Homework 02/09/2024

Question 1

Differences between prokaryotic and eukaryotic cells

Answer 1

Prokaryotic and Eukaryotic cells are the same in that these cells:
- are the basic units of life activities
- are capable of self-regulation
- are highly complex and organized
- share similar structure, composition and metabolic features; plasma membrane, DNA & RNA and ribosomes

Prokaryotic and Eukaryotic cells differ in:
1. The presence of a Nucleus
Prokaryotic cells lack a nucleus and hereby have DNA & RNA freely spread throughout the cell plasma, while eukaryotic cells have a distinct, membrane-bound nucleus containing DNA & RNA

2. Organelles
   Prokaryotic cells lack membrane-bound organelles like mitochondria, endoplasmic reticulum and Golgi apparatus, however eukaryotic cells have these membrane-bound organelles and a selection of other non-membrane organelles like the cell skeleton; microtubules, microfilaments and intermediate filaments
3. DNA Structure
   Prokaryotic DNA is usually a single circular chromosome located in the cytoplasm, while eukaryotic DNA is linear and organized into chromosomes within the nucleus
4. Cell Size
   Prokaryotic cells are generally much smaller than eukaryotic cells with eukaryotic cells being about 10 times larger when measured in micrometers
5. Complexity
   Prokaryotic cells are considered simpler in structure and extend to include eubacteria and archaea compared to the more complex eukaryotic cells like human, plant and fungal cells

Question 2

How to understand that mycoplasma is the main contaminant in cell culture

Answer 2

The features of mycoplasma which make it the main contaminant in cell culture include:

1. Lacking cell wall
   This makes the bacteria resistant to the routine antibiotics used to target the cell walls of contaminants in cell culture
2. Smallest and simplest cell (About 0.2-0.8 micrometers)
   This bacteria has the smallest volume and smallest genome which creates a flexible nature of the membrane allowing it to pass through filters that would typically trap other bacteria
3. Ribosomes as the only organelle
   Ribosomes synthesize proteins which facilitate infection and colonization by attaching to host cells
4. RNA’s and circular double-stranded DNA
   These are found in the cell membrane and provide stability and rigidity which compensate for the lack of a cell wall and increases the ability of the membrane to protect itself from mechanical damage

Question 3

The characteristic and mechanism of Covid-19
- type
- morphology and structure
- replication
- mechanism

Answer 3

1. Type
   - Covid-19 is an abbreviation for severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) which emerged in 2019.
   - It belongs to the group of coronaviruses which are enveloped, positive, single-strand RNA viruses.
2. Morphology
   - COVID-19 virus particle size is about 70-90 nm
   - The virus is contained in and transported by intracellular organelles, specifically vesicles
   - The positive, single-strand RNA of SARS CoV-2 is covered by a nucleocapsid
   - The capsid is surrounded by an envelope with membrane (M) and spike (S) glycoproteins on the outside
3. Replication
   - The spike glycoprotein of the coronavirus binds to the angiotensin converting enzyme 2 (ACE2) receptor on the host cell
   - The RNA of the virus enters the cytoplasm of the cell, finds a ribosome and is translated into protein containing the viral genome
   - This protein is continuously synthesized forming more and more coronaviruses which eventually destroy the cell and migrate to attach to nearby cells and continue replicating
4. Mechanism
   - The virus is transported through droplets in the air
   - Initially the virus infects ciliated upper respiratory tract epithelial cells
   - Then the virus promotes viral endocytosis