answers to Test Obj questions
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| What are the three main components of the plasma membrane? | Lipid, protein, and carbohydrates
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| Which is most predominant of the main components of the plasma membrane? | Lipids are most numerous but proteins comprise the largest portion by weight.
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| Why is the plasma membrane often referred to as a trilaminar sheet or lipid bilayer? | Using electron microscopy it appears as 3 layers, two outer black layers (the heads of the phospholipid molecules) and a clear (non-lipid) layer (tails of the lipid molecules) in between.
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| Name the 4 major phospholipids found in the plasma membrane. Name an additional phospholipid only found in the inner leaflet of the membrane? | Phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingomyelin and phosphatidylinositol. Phosphatidylinositol is only found in the inner leaflet.
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| What is a glycolipid and where are they found? | Phospholipids with a carbohydrate moiety attached to their head region. They are localized in only the external leaflet of the cell membrane
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| Which cell membranes contain no cholesterol as a form of lipid component? | Bacteria have no cholesterol in their cell membrane
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| What are the two main functions of the plasma membrane? | effectively separates 2 aqueous environments, hydrophobic fatty acid chains responsible for impermeable membrane to water-soluble molecules, phospholipids/proteins can diffuse laterally w/in membrane to perform critical functions, fluid mosaic model
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| What is a lipid raft? | Membrane regions enriched in cholesterol and sphingolipids, either devoid of structural protein/enriched in specific type, modifies composition/function
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| What are the various types of membrane proteins? | Peripheral and integral. Most integral membrane proteins are transmembrane in nature.
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| What is/are the functions(s) of peripheral and integral proteins? | Cell membrane proteins play an important role in cell metabolism, regulation and integration. They also function in providing receptor sites for many cell processes.
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| Which component of the cell may be attached to the membrane proteins? | Cytoskeletal elements – generally microfilaments like actin
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| What is the glycocalyx and what is its function? | The glycocalx is the surface carbohydrates (glycolipids and glycoproteins) that attach to the lipid or protein moeities of the outer layer of the cell memebrane. They function in cell adhesion, receptor sites as well as cell (‘self’) recognition.
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| How is the nuclear membrane configured? | two cell membranes (inner and outer enclose perinuclear space, think of an actual envelope
the nuclear membrane is often referred to as the nuclear envelope.
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| What dos the perinuclear space communicate with? | The lumen of adjacent cisternae of rough endoplasmic reticulum.
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| Describe the structure of a nuclear pore. | An outer octagonal ring, a central cyndical body and an inner octagonal ringh. The octagonal rings are comprised of consisting of eight nucleoporin (protein) particles
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| What is the function of nuclear pores? | To allow small molecules (40-60 kDa) to diffuse through the pore complex. Proteins of any size must contain a nuclear localization amino acid sequence to be imported into the nucleus by an energy-dependent mechanism
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| Name one thing that commonly passes through nuclear pores. | In particular the exit of ribosomal and messenger forms of RNA.
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| How does euchromatin differ from heterochromatin, structurally and functionally? | Euchromatin-dispersed chromosomal material that allows transcription
heterochromatin-clumped chromosomal material - most commonly attached to the inner aspect of the nuclear envelope which does not facilitate transcription
active nucleus exhibits mainly
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| What are the major functions of the nucleus? | It contains all the genomic information of the cell and controls all the cells activity - synthetic, metabolic, etc.
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| Name the various regions of the nucleolus. What does each represent? | fibillar center- chromatin containing repeated rRNA genes, presence of RNA polymerase I/signal recognition particle RNA
dense fibrillar component- nascent rRNA is present/undergoing processing; granular component of finish assembly of ribosomal subunits
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| What is the nucleonema? | An interconnected network of membrane-bound channels within the cytoplasm providing a separate membrane-bound compartment within the cell
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| What is a ribosome, What is its function and how is it accomplishesd? | A cell organelle responsible for protein synthesis which it accomplishes by reading cyoplasmic strands of messenger RNA and assembling the required amino acids.
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| Is the ribosome membrane-bound? | Not all ribosomes are membrane bound and the binding is only temporary during protein secretion into the rER lumen
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| What is a polyribosome? | Groups of ribsomes accumulated within the cytoplasm, generally linked by a strand of mRNA.
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| How do bound (attached) ribosomes differ from unbound (free)? | Attached ribosomes are bound to the outer surface of the membrane forming the rER cisterna. Unbound (free) ribosomes float freely within the cytoplasm.
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| What does each of these two types produce? | Bound (attached) ribosomes produce secretory or lysosomal proteins (those bound for extracellular relase of intracellular digestion) while unbound (free) ribosomes produce cytoplasmic proteins (those needed by the cell itself).
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| Why is the secretory type compartmentalized? Where is it compartmentalized? | Secretory proteins will eventually be released from the cell and lysosomal proteins are autolytic to the cell so must be membrane-bound to protect it from autodigestion. Both are compartmentalized within the lumen of the rER.
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| What is the structural configuration of rough ER? | It is found in stacks of flatted lamella (cisternae) that exhibit holes to allow cytoplasmic flow between layers as well as communication between the lumena of adjacent layers.
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| How does rought ER differ from that of smooth ER? | Smooth ER is a system of anatomosing tubular channels that lack ribsomes on the surface of the membranes.
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| In which cell types would rER predominate? sER? | Rough ER predominates in protein-secreting cells (ie. pancreatic acinar cells); smooth ER predominates in liver hepatocytes (detoxification and glycogen metabolism) and lipid hormone-secreting cells.
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| What is the structural configuration of the Golgi? | Flattened sacs (cisterane) of smooth membrane in a characteric “C” shape.
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| What is the function of Golfi? | The Golgi functions in post-translational modification, packaging and sorting of proteins secreted by the cell as well as in cell membrane recycling
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| What is the function of a lipid raft? | thought to function by serving as organizing centers for the assembly of signaling molecules, influencing membrane fluidity and membrane protein trafficking, and regulating receptor traffic
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| What are the components of a mitochondria? Cristae Intracristal space Intercristal Space Matrix granules Elementary particles | C: inner mitochondrial mem folds
IS: space w/in folds of inner mem that form cristae
IS: Space b/w cristae contains mitochondrial matrix, DNA, matrix granules
MG: stored calcium ions
EP: enzymes Krebs cycle found on matrix-side of inner mitochondrial
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| What are the two faces of the Golgi? | Forming/Cis: face closest to the rER
Maturing/Trans: AKA exit face or trans Golfi network
medial compartment (medial Golgi): B/w two compartments lies
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| What is the function of each Golgi face? | cis- receives transporting vesicles from rER. medial- site where most glycosylation occurs trans- where most of the condensing vacuoles exit the Golgi with material that is either mature or in its final maturative stages
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| What is a GERL (Golgi-ER-Lysosome)face? What does it produce? | hydrolytic enzymes destined for incorporation into lysosomes produced in rER pass directly (via transfer vesicles) to saccules of inner face of Golgi, lysosomal enzymes are subject to receptor-mediated sorting w/in trans-Golgi
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| What is the function of a lysosome | To digest materials found within, or brought into, a cell.
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| How does a primary lysosome differ from a secondary one? | A primary lysosome is a membrane-bound vesicle formed by the Golgi that contains hydrolytic enyzmes; a secondary lysosome is the result of fusion of a primary lysosome with a membrane-bound cytoplasmic vesicle (formation of a digestive vacuole).
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| What is a phagosome? | A phagosome is a membrane-bound vesicle within the cytyoplasm of a cell that contains some sort of particulate matter.
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| How are the acid hydrolases of lysosomes produced? | Through the conversion of ATP to ADP, hydrogen ions are cleaved and are moved into the membrane-bound lysosome to reduce the pH to 5.0 and maintain the potency of the acid hydrolases stored in the lysosome
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| Name the two types of phagosomes and state how they differ | A phagosome is a membrane-bound vesicle within the cytyoplsm of a cell that contains some sort of particulate matter.
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| What is a residual body? | The remaining portions of a phagosome that prove to be undigestible and are stored in membrane-bound residual bodies within the cytoplasm of the cell. These generally accumulate with age.
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| Explain endocytosis, phagocytosis. | E- attracts material to cell mem, buds off early endosome, fuses w/ 1 lysosome, forms a late endosome
P- cell membrane bound material is taken into cell, fuses with a 1 lysosome,forms digestive vacuole/2 lysosome
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| What are the clinical implications of lysosomes? | dangerous cytoplasmic organelles, mem must remain in tact or contents will cause autodigestion of the cell
Abnormal release of enyzyme contents can also cause clinical disease such as the complications involved in allergic reactions and/or arthritis.
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| How does a peroxisome differ from a lysosome? | mem-bound structures assembled from proteins synthesized on free ribosomes and then imported into peroxisomes. Proteins are targeted to the interior of the peroxisome by targeting amino acid signals. They are not cleaved after entrance into the peroxisome
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| What is the function of catalase? Why is it important? | Catalase regulates levels of hydrogen peroxide within cells as a result of oxidative reactions involving peroxisomes. Hydrogen peroxide is toxic to cells.
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| What is the function of mitochondrion? | Mitochondria function as the major energy provider of the cell. Also, intracellular resevoir for Ca ions
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| How do the two membranes that compose its shell differ? | The outer rmembrane is highly permeable and has less surface area than the inner. The inner membrane is thrown into folds (cristae) to increase its surface are and it is highly selective in its permeability.
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| What is a mitochondrial crista? | a fold of the inner mitochondrial membrane projecting into the mitochondrial matrix. It serves to increase surface area of the inner mitochondrial membrane
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| Where are the enzymes for the Kreb's cycle located? | The cristae contain adensosine triphosphate (ATP) synthase, proteins of the respiratory electron transfer chain, and transport proteins that regulate the flow of metabolites in and out of the mitochondrial matrix
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| How do cytoplasmic proteins destined for the mitochondria get there? | Enzyme proteins transported to the mitochondrial matrix must cross both outer and inner mitochondrial membranes and required targeting polypeptide signals and chaperones to enable proteins to reach the matrix via receptors on both membranes
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| What is an elementary particle? Name its subdivisions and where it is found. | site of the ATP synthase enzyme complex that synthesizes ATP from ADP and inorganic phosphate. It is composed of an F0 portion inserted into the inner mitochondrial membrane, and an F1 portion or headpiece that extends into the mitochondrial matrix.
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| What is the implication of mitochondrial RNA and DNA? | Mitochondrial DNA and RNA indicate they are semiautonomous organelles, capable of directing synthesis of their structural proteins while nuclear DNA directs synthesis of mitochondrial enzymes
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| Explain Autopagy. | endoplasmic reticulum encloses aged cell comp, form autophagosome, fuses w/ 1 lysosome
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