cytoplasm & cytoplasmic organelles

what is the function of organelles?

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

what are inclusions?

- products of organelles
- have no active role in metabolism

what is the cytoplasmic matrix made up of?

soluble proteins and enzymes involved in glycolysis

what are the membranous organelles of the cell?

- Rough and smooth ER
- golgi apparatus
- lysosomes
- peroxisomes
- mitochondria

what are the non-membranous organelles of the cell?

- ribosomes
- microtubules
- actin filaments
- intermediate filaments
- centrioles
- basal bodies

what are the inclusions of the cell?

- secretory vesicles
- pigment granules
- neutral fat
- lipid droplets
- glycogen
- stored waste product

what do ribosomes look like under light microscope?

- not visible
- basophilic appearance (dark blue/purple) due to the phosphate groups in RNA

what do ribosomes look like under transmission electron microscope?

- visible
- appear electron dense because they absorb electrons

what are polyribosomes?

ribosomes clumped together with mRNA and attached to the ER

what produces ribosomes?

rough ER and nucleolus

what are ribosomes composed of?

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

where is RNA synthesized?

in the nucleus

where do synthesized proteins go?

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

how do subunits go to cytoplasm?

through nuclear pores

what is the function of ribosomes?

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

what is the rough endoplasmic reticulum?

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

where is the rough ER abundant?

in cells specialized with protein secretion (basophilic cells)

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

what is the smooth endoplasmic reticulum?

extension of the rough ER which forms networks if membranous tubules

what is the function of smooth endoplasmic reticulum?

transfer proteins to golgi

what is the smooth ER abundant?

- liver cells (detoxifying enzymes)
- muscle cells (break down glycogen)
- cells that produce glycogen, lipids or steroids

explain this picture

plasma cells which have a lot of rough ER

explain this picture

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

what is the golgi apparatus?

3 - 20 flattened polarized cisternae (membrane sacs)

which face of GA is mature?

the trans face which is concave

which face of GA is immature?

the cis face which is convex

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

in what direction do proteins travel through the GA?

from cis to trans

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

what are lysosomes?

- intracellular digestive organelles
- DOUBLE membrane
- surround hydrolytic enzymes formed in GA

what do lysosomes look like under EM?

- electron dense granules
- take on basophilic colour because lysosomal enzymes work under an acidic environment

what are the functions of lysosomes?

- autophagy (digestion of old organelles)
- autolysis (destruction of own cell)
- digesting materials taken by endocytosis

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

what is on the surface of lysosomal enzymes?

mannose-6-phosphate

what is a primary lysosome?

- pure lysosome freshly bud off of GA
- contains inactive digestive enzymes
- cannot undergo digestion
- can't eliminate content

what is a secondary lysosome?

- fusion of primary lysosome and endosome
- contains active digestive enzymes
- undergoes digestion
- can eliminate content

what are indigestible materials known as?

residual bodies

where do residual bodies accumulate?

- heart cells, muscle cells and neurons
- form intracellular pigments such as lipofuscin or age pigment

where are peroxisomes found?

liver

what are peroxisomes?

- single membrane-bound
- self-replicating
- formed in the ER
- associated with free ribosomes

function of peroxisomes

detoxification of H2O2 to produce water and oxygen

structure of mitochondria

- outer membrane (limits organelles)
- inner membrane (folded to form cristae)
- matrix

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

passive diffusion

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

active transport

what does the mitochondrial matrix consist of?

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

why is the mitochondria self-replicating?

the matrix contains DNA, RNA and ribosomes

what is the cytoskeleton?

dynamic 3D structure that fills the the cytoplasm

cytoskeleton function

important for movement and stability of the cell

what are the primary fibers of the cytoskeleton

- microfilaments
- microtubules
- intermediate filaments

what are microfilaments?

- fine filled protein fibers
- composed predominantly of f-actin (thin)
- contains myosin

what are microtubules?

- cylindrical hollow tubes
- composed of 13 subunits of tubulin arranged in a polarized ring
- subunits are termed alpha and beta

how do microtubules grow?

- via subunit polymerization
- grow from the +ve end
- under control of Ca2+ and MAP

how do microtubules help build other organelles?

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

what organelles do microtubules help build?

- cilia
- flagella
- centrioles (used in cell division)
- spindle fibers

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

what are intermediate filaments?

- provide tensile strength
- present in keratins (epithelium), desmin (muscle) and neurofilaments (neurons)

where are all 3 fibers found?

cytoskeleton of epithelial cells in the intestine

what are centrioles?

- rod organelles
- found in pairs
- 9 sets of 3 microtubules

what is this?

inclusions of glycogen in liver cells

what is this?

inclusions of secretory vesicles in pancreatic cells

how do lipid droplets look like under LM?

- do not stain
- extracted by organic solvents
- appear to by empty

how do lipid droplets look like under EM?

- stain electron dense by osmium tetroxide
- not delaminated by phospholipid monolayer