Chapter 7: Inside the cell
The cell is the basic unit of structure and function in living organisms.
There are two fundamental cell types: prokaryotic cells and eukaryotic cells.
Prokaryotic Cells- Fig. 7.1 A Prokaryotic Cell
Archaea and bacteria
Most prokaryotic cells are relatively small in size compared to eukaryotic cells
The size of prokaryotic cells is probably limited by the distance that molecules
must diffuse or be transported inside the cell.
Are structurally simpler in design
Plasma membrane surrounds the cytoplasm, which collectively refers to the
contents of the cell.
Have few or no subdivisions delimited by internal membranes
Interestingly, recent research has identified membrane bound organelles or
cytoskeletons of protein filaments in a few prokaryotic species.
No membrane bound nucleus
Ribosomes involved in protein synthesis
Eukaryotic Cells- Fig. 7.6 Animal and Plant Cells
Fungi, Protists, Plants and Animals
Are relatively larger in size compared to prokaryotic cells
The evolution of large cell size is thought to have made it possible for eukaryotic
cells to act as predators; organisms that kill and consume organisms.
Ions and small molecules such as ATP, amino acids and nucleotides cannot
diffuse across a large volume quickly.
MTOC- Microtubule organization centre
Fig. 7.7 The Nucleus is the Eukaryotic Cell’s Information Storage and Retrieval
The genetic or hereditary information is encoded in DNA, which is a component
of the chromosomes inside the nucleus.
Is surrounded by a nuclear envelope (a double membrane)
Contains chromosomes (chromatin: DNA and histone proteins), which carry the
cell’s genetic information.
Contains the nucleolus, which is the side of rRNA synthesis and ribosome
assembly. Fig. 7.8 Ribosomes are the Site of Protein Synthesis
Eukaryotic ribosomes are similar in structure to bacterial and achaeal ribosomes,
though not identical. They are composed of large and small subunits, each of which
contains both RNA molecules and proteins.
Some are present in the cytosol (fluid component of the cell’s cytoplasm)
Eukaryotic ribosomes are composed of RNA and protein
Consists of small and large subunits
Are involved in protein synthesis
Some are located outside the cell
Fig. 7.9 Rough ER is a Protein Synthesis and Processing Complex
Rough ER is a system of membrane-bound sacs and tubules with ribosomes
attached. It is continuous with the nuclear envelope.
Rough Endoplasmic Reticulum (rough ER)
Consists of a network of membrane- bound tubules and sacs
Has ribosomes studded into the cytoplasmic surface of the membranes, where
secreted and transmembrane proteins are manufactured.
Enzymes, which fold and modify proteins, are present inside the rough ER’s
The interior of the rough ER is called the lumen. Inside the lumen, proteins
undergo folding and other types of processing.
Hundreds of thousands of ribosomes are attached to the rough ER
The ribosomes associated with the rough ER are responsible for proteins
synthesis that will be inserted into the plasma membrane, secreted to the cell
exterior or shipped to an organelle called the lysosome.
Fig. 7.10 The Golgi Apparatus Is a Site of Protein Processing, Sorting and Shipping
The Golgi Apparatus is a collection of flattened vesicles called cisternae.
Consists of cisternae (flattened, stacked sacs)
The cis face receives products from the rough ER; which pass through before
reaching their final destination (through vesicles). Example: insulin
The trans face sends products to their destination (to the vesicles which then
sends them outside the cell).
Allows for processing of things
Close to rough ER, smooth ER is farther away Fig. 7.11 Smooth ER is a Lipid- Handling Centre and a Storage Facility
Smooth ER is a system of membrane-bound sacs and tubules that lacks
Smooth Endoplasmic Reticulum
Lacks ribosomes on the cytoplasmic surface of the membranes
Enzymes are present, which are involved in several functions such as lipid
synthesis, detoxification of harmful materials and calcium ion reserves
(development of bone).
TEM photos of SER versus GA
Fig. 7.12 Peroxisomes are the Site of Fatty Acid Processing
Peroxisomes are globular organelles with a single membrane. There is a high
level of peroxisomes within the liver.
Are single-membrane bound organelles (mitochondria= double membrane).
Locations of oxidative reactions
Contain catalase, which is an enzyme that converts hydrogen peroxide into
oxygen and water.
Fig. 7.13 Lysosomes are Recycling Centres
Lysosomes are usually oval or globular and have a single membrane.
Are single-membrane bound organelles
Participate in solid waste processing and the storage of materials
Have an acidic interior
Possess digestive enzymes (acidic hydrolases) to breakdown macromolecules
Digest dead/ exhausted organelles (example: mitochondria)
Recycle and reuse components of organelles
Fig. 7.14 Two ways to Deliver Materials to Lysosomes
Materials can be transported to lysosomes after phagocytosis or via autophagy.
a) Phagocytosis- the plasma membrane detects a smaller cell or food particle and
begins to engulf it and becomes a phagosome. It is delivered to a lysosome,
which takes it in and begins digesting it. Small molecules from the digested food
particles are released into the cytosol.
b) Autophagy- a damaged organelle is surrounded by a membrane, the membrane-
bound organelle is delivered to the lysosome which begins to engulf it. Small
molecules from the digested organelle are recycled into the cytosol. Arthritis- leaky lysosomes are breaking down lubricating organelles (can’t tell the
difference between functioning cells and phagocytes.
Fig. 7.15 Receptor- Mediated Endocytosis May Lead to Lysosome Formation
Endosomes created by receptor-mediated endocytosis may mature into
Macromolecules outside the cell bind to the membrane proteins that act as
The plasma membrane folds in and pinches off to form a vesicle called an early
The early endosome undergoes a series of processing steps including activation
of proton pumps that lower its pH.
The early endosome matures into a late endosome that receives digestive
enzymes from the Golgi apparatus.
The late endosome eventually matures into a functional lysosome.
Fig. 7.16 Vacuoles are Storage Centres
Vacuoles are variable in size and function, depending on the type of plant. Some
contain digestive enzymes and serve as recycling centres; most are large storage
Not in animal cells; no need for chlorophyll or defense against herbivores.
Found in fungi and plants
Occupy a large portion inside the cell
Serves as storage depots for water, ions and proteins
In plant cells, vacuoles may contain pigments or may house noxious substances
for chemical defense against herbivores.
Fig. 7.17 Mitochondria are Power-Generating Stations
Mitochondria are variable in size and shape, but all have a double membrane
with sac-like cristae inside.
Sites of ATP production
Possesses two membranes (the inner membrane has folds or cristae, the outer
membrane is smooth).
Possess their own mitochondrial DNA, produce their own ribosomes
Greater surface area= mass production of ATP
Are capable of dividing independent of cell division Fig. 7.18 Chloroplasts Are Sugar- Manufacturing Centers
Many of the enzymes and other molecules required for photosynthesis are
located in membranes inside the chloroplast. These membranes are folded into
thylakoids and stacked into grana.
Have a double membrane (both inner and outer membranes are smooth)
Inner membrane houses thylakoids (flattened sacs stacked in grana)
Grana- increase surface area= generation of energy