Notes

biology test 2 study prep
1. know the definition and function for each of the following
a. cell membrane
definition:a biological membrane that seperates the interior of the cell from the outside enviroment consisting of lipid bilayer and protiens
function: The cell membrane controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules.[3] In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signalling and serve as the attachment surface for several extracellular structures, including the cell wall, the carbohydrate layer called the glycocalyx, and the intracellular network of protein fibers called the cytoskeleton.
B.nucleoid
definition: is an irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material, called genophore. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane.
Function: The genome of prokaryotic organisms generally is a circular, double-stranded piece of DNA, of which multiple copies may exist at any time. The length of a genome widely varies, but generally is at least a few million base pairs. As in all cellular organisms, length of the DNA molecules of bacterial and archaeal chromosomes is very large compared to the dimensions of the cell, and the genomic DNA molecules must be compacted to fit.
c.lysosomes
Definition: is a membrane-bound organelle found in many animal cells and most plant cells.
Function: They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins, and its lumenal proteins. The lumen's pH (4.5–5.0)[1] is optimal for the enzymes involved in hydrolysis, analogous to the activity of the stomach. Besides degradation of polymers, the lysosome is involved in various cell processes, including secretion, plasma membrane repair, cell signaling, and energy metabolism
The lysosomes also act as the waste disposal system of the cell by digesting unwanted materials in the cytoplasm, both from outside the cell and obsolete components inside the cell. Material from outside the cell is taken-up through endocytosis, while material from the inside of the cell is digested through autophagy.
d. plasmodesmata
definition: are microscopic channels which traverse the cell walls of plant cells[2] and some algal cells, enabling transport and communication between them
E.nuclear pore complex
definition: A nuclear pore is a part of a large complex of proteins, known as a nuclear pore complex that spans the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are an average of 1,000 nuclear pore complexes (NPCs) in the nuclear envelope of a vertebrate cell, but it varies depending on cell type and the stage in the life cycle.[1] The human nuclear pore complex (hNPC) is a 110 MDa structure. The proteins that make up the nuclear pore complex are known as nucleoporins. About half of the nucleoporins typically contain solenoid protein domains—either an alpha solenoid or a beta-propeller fold, or in some cases both as separate structural domains. Each NPC contains at least 456 individual protein molecules and is composed of 34 distinct proteins (nucleoporins).[2] The other half show structural characteristics typical of "natively unfolded" or intrinsically disordered proteins, i.e. they are highly flexible proteins that lack ordered tertiary structure.[3] These disordered proteins are the FG nucleoporins, so called because their amino-acid sequence contains many phenylalanine—glycine repeats.[4]

Nuclear pore complexes allow the transport of molecules across the nuclear envelope. This transport includes RNA and ribosomal proteins moving from nucleus to the cytoplasm and proteins (such as DNA polymerase and lamins), carbohydrates, signaling molecules and lipids moving into the nucleus. It is notable that the nuclear pore complex (NPC) can actively conduct 1000 translocations per complex per second. Although smaller molecules simply diffuse through the pores, larger molecules may be recognized by specific signal sequences and then be diffused with the help of nucleoporins into or out of the nucleus. It has been recently shown that these nucleoporins have specific evolutionary conserved features encoded in their sequences that provide insight into how they regulate the transport of molecules through the nuclear pore.[5][6] Nucleoporin-mediated transport is not directly energy requiring, but depends on concentration gradients associated with the RAN cycle. Each of the eight protein subunits surrounding the actual pore (the outer ring) projects a spoke-shaped protein over the pore channel. The center of the pore often appears to contain a plug-like structure. It is yet unknown whether this corresponds to an actual plug or is merely cargo caught in transit.
F. mitochondria
definition:The mitochondrion (plural mitochondria) is a double-membrane-bound organelle found in most eukaryotic organisms. Some cells in some multicellular organisms may, however, lack them (for example, mature mammalian red blood cells). A number of unicellular organisms, such as microsporidia, parabasalids, and diplomonads, have also reduced or transformed their mitochondria into other structures.[1] To date, only one eukaryote, Monocercomonoides, is known to have completely lost its mitochondria.[2] The word mitochondrion comes from the Greek μίτος, mitos, "thread", and χονδρίον, chondrion, "granule"[3] or "grain-like". Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.[4] A mitochondrion was thus termed the powerhouse of the cell.[5]
G. smooth ER
definition:The endoplasmic reticulum (ER) is a type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum occurs in most types of eukaryotic cells, but is absent from red blood cells and spermatozoa.

There are two types of ER: rough endoplasmic reticulum and smooth endoplasmic reticulum. The outer (cytosolic) face of the rough endoplasmic reticulum is studded with ribosomes that are the sites of protein synthesis. The rough endoplasmic reticulum is especially prominent in cells such as hepatocytes. The smooth endoplasmic reticulum lacks ribosomes and functions in lipid synthesis but not metabolism, the production of steroid hormones, and detoxification.[1] The smooth ER is especially abundant in mammalian liver and gonad cells.
H.peroxisome
definition:A peroxisome (IPA: [pɛɜˈɹɒksɪˌsoʊm])[1] is a type of organelle known as a microbody, found in virtually all eukaryotic cells.[2] They are involved in catabolism of very long chain fatty acids, branched chain fatty acids, D-amino acids, and polyamines, reduction of reactive oxygen species – specifically hydrogen peroxide[3] – and biosynthesis of plasmalogens, i.e., ether phospholipids critical for the normal function of mammalian brains and lungs.[4] They also contain approximately 10% of the total activity of two enzymes in the pentose phosphate pathway, which is important for energy metabolism.[4] It is vigorously debated whether peroxisomes are involved in isoprenoid and cholesterol synthesis in animals.[4] Other known peroxisomal functions include the glyoxylate cycle in germinating seeds ("glyoxysomes"), photorespiration in leaves,[5] glycolysis in trypanosomes ("glycosomes"), and methanol and/or amine oxidation and assimilation in some yeasts.