Organization of Cells: Part II
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What is included in the endomemembrane system?
- Nuclear Envelope
- Endoplasmic Reticulum
- Golgi Apparatus
- Various Vesicles and Vacuoles
- Plasma Membrane
What tasks does the endomembrane system carry out?
- Synthesis of Proteins
- Transport of proteins into membrane and organelles or out of the cell
- Metabolism and movement of lipids
- Detoxification of poisions
How are the membranes in the endomembrane system related?
They are related through physical continuity or by the transfer of membrane segments as tiny vesicles.
Which organlle acounts for more than half the total membrane in a Eukaryotic cell?
The Endoplasmic Reticulum (ER)
What does endoplasmic and reticulum mean?
- Endoplasmic-"Within the cytoplasm"
- Reticulum-"Little Net"
The ER consists of a network of membranous tubules and sacs called _______.
What is the internal compartment of the ER called?
The ER lumen (cavity) or cisternal space.
What separates the ER lumen from the cytosol?
The ER Membrane.
Where does Smooth ER get its name?
Because it lacks ribosomes.
Where does rough ER get its name?
Because it is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope.
What are the functions of the smooth ER?
- Synthesis of Lipids
- Metabolism of Carbohydrates
- Detoxification of drugs and poisons
- Storage of calcium ions
What steroids are produced by the smooth ER?
Sex hormones of Vertebrates and the various steroid hormones secreted by the adrenal gland.
Where would there be cells rich in smooth ER?
How does the smooth ER "Detoxify"?
By adding a hydroxyl group to drug molecules, making them more soluble and easier to flush from the body.
How does the smooth ER contract muscle cells?
Because it stores calcium ions. The smooth ER pumps calcium ions from the cytosol into the ER lumen, when a muscle cell is stimulated, the calcium ions rush back across the ER membrane into the cytosol and trigger contraction of the muscle cells.
What cells would be rich in rough ER?
Explain a function of the ribosomes in the rough ER that benefit pancreatic cells.
Pancreatic cells synthesize the protein insulun in the ER and secrete this hormone in the bloodstream.
Most secretory proteins are _________.
What is a glycoprotein?
A protein that has a carbohydrate covalently bonded to them.
Vesicles in transit from one part of the cell to another are called ________ ________.
How does the rough ER grow in place?
It adds membrane proteins and phospholipids to its own membrane.
What are the functions of the Rough ER?
- Making secretory proteins
- A membrane factory
What happens in the Golgi Apparatus?
Products of the ER are modified, and stored, and then sent to other destinations.
What does the Golgi Apparatus consist of?
Flattened membranous sacs-cisternae-looking like a stack of pita bread.
What are the two sides of a Golgi Stack referred to as?
As the cis and trans face.
Where is the cis face located?
Near the ER. Transport vesicles move material from the ER to the Golgi Aparatus.
What does the trans face do?
It gives rise to vesicles that pinch off and travel to other sites.
What is the Golgi Apparatus specialized for?
When are products of the endoplasmic reticulum modified in the Golgi Apparatus?
During their transit from the cis region to the trans region.
What happens to glycoproteins as they pass through the Golgi Apparatus?
They have their carbohydrates modified, first in the ER, then as they pass through to Golgi.
What besides glycoproteins are altered in the Golgi ?
The Golgi Apparatus manufacture _______.
- Example: Pectins and certain noncelluouse polysaccharides are made in the Glogi and then incorporated along with cellulous into their cell walls.
According to the Cisternal Maturaion model, how does a Golgi work?
The cisternae of the Golgi actually progresses forward from the cis to the trans face, carrying and modifying their cargo as they go.
How does the Golgi differentiate what goes where?
Molecular identification tags, such as phosphate groups added to the products sort them like mailing labels. Transport vesicles may recognize "docking sites" on the surface of specific organelles or on the plasma membrane.
What is a Lysosome?
A membranous sac of hydrolytic enzymes that an animal cell uses to digest macromolecules.
Explain the contents of the Lysosome.
The inside is an extremely acidic enviorment, and if it were to break open the enxymes may not be very active because the cytosol has a neutral pH.
How are Hydrolytic enymes and lysosomal membrame made?
They are made by the rough ER and then transferred to the Golgi for further processing.
What is phagocytosis?
How is the food vacuole formed?
It is formed by phagocytosis, and then it fuses with a lysosome, whose enzymes digest the food.
What is a macrophages?
A type of white blood cell that helps defend the body by engulfing and destroying bacteria and other invaders.
What is autophagy?
- A process where lysosomes use their hydroltic enzymes to recycle the cell's own organic material.
- A damaged organelle or small amound of cytosol becomes surrounded by a double membrane and a lysosome fuses with the outer membrane of the vesicle. The lysosomal enzymes dismantle the enclosed material, and the organic monomers are returned to the cytosol for reuse.
A human liver cell, recycles ____ of it's macromolecules each week.
Explain Tay-Sach's disease.
A lipid-digesting enzyme is missing or inactive and the brain becomes impaired by an accumulation of lipids in the cells.
Where do Vaculoes come form?
- They are derived from the ER and Golgi.
- Thus Vaculoes are an integral part fo the cell's endomembrane system.
What do Contractile vacuoles do?
They pump excess water out of the cell, therby maintaining a suitable concentration of ions and molecules inside the cell.
T or F: In plants and fungi, certain vacuoles carry out enzymatic hydrolosis, a function shared by lysosomes in animal cells.
How can vacuoles help protect the plant against herbivores?
By storing compounds that are poisonous or unplatable to animals.
How can vaculoes help pollinate flowers?
Some vacuoles contain pigments , such as red and blue, that help attrat pollinating insect to flowers.
What is the role of the central vacuole?
It develops by the coalesence of smaller vacuoles. The solution inside is called the cell sap. It is the plant's main repository of inorganic ions, including potassim and chloride.
T or F: The ratio of plasa membrane surface to cytosolic volume is sufficent, even for a large plant.
What metabolic process if a mitochondrion the site for?
Cellular respiration: A metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels.
What process is a chloroplast the site for?
Photosynthesis: They convert solar energy to chemical eergy by absorbing sunlight an suing it to drive the synthesis or organic compuonds such as surgars from carbon dioxide to water.
What is a peroxisome?
An oxidative organelle.
Explain the endosymbiotic theory.
- A Eukaryotic cell engulfed an oxygen-using nonphotosynthetic prokaryotic cell. They became endosymbiont.
- At least one of these cells must have taken up a photosynthetic prokaryote, becoming the ancestor of the eukarotic cells that contian chloroplasts.
Evidence that supports the endosymbiotic theory.
- Mitochondria and typical chloroplasts have two membranes surrounding them.
- Mitochondira and Chloroplasts contain ribosomes, as well as circular DNA molecules attached to their inner membranes. (This DNA programs the synthesis of some of thei own proteins, which are made on the ribosomes inside organelles.
- Mitochondira and Chloroplasts are autonomous organlles that grow and reproduce within the cell.
Mitochondira: The outer membrane is smooth, but the inner membrane is convoluted, with infoldings called ______.
What does the Mitochondiral matrix contain?
It includes many different enzymes, as well as the mitochondrial DNA and ribosomes.
Mitochondira are generally in the range of _-__ um long.
Chloroplasts are ______ shaped, and are about _-_ um in length.
Lense shaped, and are about 3-6.
What is a thylakoid?
Flattened, interconnected sacs in chloroplasts.
The ______ are made of stacks of _______, and the fluid outside the thylakoid is the _____.
Ganum, thylakoid, stroma.
Where is the chloroplasts DNA located?
In the stroma.
How does a Peroxisome work?
They contain enzymes that remove hydrogen atoms from various subsrates and transfer them to oxygen, thus produing hydrogen peroxide.
Explain a peroxisome in a liver cell.
Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen.
What is a glyoxysome?
They are found in fat-storing tissues of plant seeds. These organlles contain enzymes that initiate the conversion of fatty acids to sugar, which the emerging seedling uses as a source of energy and carbon until it can produce it's own.
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