Unit 1 - section 6

Question 1

What structure is responsible for maintaining the shape, structure and position of all cell organelles?

Answer 1

Cytoskeleton

Question 2

What happens to the cytoskeleton during cell division?

Answer 2

It is remodelled

Question 3

What is the cytoskeleton composed of?

Answer 3

Consists of different types of proteins extending throughout the cytoplasm, such as microtubules

Question 4

What globular proteins are microtubules formed from?

Answer 4

Composed of hollow straight rods made of globular proteins called tubulins

Question 5

What is the function of microtubules?

Answer 5

Govern the location and movement of membrane-bound organelles and other cell components

Question 6

In what types of cell can you find can microtubules and where do they radiate from?

Answer 6

Found in all eukaryotic cells and radiate from the centrosome

Question 7

What type of fibres do microtubules form during cell division?

Answer 7

Spindle fibres

Question 8

What is the function of the cell cycle?

Answer 8

Regulates the growth and replacement of genetically identical cells throughout the life of the organism

Question 9

What condition could result from the uncontrolled decreased in the rate of cell cycle?

Answer 9

Digenerative diseases

Question 10

What condition could result from an uncontrolled increase in the rate of the cell cycle?

Answer 10

Tumor formation

Question 11

Describe the 3 stages of interphase

Answer 11

G1 - first gap phase where proteins and organelles are synthesised
S - synthesis phase for continued growth and DNA replication
G2 - second gap phase where proteins and organelles are synthesised

Question 12

What are the stages of mitosis?

Answer 12

Interphase - protein synthesis occurs and organelles are made. Cell grows and DNA is replicated
Prophase - chromatin condensed into sister chromatids and mitotic spindle forms between centrosomes
Metaphase - nuclear membrane breaks up and centrosomes are now at opposite poles. Chromosomes line up at metaphase plate. Microtubules attach to kinetochore
Anaphase - microtubules shorten pulling sister chromatids apart to opposite poles
Telophase - cell lengthens and nuclear membrane reforms around chromosomes at each pole. Chromosomes begin to uncoil
Cytokinesis - cytoplasm divides creating two new identical cells

Question 13

What is the role of spindle fibres during M phase?

Answer 13

To divide the genetic material in a cell so that the chromosomes are divided equally between the two daughter cells that are forming

Question 14

Where is the metaphase plate located?

Answer 14

On the equator of the cell

Question 15

Describe the formation of daughter nuclei

Answer 15

Interphase - protein synthesis occurs and organelles are made. Cell grows and DNA is replicated
Prophase - chromatin condensed into sister chromatids and mitotic spindle forms between centrosomes
Metaphase - nuclear membrane breaks up and centrosomes are now at opposite poles. Chromosomes line up at metaphase plate. Microtubules attach to kinetochore
Anaphase - microtubules shorten pulling sister chromatids apart to opposite poles
Telophase - cell lengthens and nuclear membrane reforms around chromosomes at each pole. Chromosomes begin to uncoil

Question 16

What is cytokinesis?

Answer 16

Stage where the cytoplasm divides creating two new identical cells

Question 17

What are the 3 checkpoints that occur during the cell cycle and what are their functions?

Answer 17

G1 checkpoint - occurs towards the end of G1. Checks sufficient cell growth has occurred and that other conditions are satisfied before allowing the cell to enter S phase
G2 checkpoint - occurs at the end of G2. DNA replication must be completed for the cell cycle to continue
M checkpoint - occurs during metaphase and controls entry to anaphase. Checks that chromosomes are aligned correctly on the metaphase plate and therefore ensures that each daughter cell receives the correct number of chromosomes

Question 18

Which checkpoint is the most significant for most cells?

Answer 18

G1 checkpoint

Question 19

What occurs if the G1 checkpoint is not passed?

Answer 19

The cell will exit the cycle and switch to the G0 phase, a non dividing state, instead of completing the cycle and dividing

Question 20

What happens to cell size at G1 checkpoint?

Answer 20

It is checked to ensure sufficient cell growth has occurred

Question 21

What accumulates at G1?

Answer 21

Cyclin proteins

Question 22

What is the role of Cdks in the control of the cell cycle?

Answer 22

As the cell size increases during G1, cyclin proteins accumulate and combine with kinases to form regulatory protein molecules which are known as cyclin-dependent kinases (Cdks)
Cdks cause the phosphorylation of proteins that stimulate the cell cycle. If a sufficient threshold of phosphorylation is reached the cell cycle moves onto the next stage

Question 23

What occurs if the threshold of phosphorylation is not reached?

Answer 23

Cell is held at a checkpoint

Question 24

Which protein is activated when DNA is damaged?

Answer 24

p53

Question 25

What are 3 things that might occur if DNA is damaged during S phase?

Answer 25

p53 can activate DNA repair proteins to repair the DNA damage
p53 can stop the cell cycle at the G1 checkpoint - this can allow DNA repair proteins time to recognise and fix the DNA damage so the cell can restart the cell cycle
If the DNA damage is too severe p53 can initiate apoptosis

Question 26

What is apoptosis?

Answer 26

Programmed cell death

Question 27

What are the 2 classes of enzymes involved in apoptosis?

Answer 27

DNAases

Proteinases

Question 28

How are death signals which originate from outwith or within cells triggered?

Answer 28

Outwith: cell death signals can be triggered from outwith the cell (for example from lymphocytes) a signal binds to a surface receptor activating protein cascades that trigger active caspases. These can activate DNAase that destroy the cell
Within: death signals can be triggered from within the cell (for example as a result of DNA damage) p53 proteins activate capase cascade. In the absence of growth factors apoptosis may be initiated

Question 29

What is another solution that may give rise to apoptosis?

Answer 29

During human embryonic development programmes cell death occurs on the cells between the fifers and toes. Allowing individual digits to form