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MICB 201 > 2. Cell Structure > Flashcards

2. Cell Structure Flashcards

1
Q

What is the shape of coccus prokaryotes?

A

A sphere

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2
Q

What shape is a rod, bacillus prokaryote?

A

Straight cylinder.

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3
Q

What shape are spirillum prokaryotes?

A

Spiral cylinder.

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4
Q

What is the shape of vibrio prokaryotes?

A

Bent/curved cylinder.

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5
Q

What are hypha prokaryotes?

A

Prokaryotes that form webs or threads.

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6
Q

What are plasma prokaryotes?

A

Watery, fluid, indicating an irregular shape.

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7
Q

What percentage of bacterial and archael wet weight does water make up?

A

70%.

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8
Q

What is the dry weight of a prokaryotic cell made up of?

A

Proteins, some RNAs, DNA and mRNA, lipids and polysaccharides.

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9
Q

Define cellular differentiation.

A

The ability of a cell to exist in different morphological and functional forms depending on what genes are expressed in the cell.

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10
Q

Why are most prokaryotic cells microscopic?

A

Surface area to volume issues, ribosome issues, diffusion issues, and dilution issues.

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11
Q

What are permease proteins?

A

Membrane proteins that transport nutrients.

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12
Q

Define ABC transporters.

A

ABC transporters are proteins that do not work alone, they consume ATP on the side of cytosolic side.

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13
Q

Do bacteria have histones?

A

No but they have histone like proteins.

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14
Q

Do archaea have histones?

A

Yes.

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15
Q

What special thing do planctomycetes have?

A

They have a membrane around their nucleoid. They are said to have a structure called a nuclear body.

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16
Q

What colour do gram-positive and gram-negative cells stain?

A

Gram-positive cells stain purple and Graham negative cells stain red.

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17
Q

What is peptidoglycan?

A

PG is a mesh like molecule composed of two parts: a glycan chain and a tetrapeptide. The glycan chain is made of two amino sugars: N-acetylglucosamine (NAG) amd N-acetylmuramic acid (NAM) joined by strong covalent bonds in O-glycosidic linkages. The tetrapeptide is a sequence of four amino acids joined by strong covalent bonds in peptide linkages. The NAM of the glycan chains are X-linked to each other through AA3 and AA4 of their tetrapeptides.

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18
Q

What is the function of peptidoglycan?

A

To protect bacterial cells from osmotic lysis in a hypotonic environment. However, peptidoglycan cannot prevent plasmolysis, which is what happens in hypertonic environments.

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19
Q

Which two phyla do the gram-positive cell wall exist?

A

Firmicutes and actinobacteria.

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20
Q

What do gram-positive cell walls have besides PG?

A

Gram-positive cell walls contain polymers of phosphorylated sugar alcohols called teichoic acids (attached to NAM) or lipoteichoic acids (attached to sugar of head group of lipid). They also have wall associated proteins exposed on cell surface.

21
Q

What do gram-negative cell walls have besides PG?

A

And outer membrane, outer membrane and PG interactions, and lipopolysaccharides.

22
Q

Describe the outer membrane.

A

A lipid bilayer structure about the same thickness as the cytoplasmic membrane with embedded proteins that perform a variety of functions.

23
Q

Describe OM &PG interactions.

A

Proteins interact in non-covalent matters, and this anchors the outer membrane to the peptidoglycan, forming the cell wall unit. In some bacteria, and additional protein called lipoprotein also functions to anchor the PG to the OM.

24
Q

Define lipopolysaccharides.

A

Lipopolysaccharides dominate the outer leaflet of the OM. There are three parts to LPS. Lipid a is composed of several hydrocarbon tales anchored to a sugar derivative. The R-core is composed of sugars many of which puts us negatively charged chemical groups. The O-polysaccharide is also composed of sugars, in this case and charge the sugars, and extends many nanometers from the cell surface.

25
Q

Defined the permeability of the OM.

A

It is less permeable than the cytoplasmic membrane due to stronger lateral interactions between LPS molecules than between phospholipid molecules which lowers the fluidity of theOM.

26
Q

What are some OM transport proteins?

A

Porins, large channel porins, small channel porins.

27
Q

What is the function of the OM?

A

They provide extra barrier and is protective in nature.

28
Q

Define surface layers/S layers.

A

S layers are composed of many copies of the same protein arranged in a geometric pattern completely covering the cell wall. In both gram-positive and gram-negative bacteria, S layers are anchored noncovalently to PG and LPS, respectively.

29
Q

What are the functions of the S layer?

A

It remains a mystery. In those cases where S layer function is known, they perform different functions in different bacteria.

30
Q

Describe the cell walls of archaea.

A

Several kinds of archaeal cell walls possess a rigid polysaccharide component. In bacteria this is always peptidoglycan, but in archaea, different organisms make different kinds of polysaccharides. Some archaea synthesize a molecule called pseudopeptidoglycan. Archaea also have S layers, but they are an integral cell wall component. In many archaea, S layers are the cell wall.

31
Q

What is the general definition of a capsule?

A

If an organism possesses a capsule, it covers all underlying structures except for protein appendages such as flagella and pili.

32
Q

Define the two types of capsules.

A

Polysaccharide capsules: chains of sugars, often a single repeated sugar. Polypeptide capsules: chains of amino acids, often a single repeated amino acid. There can also be capsules composed of both sugars and amino acids.

33
Q

How are capsules anchored?

A

In gram negative bacteria, capsular polysaccharide is frequently anchored to the cell via phospholipids or by replacing the o-polysaccharide portion of LPS. In gram-positive bacteria, capsules are linked to the NAM & NAG sugars making up peptidoglycan.

34
Q

What is slime?

A

Material excreted similar to capsular material into the environment.

35
Q

Describe archaeal capsules.

A

It seems that they only make polysaccharide capsules and the sugar composition of archaeal capsules is more heterogeneous than bacterial capsules.

36
Q

What are the functions of capsules?

A

Protection from desiccation, protection from phagocytosis, attachment to surfaces, and protection from virus infections.

37
Q

What are stalks?

A

It is something part of some bacteria‘s reproductive cycle and it is like a leg that holds the bacteria to a surface. It can also hold the cell body above the surface the organism is attached to to get more nutrients.

38
Q

What is a holdfast?

A

A polysaccharide at the end of a stalk that serves as adhesive material for attachment to surfaces.

39
Q

What are hami?

A

They are long, barbed, protein grappling hooks. They are only made by those archaea who’s cell wall consist of a protein rich outer membrane. Hami are used for attachment to surfaces with the pickles and hooks. They can also allow archaea to attach to each other.

40
Q

What are the three most common forms of motility?

A

Swimming, twitching, gliding.

41
Q

Describe exoflagellar swimming.

A

It depends on long filamentous appendages called exo flagella. Monotrichois organisms possess a single flagellum, peritrichous organisms possess many flagella, lopotrichous organisms possess a tuft of many flagella present in the single location on the cell surface.

42
Q

Describe the composition of exo flagella.

A

The flagellar filament is a rigid helical structure composed of many copies of a single major proteins called flagellin. The filament is attached via a hook protein to a rod protein which is embedded in the membrane and wall by several protein rings. There is also a motor protein at the base of the flagellum.

43
Q

Describe archaeal exo flagella.

A

It’s molecular structure is completely unrelated to bacterial flagellum and is actually more similar to type 4 pilli.

44
Q

Describe endoflagellar swimming.

A

And the flagella are anchored in the cytoplasmic membrane at the poles of the cell. They spiral outside the peptidoglycan but inside the outer membrane.

45
Q

Describe the twitching motility.

A

It is the jerky movement of a prokaryote along a surface mediated by the extension and retraction of a structure called a type 4 pillus.

46
Q

Describe the structure of type 4 pili.

A

They are composed of multiple protein subunits called pilin. Usually one type of pilin dominates the structure along with smaller numbers of other pilin subunits. They are held together by the hydrophobic effect.

47
Q

What are the functions of type 4 pili?

A

Attachment of organisms to surfaces, horizontal gene transfer, twitching motility.

48
Q

Describe how twitching motility works.

A

It is driven by the consumption of ATP and the type 4 pili can be extended and retracted.

49
Q

Describe gliding motility.

A

Bacteria move over a surface not in a jerky manner but in a smooth, continuous motion without the help of flagella or pili.

MICB 201 (9 decks)

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