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IMMS > Cell Ultrastructure > Flashcards

Cell Ultrastructure Flashcards

1
Q

Nucleus function

A

Largest membrane bound organelle
Storage and transmission of genetic information
Information coded in the DNA synthesises the protein determining the structure and function of the cell

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2
Q

Nucleus structure

A

Double membrane (nuclear envelope) with gaps called nuclear pores
RNA moves out via pores
DNA and proteins form chromatin- a mass of genetic material
At cell division chromatin becomes chromosomes and condenses
Nucleolus

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3
Q

Nucleolus

A

No membrane
Site of DNA transcription
Forms ribosomal RNA (rRNA)

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4
Q

Mitochondria function

A

Site of oxidative -phosphorylation

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5
Q

Mitochondria structure

A

Outer membrane- lipid synthesis and fatty acid metabolism
Inner membrane- respiratory chain (electron transport)
Matrix- Krebs cycle
Intramembranous space- nucleotide synthesis (ADP-ATP)

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6
Q

Vesicles structure

A

Very small spherical membrane bound organelles which transport and store material and exchange cell membrane between compartments

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7
Q

Vesicles types

A

Cell-surface derived pinocytotic and phagocytotic vesicles, Golgi- derived, ER-derived, lysosomes, peroxisomes
• Lysosomes - derived from Golgi, site at which proteins are degraded. H+-ATPase on endosome membrane creates low internal pH5, contain acid hydrolases that degrade proteins, formed by fusion of hydrolase vesicles and endosomes. Contain digestive enzymes
• Peroxisomes - small membrane-bound organelles containing enzymes which oxidise long-chain fatty acids. Involved in process by which fatty acids are broken down to generate ATP. Toxic hydrogen peroxide broken down by peroxisomes

Endosome- membrane bound vesicular tubular structures that live between Golgi and membrane

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8
Q

Vacuole function

A

Hold various solutions or material- can have been created, stored or excreted and that have been phagocytosed or engulfed

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9
Q

Vacuole structure

A

Chamber surrounded by a membrane- semi-permeable that only lets certain molecules through

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10
Q

Golgi apparatus structure

A

Parallel stacks of membrane
Located close to the nucleus
In most cells cannot be seen- very clear in plasma cells (perinuclear hoff)
3 parts: cis-Golgi, medial and trans-Golgi

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11
Q

Golgi apparatus function

A

Processes and modifies macromolecules synthesised in the endoplasmic reticulum

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12
Q

Cis-Golgi

A

Nuclear facing- receives from rER
protein phosphorylation occurs here

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13
Q

Medial Golgi

A

Modifies producers by adding sugars
Forms complex oligosaccharides by adding sugars to lipids and peptides

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14
Q

Trans-Golgi

A

Proteolysis of peptides into active forms and sorting of molecules into vesicles which bud from the surface

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15
Q

Rough endoplasmic reticulum structure

A

Rough due to ribosomes on surface
Highly folded flat membrane sheet

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16
Q

Rough endoplasmic reticulum function

A

Site of protein synthesis

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17
Q

Smooth endoplasmic reticulum structure

A

Highly folded, flattened membrane sheets

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18
Q

Smooth endoplasmic reticulum function

A

Site of lipid synthesis
Proteases and store synthesised proteins

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19
Q

Ribosome structure

A

2 subunits attached to the rER

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20
Q

Ribosome function

A

Acts as a large catalyst
Translate genetic code into chains of amino acids
Deposits protein into the rER to undergo further modification
3-5 amino acids per second in protein production

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21
Q

Cytoplasm function

A

Site of glycolysis

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22
Q

Cytoplasm structure

A

Fluid that fills the cell, includes the cytosol and filaments, proteins, ions and macromolecular structures as well as organelles. NA the nucleus

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23
Q

3 components of cytoplasms:

A
  1. Cytoskeleton with associated motor proteins
  2. Organelles and other multi proteins complexes
  3. Cytoplasmic inclusions and dissolved solute
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24
Q

Plasma membrane function

A

Controls passage of various molecules
Physical barrier
Selective permeability
Endo-/exocytosis
Cell signalling

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25
Q

Plasma membrane structure

A

Double layer of phospholipids (hydrophobic head and hydrophilic tail)

5 types attached to phosphate group:
1. Serine (PS- phosphatidyl-serine)
2. Choline (PC- phosphatidyl-choline)
3. Inositol (PI- phosphatidyl-inositol)
4. Ethanolamine (PE- phosphatidyl-ethanolamine)
5. Sphingomyelin (SM)

Cholesterol
Membrane proteins 9receptors/channels)
Carbohydrate groups which attach to proteins to form glycoproteins or glycolipids
Sphingolipids

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26
Q

Microtubules

A

25 nm
Eg tubulin (alpha and beta which arrange into groups of 13 to form hollow tubes)
Arise from centromere
Found in all cells (except erythrocytes as have no nucleus so no cell division)

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27
Q

Intermediate filaments

A

10nm
6 protein types
Anchored transmembrane proteins which can spread through tissues

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28
Q

6 types of intermediate filaments

A
  1. Cytokeratins: epithelial cells.
  2. Desmin: myocytes.
  3. Glial fibrillary acidic protein: astrocytic glial cells.
  4. Neurofilament protein: neurons.
  5. Nuclear laminin: nuclei of all cells.
  6. Vimentin: mesodermal cells.
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29
Q

Microfilaments

A

5nm
Actin forms a mesh (cell cortex) on inner surface of cell membrane

Globular G-actin polymerises into filamentous F-actin.

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30
Q

Centrosome structure

A

Made from 2 centrioles which are microtubules rings

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31
Q

Centrosome function

A

Organise microtubules and provide structure for cell
Pull chromatids apart during cell division

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32
Q

Lysosomes

A

Contain digestive enzymes
Waste disposal system and site of breakdown for most molecules
Derived from Golgi
H+ ATPase on membrane creates low pH (pH5) to enable acid hydrolysis to function

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33
Q

Endosomes

A

Membrane bound vesicular and tubular structure that live between Golgi and membrane

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34
Q

Peroxisomes

A

Small membrane bound organelles containing enzymes which oxidase long chain fatty acids
Involved in process by which fatty acids are broken down to generate ATP
Hydrogen peroxide is toxic to cells by destroyed by peroxisomes

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35
Q

Tight junctions

A

Seals neighbouring cells together i in an epithelial sheet to prevent leakage

prevent diffusion between cells- can establish a gradient for absorption or secretion of molecules from or into the gut and act as a barrier as only water and some small molecules can pass through

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36
Q

Adherens

A

Joins an actin bundle in one cell to a similar bundle in another cell

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37
Q

Desmosomes

A

Joins the intermediate filaments in one cell to a neighbour

plaques that form physical joints between cells and connect the cytoskeletons of adjacent cells - spread forces across several cells eg in epithelia exposed to abrasive forces, skin.

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38
Q

Gap junctions

A

Allows passage of small water soluble ions and molecules so cells are electrically coupled

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39
Q

Hemi-desmosomes

A

Anchor intermediate filaments in a cell to the basal lamina

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40
Q

Where are cytokeratins found

A

Epithelial cells

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41
Q

Where is desmin found

A

Myocytes

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42
Q

Where is vimentin found

A

Mesodermal cells

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43
Q

Where is nuclear laminin found

A

Nucleus of all cells

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44
Q

Where is neurofilament protein found

A

Neurones

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45
Q

Where is glial fibrillary acidic protein found

A

Astrocytic glial cells

46
Q

Anti-phospholipid syndrome

A

• systemic auto-immune disease
• Antibodies bind to beta 2-glycoprotein-1 on cell membranes
• Initiates inappropriate blood clotting (thrombosis)
• Significant cause of pregnancy morbidity and early miscarriage

47
Q

Fluid-mosaic model

A

mosaic as a mix of membrane proteins free to move in a sea of lipid

48
Q

Why are membranes important

A

• cell signalling - source of lipid processors
• cell polarisation
• compartmentalisation - ionic gradients, diffusion, membrane potential
• tightly regulated - disease disrupts this
• Endo/exocytosis
• Physical barrier
• Selective permeability to control passage of molecules
• Anchors cell to extracellular matrix and adjacent cells

49
Q

Glycerophospholipids

A

amphipathic (hydrophobic and hydrophilic)
Fatty acid tails:
• non-polar, hydrophobic,
• saturated C-C bonds,
• unsaturated cis C=C bonds lead to kink in hydrophobic tail
• significant variation in length
Glycerol backbone (3C)
Phosphate group- negative charge at physiological pH (polar, hydrophilic)

50
Q

Function of lipid bilayer

A

• form compartments
• allow lipid-soluble substances to enter + leave cell
• prevent water-soluble substances entering + leaving cell
• make membrane flexible and self-sealing

51
Q

5 types of phospholipid in membrane

A
  1. Serine (PS- phosphatidyl-serine)
  2. Choline (PC- phosphatidyl-choline)
  3. Inositol (PI- phosphatidyl-inositol)
  4. Ethanolamine (PE- phosphatidyl-ethanolamine)
  5. Sphingomyelin (SM)
52
Q

Lipid bilayer

A

Leaflet specific orientation
Leaflet ‘flip’- thermodynamically unstable
Outer layer: Sphingomyelin and enriched for PC
Inner layer: enriched for PE. PS (signal for apoptosis) and PU majority in inner leaflet

53
Q

Membrane fluidity

A

• movement of phospholipids and proteins
• Facilitates inter- and intra-cellular signalling (phosphoatidylinositol)
• Temperature and structure dependent phase transitions

54
Q

Cholesterol in membrane

A

Very hydrophobic
Fit between the phospholipids and bind to the hydrophobic tails, causing them to pack more closely together. This restricts the movement of the phospholipids, meaning the membrane is less fluid and more rigid

55
Q

Function of cholesterol in membrane

A

• reduce lateral movement of other molecules
• make membrane less fluid at high temperatures
• prevent leakage of water + dissolved ions
• help cell maintain shape e.g. Red blood cells which aren’t supported by other cells as free in blood

56
Q

How can substances cross epithelial

A

Substances can cross epithelial by paracellular pathway (between adjacent cells)- limited by presence of tight junctions- or transcellular pathway (moves into epithelial cell diffuses through cytosol and exits across opposite membrane)

57
Q

Paracellular pathways

A

between adjacent cells)- limited by presence of tight junctions

58
Q

Trans cellular pathway

A

moves into epithelial cell diffuses through cytosol and exits across opposite membrane

59
Q

Epithelia

A

• require polarisation of plasma membrane - apical vs basolateral surfaces
• permits cell specific function - secretion/absorption
• strongly adhere to neighbours - tight junctions
• Eg parietal cell (gastric pits), intestinal epithelium, nephron

60
Q

Apical membrane

A

Lumen side of epithelial

61
Q

Basolateral membrane

A

Blood side of epithelial

62
Q

Proteins in membrane

A

Interspersed throughout cell-surface membrane
Embedded in 2 ways:
1. peripheral membrane proteins occur in the surface of bilayer and don’t extend completely across it. Act to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules such as hormones
2. integral proteins- span whole width of bilayer and are protein channels or carriers. Channels form water-filled tubes to allow water-soluble ions to diffuse across. Carrier proteins bind to ions or molecules e.g. Glucose/Na+, then change shape in order to move these across the membrane

63
Q

Peripheral membrane proteins

A

occur in the surface of bilayer and don’t extend completely across it. Act to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules such as hormones

64
Q

Integral proteins in membrane

A

span whole width of bilayer and are protein channels or carriers. Channels form water-filled tubes to allow water-soluble ions to diffuse across. Carrier proteins bind to ions or molecules e.g. Glucose/Na+, then change shape in order to move these across the membrane

65
Q

Function of proteins in membrane

A

• provide structural support
• act as channels transporting water-soluble substances across the membrane
• allow active transport through carrier proteins
• form cell-surface receptors for identifying cells
• help cells adhere together
• act as receptors e.g. For hormones

66
Q

Glycoproteins in membrane

A

Carbohydrate chain attached to extrinsic proteins on outersurface of membrane
Functions:
• act as recognition sites
• help cells attach to eachother, forming tissues
• allow cells to recognise one another e.g. Lymphocytes

67
Q

Glycolipids in membrane

A

Carbohydrate section extends from phospholipid belayer to get as a cell-surface receptor for specific chemicals e.g. ABO blood system
Functions:
• act as recognition sites
• help maintain stability of membrane
• help cells attach to eachother, forming tissues

68
Q

Membranes and pH

A

• both extremes damage protein
• Inhibits cell function critical role for acid:base homeostasis- plasma Ca2+ and cell membrane excitability/permeability

69
Q

Temperature and membranes

A
  1. Below O°C = phospholipids are rigid and closely packed together as have little energy. Channel + carrier proteins deform, increasing permeability. Ice crystals may form and pierce membrane. Also, slower rate of diffusion
  2. Between 0-45°C = more energy so phospholipids move around more- membrane more permeable
  3. Above 45 °C = bilayer starts to melt + breakdown, membrane more permeable. Proteins in membrane begin to denature, damaging membrane
70
Q

Lethal triad

A

Hypothermia
Reduced coagulation
Acidosis

71
Q

Membrane permeability

A

• phospholipid bilayer modified by- C=C bonds, cholesterol, temperature
• Freely permeable- water (aquaporins), gases (eg CO2, N2, O2), small uncharged polar molecules (eg ammonia, urea, ethanol)
• Impermeable to- ions, charged polar molecules (eg ATP, glucose-6-phosphate), large uncharged polar molecules (eg glucose)

72
Q

Uniport membrane proteins

A

Transport single substance
Passive
Eg glucose via Glut-1

73
Q

Anti port membrane proteins

A

2 substances in opposite directions.
Energy from ATP hydrolysis
eg 3 Na+/ 2 K+ ATPase

74
Q

Symport membrane protein

A

2 or more substances in the same direction.
Indirectly from ATP hydrolysis, ion gradient used
eg Na+/ glucose nutrient transport

75
Q

Ion channels

A

• integral membrane protein
• Alpha-helix
• Hydrophobic amino acids interface with hydrophobic phospholipid tail.
• Hydrophilic pore for ion passage
• Selective: Charge and I on size
• Gated (usually)

76
Q

What substances move via simple diffusion

A

Ketone bodies, blood gases, water (aquaporin), NH3, urea, free fatty acids

77
Q

What substances move via facilitated diffusion

A

Glucose (GLUT-1), GLUT family

78
Q

What substances move via primary active transport

A

Ions (Na+, K+, Ca2+, H+, HCO3-), Water-soluble vitamins- Energy direct from ATP

79
Q

What substances move via secondary active transport

A

Ions (renal tubule; fluid balance), Symporters (Na+ + X)- Indirect energy from ion gradient

80
Q

What substances move via ion channels

A

Voltage gated, leak channels

81
Q

What substances move via pino-/phagocytosis

A

Vesicles

82
Q

Diffusion

A

NET movement of particles from an area of high concentration to an area of low concentration
• Down the concentration gradient
• Random movement caused by natural kinetic energy of particles (thermal motion)
• Passive process so equilibrium is reached
• O2 and CO2 can diffuse through membrane as small and non-polar so lipid-soluble
• Flux = amount of material crossing a surface in a unit of time

83
Q

Flux

A

amount of material crossing a surface in a unit of time

84
Q

Factors affecting rate of diffusion

A

• steepness of concentration gradient (Co-Ci) = greater difference in concentration means a greater difference in the number of molecules passing in the 2 directions so faster rate
• temperature = particles have more kinetic energy so move faster meaning a faster rate
• surface area (A) = greater the surface area, the greater the number of particles that can diffuse across at any one moment so a faster rate, e.g. Microvilli, root - hair cells
• thickness of exchange surface (P) = the thinner the exchange surface, the faster the rate

85
Q

Facilitated diffusion

A

• Large or charged particles diffuse through carrier or channel proteins in the membrane
• Carrier proteins: high specific e.g. For glucose only
1. When a specific molecule is present, it binds with the protein
2. this causes the carrier protein to change shape in such a way that the molecule is released to the inside of the membrane
3. The carrier then returns to its original shape
• Channel proteins: form hydrophilic pores in the membrane for charged particles, e.g. Ions, to diffuse through
• Specific to water-soluble ions. The channels are selective, opening when the ion binds to it, causing it to change shape in a way that opens one side and closes the other- ‘gated’
• Aquaporin = water channel protein

86
Q

Factors affecting rate of facilitated diffusion

A

• concentration gradient
• number of channel or carrier proteins = when all are saturated, Vmax is reached

87
Q

Which cells have a high number of carrier proteins

A

Neuron, kidney and muscle cells

88
Q

Osmosis

A

the NET movement of water from a high water potential to a low water potential through a partially permeable membrane
Passive process due to kinetic energy of particles
Water potential = the concentration of soluble molecules in a solution (the tendency of water to move out of solution)
Water = 0 kPa
Water + solute = -x kPa
Osmolarity = total solute concentration of a solution

89
Q

Factors affecting rate of osmosis

A

• water potential gradient
• thickness of exchange surface
• surface area
• Type and number of aquaporin channels

90
Q

Hypertonic solution

A

Water moves out of cell into solution
Cell shrinks

91
Q

Hypotonic solution

A

Water moves into cell from solution
Causes cell to swell

92
Q

Isotonic

A

No NET movement of water

93
Q

Osmolarity

A

Total solute concentration of a solution

94
Q

Water potential

A

The tendency of water to move out of a solution

95
Q

Active transport

A

the movement of molecules or ions from a region of low concentration to a region of high concentration, against the concentration gradient, using ATP and carrier proteins
1. The carrier proteins span the plasma membrane and a specific molecule or ion binds to the receptor site
2. On the inside of the cell/organelle, ATP binds to the protein, causing it to split into ADP + Pi. As a result, the protein molecule changes shape and opens to the opposite side of the membrane, releasing the molecule/ion
3. The phosphate molecule is released from the protein, which causes the protein to revert back to its original shape

96
Q

Factors affecting rate of active transport

A

• speed of individual carrier proteins
• number of carrier proteins present
• rate of respiration- availability of ATP

97
Q

Two means of coupling energy to transporters

A

-direct use of ATP in primary active transport (eg Na+/K+ pump)
-the use of an electrochemical gradient across a membrane to drive the process in secondary active transport (eg co transport)

98
Q

Cotransport

A

the coupled movement of two different substances together across a cell membrane via a carrier protein e.g. Amino acids or glucose with Na+ in the mammalian ileum
1. Sodium ions are actively transported out of the epithelial cells, by the Na+/K+ pump, into the blood
2. This establishes a concentration gradient - the higher concentration of Na+ in the lumen of the ileum than inside the cell
3. Sodium ions then diffuse down their conc gradient into the epithelial cell, via a sodium-glucose co-transporter protein, carrying a glucose molecule with it
4. The concentration of glucose is now higher in the cell than the blood, so glucose diffuses by facilitated diffusion into the blood

99
Q

Secondary active transport

A

the downhill flow of an ion is linked to the uphill movement of a second solute either in the same direction as the ion (cotransport) or in the opposite direction of the ion (countertransport).

100
Q

Endocytosis

A

small pockets that pinch off the plasma membrane to produce intracellular, membrane bound vesicles that enclose a small volume of extracellular fluid

101
Q

3 types of endocytosis

A

Pinocytosis
Phagocytosis
Receptor-mediated endocytosis

102
Q

Pinocytosis

A

endocytosis vesicle encloses a small volume of extracellular fluid. Nonspecific. Usually contains ions, nutrients or small molecules

103
Q

Phagocytosis

A

cells engulf bacteria or large particles such as cell debris from damaged tissues (pseudopodia fold around particle)

104
Q

Receptor-mediated endocytosis

A

molecules bind to receptors on plasma membrane, causing it to undergo a conformational change which triggers endocytosis.

105
Q

Exocytosis

A

membrane-bound vesicles in cytoplasm fuse with plasma membrane and release their contents to outside of the cell
Allows portions of membrane to be replaced and secretion of synthesised molecules from cell

106
Q

Nernst equation

A

Determines diffusion potential

107
Q

Cholera

A

Cholera toxin modifies GPCR —> increases cAMP —> increases ion transporters in cell membrane —> increases secretion of ions and H2O into gut —> diarrhoea and dehydration

108
Q

GPCRs

A

Receptor- primary specificity
G protein - secondary specificity- determines 2nd messenger
Gs —> AC —> increases cAMP
Gi—| AC —> decreases cAMP
Gq —> PLC —> DAG + IP3

109
Q

Which 3 types of cell are called professional antigen presenting cells

A

B cells
Dendritic cells
Macrophages

110
Q
  1. What are the 3 types of cytoskeleton and what size are they each?
A
  1. Types of cytoskeleton filaments: actin 5nm, intermediate filaments eg desmin/nuclear laminin/vimentin/keratin 10nm, microtubule 25nm
111
Q

Which one of the following is the role of the trans golgi in a cell?

A

Proteolysis of peptides and packages them into vesicles

IMMS (6 decks)

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