Cell Structure Exam 2

The appearance of cells involved what 4 phases?

1. Abiotic synthesis of simple organic compounds

2. Abiotic polymerization of these into macromolecules

3. Emergence of a macromolecule capable of replication & storing genetic info

4. Encapsulation of 1st living molecule within a simple membrane

What was the Stanley Miller Experiment?

Abiotic synthesis of organic molecules from CH4, NH3, H2, & H2O.

• Results: amino acids & nucleotides were observed in the end product.

_____ may have been the first informational molecule. Why?

RNA - “RNA World”

• Deoxyribonucleic acids are derived enzymatically from corresponding ribonucleotides

• Ribozymes can form enzymatic reaction

• Primordial lipids may have come together in an early ocean, trapping RNAs & forming the first protocells

What was the theoretical order of appearance between these 4 things: RNA, lipids, DNA, Amino acids?

1. RNA

2. Amino acids

3. Lipids

4. DNA

What are the 3 domains of life & how are they connected?

Archaea, Bacteria, Eukarya

• Bacteria & archaea are as divergent from each other as eukarya & bacteria are

* For each property, describe the feature in bacteria, archaea, and eukaryotes.

1. Nucleus & Membrane-Bound Organelles

2. Cell Wall

3. Form of chromosomal DNA

4. Ribosome size

1. Nucleus & Membrane-Bound Organelles:

• * Bac & Archaea (Proks) don’t have, Euks have

2. Cell Wall

• Bac: Peptidoglycan, Archaea: proteinaceous or peptidoglycan-like, Euks: cellulose & pectin in plants, cellulose or chitin in fungi, none in animals

• * Proks & some Euks (Plants & Fungi) have, some Euks (Animals) don’t

3. Form of chromosomal DNA

• Bac: circular w/ few associated proteins, Archaea: circular w/ associated proteins, Euks: linear w/ associated proteins

4. Ribosome size

• Bac: 70S, Archaea: 70S, Euks: 80S

* Q: What are the 2 requirements for an efficient reaction involving macromolecules? (think macromolecule synthesis, addition of monomers)

2 or more molecules come close enough AND there’s a high concentration of the molecules

* Why is cell size limited?

What happens as cell size increases?

The surface area to volume ratio:

• Ratio is highest for small cubes

• Crucial so cell can transport things in and out fast enough to survive

As cell size increases:

• Molecular concentration falls (mols can’t enter fast enough & have to travel further)

• Reaction rates slow down (fewer collisions)

* What is an example of a characteristic that some cells have to maximize their surface area?

Microvilli

* Q: What happens when the same amount of juice (think macromolecules) is present, but the cell size increases?

Molecular concentration decreases AND reactions become slow

* Describe the structure of a prokaryotic cellular system:

1. Chromosomal DNA organized as a nucleoid, some contain extra-chromosomal DNA called plasmid

2. Plasma membrane

3. External cell walls

4. Other structures: ribosomes, pilus, flagellum

* What are 3 eukaryotic strategies for dealing with larger cell sizes?

1. Cytoplasmic streaming (cyclosis in plants) to move cytoplasmic contents around to all parts of a cell

2. Movement of molecules through vesicles transported along motor proteins

3. Internal organelles that concentrate mols for particular function

Name the parts of an animal cell:

1. Centrosome - DIFFERENT

2. Centriole - DIFFERENT

3. Lysosome

4. Ribosomes

5. Cell membrane

6. Smooth ER

7. Rough ER

8. Nucleus (nuclear pore, nucleolus, nucleoplasm, nuclear envelope)

9. Mitochondria

10. Cytoplasm

11. Cytoskeleton - DIFFERENT

12. Secretory vesicles

13. Golgi Apparatus

14. Peroxisome

Name the parts of an plant cell:

1. Chloroplast - DIFFERENT

2. Ribosomes

3. Rough ER

4. Smooth ER

5. Nucleus (nuclear pore, nucleolus, nucleoplasm, nuclear envelope)

6. Cell wall - DIFFERENT

7. Cell membrane

8. Golgi Apparatus

9. Peroxisome

10. Cytoplasm

11. Vacuole (large central) - DIFFERENT

12. Mitochondria

13. Lysosome

* Describe the Plasma Membrane.

Lipid bilayer with membrane proteins

• Proteins in the plasma membrane are typically glycoproteins (with short carb side chains attached) on the external side of the membrane

* What is the Cytoskeleton & what does it do?

In eukaryotic cells, 3D array of interconnected proteinaceous structures

Function: provide structure, perform mechanical functions, mediate transport

* Q: Which of the following types of cells does NOT have a cell wall?

Animal cells

• Bac, plant & fungal cells all have cell walls

* What does the endomembrane system do?

What organelles make up the endomembrane system?

Synthesizes proteins & lipids destined for various organelles, the cell membrane, or secretion. Proteins are packaged then directed to destinations in vesicles.

Organelles: ER (smooth & rough), Golgi, Endosomes, Lysosomes

* What do Ribosomes do & how do they differ in bac, archaea, and euks?

Synthesize proteins

Found in all cells (bac, euk, archaea) but differ in their size, composition, & types of ribosomal RNA

* What are the functions of the Golgi Apparatus?

Trafficking, processing, & sorting of newly synthesized membrane & secretory proteins & lipids

* What are the functions of Lysosomes?

Organelle of endomembrane system that contains digestive enzymes (acid hydrolases), degrade material taken up from outside cell & digest obsolete components of the cell itself

• Can degrade all major biological macromolecules

• Highly acidic inside (pH 4-5)

* What are Peroxisomes & what do they do?

Resemble lysosomes in size & appearance & prominent in liver & kidney cells of animals

Functions: detoxify hydrogen peroxide into water & oxygen which is highly toxic to cells. Also oxidize long chain fatty acids.

* What are the functions of Vacuoles?

Membrane-bound

Animal & yeast cells: used for temporary storage or transport

Plant cells: central vacuole with high solute concentrations used to maintain Turgor Pressure in cell

* What is the function of Mitochondria & what are their parts?

Site of aerobic respiration

• Outer membrane

• inner membrane

• matrix

• inter-membrane space

• cristae (foldings that increase surface area)

What are the similarities between mitochondira, chloroplasts, & bacteria?

• All have circular DNA without associated proteins & can synthesize their own RNA & proteins

• Similar rRNA sequences, ribosome size, & factors used in protein synthesis

• Mitochondria & chloroplasts surrounded by double membrane

  • Inner membrane has bac-like lipids & outer has euk lipids

What is the Endosymbiont Theory?

1. A protoeukaryotic cell engulfed an oxygen-using bac. which then became independent inside cell (mitochondria)

2. Descendent then engulfed photosynthetic bac. that also became independent inside cell (chloroplasts)

* What is the function & the components of the Nucleus?

Information center of the eukaryotic cell

Components: Nuclear envelope, nuclear pores, nucleolus, nucleoplasm, chromatin

Describe viruses:

Virus: infectious nucleic acids (DNA or RNA) surrounded by a protein coat & sometimes lipid bilayer envelope

• Incapable of free-living

• Infects animals, bac, plants, etc., using host’s synthetic machinery to produce more virus particles

Describe viroids:

Viroid: infectious, small circular RNA molecules

• Cause plant diseases

• Simpler than viruses, smallest known infectious agents

• Don’t exist freely & transmitted when surfaces of plant cells are damaged

Describe prions:

Prions: infectious protein mols (no nucleic acids)

• Abnormally folded versions of normal cell proteins that convert other normal proteins to their abnormal form

• Ex: Mad cow disease

* What are the 5 functions of membranes?

1. Boundary & permeability barrier

2. Organization & localization of functions (organelle membranes)

3. Transport processes

4. Signal detection

5. Cell-to-Cell interactions

What is the Fluid Mosaic Model?

Envisions a biological membrane as 2 fluid layers of lipids with proteins within and on the layers

* Most integral membrane proteins have 1+ _________ segments that span the lipid bilayer and carbohydrate side chains attached to the _________ segments on the outer membrane surface.

hydrophobic, hydrophilic

* What are lipid rafts?

Membrane microdomains. Localized regions of membrane lipids involved in cell signaling. (Membranes are * nonhomogenous)

• In the outer monolayer of animal cells, have elevated levels of cholesterol & glycosphingolipids & are less fluid than the rest of the membrane

• Function: Bind to and concentrate proteins at certain positions on the plasma membrane.

* Q: You collect 1000 red blood cells with a combined surface area of 8cm². You dissolve the plasma membranes of these cells with benzene and layer the phospholipids on the surface of water, so the phospholipids form a monolayer. What would you predict the surface area of your layed phospholipids to be?

16cm²

• 8cm² in the bilayer, stretched into a monolayer (x2)

* What is the fluid part of the fluid mosaic membrane model?

What is the mosaic part of the fluid mosaic membrane model?

Fluid: Lipids

• Phospholipids, glycolipids, sterols

Mosaic: Lipid rafts & (more importantly) Membrane proteins

* Two monolayers of membrane are asymmetric!!! in lipids & proteins present in each

* Q: What are the most abundant lipids (Important) in animal cell membranes?

Phospholipids

• Different membranes have different types & compositions

Compare the general structural differences between Phospholipids, glycolipids, and sterols.

Phospholipids

1. Phosphoglycerides: Choline, phosphate (polar head group), glycerol (backbone), 2 fatty acids

2. Sphingolipids: Choline, phosphate, sphingosine, 1 fatty acid

Glycolipids - difference = sugar head group instead of polar

1. Glycoglycerolipids: Galactose (carb), glycerol, 2 fatty acids

2. Glycosphingolipids: Galactose, sphingosine, 1 fatty acid

Sterols

1. Rigid 4-ring (steroid) structure

2. Short hydrocarbon tail and a small polar OH group

* Where are sterols commonly found?

* What is the main sterol in animal cell membranes, where is it found, & what does it do?

Membranes of most euks contain significant amounts of sterols.

Main sterol in animal cell membranes: cholesterol, needed to stabilize & maintain membranes.

• Found in inner and outer layers of plasma membrane

• Acts as fluidity buffer - dec fluidity at temps above Tm, inc fluidity at temps below Tm (due to rigidity)

• Dec permeability of membrane

* What does membrane asymmetry mean?

* When is membrane asymmetry established?

The * difference between monolayers regarding the kinds of lipids present & the degree of saturation of fatty acids in phospholipids & the kinds of proteins present

• Most glycolipids in plasma membrane of animal cells are in the outer layer

Established during membrane synthesis

* What are the 3 types of lipid movements?

Rapid & random:

1. Rotation

2. Lateral diffusion

Rare:

3. Traverse diffusion or “Flip-flop”: requires hydrophilic head group to pass through hydrophobic membrane interior & flip to other monolayer. Smooth ER has proteins that catalyze this called flippases/phosphlipid translocators. Energetically unfavorable.

* What are the 3 factors that regulate membrane fluidity & how do they do it?

1. Temperature

• Fluidity increases as temperature increases

2. Fatty acid structure: Saturation & Length of Hydrocarbon tail

• Unsaturated fatty acids increase membrane fluidity (pack loosely) - greater effect than length

• Fluidity increases when tail length decreases

3. Incorporation of sterols (like cholesterol)

• Rigidity of sterol structure reduces membrane fluidity at higher temperatures

• Sterol structure increases membrane fluidity at lower temperatures (stops fatty acids from packing)

What does the fatty acid notation look like?

(16:0) - first number is number of carbons, second number is number of double bonds in hydrocarbon chain

What does the freeze-fracture method do?

Splits a membrane into its 2 layers to see proteins

* What are the 3 different classes of membrane proteins & their subclasses?

1. Integral membrane proteins

• Integral monotopic (embedded in 1 surface & doesn’t span membrane)

• Singlepass, multipass, multi-subunit

2. Peripheral membrane proteins

• On surface of membrane

3. Lipid-anchored membrane proteins

• Fatty acid or isoprenyl anchor

• GPI anchor

* Describe integral membrane proteins.

Embedded in lipid bilayer b/c of their hydrophobic regions

The trans-membrane hydrophobic segment can be an alpha-helix or beta-barrel composed of beta sheets

* Describe peripheral membrane proteins & their interactions with integral membrane proteins & the membrane.

Hydrophilic & located on surface of bilayer

Interact with integral membrane proteins & the membrane through weak electrostatic interactions & hydrogen bonding.

* Describe lipid-anchored membrane proteins.

Hydrophilic & attached to the bilayer by covalent attachments to lipid molecules embedded in the bilayer.

Requires covalent modification of the proteins to anchor.

* Can membrane proteins move across the membrane from 1 surface to another?

* Can membrane proteins move at all?

How are all of the molecules of a particular protein oriented?

No, unlike lipids they cannot move across the membrane once in place.

Some membrane proteins can move freely, others can’t b/c they’re anchored to protein complexes.

All of the molecules of a particular protein are oriented the same way in the membrane.

What are the reasons for restricted protein mobility in membranes?

1. Anchoring to cytoskeletal components

2. Anchoring to extracellular structures or neighboring cells

3. Large protein complexes that can only move sluggishly in the membrane

4. Incorporation into lipid rafts

* Many membrane proteins are glycosylated!! (Important to know) What does that mean? Where does glycosylation occur?

They are glycoproteins (carb side chains covalently linked to amino acid chains)

Glycosylation occurs in the ER & Golgi compartments

* Q: Which type of membrane proteins are the easiest to dissociate from membranes?

Peripheral membrane proteins

* Q: How are proteins inserted into the phospholipid bilayer?

1. Through a transmembrane domain made of hydrophobic amino acids (can be alpha helix or B-barrel)

2. Through covalently attached lipids

* What is passive transport & what are the 2 types?

* What is active transport?

Passive: Movement from high to low concentration along/down a gradient without net energy input (exergonic, neg ΔG), nondirectional

1. Passive/Simple diffusion (like Osmosis)

2. Facilitation diffusion: requires protein

Active: Movement from low to high concentration against/up a gradient (charge or concentration); (endergonic, pos ΔG), directional

• Requires energy (ATP or coupled transport) & protein (carrier, channel)

• Or Endocytosis & Exocytosis

* What are the 4 important considerations for passive/active transport?

1. Solute properties (charge, size, etc.)

2. Relative solute concentrations

3. Availability of specific transmembrane proteins

4. Availability of an energy source

* The movement of a molecule that has no net charge is determined by its ________________.

* The movement of an ion is determined by its __________________.

Concentration gradient

Electrochemical potential (combination of concentration gradient & charge gradient/membrane potential)

* What types of solutes do simple diffusion, facilitated diffusion, and active transport each move?

Simple Diffusion: gases, small polar (H2O, glycerol, ethanol), small nonpolar (O2, CO2), large nonpolar (oils, steroids)

Facilitated Diffusion: small polar (H2O, glycerol), large polar (glucose), ions (Na+, K+)

Active Transport: large polar (glucose), ions (Na+, K+)

* Give examples of each type of transport in the red blood cell:

1. Simple diffusion

2. Facilitated diffusion using carrier proteins

3. Facilitated diffusion using channel proteins

4. Active transport using ATP-requiring pumps

1. Simple diffusion: O2, CO2, H2O diffuse directly across membrane relative to their concentrations in & out of cell

2. Facilitated diffusion using carrier proteins: GLUT1 transports glucose (large polar) inside, where glucose concentration lower

3. Facilitated diffusion using channel proteins: Aquaporins move H2O in & out quickly relative to solute concentration

4. Active transport using ATP-requiring pumps: Na+/K+ pump moves Na+ out and K+ in, driven by ATP hydrolysis

Describe the function of Erythrocytes (red blood cells).

Erythrocytes take up O2 in the lungs, where concentration is high, & release it in the body tissues where concentration is low.

Opposite for CO2. CO2 is taken up in the body tissues, transported to the lungs as bicarbonate, then expelled at CO2.

* Osmosis

* Osmolarity

Osmosis: Diffusion of H2O across a selectively permeable membrane (permeable to H2O but not to solutes)

• Moves towards region of lower H2O concentration, or higher solute concentration

Osmolarity: relative concentration of solutes between cytoplasm & extracellular solution

* Hypertonic vs. Hypotonic vs. Isotonic

Cell in Hypertonic solution: Higher solute concentration outside cell

• Water moves out & cells shrivel

Cell in Hypotonic solution: Lower solute concentration outside cell

• Water moves in & cells lyse (pop)

Cell in Isotonic solution: Equal solute concentration in & out of cell

• Water moves in & out normally

*Water moves from hypotonic to hypertonic

How do cells with cell walls function in hypotonic or hypertonic solutions?

Cell walls keep cells from swelling or bursting in hypotonic solutions. Cells instead become very firm from built-up turgor pressure.

In hypertonic solution, plasma membrane pulls away from cell wall (plasmolysis)

* How do cells without cell walls (animal cells) function in hypotonic solutions?

Hypotonic solution: Pump out inorganic ions, reducing the intracellular osmolarity and stopping water from flooding in

* How do solute size, polarity, and charge affect simple diffusion?

Membrane is more permeable to smaller molecules, nonpolar substances, and uncharged molecules

• Ions usually are surrounded by H2O molecules which have to be removed with energy

* Q: Give examples of 2 molecules that can enter cells by diffusion in the absence of a transporter protein.

O2 and CO2 (nonpolar, small, no charge)

* Facilitated diffusion uses what 2 types of proteins?

1. Carrier proteins

2. Channel proteins

* How do carrier proteins work to transport substances in and out of a cell?

Alternate between 2 conformational states:

• In one state, the solute-binding site of the protein is accessible on 1 side of the membrane

• Then forms a complex with the solute

• Then the protein shifts and triggers solute release on the other side

Site-specificity for substrates

Ex: Glucose & GLUT1 transporter protein

* Basically know that some transport proteins change their 3D conformation upon binding to solutes

* Uniport vs. Coupled Transport - Carrier Proteins

Uniport: a single molecule moving down its concentration gradient via a uniporter protein, which does not require energy input (Facilitated diffusion)

Coupled: 2 substances moving together, either in the same direction (* Symport) or opposite directions (* Antiport), with the energy from one solute's movement down its gradient powering the other's movement against its gradient (Indirect active transport)

* What is an example of an antiport carrier protein in erythrocytes?

The Anion Exchange Protein: facilitates reciprocal exchange of Cl- and HCO3- ions in a 1:1 ratio

• Reversible, specific, dependent on concentration gradient

• In tissues, CO2 diffuses into red blood cells, converts into HCO3-, which moves out of cell as concentration rises while Cl- moves in (to maintain charge balance) - reverse process in lungs

* How do channel proteins work in facilitated diffusion? What are the types of channel proteins?

Form hydrophilic transmembrane channels that allow * only specific solutes (Important) to cross the membrane directly

• Ion channels, porins, aquaporins

What are ion channels?

* How are they unique?

What are the 4 types of ion channels?

Tiny pores lined with hydrophilic atoms

* Remarkably selective for specific ions

Direction of ion movement depends on electrochemical gradient

Types:

1. Ligand-gated (need ligand to bind to open)

2. Mechanically-gated (open with pressure)

3. Always open

4. Voltage-gated (open with change in charge)

What are porins?

They are pores on outer membranes of bac, mitochondria, & chloroplasts that are larger & less specific than ion channels

Multipass transmembrane proteins (B-barrels) that allow rapid passage of various solutes 

What are aquaporins?

Allow rapid passage of water through membranes of red blood & kidney cells in animals, & root cells & vacuolar membranes in plants (even though water is polar)

* Direct active transport vs Indirect (or secondary) active transport

Direct: Uses energy from ATP hydrolysis (exergonic) to drive a solute against its gradient.

• Ex: Na+/K+ ATPase (P-type)

Indirect: Uses symport or antiport coupled transport to drive one solute up its gradient while another solute moves down its gradient (releasing energy)

• Wants to move one solute unfavorably, so moves another solute favorably with it

• Ex: Na+/glucose symporter (bring Na+ in favorably along with glucose unfavorably)

What are the 4 types of ATPases used in direct active transport?

• P-type: maintain membrane potential (ex: Na+/K+ pump)

• V-type: Keep pH low by pumping protons into organelles

• F-type: Synthesize ATP with proton pumps

• ABC-type: Transporters of solutes

* 1. For the Na+/K+ pump, which ion is more on the outside & which is more on the inside of the cell?

2. What is this pump important for?

3. What are its 2 conformation states?

4. What triggers the change in conformation states?

1. More Na+ on outside, more K+ on inside, constantly pumping Na+ out & K+ in

2. Transmission of nerve inputs, sending signals across body

3. E1: open to inside of cell & has high affinity for Na+ ions (wants them out); E2: open to outside of cell & has high affinity for K+ ions (wants them in)

4. Phosphorylation & dephosphorylation from Na+ & K+ binding triggers changes to protein pump

1. * What drives indirect active transport?

2. What molecules are continuously being pumped out of cells?

1. Ion gradients - inward transport of molecules up their gradients is coupled to & driven by simultaneous inward movement of mols down their gradients (or vice versa)

2. Na+ and H+

* What gradients are important for uncharged solutes vs charged solutes?

Uncharged: concentration gradient across membrane

Charged: concentration gradient & electrical potential (electrochemical gradient together)

* What are the 5 components of the endomembrane system and what do they do?

1. Endoplasmic reticulum: sites for protein synthesis, processing & sorting (rough ER), & lipid synthesis (smooth ER)

2. Golgi complex: membrane lipid & protein sorting, packaging, & trafficking

3. Endosomes: carry & sort material brought into cell

4. Lysosomes: digest ingested material & unneeded cell components

5. Vesicles: traffic material between the ER and Golgi and to and from both the plasma membrane and other membrane bound organelles

*All have double membranes

* ER cisternae vs. ER lumen:

ER cisternae are the physical sacs or tubules of the ER, and the continuous space within them where proteins & lipids are folded & processed is the ER lumen.

* 1. What are the structural differences between the Rough ER and the Smooth ER?

2. How much of each are present in eukaryotic cells?

1. Rough: studded w/ ribosomes, large flattened sheets; Smooth: No ribosomes, smooth tubular structures

2. There’s variation in the relative amounts of each; cells involved in synthesis of secretory proteins have more rough ER, cells producing steroid hormones have more smooth ER

* How are proteins synthesized & processed in the Rough ER?

1. Ribosomes on cystolic side of rough ER synthesize proteins for endomembrane system

2. Signal recognition particle binds to signal peptide on the protein as the ribosome is synthesizing protein from mRNA - brings protein & ribosome complex over to ER membrane

3. Newly synthesized proteins are inserted into Rough ER through a pore complex as they are synthesized (co-translationally) - folding occurs within lumen

* What are the 5 functions of the Rough ER?

1. Biosynthesis of proteins

2. Initial steps of protein glycosylation (addition of carbs)

3. Folding of polypeptides

4. Recognition & removal of misfolded proteins

5. Assembly of multimeric proteins

* What are the 5 functions of the Smooth ER?

1. Drug detoxification

2. Carbohydrate metabolism

3. Calcium storage

4. Steroid Biosynthesis

5. Membrane Biosynthesis

How does the Smooth ER perform Drug Detoxification?

1. CYP = large family of integral proteins in membrane of smooth ER

2. Involves hydroxylation - add OH to make mol. polar & excretable

How is the Smooth ER involved in Carbohydrate Metabolism?

1. Breakdown of stored glycogen (esp in liver cells)

2. Dephosphorylates glucose for excretion & use

How is the Smooth ER involved in Calcium Storage?

Sarcoplasmic reticulum of muscle cells

• ER lumen contains calcium binding proteins

• Calcium pumped into ER then released when needed for muscle contraction

How is the Smooth ER involved in Steroid Biosynthesis?

Smooth ER in some cells synthesizes cholesterol, other sterols, & steroid hormones

1. * What organelle is the primary source of most membrane lipids?

2. * How does this membrane biosynthesis process work? What protein is needed?

1. Smooth ER

2. Fatty acids for phospholipids synthesized in cytoplasm & incorporated on cytosolic side of ER membrane (can’t cross ER double membrane)

• Phospholipids then transferred to lumenal side of bilayer using phospholipid translocators/flippases (proteins)

• Then the other half of phospholid bilayer grown

* Q: Flippase is a _______ involved in flipping a ______.

protein, lipid

* What are the components of the Golgi Apparatus and how does it work with the ER?

• Functionally & physically linked to ER

• Glycoproteins & membrane lipids from ER are sorted & packaged for transport

Components:

1. Cis-Golgi Network (CGN): oriented towards ER

2. Medial cisternae

3. Trans-Golgi Network (TGN): oriented away from ER

* What is a Golgi stack?

A series of 3-8 cisternae

• Varies by cell type

What are the 2 models that depict the flow of lipids & proteins through the Golgi Complex?

1. Stationary Model: each cisterna in Golgi is a stable structure & materials are transported by shuttle vesicles

2. Cisternal Maturation Model: Golgi cisternae are transient compartments which gradually move & change from beginning of stack (CGN) to end of stack (TGN) continuously

* A protein’s processing often occurs throughout its trafficking through both the
ER and Golgi. What is an example of this?

* Glycosylation of proteins to form glycoproteins

1. Glycosylation starts on cystolic side of ER membrane

2. After, flippase switches glycosylated complex to interior side of ER membrane

3. Glycosylation continues til core oligosaccharide (carb) is complete

4. Oligosaccharide then transferred to transmembrane protein & trimmed

5. Glycosylation completed in Golgi

Intracellular protein sorting:

* Postranslational import vs. Cotranslational import

Postranslational sorting: Ribosomes form proteins in cytosol & completed protein remains there, enters nucleus, or imported into organelle

Cotranslational sorting: Ribosomes build proteins into the ER, where they stay or go to Golgi, then secreted, used in membrane, or sent to lysosome

Protein directing is called _________.

Protein transport is called _________.

sorting

trafficking

1. * What are protein or lipid tags?

2. What would happen as a result of an accidental change in a protein tag sequence?

1. Protein tag: An amino acid sequence, hydrophobic domain, carb side chain (oligosaccharides), etc. that allow the endomembrane system to traffic them to their proper location in the cell

2. Lipid tag: membrane lipid tagged to help vesicles reach destination

*Tags can also exclude material from certain vesicles

2. It may change where the protein ends up

* What are protein Retention tags for?

Prevent some proteins from escaping the ER (they’re needed there)

• Ex: RXR tag

* What are protein Retrieval tags for?

Retrieve some proteins from the Golgi back to the ER

• Short C-terminal sequences of amino acids

• Tag binds to receptor, complex packed into transport vesicle for return to ER

How is it determined into which Golgi cisternae proteins will be incorporated?

According to the length of their membrane-spanning, hydrophobic domains

• The thickness of the membranes in the Golgi increase from the CGN to the TGN

• Proteins move from Golgi compartment to compartment until membrane thickness exceeds the length of transmembrane domains & then proteins are sent back to where they need to be