Chapter 4: Functional Anatomy of prokaryotic and eukaryotic cells

Question 1

What is the glycocalyx?

Answer 1

A sticky, secreted, gelatinous polymer outside of the cell wall.

Question 2

When is the glycocalyx known as a capsule?

Answer 2

If the substance is organized and firmly attached to the cell wall.

Question 3

When is the glycocalyx known as a slime layer?

Answer 3

If the substance is unorganized and only loosely attached to the cell wall.

Question 4

What is the function of the glycocalyx?

Answer 4

It is an important component of biofilms because it helps cells adhere to target environment, allowing growth on various surfaces. It also protects against dehydration and allows for nutrient conservation.

Question 5

What are fimbriae?

Answer 5

Hair like appendages. Shorter, straighter, thinner than flagella.

Question 6

What is the function of Fimbriae?

Answer 6

Used for attachment and DNA transfer rather than motility. They can be at poles or distributed over the surface. They are involved in forming biofilms and other aggreations. They also adhere to epithelial surfaces of the body.

Question 7

What are and what is the function of pili?

Answer 7

They are longer than fimbriae; there are only 1-2 per cell; they are involved in motility and DNA transfer; They are used in twitch motility as a grappling hook. Conjugation sex pili are specific to function of conjugation (DNA Exchange).

Question 8

Different arrangements of flagella?

Answer 8

Long filamentous appendages that propel bacteria. Monotrichous: one flagella at one pole; Amphitrichous: flagella at both poles; Lophotrichous: tuft of flagella at one pole; Peritrichous: distributed over entire cell.

Question 9

What are the three basic parts of the flagella?

Answer 9

Filament: long outermost region, constant diameter.
Hook: filament attaches to hook
Basal Body: anchors flagellum to cell wall.

Question 10

What are axial filaments?

Answer 10

Bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell.Similar in structure to flagella, the rotation of filaments produces movements of the outer sheath, that propels in spiral motion (this is effective in propelling through bodily fluids.)

Question 11

Cell wall of Prokaryotic Cells

Answer 11

Composed of peptidoglycan which consists of a repeating disaccharide glued together by polypeptides to form a lattice that surrounds the entire cell. Breaking down the disaccharide of peptidoglycan, you find monosaccharides known as N-acetylglucosamide and N-acetylmuramic acid. These are linked in rows of 10-65 sugars to form a carbohydrate backbone (glycan). Adjacent rows of glycan are linked by polypeptide chains in the shape of D and L. The chains may be linked by peptide cross bridges.

Question 12

What effect does penicillin have on cell walls?

Answer 12

It interferes with the linking cross bridges, weakening the cell wall and causing lysis.

Question 13

What are the main differences between Gram+ and Gram- cell walls?

Answer 13

Gram+ have many layers of peptidoglycan. Their cell walls contain techoic acids and phosphate. Because techoic acids have a negative charge, they may bind and regulate the movement of cations in and out of the cell. They also promote growth and prevent breakdown, as well as providing antigenic specificity, making it possible to identify gram+ bacteria. Gram- have a thin layer of peptidoglycan and an outer cell membrane. The tin layer of peptidoglycan =more susceptible to mechanical breakage. The outer lipopolysaccharide layer has a strong negative charge that helps the cells avoid phagocytosis, but lyse and phagocytize other cells. The membrane also provides a barrier to antibiotics, digestive enzymes, and certain dyes.. There are proteins in the membrane called porins that form channels for nutrients.

Question 14

What are 3 components of the Gram- lipopolysaccharide layer?

Answer 14

Lipid A (an endotoxin associated with dilation of blood vessels, shock, and blood clotting); a core polysaccharide (provides structural stability); and an O polysaccharide (functions as an antigen and is useful in distinguishing Gram- bacteria. This third component is comparable to Techoic acids in Gram+.

Question 15

Cell Walls of Archaea

Answer 15

Like other living organisms, archaea have a semi-rigid cell wall that protects them from the environment. The cell wall of archaea is composed of S-layers and lack peptidoglycan molecules with the exception of methanobacteria who have pseudopeptidoglycan in their cell wall.

Question 16

Mycoplasma

Answer 16

Mycoplasma refers to a genus of bacteria that lack a cell wall. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis.

Question 17

What evidence supports the endosymbiotic theory of evolution?

Answer 17

New mitochondria and plastids are formed only through a process similar to binary fission.
In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate. This shows that the plastid regeneration relies on an extracellular source, such as from cell division or endosymbiosis.
Transport proteins called porins are found in the outer membranes of mitochondria and chloroplasts, are also found in bacterial cell membrane.[20][21][22]
A membrane lipid cardiolipin is exclusively found in the inner mitochondrial membrane and bacterial cell membrane.[23]
Both mitochondria and plastids contain single circular DNA that is different from that of the cell nucleus and that is similar to that of bacteria (both in their size and structure).
The genomes, including the specific genes, are basically similar between mitochondria and the Rickettsial bacteria.[24]
Genome comparisons indicate that cyanobacteria contributed to the genetic origin of plastids.[25]
DNA sequence analysis and phylogenetic estimates suggest that nuclear DNA contains genes that probably came from plastids.
These organelles’ ribosomes are like those found in bacteria (70S).
Proteins of organelle origin, like those of bacteria, use N-formylmethionine as the initiating amino acid.
Much of the internal structure and biochemistry of plastids, for instance the presence of thylakoids and particular chlorophylls, is very similar to that of cyanobacteria. Phylogenetic estimates constructed with bacteria, plastids, and eukaryotic genomes also suggest that plastids are most closely related to cyanobacteria.
Mitochondria have several enzymes and transport systems similar to those of bacteria.
Some proteins encoded in the nucleus are transported to the organelle, and both mitochondria and plastids have small genomes compared to bacteria. This is consistent with an increased dependence on the eukaryotic host after forming an endosymbiosis. Most genes on the organellar genomes have been lost or moved to the nucleus. Most genes needed for mitochondrial and plastid function are located in the nucleus. Many originate from the bacterial endosymbiont.
Plastids are present in very different groups of protists, some of which are closely related to forms lacking plastids. This suggests that if chloroplasts originated de novo, they did so multiple times, in which case their close similarity to each other is difficult to explain.
Many of these protists contain “primary” plastids that have not yet been acquired from other plastid-containing eukaryotes.
Among eukaryotes that acquired their plastids directly from bacteria (known as Archaeplastida), the glaucophyte algae have chloroplasts that strongly resemble cyanobacteria. In particular, they have a peptidoglycan cell wall between the two membranes.
If a cell’s mitochondria or chloroplasts are removed, they do not have the means to create new ones.[26]