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4-2 Notes
THE ENDOMEMBRANE SYSTEM
Membranes are interrelated directly through physical contact or indirectly through vesicles

Vesicles = Membrane-enclosed sacs that are pinched-off portions of membranes moving
from the site of one membrane to another.
Includes: Nuclear envelope, Endoplasmic reticulum, Golgi apparatus, Lysosomes, Vacuoles, and
Plasma membrane.
3) ENDOPLASMIC RETICULUM (ER) – extensive membranous network of tubules and
sacs (cisternae)

Two Types:
o Smooth ER

Participates in the synthesis of lipids, phospholipids and steroids

Detoxification drugs and poisons
o Rough ER

studded with ribosomes

continuous with outer membrane of the nuclear envelope

Make secretory proteins and membrane, often in the following process:
(“secreted”)
Ribosomes attached to rough ER make secretory proteins.
↓
Growing polypeptide is threaded through ER membrane into the lumen or cisternal space.
↓
Protein folded into its native conformation
↓
Functional/Carbohydrate Groups are added
↓
Protein departs in a transport vesicle pinched off from ER
4) GOLGI APPARATUS = Organelle made of stacked, flattened membranous sacs that
modifies, stores and packages products of the endoplasmic reticulum.

Vesicles may transport macromolecules between the Golgi and other cell structures

Modifies proteins by adding: carbohydrate/sugar or phosphate groups

Labels products for secretion.
5) LYSOSOMES = membrane-enclosed bag of hydrolytic enzymes that digest all major classes
of macromolecules (lipases, carbohydrases, proteases, and nucleases).

Functions
o Intracellular digestion

Ex. Phagocytosis = cellular process of ingestion.
o Recycle cell’s own organic material

Monomers are released
o Programmed cell death = Apoptosis
Ex. Fingers and toes are formed that way in human embryos
6) VACUOLE = membrane-enclosed sac that is larger than a vesicle

3 types:
o Food vacuole
o Contractile vacuole = vacuole that pumps water from the cell
o Central vacuole = Large vacuole found in most mature plant cells

enclosed by a membrane called tonoplast

Plays a role in plant growth by absorbing water and elongating the cell

Stores organic compounds, inorganic ions, dangerous metabolic byproducts, pigments, and unpalatable (yucky!) compounds
7) PEROXISOMES = contain specialized enzymes to breakdown peroxide

in nearly all eukaryotic cells

2 H2O2  2 H2O + O2
(bad)
(good)
MITOCHONDRIA AND CHLOROPLASTS ARE MAIN ENERGY TRANSFORMERS

Enclosed by double membranes

Are NOT part of endomembrane system

Contain ribosomes and their own DNA that programs a portion of their protein synthesis

Are Semi-autonomous organelles that grow and reproduce within the cell
8) MITOCHONDRIA = Organelles which are the sites of cellular respiration

Makes ATP and is found in nearly all eukaryotic cells

The more energy (ATP) needed = more mitochondria

Parts include:
o Smooth outer membrane
o Convoluted (wavy) inner membrane
o Intermembrane space
o Mitochondrial matrix

Contains enzymes that catalyze many metabolic steps of cellular
respiration (i.e. the Krebs Cycle)
9) CHLOROPLASTS = sites of photosynthesis

Parts include:
o Intermembrane space
o Thylakoids = Flattened membranous sacs inside the Chloroplast

Thylakoids form a 3rd membrane system

Thylakoid space = Space inside the thylakoid

Chlorophyll is found in the thylakoid membranes.
o Stroma = Viscous fluid outside the thylakoids
10) Cytoskeleton = A network of fibers throughout the cytoplasm that forms a dynamic
framework for support and movement and regulation

Gives mechanical support

Helps maintain its shape

Enables cell to change shape

Directs cellular “traffic” – like organelle movement

Transmits signals

3 types of fibers

Microtubules (largest)

Organized by the microtubule organizing center (MTOC)

Functions

Cellular support (reinforce cell shape)

Tracks for organelle movement

Separation of chromosomes during cell division

Forms centrosomes and centrioles
o Centriole = Pair of cylindrical structures located in the
centrosome of in animal cells
o Cilia and flagella = Locomotor organelles
Cilia
Flagella
Occur in large numbers
1 or a few per cell
Smaller
Longer
ULTRASTRUCTURE:

Are extensions of plasma membrane

Core is 9 doublets of microtubules arranged in a ring with 2 single
microtubules in the center (9 + 2 pattern).

Microfilaments (smallest ones)

Formed from actin linked into long chains and wound into a helix

Pinches an animal cell in two during cell division

Elongation and contraction of pseudopodia during amoeboid
movement

Cytoplasmic Streaming (cyclosis) = Flowing of the entire
cytoplasm around the space between the vacuole and plasma
membrane in a plant cell.

Intermediate Filaments (medium-sized)

Constructed from keratin subunits

Very strong
*Both Microfilaments and Intermediate Filaments bear tension  resist popping