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Microbiology Bevington > Bevington 5 cytoskeleton, cell movement & division > Flashcards

Bevington 5 cytoskeleton, cell movement & division Flashcards

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1
Q

Cytoskeleton in Eukaryotes
Function:
x5

A
  1. Maintaining cell shape
  2. Positioning of organelles
  3. Movement of vesicles
  4. Cell motility
  5. Cell division
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2
Q

Cytoskeleton in Eukaryotes

Three major components

A
  1. Microfilaments (actin proteins)
  2. Microtubules (tubulin proteins)
  3. Intermediate filaments (keratin proteins)
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3
Q

1) Actin microfilaments:

structure

A

filamentous F-Actin polymers made of globular G-Actin sub-units

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4
Q

1) Actin microfilaments:

Function

A 
	Resist tension on cell
	Transport of membrane-packaged material across plasma membrane 
	Localised contractions of cell
	Cleavage furrows
	Amoeboid movement
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5
Q

Actin filaments pulled together by

A

heads of motor proteins:

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6
Q

Myosins head of actin filaments function

A

=>hydrolyse ATP& use energy to “walk” away from “minus” end (i.e. the more pointed end) of actin filament.
- Actin monomer units added to “plus” end
= molecular basis of muscle contraction

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7
Q

Things that use “amoeboid” movement

A

of a wide range of eukaryotic cells over a solid surface;
- Single-celled organisms (amoebae)
- In mammals –
• Fibroblasts in connective tissue (Lecture 6)
• Osteoblasts & osteoclasts in bone

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8
Q

Immune System movement:

A

Move through blood vessel walls & tissues in animals => leukocytes (white blood cells)(e.g. Monocytes, Macrophages & Neutrophils) phagocytose invading bacteria,

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9
Q

AMOEBOID MOVEMENT

process

A

Polymerisation pf cortical actin in lamellipodium
=> initial protrusion of front edge of cell, introduces tension into actin cortex. => relieved by contraction of rear edge of cell, driven by ATP hydrolysis of Myosin II molecules, moving over actin cortex.

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10
Q

Microtubules

Structure:

A

 Hollow tubes = tubulin dimers (α- and β-tubulin)
 Movement = kinesin & dynein motor proteins (analogous to myosin on F-Actin).
 Easily assembled/disassembled

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11
Q

Microtubules

Function:

A

 Compression resisting – supports cell structure
 Movement of vesicles
 Cell division (mitosis & meiosis)

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12
Q

Microtubules – Labelling conventions

 “Plus” end =

A

growing end tubulin sub-units are added, “anterograde” end => cellular “cargo” (such as secretory vesicles) are usually carried to this end i.e. away from nucleus=> plasma membrane

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13
Q

Kinesins =>

A

to “Plus” end

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14
Q

Dineins =>

A

to “Minus” end

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15
Q

Cilia

Functions:

A

Fluid circulation (e.g. moving mucus in mammalian respiratory tract)

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16
Q

Flagella

Functions:

A

larger, beat in different way & limited to 1 per cell e.g. driving movement of animal sperm

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17
Q

Bacterial cells can also have flagella, but

A

structure, evolutionary origin & mechanism of action are different. (flagellin)

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18
Q

Intermediate filaments

Structure:

A

Keratin proteins => fibrous subunits=> super-coiled together.
 Form cage-like networks throughout cell
 Do not readily disassemble.
 Mechanical toughness of these structures is particularly apparent in extra-cellular forms of keratins derived from epithelial cells in vertebrates=> skin scales, hair, nails, horn etc

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19
Q

Intermediate filaments

Functions inside cells:

A
  • Resist tension
  • Maintain cell shape
  • Fix position of nucleus and organelles
  • Form nuclear lamellae (lamin proteins)
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20
Q

CELL DIVISION

Single-celled organisms:

A

-cell division is reproduction
– Single-celled eukaryotes use mitosis
– Prokaryotes use binary fission

21
Q

CELL DIVISION

Multi-cellular organisms:

A 
cell division:
Meiosis: Generation of gametes
Mitosis: 
–	Development from fertilised egg
–	Growth
–	Tissue renewal and repair
22
Q

Prokaryotic binary division:

A

Splitting of single-cell organism into 2 daughter organisms = “division in half”.

23
Q

Prokaryotic binary division:

Process:

A
  1. Single bacterial chromosome
  2. Replication begins at Origin of Replication
  3. Origins of replication move to opposite poles of cell
  4. Cell elongates as replication continues
  5. Cytokinesis
    No nuclear envelope. Role of cytoskeleton unclear.
24
Q

Mitosis Interphase:

A

G1 : Reproduction of organelles which have their own genome (DNA)
S: DNA Synthesis
G2: More growth

25
Q

Interphase G1 :

A

: Reproduction of organelles which have their own genome (DNA)

26
Q

Interphase S:

A

DNA Synthesis

27
Q

Interphase G2:

A

More growth

28
Q

Mitosis: 5 phases

A
  1. Prophase
  2. Prometaphase
  3. Metaphase
  4. Anaphase
  5. Telophase
29
Q

Replication of Chromosomes

A
  • cell has several chromosomes depending on species
  • Each chromosome contains a single molecule of DNA
  • S-phase: chromosome is duplicated =>2 sister chromatids
  • Mitosis: 2 sister chromatids separated, => into 2 daughter cells.
30
Q

Replication of Chromosomes

End of G2 creates

A

Duplicates of:

  1. DNA
  2. Organelles
  3. Centrioles (in the centrosome)
  4. Other cell building blocks
31
Q

M Phase

A

(Mitosis & Cytokinesis) in animal cell

32
Q

Centrosome:

A

structure in cytoplasm = organising mitotic spindle

33
Q

Centriole:

A

pair of structures in each centrosome =specialised microtubules & a complex system of associated proteins. Their role is not well understood

34
Q

Centromere:

A

point 2 sister chromatids of a chromosome are connected

35
Q

Kinetochore:

A

= protein structure forms at centromere during mitosis

36
Q

Kinetochore Microtubules:

A
  • 1-40 microtubules attach to each Kinetochore
  • During Anaphase (see later) Motor Proteins pull separated sister chromatids along microtubule
  • dismantled behind moving chromosome
37
Q

Prophase:

A

Chromatin condenses => mitotic” chromosomes, Centrioles move apart & microtubules from cytoskeleton disassemble & form spindle & aster

38
Q

Prometaphase:

A

spindle microtubules = 2 populations:

i. (Kinetochore microtubules) attached to the Kinetochore of the chromosomes
ii. (Non-kinetochore microtubules)
- nuclear membrane fragmented

39
Q

Metaphase:

A

Spindle complete &asters extend to plasma membrane, Centrosomes at opposite poles of cell. Kinetochore microtubules attached to chromosomes =>tension => chromosomes line up middle of cell plane = metaphase plate.

40
Q

Anaphase:

A

Kinetochores cleaved by Separase enzyme. Chromatids move to poles of cell by:
Kinesin motor proteins walking towards poles & Microtubules pulled in by motor proteins at poles. Non-kinetochore microtubules pulled apart by kinesin motor proteins, causing cell to elongate.

41
Q

Telephase:

A

Nuclear envelope reforms. Chromosomes become less condensed & nucleolus reappears, spindle disassembles & interphase cytoskeleton re-forms

42
Q

Non-kinetochore microtubules:

A

Pushed past each other by kinesin motor proteins & elongated by + of extra tubulin subunits = overlap

43
Q

Cytokinesis ANIMALS:

A

ATP-powered myosin = contraction of actin microfilaments in cortex of cell & Cleavage furrow forms

44
Q

Cytokinesis PLANTS:

A

Vesicles containing cell wall material travel along microtubules to middle of cell. Vesicles fuse => cell plate => Cell wall & plasma membrane fuse with cell plate.

45
Q

Mitotic spindle:

A

microtubules & associated proteins= α- and β- tubulin proteins, obtained by partly dismantling cell’s microtubule cytoskeleton
Spindle anchored to centrosome, replicates during G2 of interphase

46
Q

Asters :

A

Short microtubules, to anchor spindle to plasma membrane

47
Q

Reproduction of Eukaryotic organisms:

Asexual:

A

Mitosis: Splitting of a single-celled organism into 2 daughter organisms

48
Q

Reproduction of Eukaryotic organisms:

Sexual:

A

Meiosis: specialised variant of Mitosis in Germ Line cells in production of haploid gametes

Microbiology Bevington (6 decks)

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