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abs - histology > Cell Organelles > Flashcards

Cell Organelles Flashcards

1
Q

What are free ribosomes?

A

typically synthesis cytosolic and cytoskeletal proteins (e.g. microtubules, intermediate filaments) and proteins for import into the nucleus, mitochondria and peroxisomes

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2
Q

What are the ribosomal components of the RER?

A

typically synthesis proteins that may require further processing before incorporation into membranes, stored in lysosomes or eventually secreted from the cell.

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3
Q

Movement of polypeptides in the RER

A

1) The nascent polypeptide contains a signal peptide (red) that binds a signal recognition particle (SRP) (red) which inhibits further polypeptide elongation.
2) The SRP-ribosome-nascent peptide complex binds a SRP receptor (black) on the ER membrane.
3) SRP (red) releases the signal peptide (red) allowing translation to continue and translocation through the ER membrane.
4) Inside the RER lumen the signal peptide is removed.

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4
Q

What are the functions of the ER?

A

1) Cleavage of signal peptide
2) Protein folding
3) Attachment of oligosaccharides
4) Smooth ER synthesize phospholipids, fats, and steroids
5) Has enzymes responsible for detoxification of drugs and other harmful substances

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5
Q

Protein folding in the RER

A

1) The signal peptide(red) is cleaved by signal peptidase.
2) The elongating polypeptide (green) pushes itself into the lumen and concurrently is pulled by chaperone proteins into the ER lumen.
3) Upon release the maturing polypeptide chain undergoes proper folding and posttranslational modifications.
4) Proteins that cannot be properly folded are translocated into the cytosol, conjugated to ubiquitin and degraded by proteosomes.

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6
Q

explain the posttranslational modification in the RER including initial (core) glycosylation of asparagine (Asn) residues of glycoproteins

A

Saccharide moieties are attached to dolichol (lipid) through a pyrophosphate linkage (one phosphate linked to dolichol, and the second phosphate is linked to the saccharide) which is then transferred to the asparagine residue of nascent polypeptide chains.

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7
Q

Vesicular transport between the RER and Golgi is regulated by?

A

COPs; Coat protein-II (COP-II) promotes forward movement of vesicles while COP-I promotes retrograde movement of vesicles. The KDEL receptor mediates the retrieval of misfolded proteins from the Golgi apparatus back to the ER.

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8
Q

The mannose-6-phosphate marker, added in the cis Golgi determines?

A

segregation to lysosomes

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9
Q

During synthesis of lysosomal proteins addition of M6P in the Golgi targets?

A

proteins to lysosomal vesicles

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10
Q

Acid hydrolases in primary lysosomes exhibit optimal enzymatic activity at what pH? whereas they are largely inactive at pH _____ (cytosolic). Hence, primary lysosomes must fuse with other membrane bound organelles to maintain optimal hydrolytic activity when forming?

A

pH 5; pH 7.2; secondary lysosomes.

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11
Q

What forms from the fusion of a primary lysosome and another vesicle?

A

Secondary vesicles

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12
Q

Peroxisomes Generates H202: RH2 + O2 to R + H202 which oxidizes?

A

harmful substances
Detoxifies alcohol and other
harmful chemicals

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13
Q

Peroxisomal enzymes perform?

A

β-oxidation of long-chain fatty

acids (first step of catabolism)

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14
Q

Evidence for a Prokaryote Origin of Mitochondria

A
  1. Each mitochondrion contains its own small circular chromosome of DNA (just like prokaryote organisms), ribosomes, mRNA and tRNA, all similar to corresponding bacterial components.
  2. New mitochondria originate by fission (like prokaryotes) from pre-existing mitochondria (i.e. not by mitosis).
  3. Each mitochondrion has a double membrane, the outer from the ancestral host cell, the inner from the symbiotic prokaryote.
  4. The closest relatives of mitochondria (genotyping) are the rickettsia bacteria, which are modern-day intracellular parasites of eukaryotic cells.
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15
Q

Elementary particles act as

A

proton pumps that facilitate the synthesis of ATP

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16
Q

Flow of protons down the electrochemical gradient through the elementary particles causes?

A

rapid rotation of specific polypeptides (rotor)

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17
Q

The mechanical energy of protein rotation is converted to

A

stored chemical energy by the synthesize ATP. Protons are then actively pumped back into the intermembrane space and the cycle repeats.

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18
Q

Mitochondria synthesize most ATP during ___ ___ and sequester excess _____ ____

A

aerobic respiration; cytoplasmic calcium

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19
Q

Damaged mitochondria release?

A

calcium

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20
Q

Melanosomes:

A

membrane enclosed granule containing melanin

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21
Q

Lipofuscin:

A

membrane enclosed lipid-containing residues of lysosomal digestion, aka type of residual body (tertiary lysosome)

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22
Q

two types of pigment granules?

A

melanosomes and lipofuscin

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23
Q

Four types of cytoplasmic inclusions

A

melanosomes, lipofuscin, glycogen and lipid

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24
Q

Cytoplasmic Inclusion: Glycogen

A

stores of glycogen are an energy source whereby glycogenolysis degrades glycogen into individual molecules of glucose, no membrane

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25
Q

Cytoplasmic Inclusion: Lipid

A

triglycerides in storage form

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26
Q

Actin consists of ?

A

globular monomers (G) that assemble in the presence of K+ and Mg2+ into a double stranded helix of filamentous (F) actin.

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27
Q

Monomers are added to the plus end of actin during?

A

assembly and dissociate from the minus end during disassembly.

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28
Q

Functions of Actin (4)

A
  • Intracellular movement
  • Muscle contraction
  • Membrane structures - microvilli and stereocilia
  • Locomotion - cell cortex - cortical flow model
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29
Q

Actin filaments in cells firmly attached to a substrate form?

A

stress fibers that play a role in contractility (cell shape) and motility of the entire cell and/or organelles within the cell.

30
Q

Actin filaments have a structural role by forming?

A

the terminal web attached to zonula adherens underlying the apical cytoplasm.

31
Q

Actin filaments within microvilli and stereocilia anchor into the

A

terminal web

32
Q

Migrating cells may exhibit finger-like projections (red) of actin filled ___.

A

filopodia; Filopodia also have roles in sensing, locomotion and cell-cell interaction. Actin filaments are also essential for process extensions such as dendrites and axons in neurons.

33
Q

Actin filaments are also essential for process extensions such as?

A

dendrites and axons in neurons

34
Q

Microtubules are a

A

heterodimer of α and β subunits. Free dimers may polymerize to form a microtubule with a slight spiral organization and polarity (+ and – ends).

35
Q

Microtubules may exist as (3)

A
  1. individual fibers
  2. grouped as doublets with other proteins in cilia
  3. as a triplets in centrioles.
36
Q

Microtubule fibers individually can be observed as?

A

the mitotic spindle (red) of dividing cells, and also in the axons of neurons and variously distributed in the cytoplasm of most cells

37
Q

Microtubule fibers can also function as

A

structures (railway tracks) that are used to transport synaptic vesicles in neurons

38
Q

An axoneme describes the organization of microtubules into doublets and partial doublets with other proteins to form?

A

the core of cilia (flagella) and the sperm tail

39
Q

A centriole describes the organization of microtubules into?

A

triplets

40
Q

Two orthogonal centrioles constitute a centrosome.

A

centrosome

41
Q

Pairs of centrioles (a centrosome) are also described as

A

microtubule organizing centers (MTOC) in mitotic cells, which nucleate the mitotic spindle

42
Q

A basal body is a centriole that

A

nucleates the axoneme of cilia

43
Q

Three forms of microtubule structures

A
  1. Microtubule fibers
  2. axoneme
  3. centrioles
44
Q

Centrioles in the form of basal bodies and centrosomes (paired centrioles) give rise to

A

microtubules

45
Q 
Dominant Microtubule
Organizing centers (MTOC) are the centrosome which
A

act as nucleating sites for polymerization

46
Q

Microtubules are responsible for

A

axonal transport

47
Q

Motile cilia:

A

contain a central doublet of microtubules

48
Q

Primary cilia:

A

lack a central doublet of microtubules, non-motile, sensory function (e.g. olfactory epithelium neurons)

49
Q

Cilia:

A

Ineffective ciliary movement impairs mucociliary clearance resulting in mucus retention. This predisposes to recurrent chest infections, which may progress to bronchiectasis.

50
Q

Types of Intermediate Filaments (4)

A
  1. Nuclear lamins
  2. Vimentinlike proteins
  3. Keratins
  4. Neuronal Intermediate
51
Q

Component polypeptides in Nuclear Lamins and their cellular location

A

lamins A, B and C; nuclear lamina of eukaryotic cells

52
Q

Component polypeptides in Vimentinlike proteins and their cellular location

A

vimentin; many cells of mesenchymal orgin, often expressed transiently during development
desmin; muscle
glial fibrillary acidic protein; glial cells (astrocytes and Schwann cells)
peripherin; neurons

53
Q

Component polypeptides in Keratins and their cellular location

A

type I (acidic) and type II (neutral/basic); epithelial cells and their derivatives (e.g. hair and nails)

54
Q

Component polypeptides of neuronal intermediate and their cellular location

A

neurofilament proteins NF-L, NF-M and NF-H; neurons

55
Q

Keratin filaments (red) attach to

A

desmosomes to form a framework within the cytoplasm

56
Q

Accumulation of keratin in the epidermis provides a barrier to

A

reduce dehydration in terrestrial vertebrates

57
Q

Keratins consist of at least 30 isoforms which can

A

vary in expression in different grades of tumor cells

58
Q

Zonula occludens (tight junctions) form a?

A

band encircling the apical end of the cell.

59
Q

Zonula occuludens prevent?

A

movement of molecules between the lumen and intercellular space. Hence, they maintain a polarity between the apical and basolateral space. Molecules crossing an epithelial sheet must pass through a cell rather than between/around the cells

60
Q

Zonula occludens form a seal between

A

opposing cell membranes due to interactions between transmembrane proteins, claudin and occludin, of each cell.

61
Q

Zonula adherens encircle? and It functions to?

Cell adhesion is mediated by cadherin proteins. The cadherins bind catenin that is linked via actin-binding proteins to actin filaments (green). These actin filaments form the terminal web that help to anchor actin filaments originating from microvilli at the apical pole of epithelial cells.

A

epithelial cells immediately below the zonula occludens; anchor cells to each other.

62
Q

Cell adhesion is mediated by? The cadherins bind?

A

cadherin proteins; catenin that is linked via actin-binding proteins to actin filaments. These actin filaments form the terminal web that help to anchor actin filaments originating from microvilli at the apical pole of epithelial cells.

63
Q

Desmosomes (macula adherens) form?

A

“spot welds” around the cell perimeter for attachment of cells to each other

64
Q

A half-desmosome (hemi-desmosome) anchors?

A

the basal cytoplasm to the basal lamina of the basement membrane (basal lamina plus lamina reticularis)

65
Q

Neurons have specialized desmosome-like structures

A

called synaptic clefts where neurotransmitters are released.

66
Q

Each desmosome consists of

A

transmembrane interacting proteins, desmoglein and desmocollin (cadherin family) that insert into a dense attachment plaque (red) consisting of anchoring proteins, plakoglobin and desmoplakin that then binds keratin.

67
Q

In hemi-desmosomes, cadherins are replaced with

A

integrins to anchor the cell to the basal lamina

68
Q

Gap junctions mediate? Small molecules (e.g. sodium, potassium, chloride) pass through channels less than in size to mediate signal transduction for coordinated function such as rhythmic contractions. Because of this property they can be used to rapidly transmit electrical signals between cells, e,g, neurons).

A

rapid communication between cells

69
Q

Small molecules (e.g. sodium, potassium, chloride) pass through channels less than ____ in size to mediate signal transduction for coordinated function such as ____ _____. Because of this property they can be used to?

A

1.5 nm; rhythmic contractions; rapidly transmit electrical signals between cells, e,g, neurons).

70
Q

In gap junctions, six connexin proteins form a _____. Two aligned connexons form an open channel between cells. The connexons have a hydrophilic core.

A

connexon

71
Q

Two aligned connexons form an?

A

open channel between cells; The connexons have a hydrophilic core.

abs - histology (9 decks)

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