lecture 8 - cell division

Question 1

what types of cell division is there?

Answer 1

unicellular organisms
- reproduce by cell division
- commonly through binary fission
multicellular organisms depend on cell division for:
- development from a fertilised cell
-growth
-repair
-cell division occurs via mitosis or meiosis

Question 2

describe cell division

Answer 2

• results in genetically identical daughter cells
• cells duplicate their genetic material before they divide, ensuring that each daughter cells receives an exact copy of the genetic material, DNA
• the DNA molecules in a eukaryotic cell are packaged into chromosomes
• eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division

Question 3

describe cell division in animals

Answer 3

• somatic cells have two sets of chromosomes (one set from each parent). they all have the SAMe chromosomes
• gametes (germ cells/ova + sperm) have only one set of chromosomes. these are produced by a special type of cell division called meiosis

Question 4

what happens in prokaryotic cell division?

Answer 4

binary fission
- asexual reproduction where a cell expands and then divides in two.
- in bacteria, DNA is free-floating in the cytoplasm, and does not have a membrane- bound organelles.
- very important to replicate the DNA so that the daughter cells have identical genetic information
>binary fission does not occur indefinitely for all bacteria
- growth limited by number of nutrients available to the bacteria
- also may choose to enter dormancy

Question 5

what happens in eukaryotic cell division?

Answer 5

• eukaryotic cells usually have more DNA than prokaryotes
• this needs to be condensed and packaged into chromosomes
• this is a carefully coordinated complex process that occurs via a cell cycle and mitosis

Question 6

what happens to chromosomes during cell replication?

Answer 6

• each duplicated chromosome has two sister chromatids which separate during cell division.

Question 7

what is a centromere?

Answer 7

• site where the two chromatids are held together
• reduce complexity of sorting task
• keeps pairs together

Question 8

briefly describe the stages in the eukaryotic cell cycle

Answer 8

two phases

• interphase (G1,S and G2)
• mitotic phase (M)

Question 9

describe the mitotic phase

Answer 9

consists of

• mitosis, the division of the nucleus
• cytokinesis, the division of the cytoplasm.
• typically lasts only 30-60min. (depending on cell type)
• is the period where cells are “overtly” dividing
• all other activities are put on hold. This is because the “normal” internal organisation of the cell is disrupted in this stage.

Question 10

describe the interphase

Answer 10

Consists of:

• Gap 1 (G1) - normal cell metabolism
• s: when DNA replication occurs
• Gap 2 (G2) - preparation for cell division
• most cells spend most of their time in this phase. it may last for hours, days, weeks or longer.
• during this phase, cells grow to their mature size.
• interphase cells are metabolically active. E.g., glucose oxidation, synthesis of macromolecules

Question 11

what happens in Pre-mitosis? (interphase G2 phase)

Answer 11

in the G2 phase, the cell is preparing to enter mitosis:

• DNA has been duplicated in the previous S phase
• duplicated DNA still in the form of chromatin

Question 12

what happens in Mitosis 1: prophase?

Answer 12

• DNA condenses from chromatin into X-shaped chromosomes

- centrosome divides and along with microtubules, form the mitotic spindle.

Question 13

what happens in mitosis 2: prometaphase?

Answer 13

• kinetochores are protein structures on chromosomes that bind to microtubules
• chromosomes are anchored to the mitotic spindle via kinetochores

Question 14

what happens in mitosis 3: metaphase?

Answer 14

• the mitotic spindle moves the chromosomes to the middle of the cell
• cystoskeletal elements are used as well, one type to elongate and push apart the cell, the other to contract and pull the chromatids apart

Question 15

what happens in mitosis 4: ANAPHASE?

Answer 15

• microtubules pull sister chromatids apart

- as the microtubules contract, the chromatids are pulled into opposite ends of the cell.

Question 16

what happens in mitosis 5: telophase

Answer 16

• two sets of chromosomes separated during anaphase are used to create new nuclei
• cell splits into 2 via cytokinesis

Question 17

describe cytokinesis

Answer 17

• actin filaments congregate near metaphase plate to form a ring around inside of the cell
• pinching action separates cytoplasm into two separate cells
  the mechanisms of cytokinesis is different across different organisms

Question 18

what is the role of centrosomes in mitosis?

Answer 18

organising the microtubules that form the mitotic spindle

Question 19

what are some specialised types of cells that have different methods of replication?

Answer 19

• some cells never divide, i.e., nerve cells, muscle cells ad other differentiated cells that are stuck in the G0 phase.
• cells that normally don’t divide but can induced to do. e.g., liver and skin cells to respond to wounding

Question 20

what happens when cell division goes wrong?

Answer 20

• uncontrolled growth of cells = cancer

- incorrect sorting of chromosomes = down syndrome.