6. Comparative structural and functional characteristics of prokaryotic and eukaryotic cells

Question 1

Prokaryotic cells

Answer 1

Prokaryotes are:
- Small and simply organised
- Unicellular organisms
- Have no nucleus
- They are united in 2 groups:
->Eubacteria (true bacteria) e.g. actual bacteria, actinomycetes, Photosynthesizing cyanobacteria
->Archaebacteria e.g. Halobacteria, Methanogenic, Eocytes (thermophilic bacteria), is closest to eukaryotes in the structure of rRNA and ribosomes.

Question 2

Eukaryotic Cells

Answer 2

• Possess a nucleus
• Are multicellular (animals and plants) - exception are protozoa because they are single-celled
• Large and complex
• Thought to be evolved from archeabacteria

Question 3

Structure of Prokaryotic cell

Answer 3

• Unicellular
• Shape - rods, spheres, spirals etc.
• Cell membrane
• Nucleoid - contains genetic material and is irregularly shaped
• Bacterial chromosome - large ring-shaped DNA molecule
• Cytoplasm contains: Ribosomes, Plasmids, Mesosome (from mesosome starts the cell division- called invagination of cell membrane )
• Cell wall
• Capsule (in some) and others have 2nd outer lipid membrane
• Flagella (in some)
• Pili
• NO intracellular membranes (exception: photoautotrophic cyanobacteria)

Question 4

Structure of Eukaryotic cell

Answer 4

Eukaryotic cells consist of 2 parts:
1. Cytoplasm, which consists of:
- Cell matrix (cytosol) - structures of cells are located here
- Cell inclusion (are in some organisms) - deposits substances that are used in metabolism/ are waste products.

-> Examples for cell inclusion:
- Glycogen granules in liver, muscle, cartilage, nerve cells.
- Lipid droplets in adipose connective tissue, adrenal glands, Leydig cells in the testis, lutein cells in the ovary.
- Crystalloid inclusions in the nucleus, cytoplasm, mitochondria,

• Pigments:
  -> endogenous – hemoglobin, myoglobin, iron pigments, melanin, lipofuscin
  -> exogenous – coal dust, dyes

2. Nucleus - genetic and regulatory center of the cell where the replication and transcription take place.

Cell is covered by CELL MEMBRANE (plasma membrane, plasmalemma)

Question 5

Compartmentalization of Eukaryotic cell

Answer 5

Compartmentalization of the cell is the
differentiation of different functions in the cell by
separating membrane structures (organelles).

Question 6

Structure of Cell Membrane (Plasmalemma)

Answer 6

• Phospholipids
• Cholesterol
• Proteins
  -> Depending on its position relative to the lipid double layer they are: INTEGRAL - pierce membrane, or PERIPHERAL - on outer and inner surface
  -> Depending on their functions, they are:* transmitters; ion channels; enzymes; receptors; adhesive molecules*
• Carbohydrates - connected to the lipids and proteins in the form of:
  -> Glycolipids - for immune response, etc.
  -> Glycoproteins - for cell recognition, aglutination, etc.

Question 7

Structure of the cell skeleton (cytoskeleton)

Answer 7

• Cytoskeleton is a network of protein filaments that maintains cell shape and compartmentalization.
• Functions of the cytoskeleton:
  ->Participates in cell division
  ->Enables cell movement (e.g., cilia)
  ->Plays a role in cell defense
  ->Facilitates intracellular transport (movement of vesicles and organelles)
• Components of the cytoskeleton:
  ->Microtubules - made from protein tubulin
  ->Microfilaments - made from actin
  ->Intermediate filaments (in animals)
  Examples:
  - Keratin in epithelial cells
  - Desmin in muscle cells

Question 8

Intercellular substance (extracellular matrix - ECM)

Answer 8

ECM is an amorphous intercellular substance in which cells are located.

ECM is formed by four main groups of compounds:
- Fibrillar proteins: collagen type I-III, elastin, fibrillin
- Adhesive proteins: laminin, type IV collagen, fibronectin
- Proteoglycans: chondroitin sulfate, keratin sulfate, heparin sulfate
- Nonsulfide glycosaminoglycans: hyaluronic acid

ECM and cells within it that perform the same functions form tissues.

Connective tissue has the most massive ECM, including collagen, elastin, and fibrillin.

In other tissues, such as epithelial tissue, the ECM is almost absent.