Cellular
Organelles
6.3 & 6.4
Organelles covered today
 Nucleus & nuclear envelope
 Ribosomes
 Endomembrane system
 Endoplasmic reticulum (ER)
 Golgi apparatus
 Lysosomes
 Vacuoles
Nucleus - Structure
 Contains the DNA packaged into genes on chromosomes
 Nuclear envelope is a double membrane that separates
nucleus from cytoplasm
 Pore complex lines each nuclear pore and regulates entry &
exit (RNA leaves through the pores)
 Nuclear lamina lines inner surface & help maintain shape
 Nuclear matrix is a framework of fibers extending
throughout the interior of the nucleus
Organization of DNA
 DNA is organized into discrete units called chromosomes
 Each chromosome is made up of chromatin (complex of
proteins and DNA)
 Chromatin is the uncoiled form of DNA
 Chromosomes is the coiled up form of DNA that takes
shape when the cell is about to divide
Chromosome Number
 Every human cell has 46 chromosomes that occur in pairs
called homologous pairs
 So we have 23 homologous pairs of chromosomes
 The exception is the sex cells or gametes (sperm & egg)
which have 23 chromosomes.
 This preserves chromosome number from one generation
to the next
Nucleolus
 Structure in the non-dividing nucleus – appears as a mass
of densely stained granules and fibers
 Ribosomal RNA (rRNA) is synthesized from instructions
contained in the DNA
 Proteins imported from the cytoplasm are assembled with
rRNA into large and small ribosomal subunits
 Small & large subunits exit nucleolus where they can
assemble proteins
Ribosomes
 Made of ribosomal RNA and proteins
 Main function: carry out protein synthesis
 Cells that make a large number of proteins have a high
percentage of ribosomes (example: pancreas)
 Two types of ribosomes – both contain large & small
subunits
 Free ribosomes – suspended in the cytoplasm and make
proteins that function within the cytoplasm
 Bound ribosomes – attached to the outside of the ER and
make proteins that are inserted into membranes or exported
from the cell.
Endomembrane system
 Functions in the cell:
 Synthesis of proteins
 Transport of proteins into membranes or out of the cell
 Metabolism and movement of lipids
 Detoxification of poisons
 System is connected through direct contact or by transfer
of vesicles
 Organelles of the Endomembrane system: nuclear
envelope, ER, Golgi, lysosomes, vacuoles, plasma
membrane
Endoplasmic Reticulum
 Extensive network of membranes that is continuous with
the nuclear envelope (surrounds it)
 Two sections of the ER
 Smooth ER – contains no ribosomes
 Rough ER – surface is covered with ribosomes
Smooth ER
 Functions of the Smooth ER:
 Synthesis of lipids (oils, phospholipids, steroids)
 Metabolism of carbohydrates
 Detoxification of drugs and poisons by adding hydroxyl
groups to make them more soluble and easier to flush from
the body
 How does this relate to addiction? More drugs & alcohol = more
smooth ER and enzymes to increase the rate of detoxification.
This increases tolerance to the drugs which means you need
more of it to achieve desired effect.
Rough ER
 Functions of Rough ER
 Transport of proteins out of the cell
 Ribosomes are attached that undergo protein synthesis
 Make proteins that will be secreted from the cell
 These proteins leave ER in a vesicle (little vehicle)
 Membrane factory for the cell
 It grows in place by adding membrane proteins and
phospholipids to its own membrane
Golgi
 Manufacturing, warehousing, sorting, and shipping center
for the cell
 Products of the ER are modified and stored and then sent
to their final destination
 Consists of flattened membranous sacs
 Vesicles are concentrated around the golgi bringing things
to it and away from it
Sides of the Golgi
 The golgi has two sides to it:
 Cis face – receiving department
 Side facing the ER
 Trans face – shipping department
 Side facing the plasma membrane
 Proteins come from the ER in transport vesicles and fuse to
the Cis face and are modified and leave in vesicles from the
trans face (alphabetical order C – T)
Lysosomes
 Sac of hydrolytic enzymes that an animal cell uses to digest
macromolecules
 Sacs are highly acidic and enzymes are designed to work best
there
 If a sac breaks open no damage is done because cytoplasmic pH
is neutral
 Made by the rough ER
 Intracellular digestion of nutrients & damaged organelles
 Disorders: Tay-Sachs – a lipid digesting lysosome is missing and
the brain becomes impaired by lipid buildup.
Vacuoles
 Compartments for storage
 Types:
 Food vacuoles
 Contractile vacuoles (water pumps)
 Central vacuoles (water storage in plants)
Central Vacuole
 Tonoplast surrounds the central vacuole
 Stores organic compounds
 Stores potassium & chloride (inorganic compounds)
 Disposal sites for harmful compounds
 Contain pigments that color the cells to help attract
pollinators
 Contain poisonous compounds to help protect against
herbivores
 Major role in the growth of plants
Review of the Endomembrane
System