Cell Biology Flashcards
Organelle
Small structure within a cell that carries out specific cellular functions (typically membrane bound in Eukaryotes with own lipid bilayer membrane)
Summary Nucleus
Contain and protect DNA; transcription;
Partial assembly of ribosome in nucleolus
2 surrounding Membranes
Summary Mitochondria
Produce ATP via Krebs cycle and oxidative phosphorylation
2 surrounding membranes
Summary Ribosomes
Synthesize proteins
Not membrane bound
Summary Rough Endoplasmic Reticulum
Location of synthesis/modification of secretory, membrane-bound, and organelle proteins
1 surrounding membrane
Summary Smooth Endoplasmic Reticulum
Detoxification and glycogen breakdown in liver, steroid synthesis in gonads
1 surrounding membrane
Summary Golgi Apparatus
Modification (i.e. Glycosylation) and sorting of protein, some synthesis
1 surrounding membrane
Summary Lysosomes
Contain acid hydrolases that digest various substances
1 surrounding membrane
Summary Peroxisomes
Metabolize lipids and toxins, releasing H2O2
1 surrounding Membrane
Nucleus
Site of replication, transcription, splicing
Contains the genome and surrounded by nuclear envelope. Not a fluid membrane, nuclear matrix/scaffold supports the organelle and provides overall structure
Genome
Eukaryotic Genome organized into linear molecules of double stranded DNA (Chromosomes)
Genes can be mapped genetically and physically to the chromosome they reside on (a locus)
Nuclear matrix may play a role in regulating gene expression (DNA in chromosomes attached to matrix at specific sites)
Nucleolus
Region within nucleus that functions as the ribosome factory
Consists of loops of DNA, RNA polymerases, rRNA and protein components of the ribosome (to partially assemble the ribosome)
Ribosome maintained inactive until exported from nucleus and assembled fully in cytoplasm
Nuclear Envelope
2 lipid bilayer membranes. Inner facing inside, outer facing cytoplasm.
Outer membrane continuous with some membrane of the ER (lumen)
Envelope is punctuated with nuclear pores that allow things to enter and exit the nucleus (smaller than 60 kD) –> larger proteins must contain a nuclear localization sequence that imports them into nucleus (after cytoplasmic ribosome translation)
Chromatin
Heterochromatin - densely packed chromatin with inaccessible genes (turned off)
Euchromatin - loosely packed chromatin that allows genes to be activated
Mitochondria
Site of Oxidative Phosphorylation
Matrix is interior of the mitochondria (bound by innter and outer membranes) that contains enzymes of the Krebs Cycle
Inner membrane of the mitochondria is location of ETC and ATP synthase (impermeable and folded into projections called cristae)
Space between two membranes is known as intermembrane space
Exhibit Maternal Inheritance
Endosymbiotic Theory of Mitochondrial Evolution
Mitochondria originated as independent unicellular organisms living within larger cell
Mitochondrial Genome
Smaller version of cellular genome consisting of single circular DNA molecule
Encodes for rRNA, tRNA, several proteins (including what’s necessary for ETC and ATP Synthase complex)
Endoplasmic Reticulum
Rough ER - ribosomes bound to surface, site of protein synthesis for proteins targeted to enter secretory pathway
Smooth ER - Not actively involved in protein processing; can contain enzymes involved in steroid hormone biosynthesis or in degradation of environmental toxins
Rough ER
Protein Synthesis occurs in either free ribosomes or RER-bound ribosomes
Post-translational modification of proteins occurs in Rough ER (ex. glycosylation, disulfide bond formation)
All Protein translation starts in cytoplasm. Signal sequence means translation is continued on in rough ER ribosomes
Secretory pathway
If N-terminus has signal sequences, protein is a part of the secretory pathway/endomembrane system.
Recognized via signal recognition particles, the signal sequence is removed and translation continues in cytoplasm on free ribosomes.
No signal Sequence means translation continues in cytoplasm on free ribosomes
Signal Sequence (+)
Default (nothing but signal sequences) results in secretion
Transmembrane domain (special signal sequence not removed) means the protein has hydrophobic residues, allowing it allow localization to the plasma membrane (integral membrane protein)
Otherwise, needs a targetting signal to go elsewhere (GEL = Golgi, E.R., Lysosome)
Signal Sequence (-)
Default is cytoplasm
With a localization signal, can go to either nucleus, mitochondria, or peroxisome
Golgi Apparatus
Modification of proteins made in RER (important in the modification of oligosaccharide chains)
Sorting an sending proteins ot their correct destination
Synthesizes macromolecules (ex. polysaccharides) for secretion
Protein traffic at Golgi apparatus is unidirectional (cis -> trans) but protein route is determined by signals within the protein that determine which vesicle a protein is sorted into in the trans
Cis/trans stack of Golgi
Cis - portion nearest rough ER
- Vesicles from ER fuse with this stack where they are modified and transfered
Medial - middle
Then sent to medial stack
Trans - farthest from rough ER
- Pass Through Trans stack, protein leave golgi in transport vesicles
- As vesicle moves from trans Golgi to surface, fuses with cell membrane (contents released extracellularly via exocytosis unless proteins bound to vesicle membrane)
