Cell Ultrastructure & Proteins Flashcards

Question

Outline the secretory pathway and the two types of vesicle.

Answer 1

virtually all proteins synthesised on ribosomes in cytosol or on RER. Each protein contains a strong sorting signal to direct it to correct site in the cell (imperative) Nearly all proteins move into the RER as they are still being synthesised Moved to Golgi packaged into Secretory vesicles or transport vesicles to leave the Golgi Costitutive Secretion: regulated uses transport vesicles no external signal is required for protein secretion thus occur continuously Regulated secretion: uses secretory vesicles that can hold proteins until an extracellular signal arrives causing rapid release via exocytosis If they are not needed and become defective over time degraded by lysosomes

Answer 2

can result in change in amino acid sequence of DNA --> alter way protein folds and functions e.g. CFTR deletion of phenyalanine at position 508 on chromosome 7 mutated protein folds incorrectly retained in RER and never reaches the CSM.

Answer 3

Imbalance in cells folding response leading to ER stress this leads to accumulations of miss-folded proteins --> formation on aggregates as they are not removed properly prevents cellular functioning leading to cell death Alzheimers and Huntingtons

Answer 4

control what substances enter and exit the cell/organelles through selective permeability (hydrophobic core barrier to polar charged molecules) Allow for compartmentalisation and division of labour Surface for chemical reactions

Answer 5

Fluid PPL can move laterally within monolayer so too can proteins. PPL can also flip between monolayers Mosaic= protein molecules interspersed within membrane

Answer 6

Amphipathic molecules (polar phosphate head & non polar hydrophobic c tail) Tails can be saturated (no C double bonds) pack tighter together more van de walls between molecule less fluid or can be unsaturated resulting in kinky tails and less VDW's more fluid Hydrophilic head faces extracellular and intracellular aqueous environments polar tails form hydrophobic core barrier to water soluble charged molecules

Answer 7

Phosphatidylcholine Phosphatidylserine Sphingomyelin

Answer 8

Short rigid molecule fills in gaps between neighbouring PPL stabilising interactions between them particularity between unsaturated tails Stiffens the bilayer making it less fluid

Answer 9

Glycolipids= cell to cell adhesion | Glycoproteins cell to cell recognition

Answer 10

Tend to be a helices. Polar peptide bonds in hydrophobic core. Atoms in pp backbone form H bonds with each other forming a more stable a helix. Do occasionally get B pleated sheets spanning core but create B barrels (porins found on mitochondrial envelope) hydrophilic R groups on inside of barrel

Answer 11

Small hydrophobic molecules (02 CO2 steroid hormones) can lipophilic Some small polar molecules can pass in small volumes eg. water Large Uncharged molecules e.g glucose cannot pass Any ions and charged molecules (protein hormones) cannot pass

Answer 12

Passive molele down its diffusion gradient ion down its electrochemical gradient. no input of energy Active moving a molecule against its concentration gradient requiring an input of energy

Answer 13

composite of two forces one due to a concentration gradient and one due to voltage differentials.

Answer 14

To drive transport across membranes | To maintain the osmotic balance of cells

Answer 15

movement of non-polar lipophilic molecules down concentration gradient

Answer 16

movement of charged/polar and large molecules down their concentration or electrochemical gradients using either channel proteins or transporter proteins

Answer 17

``` Intrinsic non directional channels hydrophilic R groups outside of protein Do have some selectivity: Leak channels (open all time in neurones) Voltage-gated channels Ligand gated ion channels Open when ligand binds Mechanically gated channels ```

Answer 18

much more selective than CP's molecules must have a specific complimentary shape to binding site on transport protein --> binding results in conformational change and the molecule being brought into the cell Can reverse direction if conc gradeitn changes e.g. glucose transporters in the gut

Answer 19

use energy from hydrolysis and dephosphorylation of ATP & subsequent phosphorylation of transporter to move a molecule against its concentration gradient. e.g. Na+/K+ pump 3Na bind intracellularly moved out of the cell due to phosphorylation and allostery of transport protein 3Na+ released extracellularly allows binding of 2K+ dephosphorylation of protein returns to original conformation and 2 K+ brought into cell. Movement of Na+ out of the cell essential maintains EC gradients and allows Na+ transporters to work

Answer 20

work by coupling the movement of one molecule with its concentration gradient with the movement of another molecule against its concentration gradient Symporters and Antiporters E.g Na+/Glucose symporter in PCT Na= binds to specific cooperatively along with gluose (both must be present for symporter to work). Na+ moved into the cell down its EC gradient and Gluc moved into the cell down its conc gradient. (must then have uniporters on basal side of cell to move gluc out of cell into blood)

Answer 21

cell surface membrane folds to form a vesicle: Phagocytosis: cell takes in solid material in large quantities these cells are phagocytes and engulf bacteria surrounding them in a phagocytic vesicle Pinocytosis: cell take in liquid material in large quantities very small vesicles are formed via micropinocytosis e.g uptake of nutrients by an ovum from follicle cells

Answer 22

removal of waste products or secretion of useful products out of the cell