Cell Bio Exam 1 Flashcards
What is unique about the reproductive system of C. Elegans?
They are self fertile hermaphrodites, meaning that they produce both sperm and egg and fertilize themselves
Describe the life cycle of C. Elegans.
1) ex-utero embryonic development 2) Four larval stages 2a) Dauer stage 3) adult
In which stages of C. Elegans development are sperm made?
In the L3 and L4 stage. After that only eggs are made.
What is the Dauer stage in C. Elegans development?
It is a shunt pathway in development that allows for the development to pause in times of malnutrition, crowding, or high temperatures. They can remain in this state for up to four months.
What sex chromosomes does the hermaphrodite C. Elegans have? What about the males?
Hermaphrodite: XX Male: XO
What use do the male C. Elegans have for genetic crosses?
They are used to pass mutations from one strain to another. When crossed with a hermaphrodite, 50% of the progeny will be hermaphrodites and 50% will be males.
What is the proctodeum?
The structure on the male C. Elegans that transfers the sperm to the hermaphrodites.
What does par stand for?
Partitioning
What are the three major cellular phenotypes of the Par genes?
1) asymmetric first cellular division 2) orientation of mitotic spindle 3) Localization of P granules to the posterior to form germline
What is meant by polar in cell biology?
As symmetrical distribution of proteins and cellular components throughout a cell. Ex: apical and basolateral portions of epithelial cells
What does polarity establish in the first cell of C. Elegans?
It distinguishes the anterior-posterior axis.
Which region does the actin/myosin cytoskeleton shift to during the one cell stage of C. Elegans development?
It shifts to the anterior side. This “scaffolding” localizes to this region because of the Par3-Par6-PKC complex
What is a maternal effect mutant?
When the offspring displays the expected phenotype of the mother regardless of its own genotype. A first generation homozygote will have a wild type phenotype, but then all of the following generation will show the mutant phenotype
Null allele
Complete loss of function allele
Deletion mutant
Gene is removed from the chromosome ( can be a null allele)
Hypomorphic allele
Gene product will have some remaining function
What are kinases?
Enzymes that add phosphates to other molecules
What are the three components of cell theory?
(1)cells are the fundamental units of life (2) all living organisms are made of cells. (3) all cells come from other cells
What are the major challenges to cell theory?
(1) What about viruses? (2) Bacteria: the cell is the organism (3) Where did the first cell come from?
What are the three major branches of the phylogenetic tree?
Bacteria, archaea and eukaryia
What are the general steps of chemical evolution?
(1) Formation of small organic molecules (2)Combination of these molecules into larger molecules (3) Enclosure in a membrane (4) Reproduction
What is the primordial soup?
The warm aquatic conditions on earth as it cooled after formation
What are the three major methods of studying cells?
(1) Model organisms (2) Cell cultures (3) Cell-free systems
What are the advantages of cell cultures?
You can isolate large numbers of cells; you can have greater access to the cell of interest; you do not have to maintain the whole animals
What are the disadvantages of cell cultures?
Cells are not in their natural environment; The cells do not reproduce unless they are transformed (immortalized with cancer cells)
Describe the cell-free system for studying cells.
Cells are homogenized and then the membrane reformes into microsomes, which are small vesicles that still contain the transmembrane proteins. The microsomes can be separated using centriguation.
What are the components of the plasma membrane?
Lipids, proteins, carbohydrate-modified proteins/lipids, cholesterol
What are the major functions of the plasma membrane?
(1) Barrier between external and internal environments. (2) Selectively allows materials in and out of the cell (3) Convey information about the external environment to the cell nucleus (4) Anchorage to exterior and interior structures (5) Energy transfer
Describe Overton’s contribution to the Membrane Model.
Saw that non-polar dyes could cross membranes of root hairs of plants. Proposed that cells were “coated” with lipids
Describe Langmuir’s contribution to the Membrane Model.
Performed in vitro experiments. Thought lipids were in a monolayer. Was the first to propose that lipids organize their hydrophobic tails together.
Describe Garter and Grendel’s contribution to the Membrane Model.
Worked with RBC membranes. Concluded that lipids form a bilayer with the hydrophobic tails in the center of the bilayer
Describe Davson and Danielli’s contribution to the Membrane Model.
Proposed that the lipid bilayer membrane was coated with proteins. Observed that the membrane was acting selectively and different cell types had different electrical resistances.
Describe Robertson’s contribution to the Membrane Model.
Used electron microscopy to view the cell membrane. Saw the “railroad” appearance of the membrane. Didn’t disprove the Davson and Danielli model.
Describe Singer and Nicolson’s contribution to the Membrane Model.
Measured the thickness of the membrane and determined that it was too thin to be a protein-lipid sandwich. They suggested that proteins must be scattered within the lipid bilayer.
What is the fluid mosaic model of the membrane?
Fluid meaning that the lipids move laterally and are not fixed in position. Mosaic meaning that there is a very high degree of variation of types of proteins and lipids
What holds together membranes?
Non-covalent forces. The combination of a high number of low-affinity bonds creates a strong membrane.
Which component of the membrane is structural? Which is functional?
Lipids are structural. Proteins are functional
Describe the structure of the lipid bilayer of the membrane?
The hydrophobic fatty acid portion of the lipids are the tails that turn toward other hydrophobic fatty acid tails. The phosphate group is hydrophilic and faces toward the aqueous medium
What type of bond is found in a phospholipid?
Phosphoester linkages connect the phosphate group to the glycerol backbone
Describe the structure of phosphatidylcholice
A phospholipid with choline bound to the phosphate group. Choline structure: (CH3)3-N+-CH2CH2OH
What is the structure of ethanolamine?
CH2-CH2-NH+
What is inositol?
A cyclic alcohol containing 5 OH groups
What is PIP2?
Phosphatidylinositol 4,5 Bisphosphate. The inositol ring has 2 phosphate group on C4 and C5. Important molecule for “cell signalling” as a second messenger
Describe sphingolipids
A complex group of lipids that all contain sphingosine
Describe sphingomyelin
A sphingolipid with stearic acid as an R group. A huge component of the brain that is affected in neurological Multiple Sclerosis
Describe the symmetry of the lipid membrane.
The lipid membrane is asymmetric with inner and outer leaflets having specific compositions and identities
What are glycoproteins?
Proteins with a carbohydrate attached to them. Often play a major role in cell-cell signalling. 90% of carbohydrates on cell surface are attached to proteins
What are the two major divisions of glycoproteins?
N-linked: connected to asparagine residues. O-linked connected to serine or threonine residue
Describe the structure of cholesterol.
Four rings with a non-polar hydrocarbon tail and a polar head group.
What percentage of a membrane can be composed of cholesterol?
Up to 50%
Why does cholesterol enter the membrane?
It provides stiffness by inserting between fatty acids of the membrane
What are the 4 types of membrane proteins?
(1) Integral (2) Transmembrane (3) Peripheral (4) Anchored
What is an anchored membrane protein?
Proteins held near the membrane by another molecule. Ex: GPI anchors on the extracellular surface
What are GPI anchors?
a glycolipid that can be attached to the C-terminus of a protein during posttranslational modification. It is composed of a phosphatidylinositol group linked through a carbohydrate-containing linker
What amino acid connects the prenyl group to the lipid chain?
Cysteine
What are the functions of transmembrane proteins?
Transporters, anchors, receptors, enzymes
What types of amino acid residues are found within the membranes?
Hydrophobic amino acids
What is a hydrophobicity plot?
A plot showing the hydrophobic regions of peptides that are likely to be transmembrane domains
What is FRAP?
Fluorescence Recovery After Photobleaching. A technique used to bleach fluorescently labeled lipids. This process is used to show that lateral movement of lipids occurs.
Do all membrane lipids move laterally?
NO. Some membrane lipids and proteins are “tethered” to the cytoskeleton and do not move laterally. Internal and external factors limit membrane protein movement
What are the different types of lipid movement in the membrane?
Rotation, lateral diffusion, and transverse movement (flip-flopping)
What are Lipid Rafts?
Regions in the membrane that are more ordered and tightly packed than the surrounding bilayer, but float freely as a unit within the membrane bilayer
What is caveolin?
a sub-type of lipid raft protein that causes “Little Caves” to form in the membrane. These proteins play specialized roles in signal transduction, endocytosis, and infection by bacteria and viruses.
What are the separate functions of the basal side and the apical side of epithelial cells?
The basal side is specialized for anchorage to the extracellular matrix. The apical side is the site of secretion and endocytosis
Why are red blood cells ideal for studying membranes?
They are easy to obtain, have no nuclei or organelles. They are also easy to empty and produce “ghosts” of lipids and membrane proteins only.
What are spectrins?
They are the largest and most prevalent proteins in the membranes of RBCs
What protein is Band 3 from the SDS PAGE of a red blood cell?
Anion Exchanger 1
What are the scaffolding proteins that give cells their shape?
Spectrin and Ankyrin
Describe the structure of the spectrin fibers within the RBCs?
Multiple spectrin fibers are joined to the peripheral protein ankyrin, which is non-covalenly bonded to the integral protein Band 3 (AE1). These connections form together into a “Buckyball” shape
What is Hereditary Spherocytosis?
A spectrin mutation that results in round red blood cells that get stuck in capillaries
What is SCA5?
Spinocereballar ataxia type 5: a neurodegenerative disease affecting a membrane proteins involved in glutamate signalling
What is Cardiac arrhythmia?
An abnormal hearbeat due to defective electrical signaling in the cardiac tissue
Why do red blood cells repel each other?
They are 60% glycosylated, giving the surface of RBCs a negative charge. This prevents agglutination
Describe diffusion
The process of solutes passively moving from areas of high concentration to areas of low concentration
What is semipermeable?
The membrane is semipermeable because small molecules like water, O2, CO2 and NO can pass through, but larger molecules are unable to cross without help
What happens to a cell in hypertonic medium?
A cell in a hypertonic medium will shrivel because water will move out of the cell to try to lower the extracellular solute concentration
What is facilitated diffusion?
Passive movement of particles that is 50,000x faster than diffusion due to assistance from a transporter protein
What is a symporter?
The transport of two different molecules in the same direction across a membrane. Uses the concentration gradient of one of the molecules to drive the movement of the other
Describe the Na+/K+ ATPase
A pump that hydrolyzes 1 ATP to move 3 sodiums out and 2 potassiums into the cell
Describe voltage-gated potassium channels
Six alpha helices form two regions: a voltage sensing domain and a pore domain. The voltage sensing domain has several + charged amino acids
How do voltage gated channels work?
When the membrane is depolarized, the S4 helix moves and the entire protein changes shape to an open position.
What is the Glycocalyx?
The “sugar coat” of carbohydrates that extend from the plasma membrane to surround most cells
What are the functions of the glycocalyx?
Support, Protection, Receptors, Signaling
What is the basement membrane?
A highly conserved tissue layer that epithelial cells are anchored to. It is made of Type IV collagens, lamnins, perlecan, and nidogens
What is the extracellular matrix?
The protein and carbohydrate environment NOT directly connected to the cell
How is ECM produced?
Cells synthesize these materials and export them
Describe the structure of most ECM proteins.
They are long, filamentous proteins that weave together to form a netweork
How do ECM proteins often interact with each other?
Through the process of self-assembly they can interact via binding domains for each other within each secondary structure
What are protein domains?
Independently folding portions of a polypeptide
What is the main function of collagen?
Tensile strength: resistance to being pulled apart
Where can each type of Collagen I through IV be found?
(I) Skin, tendon, vascular, BONE (II) Cartilage (III) with type I (IV): basement membranes
Which type of collagen is fibrillar? Which is network?
I through III are fibrillar. IV is network
What is procollagen?
The three alpha chains of collagen assembled into a triple helix in the lumen of the ER
What molecule cleaves procollagen to form collagen?
Procollagen peptidase removes both ends of the molecule to form collagen
What macro-structure does collagen spontaneously associate into?
The molecules form fibrils, which then associate with each other to form fibers
What is the common repeating amino acid sequence within collagen alpha chains?
Gly-Pro-X or Gly-X-Hyp (Hyp=hydroxyproline, a proline with an OH group)
Within the triple helix of collagen, which direction do the Gly H residues point?
They point toward the interior of the triple helix. The side chains of proline and hydroxyproline point out
How is the collagen triple helix stabilized?
By forming hydrogen bonds between the individual chains
What compound is responsible for the hydroxylation of proline and lysine in collagen?
Vitamin C converts Proline and Lysine via prolyl hydroxylase and lysyl hydroxylase, respectively
What happens in Scurvy?
Lack of vitamin C leads to weak tensile strength of collagen, which causes weak connective tissue
Describe the crosslinking of collagen molecules.
Covalent bonds can be formed when lysine residues are oxidized to form two aldehyde derivatives. These aldehydes are then dehydrated to from an aldol cross link
What happens to collagen fibers over time?
They begin to cross link to non-collagen ECM molecules. This is often a cause of the stiff joints of elderly individuals
What is the NC1 domain of collagen alpha?
Non-collagenous domain: a globular domain found at the end of collagen alpha strands
Describe the network that is formed by collagen IV
The 3 NC1 domains at the end of a collagen triple helix bind to the NC1 domains of other triple helices. At opposite end of the helix, 7S domains bind to each other to form a network of collagen IV
What occurs in osteogenesis imperfecta?
Collagen Type I: an amino acid other than glycine is substituted into the strand, preventing proper formation of the triple helix. This leads to malformed and brittle bones
What occurs in achondrogenesis and hypochondrogenesis?
Collagen Type II: An autosomal dominant mutation that causes bones to be short and underdeveloped. Most individuals die before or shortly after birth
What occurs in Ehlers-Danlos Syndrome?
Collagen Type III: Reduced amounts of Collagen III lead to hypermobile joints and stretchable skin
What are elastins?
Proteins that make up elastic fibers of the ECM and allow for stretchability and elasticity. They are rich in Gly and Pro residues and have crosslinkend Lys residues
What are laminins?
A network-froming basement membrane molecule that is a substrate for migrating cells
What is the function of entactin?
Entactin connects laminin and collagen in the ECM
What is Fibronectin (Fn)?
A secondary structure where binding domains are located for heparin, collagen, and other membrane molecules. RGD is the binding motif for the receptor integrin
What are integrins?
Transmembrane receptors that are dimers (alpha and beta) with extracellular heads that bind to ECM molecules. They are important signaling molecules
What are the conformations for active and inactive integrin?
The active form is upright and bound to collagen. The inactive form is bend down
How is integrin activated?
Binding of ligands IN THE CELL can result in activation of the extracellular region of the receptor.
What are the two major functions of integrins?
Adhesion to the ECM and Signal transduction to the cell nucleus
What is the role of Integrins in blood clotting?
Platelets have integrin dimers that bind to RGD sequences in proteins at the site of injury. Many drugs that treat strokes and heart attackes use RGD peptides to occupy the platelet integrins and prevent clotting at the site of injury.
Describe the process of forming a Focal Adhesion.
Cells first attach to the membrane. Then they flatten out on the surface to form focal adhesions, which are the mechanical linkages between the cell and the ECM
What are the internal molecules of a focal adhesion?
actin, talin and alpha-actinin, and kinases
Where is integrin linked on actin molecules?
Integrin is linked to the ends of the actin molecules
What are desmosomes?
Button-like points of strong adhesion between adjacent tissue. Found abundantly in the skin, heart and uterus
What does the desmosome core consist of?
Desmosomal cadherins, desmocollin, desmoglein
Describe the interaction between desmocollin and desmoglein
They interact heterophilically across the intercellular space. Linker proteins bind their cytosolic domains and link them to the intermediate filament cytoskeleton.
What is plakoglobin?
The β-catenin family protein that binds desmocollin and desmoplakin on the intracellular side of desmosomes
What does desmoplakin attach to on the intracellular side of a desmosome?
Desmoplakin attaches to tonofilaments such as vimentin, desmin and keratin proteins
What is pemphigus?
A mutation affecting desmosomes that causes skin blisters due to an autoimmune response to one’s own desmosomes
What are hemidesmosomes?
A basement membrane adhesion structure made of mostly keratin. Called “Plaques” because of their dark staining structure. Plectin is a marker for hemidesmosomes.
What are tight junctions?
The most apical cell-cell contacts that prevent molecules from passing between the two cells. Proteins involved in tight junctions are occludin and claudins
Explain the role that claudins play in selectivity.
Claudins are proteins involved in tight junctions. They form a tight seal between cells, but have a large extracellular loop that forms an ion-selective pore that can allow the passage of specific ions.
What are gap junctions?
A cell-cell connection that allows the passage of molecules and ionic currents from one cell to another. They are made of six connexin subunits that form a pore. Essential for coordinated contractions in the heart.
What is the annulus of a gap junction?
The more made up of six connexin units.
What proteins are involved in the complex that establishes and maintains epithelial cell polarity?
Par3/Par6/aPKC
What general role do junctions (adherins, septate or tight) play in epithelial cells?
They separate the apical from basolateral portions of the cell, thus determining cell polarity
Along with Cdc42 or Rac, where can the Par3/Par6/aPKC complex be found in epithelial cells?
The complex recruits proteins to the apical ends of epithelial cells
What are the 4 families of transmembrane proteins that mediate direct interactions between cells?
1) Selectins
2) Immunoglobins: IgSF
3) Integrins
4) Cadherins
What are the two general types of cell-cell interactions?
Homophilic: cells with identical receptors on their surfaces interact with one another (Ex: Cadherins and IgSF)
Heterophilic: cells with different receptors interact (ex: selectins and integrins)
What are lectins?
Any carbohydrate binding protein.
Lectins are highly specific for the sugar moiety that they bind.
What are selectins?
Transmembrane proteins that bind to glycoproteins or other cells resulting in adhesion of the cells to each other
A subclass of Lectins, and also a subclass of CAM
Where are L, P, and E selectins each found?
L-selectins: Leukocytes
P-selectins: Platelets
E-selectins: Endothelial cells (blood vessels)
What cofactor is required for selectin binding?
Calcium ion
Describe how a typical selectin interacts with a leukocyte in a blood vessel
Selctins on the endothelial cells “grab” leukocytes via low affinity binding to a glycoprotein which causes the leukocyte to roll along the vessel wall. The Leukocytes stop when a high affinity bond is formed between an integrin dimer on the leukocyte and a CAM on the vessel wall. The leukocyte can then pass through the vessel wall and begin the inflammatory response.
What is N-CAM?
Neural cell adhesion molecule. The first known member of the CAMs family
What is ICAM?
Intracellular adhesion molecule. Binds to integrin.
These molecules have well organized loops similar to those of the immunoglobulins in their extracellular domain
What are cadherins?
A family of transmembrane glycoproteins
They form cadherin dimers on different cells to bind the cells together.
Also play a role in signaling with catenin
What are the different types of cadherins and where are they found?
E-cadherins: epithelial tissue
N-cadherins: neural tissue
P-cadherins: placenta
What role do cadherins play in embryonic development?
In the epithelial to mesenchymal transition (EMT), cells must disconnect from the epithelia and migrate inward. In order for this to occur, cadherins are removed from the cell surface during migration. Once cells reach their destination, cadherins are inserted back into the membrane.
How are the catenins involved with cadherin function?
Catenins are intracellular molecules that link cadherins with actin filaments.
After certain environmental changes, beta-catenin can leave the adherens junction and translocate to the nucleus, where it will initiate a cascade that alters gene transcription.
What are the names of the 2 cadherins involved in desmosomes?
Desmoglein and Desmocollin
What intracellular structure does an adherens junction attach to?
Adherens junctions attach to actin filaments within the cell
What intracellular structure do desmosomes attach to?
Desmosomes attach to intermediate filaments within the cell
Which junction is stronger: Adherens or Desmosome?
Desmosomes are stronger than adherens junctions
What are hemidesmosomes?
Junctions found at the basal side of cells to anchor the cell to the basement membrane.
Binding occurs via integrins (NOT CADHERINS)
What are proteoglycans?
,Proteins to which linear carbohydrate groups attach to Serine hydroxyl groups
What is the signal to begin GAG synthesis on a protein?
-SG-
What is the tetrasaccharide linker?
In proteoglycans, the first four saccharide residues are always the same: Xyl-Gal-Gal-GlcA
What is a GAG?
Glycosaminoglycans (GAG) are a type of proteoglycans made up of repeating disacharide units that are a major component of the ECM
What is a common modification of GAGs?
All GAGs can have sulfate group added to them
What is Heparan Sulfate?
A linear proteoglycan composed of uronic acid and glucosamine
Describe the sulfation of GAG chains
The sulfation pattern determines the binding sites for other molecules
There are heavily sulfated islands along the GAG chains that serve as ligand binding sites
Ex: heparan sulfate binds to FGF
What is aggrecan?
A proteoglycan that plays a crucial role in the structure of cartilage. The hyaluronic acid core is a free standing GAG. Agrecan protein branch off of the HA core molecule. The Aggrecans are heavily sulfated in chondroitin sulfate and keratan sulfate GAGs
What is unique about the synthesis of Hyaluronan?
Hyaluronan synthase is a transmembrane enzyme that puts sugars together and immediately excretes them into the ECM
What are the precursors for all GAG chains?
Uridine di-phosphate sugars
What is a red blood cell exclusion assay?
A test that shows the ability of a cell to produce ECM. A chondrocyte surrounded by RBCs will synthesize ECM that will displace the RBCs.
What are matrix metalloproteinases (MMPs)?
A family of enzymes that degrade the ECM molecules. This process is important for: embryonic development, wound healing, and normal tissue remodeling
What are TIMPs?
Tissue Inhibitors of Metalloproteinases
Balance out the activity of MMPs. The ratio between the two can tip an organ towards disease or repair.
