The Cell Cycle

Question 1

Cell Proliferation In Prokaryotes

Answer 1

prokaryotes make a copy of their genome and the copy splits into two daughter cells

Question 2

Binary Fission

Answer 2

• initiated when DNA of the bacterial chromosome is attached by proteins to the inside of plasma membrane
• as chromosome continues to replicate, the cell begins to elongate and the newly synthesized DNA is anchored to the plasma membrane
• cell continues to elongate until 2 DNA attachment sites are at opposite ends of elongated cell
• when DNA replication is complete the cell begins to constrict along midpoint of the cell
• synthesis of a new cell membrane and cell wall which will completely divide the two daughter cells

Question 3

Eukaryotic Cell Cycle

Answer 3

allows for a unicellular fertilized egg to develop into a complex organism

Question 4

Interphase

Answer 4

cell makes preparations for cell division which include the replication of DNA and an overall increase in size

Question 5

S phase

Answer 5

replication of DNA

-new molecule is associated with histones that allow for tight compaction

Question 6

G1 and G2 phase

Answer 6

prepare the cell for DNA synthesis and mitosis

Question 7

G0 phase

Answer 7

cells that are not actively dividing pause here, some cells never leave this phase

Question 8

Prophase

Answer 8

• centrosomes begin to radiate long microtubules forming a mitotic spindle
• centrosomes will become positioned at opposite poles of the cell
• spindle will become crucial for separating the chromosomes into 2 daughter cells

Question 9

ProMetaphase

Answer 9

• nuclear envelope breaks down
• microtubules are able to attach to kinetochores
• kinetochores pull the chromosomes to the poles of the cell
• other polar microtubules help push poles away

Question 10

Metaphase

Answer 10

• alignment of chromosomes at the centre of the cell in a region called metaphase plate
• kinetochore microtubules are attached to kinetochores of each sister chromatid

Question 11

Anaphase

Answer 11

• kinetochore tubules begin to shorten and sister chromatids separate into individual chromosomes that are pulled towards spindle poles
• polar microtubules push against each other and help elongate the cell
• at the end the 2 cells will have equivalent and complete set of chromosomes

Question 12

Telophase

Answer 12

2 new daughter nuclei form in the cell

• nuclear envelope reforms around the chromosomes at the opposite poles of the dividing cell
• chromosomes de condense and microtubules are broken down
• division of one nucleus into two
• mitosis has to be followed by the division of a cell into 2 individual cells

Question 13

Cytokinesis

Answer 13

separation of two cells

Question 14

Cytokinesis in Animal Cells

Answer 14

• formation of a contractile ring made up of motor proteins that contract bundles of actin fibres along the midline of the cell
• formation of a defined cleavage furrow that separates the cell into two separate daughter cells

Question 15

Cytokinesis in Plant Cells

Answer 15

• lay down a newly developed cell wall along a cell plate region in the middle
• cytokinesis is then complete when the forming cell wall fuses with the original cell wall

Question 16

Mitosis Promoting Factor

Answer 16

allows for the transition from G2 to M phase and consists of cyclin proteins and cyclin dependent kinase

Question 17

Kinases

Answer 17

-enzymes that activate/inactivate other proteins by phosphorylating key amino acids on the target proteins

Question 18

Three Cyclin CDK complexes involved in regulation

Answer 18

1. G1 cyclin-CDK complex is needed to transition from the G1 to S phase and helps prepare cell for replication
2. S-cyclin-CDK complex helps to initiate DNA synthesis
3. M-Cyclin-CDK complex initiates mitosis

Question 19

Checkpoints in the Cell Cycle

Answer 19

• serve as a form of cellular surveillance and are able to block cyclin-CDK activity if needed
• can pause cell division or can repair damage

Question 20

Three Major Checkpoints

Answer 20

1. DNA damage checkpoint at the end of G1 - only undamaged DNA will be able to enter S-phase
2. DNA replication checkpoint at end of G2-only when all DNA is replicated it will enter mitosis
3. Spindle assembly checkpoint before anaphase- only complete mitosis if all chromosomes are attached to a microtubule from the mitotic spindle

Question 21

Hunt

Answer 21

• added radioactive labelled amino acids to sea urchin eggs
• took samples of rapidly dividing embryo every ten minutes and used gel electrophoresis to visualize change in levels
• found that protein bands became darker as cell division progressed
• found one protein oscillated between increasing and decreasing called cyclin