cytoplasm & cytoplasmic organelles

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what is the function of organelles?

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what is the function of organelles?

preform metabolic and synthetic, energy requiring and generating, functions in a cell

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what are inclusions?

  • products of organelles

  • have no active role in metabolism

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what is the cytoplasmic matrix made up of?

soluble proteins and enzymes involved in glycolysis

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what are the membranous organelles of the cell?

  • Rough and smooth ER

  • golgi apparatus

  • lysosomes

  • peroxisomes

  • mitochondria

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what are the non-membranous organelles of the cell?

  • ribosomes

  • microtubules

  • actin filaments

  • intermediate filaments

  • centrioles

  • basal bodies

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what are the inclusions of the cell?

  • secretory vesicles

  • pigment granules

  • neutral fat

  • lipid droplets

  • glycogen

  • stored waste product

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what do ribosomes look like under light microscope?

  • not visible

  • basophilic appearance (dark blue/purple) due to the phosphate groups in RNA

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what do ribosomes look like under transmission electron microscope?

  • visible

  • appear electron dense because they absorb electrons

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what are polyribosomes?

ribosomes clumped together with mRNA and attached to the ER

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what produces ribosomes?

rough ER and nucleolus

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what are ribosomes composed of?

  • 2 subunits with 4 types of rRNA in the nucleus and 80 proteins in the cytoplasm

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where is RNA synthesized?

in the nucleus

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where do synthesized proteins go?

proteins go from the place of synthesis, cytoplasm, to the nucleus to be attached to rRNA

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how do subunits go to cytoplasm?

through nuclear pores

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what is the function of ribosomes?

they are the site where amino acid molecules are incorporated into protein molecules

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what is the rough endoplasmic reticulum?

a network of channels formed by continuous membranes extending to nuclear envelope

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where is the rough ER abundant?

in cells specialized with protein secretion (basophilic cells)

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explain this picture

  • proteins are made by the ribosomes on the surface of ER

  • they are then transported into the interior to be modified

  • proteins accumulate in vesicles

  • vesicles bud off the surface of ER and are transported to GA

<ul><li><p>proteins are made by the ribosomes on the surface of ER</p></li><li><p>they are then transported into the interior to be modified</p></li><li><p>proteins accumulate in vesicles</p></li><li><p>vesicles bud off the surface of ER and are transported to GA</p></li></ul>
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what is the smooth endoplasmic reticulum?

extension of the rough ER which forms networks if membranous tubules

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what is the function of smooth endoplasmic reticulum?

transfer proteins to golgi

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what is the smooth ER abundant?

  • liver cells (detoxifying enzymes)

  • muscle cells (break down glycogen)

  • cells that produce glycogen, lipids or steroids

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explain this picture

plasma cells which have a lot of rough ER

<p>plasma cells which have a lot of rough ER</p>
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explain this picture

leydig cells found in the reproductive system and have a lot of smooth ER

<p>leydig cells found in the reproductive system and have a lot of smooth ER</p>
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what is the golgi apparatus?

3 - 20 flattened polarized cisternae (membrane sacs)

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which face of GA is mature?

the trans face which is concave

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which face of GA is immature?

the cis face which is convex

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label the picture

1- vesicles that have bud off 2- trans golgi 3- mid golgi 4- cis golgi 5- smooth ER 6- rough ER 7- nucleus

<p>1- vesicles that have bud off 2- trans golgi 3- mid golgi 4- cis golgi 5- smooth ER 6- rough ER 7- nucleus</p>
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in what direction do proteins travel through the GA?

from cis to trans

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functions of GA

  • modify proteins by cutting or adding

  • removal of amino acids

  • glycosylation, sulfating and phosphorylations

  • packing vesicles

  • sorting and distributing proteins

  • repair cell membrane

  • formation of lysosomes

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what are lysosomes?

  • intracellular digestive organelles

  • DOUBLE membrane

  • surround hydrolytic enzymes formed in GA

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what do lysosomes look like under EM?

  • electron dense granules

  • take on basophilic colour because lysosomal enzymes work under an acidic environment

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what are the functions of lysosomes?

  • autophagy (digestion of old organelles)

  • autolysis (destruction of own cell)

  • digesting materials taken by endocytosis

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explain this picture

  • lysosomal enzymes are secreted in the rough ER and transported to golgi

  • in the golgi these enzymes are modified (attaching mannose-6-phosphate) and packaged

  • lysosome is then formed in the golgi and contains all the hydrolytic enzymes

  • a primary lysosome is released

<ul><li><p>lysosomal enzymes are secreted in the rough ER and transported to golgi</p></li><li><p>in the golgi these enzymes are modified (attaching mannose-6-phosphate) and packaged</p></li><li><p>lysosome is then formed in the golgi and contains all the hydrolytic enzymes</p></li><li><p>a primary lysosome is released</p></li></ul>
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what is on the surface of lysosomal enzymes?

mannose-6-phosphate

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what is a primary lysosome?

  • pure lysosome freshly bud off of GA

  • contains inactive digestive enzymes

  • cannot undergo digestion

  • can't eliminate content

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what is a secondary lysosome?

  • fusion of primary lysosome and endosome

  • contains active digestive enzymes

  • undergoes digestion

  • can eliminate content

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what are indigestible materials known as?

residual bodies

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where do residual bodies accumulate?

  • heart cells, muscle cells and neurons

  • form intracellular pigments such as lipofuscin or age pigment

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where are peroxisomes found?

liver

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what are peroxisomes?

  • single membrane-bound

  • self-replicating

  • formed in the ER

  • associated with free ribosomes

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function of peroxisomes

detoxification of H2O2 to produce water and oxygen

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structure of mitochondria

  • outer membrane (limits organelles)

  • inner membrane (folded to form cristae)

  • matrix

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how does the outer membrane prevent diffusion of contents of the mitochondrial matrix?

passive diffusion

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how does the inner membrane prevent diffusion of contents of the mitochondrial matrix?

active transport

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what does the mitochondrial matrix consist of?

electron dense granules which represent the binding sites of calcium ions and krebs cycle enzymes

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why is the mitochondria self-replicating?

the matrix contains DNA, RNA and ribosomes

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what is the cytoskeleton?

dynamic 3D structure that fills the the cytoplasm

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cytoskeleton function

important for movement and stability of the cell

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what are the primary fibers of the cytoskeleton

  • microfilaments

  • microtubules

  • intermediate filaments

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what are microfilaments?

  • fine filled protein fibers

  • composed predominantly of f-actin (thin)

  • contains myosin

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what are microtubules?

  • cylindrical hollow tubes

  • composed of 13 subunits of tubulin arranged in a polarized ring

  • subunits are termed alpha and beta

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how do microtubules grow?

  • via subunit polymerization

  • grow from the +ve end

  • under control of Ca2+ and MAP

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how do microtubules help build other organelles?

they act as scaffolding by providing tracks for them to move on

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what organelles do microtubules help build?

  • cilia

  • flagella

  • centrioles (used in cell division)

  • spindle fibers

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transport by microtubules

  • motor proteins like kinesin move along microtubules

  • powered by ATP

  • transports cellular cargo

  • transport is from the center of the cell to the periphery

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what are intermediate filaments?

  • provide tensile strength

  • present in keratins (epithelium), desmin (muscle) and neurofilaments (neurons)

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where are all 3 fibers found?

cytoskeleton of epithelial cells in the intestine

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what are centrioles?

  • rod organelles

  • found in pairs

  • 9 sets of 3 microtubules

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what is this?

inclusions of glycogen in liver cells

<p>inclusions of glycogen in liver cells</p>
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what is this?

inclusions of secretory vesicles in pancreatic cells

<p>inclusions of secretory vesicles in pancreatic cells</p>
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how do lipid droplets look like under LM?

  • do not stain

  • extracted by organic solvents

  • appear to by empty

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how do lipid droplets look like under EM?

  • stain electron dense by osmium tetroxide

  • not delaminated by phospholipid monolayer

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