Transport across cell membrane Flashcards
1
Q
What are the other names for plasma membrane?
A
Cell membrane
Plasmalemma
2
Q
What is the plasma membrane?
A
Boundary that separates the living cell from its surroundings.
3
Q
What is the benefit of plasma membrane?
A
Maintain a life supporting internal environment by regulating passage of material in and out of cell.
4
Q
What does plasma membrane exhibits?
A
Selective permeability.
5
Q
What is the fluid mosaic model?
A
Cell membrane consists of a fluid bilayer of phospholipid molecules which the proteins are embedded or associated like tiles in a mosaic pictures.
6
Q
Is the mosaic pattern static?
A
No because the proteins keep changing their positions.
7
Q
What is the structure of plasma membrane?
A
Continuous
fluid
Double layer of phospholipids
8
Q
Most constituents of plasma membrane is?
A
Amphipathic - have hydrophilic and hydrophobic regions
9
Q
Why is phospholipid the most abundant lipid in plasma membrane?
A
Hydrophobic tails are sheltered inside and hydrophilic heads are exposed to water on both sides.
10
Q
Which protein is embedded in bilayer?
A
Integral proteins
11
Q
Which protein is associated with extracellular face?
A
Peripheral proteins
12
Q
Name the carbohydrates linked on plasma membranes.
A
Glycoprotein - linked to protein
Glycolipid - linked to lipids
13
Q
Where is cholesterol located?
A
Within membrane?
14
Q
What anchors integral membrane proteins?
A
Fibers of extracellular matrix and cytoskeleton microfilaments
15
Q
Membranes are held together by?
A
Weak hydrophobic interactions
16
Q
Why do phospholipids move?
A
To maintain fluidity.
17
Q
How many times does lateral movement occur?
A
10^7 times per second
18
Q
How many times does flip flop occur?
A
once per month from one side to another, helped by flippases.
19
Q
Why must one hydrophobic core must be in optimal fluid state?
A
Easy for substance to pass through.
20
Q
Temperature that a membrane solidifies depends on what?
A
The type of lipid.
21
Q
What happens when lower than normal temperatures?
A
Membrane function inhibited
Motion of fatty acid chain is slowed.
Lipid bilayer becomes too rigid.
22
Q
Why do membranes rich in unsaturated fatty acids is more fluid?
A
Prevents packing through kink.
23
Q
What does proteins do in plasma membrane?
A
Determines most of membrane’s specific functions.
24
Q
What are two groups of proteins?
A
Extrinsic and intrinsic
25
What is peripheral aka extrinsic proteins?
Not embedded but loosely bound to bilayer surface.
26
What is integral aka intrinsic proteins?
hydrophobic segments consists of stretches of non polar amino acids coiled into alpha helices.
hydrophilic segments have hydrophilic non helical amino acid.
27
What does integral proteins do?
Penetrate hydrophobic core completely as transmembrane proteins.
28
The ends of uncoiled amino acid in integral proteins are?
Extracellular - N terminus
Cytoplasmic - C terminus
29
What does integral proteins do?
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to CS and ECM
30
How does integral proteins work as a transport?
Channel proteins is hydrophilic and passive transport that allows particular solute across membrane.
Carrier proteins brings substance from one side to another by changing its shape by using ATP in active transport.
31
How does integral proteins work as enzymes?
Its active side exposed to the adjacent solution.
Some are organized as team to carry out sequential steps of a metabolic pathway.
32
How does integral protein works as a signal receptor?
Has a binding site with a specific shape that fits chemical messengers such as hormones where message is relayed to the insides of cells.
33
Why is signal reception important in a cell?
Activates metabolic pathway
Transfer stimulus
34
What works as special identification tags on proteins?
Glycoproteins
35
How do proteins help in forming tissues?
Membrane proteins of adjacent cells hook together in gap or tight junctions to join the cells.
36
Why do proteins bond to CS?
maintain cell shape and stabilize the location of the proteins.
37
Why do proteins bond to ECM?
Coordinates extracellular and intracellular changes.
38
How do cells recognize each other?
Binding to molecules containing carbohydrates on the extracellular surface of plasma membrane
39
How is glycolipids and glycoproteins formed?
Membrane carbohydrates covalently bond to lipids and proteins.
40
What is the importance of membrane carbohydrates?
Sorting and organizing cells into tissues and organs
Basis for rejection of foreign cells by immune system.
41
What does cholesterol do within plasma membrane?
reduces membrane fluidity at moderate temperatures but hinders solidification at low temperatures.
42
How does a cell synthesize its own plasma membrane?
Synthesizing proteins through ER, ribosome, GA
43
What can pass through membrane?
Hydrophobic molecules that are non polar such as hydrocarbons
44
What doesn't pass through the membrane easily?
Hydrophilic polar molecules such as ions, sugars, glucose, water, charged ones.
45
What is passive transport?
Diffusion of substance across a membrane without any energy used.
Goes down the concentration gradient.
46
What are examples of passive transport?
Simple diffusion
osmosis
Facilitated diffusion
47
What is diffusion?
Tendency for molecules to spread out evenly into the available space caused by kinetic energy possessed by ions and molecules.
48
Where do substances diffuse?
Higher concentration to lower concentration.
49
When does molecules equally move to different sides?
During dynamic equilibrium.
50
What affects diffusion through membrane?
Membrane's permeability
Size and type of molecule diffusing
Lipid diffusion cannot be controlled by the cell since the phospholipid bilayer is made from lipids.
51
What factors determine the rate of diffusion?
Concentration gradient
Surface area
Thickness of membrane aka its distance
Temperature
52
What is Fick's Law?
The rate of diffusion is proportional to both the surface area and concentration gradient and is inversely proportional to the thickness of membrane.
53
What is osmosis?
Diffusion of water across a selectively permeable membrane.
54
How does osmosis work?
Water diffuses from dilute to concentrated solution until it is equal on both sides.
55
What is water potential?
Tendency for water to diffuse out of a solution by osmosis.
56
What is the water potential of pure water at atmospheric pressure?
psi = 0 kPa.
57
What does water potential depend on?
Solute concentration
Pressure of both sides
58
What is solute potential?
Potential of a particular solution that allow water to enter due to presence of solutes.
Negative value
59
What is pressure potential?
Hydrostatic pressure that is exerted on water in a cell.
Positive value
60
Water potential equals to?
Solute potential + Pressure potential
61
What is tonicity?
Ability of solution to cause a cell to gain or lose water.
62
What is hypotonic solution?
A solution that has low solute concentration than a cell.
63
What is hypertonic solution?
A solution that has high solute concentration than a cell.
64
What is isotonic solution?
A solution that has same solute concentration as a cell.
65
What happens when plant and animal cells are placed in isotonic solution?
P - flaccid, normal size
A - normal size
66
What happens when plant and animal cells are placed in hypotonic solution?
P - water enters, cell swells and becomes turgid
A - water enters, cell swells and bursts called lysis
67
What happens when plant and animal cells are placed in hypertonic solution?
P - water leaves, cell shrinks and plasmolysis
A- water leaves, cell shrinks and crenates
68
What does channel proteins do?
Provide corridors that allows specific molecules or small ions to cross the membrane.
69
What do gated channels do?
Open or close in response to a stimulus
70
What do carrier proteins do?
Undergoes change in shape to translocate the solute binding site across the membrane.
71
Talk about active transport.
Carrier proteins are involved.
Requires energy in ATP form.
Against concentration gradient.
72
How do carrier proteins work as ATPase enzyme?
They catalyze the splitting of ATP into ADP + phosphate through hydrolysis
Uses that energy released to change shape (smart biches)
73
Which ion is in sodium-potassium pump?
Obviously Na and K.
74
The concentration of Na is bigger at?
Extracellular fluid.
75
General describe the process of sodium-potassium pump.
1. Cytoplasmic Na binds because the protein shape has high affinity.
2. Na binding stimulates phosphorylation by ATP.
3. Protein shape changes and affinity for Na reduced and released outside.
4. New shape has high affinity for K and binds at EC which triggers release of phosphate.
5. Original shape restored and lowers affinity for K.
6. K is release and cycle repeats.
76
What is phosphorylation?
Adding a molecule and receiving a phosphate.
77
Why is it relatively negative inside the cell compared to ECM?
Out comes 3 Na+, in goes 2 K+
78
What is membrane potential?
Voltage difference across a membrane due to separation of opposite charges.
79
What drives the diffusion of ions across membrane?
Electrochemical gradient.
80
What are the combination of electrochemical gradient?
Chemical force - concentration gradient
Electrical force - effect of membrane potential
81
The membrane potential favors what kind of molecule transport?
Passive transport.
82
What is electrogenic pump?
Creates voltage during ion transportation.
Stores energy for cellular work.
83
What are the examples of electrogenic pump?
Sodium-potassium pump
Proton pump (hydrogen out of cell)
84
What is cotransport?
Active transport of a solute indirectly drives transport of other substances.
When one follows gradient, other opposes it.
85
What are the examples of cotransport?
Antiport - in and out of cell
Symport - one direction only
86
What is bulk transport?
Large molecules cross the membrane in bulk through vesicles.
Requires energy.
87
What are the two types of bulk transport?
Endocytosis - enter
Exocytosis - exit
88
What is endocytosis?
Cell takes in macromolecules by forming vesicles from the plasma membrane.
89
What are the three types of endocytosis?
Phagocytosis - eating
Pinocytosis - drinking
Receptor mediated endocytosis
90
What is exocytosis?
Transport vesicles migrate to the membrane to fuse and release their contents outside.
91
How does phagocytosis work?
Cell engulfes particles by extending pseudopodia (two false legs) around it and pack it with a membraneous sac called food vacuole.
It fuses with a lysosome containing hydrolytic enzymes that digests the particle.
92
How does pinocytosis work?
Cell gulps droplets of EC fluid into tiny vesicles formed by plasma membrane infolding.
Cell obtains molecules dissolved in the droplets.
Cytoplasmic side of the infolding membrane has coat protein.
93
How does receptor mediated endocytosis work?
Specific solutes bind to receptor proteins embedded in plasma membrane exposed to EC.
Receptors cluster in coated pits that forms a vesicle containing bound molecules.
After the materials are digested, the emptied receptors are recycled to plasma membrane by the same vesicle.
94
How does human cells take in cholestrol?
Receptor mediated endocytosis carries cholestrol in the form of low density lipoprotein (LDL)
95
Explain the uptake of LDL.
LDL attached to specific receptors in coated pits made from Clathrin.
Endocytosis forms coated vesicle in cytosol and Clathrin is removed.
Uncoated vesicle fuses with endosome.
Receptors are recycled.
Vesicle containing LDL fuses with lysosome forming a secondary lysosome.
Hydrolytic enzyme digests cholestrol from LDL.
96
Why is cholestrol uptake important in cell?
Maintain fludiity in plasma membrane.
Hormone production for reproductive.
97
Briefly describe the process of exocytosis.
Materials enclosee in a membrane vesicle from RER and Golgi body.
Vesicle approaches plasma membrane, fuses and releases its content outside.
