Unit 5:Intercellular Compartments and Protein Sorting Flashcards
What is the evolution of internal membranes of eukaryotes?
precursors of eukaryotes believed to be organisms (like bacteria) with no internal membranes
plasma membrane carried out all membrane-related functions
endomembrane system thought to have evolved as invagination of plasma membrane
mitochondria and chloroplasts thought to have evolved as endosymbionts
Why is the cytoskeleton important?
-cell shape
-cell motility
-movement / position of organelles
-movement of materials within cell
-movement of chromosomes during mitosis
What does protein sorting mean?
-the transfer of proteins into compartments where they are needed
Where does the synthesis of all proteins start?
-in the cytosol on free ribosomes
Does protein transport require energy?
Yes
What directs proteins to the right place?
-stretch of amino acids, located at N-terminus, 15-60 AAs long, that directs proteins to particular organelles
-signal sequences for nucleus, mito/chloro, peroxisomes or ER
-usually removed after sorting
-delete or transfer sequence to another protein=protein goes to wrong ‘address’
Can small molecules freely pass through nuclear pores?
Yes
Can large proteins pass though nuclear pores?
No, the passage of large proteins is active
proteins pass through nuclear pores without unfolding
What is the nuclear localization signal?
- amino acid sequence that ‘tags’ a protein for import into the nucleus by nuclear transport
what does the nuclear export signal do?
tags a protein for export
What moves out of the nucleus?
mature, properly processed mRNA
assembled ribosomal subunits (rRNA)
What moves into the nucleus?
histones, ribosomal proteins, proteins required for transcription & DNA replication
dNTPs, rNTPs
What are modifications done by the ER?
-formation of disulfide bonds
-stabilization
-addition of sugar groups
-protect
-keep in ER
-direct
-cell-cell recognition
What happens if protein production exceeds capacity?
if protein prod’n exceeds capacity to keep up with folding
- misfolded proteins accumulate
-signals lead to increased expression of chaperone proteins and other proteins that assist in folding, expansion of the ER …
-if cell still can’t keep up, UPR will trigger cell death= apoptosis
What do transport vesicles do with proteins?
-transport vesicles carry soluble proteins (in their lumens) and membrane proteins (in their membranes) between compartments
in general vesicle traffic is …
outward from ER =>Golgi =>other organelles? plasma membrane?
-inward, from plasma membrane => lysosomes
What happens in the Golgi apparatus in the secretory pathway of protein?
series of flattened sacs – cisternae
organized into functionally distinct compartments with cis (entry) face closest to ER, trans (exit) face at other end
cis – newly formed
trans – breaking away
modification of new proteins arriving from ER:
peptide chains shortened by proteases
amino acids modified
CHO groups that were added in ER modified or removed
glycosylation
different CHO groups added to different AAs (ser, thr)
“O-linked glycosylation”
most complex polysaccharides synthesized in Golgi
glycos amino glycans in extracellular matrix (animals)
pectins, hemicellulose (plant cell walls)
Constitutive secretion
-constant recreation
-unregulated
What happens to the plasma membrane during secretion?
The plasma membrane gets bigger
What happens in the endocytic Process(inward)
taking substances into cell by surrounding them with membrane
they become a membrane-bound vesicle
2 main types, based on size of vesicles formed:
pinocytosis ‘cell drinking’ – tiny vesicles formed - endosomes
done by all eukaryotic cells
phagocytosis ‘cell eating’ – much larger vesicles – phagosomes
only done by specialized cells
one more type in animal cells:
receptor-mediated endocytosis
very selective concentrating mechanisms
requires specialized receptors
What is pinocytosis?
pinocytosis “drinking”
solutes, macromolecules, fluid
‘bulk’ – any molecules present in enclosed fluid enter cell
What is phagocytosis?
phagocytosis “eating”
particles, other cells, debris
What is receptor-mediated endocytosis?
-particular molecules (ligands) for which membrane has receptors
receptors grouped in patches of membrane called coated pits
If a protein does not have a location signal where does it end up?
cytosol
Where do all proteins start synthesis?
cytosol by free ribosomes
What happens to the membrane associated with a vesicle that has exocytosed by its cargo?
the vesticle membrane fuses with the plasma membrane and becomes part of it
How many membranes does the mitochondria have?
2
How many membranes does a chloroplast have?
three
What happens when a protein is needed in the chloroplast or mitochondria
-signal sequence at N terminus
-proteins must be moved across both outer and inner membranes at special sites where layers are in contact
What steps are involved in protein import?
-proteins must be unfolded to be imported
-upon import must be folded and have the signal sequence removed
What are the two types of proteins transferred to the ER?
-water soluble proteins translocated completely across into ER lumen
-destined for secretion, or lumen of an organelle
-prospective transmembrane proteins translocated only partially across
-destined for plasma membrane, ER membrane or membrane of another organelle
What do temporary vesicles do?
-allow material to leave and enter cells
-move material between endomembrane compartments
-carry soluble proteins (in their lumens) to the plasma membrane for secretion
-move membrane proteins (in their membranes) to be expressed on the cell surface
