Ch.4 - Prokaryotic Cell Structure and Function

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Give a basic description of prokaryotic cells.

small and structurally simple
most are unicellular
most have a cell envelope

T/F: Cell envelope structure and chemistry differ among different groups of prokaryotes.


T?F: The cell envelope is always a single homogenous layer.

False. It can be a complex, multilayered structure.

Prokaryotic cells protect themselves against _____ _____ with a cell envelope.

osmotic lysis

Is the osmotic pressure of most prokaryotic cells very high or very low?

very high

How does the cell envelope prevent osmotic lysis.

It contains the pressure with a layer external to the cell membrane that resists expansion of the cell volume.

How many different types of cell envelopes are there among bacteria?


What is the most common type of cell envelope in bacteria?


What do bacteria use pili for?

To stick to things

What terms are used to describe shapes of multicellular microbes?

mycelium (like a branched filament)

What terms are used to describe shapes of unicellular microbes?


Describe the make-up of the gram-negative envelope.

cell membrane
periplasmic space containing little murein/peptidoglycan
(extracellular fluid)

Describe the make-up of the gram-positive envelope.

cell membrane
multiple layers of murein
(extracellular fluid)

Describe the make-up deinococcal envelope.

cell membrane
multiple layers of murein
outer membrane
(extracellular fluid)

Describe the make-up planctomyces envelope.

cell membrane
layer of protein
(extracellular fluid)

How does a deinococcal envelope stain?

gram +

How does the planctomyces envelope stain?

gram - (because there is no peptidoglycan)

How many types of archaeal cell envelopes are there?


What is the most common archaeal cell envelope?

a layer of protein

Where would you find pseudomurein?

the cell envelopes of microbes of the methanogen group

T/F: Some archaea have walls that consist of complex polysaccharides.


Do archea have peptidoglycan?


What term is used to describe prokaryotes without a defined cell envelope layer that have their membranes strengthened by glycolipids?


Mycoplasmas contain an extracellular layer called lipoarabinomannan. What is it and what is its function?

It is a wax that gives rigid structure to mycoplasmas.

Is mycoplasma classified as Gram + or Gram -?

Gram +

Does mycoplasma stain Gram + or Gram -? Explain.

It doesn't stain at all because it lacks peptidoglycan altogether.

Some free living prokaryotes lack a cell envelope altogether. What to they tend to have to strengthen their membranes?

a large amount of glycolipids

Murein is a form of petidoglycan in which the individual glycan strands are cross-linked to each other by the _____.


What specific type of peptide linkage exists between the two sugars that make up murein?

beta 1-4 linkage

What do NAG and NAM stand for (spell their names)?

NAG - N-acetylglucosamine
NAM - N-acetylmuramic acid

NAM has an R group composed of amino acids. The length and sequence of every chain varies except for the last two amino acids. What are they?


NAM has an R group composed of amino acids. The amino acids that is third from the end of the chain always contains what?

free amino group

Why does murein form a helical chain of alternating NAG and NAMs?

to provide support for the cell

Covalent linkages form between side chains of adjacent murein strands. Specifically, where do these linkages form?

Between the D-Alanine of one side chain and the amino acid with a free amino group (third from the end) of another side chain

What is the name of the enzyme involved in making a peptide bond between different strands of murein?


What is released in the cell to be reused when two murein chains are linked?


How does archaeal pseudomurein differ from bacterial murein?

1. Contains N-acetyltalosaminuronic acid instead of NAM
2. Linkages are beta 1-3 instead of beta 1-4
3. All L amino acids in the side chain instead of D and L

What do Gram + bacterial walls contain that are unique to them?

Teichoic acids

Name and describe the two types of teichoic acids.

Lipoteicholic acids - linked to membrane phospholipids
Wall teichoic acids - covalently linked to murein

In Gram - bacteria, what protects the murein?

the outer membrane

There are many enzymes secreted by bacteria or by fungi that attack some of the different types of murein in the Eubacteria Domain. Give an example.

lysozyme - cleaves beta 1-4 linkage between NAG and NAM

Why can Gram + bacteria tolerate loss of murein on the outer surface but Gram - can not?

Gram + have a thick layer of murein but Gram - have a very think layer that makes them vulnerable.

In a gram - bacteria, the outer leaf of the outer membrane consists of _____ and the inner leaf of the outer membrane consists of _____.


What does the Braun lipoprotein in the inner leaf of the outer membrane of gram - bacteria do?

connects the outer membrane to the murein

The outer membrane of gram - bacteria contains porin proteins that allow for what?

solute diffusion across the outer membrane

A lipopolysaccharide is composed of what three parts?

lipid A
O-specific side chain

Describe the structure of the lipid A portion of a lipopolysaccharide.

Consists of a dimer of glucosamine phosphate to some or all of whose free hydroxyl and amino groups are attached fatty acids with saturated side chains. Some of the fatty acids have a beta-OH group, which allows the attachment of additional fatty acids. (6-8 fatty acids)

Describe the function of the lipid A portion of a lipopolysaccharide.

The phosphates present create large charge density that form many hydrogen bonds to water and to the other side chains preventing nonpolar compounds from permeating the membrane.
Also, the saturated side chains are able to pack together tightly preventing hydrophobic compounds from slipping between the lipid molecules.

Describe the structure of the R-core portion of a lipopolysaccharaide.

It contains various sugars and sugar derivatives. Constant in a species.

Describe the structure of the O-specific side chain portion of a lipopolysaccharide.

It contains a sequence of five to six sugars tat repeat many times to make along chain. It varies within a species.

Give the two reasons that the outer membrane of a gram - bacteria is impermeable to both hydrophobic and hydrophilic compounds.

1. The high density of charges at the outer surface of the membrane.
2. The hydrocarbon side chains or the lipid A are saturated.

What part of a lipopolysaccharide will act as and endotoxin?

lipid A

How do dissolved compounds (~1nm in diameter) enter the gram - periplasm?

via porins

What is the periplasm of a gram - bacteria?

The compartment between the cell membrane and the outer membrane.

What are functions of the dense solution of protein present in the periplasm?

export/ import
peptidoglycan synthesis

What two main functions does the cell membrane have?

1. It separates the cytoplasm from the exterior environment.
2. Allows the cytoplasm to have a chemical composition different form the environment.

The prokaryotic cell membrane contians _____ in place of sterols.


Hopanoids are noncyclic compounds that can fold into a shape similar to that of _____.


What sterol precursor are hopanoids made from?


Some things in a cell are needed in a spacial manner and must be anchored in someway to limit their diffusion. Give an example.

FtsZ ring - starts cell division so it needs to be in the middle of the cell.

T/F: The prokaryotic cell membrane has fewer protein and fewer different proteins than most membranes.

False. It has more protein and more different proteins.

Most prokaryotes have membrane-embedded electron transport proteins to get energy from _____ or _____.

respiration or photophosphorylation

The prokayotic cell membrane is the site of synthesis of 4 types of proteins. Name them.

cell membrane proteins
outer membrane proteins
periplasmic proteins
secreted proteins

Lipids and cell walls are synthesized in what part of prokaryotic cells?

cell membrane

In prokaryotic cell membranes, _____ proteins allow the cell to determine certain aspects of the chemical or physical conditions of the environment.


The prokaryotic cell membrane may invaginate into the cell to provide extra surface area. What is the benefit to having more surface area?

It allows more places for proteins to have interaction with the outside world.

Some prokaryotes have intracellular membrane bound organelles. Give an example.

ExPortal (GAS) and thylakoids in cyanobacteria

What type of lipids make up the bilayer or monolayer of archaeal cell membranes?

ether lipids; specifically glycero-lbiphytane-diethers (instead of glycerol-fatty acid diesters)

Do prokaryotes every have chloroplasts?


What did the ExPortal Paper discussed in lab contain?

Gold particles were placed on antibodies that allowed them to be seen under an electron microscope. They were congregated in a specific location on the edge of the cell showing a specific function.

What type of linkages and chains to the lipids of eukarya and bacteria have?

ester linkages and linear chains

What type of linkages and chains to the lipids of archaea have?

ether linkages and branched chains

Where would you find a phospholipid monolayer?

in extermophiles - exteremely thermophilic archaea

In prokaryotic cells, the genetic material in a cell is a structure that lacks a nuclear envelope and a membrane. What is the structure called?


Does the size of the nucleoid change with the complexity of the cell?

Yes because more complexity means there are more genes

The nucleoid is haploid and usually contains what kind a chromosome?

A single circular chromosome

Many prokaryotes ahve on or more _____ in addition to their chromosome.


What is a plasmid and what distinguishes it from a chromosome?

A small circular DNA molecule that lacks genes essential for growth under all conditions and for core cellular functions

T/F: A microbe that lives in an area with a highly changing environment needs more genes to deal with different conditions.


T/F: All prokaryotes identified to date are haploid.


T/F: Only a few bacteria have a single supercoiled chromosome (DNA Gyrase and Histone-like proteins)

False. Most bacteria have one.

How does a supercoiled chromosome form?

1. DNA gyrase take a loop of DNA
2. Makes a double stranded cut where the loop crosses over
3. Then passes the top part of the loop through the gap, and reseals the broken DNA. This introduces one new twist to the DNA.

What does it mean for a cell to be haploid?

It has one copy of the genome/ one copy of each gene.

What is the general role of DNA gyrase?

it maintains supercoiling of chromosomes

What is the role of histone like proteins?

They are how bacteria maintain chromosomes.

T/F: The nucleoid is arranged with the origin of replication and the terminus at the same end.

False. The origin of replication and the terminus are at opposite ends.

The middle part of a prokaryotic chromosome is condensed into approximately ___ loops by special condensing proteins.


The central portions of the nucleoid are very _____ packed.


_____ and _____ are coupled (occur simultaneously) in prokaryotes.

Transcription and translation

Why is coupling in protein synthesis so important?

It is the basis for attenuation. which is a mechanism of gene regulation.

Compaction of DNA into the nucleoid requires what to be done to the DNA by polyamines?

neutralization of DNA charges

At neutral pH, is the charge of DNA positive, negative, or neutral?


_____ are small organic compounds with two, three, or four amino groups spaced approximately as far apart as the phosphates in DNA.


T/F: Because the amino groups are protonated at neutral pH, they can effectively neutralize the charges on the DNA and allow it to pack tightly.


The two principal proteins of the eukaryotic cytoskeleton are _____ and _____.

actin and tubulin

What are two functions of an actin-like cytoskeleton?

maintains cell shape
moves material during division (no mitosis)

Rod-shaped and spiral bacteria have a helical band of filaments made of an actinlike protein called _____.


MreB helps determine cell shape and is involved in what else?

intracellular motility

Structurally, how are MreB and actin similar?

tertiary structure
nothing alike as chain of amino acid

MreB appears to be involved in moving the prokaryotic equivalent of _____ to the poles.


This protein is tubulin-like and involved in bacterial cytokinesis.


How does FtsZ aid in cytokinesis of bacterial cells?

If forms a band of filaments around the middle of a prokaryotic cell and when chromosome segregation is completed, the ring contracts constricting the cell and initiating cytokinesis.

The cytoplasm of prokaryotes is a concentrated solution of proteins and small molecules. What organelle is densely packed into the cytoplasm?


Storage granules of reserve nutrients are present in cyctoplasm. Name two common ones.

glucose that forms glycogen
beta-hydroxybutyric acid forms polyhydroxubutyrate (PHB)

Phosphate is stored in membrane-bound vesicles termed _____ in some bacteria.


Describe how an acidocalcisome functions.

1. An ATP-driven calcium pump transports Ca2+ into the acidocalcisome.
2. Phosphate is transported into the acidocalcisome as pyrophosphate, then polymerized into poly-P.
3. A proton pump driven by pyrophosphate hydrolysis acidifies the acidocalcisome.

Gas vacuoles provide _____ to aquatic cells.


_____ _____ have highly hydrophobic interior surfaces and are composed of many individual gas vesicles.

gas vaccuoles

_____ allow prokaryotic cells to distinguish north from south.


Magnetosomes consist of a row of granules of a _____ mineral enclosed in a membranous invagination of the cell membrane.


Most bacteria with magnetosomes are microaerophiles, and they use the magnetosomes to fin the right concentration of _____.


An acidocalcisome is a storage area for what?


What are the purposes of the Ca+2 and H+ in an acidocalcisome?

Ca - keeps charge balanced
H - keeps it from hardening from Ca by keeping low pH

Why do gas vauoles regulate the amount of gas in a cell?

to control the depth they are in the liquid environment

Many prokaryotes have a _____ _____ of protein external to the envelope.

surface layer

What is a capsule?

a gelatinous layer of polysaccharide external to the wall (snot-like)

Give four main functions of a capsule.

1. avoid phagocytosis
2. adherence
3. pathogens use it to prevent immune system recognition
4. absorb moisture during times of dehydration

What is a biofilm?

an aggregation of cells held together in a common matrix of capsular material (often extracellular polysaccharides)

T/F: Biofilms contain only a single kind of microbe.

False. They may be mixed

Why do pores and channels for throughout a biofilm?

So that bacteria in all parts of the biofilm can get adequate nutrients.

What does a biofilm to for a motile bacteria?

Allows it to stick somewhere

_____ are fine, hair-like appendages protruding from the cell surface made up of many molecules of globular protein.


Molecules at the tip of pili are termed _____, and they have specific binding sites that allow the pilus to attach to specific structures (like proteins or anchor to start growing).


Pili are made up of what protein?


Pilins are synthesized by ribosomes on the cell membrane and secreted into the periplasm. _____ _____ proteins escort the pilins across the periplasm and transfer them to the growing pilus.

Periplasmic chaperone

Are flagella organelles?

NO!!!!! They are structures.

What purpose do flagella serve?

rotate to move cells through liquid

What causes the basal body (or rotary motor) of flagella to spin in eukaryotes and prokaryotes?

eukaryotes - hydrolysis of ATP
prokaryotes - H+ gradient

What three things can the flagella do to control the movement of the cell?

1. On
2. Off
3. Change direction - spin opposite direction = tumble

How many flagella do cells have?

Some have one.
Some have none.
Some have too many to count.

What is polar flagellation?

All flagella are at one end of the cell

What is peritrichous flagellation?

Flagella are all over the surface

How do cells decide where they want to go?

chemical attraction and repulsion

What are two types of gliding?

pili-mediated gliding
polysaccharide extrusion gliding

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