Post Midterm Week 1: Flashcards
1
Q
What does it take to make a cell?
A
- Information: which is stored in DNA and replicated through RNA and replication, all cells have information and DNA with the exception of red blood cells (erythrocytes), cells become specialized during development called differentiation
- Chemistry: When and how the building blocks of life appeared in the history of earth. Inorganic molecules formed organic molcules (lipids, nucleic acids, amino acids) —> Known as abiogenesis
- Compartments: Defined by a single or double layered lipid membrane (mitochondria which make ATP, Chloroplasts which is a sight of photosynthesis, Nucleus which replicates DNA, Vesicles which transport molecules within the cell, endoplasmic reticulum allow cells to be organized
2
Q
What is an example of differentiation?
A
Muscle cells develop a trucktile proteins for movement
Bone cells produce minerals for stronger cells.
3
Q
What is the Miller-Urey Experiment (1952)?
A
Simulate earths early conditions to test whether organic molecules to from spontaneously. First creating formaldehyde and hyrogen cyanide (carbon compounds) which are the foundation for amino acids
4
Q
What are the basic properties of cells?
A
- Highly complex and organized
- Activity controlled by a genetic program
- Can reproduce - make copies of themselves
- assimilate and utilize energy
- Carry out many mechanical reactions (enzymes)
- Engage in mechanical activities
- Capable of self regulation
- Able to evolve
5
Q
What is the distinction between prokaryotic and Eukarytoic cells?
A
Eukaryotes: Plants and animal cells. Larger and more complex. Multicellular.
Prokaryotes: Small and simple without nucleus or membrane bound organelles. Earliest forms of life on Earth.
6
Q
What is the genome?
A
Cell is the structural unit of life and the genome is the information system where stem cells are differentiated
7
Q
What is a eukaryotic cell with a unique purpose?
A
Slime molds are classified as fungi due to their spore producing nature. However they are now considered protista.
8
Q
What do viruses lack that cells have?
A
- Independent reproduction
- Cellular structure
- Metabolism
9
Q
How do cells and viruses compare?
A
Viruses do not:
- Respond to stimul
- Self regulate
- Engage in mechanical activity
- Use energy
They do everything else.
10
Q
How do viruses exist outside of cells?
A
They exist as inanimate particles called viron which is made up of a small amount of DNA or RNA that encodes a few hundred genes.
11
Q
What is the most popular classification for viruses?
A
The Baltimore classification categorizes viruses based on type of genome (RNA/DNA) and their method of replication.
12
Q
Basic structure of bacteriophage?
A
13
Q
Basic structure of influenza virus?
A
14
Q
How to virus bind to cell surfaces?
A
Via specific proteins and then enter the cell. This defines the cell types and host range.
15
Q
What are the types of host ranges?
A
Narrow: Human cold and influenza infect epithelial cells
Wide: Rabies can infect cells in dogs, foxes, bats, humans
16
Q
What are the two main types of viral infections?
A
Lytic: Production of virus particles ruptures (and kills) cell
Non-Lytic: Viral DNA is inserted in host genome - PROVIRUS infected cell can survive, often with impaired function.
17
Q
What is the result of Zikka virus?
A
microcephaly which is a condition where the head is smaller than normal and impacts early brain function including delayed motor and speech.
18
Q
What does the sarcoplasmic reticulum do?
A
Facilitates the movement of cations which are essential for muscle contractions.
19
Q
What is the structure of the plasma membrane?
A
Trilaminar with a phospholipid bilayer which is 6nm (its the oreo). Hydrophobic tails, Hydrophilic head.
20
Q
What is the difference between a micelle and a liposome?
A
Micelle is a solid ball while a liposome (has two layers) is a hollow sphere with a fluid filled centre
21
Q
What are the key features of phospholipids?
A
Phosphate Group which attached to another molecule which can change and make it diverse.
Glyceral Backbone: Made up of three carbon atoms
Made up of two tails, a straight tail made up of a straight (saturated) CH2 (Fatty acid chains), and a kinked tail (unsaturated) which is made up of both CH2 (Fatty acid chains) and H2C. A double bond gives it the kink.
22
Q
What are the different head groups for a phospholipid?
A
23
Q
What is the only phospholipid group that does not contain a glyceral backbone?
A
Sphingolipids have a sphingosine backbone which is a aliphatic amino alcohol.
24
Q
Where does phosphlipids making the plasma membrane come from?
A
Occurs at the interface of the cytosol and outer endoplasmic reterticulum membrane.
Key takeaways: Phospholipids are derived from carbohydrates via the glycolitic pathways (Building blocks are glucose metabolism). Main site for phsopholipid synthesis for other organelles. Acyl transferanse, phosphatase, phospohtransferase regulate this proces.
25
What is the endoplasmic reticulum ER?
A phospholipid factory. It produces and modifies phospholipids which need to be delivered to different parts of the cell via vesicles.
26
What is lipid movement within the leaflet like?
Lipids move easily within the leaflet but movement to other leaflets is difficult and slow
27
What are similarities amongst all membranes?
1. Approximately 6nm thick
2. Stable
3. Flexible
4. Capable of self assembly
28
What are the three classes of membrane proteins?
1. Integral: Membrane proteins span the lipid bilayer. Examples include: Transport of nutrients and ions, Cell-cell communication (gap-junctions), attachment
2. Peripheral: Membrane proteins assoicate with the surfaces of the lipid bilayer
3. Lipid-Anchored: Proteins attach to a lipid in the bilayer
29
How does temperature effect the biological membranes?
Warming increases fluidity (liquid crystal)
Cooling decreases fluidity (crystalline gel)
Fluidity is crucial to a cell function. It is determined by the nature of lipids in the membrane.
Unsaturate lipids increase fluidity
Saturated lipids decrease fluidity.
30
What are peripheral membrane proteins?
Protein will be attached to the membrane but does not go throughout the cell.
31
Why are phospholipids considered the fluid mosaic model of the biological membrane? Produced by Seymour and Nicolson
It's fluid because of the individual lipid molecules allowing its fluidity
It's a mosaic because of the diversity of particles
32
What is housed within the inner membrane of the mitochondria?
Contains a very high concentration of protein necessary for electron transport chain and ATP synthesis.
33
What are housed within the myelin sheaths?
They have very few types of transmembrane proteins and consist of plasma membrane wrapped around a neurons axon. This increases the speed at which electrical impulses propagate along the myelinated fiber.
34
Lipid composition of membrane can be changed by?
1) Desaturation of the fatty acid chain
2) Exchange of fatty acid chains
35
How to phospohlipids organize themselves?
Spontaenously, but with a focus on stability.
36
What are the four types of integral proteins? (proteins that span the entire membrane)
1. Transporter
2. Receptor
3. Enzyme Convertor
4. Anchor
37
What is the most common protein sructure in plasma membranes?
The alpha helix
38
What are tetraspanins?
A family of common transporter proteins found in multicellular eukaryotes that have a short and long extracellular domain
39
What types of compounds are able to pass through lipid bilayers easily?
Small and uncharged molecules pass through easily.
Large/polar/charged compounds cannot easily cross and specific mechanisms are required for the controlled transport of many substances. (Exampel: Ca+, Glucose, Na+, K+)
40
What are the four basic mechanisms for moving molecules across membranes?
Passive/Nonmediated
1. Simple Diffusion: Uncharged items can diffuse down to chemical gradient into the cytosol and this is unmediated by transport. Goes from high to low concentrations (Packed room). Works on small and uncharged molecules like O2. Does not allow water because of the hydrophobic tails
Passive/Non-mediated
2. Diffusion through a channel: Go down a gradient but it is not mediated because the channel isn't opening or closing. Needed to allow water molecules to go through or other charged molecules
Passive/Transporter Mediated
3. Facilitated Diffusion (Carriers): Still a chemical gradient. Transporter will now take a molecule and attach and cause some form of confirmation change that allows the transporter to open towards the inside of the cell and the molecule. (Example: Glucose Transporter, Symporter, Antiporter)
Active/Transporter Mediated
4. Active Transport: With the help of ATP, can go across the gradient so it needs some form of energy to push it through (hydrolysis of ATP). Water breaks the phosphate to create an inorganic phosphate in ADP and the energy in that is used to make the transporter open and allowing molecules to go through.
41
What is the difference between passive and active movement across cell-membrane?
Passive does not require any energy while active does.
42
What are the two types of gating systems for diffusion through ion channels?
Open or closed meaning they can respond to different stimuli.
1) Voltage Gated Channels: React to changes in charge across the membrane (usually negative inside and positive outside). Under depolarized conditions there is a tiny amount of sodium inside neurons so when a sodium channel is opened, it created action potential.
2) Ligand-Gated Channels: The channels repsonds to binding a specific molecule on its surface, a ligand. Binding of a ligand produces conformational change in the structure of the channel
43
What is tetrodotoxin?
A toxin found in aquatic animals that blocks your sodium channels which means that there is no action potential of the cell. The result of this is paralysis.
44
What are three types of carriers?
1. Glucose Transporter: Most animal cells import glucose from the blood into cells down a concentration gradient via this mechanism.
2. Symporter: Some cells need to move substances from lower concentration to higher concentration. Example: Reabsorption of glucose in kidney cells after blood filtration. (Na+ - Glucose Symporter - glucose going in with the sodium going into the cell)
3. Antiporter: The concentration gradient of one molecule is used to transport a different molecule in opposite directions.
45
What is the purpose of protein receptors?
They convert extracellular signals into intracellular signals and lead to different pathway activations (growth, movement, differentiation, death, etc.) - what are the cells next steps.
46
What is a popular form of receptor?
Release of insulin after eating to receptor on liver to allow extra storage of glucose in the liver. That glucose in the liver is stored in glycogin.
47
What are the three stages of signal transduction?
1. Binding of a ligand to a receptor
2. Signal transduction via second messengers like cAMP, calcium, or G-Protein
3. Cellular response: Cell growth, cell division, cell storage, etc.
48
What are glycogen stores?
How epinephrine activates conversion of glycogen stored in the liver to glucose is a good example of signal transduction.
49
What are anchoring proteins?
They anchor things to the cell or provide structural support. They interact with components of the extracellular matrix.
50
What is the extra cellular matrix (ECM)?
An organized network of material produced and secreted by the cell.
51
What are the functions of the ECM?
1. Cell adherence
2. Communication between cells
3. Cell shape, mechanical support, structural integrity
4. Serves as a barrier and filters out some particles.
52
What is a common example of extracellular matrix?
Skin
53
What are major components of the ECM?
Proteins like collagen, glycoproteins laminin and fibronectin, there are also proteoglycans with chains of polysaccharids
54
Do plants have an ECM?
Yes, but the plant cell walls are their ECM.
55
What is the mitochondira?
The power house of the cell that sits beside the nucleus.
56
What are the different parts of the mitochondria?
1. Cristate
2. Outer Membrane
3. Inner Membrane
57
What is the origin of the eukaryotic cell?
It was founded through endosymbiotic theory which started with:
1. Ancestral prokaryote
2. Over time the plasma membrane enfolded and formed a nucleus
3. Through endosymbiosis an ancestral eukaryotic cell engulfed aerobic bacterium which eventually became a mitochondria
4. Some cells eventually engulfed cyanobacteria which eventually became chloroplasts creating the ancestral eukaryote.
58
What is aerobic respiration?
Converts in presence of oxygen energy stored in food molecules into chemical energy stored in ATP. It produced CO2 as a by-product
59
What is photosynthesis?
Building carbohydrates using energy from sunlight and CO2. Releases O2.
60
What is the precursor to ATP?
ADP - It only had 2 phosphates. Once a third phosphate it attached it becomes ATP.
61
Why does the mitochondria have a folded inner membrane (cristae)?
For increased surface area so that we have more capacity for energy production. This is where ATP is synthesized for aerobic respiration.
62
What occurs in the outer mitochondrial membrane?
Contains enzymes with diverse metabolic functions.
Monoamine oxides that break down monoamines ingested in food.
Also has porins, which are large channels permeable to many molecules when opened.
63
What are the two aqueous compartments of the mitochondria?
1. Intermembrane space
2. Matrix: A high protein content space containing mitochondiral ribosomes and DNA.
64
What is cellular respiration?
The process by which food, in the form of sugar (glucose), is transformed into energy within cells. This energy is stored in ATP molecules, which then power all sorts of cellular process.
65
What is the difference between aerobic and anaerobic respiration?
Respiration that requires oxygen is known as aerobic respiration; respiration that occurs without oxygen is called anaerobic respiration.
66
What occurs during Aerobic respiration?
Step 1: Glycolisis where glucose is broken down to create ATP in the cytoplasm. Consumes two ATP molecules but produces 4 more + NADH + Pyruvate
Step 2: In the mitochondira, pyruvate is used to create acetly coenzyme A and CO2
Step 3: Known as citric acid cycle: Acetyle coenzyme A is used to create more NADH and FADH2, CO2, and an additional ATP Molecule.
Step 4: NADH, FADH2, and oxygen are used to create massive amounts of ATP thorugh electron transfer.
67
What occurs during Anaerobic Respiration?
No oxygen is present, ATP is creased through outher chemical processes however there is much less ATP produces.
68
What are the two forms of phosphorylation?
Substrate-level phosphorylation: Hydrolysis reaction releases enough energy to drive phosphorylation of ADP to ATP
Oxidative Phosphorylation: Chemical energy of organic molecules is transferred first to electron carriers to create an electrochemical gradient that can power ATP synthesis.
69
Coenzymes acting as electron carries can exist either as:
1. Oxidized - can accept electrons
2. Reduced - can donate electrons when returing to their oxidized state
70
What are the steps of oxidative phosphorylation?
Step 1: Complexes I-IV
Complex 1: FADH and NADH come into the electron transport chain and donate their electrons, they become oxidized (meaning they donated and can now accept)
Complex 2-3: Electrons continue to move through steps 1, 3, and 4 and pump protons for a proton gradient (more outside than inside the outer mitochondrial matrix)
Complex 4: Oxygen is the final electron acceptor - at Complex 4 - electrons combine with oxygen and protons to form water. It's the final acceptor in cellular respiration.
Step 2: ATP Synthesis: The proton gradient allows for the rush of those to go into the mitochondrial matrix and powers the production of ATP from ADP and phosphate.
71
What are chloroplasts?
Little circles or dots within the leafs that make up the inner or outer membrane (similar to mitochondria but without cristae). It is composed of the outter membrane, inner membrane, stroma and stacked thylakoid
72
What are the two part of photosynthesis?
1. Light dependent reactions: Occur in thylakoid membrane. The chlorophyll is absorbing different wavelengths of light (making plants green). Electrons enter ETC and thylakoid membrane and H+ is pumped into thylakoid lumen
2. Light-Independent reactions: Calvin cycle which occurs in stroma of chloroplasts. ATP and NADPH made in light reaction used to make CH20
73
What is apoptosis?
It is a normal process that involved programmed cell death in a coordinated sequence of events (example: gets rid of webbing between fingers)
74
What is bone morphogenetic protein?
BMP is a secreted protein that binds to BMP receptors. Expression of non-active BMP receptors in chicken embryonic hind limbs greatly reduced interdigital apoptosis and results in webbed feet.
75
How is apoptosis characterized?
1. Shrinkage of the cell
2. Blebbing (bulging) of the plasma membrane
3. Fragmentaiton of DNA and nucleus
4. Loss of attachement to other cells
5. Engulfment by phagocytosis
76
How is apoptopsis initiated?
Through intracellular stimuli like genetic damage, hypoxia, viruses.
Killer proteins like Bax causes change in mitochondria membrane potential and to leak to Cytochrome C.
77
What are two significant disease related to apoptosis?
1. Tumors: Apoptosis deficiency and uncontrolled growth.
2. Alzheimer's and Parkinsons: Too much apoptosis resulting in excessive brain atrophy.
78
What occurs in the cytoplasmic endomembrane system?
An network of interconnected organelles within the cytoplasm of eukaryotic cells that work together to modify, package, and transport lipids and proteins.
79
What is the Cytoplasmic Endomembrane System comprised of?
1. Endoplasmic Reticulum
2. Endosomal Transport Vesicles
3. Golgi Complex
4. Lysosomes
5. Vacuoles
80
What are the components of a secretory cell?
Goblet Cell: Produce mucigen granules (pre-component of mucus)
Mucin is then synthesized in the rough ER and then processed in the ER for modifications or holding
Then travels to Golgi complex for processing and finally packaged in concentrated in vesicles.
Finally derived to plasma membrane for secretion.
81
How can we track the movement of synthesis throughout a cell?
Green Fluorescent Protein
82
How does vesicular transport occur?
Utilizes transport vesicles (~50-75nm) which are small, spherical membrane-enclosed organelles that bud off donor compartment and fuse with acceptor or recipient compartment.
Can transfer from organelle to PM (and vice versa) or from organelle to organelle.
Target movement (directed) - using motor proteins and sorting signas
83
What are the key elements of vesicle tracking to a compartment?
1. Movement of vesicles: uses cytoskeleton and motor proteins. Can be anterograde or retrograde
2. Tethering vesicles to target compartment - via proteins from the Rab family of protein and other more specialized.
3. Docking of vesicle to target compartment - uses proteins called SNAREs assembly provides energy for fusion
4. Fusion of vesicle and target membrane.
84
What is endocytosis?
The process in which cells take in material. An example is phagocytosis - when a cell takes in solid fluid or bacteria.
85
What is Exocytosis?
The process in which cells exports materials outside (how it gets stuff out)
86
What is the difference between the rough and the smooth ER?
Rough ER: is associated with ribosomes. Many proteins, including those that are destined for secretion, are synthesized by ribosomes associated with the rough ER
Smooth ER: Lacks ribosomes and is the primary site of lipid synthesis
87
Functions of the smooth ER?
1. Lipid Synthesis
2. Production steroid hormones (glucorticoids, androgens, and estrogens)
3. Detoxification - liver cells contain enzymes that modify foreign compounds
4. Sequestration (storage) of Ca2+
88
Why is calcium important?
Cells invest a lot of energy to control changes in calcium concentration.
Calcium is avidly excluded from the cytosol? The principal reason is that Ca2+ does not bind to water well, which will precipitate phosphates and make proteins insoluble.
The result is calcium in the cytosol is either bound by a range of Ca2+ binding proteins, forced out through pumps and transporters, or sequestered into specific organelles.
89
What are the functions of the rough ER?
1. Synthesis of membrane phospholipids
2. Glycosylation of proteins: Additions of carbohydrate chains to specific proteins.
3. Protein folding - quality control
4. Protein synthesis, modification, and transport: Proteins targeted to ER, Proteins targeted to other endomembrane compartments, proteins targeted to plasma membrane.
90
What occurs during protein synthesis?
In the cytoplasm, ribosomes synthezise polypeptides from mRNA
Initiation factors recruit the samll ribosomal subunit and scan the mRNA for the AUG codon.
Once AUG complex found, large ribosomal subunit joins, the initiation factors are released, and a tRNA complementary to the next codon binds to the A site.
91
Where does all protein translation begin?
On free ribosomes
92
What are the ways translation is completed?
1) Free Ribosomes:
- Cytosolic proteins
- Peripheral membrane protiners
- Porteins targeted to nucleus, mitochondira, peroxisomes
2) ER Bound Ribosomes:
- Secreted proteins
- integral membrane proteins
- Soluble protiens associated with inside of endomembrane system.
93
How is the site of translation determined?
Ribosomes are targeted to the ER membrane by a specific.
The signal sequence is:
- Located in the amino-terminus
- Contians several consecutive hydrophobic amino acids
- Directs synthesis to the ER compartment
Protein moves through channel into ER for cotranslational import
94
What is cotranslational protein import?
Ribosome begins making a protein. Signal sequence appears at the start of the protein.
The SRP then binds to this sequence and pauses translation. This prevents the protein from fully forming in the cytoplasm.
The SRP is what helps with this, it binds with the SRP receptor and helps it bind. This helps the protein enter the ER and not float freely.
The protein enters through the translocon. A chaperone then comes in, binds to the protein, and folds it correctly in the ER
95
What are the 2 options for a protein targeted to the ER lumen after it is fully synthesized and properly folded?
1. It is retained in the ER lumen, if that is where the function is
2. It is transported from the ER to the Golgi complex for further modification and delivered to distal parts of the biosynthetic pathway. Some cases the final destination is outside the cell.
96
What is a peroxisome?
A type of organelle found in all eukaryotic cells and are involved in a small number of enzymatic reactions (metabolism of fatty acid chains, reduction of oxygen species, biosynthesis of plasmalogens)
97
How does peroxisome effect reduciton of oxygen species?
Peroxisome has catalase which reduces hydrogen peroxide which is a reactive oxygen species (harmful) into water and oxygen
98
What is zellweger syndrome?
a severe, inherited disorder primarily affecting newborns, caused by a lack of functional peroxisomes, which are cellular organelles essential for certain metabolic processes. This deficiency leads to various issues including neurological problems, liver dysfunction, and skeletal abnormalities, often resulting in death within the first year of life. Causes severe brain development and hypomeylination which causes reduced action potentials, apnea, abnormal renal function.
99
What is cystic fibrosis?
A disease characterized by the deletion of three nucleotides, resulting in the loss of aminoacid at the 508th position of the protein.
100
What is cotranslational protein import?
How soluble proteins get into the endomembrane system
101
What are the four steps for cotranslational protein import?
1. As a protein is synthesized by a ribosome in the cytoplasm. A signal sequence in the amino-terminal end emerges.
2. The ribosome SRP complex moves to the rough ER and binds to its receptor. This allows for positioning the ribosome near the transmembrane channel.
3. The SRP will disassociate (the SRP was preventing translation), so translation will resume and the growing polypeptide chain is threaded through the channel.
4. The final destination, it can remain in the ER if it functions there.
102
How are transmembrane proteins integrated into a membrane?
1. As a ribosome synthesizes the protein a signal-anchor sequence is produced. This directs the ribosome to the ER membrane where the growing polypetide is threaded into the translocon.
2. The ER channel releases the protein into the membrane
3. When translation is completed, the protein remains in the membrane.
103
How are type 1 single-pass transmembrane protines integrated into the membrane?
1) The translation begins on a pre-ribosome in the cytoplasm, a signal sequence is recognized by the SRP which causes translation and directs it into the ER membrane
2) The ribosome docks to the translocon and the signal sequence is cleaved allowing the growing polypeptide to pass into the ER lumon.
3) As the polypeptide elongates a stop-transfer anchor emerges (hydrophobic)
4) The translocon laterally releases the segment into the membrane into the protein
5) Then releases leaving it behind.
104
How does material move from the ER to the Golgi?
Proteins and lipids from the ER are packaged into vesicles and transported to the golgi apparatus, upon their arrival, will undergo modification, and then sent to specific organelles within the cell
105
What is the structure of the Golgi Complex?
Smooth, flattened, disk-like cisterna with ~8 or fewer, curved like a shallow bowl. Cisternae are biochemically unique.
106
What is the difference between the CGN (cis-golgi network) and the TGN (trans-golgi network)?
CGN: acts as a sorting station (whether proteins should conitnue on to the next Golgi station or shipped to the ER)
TGN: Sorts protein into different types of vesicles - vesicles go to plasma membrane or other intracellular destinations.
107
What are coat proteins?
Help the transfer of vesicles from ER to Golgi, and between the Golgi sub-compartments, is achieved by coat proteins.
108
What are coat protein complex?
Protein complexes that assemble on cytosolic surface of donor compartment membranes at sites where budding takes place.
109
What is the difference between COPI and COPII?
COPI- coated vesicles move in retrograde direction
COPII- coated vesicles move in anterograde direction.
110
What does the AP Clathrin Adaptor Protein do?
It's a coated vesicle that moves from TGN to other vesicles (e.g. lysosomes, endosomes, plant vacuoles).
Depending on what the protein is coated with, the coding helps direct them to that area.
111
What are AMPA receptors?
They are doors that allow electrical ions to enter a neuron when a message is received. More AMPA receptors means a stronger signal.
Endophiliin and Dynamin pinch the pocket to allow them to go in.
112
How do viruses exploit the clartharin mediated enocytosis to enter host cells.
The virus binds to specific cell surface receptors triggering the recruitment of adaptive proteins into the cytosolic side of the membrane.
113
What are the functions of lysosomes?
1. Autophagy: Normal disassembly of unnecessary or dysfunctional cellular components via lysosomes.
2. Degradation of internalized material. Destroy pathogens like bacteria and recycle of plasma membrane components like receptors.
114
What is the purpose of plant vacuoles?
They are involved in the regulation of cytoplasmic pH, sequestration of toxic ions, regulation of cell turgor, storage of amino acids,
115
What are the function of plant vacuole?
1. Allow for intracellular digestion
2. Mechanical Support
3. Storage
116
What is the cytoskeleton comprised of?
Dynamic network of interconnected filaments and tubes that extends throughout the cytosol of eukaryotes. They provide structural support, spatial organizaiton, intracellular support, and contractility and motility.
117
What are the three specific components of the cytoskeleten
1. Microfilaments which are comprised of actin monomers (double helixed) which are 7-9nm. Maintain cell shape, movement, vesicle transport, muscle contraction etc.
2. Microtubules which are 25nm - has two components (Alpha and Beta) - 2 major types: Axonemal MT which is organized and stable + Cytoplasmic MT which are loosely organized and dynamic
3. Intermediate filaments which are 10 nm. Made up of protein subunits. Provide structural support and mechanical strength. They are non-polar (no plus or minus end)
118
Where are microtubules assembled and disassembled?
The centresome
119
What are the 2 main types of proteins that bind microbtubules?
1. Non-Motor MAPs: Control MT organization in the cytosol. Defective Tau proteins can cause alzheimers disease
2. Motor MAPs: Two main types - kinesin and dynein. Use ATP to generate force. (Kinesin are plus end-directed, Dynein are minus end-directed)
120
How does the kinesin work?
1. ATP binds to the leading. head and induces a conformational change that swings the trailing head towards th eplus end of the microtuble.
2. The new leading head quickly binds to a tublin subunit and releases ADP, moving the kinesins cargo forward
3. In the trailing head ATP is hydrolyzed to ADP, which leads to detachment from the microtuble.
4. ATP binds to the leading head to repear
121
What is the microtuble-organizing centre
The central site of micotubule assembly found only in eukarytotic cells
2 Most important types are 1) basal bodies associated with cilia and flagella 2) and the centrosome associated with spindle formation.
122
What is actin monomer (what microfilament is made up of)
Actin is the central component of microfilmaents. It exists in cells either as a monomer (G-actin or globular) or as a polymer (F-actin or fibrous)
123
Are microfilmaents and microtubules dynamic or stable?
They are dynamic, constantly moving towards plus and minus end.
124
What are filipodia?
Thin finger like projections that extend from the lamelipodium and are made up of parallel bundels of actin. They help guide cellular direction.
125
What are lameillipodium?
Broadsheet like projection of the plasma membrane formed by the dense actin meshwork. It helps push the cell forwards.
126
What occurs during Actin Nucleation by the Arp 2/3 complex?
This complex helps the creation of branch points for the polymerization of new actin fibers.
127
What is lamellipodium?
An actin projection on the leading edge of a cell
128
What are myosins?
A superfamily of motor proteins associated with microfilaments. Divided into 2 broad groups:
1) Conventional myosins: Type II and Primary motors for muscle contraction
2) Unconventional myosins: Type 1 and 3 onwards
129
What is the purpose of unconventional myosins?
They generate force and contribute to motility in non-muscle cells
130
What is the function of the nucleus?
1. Storage, replication, and repair of genetic material.
2. Expression of genetic material.
- Transcription: mRNA, tRNA, rRNA
- RNA splicing
3. Ribosome biosynthesis
131
What is the process of nucleus storage, replication, and repair?
1./2. DNA duplex 2nm in diameter condenses into a nucleosome fiber 10nm
3. Once wrapped around nucleosome, it folds and coils into chromatic fiber 30nm in diameter.
4. Continues to coil until 1400nm in diameter and a condensed chromatid.
132
How is DNA in the nucleus damaged?
UV light exposure, chemical exposure, replication errors, cellular metabolism, ionization radiation etc.`
133
How does the nucleus express genetic material?
Transcription of mRNA, tRNA, rRNA's which begin at the promoter region (which control transcription).
134
What occurs during ribosome biosynthesis?
Noncoding RNAs do not encode proteins and include tRNA and rRNA. These RNAs are transcribed from DNA found in the nucleoulus.
135
What is the nuclear envelope
1. Nuclear membrane
- inner has intergral proteins and connects to nuclear lamina
- outer binds ribosomes and is continous with rough endoplasmic reticulum.
2. Nuclear pores
3. Nuclear lamina
136
What is the nuclear content comprised of?
1. Chromatin
2. Nucleoplasm
3. Nucleolus
137
What is the purpose of the nuclear envelope?
Separates nuclear content from cytoplasm
Separates transcription and translation processes
Selective barrier that allows limited movement of molecules
138
What does the nuclear lamina do?
A meshwork of filamentous proteins, lamins are found in animal cells only. Plants have nuclear lamina, but NOT made of lamin protins.
Provides structural support for nuclear envelope and is the attachment sites for chromatin.
139
What are nuclear pore's
Gateways between cytoplasm and nucleus - there are 3000-4000 pores. They are found where the inner and outer membrane fuses. Complex structure that involve the arrangement of different types of proteins.
140
How does a nuclear pore complex work?
There is either:
1) Passive diffusion of molecules that are 40kDA or less
2) Regulated movement of larger molecules
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What is the nuclear localization signal?
Helps with regulated movement of proteins into the nucleus. It is several positively cahrged amino acids within the protein sequence.
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Now does NLS target proteins to the nucleus?
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What is the nucleolus?
The largest structure inside the nucelus of eukaryotic cell
Primary function of the nucleolus is biosynthesis of ribosomes.
Ribosomes read RNA and join amino acids to form a polypeptide chain
