Final Exam Flashcards

Question

DNA nucleotides: a.use ionic bonds to hold base pairs together b.form the base pairs with adenine and cytosine and thymine and guanine c.have purines forming base pairs with pyrimidines d.form strands that run parallel to each other

Answer 1

C- DNA nucleotides have purines form base pairs with pyramides (AT CG)

Answer 2

The nucleus’ primary function is to protect DNA and allow genes to function. It does this by allowing DNA to replicate, regulating access to DNA, and organizing DNA. Nuclear envelope: double membrane structure that attaches to the ER cisternae to control what enters and exits the nucleus and separate the DNA from the other cellular structures. Nuclear pores: pores in the nuclear envelope regulate traffic. Large molecules like proteins cannot freely fats while small molecules like ions and water can. Chromatin: DNA organized into fibres Chromosomes: highly condensed chromatin Nucleolus: creates RNA and stores the DNA that encodes those genes Nucleoplasm: provides fluid around the envelope for suspension Nuclear Matrix: organizes chromosomes and provides a scaffold to maintain shape

Answer 3

1) Double helix: antiparallel strands of DNA coiled into a double helix to protect DNA and regulate transcription. 2) Nucleosomes: DNA wraps around histones creating “beads” that are separated by linker-DNA. (7-fold) 3) Chromatin fibre: Nucleosomes coil into chromatin fibre. (42-fold) 4) Chromatin looped domain: chromatin fibre is looped into a chromatin looped domain. (750-fold) 5) Heterochromatin: hyper condensed chromatin looped domain that is inactive and found in Interphase. This can further condense into chromosomes for mitosis. During euchromatin, the DNA is still active, but during heterochromatin, the DNA in so condensed that it is inactive.

Answer 4

The endomembrane system is a process that is used to transport cargo through exocytosis or endocytosis. Nucleus: nuclear envelope and pores connect to the ER cisternae for cargo to travel out of the nucleus Endoplasmic Reticulum: organized flattened disks called cisternae that connect to the nucleus - RER - has ribosomes for protein translation and modification - SER - does not have ribosomes, so it synthesizes lipids, converts carbohydrates to glucose, and regulates calcium ion levels Transport Vesicles: shuttles cargo between organelles by budding off lipid membranes, transporting across the cell, and fusing with acceptor membranes to release cargo Golgi Apparatus: labels proteins with signals to direct cargo to its final destination - Cis - receives proteins from the ER - Medial - sugar groups, called oligosaccharides, are added to proteins and lipids or are modified - Trans - performs final packaging and sorts cargo to its final destination Endosomes: gather content coming into the cell through endocytosis and sorts it to its final destination Lysosomes: break down proteins, lipids, and sugars Peroxisomes: break down molecules the produce hydrogen peroxide in order to neutralize the cell and mitigate damage

Answer 5

The first step of getting a protein into the endomembrane system is allowing the protein to get inside the lumen of the ER. The location of protein synthesis on the ribosomes of the RER is important because it allows proteins to be transported directly into the endomembrane system, following translation. Translocation is the process of moving proteins into the ER and it occurs in 4 steps. First, the presence of an ER signal sequence is translated as part of the protein. Next , as the signal sequence emerges from the ribosome, it interacts with a signal recognition particle receptor that binds to the ribosome and pauses protein translation. During the pause in translation, the SRP docks onto the ER membrane by interacting with a SRP receptor called the translocon, which allows and facilitates the translocation of the protein into the ER. Translation restarts and once the protein has translated into the ER, the signal peptide sequence is cleaved, translation finishes, and the protein fold inside the lumen. If the protein is destined to embed in the lipid membrane, the transmembrane signal sequence anchor with be recognized initiating the process of embedding into the lipid bilayer. The transmembrane signal sequence embeds into the lipid bilayer and become the transmembrane domain of the protein once it is mature and functional.

Answer 6

Once in the lumen, proteins can fold with the help of PDI and BiP. PDI forms disulfide bonds between the thrill groups in the side chain of cysteines to help the protein fold properly and stabilize it. BiP, termed chaperonins help fold polypeptides by binding hydrophobic patches, bringing them together to help them fold into the hydrophobic interior of mature proteins. It does this until it can no longer access hydrophobic patches. Once folded, proteins, lipids, sugars, and functional groups are added to the protein, peptide bonds are cleaved, and the signal sequence at the N-terminus is removed.

Answer 7

Primary: linear peptide sequence from N->C terminus (polypeptide chain) Secondary: either alpha helixes that are coiled with H-bonds between every 4th amino acid, or beta pleated sheets that form rows of amino acids in a parallel or antiparallel manner Tertiary: 3D structure of a complete protein that was folded by chaperones and disulfide bonds (myoglobin) Quaternary: multiple tertiary proteins assembled into a complex with subunits (hemoglobin or histones)

Answer 8

1a) Cargo selection: signal sequences and receptors on the membrane gather cargo to the area of the membrane that will be turned into a vesicle. 1b) Coat proteins: coat proteins from the cytosol bind to the area on the membrane that will become the vesicle and cause receptors and other proteins with signal sequences to cluster on the surface of the membrane. 2) Budding: coat proteins interact with cytosolic adaptor proteins to form a mesh-like basket that pulls the membrane into a bulging shape that will become the vesicle. 3) Scission: Dynamin cuts the membrane to pinch off the budding vesicle and release is into the cytoplasm. 4) Uncoating: coat and adaptor proteins are disassembled and recycled. 5) Transport: vesicles attach to motor proteins, like kinesin, in the cytosol to move along the microtubules of the cytoskeleton for control of direction and destination. 6) Tethering: at its destination, tether proteins attach to a receptor on the acceptor membrane to find the correct acceptor target proteins 7) Docking: when acceptor target proteins are found, the vesicle docks on the surface. 8) Fusion: the lipid membrane become continuous with the acceptor membrane with the interaction of v-SNAREs and t-SNAREs (v-SNARE = vesicle) 9) Disassembly: remaining tether, fusion, and receptor proteins are disassembled and recycled back to the initial organelle. The cargo is released into the accepting organelle.

Answer 9

Endocytosis is the import of cargo from out of the cell into the cell. Initially, Clathrin forms a vesicle initiating invagination of the plasma membrane to form a vesicle that can take cargo from outside of the cell to the early endosome. During uncoating, Clathrin disassembles with the help of cytosolic proteins Auxillin and Hsc 70. The early endosome is made up of vesicles from the plasma membrane and trans golgi network that contain cargo and cargo receptors. Vesicles with M6P and their cargo (proton pumps, LIMPs, and hydrolases) fuse with the endocytic vesicle forming the early endosome. Proton pumps begin to acidify the lumen decreasing the pH to 6.4-6.8 so that the cargo receptors and M6P receptors change shape and release their cargo. Depending on their signal sequences, some cargo and receptors can be sent to storage granules, across the cell, or into the cell. The early endosome then matures into the late endosome where the pH is 5.0-6.0 and receptors and cargo is still recycled and degraded into essential building blocks like sugar and amino acids. When the pH reaches levels lower than 5.0, proteases are activated to convert the late endosome into a lysosome that has a protective glycocalyx layer of LIMPs and glycosylated proteins that protect the lysosome from self degrading of proteases.

Answer 10

COP II - shuttles from the ER to the golgi COP I - shuttles from the golgi back to the ER Clathrin - used for endocytosis and exocytosis M6P - transports cargo to the lysosome

Answer 11

Because proline is rigid and prevents the proteins from folding

Answer 12

It has a sulfur containing thiol that can form disulfide bonds with another cysteine which is significant for maintains 3D protein structure.

Answer 13

Phospholipids cluster together to form the semi-permeable plasma membrane. They are made up of a head group that determines its location in the membrane, phosphate that is the hydrophilic and charged component, glycerol that acts as a backbone, and fatty acid tails which vary in composition and bond number. They have charged head groups (PS, PE, PC) or polar head groups (PI, PG, CL) Other common lipids include: Cholesterol - have hydroxyls in rings that interact with the membrane surface Glycolipids - have a sugar carbohydrate, rather than a phosphate, for cell-to-cell signalling Sphingomyelin - have a sphingosine backbone a phosphocholine head, and a fatty acid tail

Answer 14

Micelles: droplets with fatty acid tails pointed toward the centre Liposomes: tight bilayers with a hollow middle (doughnut shape) Monolayer: single layer with head group facing water Bilayer: double layer with heads pointed toward the aqueous environment on either side

Answer 15

Plasma membranes have a cytoplasmic leaflet that faces the cytoplasm and an exoplasmic leaflet that faces the external environment. Lipid asymmetry can be observed in the leaflets as the exoplasmic leaflet has positively charged PC, sphingomyelin, glycolipids, and cholesterol, while the cytosolic leaflet has neutral or negatively charged PS, PE, and cholesterol. Lipid asymmetry is achieved with the use of floppases, flippases, and scramblases. Floppases - keep PC, sphingomyelin, and cholesterol in the exoplasmic Fippases: keep PS, PI, PE in the cytosolic Scramblases: briefly disrupt asymmetry by randomisons phospholipids

Answer 16

Can - uncharged hydrophobic molecules like O2, NO, and CO2 Cannot - large hydrophilic molecules like sugars, ions, and proteins

Answer 17

Hypertonic- more solute on the outside, so water moves out Isotonic- equal amount of solute on the inside and outside Hypotonic- lower solute on the outside, so water moves in

Answer 18

“Mosaic” refers to the multiple components of the membrane, while “fluid” refers to the ability of molecules to move freely and rapidly across the membrane. Initially, it was assumed that the plasma membrane was a homogeneous bilayer with even thickness, but this is not true as there are various phospholipid, cholesterol, and protein complexes that interact together to form lipid rafts.

Answer 19

Membrane fluidity can be altered with temperature, lipid content, cholesterol content, and protein content. Temperature: as temperature increases, fluidity increases. As it cools, the membrane becomes rigid Lipids: as chain length increases, fluidity decreases, unsaturated lipids have kinks that provide more motion and increase fluidity. Cholesterol: as concentration of cholesterol increases reaching 50%, fluidity decreased due to increased rigidity Proteins: as protein concentration increases, fluidity decreases as the membrane becomes stiff

Answer 20

Inter-membrane proteins like transporters and channels allows cells to alter gradients and move cargo in or out of the cell. Passive transport is the movement of molecules down a concentrated gradient with simple diffusion or facilitated diffusion which does not require energy. Passive transport can be done with channel proteins that form pores for water or ions to pass through the hydrophobic membrane or carrier proteins that undergo a confirmational change to allow cargo to pass through. Active transport requires energy to transport molecules against a gradient using proton pumps to build the gradients. This can be done with direct transport that uses anti-porter pumps to create gradients (Na/K), or indirect transport that uses symporters (Na/glucose). Antiporters move one molecule in and the other molecule out while symporters move molecules in the same direction.

Answer 21

Catabolism - the breakdown of macromolecules to produce energy Anabolism - the building of macromolecules that consumes energy

Answer 22

Adenine triphosphate is the primary energy source for cells that is composed of an adenine, ribose, and 3 phosphates. The energy of ATP is stored between the 2nd and 3rd phosphates and is released when the 3rd phosphate is removed.

Answer 23

High energy molecules store energy in carried electrons. These are NADH and FADH2.

Answer 24

Mitochondria have a double membrane structure that is critical for function. They have the cristae that is the inner membrane folded in on itself, where high energy compounds are converted to ATP, and the matrix that is the inside of the mitochondria where macromolecules are converted to high energy compounds.

Answer 25

Energy can be stored in carbohydrates, fats, and proteins. Carbohydrates store glycogen that in broken into glucose through de novo synthesis, and sent into the bloodstream. Fats in the form of triacylglycerols are broken down to release free fatty acids. Proteins are the least commonly used and store energy in skeletal muscle.

Answer 26

1) Glycolysis: Since catabolic reactions are exothermic, glycolysis occurs in 10 steps to allow a slow release of energy and efficient energy transfer, allowing other monosaccharides to be broken for intermediary products. During glycolysis, 1 glucose is broken into 2 G3P which is broken into 2 3-phosphoglycerates which is broken into 2 pyruvate. Overall, the net production at this stage is 2 ATP and 2 NADH. 2) Pyruvate to Acetyl-CoA: During this stage a carrier molecule brings pyruvate into the matrix from the cytosol and then the pyruvate is decarboxylated by pyruvate dehydrogenase, releasing NADH and CO2. 3) Krebs Cycle: In this stage acetyl CoA enters the Krebs cycle and combines with oxaloacetate to form a citrate, releasing CoA. Then the citrate has two carbons removed from it to create succinate, releasing 2 NADH, 2CO2, and 1GTP. The succinate is then converted back into oxaloacetate, releasing NADH and FADH2. This process occurs twice producing a net yield of 4 ATP, 10 NADH, and 2 FADH2. 4) Oxidative phosphorylation: The electron transport chain uses 4 different complexes to pump protons from the matrix into the inter membrane space, using electrons from the high energy compounds NADH and FADH2. This produces a chemiosmotic gradient that drives phosphorylation of ADP into ATP with ATP synthase. Overall there is a theoretical yield of 36 ATP and an actual yield of 30 as NADH actually produces 2.5 ATP and FADH2 produces 1.5 ATP. If there is excess ATP, it will be converted into and stored as creatine phosphate by the help of kinases.

Answer 27

If there is no oxygen present fermentation is caused so that NADH can be oxidized to further produce ATP. Pyruvate will either be turned into lactate (animals) or ethanol (plants).

Answer 28

Free fatty acids combine with CoA to make a fatty acyl-CoA ester by consuming 2 ATP. If the chain is short enough, it will diffuse directly into the matrix, but if it is not, it will be transported into the matrix with use of a carnitine shuttle. Once in the matrix, fatty acids are broken down, 2 carbons at a time, to release acetyl-CoA, NADH, and FADH2 for the Krebs cycle.

Answer 29

Nitrogen is removed by proteins by D emanation and converted to urea. Depending on the amino acid structure, there are different locations for the metabolism of protein. Three carbon molecules will be used to enter glycolysis, acetyl-CoA can directly enter the Krebs cycle, and intermediaries can enter the Krebs cycle.

Answer 30

Brain - glucose or ketones Heart - fatty acids Skeletal muscle - glycogen during exercise and fatty acids during rest

Answer 31

Cell-to-cell Communication is required for specialized cells to do their functions. It is achieved by the release of substances from a cell that travels to another cell to change its function. When cells sense signals, they trigger a cascade of events causing the cell to make an appropriate response. This can be extracellular and intracellular where the information is received from outside of the cell that causes the information to be collected and responded to inside the cell.

Answer 32

Gap junctions are formed by to connexons docking together to form channels from one cell to another for chemical signals, like ions and small signalling molecules, or electrical signals to move through. They are highly gated and can open or close to protect cells from dangers of neighbouring cells.

Answer 33

Autocrine: effect the same cell by diffusing through the extracellular space. Paracrine: effect nearby cells by diffusing through the extracellular space. Endocrine: effect distance cells by trolling through the bloodstream Neurotransmitters: excitatory signals release neurotransmitters into the synapse where they bind to a target receptor, are degraded by enzymes, or are taken back up by the presynaptic cell.

Answer 34

Linear: 1 receptor to 1 signalling protein Convergent: several receptors to 1 signalling protein Divergent: 1 receptor to several signalling proteins Multi-branched: combination of convergence and divergence

Answer 35

Signals are typically ligands that form a complex with a bio molecule in the extra cellular space and bind to a receptor on a target protein to trigger a signalling response. These can be membrane impermeable, which bind to a receptor protein on the cell surface, membrane permeable, which are steroids that can penetrate the membrane and interact with cytosolic receptors, or physical signals like pressure, temperature, and light.

Answer 36

GPCR: GPCRs are coded by hundreds of genes, and have a combination of seven transmembrane domains (H1-H7). They have a heterotrimeric G-protein with alpha, beta, and gamma subunits. When a ligand binds to a GPCR receptor, it activates a confirmational shape change that further activates coupled G-protein subunits. Ion Channel Receptors: A channel in the plasma membrane that opens to allow ions through when a ligand binds, causing a conformational shift that opens pores. Guanylate Cyclase: Found in the membrane with an external ligand binding domain, transmembrane domain, and internal catalytic domain. They can also be found in the cytosol serving as a target for membrane soluble ligands. Protein Kinase: Protein kinase receptors phosphorlate proteins with serine, threonine, or tyrosine. Depending on what is phosphorlated, they are either RTK or S/TKR. before ligand binding, receptors are separate polypeptides with inactive domains. A signalling molecule causes subunits to dimerize and transautophoshporylation to occur. When the cytoplasmic tail is brought close to another domain, it’s domain is phosphorylated resulting in amino acids that can act as binding sites for other signalling proteins. When the ligand releases, amino acids are dephosphorylated by a phosphoprotein to inactive the receptor. Transmembrane Scaffolds: Transmembrane scaffolds do not have a single function as they form in clusters of receptors to bring signalling proteins together, regulate signal transduction, and isolate signal pathways. Nuclear Receptors: Nuclear receptors are found in the cytosol where they bind to ligands or steroids, move into the nucleus, bind to SRE’s on DNA, and regulate gene expression. These are known as transcription factors.

Answer 37

Signalling proteins are used to transmit and amplify signal information or mobilize second messengers. They are highly mobile enzymes that catalyze reactions or bind to other enzymes. G-proteins: Monomeric G-proteins are single peptides with two binding sites, the GTP or target protein binding sites, and a GTPase domain. GTP activates G proteins so that they can bind to target protein and cleave the GTP to inactivate. Heterotrimeric G-proteins have 3 polypeptides that anchor to the plasma membrane and are activated by GPCR. Heterotrimers are inactive when bound to GDP until a ligand binds changing confirmation to interact with G proteins. GDP is converted to GTP on the alpha subunit, causing the active subunits to separate and find downstream targets propagating a signal pathway. The alpha subunit then cleaves GTP into GDP and the subunits return to an inactive state. Protein Kinases: Once activated, protein kinases activate other kinases and signalling proteins, phosphorylating effector proteins like enzymes. Calcium Binding Proteins: When Ca2+ concentrations rise, calmodulin induces a conformational change to bind to target proteins causing downstream effects. Adenyl Cyclase: ATP is converted to cAMP which binds to the alpha subunit of heterotrimeric G proteins. With adenyl cyclase, multiple pathways converge for a single response. Lipid Kinases: Lipid kinases phosphorylate phospholipids in the cytoplasmic leaflet, resulting in a confirmational change so that it can bind to target proteins and pass the signal down a pathway. Adaptor Proteins: Adaptor proteins are not receptors or enzymes. They have binding domains that recognize phosphorlated amino acids and activated structures on signalling proteins. Adaptor proteins are important as they hold elements together at the right time and place.

Answer 38

Second messengers are non-protein ions or molecules that relay signalling information from signalling proteins to other cellular targets. They are small in size, diffuse rapidly, amplify signals, and do not hang in the cytosol for a long period of time. Ex) cAMP, cGMP, CA2+, DAG, IP3, NO

Answer 39

GPCR‘s respond to ligand binding and interact with heterotrimeric G-proteins that bind to GTP and dissociate from GPCR. Gas-GTP activates adenyl Cyclase, converting ATP to cAMP, which binds to PKA that phosphorylates CREB so that it can bind with CBP initiating transcription.

Answer 40

Ga-GTP binds to PLC that breaks down PIP2 to release DAG and IP3 which opens the CA2+ channel for DAC and CA2+ to bind to PKC.

Answer 41

FGFs bind to FGFRs forming phosphotyrosines that bind to Grb2, which binds to SOS, which binds to Ras that replaces GDP with GTP and binds to Raf that phosphorylates MEK that phosphorylates Erk which enters the nucleus and activates transcription factors.

Answer 42

Lysosomes breakdown damaged organelles, nucleic acids, or lipids. Cellular contents and proteases are tagged with M6P signals so that they can be delivered to an endosome via the endomembrane system. Once in the lysosome, proteases cleave membrane and soluble proteins that are not endogenous and are from others organelles. As well, enzymes cleave fats, sugars, and other organelles. Once molecules are broken down into their basic parts, they are sent to the cytosol for reuse.

Answer 43

Proteasomes require the post-translational modification, ubiquitination, before degrading intracellular proteins in the cytosol or nucleus. Cytosolic proteasomes degrade damaged proteins that are tagged with polyubiquitin chains to be targeted to and recognized by proteasomes. Damaged nuclear proteins are polyubiquitinated and degraded by proteasomes in the nucleus.

Answer 44

Peroxisomes keep and use reactive oxygen species like peroxide, ions, and free radicals with enzymes including catalase. Peroxisomes are small, membrane enclosed organelles that contain enzymes, which catalyze metabolic reactions, and peroxins that are synthesized in the cytosol and targeted to peroxisomes by PTS‘s. Although hazardous, peroxisomes have important decomposing functions for cargo like uric acid, amino acids, and a long chain fatty acids.

Answer 45

Apoptosis is an energy consuming programmed cell death that kills cells cleanly and carefully. It is used to protect the body from damaged cells that don’t function properly. It occurs in four steps initiation, blebbing and enzyme activation, structure change, and engulfment. During initiation, severe damage or trauma turns on intrinsic pathways at the outer membrane of the mitochondria. Immune cells release death ligands that attach to death receptors activating an extrinsic pathway to apoptosis. During blebbing and enzyme activation, the cell shrinks and forms blebs. Caspases are also activated, to cleave and activate executioner caspases. During structural change, the cell’s DNA is fragmented, nuclear membrane breaks down, nucleus and cytoskeleton disassemble, and phospholipid content changes exposing PS in the exoplasmic leaflet. Lastly, during engulfment, phagocytes endocytose apoptotic bodies and digest them with phagocytic lysosomes, causing minimal disturbance.

Answer 46

Necrosis is a result of cellular injury that cannot be repaired. Injured cells show swelling in the mitochondria and endoplasmic reticulum, or blebbing, but can recover. When the damage cannot be repaired, necrosis occurs in three steps: damage, swelling, and destruction. Toxins, heat, radiation, freezing, ischemia, pathogens, and mechanical trauma can cause damage to the cell. when damaged, organelles lose their structure and swell, vacuoles form, and DNA is degraded. The cell membranes eventually lose their structural integrity and have holes that can be seen with a microscope. Content spills producing inflammatory signals, mitochondrial proteins are released, and lysosomal contents are exposed triggering apoptosis of nearby cells.

Answer 47

Signal transduction is the conversion of an extracellular signal to a cellular response.

Answer 48

Protein kinase receptors

Answer 49

Signal amplification allows for a small amount of signal to produce a substantial effect within a cell.

Answer 50

The cytoskeleton is a filamentous array of structural proteins that occupy a large portion of the cytosol and extend through the cytoplasm from organelle to organelle and to the plasma membrane. The cytoskeleton permits signaling, vesicular transport, and motility. As well, it defines cell shape and content distribution. The cytoskeleton is made up of proteins that a line to permit cellular functions and contribute to mechanical strength. These proteins include intermediate filaments, microtubules, an actin.

Answer 51

Intermediate filaments are analogue us to bones as they are the strongest cytoskeleton filaments which provide mechanical strength for cells to resist shape change. They are polymers with tissue and cells specific expression that assemble and disassemble depending on post translational modification. The primary structure of an intermediate filament is a polymer of amino acids linked by peptide bonds. The secondary structure is alpha helices that give long coiled structure with hydrogen bonds which stabilize structure, resisting stretching and preventing collapse. The tertiary and quaternary structures have monomers, dimers, and tetramers. Monomers are tertiary, but when they wrap making coiled coils, they maximize hydrogen bonds as quaternary structures giving strength to the filament. When dimers assemble in antiparallel and staggered formation, they increase strength. Intermediate filaments assemble in three steps. The first step is when a unit length filament is formed by eight tetramers. The second step is when unit length filaments come together to form immature filaments that interact loosely end to end. The third step is when immature filaments compact to form mature filaments that are fully assembled. The post translation on modifications that intermediary filaments experience are phosphorylation and glycosylation. Phosphorylation and glycosylation occur in the head or tail domains of subunit proteins. Phosphorylation leads to dissolution but when phosphorus is removed by phosphatases, intermediate filaments reform.

Answer 52

Lamin: found in the nucleolus - forms nuclear matrix to protect chromatin Desmin: connects cell structures together giving muscle structural integrity Keratin: Binds to desmosomes to form a complex like hair, skin, or nails

Answer 53

Microtubules define how things are trafficked through the cytoplasm creating specific bi-directional routes where cargo can attach anywhere. Assembly is organized and occurs with many proteins at MTOCs in the cell. Microtubules are made of dimerized tubulins, which are globular with similar shapes that bind head-to-tail to form dimers. Both tubulins have GTP but beta tubulin can cleave GTP and change shape when bound to GDP. Initially dimers spontaneously assemble unstable polymers that can fall apart. After 6 dimers have formed, they grow laterally and longitudinally as a protofilament. 13 protofilaments can form a sheet that rolls into a tube and acts as a nucleation site. Diemers come and go either assembling or disassembling the microtubule.

Answer 54

Assembly: When GTP is bound to beta tubulin, polymerization is favoured and dimers attach Disassembly: When GTP is hydrolyzed to GDP, the dimer changes to promote depolymerization Polarity: Each end of the microtubule is different and has polarity with either positive or negative ends. Dimers prefer binding to positive ends

Answer 55

Microtubules need to be very responsive growing, shrinking, and changing direction rapidly. GTP cap: Growing microtubules have a cap of GTP subunits at the tip Hydrolysis: GTP hydrolysis exposes GDP-bound subunits at the tip Depolymerization: Catastrophic depolymerization occurs Recap: Enough GTP subunits bind to recap microtubules and stop depolymerization Growth: Microtubule can resume growing when GTP bound dimers are available Catastrophe: rapid depolymerization of dimers at the plus and shortens microtubules. This can be fixed with capping or rescue. Capping is when the plus and binds to capping proteins to stabilize and keep the dimers polymerized. Rescue is when GTP bound dimers or other proteins rescue the microtubule.

Answer 56

MAPs stabilize, cross-link, bundle, and cut microtubules, while motor proteins regulate trafficking. Kinesin and Dynein are motor proteins that walk toward the positive and negative ends respectively. Motor proteins have heads that bind to the microtubules and tails that bind to the cargo. 1) Head 1 is attached to the microtubule while head 2 is attached to ADP 2) ATP binds to head 1 causing a conformation change that makes head 2 swing around 3) Once head 2 is over a binding site, it binds to the microtubules and releases the ADP 4) The ATP at head 1 undergoes hydrolysis so that it is now ADP, causing head 1 to release the microtubule 5) The process repeats but with ATP binding to head 2, causing head 1 to swing around

Answer 57

Like microtubules, actin filaments are composed of globular proteins and have motor proteins that initiate movement. Differently, actin filaments contribute to cell structure and movement. Different types of actin monomers make the actin cytoskeleton and give a specific function. They are similar to a double coil structure that has high tensile strength that can withstand pulling. Actin filaments are also polarized with barbed ends (+) and pointed ends (-). Actin filaments are polymerized in three steps. In the first step, nucleation, a third monomer binds to a dimer forming a nucleus trimmer for an actin filament core. In the second step, elongation, monomers add to the nucleus in both directions, favouring the plus end, dynamically. In the third step, the rate of assembly is equal to the rate of disassembly and elongation stops. Treadmilling occurs when the Acton filament stays the same length but moves due to favoured addition and removal of monomers. Treadmilling is regulated by ATP-actin concentration. If the ATP-actin concentration is above the critical concentration, actin monomers are added to the ends allowing for rapid adjustment.

Answer 58

Monomer-binding: Bind to actin monomers and influence polymerization Nucleating: Bind to actin polymers increasing stability and growth Capping: Bind to positive or negative ends to stabilize the polymer preventing assembly and disassembly Severing/Depolymerization: Bind to actin polymer inducing depolymerization or severing Cross-linking: Allow side-to-side linkage of actin polymers to form actin bundles Membrane anchors: Link actin filaments to non-actin structural proteins like integrins Motor proteins (myosin): Bind to actin filament to allow movement. Motor proteins are made up of a motor, regulatory region, and tail. The motor is constructed of a heavy chain that binds to the actin filament and ATP. The regulatory region is constructed of one heavy and two light chains that move back-and-forth as myosin moves. The tail binds to cellular proteins and myosins.

Answer 59

The movement of actin filaments occurs through hydrolysis, the stage where actin binds, and the movement itself. With ATP bound to the motor domain, the myosin is unbound to the actin filament. Hydrolysis of ATP to ADP and an inorganic phosphate causes a confirmational shift in the regulatory domain, swinging it like a lever. The motor domain then binds to the actin filament and the inorganic phosphate is released from the myosin, causing another confirmational change that pulls the myosin along the actin filament. ADP is then released and the binding of a new ATP causes the myosin to unbind from the actin filament. In most cases, myosin moves toward the barbed, or plus, end of the actin filament.

Answer 60

Migration is the process of cells actively moving that takes coordination to move while keeping contents intact and functional. Rapid assembly and disassembly is what generates the forces and coordination needed for migration. Actin filaments are what produce the pushing and pulling by polymerizing near and pushing the plasma membrane while disassembling other actin filaments for more monomers. The hydrophobic interaction of the plasma membrane prevents it from ripping. The proteins involved in migration are filopodia, lamellipodia, and stress fibers. filopodia are thin parallel bundles with a positive end at the membrane, these extend in the direction of motion. Lamellipodia Are large sheets with the positive end at the membrane while the protein distends a wide amount in the direction of motion. Stress fibres form around integrant with their positive end facing inward. They anchor to allow motion forward. The integrins and monomers involved with stress fibres recycle to provide monomers for filopodia and lamellipodia. As filopodia and lamellipodia extend, integrins bind to the extra cellular matrix and the actin filaments bind to those integrins for an anchor.

Answer 61

The cell cycle is a series of phases that cells pass to divide. G1: Cells are not committed to dividing but they are active and growing G0: Cells are resting -these are quiescent cells G1/S Checkpoint: Cells are checked for DNA damage, after this checkpoint the cell commits to progression S: Cell replicates its genome and centrosome to prepare for division S/G2 Checkpoint: DNA integrity is checked G2: This is the last chance for growth where the cytoplasm and contents increase G2/M Checkpoint: A large scale rearrangement to structure is done to facilitate mitosis M: Mitosis occurs

Answer 62

The p53 protein is a tumour suppressor protein that ensures cells with DNA damage do not divide. It also initiates apoptosis if mutated cells are found. If the p53 protein is dysfunctional, cells can invade apoptosis and irregularly and rapidly divide.

Answer 63

Mitosis is an important phase where the parents sell divides into two daughter cells, it is risky as lots of errors can occur. Interphase: Cells grow and prepared to divide. This is where DNA replication occurs Prophase: During chromosome condensation, chromosomes condense and replicate into sister chromatids that connect at the centromere where the kinetochore and mitotic spindle later attach, the endomembrane dissolves into vesicles. The vesicles and mitochondria randomly distribute around the cell. After chromosome condensation the nuclear envelope dissolves, releasing chromosomes to the cytosol, microtubule networks form the mitotic spindle around centrosomes that are formed by centrioles and proteins. Centrosomes move to opposite ends with tubulin and motor proteins. Prometaphase: Kinetochore forms and binds to chromatids at each side of the centromere. There are two kinetochore per side that use ATP to polymerize and depolymerize microtubule spindle fibers. Metaphase: Chromosomes in the spindle equator attached to kinetochore microtubules which pull apart. Here there is a mitotic spindle checkpoint that verifies the chromosomes are aligned. Anaphase: Proteins that bind sister chromatids are cleaved and the kinetochore shortens, moving chromosomes apart. Chromosomes meet their maximum condensation level, and the microtubules organize around the spindle equator. Telophase: The nuclear membrane reforms along with the cytoskeleton and endomembrane system Cytokinesis: A contractile ring forms where the spindle equator used to be. This contractile ring tightens to divide the cell, snapping the plasma membrane. Due to the hydrophobic nature of the plasma membrane, it reseals spontaneously.

Answer 64

Cyclins associate with progression at checkpoints, while CDKs bind to cyclins to become activated so that they can phosphorylate other proteins to trigger the next stage.

Answer 65

B- fibrin is not a cytoskeletal protein

Answer 66

Cell junctions are membrane proteins that facilitate cell-to-cell attachments for communication and barriers. They can be endothelial, which line blood vessels to create barriers, or epithelial, which line organs resting on the basement membrane ECM separating epithelial cells from connective tissue. Cell junctions are composed of adhesion proteins called junction complexes. These junction complexes are: Tight Junctions: divide the membrane into apical and basal surfaces, connecting to the cytoskeleton and regulating paracellular transport. Adherens Junctions: cadherins bind to other cadherins, overlapping to give bond strength in neural synapses and cardiac muscle cells. Desmosomes: link to the cytoskeleton and act like snaps to provide integrity to the skin and cardiac muscle. Hemidesmosomes tether to basement membranes, attaching epithelial cells to the ECM.

Answer 67

The extracellular matrix is a network of molecules that fills spaces between cells to provide external structure and support, holding tissues together. The basement membrane has collagen sheets and proteins that are a structural foundation, barrier, and network on the outside of tissues. Collagen: the main protein in the ECM. It exists as a triple helix that cross links to form fibrils which form collagen fibres. Multiple types of collagen are specific to different tissue types. Fibronectin: glycoproteins that connect cells to collagen matrices, functioning in cell adhesion, they are expressed as diners, and bind to integrins. Interactions with the cytoskeleton cause fibronectin dimers to straighten and associate with other fibronectins, resulting in fibrils at the cell surface. Elastin: responsible for giving elasticity to tissues, allowing them to return back to their original shape after being distorted by an external force. Elastin has hydrophobic and hydrophilic regions that facilities the ability to return to its original shape. Laminins: provide an adhesive substrate for cells and strengthen the ECM. Laminin forms triple helical coils that form a cross-like “t” structure with multiple binding sites for ECM proteins. Each end of the structure forms a connection with a neighbouring molecule to handle tension in multiple directions, giving a great deal of strength to the ECM. Proteoglycans: hydrated gel that is resistant to compressive forced, they are critical for structures like cartilage in our joints. They consist of a prote polypeptide core and attached sugar residues. They are complimentary to structural proteins like collagen and elastin.

Answer 68

Tissues are a group of cells that collectively carry out a function. The four main types of tissues are: Epithelial: form a barrier to protect the inside of the body. - Skin: made of several epithelial tissue types that vary structurally in thickness - Glands: pocket-like structures that release secretions via ducts. They can be exocrine or endocrine - Digestive Tract: absorb secrete and protect from mouth to anus. Various cells can excrete glycosylated proteins to form a mucous layer for acid protection , release enzymes or HCl to break down food, and move nutrients or waste across epithelial layers Nervous: use electrical communication to carry information across long distances. Ion concentrations create electric potential for signalling and rapid cell communication Muscle: convert chemical and electrical signals to mechanical movement. Muscle tissue is rush in actin-myosin and is composed of skeletal, smooth, and cardiac muscle cells. Skeletal muscle moves the skeleton, smooth muscle tissue lives the digestive system, blood vessels, and anywhere with contractile activity, and the cardiac muscle is found in the heart to pump blood Connective: make up the ECM, filling spaces between cells to provide strength and cushioning.

Answer 69

Cells are the basic unit structure of life > tissues are a group of cells that carry out a specific function > organs are composed of 2 or more tissue types > body systems are composed of 2 or more organs (11 body systems) > organisms are the final level of organization that consist of all previous levels.

Answer 70

Homeostasis is the ability to regulate and maintain an internal environment, regardless of external influences. Homeostasis allows the body to counter change and support life by reaching set points and parameters. Homeostatic control systems are composed of the sensor, which detects the variable, integrator, which compares the variable to a set point, and the effector, which initiates a change to restore the set point. When the set point is reached, the integrator stops communicating and the effector stops. This can be intrinsic where the control systems are all located in the same tissue, or extrinsic where there is at least one regulatory mechanism outside of the tissue or organ. Feedback loops occur when the effector causes a change that is sensed by the sensor. A negative feedback loop is when a change in the environmental parameter causes the effector to restore the set point. A positive feedback loop is not homeostatic, it is when an effected causes a change that amplifies the signal.