MODULE 1: Cells Flashcards
Cytosol
metabolic pathways, protein synthesis, cytoskeleton
Cytosol is the intra-cellular fluid that is present inside the cells (cytoplasm is a cell component, not fluid)
Nucleus
DNA and RNA synthesis
Endoplasmic Reticulum
synthesis for lipids, proteins (for distribution to many organelles and plasma membrane)
Lysosomes
intracellular degradation
Highly acidic organelles that contain hydrolytic enzymes that degrade proteins, nucleic acids, oligosaccharides and lipids
- Lysosome acidity is maintained by a proton pump
- Membrane proteins are highly glycosylated to protect the membrane from digestion by the hydrolases
- Membrane contains metabolite transporters to transfer final products of digestion (amino acids, sugars, nucleotides) to the cytosol where they can be excreted/used by cell.
Endosome
sorting endocytosed (vesicled) material
Mitochondria
powerhosue of cell; ATP synthesis by oxidative phosphorylation
phosphorylation
how ADP + P –> ATP
Golgi apparatus
modification, sorting, packaging of proteins and lipids for either secretion or delivery to another organelle
Chloroplast
(in plants) ATP synthesis and carbon fixation by photosynthesis
Peroxisomes
Organelles that help with Oxidation of toxic molecules
Where are cellular proteins synthesized?
On the cytoplasmic ribosomes (except the few mitochondrial proteins)
How do proteins know to go to the right organelle?
They have amino acid sequences and signal. sequences, which are recognized by receptors that target them
How is orientation of protein determined across the membrane of an ER?
Internal hydrophobic stop/start sequences.
How do proteins go through the nuclear membrane?
Mediated by nuclear pores, the nuclear localization signal is recognized by the nuclear import receptor that interacts w/ cytosolic fibers from the pore.
How do proteins import into the mitochondria?
Same as nucleus mostly. Signal recognized by OUTER membrane receptor that brings protein to OUTER membrane translocator that interacts w INNER translocator to import protein.
What is ER quality control?
Chaperones (like calnexin) fix misfolded proteins
What is the Unfolded Protein Response? (UPR)
Sensors detect a misfolded protein in the ER and induce:
1) ER expansion
2) Gene activation of chaperones and other proteins associated with ER quality control
3)Inhibition of protein synthesis to prevent accumulation of more unfolded proteins.
4) IF ER can’t cope, UPR directs the cell to (cell-f) self-destruct vis apoptosis
Apoptosis
Cell dies in these steps:
Cell shrinks.
Cell fragments.
Cytoskeleton collapses.
Nuclear envelope disassembles.
Cells release apoptotic bodies.
Secretory Pathways
newly made lipids and proteins delivered from the ER via the Golgi to the cell surface and exocytosis
(ER -> Golgi -> PM)
Endocytic Pathway
internalization of extracellular material at the cell surface that is targeted first to endosomes and then to lysosomes for degradation
(PM -> Endosomes -> lysosomes)
Golgi main functions after proteins are delivered to the CIS face:
- Protein modification
- Protein targeting
Protein modification
As proteins traverse the Golgi stack, their oligosaccharides (large saccharides) are modified generating complex oligosaccharides
*Most multiple and varied glycan (sugar) modifications in the cell are made in the Golgi apparatus
Protein Targeting
after traversing Golgi, proteins exit the TRANS face of the Golgi stack in transport vesicles for delivery to different cellular destinations
What causes Diabetes?
Defective Insulin Secretion. Endocrine insulin secreting B cells store insulin in granules that are released following a large meal in response to increased glucose levels.
What are Exocrine acinar cells?
Cells in the pancreas that secrete digestive enzymes into the gut to aid in proper digestion
Constitutive Exocytosis
Vesicles buf grom the TGN (trans-Golgi network) and fuse directly with the plasma membrane.
Regulated Exocytosis
TGN vesicles fuse with a secretory vesicle toast only fuses with the plasma membrane upon receiving receipt of an extracellular signal. Ionic conditions in the TGN induce protein aggregation that facilitates packaging into secretory vesicles
protein aggregation
abnormal association of proteins into larger aggregate structures which tend to be insoluble.
Clathrin
Type of protein that coats transport vesicles that drives vesiculation
vesiculation
the presence or formation of vesicles
Vesicles
A small sac formed by a membrane and filled with liquid
Membrane tethering
identification process
mediated by Rab proteins, their effectors and specific tethering proteins
Reversible
70 different Rabs
Membrane docking
Membrane fusion process (vesicles gets released into cell)
Endosome fusion process
Early endosomes carry Rab5 that allows them to recognize each other and fuse.
They mature into late endosomes and the fuse with degradative lysosomes
Endocytosis
- Invagination of the plasma membrane
- Pinching off an endocytic vesicle
- Delivery of the ingested material to an early endosome
Pinocytosis (cellular drinking)
- Ingestion of fluid and molecules via vesicles smaller than 150nm diameter
- Is mediated primarily (not exclusively) by clathrin coated pits and vesicles
Phagocytosis (cellular eating)
Ingestion of large particles such as microorganisms or cellular debris
Include cells like macrophages, neutrophils, white blood cells.
Help defend us against infection by ingesting bad stuff
Endosomes
sorting stations in the endocytic pathway
In a polarized epithelial cell, endosomes mediate transcytosis -> transfer of select cargo from the apical to basolateral membranes and vise versa
(it goes top to bottom; apical, lateral, basal membranes)
Intermediate Filaments
Rope like fibers with diameter around 10 nm. Can extend across the cytoplasm, distributing the mechanical stresses in an epithelial tissue. Very flexible. Don’t rupture under stress
Include cytoplasm keratin, vimentin, neurofilaments, and nuclear lamin
Microtubules
hollow cylinders made of protein tubulin. One end attached to microtubule organizing center called centrosome. Will rupture under stress.
Microtubule motors
hollow cylinders made of protein tubulin. One end attached to microtubule organizing center called centrosome. Will rupture under stress. (largest diameter)
Actin Filaments
(microfilaments) Helical (DNA shape) polymers of protein actin. (smallest diameter) Most highly concentrated in cortex (layer of cytoplasm right beneath the PM)
Tight Epithelial Junctions
barrier function; prevent fluid transport b/ween cells. Linked to actin cytoskeleton
Adherens Epithelial Junctions
Adhesive function; support tight junctions; linked to actin cytoskeleton ring around apical surface of epithelial cell VIA homotypic adhesion molecules called Cadherins
Desmosomes
Adhesive; mechanical structure (SCAFFOLD) to cell. Linked to intermediate filaments (keratin) that also connect to substrate-bound hemi-desmosomes
Cadherins
homotypic adhesion molecules that link adherens junctions to actin cytoskeleton
Simple epithelia
Single layer of epithelial cells
all cells contact the basement membrane
better for transport
Stratified epithelia
Multilayered
not all cells contact basement membrane
better for protection
Epidermolysis Bullosa Simplex
Family of human skin diseases associated with keratin mutations
Keratin
As part of the epithelial cytoskeleton, keratins are important for the mechanical stability and integrity of epithelial cells and tissues
Nuclear Lamins
intermediate filaments that form a supporting network under the nuclear membrane (extension of ER) contains nuclear pores
Progeria
Rare genetic diseases that causes a child’s body to age fast. Most kids don’t live past 13.
Due to shortened lamin A whose farnesyl (lipid anchor) can’t be removed, therefore lamin piles up at nuclear envelope
Actin Treadmilling
ATP bound actin is added to the + end and dissociates slower from the filament than ADP actin. Looks like it’s moving
Actin filament organization
Forms multiple cellular structures
Regulated by expression of Rho GTPases and actin binding proteins
Cell migration
mediated by + end protrusion of ARP-dependent branched actin arrays to form lamellipodia (front foot of cell) that are stabilized by the de novo formation of focal adhesions at the leading edge
Contraction of the rear of the mitigated cell due to myosin-I mediated sliding of the plasma membrane across actin filaments
Basically how it crawls around
Skeletal Muscle
sarcomere contractions occur by sliding of myosin-2 filaments along acting filaments. Controlled by influx of calcium from extracellular space VIA T tubules that induce action potential thru calcium release from sarcoplasmic reticulum, inducing a conformational change in troponin that enables the myosin head to interact with actin filament
What’s a Microtubule organizing center?
where microtubules grow from
grown by GTP-dependent dynamic instability and are stabilized by interaction with microtubule capping proteins
GTP
an energy-rich nucleotide analogous to ATP that is composed of guanine, ribose, and three phosphate groups and is necessary for peptide-bond formation during protein synthesis.
Epithelial Cells
a type of cell that covers the inside and outside of the surfaces of your body
Mesenchymal Cells
multipotent STEM CELLS found in bone marrow that are important for making and repairing skeletal tissues, such as cartilage, bone and the fat found in bone marrow
Microtubule motors
transport cargo along MTs. Kinesin towards the + end and dynein towards the - end. Dynein activity in MT doubles promotes bending of flagella and cillia
Microtubule motors
transport cargo along MTs. Kinesin towards the + end and dynein towards the - end. Dynein activity in MT doubles promotes bending of flagella and cillia
Cilia
small hairs inside lungs. Their movement on the respiratory epithelium clear mucus and reduce infection
Cystic Fibrosis
Reduced activity of the CFTR chloride channel results in denser mucus that can’t be cleared by cilia and leads to infection
Actin
-highly abundant
- protein present in all eukaryotic cells and has pivotal role in muscle contractions + cell movements
- helps maintain cell shape
