1.Cells and Proteins

Question 1

What are prokaryotes cells?

Answer 1

Cells such as bacteria and blue-green algae that does not have a “true nucleus” Nuclear material is free in cytoplasm.

Question 2

What are eukaryotes?

Answer 2

All organisms apart from bacteria and the cyanobacteria, are classified as eukaryotes because their calls contain a true nucleus- the nucleus is enclosed by a double membrane.

Question 3

What is a cytoskeleton?

Answer 3

It consists of different protein structures including microtubules in all eukaryotic cells and it extends throughout the cytoplasm.

Question 4

What does the cytoskeleton do?

Answer 4

• Provides a framework that gives mechanical support and shape to cells.
• The cytoskeleton consists of different protein structures (these proteins include microtubules)

Question 5

What is the origin and structure of microtubules?

Answer 5

They are hollow tubes that radiate from the microtubules-organising center (MTOC)

Question 6

What protein are microtubules made of?

Answer 6

Tubulin

Question 7

What is the main functions of microtubules?

Answer 7

• Microtubules allow the movement of membrane bound organelles
• Responsible for the movement of chromosomes during meiosis and mitosis
• In animal cells it is responsible for the division of the cytoplasm called cytokinesis

Question 8

What happens to microtubules during mitosis?

Answer 8

They from spindle fibres and are active during cell division to move chromosomes and separate chromatids. They must be assembled and disassembled to function as spindle fibres.

Question 9

What is cytokineses?

Answer 9

The division of the cytoplasm

Question 10

What does the dynamic nature of the cytoskeleton?

Answer 10

The cytoskeleton is continually changing to provide support and movement in cell. Microtubules can break up and reform (controlled by centrosome or MTOC)

Question 11

What is polymerisation?

Answer 11

The formation of microtubules

Question 12

What is depolymerisation?

Answer 12

Breakdown of microtubules.

Question 13

What are the two major stages of the cell cycle?

Answer 13

• Interphase (period of cell growth and DNA replication)
• Mitosis (segregation of replicated chromosomes)

Question 14

What are the three sub-phases of interphase?

Answer 14

G1 - Growth
S - Synthesis
G2 - Growth

Question 15

What are the between cell divisions phases called?

Answer 15

Interphase

Question 16

What is G1 phase?

Answer 16

G1 is the first period of cell growth stage. This is where the cell doubles in size and many chromosomes are synthesised.

Question 17

What is the S Phase?

Answer 17

DNA replication occures - chromosomes are replicated to form two chromatids centrioles.

Question 18

What is the MTOC and what happens to it during mitosis?

Answer 18

MTOC normally controls the cytoskeleton but during mitosis the cytoskeleton breaks down and the sub-units are reassembled to from the spindle which grows out from the two MTOC.

Question 19

What is the G2 phase?

Answer 19

This is a further period of cell growth in preparation for the M-phase. Sufficient reserves of ATP build up to last cell through rest of cycle.

Question 20

Roughly how long does interphase last?

Answer 20

80% of the time.

Question 21

Why is cell division so important?

Answer 21

Each daughter cell must have a complete set of genetic instructions in order to be able to function.

Question 22

What are the four phases of mitosis?

Answer 22

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 23

What happens in prophase?

Answer 23

• DNA condenses into chromosomes each consisting of two sister chromosomes each consisting of two sister chromatids joined at the centrosome
• Nuclear membrane breaks down
• Spindle microtubules extend from the MTOC by polymerisation and attached to chromosomes via their kineticore (in the centrosome region)

Question 24

What happens in metaphase?

Answer 24

• Centrioles move to poles
• Chromosomes are aligned at the metaphase plate

Question 25

What happens in anaphase?

Answer 25

As spindle microtubules shorten by depolymerisation sister chromatids are separated and the chromosomes are pulled to the opposite poles.

Question 26

What happens in telophase?

Answer 26

• The chromosomes decondense
• New nuclear membrane reforms around them

Question 27

What happens during cytokinesis?

Answer 27

During the cytoplasm divides and 2 new daughter cells are formed. They are genetically identical to mother cell.

Question 28

What happens during cytokinesis in animal cells?

Answer 28

Cytokinesis splits and new plasma membrane forms.

Question 29

What happens during cytokinesis in plant cells?

Answer 29

New cell walls form from the middle lamella which splits the cytoplasm.

Question 30

What is a checkpoint?

Answer 30

Checkpoints are mechanisms within the cell that assess the condition of the cell during the cell cycle.
Checkpoints will halt the progression to the next phase until centrian requirements are met.

Question 31

What are the checkpoints?

Answer 31

At G1, G2 and metaphase.

Question 32

What is cyclin?

Answer 32

Cyclin is a protein that accumulate during cell growth are involved in regulating the cell cycle.

Question 33

What happens to cyclin during the G1 phase?

Answer 33

As the cell size increases during G1 cyclin proteins accumulate.
Cyclin then combines with regulatory proteins called Cyclin-dependent kinases (cdks) and activate them. This forms a cyclin-cdk complexes.

Question 34

What does active cdk cause?

Answer 34

The phosphorylation of proteins that stimulate the cell cycle.

Question 35

What happens when there is sufficient and insufficient phosphorylation?

Answer 35

If sufficient phosphorylation is reached, progression to the next stage.
If an insufficient threshold is reached, the cell is held at a checkpoint.

Question 36

What is the G1 checkpoint assessing for?

Answer 36

• Cell size
  -Nutrients
• Environmental factors