1
Q
what are membranes
A
continuous unbroken sheets that enclose compartments
allows fusion w/o losing continuity
2
Q
what are diff membranes in a cell
A
cell (plasma) membrane -> physically separates cells from external envrionment
nuclear envelope
mitochondrial membranes
chloroplast membranes
lysosomal membrane
endoplasmic reticulum`
3
Q
what are different membrane functions
A
- compartmentalization -> compartments have diff contents and activities
- provide selectively permeable barrier -> prevent unrestricted exchange of molecules
- transporting solutes -> exchange of molecules across membrane
- scaffold for biochem activities
- responding to external signals -> signal transduction
- intercellular interaction -> mediates interaction between cell and neighbours
- energy transduction -> converson of one form of energy into another
4
Q
what are the components of the cell membrane structure
A
- phospholipids
- proteins
- carbohydrates
5
Q
what lipids is the membrane composed of?
A
2 layers of lipids and the major type: phospholipids
6
Q
what are the 2 regions of phospholipids?
A
hydrophilic -> head grp
- glycerol, phosphate grp and a polar grp
hydrophobic -> fatty acid tail
7
Q
how do phospholipids arrange themselves?
A
spontaneously
depends on size of polar head grps
micelles or bilayers
8
Q
what are micelles
A
when phospholipids arrange themselves and the head ends up being large/bulky w/ one hydrophob tail that is buried forms spheres: micelles
9
Q
what is a bilayer
A
when phospholipids arrange themselves and the head ends up being smaller and having 2 hydrophob tails, a bilayer is formed with a closed structure & inner space
10
Q
what happens when phospholipids are added to a test tube of water
A
they spontaneously form enclosed bilayers -> liposomes
11
Q
what are liposomes
A
enclose an inner space -> a bilayer make effective cell membranes
12
Q
why are membranes self healing?
A
because of bilayer arrangement -> phospholipids spontaneously rearrange
due to tendency of water to exclude nonpolar molecules
13
Q
why are membranes “dynamic”
A
continually moving, forming and re-forming -> membranes are said to be fluid
14
Q
how are membranes fluid
A
lipids can move laterally within the membrane
movement is affected by nature of the phospholipid tails
15
Q
what features of lipids can affect fluidity
A
length of tails:
- longer = less fluid
presence of C-C double bonds:
- fewer = less fluid
cholesterol (inserts into the lipid bilayer of animal cell membranes):
- can increase/decrease fluidity depending on temp
16
Q
what are lipid rafts
A
lipids and other components such as proteins may be found in discrete regions of the membrane
specialized microdomains that serve as platforms for various cell processes
17
Q
do lipids move in the plane of the membrane?
A
yes, they rarely move between the layers of the bilayer -> lipid flip-flop
makes it possible for layers to differ in composition
18
Q
what are the functions of membrane proteins
A
- transporters that move ions and molecules
- receptors that allow cell to receive signals
- enzymes that catalyze chem reactions in the cell
- anchors that attach to other proteins
19
Q
what are the 2 types of membrane proteins
A
- integral:
permanently associated with membrane and can span the entire lipid bilayer (transmembrane) - peripheral:
temporarily associated with lipid bilayer or with integral proteins via non covalent bonds
- can be cytoplasmic or extracellular
20
Q
what are membrane carbs
A
all face outward to extracellular space
covalently linked to either:
- protein -> glycoprotein
- lipid -> glycolipid
21
Q
what is the fluid mosaic model
A
core of membrane is lipid bilayer
liquid bilayer is a fluid that allows molefules to move laterally within the membrane
contains a mosaic (mixture) of diff types of molecules -> lipids, proteins and carbohydrates
membranes are dynamic structures in which components are mobile and capable of coming together to engage in various types of transient interactions
22
Q
what molecules are more permeable than others?
A
gases are more permeable, nonpolar molecules (ex. lipids) can move across the bilayer
small uncharged polar molecules can move across bilayer
23
Q
what molecules are too large to move across the membrane
A
macromolecules (carbs and proteins)
24
Q
movement of substance INTO the cells
A
influx
25
movement of substance OUT the cells
efflux
26
what is influx
movement into cells
27
what is efflux
movement out of cells
28
what is it when efflux or influx exceeds the other
net flux
29
what is net flux
when efflux or influx exceeds the other
30
what is diffusion
spontaneous process
net movement of molecules from area of high concentration to area of low concentration
net movement stops when no concen gradient -> random motion in both directions
31
what is passive transport
occurs across a membrane via diffusion -> no energy required
driven by concentration gradient across the membrane
32
what are the 2 mechanisms for passive transport
1. simple diffusion -> thru the cell membrane
- small molecules (O2, CO2)
- hydrophobic molecules (triaglycerols)
2. facilitated diffusion ->down the concentration gradient thru a protein transporter
33
what are the 2 kinds of membrane transporters
1.
- channel formed by integral membrane proteins: surround aqueous pore
- permeable to specific molecules: selective
- some exist in either open or closed conformation: gated channels
2. specific molecules bind to transporter and moves down concentration gradient
- molecule binds to carrier protein on one side of membrane -> triggers conformational change in carrier protein
- molecule is now exposed to other side of membrane -> diffuses down concentration gradient
33
what is osmosis
diffusion of water across a semi-permeable membrane
concentration gradient of H2O causes molecules to move from a higher H2O to a lower H2O
osmotic pressure is key -> important to consider the tonicity of the solution a cell is surrounded by:
- if equal on both sides of membrane: isotonic
34
what is a hypERtonic solution
higher solute than the cell
water molecules move OUT of the cell thru semiperm membrane, into the surrounding solution
water moves out, cell shrinks
animal cells shrivel and die -> crenation
plant cell will pull away from surrounding cell wall -> plasmolysis
35
what is a hypOtonic solution
lower solute than cell
water molecules will move from the solution, thru the semiperm membrane and INTO the cell
water moves in, cell will swell
animal cells will swell and eventually burst -> hemolysis (red blood cell)
plant cells will push against surrounding cell wall -> turgid (turgor pressure)
36
what is the difference between hypertonic and hypotonic
hypertonic -> water molecules LEAVE
hypotonic -> water molecules ENTER
37
what is active transport
movement of substances against concentration gradient
38
how does active transport operate
active energy coupled transport requires energy
uses protein carrier -> active transporter
substance binds to transporter and moves against the gradient
active transporter changes conformation upon binding to substance -> movement is in one direction
39
what are the 2 types of active transport
primary active transport and secondary active transport
40
what is primary active transport
sodium potassium pump - Na+/K+-ATPase
only present in animal cells - moving Na+ ions out of the cell and K+ ions into the cell
Na+/K+ pump uses energy released from hydrolysis of ATP to move 3 Na+ ions and 2 K+ ions against the gradient
the sodium and potassium ions move in opposite directions -> Na+/K+-ATPase is an antiporter
41
what are the steps of the Na+/K+-ATPase transport cycle?
1. Na+ ions binds to the transport protein on inside of membrane
2. ATP is hydrolyzed -> Pi transferred to the transport protein
3. conformation of Na+/K+ ATPase is changed
4. Na+ ions are released to external space
5. K+ ions bind on outside of membrane
6. phosphate group on the transport protein is removed
7. Na+/K+-ATPase transport protein snaps back to its og conformation
8. K+ ions move inside of cell
42
what is and causes an electrochemical gradient
gradient that has both an electrical (charge) component and a chemical component
energy stored in the concen gradient that is established thru primary active transport
can drive movement of other molecules thru secondary active transport
43
what is secondary active transport
cells use transport proteins to move ions across the membrane -> drives the movement of other substances against their concentration gradient
cells may actively pump protons across the membrane using ATP
- pump creates a proton concentration gradient (chemical gradient)
because the protons are charged, the proton concentration gradient is also an electrical gradient
- movement of protons down their gradient drives movement of other molecules against their gradients -> secondary active transport (co-transport)
44
what is the difference between primary and secondary active transport
primary: uses chemical energy of ATP directly
secondary: uses electrochemical gradient
45
what are the 2 types of co-transport
antiport - 2 solutes move in opposite directions (ex. Na+ and H+)
symport - 2 solutes move in the same direction (ex. Na+ and glucose)
46
explain the glucose example of secondary transport
glucose can be taken up by an intestinal cell against its concentration gradient using secondary transport
uptake by co-transport occurs at apical plasma membrane of intestinal cell
glucose then diffuses thru cytoplasm of intestinal cell
at basal plasma membrane -> glucose travels to bloodstream via facilitated diffusion
47
what is the endomembrane system?
eukary cells have an internal set of membranes that define the organelles
the system of interconnected organelles within the cell
48
what are typical components to the endomembrane system in an ANIMAL cell
1. endoplasmic reticulum (ER)
2. golgi apparatus
3. lysosomes
4. mitochondria
5. cytoskeleton
6. nucleus
49
what is an endoplasmic reticulum
apart of endomembrane system in eukaryotic cells
involved in the synthesis of proteins and lipids
49
what is the golgi apparatus
apart of endomembrane system in eukaryotic cells
modifies proteins and lipids produced by ER
acts as a "sorting station"
50
what are lysosomes
apart of endomembrane system in eukaryotic cells
specialized vesicles derived from golgi apparatus
contain enzymes that break down macromolecules such as proteins, nucleic acids, lipids, and complex carbs
51
what is the mitochondria
apart of endomembrane system in eukaryotic cells
specialized organelles that harness energy for the cell from chemical compounds like sugars and convert it into ATP
51
what is the cytoskeleton
apart of endomembrane system in eukaryotic cells
protein scaffold that provides cell structure
52
what are typical components to the endomembrane system in a PLANT cell
similar features to animal cells but additionally:
1. cell wall
2. vacuoles
3. chloroplasts
52
what is a cell wall
apart of endomembrane system in eukaryotic cells, SPECIFICALLY PLANT CELLS
provides additional support to the cell
52
what are vacuoles
apart of endomembrane system in eukaryotic cells, SPECIFICALLY PLANT CELLS
contribute to the structure by maintaining turgor pressure
53
what are chloroplasts
apart of endomembrane system in eukaryotic cells, SPECIFICALLY PLANT CELLS
where photosynthesis takes place -> convert energy from sunlight into simple sugars/chemical energy that the cell can use
53
what is the cytoplasm
entire contents of the cell minus the nucleus
54
what is the cytosol
region outside the organelles but inside the plasma membrane
55
how are the membranes surrounding internal organelles in eukaryotic cells connected?
1. physically connected by membrane bridges
2. transiently by vescicles -> form by budding off an organelle
56
what are the specific functions that the endomembrane allows to take place within defined spaces of the cell
plasma membrane and nuclear envelope
er and golgi apparatus
lysosomes
vesicles that moves between the above
57
what is the purpose of bulk transport
cells also need to bring in and remove larger molecules/particles across the membrane
need to do this w/o breaking continuity of cell membrane
58
what is exocytosis
process where a vesicle fuses with the cell membrane
vesicle that has budded off from endomembrane system can fuse with plasma membrane and deliver its contents into extracellular space
59
what is endocytosis
process where material from outside cell is brought into a vesicle that can then fuse with other organelles
60
what are common characteristics among variations of endocytosis
cell membrane invaginates: forms a pocket around the target material
the pocket pinches off inside cell: results in material surrounded by a newly created intracellular vesicle formed from the cell membrane
61
what are variations of endocytotic processes
1. phagocytosis (delivery to a lysosome via a phagosome)
2. pinocytosis (extracellular fluids taken up without recognition by plasma membrane surface - "cell drinking")
3. receptor-mediated endocytosis (cell membrane receptor proteins have binding specificity for certain substances)
62
what is phagocytosis and how does it work?
what: uptake of particulate matter, delivery to a lysosome via a phagosome
how:
1. phagosome fuses with primary lysosome to form secondary lysosome -> activates lysosomal hydrolytic enzymes.
2. contents are then digested in secondary lysosome
63
what is pinocytosis
"cell drinking" - extracellular fluids taken up without recognition by plasma membrane surface
results in smaller vesicles and the vesicle does not need to merge with a lysosome
any molecules present in the enclosed fluid enters the cell
64
what is receptor-mediated endocytosis
cell membrane receptor proteins have binding specificity for certain substances
coated pit is the site where receptors on extracellular side are concentrated (indented surface)
clathrin is attached to the cytoplasmic side (dynamic changes bring vesicle into cell)
material is then delivered to a network of tubules and vesicles -> endosomes
- early endosomes are located near peripheral region of cell
- late endosomes are in the interior part of cell, receives material from early endosomes and golgi apparatus
65
what are nuclear pores
allows molecules to move in and out of nucleus
essential for nucleus to communicate with rest of cell
65
what is the nucleus in the endomembrane system
innermost organelle of endomembrane system
stores cell's DNA
nuclear envelope is a double membrane that surrounds the nucleus and consists of 2 membranes - inner and outer)
nuclear membrane is perforated by protein openings called nuclear pores -> allow molecules to move in and out
pores are essential for nucleus to communicate with rest of the cell
66
what is the rough endoplasmic reticulum (RER)
apart of ER
ribosomes associated with the membrane and exposed to the cytosol
ribosomes are sites of protein synthesis -> amino acids are assembled into polypeptides
ribosomes may also be free in cytosol
67
what is the smooth ER (SER)
lacks ribosomes: parts of smooth ER bud off to produce vesicles that are free to move in cytosol
SER is site of fatty acid and phospholipid synthesis
lot of SER in cells that are specialized for lipid production
68
where is the golgi apparatus located?
not physically attached to ER, next step for vesicles that bud from ER
69
what are the 3 functions of the golgi apparatus
3 functions:
1. further modify proteins and lipids produced in ER
2. sort proteins/lipids as they move to final destination
3. add carbs to proteins and lipids
70
the golgi apparatus consists of flatted sacs called _____
consists of flattened sacs called "cisternae"
- surrounded by small vesicles which transport proteins from ER to golgi apparatus and cell membrane/other organelles
71
what do the enzymes within the golgi apparatus do?
chemically modify proteins and lipids
each step is performed in a diff region of the golapp -> diff sets of enzymes catalyze specific reactions
ex. glycosylation: process where carbs (glycans) are covalently linked to lipids/specific amino acids of proteins
72
what does phagocytosis provide?
1. nutrition -> products move into cytoplasm
2. defence -> kill microorganisms
- done by professional phagocytes in animals (macrophages and neutrophils)
- lysosome contains lysozyme (enzyme that degrades bacterial cell walls)
- acidic pH in lysosome kills some microorganisms
- oxidases on inner surface of phagosome produce H2O2 (kills some bacteria)
73
where is the endoplasmic reticulum located and how large is it
outer membrane of nuclear envelope is physically cont. with the ER
large organelle in most cells
74
what is the specific function of the ER and what is it a network of?
produces many of the lipids/proteins used inside/outside cell and is a network of interconnected tubules and flattened sacs (interior = "lumen")
75
if the ER is large, how does it fit in cell?
highly folded nature allows for a large membrane surface area to fit inside cell
76
what are the 2 components of the ER?
RER & SER
(rough and smooth)
77
how are lysosomes derived from the golgi apparatus?
golapp degrades damaged/unneeded macromolecules (lipids, proteins, nucleic acids, and complex carbs), which then can be packaged into vesicles that fuse with lysosomes
78
where are enzymes found inside a lysosome synthesized?
in the RER, then sorted in the golgapp, then packaged into lysosomes
79
what is the purpose of the protein pump in the lysosome
keeps pH acidic, at around 5
80
why is it important to keep contents of lysosome separate from rest of cell?
because optimal pH is around 7(neutral), proteins and organelles within cytosol would degrade if exposed to pH found in lysosomes
81
what are 2 membranous organelles that are not part of the endomembrane system (EMS)
mitochondria and chloroplasts
82
what is common to both mitochondria and chloroplasts
specialized harnessing energy for the cell
semi-autonomous -> grow and multiply independently and contain own circular genomes
83
how are mitochondria shaped?
rod-shaped -> present in almost all eukaryotic cells
84
what are the 4 parts to mitochondria
1. outer membrane
- integral proteins: form large, nonselective membrane channels (porins)
2. intermembrane space: aqueous compartment between outer and inner membrane
3. inner membrane: highly convoluted (folded, twisted, coiled) -> electron transport chain and ATP synthase
4. matrix: citric acid cycle, ribosomes, DNA
85
what is the structure of chloroplasts
surrounded by a double membrane and have an internal membrane bound compartment -> thylakoid (flattened membrane sacs within chloroplast)
lumen -> space inside thylakoid
grana -> orderly stacks of thylakoids
stroma -> space surrounding thylakoids
86
what is the thylakoid membrane
the third membrane in the interior of the chloroplast
contains light-collecting molecules -> pigments
- chlorophyll is most common (prod green colour seen in many plants)
87
what is the origin of chloroplasts
resemble cyanobacteria (photosynthetic bacteria) in organization and biochem
- originated as an endosymbiotic relationship between a cyanobacterial cell that had been engulfed by a eukary cell
88
what is the origin of mitochondria
resemble free-living bacteria in organization and biochem
- originated as endosymbiotic bacteria, proteobacteria, similar to chloroplasts
BIOL130
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