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Biology 103 1 sem > Weeks 4 & 5 > Flashcards

Weeks 4 & 5 Flashcards

1
Q

Cytoskeleton -

A

network of filaments extending throughout the cytoplasm

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2
Q

Cytoskeleton is composed of 3 types of filaments:

A
  1. Microfilaments: actin filaments, the thinnest components
  2. Intermediate filaments: filaments with middle-range diameters, composed by different types of proteins
  3. Microtubules: tubulin filaments, the thickest of the three components of the cytoskeleton
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3
Q

Microtubules structure -

A

hollow tubes; walls consist of 13 columns of tubulin molecules

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4
Q

Microtubules diameter

A

25 nm w/ 15-nm lumen

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5
Q

Microtubules protein subunits:

A

tubulin

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6
Q

Microtubules main fns (4):

A
  1. maintenance of cell shape
  2. cell motility
  3. mitotic spindle formation => chromosome mvmnt in cell division
  4. organelle mvmnts
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7
Q

Microtubules can increase or decrease in size by

A

addition or removal of monomers

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8
Q

Microtubules consist of

A

α & β tubulin dimers => form 13 protofilaments
each dimer has 2 GTP bound:
(+) end: fast polymerisation (addition of monomers)
(-) end: slow polymerisation

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9
Q

The continuous polymerisation or depolymerisation of microtubule is controlled by:

A

GTP hydrolysis:
-GTP attached to β-tubulin hydrolyzed to GDP during tubulin polymerisation
-The GTP bound to α-tubulin does not hydrolyze during tubulin polymerisation (has structural role)

also by Cytosolic calcium concentration: [Ca+2] > 0.5 mM => depolymerisation

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10
Q

Drugs that affect microtubule stability/formation:

A

Αnti-mitotic drugs: inhibit the mitotic spindle formation, for ex:
Colchicine, anti-inflammatory: binds to tubulin monomers => inhibits microtubule polymerisation = stopes mitotic spindle formation (acts in profase)
Τaxol, anti-cancer: binds to tubulin monomers => stabilises microtubules by inhibiting their depolymerisation during mitotic (acts in anaphase)

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11
Q

Microtubule polymerisation begins at the

A

ΜΤOC (Microtubule organizing centers) of the cells

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12
Q

Microtubule organizing centers (MTOC) (4), how microtubules are oriented:

A
  • Centrosome: in most non-dividing cells
  • Βasal body: in flaggelated and ciliated cells
  • Polar body: in some fungi (part of the nuclear envelope)
  • Chromosomal kinetochores of the mitotic spindle: in dividing cells (during metaphase)

Microtubule orientation:
- Τhe (-) end is oriented towards the cell center (MTOC)
- The (+) end is oriented towards cell periphery

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13
Q

Centrosome structure

A

has 2 centrioles (centriole pair), each consists of 9 triplets of microtubules (9+0 arrangement), at right angles to one another

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14
Q

Pericentriolar material (cloud)

A

space around centrosome, contains γ-tubulin, which:
- facilitates the nucleation of the α/β tubulin dimers by binding to the (-) end of microtubules
- induces their nucleation (polymerisation) by forming rings into which the microtubule assemble and elongate

fn: microtubule nucleation (initiation of polymerisation)

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15
Q

Microtubules: role in motility

A
  • used as “monorails” for the mvmnt of cellular cargo (vesicles, organelles and chromosomes)
  • from the cell centre to the periphery and vice versa
  • interact w/ motor proteins to produce motility
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16
Q

Motor proteins in cytosol (2) and fn

A

fn: transport cellular cargo toward opposite ends of microtubules

Dynein: involved in transport from periphery to the cell center (retrograde to microtubule; from + to – end)
Kinesin: involved in transport from the cell center to the periphery (anterograde to microtubule; from – to + end)

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17
Q

Cilia and flagella: what are they and microtutubles arrangement

A

– permanent locomotor appendages of some eukaryotic cells
– contain specialized arrangements of microtubules: 9 pairs around 2 single central ones = 9+2 arrangement

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18
Q

Flagella

A

• Typically a single flagellum per cell (in eukaryotes)
• Flagella motility pattern: snakelike motion
• Example: sperm cells

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19
Q

Cilia

A

• Typically a lot of cilia per cell
• Ciliary motility pattern: back-and-forth motion
• Example: trachea cells, protists, fallopian tubes

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20
Q

Αxoneme -

A

The central strand of a cilium or flagellum

axoneme is surrounded by the PM

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21
Q

Axonemal proteins:

A
  • Dynein: motor protein responsible for motility (diff from cytosolic: bigger, more ATP): bending mvmnt of cilia & flagella
  • Nexin: connects microtubule doublets (pairs) between them
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22
Q

Basal body:

A

protein structure found at the base of a eukaryotic cilium or flagellum. Consists of 9 triplets of microtubules (like centrioles => 9+0 arrangement).

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23
Q

Why movement of cilia & flagella diff?

A

due to the diff in length, essentially mvmnt is the same

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24
Q

Motor proteins & their fns (4):

A
  • cytosolic kinesin: vesicle and organelle transport from the cell centre to the periphery (anterograde to microtubule; from – to + end) [Karry Kargo trucK]
  • cytosolic dynein: vesicle and organelle transport from periphery to the cell centre (retrograde to microtubule; from + to – end) [Dive Down Dynein the centre of the cell]
  • axonemal dynein: on axonemal microtubules; causes movement of cilia/flagella.
  • spindle kinesin: mitotic spindle assembly and chromosome segregation during cell division
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25
Q

All the motor proteins have ATPase activity

A

=> ATP hydrolysis => produce energy used for motility

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26
Q

Subcellular structures composed of microtubules:

A

cilia: 9+2 (9 doublets + 2 central microtubules)
flagella: 9+2 (-II-)
centriole: 9+0 (9 triplets + 0 central microtubules)
basal bosy: 9+0 (-II-)
centrosome: 2 centrioles places @ right angles to each other

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27
Q

Microfilaments structure:

A

2 intertwined strands of actin

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28
Q

Microfilaments diameter

A

7 nm

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29
Q

Microfilaments’ protein subunit

A

Actin

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30
Q

Microfilaments’ main fns (5):

A
  • maintenance of cell shape (ex: microvili core of intestinal epithelial cells)
  • changes in cell shape (formation of pseudopodia: filaments in direction of cell mvmnt polymerize and depolymerize in opposite direction)
  • muscle contraction (actin-myosin contractile system)
  • cell motility (pseudopodia + cytoplasmic streaming in plant & large fungal cells)
  • cell division
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31
Q

Microfilament polymerisation

A
  • Energy provided by ATP hydrolysis
  • Filamentous F-actin is assembled from globular G-actin subunits containing bound ATP
  • growth at + end, dissociation of actin-ATP at - end
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32
Q

Intermediate Filaments’ Functions (2) and characteristics (2):

A

– Support cell shape: provide tissue w/ resistance to mech stress
– Fix organelles in place: participate in cell junction formation (ex: epithelial cell desmosomes by kadherin)
– More permanent than other filaments
– Composed of different protein family categories (e.g. keratins)

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33
Q

Intermediate filament types, where found (6):

A
  • Keratin: in epithelial cells
  • Desmin: in muscle cells
  • Vimentin: in mesenchymal cells
  • Neurofilaments: in neurons
  • GFAP (glial fibrillary acidic proteins): in neuroglia (glia)
  • Lamins: in nuclear envelope
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34
Q

Keratins:

A

• Found in epithelial and epidermal cells
• In epithelial cell desmosomes => cytokeratins
• Major component of hair and nails, in intestinal epithelium, squamous epidermal epithelium

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35
Q

Desmin

A

• In muscle cells
• Connects myofibrils and Ζ-disks of the sarcomeres to each other

Sarcomere: basic unit of contraction of striated muscle tissue= the area between the two Z-disks.
Z-disk: a thin, dark disk that transversely bisects a striated muscle fiber.
Vimentin (another IF) also participates in Z-disk structure organisation in muscle cells

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36
Q

Glia fibrils

A
  • in neuroglia

• Neuroglia (glia): non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the nervous system.
• Glia fibrils: found in neuroglia (e.g. astrocytes)
- GFAP= Glial Fibrillary Acidic Protein => polymerised to form glia fibrils
- Role in astrocytic projection formation => CNS morphology

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37
Q

Lamins

A

lamin filaments found in the inner site of the nuclear envelope: provide structural support => make up nuclear envelope

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38
Q

Clinical correlations: cytoskeletal disorders

A

Chediak-Higashi syndrome

Kartagener’s syndrome

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39
Q

Chediak-Higashi syndrome:

A

microtubule-based lysosomal mobility inhereted defect (lysosomal trafficking deffect)
=> reduced fusion of phagosomes and lysosomes during phagocytosis
=> recurrent infections (inability to destroy microorganisms by phagocytosis)

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40
Q

Kartagener’s syndrome:

A
  • immotile cilia/flagella due to axonemal dynein arm inherited defect.
  • Results in male and female infertility (immotile sperm), sinusitis (bacteria and particles not pushed out)
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41
Q

Extracellular structures:

A
  • cell walls of plant cells
  • the extracellular matrix (ECM)
  • intracellular junctions
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42
Q

ECM of animal cells:

A
  • covers animal cells
  • consists of: glycoproteins and proteoglycans
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43
Q

Glycoproteins -

A

glycosylated proteins (proteins with attached carbohydrate residues) e.g. collagen, fibronectin, laminin

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44
Q

Proteoglycans -

A

proteinated carbohydrates
(carbohydrates with attached protein residues)

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45
Q

ECM functions

A
  • support
  • adhesion
  • movement
  • regulation of gene expression
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46
Q

ECM components
Major proteins and glycoproteins (5):

A
  • Collagen: major ECM glycoprotein (12 types)
  • Fibronectin: ECM glycoprotein that connects to plasma membrane proteins (integrins) and to other ECM components (e.g. collagen) => connects plasma membrane with extracellular molecules
  • Laminin: basement membrane glycoprotein
  • Entactin: basement membrane glycoprotein
  • Εlastin: connective tissue protein
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47
Q

ECM components
Proteoglycans

A

composed of proteins + glucosaminoglycans (GAGs)

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48
Q

Integrins

A
  • transmembrane proteins that bind to several ECM components
  • CAMs - Cell adhesion molecules: Cell surface transmembrane proteins that bind to the different ECM components
  • Heterodimers made of one α and one β subunit
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49
Q

Inregrins’ extra- & intracellular domain:

A
  • Extracellular domain: binds to the ECM glycoproteins (e.g. fibronectin) via a specific tripeptide sequence (Arg-Gly-Asp= RGD sequence)
  • Intracellular domain: binds to cytoskeletal filaments (microfilaments or intermediate filaments)
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50
Q

Integrins Function:

A

link ECM components to cytoskeletal components inside the cell
=> Activation of cell-signalling pathways
=> signal transduction
=> cell survival/proliferation

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51
Q

Collagen: what, produced by, structure

A
  • Major ECM glycoprotein and most abundant protein in the human body.
  • 12 different collagen types (I-IV most common)
  • produced by fibroblasts, epithelial cells
  • Structure: 3 helical chains (triple helix); Repetitive motif Gly-X-Υ (X,Υ= proline, hydroxyproline, or hydroxy-lysine)
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52
Q

Basement membrane (basal lamina):

A

specialized ECM type that separates epithelium/mesothelium/endothelium from underlying connective tissue

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53
Q

Impt collagen types:

A

Type I (most common)
- skin, tendon, organs, bone
- associated syndrome: Reduced production in osteogenesis imperfecta (OI) type I.

Type II
- cartilage

Type III
- skin, blood vessels, uterus, fetal tissue, etc
- associated syndrome: deficient in vascular type Ehlers-Danlos syndrome (osteoarthritis)

Type IV
- basement membrane
- associated syndrome: Defective in Alport syndrome - glomerulonephritis

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54
Q

osteogenesis imperfecta (OI) type I is associated w/

A

reduced production of collagen type I

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55
Q

vascular type Ehlers-Danlos syndrome (osteoarthritis) is associated w/

A

Collagen type III is deficient

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56
Q

Alport syndrome (glomerulonephritis) is associated w/

A

Defective collagen type IV

57
Q

Fibronectin and fn

A
  • Major ECM glycoprotein
  • Function: cell attachment to ECM components
  • Fibronectin has domains for binding integrins (cell surface receptors) and other ECM glycoproteins/proteoglycans (e.g. collagen, heparin, etc).
    => It mediates cell adhesion to the ECM
58
Q

Εlastin

A
  • stretchy protein in connective tissue
59
Q

Elastin Function -

A

allows many tissues (e.g. blood vessels, lungs, ligaments, vocal cords) to resume their shape after stretching or contracting

(Major arterial extracellular component => confers elasticity)

60
Q

Εlastic fibers structure:

A

consist of glycoproteins (e.g. fibrillin) connected with cross-linked elastin

61
Q

Elastin Clinical correlations:

A
  • Marfan syndrome: connective tissue disorder caused by a defect in fibrillin, a glycoprotein that forms a sheath around elastin (in elastic fibers)
  • Wrinkles of aging are due to reduced collagen and elastin production
62
Q

Laminin

A
  • Located mainly in basement membrane, synthesized by adjacent epithelial cells
  • Binds to basement membrane components (collagen ΙV, heparin, etc) and cell surface receptors (e.g. integrins)
  • Fn: connects epithelial cells with the ECM (mainly basement membrane)
63
Q

Entactin

A
  • ECM glycoprotein
  • Binds to basement membrane components (laminin, collagen IV and proteoglycans) only (does not bind to integrins)
  • Fn: Assists assembly of basement membrane components (ex: Links laminin with collagen in the basement membrane)
64
Q

ECM proteins and glycoproteins (summary)

A

Collagen: Most abundant glycoprotein. Organizes and strengthens extracellular matrix. Binds to the cell (via integrin)
Fibronectin: Connects cells (via integrins) to ECM components (e.g. collagen)
Laminin: Connects cells (via integrins) to basement membrane components
Entactin: Connects basement membrane components between them
Elastin: Major component of elastic fibers together with fibrillin

65
Q

Proteoglycan composition:

A

core protein (5-10%) + GAG (90-95%)

ex: aggrecan

66
Q

Glucosaminoglycans (GAGs):

A

Polysaccharide composed from a repetitive disaccharide unit (70-200 units)

Disaccharide unit composed of: N-acetyl-glucosamine or N-acetyl-galactosamine + glucuronic acid or iduronic acid

67
Q

4 GAG groups (types):

A
  1. Hyaluronic acid (hyaluronan), isn’t linked to core protein
  2. Chondroitin sulfate and dermatan sulfate, linked to core protein
  3. Heparin and heparan sulfate, linked to core protein
  4. Keratan sulfate, linked to core protein
68
Q

Common proteoglycans:

A
  • aggrecan (aggrecan aggregate = aggrecan + hyaluronic acid, found in cartilages)
  • perlecan
69
Q

Intercellular Junctions

A

what neighbouring cells in tissues,
organs, or organ systems often adhere, interact, and communicate through

70
Q

Intercellular Junctions fn:

A

help coordinate the behavior of all cells in a tissue

71
Q

Types of intercellular junctions:

A

Animal cells:
– Tight junctions
– Desmosomes
– Gap junctions
Plant cells
– Plasmodesmata (connect neighbouring plant cells through plant cell walls)
- Channels (communicating junctions) - allow molecule exchange

72
Q

Types of intercellular junctions in animals (3):

A

connect, but NO molecule exchange:
1. Tight junctions: prevent leakage of fluid across a layer of cells (occluding junctions)
2. Desmosomes: fasten cells together into sheets (anchoring junctions); attach muscle cells to each other in a muscle

ALLOW molecule exchange:
3. Gap junctions: serve as channels allowing ions and small molecules across cells => facilitate communication between cells in tissues (communicating junctions)

73
Q

Some ‘muscle tears’ involve the rupture of

A

desmosomes

74
Q

plasma membrane -

A

boundary that separates the living cell from its non-living surroundings

75
Q

Properties of plasma membrane (3):

A
  1. Fluidity - constant movement of the PM components
  2. Mosaicism - presence of many different molecules
  3. Selective permeability - PM allows some substances to cross it more easily than others
76
Q

Liposomes

A
  • are formed by phospholipids in aqueous environment
  • bilayer spherical structures
  • used for efficient delivery of certain drugs/compounds to the cells
77
Q

Membrane lipids (make up lipid bilayer):

A

• Phospholipids: the major membrane lipid type
• Glycolipids
• Sterols

78
Q

2 types of phospholipids:

A
  • Phosphoglycerides: basis - glycerol + 2 fatty acids + phosphate + organic molecule (Phosphatidyl-choline, Phosphatidyl-ethanolamine, Phosphatidyl-serine, Phosphatidyl-inositol)
  • Phosphosphingolipids: basis - sphingosine + 1
    fatty acid + phosphate + organic molecule (sphingomyelin (only in animal cell membrane))
79
Q

Glycolipids and glycosphingolipids structure

A
  • Glycolipids: sugar(s) + lipids (glycosylated lipids)
  • Glycosphingolipids: sphingosine + 1 fatty acid + sugar residue(s)
80
Q

Common membrane glycolipids

A

Glycosphyngolipids:
Cerebrosides: a monosaccharide
Gangliosides: oligosaccharide residue

81
Q

Sterols: what & where?

A

Sterols: steroid alcohols (steroids): on animal cell membrane

Phytosterols: in plant cell membranes

Ergosterol: in fungal and protozoal cell membranes

82
Q

Membrane lipids of animal cells (summary)

A

Membrane lipids:

  1. Phospholipids
    1a. Glycerophospholipids (glycerol + 2FA + PO4 + alcohol) = Phosphoglycerides
    1b. Phosphosphingolipids (sphingosine + 1FA + PO4 + choline) = Phosphosphingolipids - sphingomyelin
  2. Glycolipids - Glycosphingolipids (sphingosine + 1FA + mono- (cerebroside) / oligosaccharide (ganglioside))
  3. Cholestreol (steroid compound)
83
Q

Phosphatidyl-choline structure

A

Alcohol: Glycerol
FA: 2
Phosphate: yes
Organic molecule: Choline
Sugar molecule: no

84
Q

Phosphatidyl-serine structure

A

Alcohol: Glycerol
FA: 2
Phosphate: yes
Organic molecule: Serine
Sugar molecule: no

85
Q

Phosphatidyl-ethanolamine structure

A

Alcohol: Glycerol
FA: 2
Phosphate: yes
Organic molecule: Ethanol-amine
Sugar molecule: no

86
Q

Phosphatidyl-inositol structure

A

Alcohol: Glycerol
FA: 2
Phosphate: yes
Organic molecule: Inositol
Sugar molecule: no

87
Q

Sphingomyelin structure

A

Alcohol: Sphingosine
FA: 1
Phosphate: yes
Organic molecule: Choline
Sugar molecule: no

88
Q

Cerebrosides structure

A

Alcohol: Sphingosine
FA: 1
Phosphate: no
Organic molecule: no
Sugar molecule: monosaccharide

89
Q

Gangliosides structure

A

Alcohol: Sphingosine
FA: 1
Phosphate: no
Organic molecule: no
Sugar molecule: oligosaccharide

90
Q

The Fluidity of Membranes: role of phospholipids

A

The type of hydrocarbon tails in phospholipids affects the fluidity of the plasma membrane:
- Unsaturated hydrocarbon tails with kinks => higher fluidity (fluid PM)
- Saturated hydrocarbon tails => lower fluidity (viscous PM)

91
Q

The Fluidity of Membranes: role of cholesterol

A

has different effects on membrane fluidity at different temperatures:
- At warm temperatures (37°C), cholesterol restrains movement of phospholipids => reduces fluidity
- At cool temperatures, it maintains fluidity by preventing tight packing

92
Q

Membrane protein categories:

A

(a) Integral:
- transmembrane: completely span the membrane
- Lipid-bound: attached to a membrane lipid

(b) Peripheral: Loosely bound to the surface of the membrane on internal or external side

93
Q

Integral transmembrane proteins

A
  • span the cell membrane 1 or more times
  • Penetrate the hydrophobic core of the lipid bilayer
  • Their hydrophobic region contains non-polar amino acids
94
Q

Integral transmembrane proteins, 2 types of secondary structure:

A
  • α-helical structure: e.g. growth factor receptors (EGFR), insulin, membrane immunoglobulins (Ig)
  • β-pleated sheet structure (β-barrel): e.g. bacterial porin
95
Q

EGFR:

A

Epidermal Growth Factor Receptor

  • Overexpressed in many cancers (ex: breast cancer)
  • Single-pass transmembrane protein with α-helical structure
96
Q

Integral lipid-bound proteins, how attached and their fn

A
  • Attached to the plasma membrane through a covalent bond with a lipid molecule
  • Directly attached to the lipids at the internal side of the plasma membrane
  • Indirectly attached to phosphatidyl-inositol at the external site of the plasma membrane through an oligosaccharide chain
  • Fn: hydrolases, receptors
97
Q

Peripheral proteins and fn

A
  • interact with the polar surfaces of the membrane or with proteins embedded in the membrane
  • Internal membrane proteins fn: connection with the cytoskeleton

ex: erythrocyte spectrin

98
Q

Six major functions of membrane proteins

A
  1. Transport (transmembrane proteins; either hydrophilic channel across the membrane that is selective for a particular solute or shuttle a substance from one side to the other by changing shape)
  2. Enzymatic activity
  3. Signal transduction.
  4. Cell-cell recognition (some glycoproteins serve as identification tags that are specifically recognized by other cells)
  5. Intercellular joining (gap junctions, tight junctions)
  6. Attachment to the cytoskeleton and ECM
99
Q

Membrane carbohydrates: where & fns

A

where: on the external side of PM

fn: Cell-cell recognition - cell’s ability to distinguish one type of neighbouring cell from another

100
Q

3 types of membrane-associated carbohydrates (glycocalyx):

A
  • Glycoproteins: carbohydrates covalently bonded to proteins (content: protein > carbohydrates); where: membrane and ECM
  • Glycolipids: carbohydrates covalently bonded to lipids; where: membrane only
  • Proteoglycans: proteins covalently linked to carbohydrates (content: carbohydrates > protein); where: ECM only
101
Q

Glycocalyx -

A

carbohydrate cover on the external side of the cell membrane protecting the cell surface from mechanical/chemical damage

ex: the human blood cell types A, B, AB and O reflect variation in the RBC surface carbohydrates

102
Q

What molecules can pass through the membrane rapidly?
and ex

A

Hydrophobic (non-polar) molecules: are lipid-soluble => can pass through the membrane rapidly

ex: CO2, O2, hydrocarbons

103
Q

What molecules can pass through the membrane?
and ex

A

Hydrophilic (polar) molecules: not lipid-soluble

ex: sugars, ions - charged

104
Q

Transport Proteins

A
  • Allow passage of hydrophilic substances across the membrane
  • Most are extremely specific for the substance they are transporting
105
Q

2 types of Transport Proteins:

A
  1. Channel proteins: transport proteins that have a hydrophilic channel through which certain molecules or ions pass
    ex:
    - Aquaporins: special transport proteins for water
    - Ion channels: transport proteins for ions
  2. Carrier proteins: transport proteins that bind to molecules and change shape to shuttle them across
    ex: glucose transporters GLUT
106
Q

Types of transport of molecules through the PM:

A
  1. Active transport: transport of a substance across a membrane that requires energy investment
  2. Passive transport: transport of a substance across a membrane with no energy investment, b/c it favours dynamic equilibrium
107
Q

Passive transport results in:

A

equalization of the concentration of a substance in the internal and external membrane region (equilibrium)

108
Q

2 types of passive transport processes:

A
  1. Diffusion: movement of solute molecules across the PM down their concentration gradient (from high solute to low solute)
  2. Osmosis: movement of solvent (water) molecules across the PM against the solute
    concentration gradient (from low solute to high solute); occurs when diffusion can’t
109
Q

facilitated diffusion -

A
  • Larger molecules and ions require to be transferred by transport proteins (e.g. ion channels, carrier proteins), w/out E
  • Movement of molecules is always down their concentration gradient (from high solute concentration to low solute concentration)
110
Q

dynamic equilibrium -

A

as many molecules cross one way as cross in the other direction (equal molecule distribution)

111
Q

Channel proteins -

A
  • Channels that allow a specific molecule or ion to cross the membrane

ex: water channels (aquaporins), ion channels (gated)

112
Q

Carrier proteins -

A
  • Bind to the solute and undergo a change in shape that translocates the solute-binding site across the membrane => shuttle molecules across

ex: GLUT

113
Q

Cystic fibrosis - transporter protein disorder:

A

mutation in chloride ion channel protein => viscous secretions in respiratory tract => pulmonary infections

114
Q

Cystinuria (kidney disease) - transporter protein disorder

A

mutations in a renal membrane carrier protein => prevention of cysteine reabsorption into the blood => concentrates in urine => kidney stone formation (crystals)

115
Q

Osmosis

A
  • movement of water across a semipermeable membrane
  • affected by the concentration gradient of dissolved substances
  • occurs when the molecules/ions of a solute cannot pass through the PM (semipermeable)
116
Q

hypotonic

A

area of lower solute/higher water concentration
(water moves from here)

117
Q

hypertonic

A

area with higher solute/lower water concentration (water moves to here)

118
Q

isotonic solution -

A

result of osmosis: substance concentrations of the 2 areas become equal (equilibrium is reached)

119
Q

Tonicity: what, depends on, affects more which cells

A
  • the ability of a solution to cause a cell to gain or lose water
  • depends on the concentration of solutes that cannot penetrate the membrane
  • has a great impact on cells without walls, b/c cell walls protect cells against osmotic pressure
120
Q

Cells w/out cell walls in Hypotonic solution

A

Lysed

121
Q

Cells w/out cell walls in isotonic solution

A

Normal

122
Q

Cells w/out cell walls in Hypertonic solution

A

Shriveled, shrink (water out)

123
Q

Cells w/ cell walls in Hypotonic solution

A

Turgid (normal)

124
Q

Cells w/ cell walls in Isotonic solution

A

Flaccid

125
Q

Cells w/ cell walls in Hypertonic solution

A

Plasmolysis

126
Q

Osmosis in animal vs plant cells

A

Hypertonic solution
- Animal cells: Shrivelled (cells lose water and shrink) => lethal upon prolonged exposure
- Plant cells: Plasmolysis (lethal upon prolonged exposure)

Isotonic solution
- Animal cells: Optimum (normal) state
- Plant cells: Flaccid (not rigid enough)

Hypotonic solution
- Animal cells: Lysis (lethal immediately), b/c cells absorb water and burst
-Plant cells: Turgid (rigid) => Optimum (normal) state

127
Q

Active Transport

A

– Moves substances against their concentration gradient (from low concentration to high concentration) => allows cells to maintain concentration gradients that differ from their surroundings
– Requires energy, usually in the form of ATP
– performed by specific membrane
proteins (ion pumps, for ex: sodium-potassium (Na+/K+) pump)

128
Q

Structure of ATP:

A

adenine + ribose + 3 Phosphate groups

129
Q

Membrane potential -

A
  • voltage difference across a membrane, which is created by differences in the distribution of positive and negative ions
  • cytoplasm is negatively (-) charged compared to the outside
  • Μembrane potential acts like a battery and favors:
  • passive transport of cations (+) into the cell
  • passive transport of anions (-) out of the cell
130
Q

how Na+/K+ pump contributes to the creation and maintenance of the membrane potential

A

– transports 3 Na+ out and 2 K+ in = net transfer of one (+) charge out

131
Q

Electrochemical gradient -

A

combination of two forces driving the diffusion of an ion:
– a chemical force = the ion’s concentration gradient
– an electrical force = the effect of the membrane potential on the ion’s movement

132
Q

Electrogenic pumps -

A

transport proteins that generate voltage across a membrane => create membrane potential (Na+/K+ pump in animals) => E source

133
Q

Cotransport -

A

– Coupled transport of substances by a membrane protein (cotransporter)
– Active transport driven by indirect spending of E
– The concentration gradient of one substance indirectly drives the active transport of another substance

ex: passive transport of Η+ to the inside of the cell by diffusion coupled with active transport of sucrose

134
Q

Bulk transport of large macromolecules across the PM occurs by

A
  • exocytosis & endocytosis - transport of large macromolecules across the membrane using transport vesicles
  • Active transport processes: vesicle formation requires E
135
Q

Exocytosis

A
  • Transport of macromolecules packaged in vesicles from the inside of the cell to the outside via fusion of the transport vesicles with the plasma membrane

ex: pancreatic cells produce insulin and secrete it to the extracellular fluid by exocytosis

136
Q

Endocytosis -

A
  • Transport of macromolecules from the outside of the cell to the inside via formation of transport vesicles as a projection/extension of the plasma membrane to the inside of the cell (new vesicles form from PM)
137
Q

Three types of endocytosis

A
  • Pinocytosis: the intake of liquid or soluble material by the cell
  • Phagocytosis: the intake of solid/insoluble material by the cell or ingestion of whole cells (e.g. microorganisms)
  • Receptor-mediated endocytosis: the intake of specific molecules selected by a receptor
138
Q

Phagocytosis

A
  • cell engulfs a solid particle (macromolecule or microorganism) in a vacuole (phagosome/food vacuole) => it then fuses with a lysosome to digest the particle (phagolysosome formation)

ex: macrophages - Specialized immune cells that are able to engulf microorganisms: Cell membrane receptors recognize the microorganism => Pseudopodia are formed around the microorganism and enclose him into a vesicle (phagosome) => destruction by lysosomes

139
Q

Receptor-mediated endocytosis

A
  • Special type of endocytosis
  • Binding of ligands to receptors triggers vesicle formation

ex: cholesterol uptake by hepatocytes

Biology 103 1 sem (8 decks)

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