membrane structure, function and transport Flashcards
1
Q
what is the simplest collection of matter that can be considered a living entity
A
a cell
2
Q
how does a light microscope work
A
visible light is passed through the specimen and then through the glass lenses. the lenses refract the light so that the image is projected into the eye or into the camera
3
Q
what are the 3 important parameters in microscopy
A
resolution
magnification
contrast
4
Q
what is magnification
A
the ratio of an objects image size to its real size
5
Q
what is resolution
A
a measure of the clarity of the image - it is the minimum distance two points can be separated and still be distinguished as separate points
6
Q
the light microscope cannot resolve detail finer than …….……. micrometres regardless of the magnification
A
0.2
7
Q
what is contrast
A
the difference in brightness between the light and dark areas of an image
8
Q
how can contrast be enhanced
A
we can stain certain components of the specimen to make them stand out
9
Q
how does the electron microscope work
A
it focusses a beam of electrons through the specimen or onto its surface
10
Q
…….………. is inversely related to the wavelength of light (or electrons) a microscope uses for imaging
A
resolution
11
Q
electron beams have much longer/shorter wavelengths than visible light
A
shorter
12
Q
what is the highest resolution an electron microscope can achieve
A
2 nm
13
Q
what is a scanning electron microscope used for
A
useful for detailed study of topography of a specimen
14
Q
how does a scanning electron microscope SEM work
A
the electron beam scans the surface of the sample, usually coated with a thin film of gold
the beam excites electrons on the surface and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal sent to a video screen
the result is a 3D image of the specimen
15
Q
how does a transmission electron microscope TEM work
A
it aims a beam of electrons through a very thin section of the specimen
the specimen has been stained with atoms of heavy metals which attach to certain cellular structures, enhancing the electron density of some parts of the cell compared to others
the electrons passing through the specimen are scattered more in the denser areas, so fewer are transmitted
the image displays a pattern of transmitted electrons
16
Q
what is a transmission electron microscope used for
A
it is used to study the internal structure of cells
17
Q
what kind of lenses do SEM and TEM use and why
A
they use electromagnets as lenses to bend the paths of the electrons ultimately focusing the image onto a monitor for viewing
18
Q
what is a disadvantage of the electron microscope
A
methods used to prepare the specimen kills the cells
19
Q
specimen preparation for any kind of microscopy can introduce artefacts. what are these
A
structural features seen in micrographs that do not exist in the living cell
20
Q
microscopes are the most important tools for which field of study
A
cytology - the study of cell structure
21
Q
what is biochemistry
A
the study of the chemical processes (metabolism) of cells
22
Q
what is cell fractionation
A
a technique used to study the structure and function of cells
it takes apart and separated major organelles and other subcellular structures from one another
the piece of equipment used is called a centrifuge
at lower speeds the pellet consists of larger components
at higher speeds the pellet consists of smaller components
23
Q
what is the difference between stains used for light and electron microscopy
A
light microscopy stains are coloured molecules that bind to cell components, affecting the light passing through
stains for electron microscopy involve heavy metals that affect the beams of electrons
24
Q
eukaryotic cells have internal ………… that compartmentalize their functions
A
membranes
25
what are the 2 distinct types of cells
prokaryotes and eukaryotes
26
organisms of the domains bacteria and archaea consist of what type of cells
prokaryotes
27
protists, fungi, animals and plants all consist of what type of cells
eukaryotes
28
all cells are bonded by what kind of membrane
plasma membrane
29
inside all cells is a semifluid, jelly like substance called what
the cytosol - where glycolysis happens - where cellular components are suspended
30
TRUE/FALSE all cells contain chromosomes
TRUE - they carry genes in the form of DNA
31
TRUE/FALSE all cells contain ribosomes
TRUE
32
what are the major differences between eukaryotes and prokaryotes
location of DNA - in E most of the DNA is found in the nucleus which is bounded by a double membrane. in P DNA is concentrated in a region that is not membrane enclosed, called the nucleoid
almost all prokaryotes lack the organelles with specialised structure and function that eukaryotes have
33
the interior of both eukaryotic and prokaryotic cells is called what
the cytoplasm
| in eukaryotes this is the region between the nucleus and the plasma membrane
34
instead of membranes some prokaryotes have internal regions surrounded by what within which specific reactions take place
proteins
35
eukaryotic cells are generally much larger/smaller than prokaryotes
larger
36
what is the typical diameter of bacteria cells
1-5 micrometres
37
what is the typical diameter of eukaryotic cells
10-100 micrometres
38
as a cell increases its size its surface area grows proportionally less/more compared to its volume
less
39
a smaller/larger object has greater surface area to volume ratio
smaller object
40
many cells have long thin projections called microvilli why are these useful
they increase surface area without an appreciable increase in volume
41
what are the advantages of having organelles
they provide microenvironments that support specific metabolic functions
they allow reactions that are not compatible to occur simultaneously within the cell
42
why do plasma membranes and organelle membranes participate directly in the cell' metabolism
because they have many enzymes built into the membranes
43
what is the basic fabric of most membranes
the phospholipid bilayer with proteins embedded in it
44
what part of a eukaryotic cell contains most of the genes
the nucleus - some genes are located in the mitochondria and chloroplasts
45
what is the pore complex of the nuclear membrane
the nuclear envelope is perforated by pore structures - the pore complex is an intricate protein structure that lines each pore
it plays an important role in the cell by regulating the entry and exit of proteins, RNAs, large complexes and macromolecules
46
apart from at the pores, the nuclear side of the envelope is lined by what
the nuclear lamina - a netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope
47
how is DNA organised in the nucleus
into units called chromosomes
48
the complex of DNA and proteins making up the chromosomes is called what
the chromatin
49
what is the prominent structure in the non dividing nucleus
nucleolus
- where rRNA is synthesised from instructions in the DNA
- proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes. these subunits then exit the nucleus through the pores in to the cytoplasm where a ribosome can be assembled
50
the nucleus directs protein synthesis by synthesising what according to instructions provided by DNA
mRNA
51
how is mRNA transported to the cytoplasm from the nucleus
via the nuclear pores
52
what are ribosomes made of
rRNA
53
why are ribosomes not considered as organelles
because they are not membrane bounded
54
what are the 2 cytoplasmic locales where ribosomes build proteins
free ribosomes are suspended in the cytosol
| bound ribosomes are attached to the outside of the ER or nuclear envelope
55
TRUE/FALSE bound and free ribosomes are structurally identical
TRUE - ribosomes can play either role at different times
56
most proteins made on free ribosomes function where
the cytosol
57
bound proteins generally make proteins that function where
they are inserted into membranes for packaging within certain organelles or for export from the cell
58
what does the endomembrane system include
it includes the ER, nuclear envelope, Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles and the plasma membrane
59
what tasks does the endomembrane system carry out
synthesis of proteins
transport of proteins into membranes and organelles or out of the cell
metabolism and movement of lipids
detoxification of poisons
60
the membranes of the endomembrane system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles. What are vesicles
sacs made from membrane
61
are the membranes of the endomembrane system identical
no - moreover, the thickness, composition and types of reaction of a membrane are not fixed and may be modified several times
62
what is the ER made of
a network of membranous tubules and sacs called cisternae
the ER membrane separates the ER lumen or cisternal space from the cytosol
the space between the 2 membranes of the nuclear envelope is continuous with the lumen of the ER
63
what are the 2 distinct regions of the ER
smooth ER
| rough ER
64
what does the surface of smooth ER lack
ribosomes
65
ribosomes are studded on the outer surface of which type of ER
rough
66
…….……….. are attached to the cytoplasmic side of the nuclear envelopes outer membrane, which is continuous with the ER
ribosomes
67
what are the functions of the smooth ER
```
contribute in:
synthesis of lipids
metabolism of carbohydrates
detoxification of drugs and poisons
storage of calcium ions
```
68
detoxification of drugs by the ER usually involves adding which functional group
hydroxyl groups - this makes them more soluble in water and easier to flush out
69
what are the functions of the rough ER
proteins enter the ER from bound ribosomes and form glycoproteins by attaching carbohydrates. the ER keeps these proteins separate from the proteins in the cytosol produced by free ER. the secretory proteins depart form the ER in vesicles from a region called the transitional ER
rough ER is a membrane factory for the cell - it grows by adding membrane proteins and phospholipids into its own membrane. as polypeptides destined to be membrane proteins grow from the ribosomes they are inserted into the ER membrane
phospholipid synthesis - ER membrane enzymes synthesis phospholipids from precursors in the cytosol
70
most secretory proteins are what type of protein
glycoproteins - proteins with carbohydrates covalently bonded to them
71
what are vesicles in transit from one part of the cell to another called
transport vesicles
72
after leaving the ER where do many of the transport vesicles travel
to the Golgi apparatus
73
what happens to products of the ER in the Golgi apparatus
they are modified and stored and sent to other locations
74
what are the flat membranous sacs called that make up the Golgi apparatus
cisternae
75
the membrane of each cisterna in the Golgi apparatus separates tits internal space form what
the cytosol
76
what are the 2 sides of a Golgi stack referred to as
the cis and trans faces which act as the receiving and shipping departments respectively
77
how does a transport vesicle that has bud from the ER add its lumen contents to the Golgi apparatus
it fuses with the Golgi membrane on the cis side
78
how do vesicles leave the Golgi apparatus to go to other locations
they leave via the trans side
79
give some examples of the tweeking that the Golgi apparatus does to products of the ER
remove and substitute sugar monomers
| alter membrane phospholipids
80
many polysaccharides secreted by cells are products of what cell structure
the Golgi apparatus
81
how does the Golgi stack label its products and target them for various parts of the cell
by adding identification tags such as phosphate groups
82
how do vesicles know where to take Golgi apparatus products
they may have external molecules on their membranes that recognise parts of particular organelles
83
in what environment to lysosomal enzymes work best
acidic environment
84
what can happen if a large number of lysosomes leak in a cell
the cell becomes digested due to the acidity
85
what structure makes hydrolytic enzymes and lysosomal membrane
the rough ER and are then modified in the GA
86
how are is the lysosomal membrane not damaged by the acidic conditions of the lysosome
the shapes of the proteins protect vulnerable bonds from enzymatic attack
87
what are the 3 steps in lysosome phagocytosis
1. lysosome contains active hydrolytic enzymes
2. lysosome fuses with food vacuole
3. hydrolytic enzymes digest food particles
88
what are the 3 steps in lysosome autophagy
1. lysosome fuses with vesicle containing damaged organelles
2. hydrolytic enzymes digest organelle components
3. the resulting small organic compounds are released into the cytosol for reuse
89
what are vacuoles
large vesicles derived from the ER and Golgi apparatus
90
what is the result of the vacuole membrane being selective in solute transport
the solution inside the vacuole varies from the cytosol
91
by what process are food vacuoles formed
phagocytosis
92
what do contractile vacuoles do
pump excess water out of the cell of fresh water eukaryotes
93
how can vacuoles help protect plants
they can store poisonous substances to protect them from animals
94
what is the solution inside the vacuole called
the cell sap
95
describe in 6 steps the flow through the endomembrane system
1. the nuclear envelope is connected to the rough ER which is also continuous with the smooth ER
2. membranes and proteins produced by the ER move via transport vesicles to the Golgi
3. the Golgi pinches off transport vesicles and other vesicles that give rise to lysosomes, other types of specialised vesicles and vacuoles
4. the lysosome is available for fusion with another vesicle for digestion
5. a transport vesicle carries proteins to the plasma membrane for secretion
6. the plasma membrane expands by fusion of the vesicle and proteins are secreted from the cell
96
what does the endosymbiont theory state
1. an ancestor of eukaryotic cells engulfed an oxygen using nonphotosynthetic cell
2. the engulfed cell became and endosymbiont (a cell living in another)
3. this developed into a eukaryotic cell with a mitochondrion
4. one of these cells took up a photosynthetic prokaryote becoming the ancestor of eukaryotic cells that contained chloroplasts
97
what evidence supports the endosymbiont theory
mitochondria and chloroplasts have double membranes
chloroplasts have an internal system of membranous sacs
like prokaryotes, mitochondria and chloroplast contain ribosomes and circular DNA
mitochondria and chloroplasts are autonomous (independent) - they grow and reproduce independently
98
describe the structure of the 2 membranes of the mitochondrion
both membranes are made from phospholipids
the outer membrane is smooth
the inner membrane is convoluted with infoldings called cristae
99
what is the intermembrane space of the mitochondrion
the area between the 2 membranes
100
what is the mitochondrial matrix
the area enclosed by the inner membrane which contains many enzymes, mitochondrial DNA and ribosomes
101
what gives the inner mitochondrial membrane a large surface area
the cristae
102
what is the green pigment that chloroplasts contain called
chlorophyll
103
what is the membranous system inside the chloroplast called and what is it made of
thylakoids - flattened interconnected sacs
they contain stacks called grana
the fluid outside the thylakoid is called the stroma which contains DNA, ribosomes and enzymes
104
what are the 3 membrane compartments of the chloroplast
intermembrane space (between the membranes)
the stroma
the thylakoids
105
what is a plastid
found in cells of photosynthetic eukaryotes - closely related to chloroplasts
106
what is a peroxisome
an organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen, producing then degrading hydrogen peroxide to water
107
what do glyoxysomes do
they contain an enzyme that converts plant fatty acids to sugars which seedlings use as a source of energy and carbon until they can photosynthesise
108
what are the functions of the cytoskeleton
1. give mechanical support to the cell and maintain its shape (important because animal cells lack walls)
2. provides anchorage for many organelles and cytosolic enzymes
3. it contributes to cell motility
109
what to things need to interact for cell motility
the cytoskeleton and motor proteins
110
describe microtubules
- they are the thickest fibre of the cytoskeleton
- they are hollow tubes composed of globular tubulin dimers (2 subunits) made of beta and alpha tubulin
main functions
- maintenance of cell shape
- cell motility (cilia and flagella)
- chromosome movement in cell division
- organelle movements
111
describe intermediate filaments
- fibrous proteins e.g. keratin coiled into cables
- intermediate thickness
main functions
- maintenance of cell shape
- anchorage of nucleus and other organelles
- formation of nuclear lamina
112
describe microfilaments
- two intertwined strands of actin
- thinnest
main functions
- maintenance of cell shape
- changes in cell shape
- muscle contraction
- cytoplasmic streaming in plant cells
- cell motility (amoeboid movement)
- division of animal cells
113
how do microtubules change length
they can grow by adding tubulin dimers
| they can disassemble by removing dimers that can then be used in microtubules elsewhere
114
what is the plus end of a microtubule
the end that can assemble and disassemble the quickest
115
give some examples of how microtubules are involved in cellular activities
- they serve as tracks along which organelles with motor proteins can move
- microtubules guide vesicles from the ER to the Golgi and then to the plasma membrane
- microtubules are involved in separation of chromosomes during cell division
116
what is a centrosome
a region that is often located near the nucleus from which microtubules grow out of - these microtubules function as compression-resisting girders of the cytoskeleton
117
what is a centriole
they are found in pairs within the centrosome each centriole is composed of 9 sets of triplet microtubules arranged in a ring
118
what are cilia and flagella
- microtubule containing extensions that project form the cells
- cilia and flagella often act as locomotor appendages
- there are often many cilia per cell but only one or two flagella per cell. A cell cannot have cilia and flagella
- flagella and cilia differ in their beating patterns
119
describe the motion of flagella
a flagellum moves in an undulating motion
flagella bending involves dynein proteins, bound on each microtubule doublet
dynein has two projections that move using energy from ATP hydrolysis
One projection remains attached to the microtubule whilst the other detaches and binds further along
this causes an bend
this repeated motion creates wave like movement
120
describe the motion of cilia
cilia have motor proteins that travel along the microtubules and create a bend.
a power stroke occurs resulting in the cilia moving back by 90° so they are perpendicular to the original position.
During a recovery stroke the cilia bend and slowly return to the original position.
This repeated motion of the cilia moving back and forth drives cell movement
121
describe the structure that cilia and flagella share
9 doublets of microtubules are arranged in a ring with 2 single microtubules in its centre (the 9+2 arrangement)
the microtubule assembly is anchored in the cell by a basal body (similar to a centriole) with a 9+0 arrangement
122
how do dyneins work
dyneins are attached along each outer microtubule doublet
dynein has 2 projections that walk along the microtubule of the adjacent doublet using ATP to power this
One projection remains attached to the microtubule whilst the other detaches and binds further along
this causes an bend
doublets and the central microtubules are held together by proteins so that when the dynein travels along the microtubule, the unit is held together and bends as a whole
123
TRUE/FALSE microtubules and microfilaments are present in all eukaryotic cells
TRUE
124
what is the main role of microfilaments in the cytoskeleton
to bear tension
| muscle contraction
125
the 3D network formed just inside the plasma membrane is formed by what kind of microfilaments what is its function
cortical microfilaments
| helps support the cell's shape and gives the cortex the semisolid consistency of a gel
126
what is the cortex
the outer cytoplasmic layer of the cell
127
describe amoeboid movement
amoeba form temporary cytoplasmic extensions called pseudopodia
results from changes in structure of actin filaments (microfilaments) in the cytoskeleton.
The actin filaments interact with myosin, causing cell contraction that results in the cell being pulled forward.
The cytoplasm consists of fluid plasmasol surrounded by plasmagel. The pseudopodia are formed when the plasmagel is converted to plasmasol and travels to the front of the cell
This movement launches the cell forward
128
what is cytoplasmic streaming
a circular flow of cytoplasm within cells - speeds up distribution of materials
it occurs due to actin protein interactions
129
TRUE/FALSE intermediate filaments are found in all eukaryotic cells
FALSE they are only found in some animal cells
130
which two components of the cytoskeleton specialise in bearing tension
intermediate filament and microfilament
131
which of the components of the cytoskeleton differ in diameter and composition
intermediate filaments - they are not always the same whereas microtubules and microfilaments are always the same composition
132
which of the components of the cytoskeleton is the most permanent
intermediate filaments - they are still there after the cell dies e.g. the skin contains lots of keratin filaments
133
which of the components of the cytoskeleton forms a cage around the nucleus to fix it in position
intermediate filaments
134
which of the components of the cytoskeleton makes up the nuclear lamina (this lines the interior of the nuclear envelope)
intermediate filaments
135
which of the components of the cytoskeleton can function on its own in its various forms to provide the entire framework of the cell
intermediate filaments
136
what is one of the main features that distinguishes plant cells from animal cells
animal cells don't have a cells wall
137
what is thicker the plasma membrane or the plant cell wall
the cell wall
138
what is the primary cell wall
the cell wall of a young plant that is relatively thin and flexible
139
between the primary cells walls of adjacent cells lies the ………...
middle lamella
140
what is the middle lamella
a thin sticky layer containing pectins (polysaccharides) that glues the cells together
141
describe the secondary cell wall
the cell wall of a mature plant between the plasma membrane and the primary cell wall
it is a strong durable matrix that protects and supports the cell
142
what is the extracellular matrix
made of glycoproteins (e.g. collagen) and carbohydrates
| it helps coordinate the behaviour of all the cells of that tissue
143
in the EMC where are collagen fibres found
embedded in web of proteoglycan complexes
144
in the ECM what does fibronectin do
attaches the ECM to integrins embedded in the plasma membrane
145
what are integrins
membrane proteins that bind to the ECM on the outside and to associated proteins on microfilaments on the inside
the linkage allows signals to be transmitted
they are transmembrane proteins
146
what is a proteoglycan complex
consists of hundred of proteoglycan molecules attached noncovalently to a single polysaccharide molecule
147
what is meant by the selective permeability of the plasma membrane
it allows some substances to cross it more easily than others
148
what is the fluid mosaic model
a mosaic of protein molecules in a fluid bilayer of phospholipids
149
by what interactions are membranes held together
hydrophobic interactions (weaker than covalent bonds)
150
can adjacent phospholipids in the bilayer switch positions
yes and they can do so very rapidly
151
how do proteins in the membrane of a cell move
in a highly directed manner, driven along cytoskeletal fibres in the cell by motor proteins connected to the membrane proteins' cytoplasmic regions
some proteins are immobile, often due to being attached to the ECM or the cytoskeleton
152
with decreasing temperature a membrane remains fluid for longer if its structure is what
rich in phospholipids with unsaturated hydrocarbon tails (cannot pack together as closely not as many interactions to overcome, lower mp)
153
what is the effect of cholesterol on membranes
it hinders the close packing so the membrane remains fluid for longer with decreasing temperature
154
how can fluidity affect membranes
too fluid - can't support protein function
| too solid - renders some proteins inactive because they can't move
155
what part of the membrane most influences its function
the membrane proteins
156
what are integral proteins
proteins that penetrate the phospholipid bilayer
transmembrane proteins span the entire bilayer whereas other integral proteins extend only partially into the hydrophobic interior
157
what is usually the secondary structure of the hydrophobic parts of an integral protein
alpha helix
158
what are peripheral proteins
proteins that are not embedded in the membrane but are instead loosely bound to the surface and often exposed to parts of integral proteins or the ECM
159
can proteins be found on the cytoplasmic side of the membrane
yes they can be held in place by attachment to the cytoskeleton
160
what are the 6 main functions of membrane proteins
```
transport
enzyme activity
signal transduction
cell-cell recognition
intercellular joining
attachment to the cytoskeleton and ECM
```
161
discuss HIV in terms of membrane proteins
CD4 protein attached to the membrane helps HIV infect cells leading to AIDS
Some people don't develop AIDS
they don't produce CCR5
if HIV doesn't bind to both CD4 and CCR5 then AIDS won't occur
162
how do cells recognise each other
by binding to molecules often containing carbohydrates on the extracellular surface of the plasma membrane
163
what are the 4 steps in making a membrane
1. lipids and proteins synthesised in association with the ER. in the ER carbohydrates are added to the transmembrane proteins, making glycoproteins
2. in Golgi the glycoproteins undergo further carbohydrate modification and the lipids become glycolipids
3. glycoproteins, glycolipids and secretory proteins are transported in vesicles to the plasma membrane
4. vesicles fuse with the plasma membrane and secretory proteins are released from the cell by exocytosis and glycoproteins and glycolipids are positioned on the membrane
164
what are channel proteins
transmembrane transport proteins that have a hydrophilic channel that certain molecules or ions can pass through
165
what are carrier proteins
transport proteins that that bind to their substance and change shape to facilitate passage
166
what is the diffusion of a substance over a biological membrane called
passive transport
167
a solution with a higher/lower solute concentration has a lower free water concentration
higher
168
what is the diffusion of water across a membrane called
osmosis
169
what is tonicity
the ability of a surrounding solution to cause a cell to gain or lose water
170
what is an isotonic solution
the solution is the same concentration as the inside of the cell
171
what is a hypertonic solution
greater concentration than the inside of the cell
172
hypotonic solution
lower concentration than the inside of the cell
173
what happens to the flow of water in isotonic, hypertonic and hypotonic solutions
isotonic - no change
hypertonic - water leaves cell the cell shrivels
hypotonic - water enters cell the cell lyses
this is why we need osmoregulation
174
what structure of plants, prokaryotes and fungi can help maintain the cell's water balance
the cell wall - it expands only so much before it exerts pressure back on the cell
175
when a cell wall exerts pressure on a cell once it has expanded what is this pressure called
turgor pressure - it opposes further water uptake
176
what is a cell like if it is turgid (healthy state)
very firm - when in hypotonic solution
177
what is a cell like if it is flaccid (wilted)
limp - when in isotonic solution
178
what is plasmolysis
it happens when a cell shrivels and its plasma membrane pulls away from the cell wall - happens when the plant cell (fungi and bacteria too) is in a hypertonic condition - the plant wilts and dies
179
what is facilitated diffusion
when substance pass through the membrane with help form transporter proteins (channel and carrier proteins)
180
what are ion channels
channel proteins that transport ions
181
what ae gated channels
channel proteins that open and close in response to stimuli (voltage or ligand gated)
182
why is facilitated diffusion considered a passive movement
because the solute is moving down its concentration gradient - a process that requires no energy
183
what is active transport
pumping of a solute against its concentration gradient across the membrane - this requires energy
184
what type of transport proteins carry out active transport
carrier proteins - pumps
185
what is voltage
electrical potential energy
186
which side of the membrane is most negative
the cytoplasmic side
187
what is the voltage across a membrane referred to as
the membrane potential
188
what are the steps in the sodium potassium pump
1. 3 Na bind to pump from cytoplasm
2. pump phosphorylated by ATP
3. conformational change releases Na to the extracellular environment
4. high affinity for K so 2 bind which triggers release of phosphate
5. conformational change releases K into the cytoplasm
189
what is the electrochemical gradient
the net force when considering the chemical gradient and the electrical gradient
190
what is a transport pump that generates voltage across a membrane called
an electrogenic pump
191
give an example of an electrogenic pump
```
sodium potassium pump (main one in animal cells)
proton pumps (main one in plants, fungi and bacteria)
```
192
what does the proton pump to
actively transports hydrogen ions out of the cell - usually using ATP hydrolysis a an energy source
193
what is cotransport
when the downhill movement of a substance is coupled to the uphill movement of another substance
e.g. the diffusion of H down its electrochemical gradient into the cell to drive the uptake of sucrose. a H pump maintains the concentration gradient of hydrogen so it continues to move into thee cell
194
bulk transport across the membrane occurs by which processes
endocytosis and exocytosis
195
what is exocytosis
when the cell secretes certain molecules by fusing with the plasma membrane
- a transport vesicle from the Golgi moves along microtubules of the cytoskeleton to the plasma membrane
- specific proteins rearrange the lipid molecules of the 2 bilayers so that the 2 membranes fuse
- the contents of the vesicle spill out the cell ad the vesicle membrane becomes part of the plasma membrane
196
what is endocytosis
reverse exocytosis
the cell takes in molecules and matter by forming new vesicles from the plasma membrane
- the plasma membrane sinks inwards to form a pocket
- the pocket then pinches in forming a vesicle containing material from the outside of the cell
197
what are the 3 different types of endocytosis
phagocytosis - eating
pinocytosis - drinking
receptor mediated endocytosis
198
what causes familial hypercholesterolemia
cholesterol travels in the blood as LDLs
LDLs bind to receptors on plasma membranes and then enter the cells by endocytosis
- in the disease LDLs cannot enter the cell because their receptors are missing or defective
- the disease is characterized by very high levels of cholesterol in the blood contributing to atherosclerosis (the build up of lipids in the walls of blood cells impeding blood flow)
