BIO202 EXAM 2 Flashcards
What is the cytoskeleton?
A network of filaments and tubules that
- Provides mechanical support to the cell and maintains its shape.
- Provides the cell with mobility
- Mediates the movement of organelles and individual molecules (Within the cell)
- Regulates biochemical activities of the cell by transmitting mechanical forces.
What are microtubules?
They are hollow tubes made of the globular protein tubulin. Their walls are made up of alpha-beta polymer chains.
How are the walls of microtubules formed?
Alpha-subunits and beta-subunits polymerize into alpha-beta dimers. Those dimers then polymerize into chains that form the walls.
How do microtubules grow?
By adding alpha and beta subunits to their ends
Functions of microtubules
To Maintain the shape of the cell by resisting compression, movement of the cell, and movement of organelles. Also, the movement of chromosomes.
How does the cytoskeleton move the cell?
Not by contracting and extending but by assembly and disassembly.
Centrosomes
In animal cells, microtubules often grow from structures called centrosomes, which are made of 2 centrioles. When cells divide, the centrioles divide too. Plant cells do not have centrioles.
Cilia
Locomotive organs formed by a special arrangement of microtubules. They occur in large numbers on the cell surface. They move back and forth like an oar stroke.
Flagella
Locomotive organs formed by a special arrangement of microtubules. There’s usually a single flagellum per cell. It is the same diameter as cilium but is much longer.
Function of the basal body
anchors cilia or flagella to the cell
The core of cilia and flagella
Consists of 9 doublets of microtubules arranged in a circle, and 2 single microtubules in the center= 9+2 structure
function of dynein arms
connect the 9 doublets of microtubules
radial spokes
connects each doublet to the two central microtubules
Structure of the basal body
Has a structure identical to a centriole
Dynein-mediated movement
The dynein arms of one doublet attached to a neighboring doublet. The pull and the doublets move in opposite directions. They detach then reattach at a higher position to continue the movement.
how to cilia and flagella move?
Dynein mediated movement.
Microfilaments
2 intertwined strands of protein called actin. Polymers of globular monomers of actin.
Functions of microfilaments
They maintain the cell shape by resisting tension. Provide motility in cell division, muscle contraction, and cytoplasmic streaming.
What happens to microfilaments when muscles contract?
In muscles, actin filaments are arranged parallel to myosin filaments. When actin and myosin filaments pass each other, the cell becomes shorter.
How does the presence of microfilaments affect the cytoplasm?
It makes the cytoplasm more “rigid” -> a gel state. Less microfilaments results in the sol state. The gel state/sol state transition takes place due to actin myosin interactions. This causes cytoplasmic streaming (mainly in plants)
cytoplasmic streaming
The circular motion of cytoplasm within large cells to help distribute materials inside of the cell
Microvilli
Microfilaments are found in the center of microvilli. They are cellular projections (often on the surfaces of intestinal cells) that increase surface area to help absorb material from outside the cell
Intermediate filaments
The intermediate between microfilaments and microtubules. They are made of fibrous protein, super-coiled into thicker strands.
Proteins comprising intermediate filaments belong to the ______ family.
keratin
Functions of intermediate filaments
They maintain cell shape by resisting tension. They anchor the nucleus and other organelles. They form the nuclear lamina.
Major difference between microfilaments/microtubules and intermediate filaments.
Microfilaments and microtubules are often disassembled, but intermediate filaments are more permanent. (They support more constant features of cell shape and structure.
What are the intercellular connections in animal cells?
Gap junctions and TNTs
What are the intercellular connections in plant cells?
plasmodesmata
Which intercellular connections are permeable?
Gap junctions, TNTs, and plasmodesmata
Plasmodesmata/TNTs versus gap junctions
Plasmodesmata and TNTs are larger and can open further to move molecules. Gap junctions are smaller and cannot open more than they normally are.
Non -permeable intercellular connections
Desmosomes and tight junctions
Desmosomes
anchor adjacent cells together (ex: in cardiac muscle)
Tight junctions
Areas where membranes of adjacent cells are fused (ex. in intestinal epithelium)
Gap junction protein
connexin
6 connexin units make up a
connexon
What are gap junctions made up of?
2 connexons (one from each cell) connected to each other
TNTs (acronym for what)?
Tunneling nanotubes
How are TNTs formed?
One cell forms an actin-driven protrusion directed towards the target cell. Then, the cell protrusion fuses with the membrane of the target cell
Cargoes transferred by TNTs
lysosomal, ER, golgi vesicles are transported with the help of molecular motors, proteins, organelles, and pathogens
Structure of a phospholipid
A polar phosphate head, a glycerol backbone, and two fatty acid tails. If the fatty acid has a double bond, it is bentl
What’s a phospolipid micelle?
When the phospholipids form a circle with the heads facing outward and the hydrophobic tails are on the inside. These may exist inside a wet environment.
Membrane fluidity
Membrane lipids drift laterally and even “flip-flop”
Why do phospholipids rarely “flip-flop” in a membrane?
It invloves transitions between hydrophobic and hydrophilic environments and that requires a lot of energy.
Are membranes always fluid?
No. They solidify at low temperatures. Unsaturated fatty acids solidify at lower temperatures compared to saturated fatty acids.
The effect of cholesterol on membranes
At higher temperatures, they restrict the movement of phospholipids and reduce fluidity. At lower temperatures, they prevent the close packing of phospholipids, increasing fluidity.
Types of mosaic proteins
There are integral and peripheral
Integral proteins
Are at least partly inserted into membranes. (Most completely span it)
Peripheral proteins
Are attached to the membrane surface, but not inserted.
Functions of the cell membrane
Cell-cell recognition and communication involve specific molecules on cell surfaces. One of the most important properties of biological membranes is the ability to regulate transport into and out of the cell.
When is transport across a membrane passive and what does that mean?
It is passive when it occurs down the concentration gradient. This means that it does not require energy.
When is transport across a membrane active and what does that mean?
It is active when it occurs against a concentration gradient. This means that it requires energy.
What types of molecules typically move passively across membranes?
Hydrophobic and small, uncharged molecules.
Diffusion
Transport or a solute down a concentration gradient
Osmosis
Transport of water down ITS concentration gradient
Hyperosmostic or hypertonic
There will be a net movement of water into the cell because there is more water conc. outside of the cell
Isoosmotic or isotonic
There is no net movement of water because the conc. of water is the same inside and outside of the cell
Hypoosmotic or hypotonic
There is a net movement of water outside of the cell because there is a higher water conc. inside the cell.
Osmotic pressure
The tendency for a solution to take up water when separated from pure water by a selectively permeable membrane.
What is osmotic pressure measured in?
mOsm (The sum of concentration of all ions)
In which direction of the concentration gradient does diffusion occur?
Down the concentration gradient.
What is facilitated diffusion?
It’s an intermediate step between diffusion and active transport. It occurs down the concentration gradient but it is also facilitated by proteins.
How do transport proteins function?
Like enzymes. They bind specifically to transport substrate and exhibit saturation by transport substrate.
Na+-K+ pump facts
- A 4-protein complex that spans the membrane
- Binds 3 ions of sodium inside the cell, receives energy by phospholylation
- Changes conformation and expels sodium ions to outside
- Bind 2 ions of potassium outside the cell, is dephosphorylated and and returns to original conformation, releases potassium ions inside the cells and again binds 3 ions of sodium
What is another name for the sodium-potassium channel?
Sodium-potassium ATPase because it causes the hydrolysis of ATP
Chlorine channel
- Ion transport channel regulated by phosphorylation (cAMP dependent)
- Defects in this channel cause cystic fibrosis
- The channel is called CFTR=CF transmembrane conductance regulator
Co-transport
It increases membrane potential by removing protons.H+ gradient can drive another active transport.
Phagocytosis
A way of transporting large molecules across membranes. Non-specific engulfing and internalizing a particle
Pinocytosis
A way of transporting large molecules across a membrane. Non-specific engulfing and internalizing liquid droplets. (Same as phagocytosis it just involves liquid droplets)
Receptor-mediated endocytosis (What is it?)
specific internalizaiton (The major type of transport of macromolecules across membranes)
Receptor-mediated endocytosis
- Macromolecules bind to a specific receptor on cell surface.
- These receptors are in specific areas (Called coated pits)
- Coated pits are coated with specific protein (Clathrin) on the inner side of the membrane
- Binding results in internalization and formation of the transport vesicles (endosomes)
What are the receptors in receptor-mediated endocytosis called?
Coated pits
What are the receptors in receptor-mediated endocytosis coated with?
A specific protein called clathrin
Some functions of trans-membrane proteins
Transport, intercellular joining, enzymatic activity, cell-cell recognition, signal transduction, attachment to the cytoskeleton and ECM.
What is the result of binding with receptor-mediated endocytosis?
Results in internalization and formation of the transport vesicles (endosomes)
Examples of virus infection by endocytosis
Influenza and vesicular stomatitis virus
How to multicellular organisms communicate with each other?
Using neurons
paracrine
signals released into the extracellular fluid. They go to all cells but they are recognized only by specific cells that have receptors for the signals.
Hormonal or endocrine
signals move a long distance through vascular system or even through the air
What are the 3 stages of cell signaling?
Reception, transduction, and response.
What is reception?
The first stage of cell signaling. Cells detect an incoming signal which binds to a receptor molecule. The information carried by the signal is received by the cell.
Where are receptors located?
Usually on the surface of the cell but they can also be found with in cells. (Ex. the nucleus)
What is transduction?
Binding of signal to its receptor changes the receptor. This change begins a sequence of biochemical events (called pathway) that ends in cellular response. The information carried by the signal is transduced into the cell.
What is a cells response to cell signaling?
Almost any cellular activity. This includes growth, movement, synthesis of a molecule, or even death.
Signaling by epinephrine
Epinephrine is a hormone that can only interact with the cell via a receptor program. By binding to the receptor it causes a series of events that leads to glucose being released from the liver and into the blood during the “fight or flight” reaction
What are the signals that bind to receptors called?
Ligands
What are the 4 major types of receptors?
G protein-linked, enzymes, ligand-gated ion channels, and internal.
G protein-linked receptor
Works in a g-protein system.A signal molecule binds to the g-protein-linked receptor and causes the GDP on a g-protein to be displaced by GTP. GTP causes the g-protein to become active and interact with an activated enzyme. The activation of the enzyme causes a cellular response.
Enzyme receptors
They have enzymatic activities themselves. The extracellular part binds to the ligand and the intracellular part acts as an enzyme.
Tyrosine kinase receptor
It is a protein kinase enzyme that phosphorylates tyrosine residues within proteins (The phosphate group comes from ATP)
Cellular response to tyrosine kinase receptors
Cell division. Inappropriate activation can lead to uncontrolled cell division and cancer
Ligand-gated ion channels
A ligand attaches to an ion-channel protein which causes it to open and allows the flow of ions. When the ligand detaches from the channel, it closes and ions cannot glow.
Internal receptors
If a signal can pass through the cell membrane then there is no need for extracellular receptors. Instead, the cell uses intracellular receptors to receive such signals.
Membrane receptors
A type of signal transduction pathway. They have multiple steps and must carry information from the outside of the cell to the inside.
Internal receptors
Can carry out transduction themselves.
Advantages of multiple-step signal transduction pathways
Amplification and regulation
amplification of signal
One signal can transmit information to multiple molecules at each step
regulation with multiple-step signal transduction
More steps means more checkpoints to regulate the final response
Mechanism of multiple-step signal transduction pathways
The signal causes conformation changes in cellular proteins
Protein kinase
an enThe zyme that transfers a phosphate group from ATP to a substrate protein
The major mechanism of signal transduction
phosphorylation
IP3
Second messengers that usually activate Ca2+ channels to move Ca2+ from the ER into the cytosol
Cytostolic Ca2+
A second messenger that activates other protein components of transduction pathway either directly or via calmodulin
DAG
Second messengers that remain in the plasma membrane. It activates protein kinase C
Cellular respiration
The major catabolic pathway to produce energy from food in eukaryotes
Glycolysis
The splitting of sugar and it occurs in the cytosol. Includes 10 steps; 5 that require energy and 5 that produce energy.
Glycolysis reaction
Glucose + 2ATP»_space;> 2 pyruvate + 4 ATP + 2 NADH + 2H2O
Does glycolysis require oxygen?
No
What happens to pyruvate before it enters the krebs cycle?
It is converted to acetyl CoA
Conversion of pyruvate to acetyl CoA
First, pyruvate is transported into the mitochondrial matrix. Then, the carboxyl group is removed in the form of CO2, which diffuses out of the cell. Then, the rest of pyruvate is further oxidized and NAD+ is reduced to NADH. Finally, the oxidized acetyl group of pyruvate is attached to CoA, forming acetyl CoA.
What does the Krebs cycle do?
It takes acetyl CoA (from glycolysis), NAD+, ADP, and FAD+ to produce ATP, NADH, FADH2, and CO2
What happends following the Krebs cycle?
The energy of NADH/FADH2 is converted to ATP in the electron transport chain.
How is ATP produced?
Oxidative phosphorylation.
The electron transport chain
A collection of molecules with active groups that donate and accept electrons. In this process electrons from NADH and FADH2 pass through the electron transport chain, slowly releasing energy, which is used to drive ATP synthesis. Also, molecular oxygen is reduced to water.
What follows the ETC?
A H+ gradient is generated by chemiosmosis and this step requires O2. Then, ATP synthesis is carried out ATP synthase.
What poison inhibits the ETC?
Cyanide
What blocks ATP synthase?
Oligomycin
What abolishes H+ gradient?
DNP (dinitrophenol)
Oxidative phosphorylation
Energy is supplied by the ETC in the form of an H+ gradient across the inner mitochondrial membrane.
Chemiosmosis
The process by which ATP is produced on the inner membrane of a mitochondrion. The ETC transfers H+ from the matrix into the intermembrane space; as the H+ flow back to the matrix through the ATP synthase, the energy of their movement is used to add P to ADP, making ATP
What happens if ATP synthesis is uncoupled from the ETC?
No ATP is made, but energy is released as heat
Cellular respiration in prokaryotes
Prokaryotes don’t have mitochondria so they have the ETC in the plasma membrane. They don’t have to convert NADH TO FADH2 so they don’t lose energy in that step
Lactic acid fermentation
After glycolysis, pyruvate oxidizes NADH back to NAD+ instead of going in to the Krebs cycle. ATP is made by substrate-level phosphorylation.
Why is pyruvate a key juncture in catabolism?
It can be used in anaerobic conditions and aerobic conditions
Control of cellular respiration
Phosphofructokinase is an allosteric enzyme that’s induced by AMP and inhibitied by ATP and citrate. (Feedback inhibition)
What are the reactions of photosynthesis?
Light reactions and the calvin cycle.
Light reactions
Convert solar energy into NADPH and ATP. They release molecular oxygen by splitting of water. These reactions require light.
The calvin cycle
Converts CO2, ATP, and NADPH into sugar by carbon fixation. This does not require light.
How do light reactions convert solar energy into ATP?
photophosphorylation
How do light reactions convert solar energy into NADPH?
By transferring an electron from H2O to NADP+
Is sugar produced during light reactions?
NO
How do photosystems transfer electrons?
Cyclic electron flow and non-cyclic electron flow
Cyclic electron flow
Only takes place in photosystem I and only ATP is made. Electrons originated from photosystem I go back to photosystem I and reduce it.
Non-cyclic electron flow
Both in photosystem I and photosystem II. O2, ATP, and NADPH are made.
Why is there a need for both cyclic and non-cyclic flow?
Non-cyclic makes for similar amounts of ATP and NADPH but Calvin cycle uses more ATP than NADPH so additional ATP comes from the cyclic flow.
photophosphorylation
ATP synthesis in chloroplasts
ATP synthesis in chloroplasts is driven by
chemiosmosis
chemiosmosis
the process by which ATP is produced on the thylakoid membrane of a chloroplast. The ETC transfers H+ from the stroma into the thylakoid space; as the H+ flow back to the stroma through the ATP synthase, the energy of their movement is used to add Pi to ADP, making ATP
Cytochrome complex
electron transport chain (ETC) It pumps H+ from the stroma into the thylakoid space. H+ diffuses back and drives ATP synthase which makes ATP in the stroma where it is used in the Calvin cycle
Steps of the Calvin cycle
Step 1: Carbon fixation. Step 2: Reduction.
Step 3: Regeneration of RuBP
What happens in the carbon fixation step of the calvin cycle?
CO2 from the air is attached to a cCO2 receptor, RuBP sugar. This is catalyzed by RUBISCO (The most abundant protein on earth)
What happens in the reduction step of the calvin cycle?
Reactions use NADPH as an H+ source. Also, phosphorylation reactions occur that use ATP. NADPH and ATP come from the light reactions. 6 molecules of G3P are made. Only 1 exits the cycle to be used in the biosynthesis of other products.
What happens in the regeneration of RuBP step of the calvin cycle?
5 of the 6 G3P molecules produced during reduction step is used to recreate RuBP.
C4 plants (Calvin cycle)
Separation between CO2 fixation and Calvin cycle is spatial. Adaptation to semi-dry conditions (stomata are open only partially during hot days). First, they fix CO2 into organic acids in a specific type of cells and then they transport these organic acids to another type of cells where the organic acids enter the calvin cycle as a carbon source.
CAM plants (calvin cycle)
Separation between CO@ fixation and calvin cycle is temporal. Adaptation to dry conditions (Stomata are closed during hot days). To prevent evaporation of water through stomata during the day, they take up CO2 only at night and incorporate it into organic acids. Then, when the air is light, and ATP and NADPH are made, the organic acids enter the calvin cycle as carbon source. (All takes place in the same cells)
