4.5 - Cell division and growth

Question 1

3 prokaryotic asexual reproduction strategies (3)

Answer 1

1. binary fission
2. budding
3. fragmentation

Question 2

fragmentation

Answer 2

filamentous cells break off fragments which then grow into full-sized cells (common in filamentous cyanobacteria)

Question 3

type of gene transfer in binary fission

Answer 3

vertical gene transfer (DNA inherited by one generation from previous generation)

Question 4

binary fission (3)

Answer 4

1. DNA replication initiated in region of circular chromosome called origin of replication (ORC)
2. once replication initiated: FtsZ proteins activated (related ton cytoskeletal proteins) as well as elongation and increase in volume of cell
3. FtsZ proteins interact to form divisome (organises division of cell and synthesises new cell membrane and wall)

Question 5

budding (3)

Answer 5

1. in some bacteria daughter cell produced by mother cell at particular site
2. bacterial nucleoid divides, one moves to the forming bud
3. when bud is mature enough it is released from mother cell as daughter cell

Question 6

where in asexual reproduction by fission common outside of prokaryotes?

Answer 6

unicellular eukaryotes

Question 7

horizontal gene transfer

Answer 7

chromosomes and segments of DNA can be replicated and exchanged between different bacterial cells as a result of transposition, transformation, conjugation and transduction

Question 8

4 methods of horizontal gene transfer in prokaryotes (4)

Answer 8

1. transposition
2. transformation
3. conjugation
4. transduction

Question 9

conjugation (3)

Answer 9

1. begins when a donor F+ cell captures a recipient F- cell using a sex pilus (fine appendage)
2. F+ plasmid replicated an transferred to F- cell through sex pilus
3. original F- becomes an F+ donor

Question 10

transformation (3)

Answer 10

1. uptake of exogenous DNA from environment (often from dead cells next to living ones)
2. up-taken DNA can be broken down or integrated into bacterial chromosome
3. if up-taken DNA is a plasmid - can exist separately of bacterial chromosome

Question 11

how can transformation be exploited artificially?

Answer 11

to manipulate cells into expressing genes we want by use of engineered plasmids

Question 12

transduction (4)

Answer 12

1. movement of DNA into bacterial cell as result of viral infection by bacteriophage
2. when phage infects bacterium, breaks up host DNA and exploits cellular machinery to replicate itself
3. some bacterial DNA can be packaged into new phage head (as well as by mistake) transducing phage
4. when transducing infects new bacterial cell, it injects this DNA into new host, can. become integrated into bacterial DNA (generalised transcution)

Question 13

transposition (3)

Answer 13

1. transposons - mobile genetic elements can hop from one location on chromosome to another (can disrupt gene function if they land within a gene - causing mutation)
2. sometimes transposons take pieces of bacterial DNA with them when they move, may be left behind when they move on
3. transposons can also hop into plasmids, can be passed to another bacteria cell via conjugation

Question 14

stages of interphase (3)

Answer 14

1. G1 - cellular contents duplicated
2. S - DNA replicated and chromosomes duplicated
3. G2 - cell checks for errors

Question 15

growth factors

Answer 15

specific signals instructing eukaryotic cells to undergo cell division (healthy cells don’t unless signal received)

Question 16

key regulatory proteins that control progression through cell cycle (2)

Answer 16

1. cyclins
2. cyclin-dependant kinase (needs to bind to cyclin to be active)
   - levels of individual cyclins rise/fall throughout cell cycle

Question 17

mitotic spindle

Answer 17

responsible for aligning chromatids at metaphase and separating them at anaphase

Question 18

3 microtubules that make up mitotic spindle (3)

Answer 18

1. astral
2. kinetochore
3. interpolar

Question 19

role of microtubules in anaphase (2)

Answer 19

1. sister chromatids pulled toward opposite poles as kinetochore microtubules depolymerise
2. the 2 spindle poles are pushed apart as result of elongation and sliding of interpolar microtubules past one another

Question 20

how does cytokinesis (cytoplasm separation) occur in animal cells? (3)

Answer 20

1. contractile ring forms, gradually contracts to form cleavage furrow
2. eventually cytoplasm pinched into 2
3. membrane bilayer naturally reseals

Question 21

cytokinesis in plant cells (cytoplasm division) (3)

Answer 21

1. plant cells need to separate and rebuild section of cell wall as well
2. modified vesicles from golgi apparatus form across previous cell plate until they fuse with each other and plasma membrane
3. new cell walls form between new membranes and division occurs

Question 22

growth factors (mitogens)

Answer 22

stimulate cells to enter S phase of cell cycle and divide (animal cells require extracellular growth factors to survive, grow and divide)

Question 23

apoptosis

Answer 23

programmed cell death, regulates cell number (critical during development - to shape digits and during amphibian metamorphosis etc)