Cell Structure & Intracellular Organelles: An Overview Flashcards
nucleus
largest organelle, most cells have 1, however, skeletal muscle have >1 and RBCs have 0.
Contains the cell’s DNA complexed with histone proteins to form chromatin.
nucleosome
complex of 8 molecules of histones around which DNA is wound, appears as beads on a string. Fundamental subunit of chromatin.
heterochromatin
highly condensed DNA-protein complex, DNA is inaccessible to transcription factors, and thus is “silent” in this configuration (DNA methylated and histones deacetylated)
euchromatin
less condensed DNA-protein complex, DNA is accessible to transcription factors and thus is transcriptionally active. (DNA demethylated and histones acetylated)
nucleolus
most prominent structure within nucleus, site of rRNA trancription, pre-rRNA processing and ribosome subunit assembly
***Cells that are active in protein synthesis such as liver cells and some highly proliferative cancer cells have increased numbers of these.
nuclear pores
small, protein-lined openings in the nuclear envelope that allow for exportation of RNAs and ribosomes from nucleus to cytosol, as well as importation of transcription factors
mitochondria
organelle that converts PE from food into cellular energy under aerobic conditions, have a highly porous outer membrane and an inner membrane that is impermeable to many ions, including protons, and is convoluted, forming folds called cristae. Site of e- transport chain
mitochondrial diseases
genetic disease group that is passed down from mother to all children, variable disease symptoms/expression can occur in these diseases due to different mutation loads: can be different # mutations per organelle, different # organelles with mutations per cell, and different # cells with mutated organelles per tissue/organ system.
ribosomes
protein synthesizing machinery of the cell, free scattered in the cytosol or bound to ER membrane. Made up of large and small subunits (Euks: 80S = 60S + 40S, Proks: 70S = 50S + 30S)
80s, 60s, 40s
eukaryotic ribosomal subunits
endoplasmic reticulum
network of flattened sacs and branching tubules that extends throughout the cytoplasm, function to produce and process various proteins, lipids, toxins
rough ER
organelle covered in ribosomes, involved in production and processing of membrane-embedded and secretory proteins
smooth ER
organelle involved in production of lipids, detox of drugs and poisons, and calcium storage
golgi apparatus
organelle made up of several flattened, stacked sacs, referred to as cisternae. Considered the shipping and distribution center for the cell’s chemical products - modifies proteins and distributes things back to ER or out to cell membrane. Protein modifications here include: glycosylation, sulfation, phosphorylation, and proteolysis.
cis
face of golgi apparatus where substances enter from the ER for processing
trans
face of golgi apparatus where substances exit in vesicles or lysosomes
lysosome
organelle that is filled with hydrolytic enzymes, degrades intracellular molecules - primarily degrades extracellular proteins that were taken up by endocytosis or engulfed by autophagosomes. Lumen is acidic which activates the enzymes (hydrolases).
peroxisomes
small organelles that contain enzymes linked to metabolic pathways such as beta oxidation of long-chain fatty acids. The enzymes use molecular oxygen to neutralize free radicals, releasing H2O2, which must be converted to H2O by catalase. (most abundant in liver cells)
proteasomes
small cytoplasmic protein complexes degrade proteins, involved in the quality control of endogenously synthesized proteins by marking misfolded and denatured proteins for degradation, also degrades TFs, cyclins, and proteins encoded by viruses and intracellular pathogens.
**Uses polyubiquitination to tag for degradation.
centrosome
consists of a bound pair of centrioles surrounded by a shapeless matrix of dense material. During cell division - directs migration of chromosomes to opposite ends of the cell (spindle apparatus). In non-dividing cells, centrioles attach to the inner side of the membrane to form a basal body - which forms a cilia/flagella or non-motile primary cilium.
membrane asymmetry
negatively charged lipids are usually found on the inner leaflet of the plasma membrane while positively charged lipids are found on the outer leaflet. Disorganization of this usually indicates cell damage.
flippases
one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein moves lipids from the outer monolayer to the inner monolayer with the help of ATP (because this is against the gradient)
floppases
one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein moves lipids from the inner monolayer to the outer monolayer with the help of ATP (because this is against the gradient)
scramblases
one of the 3 protein families responsible for the generation, maintenance, regulation, and dissipation of lipid asymmetry in the plasma membrane; this protein exchanges lipids between monolayers in either direction toward equilibrium, without the use of ATP.
