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HCB Objectives 2
Identify/functions of:
fluid-mosaic model: cell membrane is a fluid collection of phospholipids,
proteins, and various other elements. When looked at from afar, these tiny elements form
a “mosaic”
phospholipid: main component of the cell membrane; has a hydrophilic head and
hydrophobic tail
cholesterol: lipid component of the cell membrane that increases intracellular
permeability, but decreases cell membrane fluidity
membrane proteins: a protein found in the plasma membrane
transmembrane protein: a protein that spans the cell membrane (an
integral membrane protein)
lipid-linked protein: a protein bound to lipids on the plasma membrane
(can be either extracellular or cytoplasmic; an integral membrane protein)
integral membrane protein: a protein embedded in or covalently attached
to the plasma membrane
peripheral membrane protein: a protein that is not covalently attached to
the plasma membrane
glycocalyx: network of sugars covalently attached to membrane or membrane
submembrane cytoskeleton: composed of peripheral membrane proteins, gives
stability to the membrane and anchors transmembrane proteins
nuclear envelope: similar to cell membrane; inside of cell, membrane that
surrounds the nucleus
nuclear pore: similar to a channel in the cell membrane; allows larger elements to
enter the nuclear space
chromatin: DNA that is not tightly wound to make chromosomes
euchromatin: least tightly wound DNA; may be wrapped around histones, but if
so, is definitely not condensed. Appears as darker of the two chromatins under a
heterochromatin: more condensed DNA; wrapped around histones and may be
supercoiled. Appears as darker of the two chromatins under a microscope.
histones: proteins in the nucleus that DNA wraps around. The “hair-curlers” for
DNA “hair”
nucleolus: the innermost and most prominent part of the nucleus. Where
ribosomes are manufactured; thus, cells making lots of proteins will have larger nucleoli
than those not actively synthesizing proteins
RER: endoplasmic reticulum with ribosomes studded on it to give “rough”
appearance. Active site of non-cytoplasmic protein manufacturing.
signal peptide: first 20 or so amino acids that will send protein to the RER and is
later cleaved by proteases in the RER. For shipping to lysosomal, secretory, or
membrane-bound proteins.
glycosylation: adding sugar to a newly translated protein destined for the
lysosome, secretion, or the plasma membrane. Begins in the RER.
golgi apparatus: cis, medial, and trans: site where proteins are trafficked after
translation in the RER (cis first, then medial and trans). This is the “mail center” of the
cell, proteins are processed here and shipped to their correct destination.
mannose-6-phosphate: lysosomal signal put onto proteins in the golgi apparatus
mannose-6-phosphate receptor: receptor on the lysosome to receive newly
translated proteins
membrane traffic: process whereby proteins come in and out of cell (elaboration
in question 2)
endosome: intracellular vesicle that forms after endocytosis of extracellular
components. Endosomes later move on to become lysosomes either by maturing or
fusing with a mature lysosome (process still unclear)
lysosome: cellular vesicle filled with acid hydrolases (low pH); destructor of any
intracellular elements (“the garbage compactor”).
SER: endoplasmic reticulum without ribosomes involved in several processes
(elaboration in question 2)
mitochondrion: site of ATP synthesis in the cell
cytoskeleton: intracellular component that gives cell shape and support
thin filament/microfilatin/actin: smallest of the three filaments, exists in
equilibrium between g-actin (single components, “globular”) and f-actin (bound strands,
“filamentous”) Is extremely important for processes such as locomotion, cytokinesis, and
attachment of cytoskeleton to plasma membrane
intermediate filament: second largest filament; much more stable and long-lived
than microfilaments; large family consisting of many different types.
glial fibrillary acidic protein (GFAP): intermediate filament found in
some types of glial cells
nuclear lamin: intermediate filaments on inner surface of nuclear
keratin: very strong filaments that form tonofilaments radiating from
desmosomes and hemidesmosomes. Extremely resistant to stress
vimentin: intermediate filament in mesenchymal cells
desmin: intermediate filament in muscle cells
neurofilament: intermediate filament in neurons
microtubule: largest of the 3 types of filaments, in equilibrium between filament
and globular arrangements, made of tubulin in heterodimer spirals, 13 to a revolution.
Important as “tracks” for protein shuffling (think about axonal transport in a neuron!)
spindle fiber formation, and is the core of flagella and cilia. Anchored by centrioles
microvillus: extension of cells with a core of microfilaments, nonmotile
terminal web: network of thin filaments at the base of a microvillus that runs
parallel to the cell membrane. Major support of thin filament core of microvillus
centriole: paired cylindrical structures, important as anchors for microtubules in
cilium: membrane covered mobile structure with microtubule core. Important for
sweeping cells out of certain areas of the body
flagellum: membrane covered mobile structure with microtubule core, larger than
cilium, found in spermatozoa to provide motility
basal body: inner core of cilia and microtubules arranged in typical 9 + 2 fashion
whereby there are 9 pairs of microtubules radiating around the periphery with a central
pair in the middle. Dynein attaches to the microtubule basal body to allow cilia/flagella
to bend (the basis of its motility)
Major molecular components in plasma membrane: phospholipids,
cholesterol, integral membrane proteins (transmembrane and lipid-linked).
Associated with these major components are the glycocalyx, and the
submembrane cytoskeleton.
Molecular organization of chromatin: Chromatin can be classified as either
euchromatin or heterochromatin.
Heterochromatin is more tightly wound and is thus more dense and
transcribed less. Because it is more dense it is more darkly stained in microscope
Euchromatin is less tightly wound and is less dense; transcription occurs
in euchromatin. It is more lightly stained in microscope slides.
Euchromatin/heterochromatin ratios can tell you whether the cell is
metabolically active or not (more euchromatin = more proteins production)
Intracellular pathways followed by endocytosis: Cell receptors on the outside
of the cell will be recycled along with components of the plasma membrane that
the receptors are bound to. Ligands will be endocytosed and either transferred to
a lysosome or will be broken down when the endosome matures into a lysosome.
Major functions of SER:
Produces cholesterol
Produces steroid hormones
Helps cell regulate Ca2+ levels by storing and releasing it
Breaks down toxins (will grow more in presence of toxins – hypertrophy
of SER shows that SER has been exposed to toxin)
Major steps in synthesis of proteins:
All proteins are translated from RNA after transcription of DNA in the nucleus.
Cytoplasmic proteins are then translated by free ribosomes in the cytoplasm.
All other proteins are translated on the RER and then sent to the Golgi for
Membrane proteins have hydrophobic regions that span the ER membrane during
translation. Thus, when they are sent in vesicles to their destination, they are already
stuck in the membrane and fuse with the membrane along with the vesicle.
Secretory proteins are proteins sent in vesicles to the plasma membrane. When
the vesicle fuses with the plasma membrane, the proteins are then sent out into the
extracellular space.
Lysosomal proteins are tagged with a mannose-6-phosphate in the cis-Golgi and
are then sorted and sent to the lysosome where they bind to mannose-6-phosphate