Week 1 (1.2)

Question 1

What is the difference between asexual and sexual reproduction?

Answer 1

Asexual reproduction: offspring receives genetic material from a single parent
Sexual reproduction: offspring receives genetic material from two parents (half the genetic material is provided by the female parent in the form of an egg and the other half is supplied by a male parent in the form of a sperm)

Question 2

How do prokaryotic cells divide?

Answer 2

→ Produce daughter cells by “binary fission” (cell replicates its DNA, increases in size, and divides into 2 daughter cells and each daughter receives 1 copy of the replicated parental DNA)
→ Steps of binary fission in bacteria
1. Circular bacterial genome is attached by proteins to the inside of the plasma membrane
2. DNA replication is initiated at a specific location of the circular DNA → “origin or replication”; proceeds in opposite direction
3. Result in 2 DNA molecules, each attached to the plasma membrane at a different site
a. At first both attachments are close together
b. Cell elongates and the 2 DNA attachment sites move apart
4. Cell is about twice its size and DNA molecules are separated
5. Constriction forms at the midpoint
6. New membrane and cell wall synthesized at site of constriction, dividing the cell into two

Result: 2 daughter cells with the asme material as parent

Question 3

How do eukaryotic cells divide?

Answer 3

→ First divide the nucleus by mitosis, then the cytoplasm into 2 daughter cells by cytokinesis
Mitosis evolved from binary fission

Cell cycle (steps within eukaryotic cell division)
Stages: 2 (M phase and interphase)

–>M phase: parent cell divides into 2 daughter cells
Stages: 2
Mitosis: separation of chromosomes into 2 nuclei)
Cytokinesis: division of cell itself into 2 separate cells

–>Interphase: time between 2 successive M phases (cell makes preparations for division, like DNA replication and cell growth)
DNA replicates so each daughter cell receives a copy
Cell increases in size so each daughter receives enough cytoplasm and organelles
Stages: 3 phases
S phase: DNA replication (doesn’t precede or follow mitosis, but is separated from it by the gap phases)
G1: between the end of the M phase and the start of S phase
Regulatory proteins (kinases) are made; these activate enzymes that synthesize DNA
Prepare for S phase
G2: between the end of the S phase and the start of M phase
Size and protein content increases
Prepare for M phase
→ G0 phase: not all cells actively divide, many pause between the M and S phase
(some stay there for long periods of time or even indefinitely, however that doesn’t mean they stop performing their function)

Question 4

What does generation time refer to?

Answer 4

Growth rate of a population of bacteria: time it takes the population of cells to double

Question 5

What are the 4 phases that we can encounter in a bacterial growth curve?

Answer 5

Lag phase, exponential, stationary, and death

Question 6

What are the characteristics of the “Lag phase”

Answer 6

Period of adjustment (adaptation to new surroundings)
- When bacteria are inoculated into a nutrient media, they need time to adjust
- Bacterial cells are growing, but not readily dividing
- Bacteria are making the tools needed to thrive in their new environment (expressing genes that encode for particular proteins (structural proteins, enzymes that break down nutrients available), integral membrane proteins, or synthesizing macromolecular building blocks for cell structure and growth) → transcription and translation
- Length depends on how different the current environmental conditions were from the last environment in which the bacteria were
- Bacteria don’t display growth at this phase

Question 7

What are the characteristics of the “Exponential phase”?

Answer 7

When bacteria have adapted fully to their surroundings they will also maximize all the benefits they can from the nutrient media → optimal conditions = bacteria want to replicate
Phase where the overall population of bacterial cells undergo binary fission at a constant rate = replication at maximum and cell number increases exponentially → 2^n (n= # of generations)
Cells are readily dividing and growth of population occurs exponentially; growth of the population is occurring at a constant rate

Question 8

What are the characteristics of the “Stationary phase”?

Answer 8

• Key nutrients in the media are beginning to deplete → bacteria begin to compete with other cells for those nutrients
• Metabolic waste products release from bacterial cells begin to build up in the environment → toxic to many bacterial cells
• Plateau: zero growth in overall population (equal amount of bacteria actively dividing as there are dying)

Question 9

What are the characteristics of the “Death phase”?

Answer 9

• Loss of nutrients, build up of waste products and lack of optimal conditions results in the death of many bacterial cells
• More cells are dying than actively dividing -> drop in the number of live cells (growth of overall population decreases dramatically)

Question 10

What are the stages of mitosis?

Answer 10

1. Prophase: chromosomes condense; centrosomes radiate microtubules and migrate to opposite poles
2. Prometaphase: spindles attach to kinetochores on chromosomes
3. Metaphase: chromosomes align in center of cell
4. Anaphase: sister chromatids separate and travel to opposite poles
5. Telophase and cytokinesis: envelope re-forms, chromosomes condense and cytoplasm divides