Chapter 4 Summary

Chapter 4.1

The plasma membrane is a phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment.
Most organelles within a eukaryotic cell are surrounded by one or more membranes.
The cytoplasm is made up of a diverse group of organelles suspended within the cytosol, as well as the cytoskeleton and various chemicals.
The cytoskeleton and extracellular matrix support cell structure and function in numerous ways.
There are many differences in the structure and components of various eukaryotic cell types

Cell information is stored in the nucleus as chromatin, DNA and its associated histone proteins.
The nucleus is the site of DNA replication, RNA synthesis and is responsible for directing ribosome synthesis.
Ribosomes are assembled in the nucleolus and are released into the cytosol through the nuclear pores; they can be free floating in the cytoplasm or membrane bound.
Ribosomes are responsible for protein synthesis, and they receive their “orders” from the nucleus in the form of mRNA
Centrosomes are made of two centrioles that lie perpendicular to each other and are made up of nine triplets of microtubules forming their cylindrical shape.
While the exact function of centrosomes during cell division is still unclear, it is thought that they assist in ensuring proper division of genetic material.

The endomembrane systems consist of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, central vacuole, and vesicles
The rough ER is responsible for synthesising and processing proteins, while the smooth ER is responsible for carbohydrate metabolism, lipid (including steroid hormone) synthesis, detoxification of some chemicals, and calcium ion storage
The Golgi apparatus receives proteins and lipids from the ER and transports, modifies, and packages them before sending these macromolecules in vesicles to their final destination.
Lysosomes act as the cells digestive system by using enzymes to break down waste and pathogens.
The central vacuole, which is only found in plant, helps maintain turgor pressure, breaks down waste, and can store various substances.

Mitochondria in all eukaryotic cells generate large amounts of ATP via cellular respiration.
Cellular respiration uses a series of chemical reactions to convert the energy stored in sugars and other nutrients into ATP in the presence of oxygen.
Chloroplasts in plants and other autotrophs make sugar via photosynthesis.
Photosynthesis harvests light energy using pigments like chlorophyll, and then uses a series of chemical reactions fix carbon dioxide into sugar.
Peroxisomes enable the oxidation fatty acids to produce acetyl CoA, which can contribute to ATP synthesis in mitochondria.
Harmful hydrogen peroxide produced by chemical reactions in peroxisomes is broken down into water and oxygen, a reaction catalyzed by the enzyme catalase.

Microfilaments are composed of actin proteins, and are essential for maintaining membrane shape and cellular processes involving movement.
Many types of microfilament-based movements require interaction with the motor protein myosin
Intermediate filaments are the most diverse type of cytoskeletal protein but are mainly involved in structural support. Different filaments are composed of different proteins, e.g., keratins, lamins, etc.

Microtubules are small, hollow tubes composed of tubulin proteins, and function to resist cellular compression, move chromosomes, and in cell motility.
Flagella and cilia are both hair-like structures that protrude from the cell and are involved in cell movement. Flagella are longer than cilia.
Many types of microtubule-based movements require interaction with the motor proteins dynein and/or kinesin.
The cytoskeleton can be visualized using fluorescence or confocal microscopy if cells have been stained using phalloidin with fluorophores attached (to stain actin microfilaments) or immunofluorescence (to stain any protein of interest, e.g., tubulin, keratin, etc.).

The cell wall is a rigid structure found outside the plasma membrane of cells from most eukaryotic groups (plants, fungi, some protists); the cell wall helps maintains cell shape.
The extracellular matrix of animal cells is a network of proteins and other molecules that surrounds and gives structural support to cells, assists in cell adhesion and in motility.
Plasmodesmata are the intercellular (cell-cell) junctions in plant cells that allow for nutrient transfer and communication between adjacent cells.
Tight junctions, adherens, desmosomes, and gap junctions are the types of intercellular junctions found in animal cells that allow for connection and/or communication between cells in various ways.

Icon for the Creative Commons Attribution 4.0 International License