Dunn M&C - Proteins & Endomembrane System

ratio of sodium (Na+) to potassium (K+)

for every three sodium ions pumped out of the cell, two potassium ions are pumped in.

electrochemical gradients

ions have ____ across membranes; the electro part is based on charge and the chemical part is based on that specific ion

integral membrane proteins

pass through the lipid bilayer

peripheral membrane proteins

can interact in four ways; 1. binds directly to the membrane (hydrophobic part that gets cozy w/ lipid tails) 2. binds only to a transmembrane protein (not directly touching the membrane) 3. interacts directly with membrane AND a transmembrane protein. 4. attached to hydrocarbon in endomembrane

lipid-anchored peripheral membrane proteins

these proteins are attached to the membrane through a covalent bond with a lipid molecule, allowing them to associate with the membrane without traversing its lipid bilayer.

peripheral membrane proteins

do not pass the lipid bilayer

soluble proteins

extracellular protein, cytosolic protein, lipid-anchored peripheral membrane proteins

proteins made at the ER

soluble extracellular proteins, integral membrane proteins

endomembrane system

refers to the set of intracellular organelles that are interconnected by vesicular traffic

• ER, Golgi, Lysosome, endosome, Plasma membranes

• NOT MITOCHONDRIA OR CHLOROPLASTS

luminal fluid

contains proteins and carbohydrates in E.R; found within the lumen of organelles such as E.R, golgi, lysosomes

vesicular traffic

means when membrane bound structures (vesicles) are budding off and/or fusing with another membrane bound structure

nuclear envelope

where the nucleus is contained; a double-membrane structure. supported by a cytoskeletal structure called the nuclear lamina, is “perforated” by nuclear pore complexes which act as gates for the nucleus and is continuous with the ER

nuclear lamina

a protein meshwork that lines the inner surface of the nuclear envelope in eukaryotic cells; cytoskeletal structur

nuclear pore complexes

Acts as gates for the nucleus and is continuous with ER, allowing selective passage of molecules between the nucleus and cytoplasm.

Small molecules pass by diffusion, whereas larger molecules, like mRNAs and most proteins, require active transport (GTP hydrolysis)

• not a channel, carrier, or transporter. it is its own structure

endoplasmic reticulum

smooth ER functions (no ribosomes): lipid/steroid biosynthesis, calcium storage (uses calcium pump)

rough ER functions (with ribosomes): membrane protein biosynthesis, studded with ribosomes, making membrane proteins continuously

rough endoplasmic reticulum

Where membrane proteins are synthesized (integral membrane proteins and proteins in the endomembrane system originate here)

• The rough spots of the ER are ribosomes — they are only there because they are translating something

smooth endoplasmic reticulum

where lipid-y stuff is synthesized

• lacks ribosomes and the primary site of lipid synthesis

signal sequence

a short amino acid sequence that directs proteins to their proper location within a cell

translocon/translocation channel

a protein that can accommodate polypeptide chains into the E.R

signal recognition particle

binds to a signal sequence in the amino-terminal end of the growing polypeptide and halts translation

signaling

a protein that is made directs a ribosome to the surface of the E.R. at the ER, the ribosomes associates w/ a translocation channel through which the protein’s synthesis is completed, resulting in a lumenal protein or an integral membrane protein

signal anchor sequences

become transmembrane domains. they are released from the translocation channel into the E.R membrane and diffuse laterally into the lipid bilayer

• becomes a transmembrane domain

vesicle

a small fluid-filled vacuole within the body; two layers, lipid bilayer

vesicular transport

a vesicle can pinch off of one membrane and fuse with another

secretion/exocytosis

vesicular transport to the cell surface or out of the cell

• E.R to Golgi to Plasma Membrane (in that order)

glycosylated

refers to the process by which sugar molecules are covalently attached to carbohydrate chains, typically occurring in the endoplasmic reticulum and Golgi apparatus

• occurs in the lumen

golgi apparatus

The integral membrane and secreted proteins are modified by carbohydrates. Packages and sorts.

consists of a series of flattened membrane sacs called cisternae

cisternae

a series of flattened membrane sacs

glycosylation enzymes

in the lumen

exocytosis

secretion from a cell whereby substances contained in vesicles are discharged by fusion of the vesicular membrane with the outer cell membrane (PM)

endocytosis

the uptake of material from outside the cell (or at the PM) by the invagination of the plasma membrane resulting in the formation of intracellular vesicles

cargo

the molecules, primarily proteins and lipids, that are transported and modified within the system, traveling from one organelle to another via membrane-bound vesicle

secretory pathway

ER —→ Golgi —→ PM

ER → Golgi → Lysosome

• purpose: biosynthesis of proteins required for lysosome functions

• ER → Golgi transport occurs via tubules rather than vesicles. These vesicles are often moved along cytoskeletal tracks by an active transport mechanism

golgi apparatus

made up of a stack of flattened, membrane-enclosed sacs. it is responsible for packing (protein modification). cargo proteins undergo extensive glycosylation and carbohydrate “editing” these cargos are directed to distinct destinations at the TGN (transgolgi network)

trans-golgi network / TGN

has three main possible destinations: the lysosome, constitutive exocytosis, regulated exocytosis

cis-face

part of golgi closest to E.R, receiving side for golgi

lysosome (TGN)

receive their enzyme-filled cargo from the trans-Golgi network (TGN) and play a critical role in maintaining cellular homeostasis by controlling the turnover of various cellular components.

constitutive exocytosis (TGN)

continuous process in which cells constantly secrete proteins and other molecules regardless of external signals.

regulated exocytosis (TGN)

a specialized process characterized by the storage of proteins and molecules in secretory vesicles that wait for specific extracellular signals (such as hormones or neurotransmitters) to trigger their release

endocytic pathway

coming into the cell, stuff outside the cell or in the plasma membrane can be brought into the cell by endocytosis

• purpose: degradation

endocytic cargo

can be recycled (sent back to the plasma membrane) or directed to a lysosome.

fluids in/out cells

extracellular fluid becomes luminal fluid in our organelles

phagocytosis

an entire extracellular particle/cell is engulfed and becomes a lysosome

autophagy

“self-eating”, the cell degrades its own organelles to become a lysosome

lysosome

an acidic and digestive organelle: proteins, lipids, nucleic acids, and carbohydrates can all be degraded by lysosomes

• functions: recycling of cellular building blocks to make new stuff

• destruction of engulfed pathogens

• breakdown of debris

acid hydrolyases

Made in the E.R, they are enzymes that catalyze the hydrolysis of various biological molecules under acidic conditions, which is crucial in the lysosomal degradation of macromolecules from the endocytic pathway. E.R.

activated by low pH and consumes water that cleaves their substrates. ONLY works at low pH

• the lysosomes are acidified by a proton pump

zip code proteins

can determine on vesicles which fusion events occur (through the different pathways)

glycosylation

the enzymatic process that attaches carbohydrates (sugars) to proteins or lipids, which is critical for the proper folding, stability, and function of these biomolecules. It commonly occurs in the endoplasmic reticulum (ER) and Golgi apparatus