Cell is the base of life. The Endomembrane system. A membranous system of interconnected tubules and cisternae Membranes of the endomembrane system vary in structure, composition, thickness and behavior The endomembrane system includes: Nuclear envelope Endoplasmatic reticulum
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A membranous system of interconnected tubules and cisternae
Membranes of the endomembrane system vary in structure, composition, thickness and behavior
The endomembrane system includes:
Plasma membrane (related to endomembrane)
Endoplasmatic reticulum (ER) – network within the cytoplasm – extensive membranous network of tubules and sacs (cisternae) which sequesters its internal lumen (cisternal space) from the cytosol.
Consist of smooth and rough ER.
Participates in the synthesis of lipids, phospholipids and steroids
Participates in carbohydrate metabolism
Detoxifies drugs and poisons
Stores calcium ion necessary for muscle contraction
Manufactures secretory proteins and membranes
Proteins to be secreted are synthesized by ribosomes attached to rough ER
Polypeptide chain is threaded through ER membrane into the lumen or cisternal space
Protein folds into its native conformation
Undergo modification: oligosaccharide are added to the proteins in order to make glycoprotein
Proteins departs in a transport vesicle pinched off from transitional ER adjacent to the rough ER site production
Glycoproteins – protein covalently bonded to carbohydrate
Oligosaccharide – small polymer of sugar units
Transport vesicle – membrane vesicle in transit from one part of the cell to another
Membrane proteins are produced by ribosomes.
Growing polypeptide anchors by hydrophobic regions into the ER membrane
Enzymes within the ER membrane synthesize phospholipids from raw materials in the cytosol
Newly expanded ER membrane can be transported as a vesicle to other parts of the cell
Golgi apparatus – organelle made of stacked, flattened membranous sacs (cisternae), that modifies, stores and routes products of the ER
Has a distinct polarity. Membranes of cisternae at opposite ends differ in thickness and composition.
Two poles are called the cis face (forming face) and the trans face (maturing face)
Cis face, which is closely associated with transitional ER, receives products by accepting transport vesicles from the ER.
Trans face pinches off vesicles from the Golgi and transports molecules to other sites
Golgi products in transit from one cisternae to the next, are carried in transport vesicles.
alters some membrane phospholipids
modifies the oligosaccharide portion of glycoproteins
target products for various parts of the cell
sorts products for secretionApparatus Golgi
Many polysaccharides including hyaluronic acid are Golgi products
The cell encloses food in a vacuole.
The food vacuole fuses with a lysosome, and
hydrolytic enzymes digest the food.
After hydrolysis, simple sugars, amino acids, and other monomers pass across the lysosomal membrane into the cytosol as nutrients for the cell.
Lysosomes recycle the molecular ingredients of organelles (autophagy).
The cell continually renews itself
Symptoms of inherited storage diseases result from impaired lysosomal function.
Lack of a specific lysosomal enzymes causes substrate accumulation which interferes with lysosomal metabolism and other cellular functions
Pompe’s disease – the missing enzyme is a carbohydrase that breaks down glycogen – glycogen accumulation damages the liver
Tay-Sachs disease – brain impairment by accumulation of lipids
Transformation of a tadpole into a frog
Disappearance of tissue between the hands fingers of human embryos
are done by digestion with lysosomes
Food vacuoles – vacuole formed by phagocytosis
Contractile vacuoles – pump water excess out of the cell (in protozoa)
Central vacuole enclosed by a membrane (tonoplast) exist in mature plants.
Membrane and secretory proteins produced by the ER flows in the form of transport vesicles to the Golgi.
Golgi pinches off vesicles:
Vesicles give rise to lysosomes and vacuoles and
fuse with and add to plasma membrane.
The membrane expends and releases secretory proteins
Enclosed by double membranes that are not part of endomembrane system (the membrane proteins are synthesized by free ribosomes)
Contain ribosomes and some DNA that programs a small portion of their own protein synthesis
Are semiautonomous organelles that grow and reproduce within the cell
Found in nearly all eukaryotes cells
Number of mitochondria depends on the cell’s metabolic activity
Are about 1 μm in diameter and 1-10 μm in length
Are dynamic structures that move, change their shape and divide
Mitochondria contain their own DNA (termed mDNA) and
are thought to represent bacteria-like organisms incorporated into eukaryotic cells over 700 million years ago (perhaps even as far back as 1.5 billion years ago).
They function as the sites of energy release (following glycolysis in the cytoplasm) and ATP formation (by chemiosmosis).
Smooth outer membrane is highly permeable to small solutes, but it blocks passage of proteins and other macromolecules
Convoluted inner membrane contains embedded enzymes that are involved in cellular respiration. It folds into a series of cristae, which are the surfaces on which ATP is generated.
Intermembrane space – a narrow region between the inner and outer mitochondrial membranes
Reflects the solute composition of the cytoplasm, because the outer membrane is permeable
Mitochondrial matrix – compartment enclosed by the inner membrane, contains enzymes that catalyze many metabolic steps of cellular respiration.
Some enzymes of respiration and ATP production are actually embedded in the inner membrane.
Plastids are also membrane-bound organelles that only occur in plants and photosynthetic eukaryotes.
They include amyloplasts, chromoplasts and chloroplasts.
Amyloplasts – colorless plastids that store starch in roots and tubers
Chromoplasts – plastids containing pigments other than chlorophyll; responsible for fruits and flowers color.
Chloroplasts – chlorophyll-containing plastids which are the sites of photosynthesis in eukaryotes.
Chloroplasts are found in eukaryotic algae, leaves and other green plant organs
Are lens-shaped and measure about 2-5m
Are dynamic structures that change shape, move and divide.
Intermembrane space – separates the two membranes
Inside the chloroplast is another membranous system – thylakoids – segregates the interior of the chloroplast into two compartments: thylakoid space and stroma.
Thylakoids function in the steps of photosynthesis that initially convert light energy to chemical energy
Collectively a stack of thylakoids are a granum [plural = grana]) floating in a fluid termed the stroma.
Photosynthetic reactions that use chemical energy to convert carbon dioxide to sugar occur in the stroma
Like mitochondria, chloroplasts have their own DNA, termed cpDNA.
Chloroplasts of Green Algae (Protista) and Plants (descendants of some Green Algae) are thought to have originated by endosymbiosis of a prokaryotic alga similar to living Prochloron (Prochlorobacteria).
Chloroplasts of Red Algae (Protista) are very similar biochemically to cyanobacteria (also known as blue-green bacteria.
Peroxisomes are roughly spherical and often have a granular or crystalline core that is probably a dense collection of enzymes. This peroxisome is in a leaf cell.
Notice its proximity to two chloroplasts and a mitochondrion.
These organelles cooperate with peroxisomes in certain metabolic functions (TEM).
Peroxisomes do not bud from the endomembrane system.
They grow by incorporating proteins and lipids made in the cytosol.
They increase in number by splitting in two when they reach a certain size.
Peroxisomes in liver detoxify alcohol by transferring H to O and producing H2O2
Peroxidase destroys toxic H2O2 by converting it to H2O
Peroxisomes convert fatty acids to smaller molecules that can be used by mitochondria in the process of cellular respiration.
In plant seeds glyoxysomes, special peroxisomes, convert fatty acids to sugar.
This provides growing seedlings with energy and carbon source.
The cytoplasm was defined earlier as the material between the plasma membrane (cell membrane) and the nuclear envelope.
Fibrous proteins that occur in the cytoplasm, referred to as the cytoskeleton maintain the shape of the cell.
Microtubules function in cell division and serve as a "temporary scaffolding" for other organelles.
Actin filaments are thin threads that function in cell division and cell motility.
Intermediate filaments are between the size of the microtubules and the actin filaments.
Ch. 6 pp. 108-111