Lecture 2 - Non-Membranous Organelles and Nucleus

Question 1

Nucleus

Answer 1

Contains all genetic material as chromatin

Question 2

Chromatin

Answer 2

A complex of DNA and protein

Question 3

Nucleosomes

Answer 3

1st level of chromatin folding. Consists of 8 histone molecules. “bead on a string”.

Question 4

Euchromatin

Answer 4

Decondensed chromatin actively transcribed; light. Seen in neurons & liver cells.

Question 5

Heterochromatin

Answer 5

Chromatin is condensed and dark, metabolically inactive/not transcribing. Seen in lymphocytes and sperm.

Question 6

Characteristic pattern of heterochromatin near nuclear envelope most likely reflects interaction with what protein?

Answer 6

Lamins, Support nuclear envelope

Question 7

Nuclear envelope

Answer 7

double membrane; outer connected to rER, inner adjacent to nuclear lamina made of intermediate filaments

Question 8

Nucleolus

Answer 8

for rRNA synthesis; ribosomal subunits are partially assembled (some needed proteins are transported back into nucleus after being synthesized in the cytoplasm) = preribosomes are exported via nuclear pore complex = ribosomes finish self-assembly in the cytoplasm.

• Also regulates cell cycle and stain intensely with hematoxylin and basic dyes.

Question 9

Metabolic labeling of cells with 3H-uracil would show up localized where?

Answer 9

Nucleolus

Question 10

Nuclear Pores

Answer 10

Openings in nuclear envelope made by fusion of inner/uter membranes

Passive diffusion of small ions and molecules; active transport (GTP dependent) of proteins, RNA, large molecules via nuclear receptors; the pores open in response to Ca2+

Question 11

Nuclear Lamina

Answer 11

A fibrous, thin electron dense protein layer adjacent to the inner surface of nuclear envelope (between membrane and marginal heterochromatin).

Major components: lamins (intermediate filament that disassemble and reassemble during mitosis). Serves as scaffolding for chromatin, NP, protein, membrane.

Question 12

Cytoskeleton

Answer 12

3D internal skeleton of cell, highly conserved in all eukaryotes.

Function: support cytoplasm, cell movement, organelle movement, chromosome segregation, communication w/external environment.

Question 13

Three components of cytoskeleton

Answer 13

1. Microfilaments or Actin (6-8nm)
2. Intermediate filaments (8-10nm)
3. Microtubules (20-25 nm)

Question 14

Microfilaments (Actin Filaments)

Answer 14

• double-stranded linear helical array; polarized
• each filament made up of single G-actin molecules that hydrolyze ATP to make up F-actin
• function: cell shape, movement, remodeling surface during phagocytosis, muscle contraction (association with myosin), anchors cell to surface (stress fibers), facilitate cell division.

Question 15

What is the polarization of microfilaments (actin filaments)?

Answer 15

polarized: (+) end is barbed/fast-growing

(-) end is pointed/slow-growing = very mobile, constant assemble/disassemble = movement!

Question 16

Where are microfilaments located?

Answer 16

Concentrated beneath plasma membrane (forms terminal web) to give cell mechanical strength; extend into microvilli and stereocillia

Question 17

What happens to a cells microfilaments under stress?

Answer 17

If cell under physical stress, cell produces more actin filaments. In epithelial cells, form adhesion junction and cell cortex. In migrating cells, form filopodia and lamellipodium.

Question 18

Actin-bundling proteins

Answer 18

Cross-link actin filaments, create bundles (in microvillus, fascin and fimbrin are ABPs that cross-link actin filaments)

Question 19

Actin-capping proteins

Answer 19

Block further addition of actin by binding to free end (ie. tropomodulin)

Question 20

Actin motor proteins

Answer 20

Hydrolyzes ATP to provide energy for movement along actin filaments

Question 21

Thin and thick filaments

Answer 21

Actin, myosin, and ABPs form structural and functional relationship to make muscles contract.

Question 22

Treadmilling

Answer 22

New molecules added to + end, old molecules discarded at – end. Membrane extends because + end works much faster; cell changes shape and forms things like microvilli. Blue Actin Bundling Proteins bundle the growing filaments and Actin Capping Proteins keep the process stable.

Question 23

Intermediate Filaments

Answer 23

No polarity, very strong and stable, rope-like fibers.

Essential for cell-to-cell and cell-to-ECM junctions, main structural support of the cell, enable cells to withstand mechanical stress when stretched.

Self-assemble = no E needed

Question 24

What are intermediate filaments made of?

Answer 24

Variable Proteins - Long coiled-coil dimers form 8 staggered tertramers.

Question 25

What do intermediate filaments anchor to?

Answer 25

plasma membrane and desmosomes

Question 26

Where are intermediate filaments found?

Answer 26

Just beneath the inner nuclear membrane.

Question 27

What are some types of intermediate filaments?

Answer 27

Keratin (epithelial)
Neurofilaments (neurons)
Lamins (nuclear lamina)
Vimentin (mesenchyme cells)

Question 28

Microtubules

Answer 28

Nonbranching long hollow cylinders

Short lives, assemble/disassemble in minutes (dynamic instability)

Function: define cell polarity, vesicle transport, attach chromosome to mitotic spindle and move chromosomes, cell elongation and movement (migration), cilia/flagella

Question 29

What is the polarization of Microtubules?

Answer 29

(+) end growing and (-) end non-growing/embedded in MTOC (Centrosome)

Question 30

What is the structure of microtubules?

Answer 30

Polymers of tubulin dimers: alpha (-) and beta (+) tubulin join as dimers dimers add head-to-head into a linear chain called protofilaments 13 circularly arrayed protofilaments form a microtubule

Question 31

Microtubule-associated proteins (MAPS)

Answer 31

Modify speed of polymerization and depolymerization of a- and B- tubulin; anchor microtubules to specific organelles; cap at the (-) end. GTP is hydrolyzed to GDP as the tubule grows.

Question 32

What makes up a cilia?

Answer 32

Doublet microtubule

Question 33

What makes up centrioles and basal bodies?

Answer 33

Triplet microtubule (Delta and Epsilon tubulin)

Question 34

Colchicine/vincristine

Answer 34

Drugs that prevent microtubule polymerization (disrupt MAPs)

Question 35

Microtubule Motor Proteins

Answer 35

Attach to organelles/structures/vesicles and propels them on microtubule track.

Ex. Dyneins and Kinesins carry each other.

Question 36

Dynein

Answer 36

Type of motor protein that is fast and large with 1-3 heads. Runs towards the MINUS end (MTOC or cilia base).

This enables cilia movement = Axonemal dynein in cilia and flagella. Cytoplasmic dyneiens transport organelles along the microtubule. Also involved in pulling chromosomes apart in mitosis and meiosis.

Question 37

Kinesin

Answer 37

Motor protein that is slower and smaller with 1-2 heads, moves towards PLUS end.

Question 38

Centrosome

Answer 38

Pair of centrioles at 90-degree angle (mother has appendages)

Formed from 9 triplets of microtubules

Question 39

Pericentriolar Matrix (PCM)

Answer 39

Surrounds centrioles, anchors microtubules

Question 40

What forms basal bodies?

Answer 40

Centrioles

Question 41

Basal Bodies

Answer 41

Each cilium requires a basal body. So, like centrioles, are composed of 9 triplet microtubules.

Question 42

What can happen if microtubules dysfunction?

Answer 42

cancer, developmental defects, karagener’s disease, PKD, retinal degeneration

Question 43

Describe PKD

Answer 43

Membrane proteins sent to the cilia in renal epithelial cells by MTs. These epithelial cells line the lumen of the urinary collecting ducts and sense the flow of urine. Failure in flow-sensing signaling results in apoptosis resulting in cysts