates important materials needed, i.e., additional proteins & more nucleotides
• Cytoplasm is thus larger

Question 17

Cell Division and the Cell Cycle

What is the S phase?

Second phase of interphase

Answer 17

• DNA is replicated resulting in two identical strandes connected by cohesion loops (sister chromatids)
• This is complex enzyme mediated process

Question 18

Cell Division and the Cell Cycle

What is the G2 phase?

Final phase of interphase before cell division

Answer 18

• Some further growth, further replication of important organelles (mitochondria and chloroplasts)
• Microtubules begin to form visable centrosomes

Question 19

Cell Division and the Cell Cycle

What is a metaphase plate?

Answer 19

• Imaginary plane running through centre of cell (like the Earth’s equator!)

Question 20

Cell Division and the Cell Cycle

What is a centrosome?

Answer 20

• Organelles comprised of two centrioles that forms the spindle fibres that will attach to chromosomes.
• Two centrioles and microtubules coming from they form the centrosome

Question 21

Cell Division and the Cell Cycle

What are kinetochores?

Answer 21

• Protein structures forming at the centromere of each chromatid
• Microtubules from the spindle fibres can attach to the kinetochore proteins to move chromosomes & pull apart and separate chromatids.

Question 22

Cell Division and the Cell Cycle

What is mitotic index?

Answer 22

• Quantifies proportion of cells currently dividing
• No. cells in a stage of mitosis/ total no. cells
• If high - tissue may be dividing too rapidly –> cancer.

Question 23

Cell Division and the Cell Cycle

What are the two events that happen in prophase?

First stage of Mitosis

Answer 23

• DNA supercoils to form visable chromosomes and the nuclear membrane dissolves into vesicles
• Centrosomes assemble spindle microtubules and migrate to the poles of the cell.

Question 24

Cell Division and the Cell Cycle

What are the two events that happen in metaphase?

Second stage of mitosis

Answer 24

• Microtubules from each centrosome attach to kinetochores of the sister chromatids forming spindles fibres.
• Fibres move the chromosomes to metaphase plate alinging with the centromes along Centre point of cell

Question 25

# Cell Division and the Cell Cycle What are the two events that happen in anaphase? | Third stage of Mitosis

Answer 25

* **Motor proteins** between microtubules in the spindle fibres cause further miragtion of centrosomes - puts enough **tension on cohesion loops to break them** * The **kinetochores** shorten spindle microtubule, moving **chromosomes to pole**

Question 26

# Cell Division and the Cell Cycle What are the three events that happen in telophase? | Final step of mitosis

Answer 26

* The nuclei membrane **reforms around chromosomes** at each pore * Chromosomes **decondense to loose chromatin** within the nucleus * Cell elongates to prepare to cytokinesis.

Question 27

# Cell Division and the Cell Cycle What are motor proteins and microtubules?

Answer 27

* Microtubules are formed from the **centromere and elongate with rings of tublin** * Between TWO microtubules are **motor proteins** * Motor proteins help pull microtubules towards the **opposite poles**, crucial for both to move chromosomes to centre of cell & create tension to break cohesion loops

Question 28

# Meiosis What are gametes?

Answer 28

* Specialized **sex cell** for the purpose of sexual reproduction * Contains **half the number of chromosomes** of a typical cell so two gametes can join togehter to create a **haploid zygote with full set of chromosomes** *Aniamls: sperm and egg* *Plants: pollen*

Question 29

# Meiosis What is meant by 'Redcution Division?'

Answer 29

* End of two rounds of division results in a **reduciton of genetic material**/ genetic material is halved in the resulting daughter cells

Question 30

# Cell Division and the Cell Cycle What are homologous chromosomes?

Answer 30

* When gametes fuse, we get a chromosome, 1 from each parent --> this pair of **same chromosomes** are homologous. * Have **same genes** in the **same positions** but the versions/alleles differ (different parents)

Question 31

# Meiosis What is a bivalent?

Answer 31

* When a set of **homologous chromosomes** each have a sister chromatid and **come together**, this forms **4 strands of DNA** called Bivalents. * Tend to overlap --> crossing over

Question 32

# Meiosis What is crossing over?

Answer 32

* Early meiosis, homologous chromosomes, each replicated. join together * Inner chromatid of each overlaps at the **chiasma**, where the chromatids **break and swap genetic material** * Causes inner chromatids to have **unique genetic combinaitions** --> no longer identical

Question 33

# Meiosis Compare Diploid vs Haploid Nuclei

Answer 33

* Cells/nuclei that have **two of each chromosome** (all homologous chromosomes) are **DIPLOID** *All somatic/body cells are diploid, 2n.* * Cells/nuclei that have **only one of each chromosome** are **HAPLOID** *Only gametes are halpoid, n.*

Question 34

# Meiosis Compare Meiosis I and Meiosis II | Note: Meiosis has 2 stages of 4 steps of cell division

Answer 34

* In these two processes - **Meiosis I** lines up **chromosomes in HOMOLOGOUS PAIRS** to separate the homologous chromosomes. * **Meiosis II** then **separates the sister chromatids**.