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LSCI 230 > 2. Structure and function > Flashcards

2. Structure and function Flashcards

1
Q

size of cells is limited because……

0.5-750 micrometers

A

surface volume ratio decrease when cell size increase. not enough surface area to support the exchange of nutrients and waste.

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2
Q

Differences between the cell structures of prokaryotes (bacteria, archaea ) vs. eukaryotes?

A
  • lack of nucleus
  • membrane- bounded organelles
  • NO mitochondria chloroplast, ER, Golgi complex, cytoskeleton, lysosome
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3
Q

membrane functions

A
  • permeability barrier
  • membrane protein: sensors, adhesions, transporters, enzymes
  • energy conservation (pmf)
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4
Q

membrane of Eukaryotes vs. Archaea

A
  • Eukaryotes: lipid bilayer

- Archaea: lipid monolayer(enhance stability, higher temperature, can live in extreme environment)

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5
Q

stabilization of membrane in Eukaryotes vs.Archaea vs. Bacteria

A
  • Eukaryotes: lipid bilayer is stabilized by sterol. (a polar head, rigid planar steroid ring structure and a non polar hydrocarbon tail)
  • Bacteria& Archaea: NO sterols
  • Animal cells: Cholesterol
  • Fungi: Ergosterol
  • Plants cells& some protozoans: Stigmasterol
  • Bacteria: hopanoids
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6
Q

Storage of DNA in Bacteria&Archaea vs. Eukarya

A

• Bacteria&Archaea:

  • circular molecule, double-stranded
  • hapoids (1 copy)
  • packaged with proteins (H-NS and other Histone-like protein), aggregates to form the nucleoid)
  • DNA in the cytoplasm, ribosomal RNA encoded on the chromosome
  • May also contain plasmids

• Eukarya:
- Linear molecules, double-
stranded.
- Generally diploid (two copies)
- Packaged with proteins (Histones) to form chromatin fibers, the chromosome.
- DNA in the nucleus
- Nucleolus:(DNA that code for ribosomal RNA, ribosomal proteins, immature ribosome)

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7
Q

DNA–> RNA–> Proteins

A

DNA–replication( DNA polymerase)—transcription(RNA polymerase) —RNA—translation (ribosome)—-protein

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8
Q

Ribosome: function?

in prokaryotes vs.eukaryotes?

A
  • Composed of ribosomal RNA and proteins, translates mRNA into amino acid chains to form proteins.
    – Prokaryotes: free in the cytoplasm or attached to cytoplasmic membrane.
    – Eukaryotes: free in the cytoplasm or bound to the endoplasmic reticulum.
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9
Q

Ribosome Svedberg unit?

A

•Prokaryotes: 30S + 50S subunits = 70S ribosome.
• Eukaryotes: 40S + 60S subunits = 80S ribosome.
- Describes the rate of sedimenta,on of a par,cle in an ultracentrifuge.
- Proportional to the size, shape and density of the particle but the relationship is not linear.

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10
Q

Cell wall

EU
BA
AR

A

EU
•Not present in animals and protozoa
• forms a tough, rigid barrier that helps protect the cell and gives its shape.
•in Eukaryotes: composed of polysaccharides
– Plants, algae, some fungi: cellulose (polymer of glucose).
– Fungi: chitin (polymer of N-acetylglucosamine).
– Also cell walls made of galactose, mannose, etc.

BA

  • withstand the intracellular osmotic pressure. shape and rigidity.
  • Gram(+) purple. 1:cytoplasmic membrane
  • Gram(-) pink. 2:outer membrane&cytoplsmic membrane

AR
- NO Peptidoglycan in the cell wall of Archeae; usually NO outer- membrane.
• Cell walls of Archaea are diverse and may consist of proteins (usually), polysaccharides, and/or glycoproteins.
• The structure of pseudomurein (pseudopeptidoglycan) is similar to peptidoglycan. It contains N- acetyltalosaminuronic acid instead of NAM and lacks D-amino acids.
• The linkage between the sugars(B 1,3) is insensitive to lysozyme, contrary to peptidoglycan(B 1,4).
• Some species of Archaea have a cell walls composed of repeating units of two or more sugars – heteropolysaccharides.
• crystalline appearance of cell wall under microscope –paracrystalline surface layers / S-layers.
• S-layer may also be found in bacteria. In this case the S-layer forms an additional layer on top of peptidoglycan (Gram-postive) OR on top of the outer membrane (Gram-negative).

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11
Q

Nucleus

A
  • Euchromatin: loosely packed, actively transcribed.

* Heterochromatin: densely packed, low level of transcription.

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12
Q

When mRNA translation information to make polypeptides, location of mRNA for making cytoplasmic proteins vs. membrane proteins & secreted proteins& vesicular protein ?

A
  • mRNA for cytoplasmic proteins: ribosome-mRNA complex stays free in the cytoplasm.
  • mRNA for membrane proteins, secreted proteins or vesicular proteins: ribosome-mRNA complex is directed to the ER.
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13
Q

ER

A
  • a system of membranous channels. The membrane is composed of a bilayer of phospholipid.
    • Rough ER: studded with ribosomes, important for protein synthesis. ( protein modification, glycosylation, and maturation.)
    • Smooth ER: no ribosomes, involved in synthesis of lipid.
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14
Q

Golgi body

A
  • further processing of proteins and their distribution. Proteins are packaged in vesicles and transported to where they are required.
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15
Q

Lysosome

A
  • internal vesicles that contains hydrolytic enzymes required for degradation of materials brought in by phagocytosis and endocytosis.
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16
Q

Mitochondria
inner membrane
outer membrane

A

• Produce most of the ATP required by the cells.
• Some protozoa do NOT have mitochondria.
• Outer membrane: many porin proteins, makes this membrane very permeable to small molecules.
•Inner membrane:
Transport proteins (regulated transport), enzymes, cytochromes, ATPases. Similar proteins are found in the membrane of bacteria and archaea.
• Matrix: enzymes (citric acid cycle), DNA, ribosomes (70S).
• Mitochondria are able to synthesize some of their own proteins, the remaining ones are imported from the cytoplasm of the cell (they are encoded on its genome).

17
Q

Chloroplast

A
  • Present in phototrophic eukarya (plants, algae).
  • Outer membrane: porins, similar to mitochondria.
  • Inner membrane: transport proteins (regulated transport).
  • Thylakoids: closed system of interconnecting sacks and tubules.
  • Stroma: circular DNA, 70S ribosomes, enzymes of the Calvin cycle.
  • Chloroplasts are able to synthesize some of their own proteins, the remaining ones are imported from the cytoplasm of the cell.
18
Q

Thylakoids

A
  • Contain enzymes and pigments that harvest light energy and the membrane- bound ATPases that use this energy to produce ATP.
  • Similar proteins are found in many photosynthe,c prokaryotes, usually in the cytoplasmic membrane.
19
Q

Cytoskeleton

A
  • a complex network of protein filaments that helps organize the cytoplasm and give the cell its shape.
  • Microtubule: α-tubulin, β-tubulin. (hollow tube)
  • Actin filament: actin.(long twisting filament, double helix strands )
  • Intermediate filament: keratin, desmin, vimentin. (french braid, thick cables)
  • Similar proteins are found in several non-spherical prokaryotes.
20
Q

Microtubules

A
  • “highways” for the transport of organelles and vesicles around the cytoplasm.
  • Kinesin&dynein (proteins) attach to vesicles/organelles and “walk” on microtubules, transporting their cargos to where they are required. hydrolyzing ATP for energy to “walk”
21
Q

Centrioles& Basal bodies

A

•organizing centers for other microtubule arrays.
• 9 + 0 construction
• Each set is composed of 1 complete microtubule
and two partial microtubules [triplets].
• Centrioles: middle of the cell
• Basal bodies: near the cytoplasmic membrane.

22
Q

Cilia&Flagella
EU
AR
BA

A 
EU
•  9 sets of microtubule [doublets].
•  9 + 2 construction
•  Covered by the plasma membrane.
• Dynein arms slide the doublets past each other, creating movement.

AR
• flagella (locomotion) & fimbriae (attachment of microorganism to surfaces)

BA
• flagellum structure:
- Gram(+) L,MS,C rings (because no pariplasm)
- Gram(-) L,P,MS,C rings
•  L–LPS
•  P – Peptidoglycan
•  MS – Membrane Superficial
•  C - Cytoplasm
•flagella both (locomotion) & fimbriae ONLY in gram(-) (attachment of microorganism to surfaces)
23
Q

Peptidoglycan of bacteria

A

• The polymerization of the sugar backbone provides rigidity to the structure in only one direction.
• Another bond, between the peptide chain of two adjacent peptidoglycan chains, provides rigidity in the other direction.
• Gram-negative: direct cross-linking.
• Gram-positive: interbridge cross-
linking.
• Cross-linking =transpeptidation.

24
Q

gram(+) vs.gram (-)

A
  • gram (+)
    •peptidoglycan: Up to 90% of cell wall
    • Teichoic Acid TA/Lipoteichoic acid LTA are covalently bonded to the peptidoglycan.
    • Sortase: covalently attach wall-associated proteins to peptidoglycan
  • Gram (-)
    • Peptidoglycan: 5-10%
    • The peptidoglycan is located in the Periplasm (the space delimited by the cytoplasmic membrane and the outer membrane)
    • Periplasm contains high [proteins] involved in diverse of functions. “protein gel”.
    e.g. nutrient acquisition, extracellular enzymatic reactions, sensing, etc.
    • Outer membrane is an atypical lipid bilayer: phospholipids in the inside layer, phospholipids and lipopolysaccharide in the outside layer (LPS layer).
    • outer membrane proteins (OMPs), e.g. porins, and lipoproteins. structural role.
    • The LPS helps protect the bacteria against a variety of substances, including an,bio,cs, and against the host defense system.
25
Q

LPS

A
  • LPS is a family of complex sugar polymers attached to a lipid moiety known as lipid A. - Lipid A is toxic to many animals, it can cause acute inflammation and vascular problems (septic shock) that can result in death.
  • Lipid A is an endotoxin. pathogenesis of Gram-negative bacterial pathogens.
  • O-specific polysaccharide
    (O antigen) consists of repeating sequences of 2-4 monosaccharides.
  • Huge diversity of O antigens so it can be used to identify different strains of one species of bacteria
26
Q

Capsule &slime layer of BA&AR

A

• BA&AR synthesize capsule or slime layer depending on its consistency. The capsule or slime layer does not confer significant strength to the cell.
• Composed of polysaccharides (vast majority) or proteins.
– Heteropolysaccharides (Majority of bacteria)
– Homopolysacchrides (Some Gram-negative)
• The capsule may be covalently bound to the outer membrane or to the peptidoglycan layer.
• capsule protects against the host defense system.

27
Q

Flagellum biosynthesis

A
  • grow from the middle, everything is assembled on the top
28
Q

Flagella movement

A
  • flagellum can be turned in two directions leads to different movement
  • clockwise rotation: bacteria stumble on itself
  • counterclockwise: moves forward
29
Q

Gliding mobility

A
  • lateral movement of surface adhesions

- secretion of mucus

30
Q

Taxis

A

Directed movement toward or away from a gradient of chemical or physical agents.
• NO attractant–random movement
• attractant present–directed movement
– Chemotaxis: chemicals, nutrients, antibiotics, etc.
– Phototaxis: light (phototrophic organisms)
– Aerotaxis: oxygen
– Osmotaxis: ionic strenght (high/low salt concentra,on)

31
Q

Fimbriae

+) (-

A 
•  Gram-positive
–  Anchored in the peptidoglycan
–  Composed of pilin proteins
–  Covalently-linked to one another
–  Assembled enzymatically by sortases.
•  Gram-negative
–  Anchored in the outer membrane
–  Composed of pillin proteins
–  Not covalently bound to one another (strand exchange)
–  Accessory proteins are needed, encoded with the fimbriae pilin genes.
  • fimbriae of Gram-negative bacteria grow from the base.
  • The assembly requires two proteins: the chaperone and the usher
  • The subunits are assembled by strand exchange (like puzzle pieces
32
Q

Endospore function

A
  • BA
  • extremely resistant to harsh environmental conditions
  • a dormant stage in the life cycle and is easily dispersed by wind, water, animal digestive system
  • most are produced by gram(+)
33
Q

Endospore structure

A

From outside to inside
• Exosporium: proteins.
• Spore coat: layers of spore-specific proteins
(keratin-like).
•Core wall
• Cortex: pep,doglycan.
• Core (cytoplasm): Ca2+, dipicolinic acid (DPA), SASPs (small, acid soluble spore proteins).
• SASPs bind to DNA and help protect it against damage (UV light).
• DPA and Ca2+ bind water, dehydrate the core.
• The core also contains proteins needed for germina,on.

34
Q

Formation of endospore

A

Sporulation stages:

  1. asymmetric cell division
  2. engulfment
  3. cortex formation
  4. spore coat, ca2+ uptake, SASPs, dipicolinic acid
  5. maturation, cell lysis
  6. free endospore

vegetative cycle:

  1. cell dividion
  2. growth
35
Q

Cell inclusions

Magnetosome

A
  • in BA& AR, inclusions/granules: store building blocks and energy reserves
  • enclosed by single layer membrane
  • confer buoyancy
  • Magnetosome contains magnetite (Fe3O4) and allows the bacteria to respond to magnetic fields (magnetotaxis).

LSCI 230 (9 decks)

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