B2 Flashcards
Integral protein
Protein embedded throughout the entire membrane, due to amphipathic nature
Peripheral protein
Protein that remains bound to the surface of the membrane, not protruding into hydrophobic section of membrane
Cholestrol
Chain of steroid lipid that sit in hydrophobic region of membrane in animal cells
How does the fluid mosaic modal explain the structure of the cell membrane?
Phospholipids are closely associated but not bound, providing the fluidity that allows cells to change shape, and facilitates transport in and out of cell by vesicles. Mosaic refers to the presence of different proteins (and others) in a non-consistent pattern
Why are phospholipid amphipathic?
Lipid tails: non-polar, hydrophobic
Phosphate group: polar, hydrophilic
What does it mean to say that the cell membrane is partially or selecively permeable?
Some substances pass through easily while others dont
Glycoprotein
Carbohydrate chain attached to the peripheral protein
Glycolipid
Carbohydrate chain attached to lipid tails
What advantage does unsaturated fatty acid provide?
Double bonds between carbons reduces the straightness of fatty acids and thus, prevents tight packing of fatty acids
Advantages of saturated fatty acids
Straighter structure, allows for a higher melting point, denser bilayer and limited expansion at higher temperatures
How does cholestrol aid membrane fluidity in animal cells?
At higher temperatures, cholestrol adds stability to the membrane and prevents overexpansion.
At lower temperatures, presence of cholestrol prevents phospholipids from packing tightly and losing fluidity
What features must be drawn on a model of the cell membrane?
Phospholipids with saturated and unsaturated fatty acids
Integral proteins
Glycolipid
Glycoprotein
Cholestrol (animals only)
Peripheral proteins
What are the different functions of membrane proteins?
Junction: joins two cells together
Enzymes: catalyses metabolic reactions
Transport: facilitates diffusion, osmosis and active transport
Recognition: glycoproteins act as markers for cell identification
Anchorage: attachment site (usually for the cytoskeleton)
Transduction: receptor for hormone (or another signalling molecule)
Example of a membrane protein that acts as an enzyme
ATP synthase
What is the problem for the membrane when it is cold?
Condensing phospholipids reduce fluidity
How do plants deal with condensing phospholipids when it is too cold?
Uses unsaturated fatty acids to preserve distance
How do animals deal with condensing phospholipids when it is tool cold?
Unsaturated fatty acids and cholestrol to preserve distance
What is the problem with the membrane when it is too hot?
Phospholipids expand and the membrane can lyse/burst
How do plants deal with expanding phospholipids when it is hot?
Use more saturated fatty acids (which are denser, take up less space and have a higher melting point)
How do animals deal with expanding phospholipids when it is hot?
Cholestrol connects phospholipids when it is hot, saturated fatty acids
Simple diffusion
Particles moving through phospholipids from an area of high concentration to an area of low concentration without requiring a protein
Facilitated diffusion
Larger or charged/polar particle moving from high to low concentration through a protein channel/carrier protein without requiring energy
Osmosis
MOvement of water through a semi-permeable membrane via passive transport from high water concentration to low water concentration
Aquaporins
Special protein channels that specifically function for the transport of water in/out of cells
Hypertonic
Having a higher concentration of solute (out of two environments)
Hypotonic
Having a lower concentration of solutes (out of two environmetns)
Isotonic
When two aqueous solutions have the same concentration of solutes
Difference between carrier proteins and channel proteins
Channels have a polar core that creates space for polar and non-polar molecules to go through
Carriers change shape as molecule move through it
Passive transport
Movement of particles across a cell membrane from an area of high to low concentration, with the concentration gradient. No energy is required
Examples of passive transport
Simple diffusion
Facilitated diffusion
Osmosis
Active transport
Movement of particles across a cell membrane from an area of low to high concentration, against the concentration gradient. Requires energy (ATP)
Examples of active transport
Protein pumps
Endocytosis/exocytosis
Which particles do simple diffusion?
Small and non-polar (fast)
Small and polar (slow)
What types of proteins can do facilitated diffusion?
Protein channels
Carrier proteins
What is the charge of the protein channel core?
Polar core
What type of molecules can travel through a protein channel (facilitated diffusion)
Small, charged/polar molecules
Can protein channels be selective?
Yes e.g. a tag that labels the carrier protein as only for glucose
What types of molecules can travel through a protein channel (facilitated diffusion)?
Larger molecules of any polarity
What particles travel through a protein pump?
Any particle going from low to high concentration
Which direction can protein pumps move particles?
Any but each protein pump can only move only direction.
How many shapes do protein pumps alternate between?
Two
Tonicity
Measure of the relative solute concentration in a solution (i.e. a comparison)
What can tonicity protect?
Direction of net water movement
If the environment has a higher solute concentration than the cell, what is the environment labelled as?
Hypertonic
If the environment has a lower solute concentration than the cell, what is the environment labelled as?
Hypotonic
If the environment has a the same solute concentration than the cell, what is the environment labelled as?
Isotonic
What does water do if the environment is hypertonic to the cell?
Leave the cell to dilute the environment, causing the cell to shrivel and lose mass
What does water do if the environment is hypotonic to the cell?
Water enters the cell, causing it to swell and gain mass. Can burst in an animal cell
What does water do if the environment is isotonic to the cell?
No net movement of water and thus, the cell remains unchanged
Endocytosis
Process by which materials enter the plasma membrane by pulling through part of it and making a vesicle
Exocytosis
Process by which particles are removed from a cell by being in a vesicle that fuses to the membrane
Gated ion channels
Protein channels that can be opened or closed
Indirect active transport
When ATP is used to move one substance but a second substance can then also move as a result of the ATP
Cell-Adhesion Molecules (CAM)
Proteins embdedded in the cell membrane that protrude out towards other cells, creating a junction
Role of golgi apparatus in exocytosis of proteins
Modify and package proteins into vesicles and then, transport vesicles to membranes where they can fuse and be expelled
Difference between a neurotransmitter gated and a voltage gated ion channel?
Which signal is required to open them
Neurotransmitter gated: chemical message required
Voltaged gated: charge difference required between environments
How is sodium and potassium pump an example of an exchange transporter?
One protein is moving sodium in one direction and potassium in the other direction i.e. when the pump changes shape to release sodium ions, potassium ions enter at the same time
Role of ATP in the functioning of the Sodium Potassium Pump
Responsible for shape changes that close the pump on the inside, and facilitate reopening on the outside
Example of indirect active transport
Sodium-dependent glucose cotransporters
Uses of cell adhesion molecules in living organisms
Junctions between cells, specialised tissues, enables cells to function as a unit
Similarities between endocytosis and exocytosis
Both require ATP to reassemble membrane
Examples of endocytosis
Immune system (phagocytosis by white blood cells)
Unicellular feeding
Endosymbiotic theory
Which particles do endo/exocytosis?
Particles too large for other forms of transport
How does endocytosis occur?
A large particle pushes on the outside of the cell membrane. When it pushes through, a vesicle is made from the membrane with the cell membrane still intact
Examples of exocytosis
Protein transport
Waste removal (uses vacuole)
Expel water (uses contractile vacuole)
What happens in exocytosis?
A vesicle (made by the Golgi Apparatus) that contains a protein fuses with the cell membrane, releasing the protein outside of the cell. The cell membrane remains intact
What is required to open a voltage-gated ion channel?
Charge difference inside adn outside the cell
Example of a voltage gated ion channel
Potassium channel
What type of movement do gated ion channels allow for (in neural transmission)?
Sudden, short changes
Explain how a potassium channel works (example of voltage-gated ion channel)
There is a negative charge inside the neuron. The ion channel is closed.
WHen the charge inside the neuron becomes positive, the ion channel opens and potassium ions flow through.
The gated ion closes against, with the inside of the neuron remaining positive
What triggers the neurotransmitter gated ion channel to open?
When a specific neurotransmitter binds to the receptor on the protein channel
Example of neurotransmitter gated ion channel
Nicotonic acetycholine receptor
Explain how the nicotonic acetycholine receptor works
Neuron 2’s membrane has a receptor on its protein channel. This protein channel is closed when the receptor is empty. Once Neuron 1 releases the neurotransmitter of acetycholine, acetycholine can bind to the receptor, allowing the protein channel to open. This means other particles can travel through
Purpose of sodium-potassium pump
Returns ions to their location post action potential
Steps of Sodium-Potassium pump
- ATP attaches to protein pump. 3 Na+ enter from the cell
- The protein pump closes, causing a phosphate to break off the ATP, releasing energy.
- The pump opens on the other side, releasing 3 Na+ and allowing 2K+ to entre.
- The phosphate detaches, closing the protein pump.
- The protein pump reopens on the other side, causing potassium to leave the cell and sodium to enter. ATP returns to restart cycle
How does a sodium-dependent glucose transporter work?
Sodium enters the cell via a sodium-potassium pump, a form of active transport. Eventually, a higher sodium concentration is reached. Once this is reached, two sodium ions bind to a protein pump. If the sodium isn’t binded, the pump won’t open. One glucose molecule binds as well. This transfers glucose to the target area (against the concentration gradient)
How was ultracentrifugation aided in cell fractionation?
Separates organelles by size, with the heaviest organelles at the bottom
Organelle
Discrete subunit of a cell that is adapted to perform one or more vital functions
Benefits of separation of nucleus and cytoplasm in eukaryotes
Protection of DNA from enzymes in cytoplasm
Translation does not begin until after transcription is completed, allowing for mRNA modifications
Benefits of compartmentalisation for eukaryotic cells
Enzymes can be concetrated to areas of use
Digestive enzymes of the lysosomes are away from the rest of the cell
pH levels are ideal for the specific function
Easier transport
How is the cell protected from harm during phagocytosis by lysosomes?
When something enters by phagocytosis, lysosomes merge with the vesicle and release enzymes into it. This allows the rest of the cell to be protected from the enzymes
Benefits of a nuclear double membrane
Nuclear processes can occur without impacts from other cellular processes
how does chromatin interact with the nuclear membrane
Inner memrbane interacts with DNA chromatin, with the aim of having the membrane be spread out
what leaves the nucleus through the nuclear pores
mRNA
ribosomal subunits
what enters the nucleus through nuclear pores
gene regulators
what cannot leave the nucleus through nuclear pores
DNA (can’t fit)
what are nuclear pores made of?
integral proteins
what produces ribosomal subunits
nucleolus
what happens to the nucleus’ bilayer during prophase?
membrane breaks off into small vesicles that migrate
what happens to the nucleus’ bilayer during telophase?
vesicles (made during prophases) rejoin to recreate the membrane
matrix
cytoplasm-like fluid area full of enzymes within the inner membrane of the mitochondria
cristae
tubular regions created by deep folds of the inner membrane of mitochondria
thylakoids
membrane-bound discs in chloroplasts, with a thin thylakoid space in each one. the organelles contain photosystems that capture sunlight
what are stacks of thylakoids called?
granum
stroma
aqueous cytoplasm-like fluid area surrounding thylakoids
cisternae
stacked, flattened sacs of membrane that the golgi apparatus consists of
clathrins
proteins in the cell membrane that help in anchoring specific proteins to certain areas of the cell membrane
purpose of the outer and inner membranes of mitochrondia
outer membrane = endosymbiotic event
inner membrane = folded to increase surface area, lined with enzymes carrying out aerobic cellular respiration
benefits of having cristae and small intermembrane space for mitochondria?
Having a thin intermembrane space allows proton gradient to build up quickly, which activates ATP synthase
Benefits of localising enzymes to either the matrix (mitochondria) or stroma (chloroplast)?
Pathways can occur more efficiently than if diffused throughout organelles
benefits of thylakoids having large surface area and small volume
allows more pigments thus more enzymes and therefore, more efficient photosynthesis. having very thin thylakoids allows for protein gradients to quickly form
difference between proteins produced by free ribosomes and ribosomes attached to the rough ER?
for free ribosomes, proteins are often used within the cell. if attached to the rough ER, proteins are usually exported outside of the cell
difference between the cis side and the trans side of the golgi apparatus?
cis = faces ER, accepts vesicles produced by ER
trans = faces membrane, vesicles bubble off golgi apparatus to go to the membrane for exocytosis
