Cells are said to be polarized when they
have an apical and basal plasma membrane.
Cells are said to be non-polarized when they
are symmetric, ie 1-type of plasma membrane like lymphocytes and erythrocytes
What two structures in cells have double membranes?
nucleus with nuclear pores and mitochondria
Anterograde flow moves from the ER toward the __________.
Two purposes of retrograde flow:
1) recover membrane
2) maintain homeostasis
Membrane vesicle transport does not include two organelles:
(specialized mechanisms are present to deliver the req selective proteins and lipids to them)
What are the two protein sorting pathways?
An a.a. sequence called a _________ is required to direct proteins to a particular organelle or pathway.
targetting sequence/signal sequence.
Each organelle has a receptor that binds this specific sequence. These receptors can be either ______ or _______.
cytosolic or membrane bound
Bound signal sequence receptors transfer polypeptides to __________ channel to pass through the lipid bilayer. This process is coupled to an energetically favorable process such as _________.
translocation, ATP or GTP hydrolysis
The nuclear matrix acts as a scaffold for _________ binding and is composed of _______ and _______ ________.
protein & intermediate filaments
The nucleus is the site of _________.
transcription of mRNA, tRNA, rRNA
T/F: The nucleolus is membrane bound?
What two things happen at the nucleolus?
1) site of rRNA synthesis
2) start of ribosomal subunit assembly
The inner membrane of the nucleus contains a fibrous protein network called ________.
The perinuclear space extends into the _______ _______.
Nuclear channels allow _______ transport.
In the nucleus, the genomic DNA is packaged into _______ chromosomes.
T/F: Primary RNA transcripts fuse through the nucleus?
False, they remain associated to the matrix
When is the nucleolus visible?
Is the nucleolus membrane bound?
Nucleolus is the site of assembly for _______.
The size of the nucleolus correlates with the level of ______ ______
What are assembled in the nucleolus prior to being exported from the nucleus?
The nuclear lamina lines the surface of the _______
Inner nuclear membrane
The nuclear lamina is composed of what three protiens?
lamins A, B & C
During what phase does the lamin of the nuclear lamina disappear with lamin phosphorylation?
Prophase when chromatin condenses
Protein subunits of nuclear pores are joined by octagonal _______
Lipid bilayers of the nuclear pores remain chemically distinct because of
radial arms that extend between the outer and inner nuclear membrane
What protein lies at the middle of the nuclear pore?
Nuclear pores allow _________ _______ transport but are freely permeable to _______ _______ ______.
receptor-mediated, smaller polar molecules
What is required for transport through nuclear pores?
Four common SER functions:
1) glucose mobilization from glycogen
2) storage of Ca²⁺
3) drug detoxification
4) lipid synthesis
To be used, glucose must be exported from the SER. The phosphate must be removed from glucose-6-phosphate by the SER bound protein prominent in liver, kidney and the GI (glucose storage reservoirs). The enzyme is called:
What is the type 1 glycogen storage disease that affects glycogen metabolism due to a genetic defect of glucose-6 phosphatase; allows for storage but unable to break down.
Von Gierke disease
What disease causes glycogen to accumulate and enlarge the liver causing chronic low blood sugar, abnormal growth and is frequently fatal?
Von Gierke disease
The SER is an intracellular storage site for _______.
What is the largest membrane system in mammalian cells?
the SER and RER which form the ER!
What is pumped into the SER by active transport (ATPase)?
Calcium is release from the SER in response to hormonal signals such as :
What is the name of a family of enzymes that reside in the membrane of the SER and use oxygen and NADPH to hydroxylate steroids and drugs?
____________ increases the water solubility of hydrophobic drugs, aiding in excretion from the body.
Hydroxylation by cytochrome p450 in the SER
Chronic barbituate (anti-anxiety) use _______ the level of cytochrome p450 and SER __________.
(causing increased drug dosage req because of desensitization effect in chronic addicts)
If carcinogens are hydroxylated by cytochrome p450s they show ________ activity.
Lipids are generally synthesized in the _______.
Phospholipids are assembled on the _________
cytoplasmic leaflet of the ER
Ceramide is the precursor of _______ and ________.
phosphosphingolipids and glycosphingolipids
Ceramide is synthesized in the _______ from ______ & _______.
ER from serine and palmitoyl CoA
The SER membrane enzyme HMG-CoA reductase synthesizes _______ which is the ______ step towards to production of ________.
T/F: Cholesterol cannot go from the ER to other membranes without going through the Golgi.
False. cholesterol can bypass the golgi
Glycolipids are only found on the ____________ side of membranes and therefore don't require _________.
Phospholipids that are mostly on the inner face of the membrane are:
PE and PS
(cholesterol is evenly distributed on throughout the membrane)
*When PS levels become too high on the extracellular side the cell is targeted for degradation
Phospholipids that are mainly on the extracellular face of the membrane are:
PC & Sphingomyelin
T/F: The ER membrane has > 50% PC?
True; the PM has < 25%
RER binds _______ for translation and translocation.
Proteins along the secretory first pass through the _______
*remember, no proteins are targetted to the mitochondria or peroxisome.
Four RER Functions
3) quality control
4) degradation of proteins that don't pass quality control
_______ _______ ______ Directs free ribosomes and mRNA to the RER membrane.
signal recognition particle (SRP)
Signal peptides are cleaved during translocation across the RER membrane by :
What are the three functional regions of ER signal sequences?
2) middle hydrophobic or neutral region
3) C terminus has small uncharged a.a. that specify signal peptidase cleavage site
Describe the sequence of events of SRP once they bind to ribosomes carrying mRNA.
1) induce arrest of elongation of protein synthesis briefly
2) bind to SRP receptor
3) GTP binding integral membrane protein
4) makes contact with translocon
The SRP consists of 6 proteins:
1) p54: involved in recruiting ribosomes making secretory proteins
2) P9/P14 binds the ribosome carrying mRNA
3) p68/p72: needed for translocation
4) p14: attaches p54 to the rest of the SRP
The topology of membrane proteins is determined in the _________
What allows for proper insertion and positioning of protein in membranes?
stop transfer anchor sequence
There are four types of integral membrane proteins
Types I,II & III are single-pass proteins
Type IV are multi-pass
What are the characteristics of integral Type I membrane proteins?
1) N-terminal cleavable signal peptide (removed and digested
2) stop transfer anchor
3) N-terminus is intracellular
What are the characteristics of integral Type II membrane proteins?
1) NO N-Terminal signal sequence
2) hydrophobic domain serves as both signal seq and membrane anchor
3) N-terminus is cytosolic
4) cluster of positively charged a.a. on N-terminus
What are the characteristics of integral Type III membrane proteins?
1) cluster of positively charged a.a. on C-terminus, so it ends-up extracellularly
2) no cleavable signal peptide
[opposite to type II]
What are the characteristics of integral Type IV membrane proteins?
1) multiple membrane-spanning domains that alternate as signal-anchor and stop-transfer sequences.
Some membrane proteins are anchored to the bilayer by covalently attached _____
Lipid anchored proteins can be either directly attached (Ras) or anchored by a ________ (lipoprotein lipase)
(glycosyl phosphatidyl inositol)
What is the principal chemical modification to most secretory and membrane proteins which begins in the ER.
What are the functions of glycosylation?
1) stabilize protein structure
2) protein-protein interactions
3) M6P targets lysosomal enzymes to lysosome
4) 3 terminal glucose residues play a role in protein folding and quality control
N-linked glycosylation occurs where?
N-linked glycosylation synthesis occurs on __________ pyrophosphate carrier.
N-linked glycosylation is linked via the amide nitrogen of ______.
O-linked glycosylation in the Golgi are attached one at a time to ______ and _____ (-OH group).
serine and threonine
Describe the three ways that ER lumen chaperones facilitate folding:
1) Heavy chain binding protein (BiP) requires ATP
2) Protein disulfide isomerases promote redox rxn connecting sulfhydryl groups b/w/ cysteine residues for secreted and membrane proteins
3) Calrecticulin & Calnexin bind glucose on N-linked proteins. Calnex = single pass TM protein
Calrect = soluble protein ('r is closest to s')
Misfolded proteins are disposed of by degradation pathway ______
ERAD - associated degredation
CFTR is a dysfunctional Chloride transporter in epithelial cell membranes that has a deletion in _______
single phenylalanine (∆F508)
Because misfolded CFTR accumulates it is targeted for degradation by ______
ERAD, meaning CFTR never reaches intended membranes
What are the clinical signs of CF:
inadequate hydration of respiratory mucus and floating stools due to a decrease in fat absorption
Secretory pathways refer to to the sorting of proteins made on ________ ribosomes.
Vesicle forming components must be _____ to the ______ membrane for re-use.
Vesicle coats have two layers, the inner known as the _______interacts with specific integral membrane proteins.
*the integral proteins may be cargo themselves en route for function in another membrane.
Cargo membrane proteins have structural features recognized by the binding site on the adaptor proteins of the coat. These structural features are called:
Recruitment is initiated by the exchange of ______ for ______.
soluble GDP for membrane-bound GTP
The exchange of GDP for GTP is catalyzed by a ________ ____ _______ already associated with the ER membrane.
Guanine exchange factor (GEF)
recruited to membrane by GTPase Sec12
They hydrolysis of GTP by the GTP binding protein that first recruited the coat is the signal for the coat to _______.
Three general levels to targeting and fusion:
1) vesicle movement
2) vesicle tethering
3) vesicle fusion
In vesicle transport, the parent membrane buds off and vesicle releases. What is the next step?
The coat protein must dissociate
Vesicle traffic is guided along the cytoskeleton's _______ & ______.
microtubules and microfilaments
Vesicle tethering is regulated by ______ class of proteins. Which form is active?
Rab (which are unique for each trafficking process)
Errors in what vesicle protein type can cause choroideremia (vision disorder)?
Rab, due to defective Rab binding escort protein
Vesicle fusion is mediated by integral membrane proteins called _________
V- and T-SNARES
(every vesicle carries one type of v-SNARE, but there are three different t-SNARES in target)
What ATPase disassembles SNARE complexes?
N-ethylmaleimide sensitive factor (NSF)
(ONCE DISASSEMBLED, V-SNARES RETURN TO THEIR ORIGINAL LOCATION by RETROGRADE TRANSPORT)
Transport for traffic from the ER to Golgi uses what protein?
COPII, recruited by GTPase Sar1
Sar1 binds to the _______ layer.
Sar1 contains Sec23 & Sec24
Outer layer contains proteins Sec13&Sec31 which bind to scaffold
If the protein in the ER is not properly folded it will fail to leave the ER because the _________ is not displayed.
The coat used by retrograde vesicles is ________
COPI has an inner layer that directly binds the _______ motif, concentrating proteins that display this motif in budding vesicles.
For soluble proteins that contain the ______ signal, there is a transmembrane protein called the KDEL receptor which binds ________ proteins that have the KDEL sites to the budding vesicle.
COPI coated vesicles carry material from the ____ golgi to the _____ golgi.
trans → cis
In the golgi, N-linked phosphorylation of ________ targets it to the lysosome.
* this is an exception, since most glycosylation in the golgi is O-linked
Sulfation of tyrosine residues occurs where?
Insulin is an example of a hormone that is _____ ______ in the TGN.
O-linked glycosylation and N-linked oligosaccharides begin in the ____ .
KDEL is a soluble, C-terminal protein signal that undergoes ________ transport.
*KKXX is for membrane proteins
The RER has a ______ pH which initiates peptide ______
higher pH (lower H+), release
The CGN has a _____ pH which aids in peptide _______
lower pH (higher H+), binding
What are the two models for anterograde golgi transport?
1) vesicle shuttle model
2) cisternal progression model
There are three main pathways for material leaving the TGN:
1) regulated secretion destined for PM (release only on demand; vesicles store proteins; insulin)
2) constitutive secretion destined for apical/basal PM *no coat protein*
3) M6P pathway for lysosomal enzymes
Defective lysosomal targeting cause _______ body disease.
Inclusion body disease (I-cell disease) means enzymes are not phosphorylated
*w/o correct targeting, material accumulates in the lysosomes in large 'inclusions'
Lysosomal targeting uses a coat protein complex called:
*initial interaction of clathrin coat with membrane depends on Arf1
Adaptor protein-1 (AP-1) is associated with
clathrin coated vesicle transport
M6P receptor releases lysosomal enzymes into a late endosome due to:
the drop in pH (~5)
Macropinocytosis, vesicles from lipid rafts and caveolin-dependent vesicles are all examples of Clathrin ________ endocytosis.
Receptor mediated endocytosis of LDL (to lysosome) is mediated by the binding of what protein in order to release cholesterol to cell?
Transferrin is a plasma protein that binds ________ and carries it to cells.
2 atoms of Fe²⁺
Low pH induces conformational change to transferrin, not __________ ________, mediating the release of _______.
transferrin receptor, Fe²⁺
Small vesicles inside of larger endosomal vesicles are called ____ _____ and are rich in _________ receptors.
multivesicular bodies, ubiquinated receptors
What are four functions of Lysosomes?
1) obtain nutrients from digested material
2) aid in combating bacterial infections
3) release of lysosomal enzymes to ECM
4) autophagy (self-eating)
Three features of lysosomal storage disorders are:
1) mental retardation
Give three examples of lysosomal storage disorders:
1) I-cell disease
3) Hunter Syndrome
The proteosome is a major non-lysosomal pathway for ATP _______ protein degradation.
Give two examples of non-lysosomal protein degradation pathways:
Polyubiquitin chains are not degraded but ________ & _________.
Released and disassembled
The number of mitochondria per cell depends on _________
the metabolic requirements of that cell
The outer membrane of the mitochondria contains a major integral membrane protein called:
The production of ATP within mitochondria is powered by a mechanism called ______ ______.
Ribosomes in the mitochondria are 70s as compared to cytosolic ribosomes which are _____
What are the 5 main functions of the mitochondria?
1) ATP production (TCA cycle, ETC, oxidative phosphorylation, β oxidation)
2) Urea cycle
3) Heme synthesis
5) regulators of programmed cell death
What two molecules are transported into the mitochondria to produce ATP?
2) Fatty acyl CoA
How many NADH and FADH₂ are produced during each turn?
The majority of proteins are in mitochondria are _________.
Imported from the cytosol where they are synthesized on free ribosomes
More genes are present on the _____ strand of single circular mitochondria genome.
The human mitochondrial genome is ________ inherited.
Mitochondrial genetic code ______ from the universal genetic code.
Mode of inheritance of mitochondrial diseases is ______ inherited.
Give three examples of Mt genetic diseases.
1) Leber's Hereditary Optic Neuropathy (LHON)
2) Nonsyndromic deafness (DEAF)
3) Myoclonic Epilepsy and Ragged Red Fiber Disease (MERRF)
Is there a treatment for LHON disease?
Cytosolic proteins that carry mitochondrial localization signals have an N-terminal _______ sequence with _____ a.a. residues which are normally _______.
amphipathic, positive, methionine
Matrix proteins are synthesized as a larger precursor with a cleavable amino-terminal mitochondrial targeting sequence called the ________.
Presequences are characterized by multiple _____ charged residues.
The precursor protein after entering the mitochondria is in the ________ conformation.
What are the three most important proteins involved in transmitochondrial transport?
TOM = bouncer; outer membrane
TIM = lets you in; inner membrane
PAM = shocks you with Hsp70 which initiates ATP hydrolysis
After inside: in the matrix and the pre sequence is cleaved by matrix peptidase; Hsp60/10 aid in folding protein into its final conformation.
SAM proteins _______ on the ____ membrane of the Mt
sort and assemble, outer
MPP proteins inside the Mt matrix are responsible for __________
cleaving the a.a. sequence
Peroxisomes are ______ membrane organelles
H₂O₂ is broken down in:
Enumerate 6 functions of peroxisomes:
1) VLC fatty acid oxidation
2) purine nucleotide degradation
3) cholesterol synthesis
4) bile acid synthesis
5) synthesis of ether-lipids (plasmalogens 1:1 ester linkage)
6) detox of H₂O₂
Peroxisomal proteins must be _____
Peroxisomal proteins are synthesized on _______ ribosomes.
Folding of peroxisomal proteins occurs ______ the peroxisome.
The peroxisome localization signal is:
Peroxisomal targeting sequence (PTS)
Pex proteins are associated with what organelle?
Is the PTS removed once inside the peroxisome?
Give two examples of peroxisomal disorders:
1) X-linked adrenoleukodystrophy (X-ALD)
- defect in single peroxisomal enzyme
- accumulation of VLC fatty acids in brain b/c defective membrane transport
- destroy myelin sheath around nerve cells
2) Zellweger syndrome (fatal genetic disorder)