Chap 12 - Cell Cycle

Question 1

Centrosome vs Centromere

Answer 1

CentroSOME - cytoskeleton component in animals.
CentroMERE - the bit that connected sister chromatids.

Question 2

Centromere structure

Answer 2

Repetitive DNA sequences that are recognised by proteins and used to bind the chromatids together.

Question 3

Cohesins

Answer 3

Complexes along the length of sister chromatids that attach them even more.

Question 4

5 phases of cell cycle

Answer 4

Mitosis (M):
- Mitosis
- Cytokinesis
Interphase:
- G phase
- S phase
- G2 phase

Question 5

Phases of mitosis

Answer 5

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase

Question 6

Prophase

Answer 6

• Chromosomes condense and cohesins form.
• Nucleoli gone.
• Centrosomes (which duplicated in interphase) move apart, with spindles beginning to form.

Question 7

Asters

Answer 7

Radial “stars” of microtubules extending from the centrosomes.

Question 8

Prometaphase

Answer 8

• Nuclear envelope fragmented
• Chromosomes fully condensed
• Kinetochores form at centromere of chromatids, which microtubules begin to attach to.

Question 9

Kinetochore

Answer 9

Large protein complex on the centromere that spindles attach to.

Question 10

Cell lengthening during mitosis

Answer 10

Spindles from opposing centrosomes are pushed apart while also lengthening.

Question 11

Metaphase

Answer 11

• All kinetochores attached.
• Centromeres lined up on the metaphase plate as they at pulled to both cell poles.
• Centrosomes in contact with plasma membrane at the poles.

Question 12

Metaphase plate

Answer 12

‘Imaginary’ plane at equator of cell that chromosomes line up in.

Question 13

Anaphase

Answer 13

Very short!
- Cohesin proteins are cleaved, chromosomes pulled apart.
- The cell is lengthened by non-kinetochore spindles.

Question 14

How chromosomes are pulled to poles

Answer 14

1. Motor proteins walk the kinetochores up the spindle towards poles.
2. Other motor proteins at the poles reel in the spindle.

Question 15

Telophase

Answer 15

• New nuclear envelope begins to form.
• Nucleoli reappear.
• Spindles depolymerised
  [End of mitosis]

Question 16

Cytokinesis

Answer 16

The division of cytoplasm with a plasma membrane inbetween.
Usually well underway during telophase, finished quickly after mitosis ends.

Question 17

Cleavage

Answer 17

One method of cytokinesis (in animals)

A shallow groove (cleavage furrow) forms where metaphase plate used to be. The ring contracts with myosin proteins until the cell pinches into two.

Question 18

Cytokinesis in plants

Answer 18

1. Vesicles containing cell wall materials produced (from Golgi)
2. Move to middle of cell and coalesce into a cell plate.
3. Cell plate enlarges until it fuses with plasma membrane.

Question 19

Binary fission

Answer 19

Doubling in size and then splitting of single celled organisms.
Involves mitosis in eukaryotes, no mitosis in prokaryotes.

Question 20

Binary fission in prokaryotes (bacteria)

Answer 20

1. DNA replication starts at origin of replication on the chromosome.
2. Two duplicated origins move to opposite ends of cell.
3. Cell elongates.
4. Plasma membrane pinched in with a protein similar to tubulin (evolutionary origin?!) and new cell wall formed.

Question 21

Weird eukaryote binary fission #1 - Dinoflagellates

Answer 21

Microtubules pass THROUGH the nucleus, then the nucleus divides similarly to prokaryotic binary fission.

Question 22

Weird eukaryote binary fission #2 - Diatoms

Answer 22

The spindles are formed and separate chromosomes inside nucleus, and nucleus then splits in two.

Question 23

G phase

Answer 23

Growth, mostly.

Question 24

S phase

Answer 24

DNA synthesis, also growth too.

Question 25

G2 phase

Answer 25

Woah growth again, and ‘preparation’ for mitosis such as centrosome duplication.

Question 26

Checkpoints in cell cycle control system

Answer 26

Important control points where triggers/inhibitors regulate the cell cycle.

Question 27

Location of important cell cycle checkpoints(3)

Answer 27

1. Near the end of G1
2. At the start of M
3. Near the end of M