Cell structure Flashcards
what is the bodys organization in order?
what do all cells have in common?
Cells are the building blocks of complex organisms. Cells that are related or work together to perform a particular function in the body are grouped into tissues, which in turn are grouped into organs that execute a specific function like digestion or respiration. Although there are many different types of cells found in the human body, all cells have some basic characteristics in common
what are all cells surrounded by?And what do they all contain?
What are some examples of cellular activites?
What are the organelles that we will discuss in this lecture? What does each organelle do?
What does the cytoskeleton do?
All cells are surrounded by a bilipid plasma membrane, and contain subcellular organelles - metabolically active structures that mediate all the activities and functions of the cell. Some of these cellular activities are protein synthesis, energy metabolism and communication with other cells. The organelles we will discuss today include the nucleus that houses the genetic material of the cell, the ribosomes and rough endoplasm reticulum (RER) that work together to synthesize proteins, the Golgi apparatus that modifies, sorts and facilitates export of proteins synthesized on the RER, the lysosomes, that digest and hydrolyze molecules taken in by the cell, and the mitochondria that generates energy in the form of ATP. Lastly, we will discuss the cytoskeleton, a system of tubules and filaments that mediate the shapes, motility and subcellular organization of the cell.
What is the largest organelle?
What shape is the nucleus? Where is it located?
What does the nucleus contain?And what is it responsible for synthesizing? Where does it synthesize it? And what does it assemble and where?
The nucleus is the largest organelle of the cell. The nucleus is spherical in shape and more or less centrally located in the cell, although some cells show variations. The nucleus contains almost all of the DNA- the genetic material- of the cell, and is responsible for RNA synthesis (in the nucleoplasm) and for ribosomal assembly (in the nucleolus).
where is the DNA stored?
What does chromatin consist of ?
What are nucleosomes?
What is the function of the histone proteins?
How is chromatin organized?
What is the difference between euchromatin and heterochromatin?
DNA is stored in the nucleus as chromatin. Chromatin consists of double helix DNA wrapped around groups of histone proteins called nucleosomes in a configuration that resembles beads on a string. The histone proteins function to help stabilize the packaging of the DNA of the cell. Chromatin is folded into either a loose, transcriptionally active form called euchromatin or a condensed transcriptionally inactive form called heterochromatin. Heterochromatin is darker staining and tends to be located near the periphery of the cell whereas euchromatin is lighter staining and more centrally located.
what else does the nucleus contain?
What does the nucleolus look like? How is it organized?
what is the nucleolus involved in?
what are the ribosomes involved in?
what does the cells nucleolus look like that are actively synthesizing proteins ?
The nucleus also contains the nucleolus, a dark-staining non-membrane bound structure that is involved in the assembly of large and small ribosomal subunits (proteins) as well as in ribosomal RNA synthesis. Ribosomes are involved in protein synthesis; In cells that are actively synthesizing proteins, the nucleolus is particularly large and prominent, and can be observed even with the light microscope. We will see examples of such cells in some of our labs (e.g. Leydig cells in the testes that synthesize testoserone).
what is the nucleus surrounded by?
what do the nuclear pores provide?
Where is all RNA synthesized in the nucleus?
what else is synthesized in the nucleus?
What do exportins do?
what so importins do?
The nucleus is surrounded by the nuclear envelope, a double membrane unit perforated by nuclear pores. The nuclear pores provide a passageway for movement of proteins and nucleic acid between the cytoplasm and the nucleus. Specifically, all the RNA synthesized in the nucleus, as well as the ribosomes synthesized in the nucleolus move from the nucleus to the cytoplasm through the nuclear pores. Proteins called exportins mediate the transport of molecules from the nucleus to the cytoplasm e.g. RNA), whereas importins mediate transport of molecules from the cytoplasm to the nucleus
what is a ribosome made of?
Where are both units of the ribosome assembled?where are they released?
what happens to the subunits once in the cytoplasm? what do they begin to do?
What do many ribosomes have the ability do?
what is a polysome? explain what does it do according to the protein being made?
Each ribosome (proteins and rRNA) is composed of a large and a small subunit. Both subunits of the ribosome are assembled in the nucleolus and then released into the cytoplasm. Once in the cytoplasm, the large and small subunits of the ribosome assemble together as they begin translating a strand of mRNA into a protein. Many ribosomes translate a single strand of mRNA at once (at different positions); these ribosomes and the mRNA are collectively called the polysome. If the protein that is being synthesized is destined to be an integral membrane (transmembrane) protein or to be exported to outside the cell (extracellular or secreted) - the polysome will translocate and associate with the rough endoplasmic reticulum.
what is the RER?
What does the RER facilitate?
what microscope can you use to see the “rough” ribosomes in the RER?
what identifies if a proteins being synth by a ribosome are going to be extracellular or membrane bound?
What does the SRP do?
what happens once the ribosome attaches to the ER surface? what are the 2 options?
The rough endoplasmic reticulum (RER) is an extensive system of interconnected membrane bound tubules and vesicles in the cytoplasm.
The RER facilitates synthesis of proteins destined to be inserted into the plasma membrane (integral membrane) or secreted into the extracellular space (secretory).
In electron micrographs the surface of the RER appears studded or “rough” due to the association of thousands of ribosomes with the RER
As these types of proteins begin to be synthesized by a ribosome, they are identified as membrane or extracellular proteins by a signal sequence at their nascent N-terminal ends.
A signal recognition particle (SRP) binds to the signal sequence and directs the ribosome to the surface of the RER (to the SRP receptor).
Once the ribosome attaches to the ER surface, the protein continues to be synthesized, and: a) if it is an integral membrane protein is inserted into the ER membrane, or b) if it is an extracellular protein, secreted to the lumen of the ER.
**where is the golgi apparatus located? **what does it look like?
what is the glogi apparatus involved in?
what are the 3 levels of the cisternae gogli? explain the order of each one.
what is located between the ER and cis-golgi?
how do proteins move in this area?
what do the vesicles contain?
how are the integral membrane proteins moved?
The Golgi apparatus is a series of flattened, slightly curved sacs resembling a stack of pancakes that is located between the RER and the plasma membrane. The Golgi apparatus is involved in sorting, modification and exocytosis (the secretion) of proteins synthesized in the RER to the plasma membrane or the extracellular space. Each Golgi sack has three levels of cisternae: The cis-face, the med-face, and the trans-face. The cis-Golgi face is closest to the RER and the trans Golgi face is closest to the plasma membrane. There is also a transitional compartment located between the ER and the Cis-Golgi, called the ER-Golgi intermediate complex (ERGIC). Proteins move from the ER to the ERGIC and through the different levels of the Golgi (cis- to med-to trans) by means of vesicles that bud from one compartment and the fuse with the next compartment. These vesicles are small circular membrane bound structures that contain the membrane proteins that were originally inserted into the RER membrane or contain the extracellular proteins that were originally inserted into the lumen of the RER. Thus integral membrane proteins are moved from the RER to the Golgi stacks to the plasma membrane by vesicle mediated transport.
how is vesicle budding and fusing between different compartment of the RER and golgi foacilitated?
how are the protein coats specified?
what are the vesicles coated with that bud from the ER to the ERGIC?
What vesicle coat is on the ones that bud from the ERGIC to the cis-golgi? and what other vesicles are coated this way?
Why are these protein coats required? what kind of function do they provide?
Vesicle budding and fusing between different compartments of the RER and Golgi are facilitated by protein coats that cover the vesicles. The protein coats are specific to the compartment level that the vesicles are in. Vesicles that bud from the ER and fuse with ERGIC are coated with a protein called Coatomer Protein II (COPII), whereas vesicles that bud from the ERGIC and fuse with the cis-Golgi are coated with a Coatomer Protein I (COPI), as are vesicles that move from the cis-to med-to trans Golgi. These protein coats are required for the vesicles budding from and fusing with different compartments and likely serve both a mechanical and a signaling function.
what happens once vesicles bud from the trans-glogi? which locations are vesicles traveling to that are coated in clathrin?
where do clathrin coated vesicles dock?
where do protens that have other final destinations go? what are they coated with?
Once vesicles bud from the trans-Golgi they are directed to different locations depending on the final destination of the proteins they carry. Integral membrane proteins or extracellular proteins that are to be inserted into the plasma membrane or released into the extracellular space in a regulated manner leave the trans-golgi network in Clathrin covered vesicles. The Clathrin-coated vesicles dock at and then fuse with the plasma membrane when they receive the appropriate signal. Proteins that have other final destinations (e.g. other organelles such as the lysosomes or constitutive (nonregulated) secretion) depart from the Golgi in non-Clathrin coated vesicles.
what is endocytosis?
what happens during cell mediated endocytosis?
when are pinocytotic vesicles formed?
what are the steps involved in receptor-medicated endocytosis?
Endocytosis is the process by which a cell ingests macromolecules, particulate matter and other substances from the extracellular space. During receptor mediated endocytosis, the cell ingests macromolecules (receptor-ligand complexes) through small vesicles (pinocytosis). The steps involved in receptor-mediated endocytosis include: a) receptor proteins (often transmembrane proteins in the cell membrane) bind to ligand molecules extracellularly, b) a Clathrin protein coat assembles beneath the receptor-ligand complexes intracellularly, c) the Clathrin beneath the receptor-ligand complexes pulls on the plasma membrane, forming a Clathrin-coated pit, and d) the Clathrin-coated pit eventually buds from the membrane as a pinocytotic vesicle. Note that the small pinocytotic vesicle has an increased concentration of ligand relative to the plasma membrane.
what happens once the pinocytotic vesicle forms?
what does the early endosome have as an acidic ph? what does this result in?
what is the early endosome sometimes called?
what happens to the receptors after uncoupling?
where is the ligand transferred to and how?
Is the mechanism of transfer of molecules between the early endosome and late endosome known? Y/N? what is one proposed theory?
Once the pinocytotic vesicle forms, it loses its Clathrin coat, and then fuses with the early endosome, a system of membrane bound vesicles and tubules that are located near the plasma membrane. The early endosome has an acidic ph of 6.0, which results in the receptors and ligands uncoupling from one another. The early endosome is sometimes called the Compartment for Uncoupling Receptors and Ligands (CURL). The receptors (e.g. low-density lipoprotein receptors) may then be recycled and sent back to the plasma membrane through small vesicles. The ligand is transferred from the early endosome to the late endosome, a similar set of tubules and vesicles located deeper within the cell- near the Golgi complex. The mechanism of transfer of molecules between the early endosome and the late endosome is not known. One theory is that it involves vesicles ferrying between the two compartments, similar to the transfer of proteins between the ER and Golgi.
what are the contents of the late endosome?
where are the ligands delivered?
What are lysosomes? what shape do they have? what is their acidity pH? what causes this acidic pH?
what do lysosomes also contain? what do these emzymes do?
where are the types of enzymes found in lysosomes?
The small diffusable molecules generated by the lysosomes will be transferred where?
The contents of the late endosome- the ligands- are delivered to the lysosome for enzymatic digestion (hydrolysis). Lysosomes are the end stage of receptor mediated endocytosis. Lysosomes are round membrane bound organelles that have a very acidic pH-5.0 generated by proton pumps located in their plasma membranes. Lysosomes also contain a variety of hydrolytic enzymes that will digest ligands into small diffusible molecules. Some of the hydrolytic enzymes found in lysosomes include sulfatases, proteases and lipases. The small diffusible molecules generated by the lysosomes will eventually be transferred to the cytosol for use by the cell or for export into the extracellular space.
what shape are mitochondria?what do they generate?
how many membranes do mitochondria have? what is each one?
What are the folds in the inner membrane made of? what does the cristae do? what is the # of cristae proportional to? how does this relate to cells in the heart vs cells in the bones?
what is the small space between the outer and inner membrane called? what is the space inside the inner membrane emcloses called?
Mitochondria are rod-shaped organelles that generate ATP-energy for the cell by oxidative phosphorylation. Mitochondria have two membranes- an outer membrane and an inner membrane. The inner membrane is folded very extensively- the folds are called cristae. The cristae increase the surface area of the inner membrane available for ATP generation. The number of cristae in a mitochondrium is proportional to the amount of energy produced by the cell. Mitochondria in cardiac cells (cells that require a large amount of energy) contain more cristae than mitochondria in osteocytes (cells that do not require much energy). The small space between the outer and inner membrane is called the intermembrane space while the large space enclosed by the inner membrane is called the matrix space.
