Survey of Eukaryotic Cell Organelles
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- What are the general components of a eukaryotic cell?
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1.Plasma membrane
2.One or more nuclei
3.Cytoplasm
4.Organelles - What are the three mechanisms by which cells move materials?
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1.Active/Passive transport
2.Gated Transport
3.Vesicular Transport - How do small, uncharged molecules move inside the cell
- Simple diffusion across a concentration gradient
- How do small, water soluble molecules move inside the cell
- Active or facilitated transport
- What molecules can move across the cell membrane in special channels (i.e. membranes surrounding the RER)
- Proteins in the process of synthesis
- Give an example of gated transport
- Movement of molecules through nuclear pores into/out the nucleus
- How does vesicular transport occur?
- By uptake of vesicles by cells via endocytosis or phagocytosis
- How does selective transport of vesicles occur?
- By the budding of vesicles of one cell binding to another cell.
- When does this occur?
- Biosynthetic-secretory pathway and the endocytic pathway in cells
- What are the three types of vesicles involved with vesicular transport?
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1.Clathrin-coated
2.COP-II
3.COP-I - What do clathrin coated vesicles tend to be involved with?
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1.Movement into the cell to cytoplasm
2.Movement from the Golgi to the cell surface - What do COP-II vesicles tend to be involved with?
- 1.Movement from the ER to and through the Golgi
- What do COP-I vesicles tend to be involved with?
- 1. Retrieval of membranes and contents
- What is the plasma membrane and what is its function?
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A selective barrier that regulates the passage of materials into/out of the cell.
Also transmits signals - Cell membranes are (homogenous/non-homogenous)in nature
- non-homogenous
- What is a lipid raft?
- Molecules group as a microdomain (less fluid than the membrane)
- Enzymatically active areas of the membrane contain high amount of ________?
- proteins
- The fluid mosaic model of the cell membrane proposes that:
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1. Membrane consists of a phospholipid bi-layer (50% mass)
2. Membrane has 50% mass in proteins (integral, transmembrane, and peripheral proteins)
3. Oligosaccharide chains on the extracellular surface - The glycolipids and glycoproteins on the surface of the cell form the ______ with a (+,-) charge
- glycocalyx, negative
- How does the membrane act to regulate the intercellular env.
- By acting as a selective barrier via the actions of integral proteins
- What are the functions of integral proteins
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1.Transport
2.Cell receptors
3.Enzymes
4.Cell adhesion - Where are tight junctions (zonula occludens) located and what is their function?
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a.Located on the luminal border between adj. epithelial cells
b.Limits the movement of proteins & lipids to that cell only.
c. Allows cells to have different compositions/functions - How big is the nucleus?
- 6-10 um diameter
- How many layers does the nuclear membrane have?
- 2
- What are the functions of the nucleus?
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1.Protection, replication, synthesis, and expression of the genome.
2. Synthesis of large and small ribosomal subunits. - Where are the two unit membranes of the nucleus continuous with each other
- At nuclear pores
- What is the perinuclear cisterna?
- The space between the 2 nuclear membranes.
- What can the outer nuclear membrane be continuous with?
- the RER
- What are the function of nuclear pores
- 1.Act as gated channels
- What is the fibrous lamina?
- Layer of intermediate filaments just inside the inner nuclear membrane
- What is the fibrous lamina composed of?
- Lamins a,b,c
- What happens when they are phosphorylated?
- The nuclear envelope disassembles
- What is chromatin
- uncondensed genetic material (DNA, histones, non-histone protein)
- What is a nucleosome?
- DNA wrapped around packets of 4 specific proteins (histones)
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Heterochromatin is/is not capable of being expressed.
Euchromatin is/is not capable of being expressed. -
Heterochromatin: Not capable
Euchromatin: Capable - What is a chromosome
- 1. A darkly-stained, rod-like body of condensed chromatin.
- What is the basic unit of a chromosome?
- A nucleosome.
- What is the nucleolus
- A dense aggregate of protein and nucleic acid.
- What happens at the nucleolus
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1.Transcription of ribosomal DNA by RNA polymerase I
2. Synthesis of ribosomal subunits - What are the 3 components of the nucleolus?
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1. The nucleolar organizing DNA
2. Nucleolema pars fibrosa (densely packed RNP fibers)
3. Nucleolema pars granulosa(maturing ribosmes) - What are the number and size of nucleoli usually related to?
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1.# of ribosomes produced
2.Protein synthesis act. of cell - Where are polyribosomal proteins synthesized?
- In the cytosol (enter the nucleus and associate w/ribosomes in nucleolus)
- How does protein/polypeptide synthesis begin?
- When the small ribosomal subunit binds to the m/tRNA in the cytoplasm. Large subunit binds afterwards
- What are polyribosomes
- The appearance of multiple ribosomes translating the same mRNA
- Accumulations of ribosomes are _____?
- basophilic
- On what type of ribosomes are proteins destined for use in the cytosol translated?
- Free ribosomes
- Secreted, lysosome-used, and integral proteins are translated where?
- Bound to RER
- What is the structure of the RER?
- Series of membrane-limited flattening interconnected cisterna containing ribosomes on the cytoplasmic surface.
- What is the function of the RER?
- 1. Synthesis of proteins for secretion, use by other organelles, and integral membrane proteins.
- What 4 characteristics will cells specialized for protein secretion have?
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1. Abundant RER
2. Prominent golgi
3. Euchromatic nuclei
4. Dense membrane-bounded secretory products. - How are proteins modified in the RER?
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1.Signal seq. cleaved by sig. peptidases
2.Glycosylation of glycoproteins
3.Post-translational modification
4.Folded
5.Assembled w/other proteins - What are the functions of the Golgi?
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1. Major site of carb synthesis
2. Sorting station for material in the cell - How does the golgi modify proteins?
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1. glycosylation of proteins nad lipids
2. phosphorylation or sulfonation of glycoproteins - What is the structure of the golgi?
- - stack of 3-10 flattened membrane-bound cisternae with dilated rims
- Where is the golgi located
- near (often apical) to the nucleus
- What are the 3 regions of the golgi?
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Cis-golgi network (forming face)
Medial golgi cisterna
Trans golgi cisterna - What are the major digestive organelles of the cell
- Lysosomes
- What are the enzymes that catalyze degradative functions called in lysosomes?
- hydrolases
- What is the structure of a lysosome?
- Single-unit membrane with a number of morphologic appearances.
- How is a low pH maintained in a lysosome?
- By membrane-bound ATP-driven pump (Exchanges NA+ for H+)
- How are materials digested by lysosomes?
- endo/pinocytosis, receptor-mediated endocytosis, phagocytosis, or autophagy
- What are proteasomes?
- multi-hydolase compounds that digest single cytoplasmic proteins
- Accumulations of SER are baso, eosinophilic?
- eosinophilic due to protein content of membranes
- What are the functions of the SER?
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1.Synth. of steroid hormones
2.Detox of lipid-sol. drugs
3.Convert water-insol drugs to more water-sol. drugs
4.Synth. of lipids for lipoproteins for cell membrane
5.Synth. of phopholipids for cell membrane
6.Glycogen metabolism
7.Ca++ ion sequestration - What are the functions of peroxisomes
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1.Degrade toxic molecules, part. in the liver and kidney
2.Beta oxidation of long-chain FA's
3.Can be involved in purine metabolism - How do oxidases work?
- By removing hydrogen
- What is the byproduct?
- Hydrogen peroxide
- What does catalase do?
- converts hydrogen peroxide to water and oxygen
- What is Zellweger syndrome?
- Defects in the transport enzymes that move peroxisomal enzymes into the membrane.
- Mitochondria are present in all cells except _____
- RBC's
- What is the s(x) of mitochondria?
- Two unit membranes that form the intermembrane space and matrix compartment
- What are the tubular cristae
- The projections of the inner mitochondrial membrane.
- Where is most of the mitochondrial protein made?
- In the nucleus (nuclear DNA) and made on cytoplasmic ribosomes.
- What are the functions of the mitochondria?
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1.Conv. of pyruvate to Acetyl-CoA
2.ATP formation
3.Ca++ sequestering
4.lipid metabolism
5.processing of intermediates in steroid synthesis - What are the 3 components of the cytoskeleton?
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1.Microtubules
2.Microfilaments
3.Intermediate Filaments - What are microtubules?
- Unbranched tubular structures composed of the protein tubulin.
- What do microtubules do?
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1.Support the force-generating actions of cilia and flagella
2.Form the mitotic and meiotic apparatus/spindle - What do the drugs colchicine, vinblastine, vincristine do and what are they used for?
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Break down microtubules; used for cancer treatment
Taxol: microtubule stabilizing - What are microfilaments composed of?
- Actin
- What are the functions of microfilaments?
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1.Motility of cytoplasmic comp's
2.form a support network under the plama membrane - What is the "molecular motor" that moves actin?
- myosin
- What are the functions of intermediate filaments?
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1.Provide tensile strength
2.Insert into desmosomes and hemidesmosomes. - What are the three types of cell junctions?
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1.Occluding Junctions
2.Anchoring junctions
3.Communicating junctions - What is the function of occluding junctions?
- To regulate the flow of material from the lumen/surface of an epithelium to the lateral intercellular space between the epithelial cells
- What do anchoring junctions do?
- provide adhesion between cells
- Where are zonula adherens located?
- at the junctional complexes in epithelial cells
- What is the zonula adherens molecule composed of?
- E-cadherin: transmembrane adhesion molecule
- What is the adhesion of zonula adherens dependent on?
- Ca++ presence
- What is the fascia adherens located?
- cardiac muscle cells
- What is another name for a macula adherens?
- desmosome
- On what side of the macula adherins is an attachment plaque through which intermediate fibers run?
- cytoplasmic side
- Between the cells of a macula adhesions, what are the extracellular parts of the transmembrane glycoproteins a part of?
- Ca++ dependent cadherin cell adhesion molecules
- What does a hemidesmosome do?
- provide adhesion btw. a cell and the basement membrane. (think thick skin)
- how are communicating junctions connected?
- by transmembrane channels or small pores
- what do connexons do
- allow diffusion of small molecules btw. cells
- how much electrical resistance is there btw. cells at gap junctions
- little
- What is the structure of connexons
- 6 integral membrane proteins in a circular arrangement
- Where do gap junctions occur
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1.Epithelials
2.Cardiac muscle
3.Bone cells
4.Smooth muscle
5.Nerve cells