Biological Principles LP 4

Peptidoglycan

the rigid layer of the cell walls of bacteria, a thin sheet composed of N-acetylglucosamine, N-acetylmuramic acid, and a few amino acids

Lipopolysaccharide

(LPS) complex lipid structure containing unusual sugars and fatty acids found in most gram-negative bacteria and constituting the chemical structure of the outer membrane

Define the following terms mature endospore, vegetative cell, and germination.

A mature endospore is a bacterial cell that is resistant to extreme environmental conditions. A vegetative cell is a cell that is actively growing instead of forming spores like endospores. Germination is the process that involves loss of refractility of the endospore, and subsequent change back to a vegetative cell.

How long may endospores remain viable in a state of "suspended animation" so to speak, and what is the evidence for this?

Endospores can last several years in a state of "suspended animation". Evidence is shown from placing endospores in agar media that then continue to grow later when they change back into their vegetative state.

Cells of Escherichia coli take up lactose via the Lac permease system, glucose via the phosphotransferase system, and maltose via an ABC-type transporter. For each of these sugars describe: (1) the components of their transport system, and (2) the source of energy that drives the transport event.

Lactose enters the cell via simple transport with Lac permease. Simple transport involves one protein that is driven by energy from the proton motive force outside of the cell. Glucose enters the cell via group translocation with the phosphotransferase system. Group translocation involves several proteins that chemically modifies the substrate to transport it into the cell. Maltose enters the cell via an ABC-type transporter. This transporter involves three proteins that uses energy from ATP to transport the substrate into the cell.

In a few sentences, write an explanation for how a motile bacterium is able to sense the direction of an attractant and move toward it.

Most prokaryotes are motile by swimming due to the flagella structure. This flagella rotates to push or pull the cell through the liquid medium.

Phototaxis

Movement of a cell toward the light

Explain in a single sentence why ionized molecules do not readily pass through the cytoplasmic membrane barrier of a cell. How do such molecules get through the cytoplasmic membrane?

Polar and charged molecules cannot diffuse through the cytoplasmic membrane due to the membrane's non-polar ends; they have to be transported through the transport proteins found in the membrane.

What function(s) does polysaccharide layers have in prokaryotes?

Polysaccharide layers provide structural support and are part of some metabolic processes in prokaryotes.

Calculate the surface-to-volume ratio of a spherical cell 15μm in diameter and a cell 2μm in diameter. What are the consequences of these differences in surface-to-volume ratio for cell function?

SA=4pi(r^2) V=(4/3)pi(r^3) The bigger the cell, the smaller the surface to volume ratio.

Why is sucrose able to stabilize bacterial cells from lysis by lysozyme?

Sucrose can stabilize bacterial cells from lysis by lysozyme because there is hydrogen bonding between the sugar and protein molecules which makes it difficult for the lysozyme to break down.

Why is the bacterial cell wall rigid layer called peptidoglycan? What are the chemical reasons for the rigidity that is conferred on the cell wall by the peptidoglycan structure?

The bacterial cell wall rigid layer is called peptidoglycan because it is composed of two sugars (glycan) and four amino acids (tetrapeptide). The long chains of peptidoglycan are cross-linked through their amino acids and glycosidic bonds connect the sugars to each other which provides rigidity to the structure.

In a few sentences, indicate how the bacterial endospore differs from the vegetative cell in structure, chemical composition, and ability to resist extreme environmental conditions.

The bacterial endospore has a thin protein covering, spore coats, the cortex, and the core which consists of the cell wall and all other cellular parts. Endospores contain small acid-soluble proteins (SASPs) that bind tightly to DNA in the core. These protect it from potential damage due to extreme environmental conditions.

Describe a major chemical difference between membranes of Bacteria and of Archaea.

The lipids in Bacteria have ester linkages that bond fatty acids to glycerol. The lipids of Archaea have ester linkages that bond glycerol to their hydrophobic side chains; they do not have true fatty acids.

What are the major morphologies of prokaryotes? Draw cells for each morphology you list. How large can a prokaryote be? How small? Why is it that we likely know the lower limit more accurately than the upper limit? What are the dimensions of the rod-shaped bacterium Escherichia coli?

The major morphologies of prokaryotes are coccus (spherical), bacillus (rod), and spirillum (spiral). A prokaryote can be as small as 0.2 um and as big as 700 um. Very large cells' nutrient uptake limits metabolism so it is hard to tell how large prokaryotes actually can be. E. coli are about 1 x 2 um.

List several functions for the outer membrane in gram-negative Bacteria. What is the chemical composition of the outer membrane?

The outer membrane mostly serves for structural support and protects against cell lysis, but it also is toxic to animals due to endotoxins in the LPS layer by lipid A. The outer membrane consists of LPS (lipopolysaccharide) and proteins. The LPS contains the lipid A, the core polysaccharide, and the O-polysaccharide.

Assume you are given two cultures, one of a species of gram-negative Bacteria and one of a species of Archaea. Other than by sequencing ribosomal RNA, discuss at least four different ways you could tell which culture was which.

You can tell which culture is which by performing pure culture counting, gram staining, DNA sequencing, or PCR polymarese chain reaction.

Endospore

a differentiated cell formed within the cells of certain gram-positive bacteria that is extremely resistant to heat as well as other harmful agents

Mitochondrion

a eukaryotic organelle responsible for the process of respiration and electron transport phosphorylation

Gram-positive

a major phylogenic lineage of prokaryotic cells containing mainly peptidoglycan in their cell wall; stain purple in the Gram stain

Gram-negative

a major phylogenic lineage of prokaryotic cells with a cell wall containing relatively little peptidoglycan, and an outer membrane composed of lipolysaccharide, lipoprotein, and other complex macromolecules; stain pink in the Gram stain

Outer membrane

a phospholipid and polysaccharide containing unit membrane that lies external to the peptidoglycan layer in cells of gram-negative bacteria

Cytoplasmic membrane

a semipermeable barrier that separates the cell interior (cytoplasm) from the environment

Group translocation

an energy-dependent transport system in which the substance transported is chemically modified during the process of being transported by a series of proteins

Chemotaxis

moving toward or away from a chemical

Endosymbiosis

the engulfment of one cell type by another cell type and the subsequent and stable association of the two cells