Unit 2 Exam Flashcards
1
Q
What is the defining feature of lipids?
A
being hydrophobic molecules
2
Q
What do lipids do?
A
function as part of membranes, signaling, and energy storage
3
Q
What are the five major types of lipids?
A
fatty acids, triglycerides, phospholipids, glycolipids, steroids
4
Q
What is the polar head made of?
A
carboxyl group
5
Q
What is the nonpolar tail made of?
A
long unbranched hydrocarbon chain
6
Q
What is the structure of a triglyceride?
A
consists of a glycerol linked to 3 fatty acids
7
Q
What is the main function of triglycerides?
A
energy storage
8
Q
What is the structure of phospholipids?
A
They are amphipathic and contain a polar head that includes a phosphate group and two non polar tails
9
Q
What do phospholipids do?
A
they are key components of cell membranes
10
Q
What are glycolipids made of?
A
they are derived from sphingosine and have a carbohydrate attached (which makes glycolipids amphipathic)
11
Q
What is the most common form of steroids?
A
cholesterol
12
Q
What does cholesterol do?
A
is a component of cell membranes and the starting part of synthesis of the steroid hormone
13
Q
What must the plasma membrane consist of?
A
lipid bilayer
14
Q
Describe the structure of the lipid bilayer plus protein sheets
A
protein-lipid-protein sandwich
15
Q
What is the fluid mosaic model?
A
proposed membranes consist of a lipid bilayer with globular proteins inserted into the lipid bilayer
16
Q
What is the fluid in the fluid mosaic model?
A
phospholipids, glycolipids, and sterols/steroids
17
Q
What affects membrane fluidity?
A
The length of hydrocarbons and the number of double bonds.
The longer the hydrocarbon chain is, the less the membrane fluidity is.
The more double bonds cause an increase in membrane fluidity (this is a very strong effect)
18
Q
What does cholesterol do in membranes?
A
acts as a fluidity buffer so when the cell is in high temperatures, the fluidity decreases and when it is in low temperature, fluidity increases, which prevents packing
19
Q
What are lipid rafts and what do they do?
A
they are a relatively stable structure in the membrane that is involved in cell signaling and helps keep the membrane stable
20
Q
What kinds of proteins are in the fluid mosaic model?
A
integral, peripheral, and lipid-anchored proteins
21
Q
What are integral proteins?
A
pass through the membrane or are inserted into it
22
Q
What are peripheral proteins?
A
associated w/ one side of the membrane but not inserted into it.
23
Q
What are lipid-anchored proteins?
A
contain a lipid group (covalently attached) that inserts into the membrane
24
Q
What do the proteins do in the membrane?
A
transport, anchors, receptors, enzymes
25
What is the difference between diffusion, facilitated diffusion, and active transport?
diffusion - direct unaided movement with a free energy gradient
facilitated diffusion - aided movement w/ free energy gradient
active transport - aided movement against the free energy gradient
26
What does 20% of E.coli genes do?
transport
27
Which molecules move best in simple diffusion?
small hydrophobic molecules, then small uncharged polar molecules, large uncharged polar molecules, and then ions
28
What do carrier and channel proteins do?
carrier - transport proteins that help molecules pass through membrane by changing shape
channel proteins - transport proteins that help molecules pass through membrane by creating a pore in the membrane (usually have a polar environment to help molecules pass)
29
What are the three types of carrier proteins?
uniport - transports one type of molecule at a time
symport - transports 2 molecules in the same direction
antiport - transports 2 types of molecules in opposite directions
30
What is the difference between direct active transport and indirect active transport?
direct - uses energy from ATP hydrolysis to power transport
indirect - transport of one solute against its concentration gradient is powered by moving another solute w/ its concentration gradient
31
What are examples of direct active transport?
Na/K pump (3 sodium out, 2 potassium in, dephosphorylation causes conformational change), proton pumps in lysosomes
32
What are examples of indirect transport?
Na/glucose symporter - Na concentration gradient powers the transfer of glucose
33
What is constitutive secretion?
continuous, independent of signals (secretion of mucus, extracellular matrix proteins)
34
What is regulated secretion?
secretory vesicles accumulate near plasma membrane and fuse w/ plasma membrane in response to signal (secretion of neurotransmitters, insulin)
35
Describe the process of exocytosis
vesicles fuse with plasma membrane and vesicle contents leave the cell
36
What usually signals exocytosis?
calcium
37
Describe vesicle fusion (SNAREs)
when the vesicle gets to its target membrane, coiled-coil tethering protein on the membrane guides the vesicle to the membrane, SNAREs proteins on the vesicle (v-SNAREs) bind to the SNARE proteins on the target membrane (t-snares) and when fusion is done, SNAP proteins release the SNAREs
38
What is clathrin-independent endocytosis?
- a type of pinocytosis in which nonspecific internalization of extracellular fluid occurs and controls cell volume and surface area
39
What is clathrin-dependent endocytosis?
molecules outside the cell bind to specific receptors in the membrane and form a coated pit of clathrin on the cytosolic membrane. This coating causes a sphere-shaped vesicle to form and the molecules that are bound to the receptor are inside the vesicle. Once the products enter the cell, the clathrin comes off and the vesicle moves on
40
What is the endomembrane system made up of?
single membraned organelles: ER, golgi, endosomes, lysosomes
41
How do vesicles move inside the cell?
ER --> Golgi --> plasma membrane
42
What is the terminology of the ER?
cisternae - sacs of ER
Lumen - space enclosed by ER
Perinuclear space - space between 2 membranes of the nuclear envelope
43
What is membrane biosynthesis in the ER?
the smooth ER is the primary source of membrane lipids (including phospholipids and cholesterol) - restricted to one monolayer of the ER, the side facing the cytosol
44
How does calcium storage work in the smooth ER?
calcium ion pumps move a high concentration of Ca2+ ions into the smooth ER lumen. (rapidly released upon cell signals)
45
What happens during carbohydrate metabolism in the rough ER?
glycogen is broken down to glucose-6-phosphate but cannot leave the cell (the glucose leaves and the glucose-6-phosphate is dephosphorylated)
46
What happens in the ER during smooth hydroxylation?
addition of hydroxyl (-OH) groups to make lipids more soluble
- helps make testosterone, estrogen, and cortisol
- also helps to detoxify drugs
47
What happens in the rough ER in the production of membrane/secreted proteins?
proteins destined for plasma membrane, secretion, or anywhere in the endomembrane system are made on the rough ER and moved through cotranslational import
48
What is cotranslational import?
the process where translation happens at the same time as a polypeptide is being imported into the ER
49
Describe the process of cotranslational import.
Ribosome binds to mRNA in the cytosol and translation begins, a short signal sequence at the N-terminus in the polypeptide chain attracts the protein signal recognition (SRP) particle, the SRP brings ribosome to the rough ER, and after translation is complete, signal peptidase cuts off the signal sequence
50
Soluble vs. Insoluble cotranslational import
soluble: signal sequence activates translocator and protein is brought through the membrane. Signal peptidase then cuts off the signal sequence and the soluble protein is released into the ER lumen.
Insoluble: hydrophobic start-transfer binding site binds to the translocator protein and weaves the protein through until the hydrophobic stop-transfer binding site is reached and signal peptidase cuts off the start-transfer sequence
51
What post-translational modifications take place in the rough ER?
glycosylation - covalent attachment of a carbohydrate onto a protein
52
What does the rough ER use for protein folding?
molecular chaperones, Binding Protein (BiP), which is a chaperone that binds to hydrophobic sequences and prevents protein aggregates
53
What happens during ERAD in the rough ER?
misfolded proteins in ER are detected and exported to cytosol for degradation
54
What are the three regions of the Golgi?
Cis-Golgi network (CGN), medial cisternae, and trans-Golgi network (TGN)
55
Where do transition vesicles move and what protein are they coated in?
from ER to CGN and coated in COPII
56
Where do shuttle vesicles move and what protein are they coated in?
they move within the Golgi or from the Golgi to the ER and are coated with COPI
57
Where do transport vesicles go and what are they coated with?
they are leaving the TGN for endosomes and are coated with clathrin
58
N-linked vs O-linked glycosylation
N-linked - carbs added onto asparagine amino acid
O-linked - carb added onto serine or threonine amino acid
59
Describe the process of glycosylation in N-linked?
begins on the dolichol phosphate lipid in the ER membrane on the cytoplasmic side, sugar groups are added on the cytosolic side of the membrane, and flippases turn the molecule around so that the carb extends into the ER lumen instead of the cytosol. More sugars are then added to form a core oligosaccharide before it gets transferred to a protein. Enzymes then come to remove some sugars in the ER for further processing in the Golgi, but this depends on the protein
60
Why is glycosylation necessary?
it is needed for protein folding and can help attract enzymes that catalyze formation of disulfide bonds
61
What parts of glycosylation occur in the ER and what parts occur in the Golgi for N-linked?
ER - biosynthesis of core oligosaccharide, initial processing of oligosaccharide, identification and removal of misfolded proteins
Golgi - phosphorylation and addition of many things
62
What are the signals to the ER and Golgi?
tells where the protein is supposed to go and can be a short amino acid sequence, a folded protein domain, and an oligosaccharide chain
63
What is ER trafficking?
tags for retention in the ER and retrieval from CGN (like KDEL)
64
What happens with proteins that have the KDEL tag?
soluble ER-specific proteins w/ KDEL tag bind to a receptor in Golgi membrane and receptor bound membranes are transported back to ER by retrograde flow of vesicles
65
How does Golgi trafficking work?
tags for retention, retrieval, and large complexes that are excluded from transport vesicles and increase in membrane thickness in Golgi from CGB to TGN and length of the membrane spanning region determines which compartment the Golgi will end up in
66
How does lysosome trafficking work?
oligosaccharide containing mannose-6-phosphate acts as a tag to signal a protein to a lysosome
67
Describe the path of proteins to the lysosome?
In the rough ER, a lysosomal enzyme is made and an oligosaccharide is attached. Once in the CGN, mannose is phosphorylated and transported to the TGN, where M6P binds to a receptor and causes the tagged protein to be packaged into vesicles going to endosome and then low pH causes dissociation of enzyme + receptor
68
How are receptors for lysosomal trafficking being recycled?
tagged protein (lysosomal enzyme) ends up in the lysosome and the receptor goes back to the TGN
69
What do lysosomes do?
isolate digestive enzymes from the rest of the cell, and are involved in phagocytosis, receptor mediated endocytosis, autophagy, and extracellular digestion
70
How do lysosomes work?
proton pumps create a low pH in lysosomes so that lysosomal enzymes can do their jobs as acid hydrolases, they can use phagocytosis, endocytosis, autophagic vacuoles, or they can release acid hydrolases to extracellular fluid
71
When does posttranslational import occur?
when the protein is going to the nucleus, mitochondria, chloroplast, or perioxisome
72
How do proteins get to the mitochondria and chloroplasts?
a transit sequence targets the protein to the correct organelle
73
How does protein targeting work in the mitochondria?
HSP70 (chaperone binds to polypeptide to keep it linear and loosely folded, then the transit sequence binds to the TOM receptor, the Hsp70 molecules detach as the polypeptide passes through the membranes and the transit sequence is cleaved by a transit peptidase. Mitochondrial Hsp70 molecules bind and release the polypeptide as it enters the matrix to help pull it through the two membranes and then the polypeptide finally folds with the help of Hsp60
74
What is the structure of the nucleus?
double membrane with a perinuclear space that is continuous with the ER lumen and contains nuclear pores
75
What do nuclear pores do?
they are large channels in the nuclear envelope that allow molecules to move between the nucleus and cytoplasm
76
What are heterochromatin?
more compact chromatin, stains dark, transcriptionally inactive
77
What are euchromatin?
loosely packed chromatin, stains lightly, active transcription
78
What is the nucleolus?
very transcriptionally active area, transcription of rRNA genes, and can be up to 25% of nucleus in very active cells
79
How does the nuclear pore work?
lined with large protein complexes, which spans both lipid bilayers. RNA is exported through these into the cytosol and proteins are imported through into the nucleus
**a lot of RNA and proteins move through nuclear pores
80
What happens during nuclear import?
nuclear proteins contain a nuclear localization sequence (NLS) that allows them to be imported into the nucleus, which binds to importin and moves into the nucleus. This importin then binds to GTP-Ran and the protein is release. The GTP-ran carries importin out of the cell
**proteins do not have to be unfolded to go through nuclear pores
81
Hydropathy
A hydrophobicity/hydrophilicity
plot of the amino acids in a polypeptide chain
82
Fluid mosaic
Model of the plasma membrane
that allows for lateral diffusion within the plane of
the membrane
83
Lipid raft
a membrane microdomain of lipids and proteins involved in cell signaling
84
Cisternal Maturation
Golgi model that
emphasizes changes to the cisternae over time
85
Retrograde
term for flow of vesicles form golgi to ER
86
What happens with nuclear export?
GTP-Ran biinds to exportin, which causes exportin to bind to cargo protein with a nuclear export signal. THE EXPORTIN, GTPran and cargo protein rna pass through nuclear pore to cytosol, and GTP-ran is hydrolyzed to GDP-Ran and exportin and cargo protein is released. The exportin then passes through the nuclear pore into the nucleus
