Organelles.

Organelles of a typical animal cell.

Because the eukaryotic clades encompassing protista, plants and fungi are not topics of focus for the new MCAT (Plants were not on the old MCAT as well), the model eukaryotic cell for our purposes is an animal cell. Comparison and contrast of animal cells with prokaryotic cells is a good starting point in review. The typical animal cell is one or two orders of magnitude larger than prokaryotic cells. Additionally, while a prokaryotic cell has no nucleus, a typical animal cell possesses a true nucleus, containing the genetic material and enclosed by the nuclear envelope. In fact, the defining feature that sets eukaryotic cells apart from prokaryotic cells is that eukaryotic cells have membrane-bound organelles. Other membrane bound organelles in animal cells include lysosomes, Golgi complex, endoplasmic reticulum, and mitochondria. Additionally, bacterial flagella are different from eukaryotic flagella. Bacterial flagella are helical filaments, each with a rotary motor at its base. Eukaryotic flagella are completely different structurally, consisting of multiple microtubules. Eukaryotic flagella lash back and forth. Another difference is that sterols and carbohydrates are generally present in the animal cell membrane, though they are absent in prokaryotic membranes. Furthermore, prokaryotic chromosomes lack histones. The mode of cell division is also different. Prokaryotes reproduce by binary fission while eukaryotic cells divide by the process of mitosis.

WikiPremed Resources



The Eukaryotic Cell Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for The Eukaryotic Cell
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals

Proficiency 

Be able to describe of the various membrane bound organelles found in animal cells.

Possess a unified structural understanding of the endomembrane system including the nuclear envelope, rough and smooth ER, and the Golgi apparatus.

Be able to describe the regulation of transport through nuclear pores.

Comprehend eukaryotic cell structure in the light of central dogma, i.e. transcription and translation.

Orient yourself for discussion of the biosynthesis of phospholipids, sphingolipids, and plasmalogens with various enzyme functions concentrated in the ER, Golgi complex, peroxisomes, and mitochondria.

Be familiar with the functional integration of lysosomes with the intracellular processes of phagocytosis, endocytosis and autophagy.

Understand the metabolic functions of peroxisomes including beta oxidation of fatty acids, formation of plamalogen, and enzyme catalase activity.

Be able to relate mitrochondrial structure to function.

Possess a solid understanding of the various cytoskeletal structures such as flagella and cilia and their related basal bodies and centrioles.

Be able to distinguish the various proteins of importance in the cytoskeleton.

Suggested Assignments

Practice terminology from the subject of the eukaryotic cell using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Read pp. 15-21 in ExamKrackers Biology II. Perform practice items 9-16 on pg. 22.

Study the eukaryotic cell web resources carefully.

Conceptual Vocabulary for The Eukaryotic Cell

Eukaryote
Animals, plants, fungi, and protists are eukaryotes, which are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton.
Cytoskeleton
The cytoskeleton is a cellular scaffolding or skeleton contained within the cytoplasm.
Cytoplasm
Cytoplasm is a gelatinous, semi-transparent fluid that fills most cells.
Cell nucleus
The nucleus is a membrane-enclosed organelle found in most eukaryotic cells which contains the cell's genetic material.
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells the primary function of which is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell.
Mitochondrion
A mitochondrion is a membrane-enclosed organelle that is found in most eukaryotic cells that. In addition to supplying cellular energy, they are involved in a range of other processes.
Organelle
An organelle is a specialized subunit within a cell, having a specific function, and separately enclosed within its own lipid membrane.
Nuclear envelope
The nuclear envelope or membrane is the double membrane of the nucleus that encloses genetic material in eukaryotic cells.
Nuclear pore
Nuclear pores are large protein complexes that cross the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus.
Chloroplast
Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. They are generally considered to have originated as endosymbiotic cyanobacteria.
Lysosome
Lysosomes are organelles that contain digestive enzymes to digest excess or worn out organelles, food particles, and engulfed viruses or bacteria.
Centriole
A centriole is a barrel shaped organelle found in most eukaryotic cells with walls usually composed of nine triplets of microtubules.
Nucleolus
The nucleolus is a sub-organelle of the cell nucleus. Its main function is the production and assembly of ribosome components.
Endomembrane system
The endomembrane system is the system of internal membranes within eukaryotic cells that divide the cell into functional and structural compartments, or organelles.
Vesicle
A vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer.
Cilium
A cilium is an organelle found in eukaryotic cells. It is a thin, tail-like projection extending approximately 5-10 micrometers outwards from the cell body.
Microfilament
Microfilaments are the thinnest filaments of the cytoskeleton found in the cytoplasm of all eukaryotic cells. These linear polymers of actin subunits are flexible and relatively strong.
Spindle apparatus
The spindle apparatus is a structure of the eukaryotic cytoskeleton involved in mitosis and meiosis, often referred to as the mitotic spindle during mitosis and the meiotic spindle during meiosis.
Cisterna
A cisterna comprises a flattened membrane disk which makes up the Golgi apparatus.
Vesicular-tubular cluster
Vesicular-tubular cluster is an intermediate compartment mediating trafficking between the endoplasmic reticulum and Golgi complex.
Peroxisome
Peroxisomes are ubiquitous organelles in eukaryotes that participate in the metabolism of fatty acids and other metabolites. They have enzymes that rid the cell of toxic peroxides.
Basal body
A basal body is an organelle formed from a centriole, a short cylindrical array of microtubules. It is found at the base of a eukaryotic undulipodium (cilium or flagellum) and serves as a nucleation site for the growth of the axoneme microtubules.
Endosymbiotic theory
The endosymbiotic theory concerns the origins of mitochondria and plastids, according to which these organelles originated as separate prokaryotic organisms which were taken inside the cell as endosymbionts.
Actin
Actin is the protein which serves as the monomeric subunit of microfilaments, one of the three major components of the cytoskeleton, and of thin filaments which are part of the contractile apparatus in muscle cells.
Intermediate filament
Intermediate filaments are cytoskeletal structures formed by members of a family of related proteins. These filaments have a diameter between that of actin microfilaments and microtubules.
Plastid
Plastids are major organelles found in plants and algae responsible for photosynthesis, storage of products like starch and for the synthesis of many classes of molecules such as fatty acids and terpenes.
Centrosome
The centrosome is the main microtubule organizing center of the cell as well as a regulator of cell-cycle progression.
Tubulin
A tubulin is one of several members of a small family of globular proteins. The most common members this family are the proteins which makes up microtubules.
Nuclear localization signal
A nuclear localization signal is an amino acid sequence which acts like a 'tag' on the exposed surface of a protein to target the protein to the cell nucleus through the nuclear pore complex and to direct it into the nucleus via its recognition by cytosolic nuclear transport receptors.
Axoneme
The axoneme is the inner cytoskeletal structure of eukaryotic cilia or flagella.
Microtubule organizing center
The microtubule-organizing center is a structure found in all plant and animal cells from which microtubules emerge.
Kinesin
Kinesins are a class of motor proteins found in cells which move on the much larger microtubule cables powerered by the hydrolysis of ATP. They are dimers reminiscent of feet on a rod.
Dynein
Dynein is a motor protein in cells which converts the chemical energy contained in ATP into the mechanical energy of movement, transporting various cellular cargo by walking along cytoskeletal microtubules towards the minus-end of the microtubule, ie. toward the center of the cell..
Undulipodium
An undulipodium is a general term for a 9+2 organelle containing a microtubule array such as eukaryotic flagella and cilia.
Nucleoporin
A nucleoporin is a type of porin which facilitates transport through nuclear pores in the nuclear envelope.
Nuclear lamina
The nuclear lamina is a dense fibrillar network composed of intermediate filaments made of lamin that lines the inner surface of the nuclear envelope in animal cells.
Nuclear export signal
A nuclear export signal is a short amino acid sequence of 5-6 hydrophobic residues in a protein that targets it for transport from the cell nucleus to the cytoplasm through the nuclear pore complex.
Autophagy
Autophagy, or autophagocytosis, is a catabolic process involving the degradation of a cell's own components through the lysosomal machinery.
Chromoplast
Found in coloured organs of plants, chromoplasts are plastids responsible for pigment synthesis and storage.
Hydrogenosome
A hydrogenosome is a membrane-bound organelle of ciliates, trichomonads and fungi which produces molecular hydrogen and ATP. This organelle is thought to have most likely evolved from mitochondria.
Lamin
Lamins are fibrous proteins having structural function in the cell nucleus.
Advanced terms that may appear in context in MCAT passages
Intraflagellar transport
Intraflagellar transport refers to the cellular process essential for the formation and maintenance of eukaryotic cilia and flagella.
Cajal body
Cajal bodies are spherical sub-organelles found in the nucleus of proliferative cells like tumor cells, or metabolically active cells like neurons. In such cells they are bound to the nucleolus by coilin proteins.
Leucoplast
Leucoplasts are a category of plastid and as such are organelles found in plant cells. They are non-pigmented, in contrast to other plastids such as the chloroplast.
Melanosome
A melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom.
Importin
Importin is a type of karyopherin which moves molecules into the nucleus by binding to the nuclear localization signal present on the molecules.
Karyopherin
Karyopherins are a group of proteins involved in transporting molecules through the pores of the nuclear envelope.
Paraspeckle
Paraspeckles are irregularly shaped sub-cellular compartments, approximately 0.2-1 micrometers in size, found in the nucleus' interchromatin space. Although the likely protein components have RNA recognition motifs, the function of these structures is not well understood.
Topogenic sequence
A topogenic sequence is a segment of a protein that ensures it acquires the proper orientation during its insertion into the endoplasmic reticulum.
Ergastic substance
Ergastic substances are non-protoplasm materials found in cells.
Amyloplast
Amyloplasts, a specialized form of leucoplasts, are non-pigmented organelles found in plant cells responsible for the storage of amylopectin
Statolith
Statoliths are a specialised form of amyloplasts involved in gravity perception by plants.
Elaioplast
Elaioplasts are a type of leucoplast which is specialized for the storage of lipids.
Proteinoplast
Proteinoplasts are sometimes called proteoplasts, aleuroplasts, or aleuronaplasts. They are specialized organelles found only in plant cells, containing crystalline bodies of protein.