MCP 1-13

Question 0

Structure of Golgi Appartaus

Answer 0

• flattened cisternae stacked together
• cis face (entry face) - adjacent to ER, sorts proteins going back to ER (ER retention signal)
• trans face (exit face) - pointing toward PM, sorts to lysosome and secretory vesicle (signal required), PM (default - no signal)
• usually located near the cell nucleus
• # Golgi stacks per cell varies by cell type

Question 1

Functions of Golgi Apparatus

Answer 1

• sorting and dispatching station for proteins and lipids made in ER
• modification of N-linked oligosaccharide chains on glycoproteins made in ER
• synthesis of O-linked oligosaccharides on proteins and lipids made in ER
• synthesis of glycosaminoglycan chains on core proteins of proteoglycans

Question 2

Modification of N-linked Oligosaccharides in Golgi

Answer 2

• sugar additions and removals (glycosidases and glycosyl transferases)
• 3 classes with varying degrees of modification: high mannose (little processing), complex (high processing), hybrid

Question 3

O-linked Glycosylation of Proteins

Answer 3

• cov. attachement of oligosacchrides to OH groups of serine or threonine residues in proteins
• occurs in Golgi, post-translationally via glycosyltransferases
• ## sugars are added to proteins one at a time (O-linked = One) top build oligosaccharide directly on protein

Question 4

Proteoglycan structure and function

Answer 4

• contain >95% carbohydrate by mass (diff. proteoglycans)
• carb chain always consists of glycosaminoglycan chains (very neg. charge 6 classes)
• attract water to form lubricants and gels and spring back when compressed
• synthesized in Golgi
• often found in animal extracellular matrix and on cell surfaces

Question 5

Synthesis of proteoglycans

Answer 5

• core protein syn. in ER, transported to Golgi
• in Golgi, glycosyltransferases act sequentially to build 4 sugar linker on serine of core protein
• repeated action of 2 glycosyltransferases add sugars to chain, sugars modified as chain grows

Question 6

Define: Glycoprotein

Answer 6

• any protein with one more covalently bound carb. units that do not contain a serial repeat
• mostly protein with a little carb (no glycosaminoglycan chain)
• most soluble/membrane proteins made in ER are glycoproteins

Question 7

Define: Proteoglycan

Answer 7

• small core protein with one or more bound glycosaminoglycans, which consist of a repeating disaccharide
• mostly carb with little protein

Question 8

Functions of glycoproteins

Answer 8

• extracellular matrix
• hormones
• lubrication and protection
• enzymes
• immunologic molecules
• cell surface antigens
• plasma proteins

Question 9

Mucins

Answer 9

• special class of O-linked glycoproteins
  ~ 80% carb by mass (a lot for a glycoprotein)
• most abundant macromolecule in mucus that covers epithelial surfaces (resp., GI, genital tracts)
• form a hydrated gel
• protect epithelial cells from noxious substances
• provides lub. to minimize shear forces

Question 10

ABO blood group antigens

Answer 10

• oligosacchride components of glycoproteins and glycolipids on surface of red blood cells
• extremely immunogenic
• important in transfusion medicine
• product of ABO gene locus determines if a sugar will be added to O to become either A (GalNAc added) or B (Gal added)

Question 11

Blood Type O (OO)

Answer 11

• No A or B antigens on RBC (do not make either transferase)
• universal donor - donated to individuals with any blood type because no A or B antigen to be recognized by recipient’s immune system

Question 12

Blood Type A (AA or AO)

Answer 12

• A antigen on RBC (makes GalNAs transferase)
• donated to A or AB blood types
• recipients recognize A antigen as “self”

Question 13

Blood Type B (BB or BO)

Answer 13

• B antigen on RBC (make only Gal transferase)

- donated to AB or B

Question 14

Blood Type AB

Answer 14

• copy of GalNAc and Gal transferase
• A and B antigens on RBC
• donated only to type AB
• receive from any blood type (universal acceptor) - don’t make antigens to either A or B antigen

Question 15

Constitutive exocytosis pathway

Answer 15

• default pathway: all proteins going thru Golgi enter this pathway unless a specific signal directs them
• vesicles bud from trans Gogli, fuse with PM (supplies with newly made lipids/proteins)
• operates continually in all cells

Question 16

Regulated exocytosis pathway (clathrin-coated vesicles)

Answer 16

• found in secretory cells (i.e. cells that secrete a lot of hormones or digestive enzymes)
• proteins in secretory vesicles, bud off from trans Golgi, fuse with PM
• release contents ONLY in response to an extracellular signal

Question 17

Define: Endocytosis

Answer 17

• uptake of material at cell surface and delivery to lysosomes for digestion via endosomes

Question 18

Define: pinocytosis

Answer 18

• aka endocytosis; “cell drinking”
• uptake of fluid and small molecules in small vesicles
• continuous process in all eukaryotic cells
• carried out by clathrin-coated pits and vesicles: Extracellular fluid trapped in pit is internalized and delivered to early endosomes

Question 19

Define: phagocytosis

Answer 19

• uptake of large particle such as bacteria in large vesicles (phagosomes)
• requires receptor activation at cell surface
• occurs in specialized cells (macrophages and neutrophils)

Question 20

Receptor-mediated endocytosis of LDL

Answer 20

• more efficient than ordinary pinocytosis
• when cholesterol is needed, cells syn./insert LDL receptors on PM
• receptor and LDL particles pulled in in clathrin-coated pits, vesicles shed coats and fuse with endosomes -> dissociation of LDL from receptor
• LDL -> lysosome -> hydrolyzed to free cholesterol -> released into cytosol for membrane syn.
• LDL receptor recycled to PM

Question 21

Familial hypercholesterolemia

Answer 21

• defect in LDL receptor gene
• cholesterol uptake blocked so it accumulates in blood
• leads to plaque formation in blood vessel walls and xanthomas in skin and tendons

Question 22

Early endosomes

Answer 22

• located near PM
• main sorting station in endocytic pathway
• endocytosed materials arrive within minutes
• low pH allows some receptors to release ligands - usually transported to lysosomes for degradation

Question 23

Late endosomes

Answer 23

• located near nucleus
• basically “immature” lysosomes
• endocytosed materials arrive from early endosomes 5-15 min after uptake
• materials eventually transported to lysosome via vesicles or conversion to lysosomes

Question 24

3 pathways of endocytosed materials

Answer 24

1. recycling: return to PM (ex. LDL receptors) 2. degradation: transport from early endosome to lysosome. Leads to decrease in receptor concentration -> receptor down regulation 3. transcytosis: return to different PM domain in polarized (basolateral membrane -> apical membrane)

Question 25

Structure and function of lysosomes

Answer 25

- principal site of intracellular digestion (all euk. cells) - contain ~40 acid hydrolases - membrane has ATP-driven H+ pump that maintains pH 5 (optimal for hydrolases) - membrane contain transport proteins (digestion products and nucleotides to cytosol) - membrane proteins heavily glycosylated to help protect from lysosomal proteases

Question 26

Delivery of lysosomal enzymes to lysosomes

Answer 26

- mannose-6-phosphate (M6P) tag added to lysosomal enzymes in ER/Golgi - sorted into transport vesicles in trans Golgi for delivery to lysosomes via endosomes

Question 27

3 lysosome delivery pathways

Answer 27

1. endocytosis: taken up into vesicles, delivered to early and late endosomes (ex. LDL) 2. phagocytosis: uptake by phagosomes, fuse with late endosomes/lysosomes. Occurs in macrophages and neutrophils ("pro phagocytes") ex. ingestion of bacteria by neutrophils 3. autophagy: digestion of pointless cell parts. Double mem surrounds organelle (forming autophagosome), fuses with late endosome/lysosome. ex. removal of expanded SER in liver

Question 28

Mucopolysaccharidoses

Answer 28

- lysosomal storage disease - defects in lysosomal enzyme required for degradation of glycosaminoglycans - results in permanent progressive cell damage. Appear normal at birth, decline in mental/physical function over time

Question 29

Oligosaccharidoses

Answer 29

- lysosomal storage disease - defects in lysosomal enzymes required for degradation of oligosaccharides - onset in infancy or early childhood, variable phenotype but facial dysmorphism and progressive mental retardation are common

Question 30

Sphingolipidoses

Answer 30

- lysosomal storage disease | - defects in lysosomal enzymes required for degradation of sphingolipids

Question 31

Inclusion-cell disease

Answer 31

- lysosomal storage disease - defect in enzyme responsible for generating M6P tag on hydrolases - hydrolases fail to target to lysosomes, so they are secreted from cell via default pathway - hydrolytic enzymes missing from lysosome - results in accumulation of many undigested substrates forming inclusion bodies - onset in infancy with dev. delay and growth failure, progresses until death by age 5-8