What’s Inside the Cell?
• Looking at cell structure, there are two broad groupings of life:
1. Prokaryotes, which lack a membrane-bound nucleus.
2. Eukaryotes, which have such a nucleus.
• Looking into groupings by evolutionary history, there are two types of prokaryotic cells,
called Bacteria andArchaea, in addition to the Eukarya.
• The prokaryotic plasma membrane surrounds the cytoplasm, a term that includes all the
contents of the cell. Prokaryotic cells generally have few or no substructures separated from the
rest of the cell by internal membranes.
• Prokaryotes have a tough cell wall that protects the cells and gives them shape and structure.
• Most prokaryotic species have one supercoiled circular chromosome containing DNAthat is
found in the nucleoid region of the cell.
• All prokaryotic cells contain ribosomes for protein synthesis. Ribosomes have a large and a
small subunit and contain both RNAand protein molecules.
• The inside of prokaryotic cells is supported by a cytoskeleton of protein filaments.
• Some prokaryotes have tail-like flagella on the cell surface that spin around to move the cell.
Eukaryotes and Prokaryotes Compared
• Major differences between typical eukaryotes and prokaryotes are as follows:
1. Eukaryotic chromosomes are found inside a membrane- bound compartment called a nucleus.
2. Eukaryotic cells are often much larger.
3. Eukaryotic cells contain extensive amounts of internal membrane.
4. Eukaryotic cells feature a diverse and dynamic cytoskeleton.
• The relatively large size of the eukaryotic cell makes it difficult for molecules to diffuse across
the entire cell. This problem is partially solved by breaking up the large cell volume into several
smaller membrane-bound organelles.
• The compartmentalization of eukaryotic cells increases chemical reaction efficiency by separating incompatible chemical reactions and grouping enzymes and substrates together.
• All eukaryotes have a large nucleus surrounded by a double-membrane nuclear envelope. The
nucleus contains the linear eukaryotic chromosomes.
• Ribosomal RNAsynthesis occurs in a distinct region of the nucleus called the nucleolus.
• Eukaryotic ribosomes are made of RNAand protein, and have a large and a small subunit.
Many ribosomes are found in the cytosol, the fluid part of the cytoplasm.
Rough Endoplasmic Reticulum
• The rough endoplasmic reticulum (rough ER) is a network of membrane-bound tubes and
sacs studded with ribosomes for protein synthesis and is continuous with the nuclear envelope.
• The Golgi apparatus is formed by a series of stacked flat membranous sacs called cisternae. It
receives products from the rough ER and sends finished products to the cell surface in vesicles.
Smooth ER and the Endomembrane System
• The smooth endoplasmic reticulum (smooth ER) lacks ribosomes and is responsible for fatty
acid and phospholipid synthesis.
• The endomembrane system, composed of the smooth and rough ER and the Golgi apparatus,
is the primary system for protein and lipid synthesis.
Peroxisomes and Vacuoles
• Peroxisomes are globular organelles bound by a single membrane in which oxidation reactions
• Plants and fungi have very large vacuoles that store water and/or ions to help the cell maintain
its normal volume.
• Lysosomes are single-membrane-bound centers for storage and/or waste processing. Materials
are delivered to the lysosomes by three processes: phagocytosis, autophagy, and receptor-
• Endocytosis is a process by which the cell membrane can pinch off a vesicle to bring outside
material into the cell. In addition to phagocytosis and receptor-mediated endocytosis, a third
type of endocytosis called pinocytosis brings fluid into the cell. Mitochondria
• Mitochondria have two membranes; the inner one is folded into a series of sac-like cristae.
The solution inside the cristae is called the mitochondrial matrix.
• Mitochondria have their own DNAand their own ribosomes. They grow and divide
independently of nuclear division and cell division.
• ATP production is a mitochondrion’s core function.
• Most plant and algal cells have chloroplasts that, like mitochondria, grow and divide
independently, have a double membrane, and contain DNA.
• Chloroplasts contain membrane-bound, flattened vesicles called thylakoids, which are stacked
into piles called grana. Outside the thylakoids is the solution called the stroma.
• Chloroplasts contain everything required to convert light energy to chemical energy—in other
words, to perform photosynthesis.
Cytoskeleton and the Cell Wall
• The cytoskeleton gives the cell shape and structural stability, and aids cell movement and
transport of materials within the cell.
• Fungi, algae, and plants have a stiff outer cell wall that protects the cell.
Cell Structure and Function
• An organelle’s membrane and its enzymes correlate with its function, and cell structure (e.g.,
the type, size, and number of organelles) correlates with cell function.
• Cells are dynamic living things with interacting parts and constantly moving molecules.
The Nuclear Envelope: ATransport Mechanism
• The nucleus is a highly organized information center for the cell. The n